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doi:10.2204/iodp.pr.342.2012

Site summaries

Site U1402

Background and objectives

The MDHDS is an engineering development intended to serve as a foundation for future penetrometer and other downhole tool formation measurements. The MDHDS is designed so that downhole tools that are in the formation can be driven into the formation hydraulically and decoupled from the heave of the drill string, which negatively impacts these measurements.

The plan for the sea trial of the MDHDS was to carry out two tests of the tool set in the water column, wash to a depth of 100 m CSF-A, test the MDHDS in situ for at least 30 min, turn on the pumps to clean the hole, take an APC core, test the tool in situ again, and take three more APC cores. The site chosen for the tests was a reoccupation of ODP Site 1073, New Jersey margin.

Principal results

After a 582 nmi transit from Bermuda to Site U1402 (Site 1073), the vessel arrived at the first expedition location to perform engineering qualification tests on the MDHDS. The vessel was at Site U1402 at 1542 h (Universal Time Coordinated [UTC] – 3 h) on 6 June 2012. Two holes were drilled at Site U1402. Hole U1402A was drilled without coring to 96.4 m CSF-A to perform MDHDS testing. Hole U1402B was drilled to 15.03 m CSF-A to obtain two cores, test laboratory equipment, and provide experience for the science staff.

Initially, the drill pope was suspended above the seafloor at 608 m drilling depth below rig floor (DRF), and the MDHDS with the T2P tool was made up for deployment using the developmental ERS tool on the Schlumberger wireline. After running the tools through the blocks, a surface test was performed to check all components prior to deployment. A communication problem with the tool was fixed and the Schlumberger wireline was run into the drill pipe to ~250 m DRF, where the ERS released prematurely, allowing the MDHDS and T2P to fall 400 m to the landing seat in the BHA. An attempt was made to relatch the ERS tool to the MDHDS without success and the Schlumberger wireline was pulled from the drill pipe. An MDHDS mechanical latch assembly with sinker bars was assembled and deployed on the coring line in an attempt to fish the MDHDS tool, but this did not work. Upon retrieval of the coring line, the sinker bars were observed to have parted from the retrieval sub overshot, leaving a configuration that was impossible to fish. The decision was made to pull the drill string out of the hole to retrieve the test equipment inside the BHA. After tripping out of the hole, the test equipment was removed from the BHA and inspected for damage. It was found that the ERS was in the unlatched position. This may have caused the tool to drop in the first place and may have been the reason the MDHDS could not be retrieved with the ERS.

The drill string was again deployed and Hole U1402A was spudded at 1405 h on 7 June, with the seafloor recorded at 650 m DRF. Hole U1402A was washed down to 96.4 m CSF-A (746.4 m DRF) and the MDHDS, T2P, and ERS were assembled and deployed for a second test. The MDHDS was lowered by the ERS to the BHA at 96.4 m DRF. The ERS was unlatched with the tether system and raised 2m above the BHA. The drill string pressure was raised, and the T2P penetrometer was successfully deployed into the formation. Temperature and pressure signals were successfully transmitted to the rig floor for 30 min and recorded downhole. When circulation was reestablished to clear the BHA of settled sediment, telemetry was lost. The ERS was then lowered and relatched into the MDHDS. However, it was found that the MDHDS could not be retrieved with the wireline system. The wireline tension was increased to ~8000 lb. It was interpreted that the MDHDS had jammed in the BHA. The ERS was released and the Schlumberger wireline was pulled from the hole, the top drive was set back, and the drill string was tripped from the hole. The bit cleared the rotary table at 0110 h, ending Hole U1402A. It was found that the tether within the MDHDS had worked between the tool and the inside of the BHA aperture, jamming the tool in place and preventing recovery. There was also significant sediment within the BHA. This concluded the MDHDS sea trial. The ERS and the MDHDS worked well in this second deployment. The in situ pressure was successfully measured and equal to 7.536 MPa, just slightly above hydrostatic pressure.

The MDHDS was successfully delivered to the BHA and released with the ERS. In addition, the inner MDHDS subassembly was successfully unlatched from the outer subassembly and the T2P was driven into the formation with no damage to the penetrometer tip. Analysis of accelerometer and pressure data showed no coupling with the drill string. Although real-time data were acquired through the tethered system, problems with the tether associated with drill string pressurization suggest that this component (real-time telemetry with a tether) is not ready for regular shipboard use.

When the MDHDS tests were concluded, several hours remained until a helicopter would arrive to exchange departing engineers with arriving science support technicians. The science party requested that a few cores be obtained from Site U1402 to test laboratory equipment and provide experience for the science staff. The vessel was offset 20 m to the east, the drill string was deployed a third time, and Hole U1402B was spudded at 0625 h on 8 June. Two cores were taken from 0 to 15 m CSF-A, with 100% recovery. Core 342-U1402B-1H was a 7 m long mudline core, and Core 2H was an 8 m long partial stroke core that suffered significant core liner damage.

While working on retrieving the second core, a scheduled helicopter arrived on deck at 0932 h with four United States Implementing Organization staff. The helicopter refueled, took on five MDHDS scientists/engineers and luggage and departed the R/V JOIDES Resolution at 1020 h. The rig floor was secured at 1330 h on 8 June, ending Hole U1402B, and the vessel was under way at full speed to Site U1403 (proposed Site JA-1A).

Analysis of cores Cores 342-U1402B-1H and 2H showed the sediment to be unconsolidated, sticky, gray to dark gray-brown Pleistocene–Holocene silty mudstone. The mud contains abundant woody organic matter and patches of sulfides as well as mollusk shell fragments. The sediment is similar to pro-glacial muds elsewhere along the continental margin. The microfossil assemblage consists of sponge and diatom fragments, a foraminifer assemblage dominated by benthic species, and a late Pleistocene calcareous nannoplankton assemblage. Both the benthic foraminifer and calcareous nannoplankton assemblages include, in addition to Pleistocene species, a mixed reworked assemblage. For example, reworked calcareous nannoplankton includes markers for the lower Oligocene, the upper Eocene, and the Cretaceous. Planktonic foraminifers are dominated by cold-water Pleistocene species. Benthic foraminifers are typical of slope water depths of 400–600 mbsl. Section 342-U1402B-1H-1 has normal magnetic polarity, and a short reversed interval was detected in Section 1H-3. A similar reversal event was reported at 14.8–15.7 m CSF-A at Site 1073 and was provisionally identified as the Laschamp or Blake excursion. Nannofossil biostratigraphy indicates that the base of Hole U1402B cannot be older than 70 ka, so we interpret the reversal at 6.15–6.20 m CFS-A to be the ~38–40 ka Laschamp excursion.

Site U1403

Background and objectives

Site U1403 (proposed Site JA-01) is the first and the deepest water site to be drilled on the J-Anomaly Ridge, pinning the deep end of the Paleogene Newfoundland sediment drifts depth transect. The site is positioned to capture deep excursions of the CCD during the Paleogene and to help improve stratigraphic control on the sediments to be drilled on J-Anomaly Ridge. A secondary goal at Site U1403 was to identify the age and lithology of a reflector-rich sediment package that lies beneath the acoustically homogeneous unit that is a primary drilling target for Expedition 342.

Principal results

After a 946 nmi transit from Site U1402, the vessel stabilized over Site U1403 at 1708 h (UTC – 2.5 h) on 11 June 2012. The original plan called for drilling three holes to a depth of ~250 m drilling depth below seafloor (DSF), but the science decision was ultimately to complete operations with two holes: Hole U1403A to 253.3 m DSF and Hole U1403B to 265.1 m DSF. Hole U1403A was spudded at 1020 h on 12 June. Water depth based on the 5.85 m long mudline core was 4944.3 mbsl. The APC system recovered Cores 342-U1403A-1H through 17H, where a hard layer was encountered at ~148 m DSF. The XCB system was deployed for Cores 18X through 29X to a final depth of 253.3 m DSF. The seafloor was cleared at 1240 h on 14 June, ending Hole U1403A. Overall core recovery for Hole U1403A was 231.82 m for the 253.3 m interval cored (91% recovery).

The vessel was offset 20 m east, and Hole U1403B was spudded at 1730 h on 14 June. The intent was to recover ~8 m in the mudline core. The 3.9 m core recovery was a surprise, yielding a water depth of 4948.7 mbsl, 4.4 m deeper than recorded in Hole U1403A. This and correlation of features across the two holes led to the suspicion that the water depth estimate for Hole U1403A was incorrect for unknown reasons. The APC was used for Cores 342-U1403B-1H through16H. The XCB was deployed for Cores 17X through 18X until we broke through the chert layers at 150.4 m DSF. The APC was again deployed for Cores 19H through 22H to 175.9 m DSF. After a partial-stroke core with 2.97 m recovery, the XCB was again deployed for Cores 23X through 32X to a final depth of 265.1 m DSF. Overall, core recovery for Hole U1403B was 229.81 m for the 265.1 m cored interval (87% recovery).

Site U1403 yielded diverse types of deep-sea pelagic sediments within five lithostratigraphic units of Pleistocene to Late Cretaceous (Campanian) age. Core recovery and condition were excellent overall and included records of the K/Pg boundary extinction event, the late Eocene Chesapeake Bay impact, and the Eocene hyperthermals ETM2 and PETM. The majority of the Paleogene is carbonate poor but relatively rich in siliceous microfossils. This record is consistent with paleodepths below the local CCD and anchors the deepest water site of the Expedition 342 depth transect. Initial results reveal episodic deepening of the CCD, which may be evidence of carbonate compensation “overshoots” that enhance carbonate deposition in the deep sea, a predicted response to transient global warming and ocean acidification events.

The downhole lithostratigraphy at Site U1403 includes foraminifer sandy clay; unfossiliferous clay; red, brown, and black chert; clay with radiolarians; clay with nannofossils and radiolarians; nannofossil ooze; and chalk. Uppermost sediments include foraminifer sand with manganese nodules that overlie a succession of unfossiliferous clay and clay with nannofossils and radiolarians. Chert horizons are present below 150 m CSF-A between intervals of radiolarian clay and nannofossil ooze and chalk. The chert horizons are typically poorly recovered. A thin, graded, green spherule horizon is present at the K/Pg boundary and interpreted as debris from the Chicxulub impact event. Underlying sediments largely consist of color-banded nannofossil chalk to a depth of ~262 m CSF-A.

At Site U1403 we recovered a sequence of Holocene–Pleistocene to Campanian sediment. Quaternary calcareous nannofossils and planktonic foraminifers are present in the uppermost 2 m of the section, but from 2 to 70 m CSF-A the sediment contains no age-diagnostic fossils. Calcareous nannofossils and radiolarians indicate a middle Eocene (44.5 Ma) and lower Eocene to K/Pg boundary sequence from ~70 to 220 m CSF-A. Radiolarian assemblages are diverse and well preserved in the middle and lower Eocene and provide the only age control between 70 and 119 m CSF-A. Preliminary biostratigraphic analysis suggests that minor hiatuses may exist in the lower Eocene and middle–upper Paleocene. Fossiliferous sequences of both the PETM and ETM2 hyperthermal events were recovered and include “excursion” calcareous nannofossil assemblages. The K/Pg boundary section appears to be biostratigraphically complete. A high-diversity uppermost Maastrichtian calcareous nannofossil assemblage occurs below the K/Pg boundary impact ejecta bed, and very low diversity, post–mass extinction assemblages occur above this bed. Lowest Danian assemblages are dominated by calcareous dinoflagellates, and a handful of Cretaceous calcareous nannofossil survivor species and are followed uphole by a record of nannoplankton recovery and diversification. Hole U1403B bottomed at ~262 m CSF-A in upper Campanian sediments consisting largely of nannofossil chalk. Planktonic foraminifers are absent or very poorly preserved through most of the succession, except for an interval of well-preserved assemblages in the lowermost Danian and uppermost Maastrichtian. Benthic foraminiferal assemblages characterized by calcareous taxa are present throughout the Paleocene to Cretaceous.

Paleomagnetic results from Site U1403 revealed a continuous series of normal and reversed magnetozones between Sections 342-U1403A-6H-1 and 16H-1 (~46–140 m CFS-A) and between Sections 342-U1403B-6H-5 and 16H-5 (~41–137 m CFS-A). This magnetic stratigraphy correlates well to Chrons C16n.1r through C22n on the geomagnetic timescale and indicates that we have collected a continuous early to late Eocene section (35.892–49.344 Ma). Site U1403 magnetostratigraphy also indicates that the distinctive gray-blue interval at 342-U1403A-6H-2, 80–120 cm, and 342-U1403B-6H-5, 50–90 cm, was deposited during Chron C16n.1n (35.706–35.892 Ma). Thus, this stratigraphic interval, which is characterized by the occurrence of euhedral feldspars and a large spike in NGR, marks the Chesapeake Bay impact event.

A partially spliced composite depth record was produced for Holes U1403A and U1403B. The mudlines could not be reliably aligned because of an inconsistency in the apparent seafloor depths between the two holes. A composite spliced record was achieved between Holes U1403A and U1403B from ~20 and 150 m core composite depth below seafloor (CCSF). Below 150 m CCSF, where chert layers were encountered in both holes, floating composite sections for the ETM2, PETM, and the K/Pg boundary and upper Maastrichtian were constructed.

Age-depth relationships are based largely upon biostratigraphic datums for radiolarians and calcareous nannofossils in Hole U1403A and a combination of paleomagnetic data from Holes U1403A and U1403B. The upper ~46 m of the sediment column at Site U1403 is undated other than an ~2 m thick layer of Holocene–Pleistocene sediment. The magnetostratigraphic identification of Chron C16n.1n (35.706–35.892 Ma) in Core 342-U1403A-6H (and discovery of the same interval in Hole U1403B) represents the first of a series of dated Paleogene horizons at Site U1403. Our correlation indicates that average clay accumulation rates from ~40 to 50 Ma were ~1 cm/k.y. and diminished to ~0.2 cm/k.y. from ~35 to 40 Ma. Average linear rates of sedimentation of ~0.6 cm/k.y. are relatively stable to ~148 m CSF-A. Between 148 and 149 m CSF-A, a ~3 m.y. interval from 50.5 to 53.7 Ma is recorded by a series of chert horizons. The lower Eocene to the PETM sequence accumulated at average linear sedimentation rates of ~1.4 cm/k.y. Immediately underlying the PETM, a highly condensed chert-rich interval with at least one hiatus between 182 and 189 m CSF-A corresponds to ~56–62 Ma. Average linear sedimentation rates of ~0.8 cm/k.y. are recorded in the interval spanning the K/Pg boundary (~62–69 Ma).

Headspace gas analysis for the purpose of safety monitoring yielded low concentrations of methane that gradually increased to 17 ppmv with depth. Other higher hydrocarbon gases were not detected. TOC content was quite low in the upper 34 m of Hole U1403A, ranging from 0.14 to 0.46 wt%, except for the interval 27–31 m CSF-A in which TOC content ranged from 1.4 to 1.7 wt%. Carbonate content varied between 0.04 and 0.80 wt% in Cores 342-U1403A-1H through 13H. In the bottom of Core 13H (~137 m CSF-A), carbonate increases to 60 wt% and fluctuates between ~2 and 40 wt% to the bottom of the recovered sequence.

Grain density values are typically low (~1.5 g/cm³) in site-specific lithostratigraphic Units I–IV, which are dominated by clay, and then increase to 1.6 g/cm³ and gradually to 1.8 g/cm³ in Unit V toward the deepest recovered sequences at the site. Porosity values are generally high (80%) in the radiolarian-rich sediments of Unit III and decrease (~60%) in the carbonate-rich section of Unit V. Magnetic susceptibility falls from Unit I into the upper 18 m CSF-A of Unit II. Below 150 m CSF-A, magnetic susceptibility shows large fluctuations between ~20 instrument units to values over 120 instrument units. These large-amplitude increases in magnetic susceptibility are linked with major events such as the ETM2, PETM, K/Pg boundary, and Campanian/Maastrichtian boundary. A further large-amplitude magnetic susceptibility peak was documented in Paleocene sediments at Site U1403. P-wave velocity increases progressively downhole in the upper 150 m CSF-A to 1550 m/s, takes a step to a velocity of 1600 m/s in the chert at the top of Unit V, and continues to increase to ~1650 m/s at the bottom of the recovered section. NGR measurements average 30 cps until 110 m CSF-A, fall to 20 cps in the nannofossil clays of Unit VI, and then show high-frequency fluctuations in carbonate sediments of Unit V.

At the conclusion of coring at 2200 h on 16 June, the hole was swept clean with 30 bbl of high-viscosity mud and the drill string was pulled from the hole to 78.43 m DSF for logging with the triple combination (triple combo) and Formation MicroScanner (FMS)-sonic tool strings. Two attempts to deploy the logging tools failed and the tools became firmly stuck inside the BHA with ~17 m of the tool string extending out from the bit. After working the tools for several hours with no progress, the wireline was severed and the pipe tripped to the surface. When the tools arrived on the rig floor it was discovered that the triple combo tool string had parted, leaving ~17 m of tools missing from the bottom of the tool string, including the density and porosity tools.

A video and sonar survey was planned to find and recover the lost tools. During deployment, the camera was shaking, vibrating, and rotating around the pipe because of strong ocean currents. At 2145 h, with the bit ~30 m from seafloor, the signals from the subsea camera and the Mesotech sonar were lost. The pipe was tripped back to the rig floor with the camera frame resting on top of the bit. Our suspicion that the coaxial cable supporting the camera system had failed was confirmed when the camera cable arrived at the rig floor.

Repair of the camera system would have taken 1–2 days, and redeployment was likely to result in the same problems. In addition, the loss of the only reentry system available for this vessel would have been detrimental to future operations. The decision not to deploy the camera system again at this site meant that we were unable to locate the lost logging tool or Hole U1403B. The drill floor was secured at 1415 h on 19 June, ending Site U1403 and Hole U1403B.

Site U1404

Background and objectives

Site U1404 is the second deepest drill site of the Expedition 342 Newfoundland sediment drifts depth transect. Principal goals included recovery of a Paleogene record of the position of the North Atlantic CCD and a more expanded record of sedimentation compared to the condensed, sub-CCD record at Site U1403. A related objective was to discover the types of sediments that contribute to the expanded, acoustically transparent sediment drift deposits that are so prominent on J-Anomaly Ridge.

Principal results

After a 4.2 nmi transit from Site U1403, the vessel arrived at Site U1404 at 1455 h (UTC – 2.5 h) on 19 June 2012. The original plan called for drilling three holes to a depth of ~250 m DSF.

Hole U1404A was spudded at 1030 h on 20 June, and the mudline was established at 4753.8 m DRF; 4742.3 mbsl), which was 35.4 m below the precision depth recorder (PDR) depth estimate. The discrepancy between the PDR depth and the drill pipe depth might have been attributable to strong currents creating an S-shape in the drill pipe or the thermal and current layering in the water column, as indicated by the poor quality of the acoustic signal received from the acoustic beacon on the seafloor. Cores 342-U1404A-1H through 32H were taken to a depth of 271.0 m DSF, with a recovery of 257.97 m. Cores 22H through 32H were partial strokes, and the hole was advanced by recovery. The XCB was deployed for Cores 33X through 36X to a final depth of 308.8 m DSF, with a recovery of 23.05 m for the 37.8 m interval cored. Overall core recovery for Hole U1404A was 281.02 m for the 308.8 m interval cored (91% recovery).

The vessel was offset 20 m east, and Hole U1404B was spudded at 2255 h on 22 June. Water depth was 4747.6 mbsl based on mudline core. Cores 342-U1404B-1H through 27H were recovered to a total depth of 228.7 m DSF. Cores 21H through 27H were partial strokes, and the hole was advanced by recovery. Eight core liners were either collapsed or broken and three of those had to be pumped out of the core barrel with a high-pressure pump. Total recovery was 228.04 m (100%).

The vessel was offset 20 m south, and Hole U1404C was spudded at 1445 h on 24 June. Hole U1404C was drilled to 16 m DSF and then cored to 44.5 m DSF (Cores 342-U1404C-2H through 4H) in an attempt to recapture a zone that potentially contained gas hydrate based on observations in the previous two holes. Seafloor and water depths were assumed to be the same as those at Hole U1404B (4759.1 m DRF; 4747.6 mbsl). The total advance was 28.5 m, with 28.98 m of core recovered (102%).

The bit cleared the seafloor at 1945 h on 24 June, ending Hole U1404C. The drill floor was secured and the vessel began moving to Site U1405 in dynamic positioning mode at 0.9 kt. The total time spent on Hole U1404C was 6.5 h. The total time spent at Site U1404 was 5.2 days.

The downhole sedimentary sequence at Site U1404 reveals four site-specific lithostratigraphic units. Unit I is ~2 m thick and composed of Pliocene–Pleistocene brown foraminiferal sandy clays and nannofossil ooze with manganese nodules and a cobble-sized dolomitic dropstone, transitioning to Pliocene brown clay with silt. Unit II is a green and greenish gray carbonate-poor Oligocene to Miocene clay that occurs in a nearly 200 m thick sequence and contains abundant diatoms, radiolarians, and sponge spicules. Unit II is divided into an upper Subunit IIa (20 m thick), which is barren of microfossils, and lower Subunit IIb (180 m thick), which contains abundant siliceous microfossils (diatoms, radiolarians, and sponge spicules) and a minor abundance of calcareous nannofossils. Unit III is an ~26 m interval of carbonate-rich nannofossil ooze alternating with clay-rich nannofossil ooze and clay that spans the lowermost Oligocene and uppermost Eocene. Unit IV is an ~75 m thick succession of clay and claystone with some intervals containing abundant radiolarians and/or calcareous nannofossils. Lithoclasts are found in the >63 μm size fraction in Site U1404 sediment, particularly in the Miocene and Oligocene sequences, and may represent IRD.

The biochronology for Site U1404 consists of a early Miocene (~19 Ma) to middle Eocene (~43 Ma) succession with a thin (~2.5 m) Pliocene–Pleistocene cover. These abyssal, carbonate-poor, green clays are challenging to date biostratigraphically, as none of the microfossil groups are continuously present and the calcareous fossils are frequently poorly preserved or absent. Planktonic foraminifers are generally absent except in the lower Miocene. Radiolarians occur more consistently from lower Miocene to middle Eocene, although they are absent in the cores spanning the Eocene–Oligocene transition. When combined with the lower to middle Eocene radiolarian succession at Site U1403, these assemblages will help to refine radiolarian biostratigraphy in the North Atlantic. Abundant diatoms suggest high productivity in the lower Miocene, supported by the occurrence of well-preserved benthic foraminifer assemblages that indicate high organic matter flux and/or oxygen consumption at the seafloor. We recovered an Oligocene/Eocene boundary interval that appears to be stratigraphically complete with variable but consistent carbonate and good preservation of calcareous nannofossils and benthic foraminifers. A succession of nannofossil events that characterizes this interval globally, including the extinction of the multiradiate discoasters and the Clausicoccus acme, is also recorded.

Geochronologic analyses suggest continuous lower Miocene–upper Oligocene and upper–middle Eocene intervals with comparatively high sedimentation rates (7.0 and 1.4 cm/k.y., respectively) and an Oligocene to Oligocene–Eocene transition with a lower sedimentation rate (1.0 to 0.5 cm/k.y.). A ~2 m.y. hiatus is inferred in the lower Oligocene (~34–32 Ma).

Methane concentrations in headspace gas samples was 1.75–28.8 ppmv. In the upper 212 m CSF-A, the concentration of methane did not exceed 4.24 ppmv. Below 212 m CSF-A (Core 342-U1404A-25H), there was a concomitant increase in methane and ethane concentrations to ~28.8 and ~1.79 ppmv, respectively. Hole U1404C was drilled and sampled to determine the presence of gas hydrates, whose presence was suggested by effervescent sediment, expelled section caps, bulging core liners, a drop in bulk density, and the presence of massive pyrite in one core. However, methane concentrations in headspace samples (1.82–2.99 ppmv) were not above atmospheric levels, no other hydrocarbon traces were detected, and uniform chlorinity profiles from rhizon samples do not suggest the presence of methane hydrates. Overall, downhole profiles of pore water components reflect

• Organic matter degradation,
• Diffusion-related gradients produced from deep sources and sinks for chemical constituents,
• Sorption of ions onto clay minerals, and
• Secular variability in seawater chemistry over the depositional age of the sediments.

Downhole analysis of sediment geochemistry shows that the sediment is nearly carbonate free (<5 wt%) in the surficial 200 m CSF-A. However, carbonate content prominently increases to >10 wt% around 60, 75, 90, and 170 m CSF-A. Between 200 and 300 m CSF-A, we observed four distinctive increases in CaCO₃ at 200–206, 208–213, 239–245, and 265–279 m CSF-A, with two less distinct events between 213 and 226 m CSF-A. The maximum carbonate content recorded is 57 wt% at 202.75 m CSF-A, coincident with the Eocene–Oligocene transition. Calculated TOC values are typically low (~0.2 wt%) with highest values (>1 wt%) in the 50–170 m CSF-A interval.

Sediment physical properties show an increasing trend in bulk density toward 1.8 g/cm³ in the carbonate-rich sections (below ~200 m CSF-A). Grain density averages 2.7 g/cm³ in Hole U1404A. Porosity is generally high in the radiolarian-rich sediment (80%) and decreases in the carbonate-rich sediment (~40%). Magnetic susceptibility measurements decrease from 100 to 2 instrument units between the top of the sediment column and ~20 m CSF-A and remain low until the carbonate content increases near the Eocene/Oligocene boundary (~204 m CSF-A). P-wave velocity increases progressively downhole and shows a small step increase to ~1630 m/s in the carbonate-rich unit (site-specific lithostratigraphic Unit III). NGR measurements vary between 20 and 55 cps and also increase downhole. A significant peak in NGR is seen at 200 m CSF-A, which corresponds to the Eocene–Oligocene transition. Color reflectance follows the same trend as magnetic susceptibility with a distinctive drop at ~15 m CSF-A and a significant increase below the Eocene–Oligocene transition.

Real-time stratigraphic correlation at Site U1404 was difficult because of a lack of strong signals in the physical property data. The greenish gray Miocene to late Oligocene sediments spanning ~20–230 m CCSF had extremely low magnetic susceptibility (below 15 instrument units, which is near the detection limit of the instrument), so only GRA bulk density data were available for real-time correlation. GRA density data contained slightly more structure than magnetic susceptibility, but few clear features existed on which to base drilling adjustments. A sudden increase in magnetic susceptibility at ~238 m CCSF corresponds to the interval immediately preceding the Eocene–Oligocene transition. The primary goal of stratigraphic correlation was to cover the coring gap between Cores 342-U1404A-23H and 24H, interpreted as the Eocene–Oligocene transition. Initial correlation suggested that Hole U1404B had not bridged this gap, suggesting a third hole might be necessary. Further consideration of Hole U1404B, including Whole Round Multisensor Logger data and lithologic interpretation of split cores, suggested that the coring gap was, in fact, covered by Core 342-U1404B-24H.

Site U1405

Background and objectives

Site U1405 is a mid-depth site on the Expedition 342 Newfoundland sediment drifts depth transect. Principal goals are

• To test the hypothesis that the seismically homogeneous package prominent on J-Anomaly Ridge is a plastered drift deposit of Paleogene age,
• To obtain a sedimentary section suited to paleoceanographic study at suborbital timescales featuring very high rates of deposition compared to those typically found in deep-sea pelagic sites (1–2 cm/k.y.), and
• To capture excursions of the Cenozoic CCD.

Principal results

The vessel arrived at Site U1405 (4280 mbsl) at 0745 h (UTC – 2.5 h) on 25 June 2012 after a 7.5 nmi transit from Site U1404. The plan for Site U1405 called for drilling three holes to a depth of ~250 m DSF.

Cores 342-U1405A-1H through 26H were recovered to 241.9 m DSF. Advanced piston corer temperature tool (APCT-3) formation temperature measurements were taken on Cores 4H, 7H, and 10H with good results. Core 26H was the first partial stroke, and the core had to be pumped out of the core barrel. The XCB was deployed for Cores 27X through 33X to a total depth of 308.6 m DSF. Overall core recovery for Hole U1405A was 270.34 m for the 308.6 m interval cored (88% recovery).

The vessel was offset 20 m east, and Cores 342-U1405B-1H through 24H were recovered to a total depth of 218.5 m DSF. An interval of 5 m was drilled without coring in an attempt to cover coring gaps in Hole U1405A. Coring the 218.5 m interval yielded 219.60 m of core (101% recovery). The vessel was offset 20 m south, and Cores 342-U1405C-1H through 25H were recovered to a total depth of 232.0 m DSF. The cored interval of 232.0 m yielded 227.77 m of core (98% recovery). The seafloor was cleared at 0200 h on 30 June, ending Hole U1405C.

After clearing the seafloor the drill string was raised to ~3500 m DRF and the vessel began moving in dynamic positioning mode to the next site at a speed of 1.5 nmi/h. The positioning beacon was left on site for a later recovery to minimize the risk of losing it during recovery in difficult weather conditions. The total time spent at Site U1405 was 4.8 days.

The lithostratigraphy at Site U1405 is composed of ~20 m of Pliocene–Pleistocene nannofossil ooze and clay (site-specific lithostratigraphic Unit I) overlying an expanded sequence (~250 m thick) of upper Oligocene through lower Miocene distinctive greenish gray clay and ooze (Unit II). Unit II contains varying abundances of radiolarians, diatoms, and nannofossils and is divided largely according to changes in carbonate content (~0 to 30 wt%). Pale carbonate-rich intervals are present around the Oligocene–Miocene transition. Some of these intervals contain common to abundant Braarudosphaera nannofossil occurrences and even thin (1–2 mm), discrete Braarudosphaera ooze layers that have been disrupted by bioturbation. Signal processing of L* data reveals significant peaks in spectral power concentrated at wavelengths of ~16 and ~4 m, indicating a possible orbital control over sediment composition that may be particularly useful for detecting hiatuses and changes in sedimentation rate.

Biostratigraphic analysis of Site U1405 shows that the site records a middle Miocene (~14 Ma) to late Oligocene (~30 Ma) succession with a thin (0–6.2 m), Pliocene–Pleistocene cover. Between 6.2 and 26.2 m CSF-A, siliceous and calcareous microfossils are absent. Below 26.2 m CSF-A, nannofossils, radiolarians, and planktonic foraminifers provide a well-defined biostratigraphy that is in good agreement with paleomagnetically determined chron boundaries. Nannofossils are predominantly abundant and moderately well preserved. Planktonic foraminifers are generally common and well preserved throughout the hole. Except for the top and bottom of the hole, radiolarians occur consistently from the early Miocene to late Oligocene. As seen at Site U1404, abundant diatoms suggest high productivity in the lower Miocene, supported by the occurrence of well-preserved infaunal benthic foraminifer assemblages that imply high organic matter flux to the seafloor. The lower Miocene interval has comparatively high sedimentation rates (3.3 cm/k.y.), whereas the Oligocene–Miocene transition has still higher sedimentation rates (~10 cm/k.y.). Paleomagnetic data indicate a potential hiatus between 19 and 21.5 Ma.

Paleomagnetic results from Site U1405 reveal a continuous series of normal and reversed magnetozones in all three holes, between ~39 and ~240 m CSF-A. Magnetozones can be straightforwardly correlated between all three holes, especially below ~90 m CSF-A. Although the pattern and stratigraphic thickness of magnetozones in all three holes is similar, there are significant offsets between the CSF-A depths of these magnetozone boundaries in Hole U1405A and those in Holes U1405B and U1505C. We primarily used nannofossil and foraminifer biostratigraphy to correlate Hole U1405A magnetostratigraphy to chron boundaries C5Br/C5Cn.1n (15.974 Ma) through C5Cn.2r/C5Cn.3n (16.543 Ma) and C6AAr.3r/C6Bn.1n (21.767 Ma) to C6Cn.3n/C6Cr (23.295 Ma) on the geomagnetic polarity timescale. This correlation provides a shipboard chronostratigraphic framework for interpreting the latest late Oligocene–middle Miocene at this site. Hole U1405A magnetostratigraphy indicates at least two substantial (1–3 Ma) unconformities during rapid (~3.3–5.7 cm/k.y.) deposition of the middle–late Miocene green clay drift deposits, whereas in Holes U1405B and U1405C, only one of these hiatuses is recognized.

Real-time stratigraphic correlation at Site U1405 was difficult because magnetic susceptibility data were below the detection limit for most of the sediment column in Holes U1405A–U1405C. A prominent color change from tan to greenish gray in the top three cores provides a clear correlation between the three holes. This was used to make initial adjustments to drilling operations in order to offset coring gaps. The majority of the recovered strata at Site U1405 were Miocene to Oligocene in age; these sediments were very homogeneous and showed few distinctive features downhole to ~200 m CSF-A. A clear color change and associated GRA bulk density peak present in all three holes provided a strong tie just below the Oligocene/Miocene boundary. This tie suggests that we successfully recovered a complete Oligocene–Miocene transition between the three holes. Whole-core physical property data series between these two ties are not straightforward to interpret. Large lateral variations may exist in the drift that cause differences in the recovered strata between each hole. As a result, most of our tie points are tentative, and the splice for Site U1405 will require postcruise revision.

Headspace gas results from routine safety monitoring revealed methane in low concentrations (1.59–3.49 ppmv). Higher molecular weight hydrocarbons were not detected in measurable amounts. Calculated TOC values are typically low (~0.2–0.5 wt%) with highest values (>2 wt%) in the middle of site-specific lithostratigraphic Subunit IIa (50–150 m CSF-A). Pore water profiles from Hole U1405A suggest organic matter degradation through manganese oxide and iron oxide metabolic pathways. The downhole pore water concentration profiles for manganese, iron, sulfate, and ammonium suggest that organic matter consumption has not driven pore fluid geochemistry to sulfate reduction. Pore fluid pH and alkalinity profiles show regular trends downhole (decreasing and increasing, respectively) and reflect changes in dissolved inorganic carbon in response to organic matter consumption. Pore fluid concentrations of calcium and strontium and elemental ratios of Sr/Ca and Mg/Ca suggest that two processes are at work: carbonate recrystallization and exchange reactions with the basaltic basement (a source of Ca and sink for Mg) and diffusion through the sedimentary sequence. Additionally, potassium concentrations have been modified through authigenic alteration of clay minerals.

Carbonate content is generally between 0 and 10 wt% but increases to 10–20 wt% in the lower portion of Subunit IIa. Several distinct intervals of high carbonate (up to 46 wt%) and low carbonate (<15 wt%) are observed. Based on the shipboard biostratigraphic and paleomagnetic derived age model, high carbonate intervals in Subunit IIa are likely to correspond with lowermost Miocene and upper Oligocene carbonate peaks observed at Site U1404. Intervals of carbonate in the uppermost Oligocene are driven by calcareous nannofossil abundance, particularly Braarudosphaera.

Almost all of the physical properties measured at Site U1405 show two major trends, both related to lithostratigraphy. Magnetic susceptibility, color reflectance parameters a* and b*, and bulk density show higher values in lithostratigraphic Unit I than Unit II, whereas porosity and water content show the opposite trend. P-wave velocity gradually increases downhole from 1500 to 1650 m/s, a typical compaction trend similar to that seen in bulk density and water content in Unit II. L* and NGR measurements show different trends in all three holes, which suggests lateral heterogeneity in the sediment section in agreement with paleomagnetic results. Subtle changes in L* likely reflect cyclic changes in calcium carbonate.

Site U1406

Background and objectives

Site U1406 (3814 mbsl) was at ~3300 mbsl paleodepth at 50 Ma (Tucholke and Vogt, 1979) and is in the mid-range of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site was positioned to capture a record of sedimentation >1.1 km shallower than the largely sub-CCD record drilled at Site U1403. Our primary scientific objectives for drilling Site U1406 were

• To reconstruct the mid-depth CCD in a primarily carbonate-dominated record;
• To obtain records of the Oligocene–Miocene and Eocene–Oligocene transition events in carbonate-rich sediments that host abundant foraminifers suitable to the construction of geochemical climate records;
• To evaluate the history of deepwater and possible northern hemisphere glaciation on sediment chemistry, grain size, and provenance; and
• To evaluate biological evolution during Paleogene climate transitions.

Principal results

The vessel arrived at Site U1406 after a 14.9 nmi transit from Site U1405, which was made in dynamic positioning mode at a speed of 1.4 nmi/h with the drill pipe suspended below the vessel. The vessel stabilized over Site U1406 at 1435 h (UTC – 2.5 h) on 30 June 2012. The plan for Site U1406 called for drilling three holes to a depth of ~250 m DSF. Cores 342-U1406A-1H through 25H were retrieved from the seafloor to 217.7 m DSF. The first partial stroke was recorded when shooting for Core 16H, and the APC was advanced by recovery for this and subsequent cores. The XCB was deployed for Cores 26X through 34X to a total depth of 283.3 m DSF. Overall core recovery for Hole U1406A was 267.30 m for the 283.3 m interval cored (94%).

The vessel was offset 20 m east, and Cores 342-U1406B-1H through 22H were retrieved to 188.8 m DSF. The XCB was deployed for Cores 23X through 30X to a total depth of 253.6 m DSF. The recovery for Hole U1406B was 241.34 m over the 253.6 m cored (95%). The vessel was offset 20 m south, and Cores 342-U1406C-1H through18H were recovered to 161.4 m DSF. The XCB was deployed to the final depth at 241.4 m DSF. Two intervals, 3 and 2 m, were drilled without coring.

After clearing the seafloor, the drill string was tripped to the surface. The BHA was set back in the derrick with the exception of the lower seal bore drill collar plus subs. The Schlumberger logging tools were then rigged up for a pass-through check on the lower portion of the BHA. The drill floor was secured at 1600 h on 6 July, ending Hole U1406C. The acoustic positioning beacon was recovered, and the vessel began the move to Site U1405 to recover the beacon left behind there. The total time spent on Site U1406 was 145.5 h (6.1 days).

At Site U1406 we recovered a sedimentary succession of deep-sea pelagic sediment of Pleistocene to middle Eocene age, with four site-specific lithostratigraphic units. Unit I is ~2 m thick and composed of Pleistocene brown foraminiferal sand and nannofossil ooze with manganese nodules. Unit II changes from brown to green Miocene and Oligocene nannofossil ooze that occurs in a ~180 m thick sequence and contains abundant diatoms and/or radiolarians in some intervals. Unit III is an ~40 m interval of carbonate-rich nannofossil ooze alternating with clay-rich nannofossil ooze and clay that spans the lowermost Oligocene, late Eocene, and middle Eocene. Unit IV marks the transition from reduced to oxidized sediment, largely nannofossil oozes, that are middle Eocene to Paleocene in age. Sand-sized lithoclasts are found in the >63 μm size fraction, particularly in the Miocene and Oligocene sequences, and may represent ice-rafted or current-transported sediment.

The uppermost brown foraminifer sandy clay and nannofossil ooze (Cores 342-U1406A-1H through 2H; 0–2.25 m CSF-A) contain nannofossils and planktonic foraminifers that indicate Pleistocene ages (nannofossil Zones NN18 to NN19). Below 2.25 m CSF-A, nannofossils, planktonic foraminifers, and radiolarians provide a well-defined biostratigraphy indicating upper lower Miocene to middle Eocene sediment. Siliceous microfossils are more poorly preserved than at Sites U1404 and U1405 in sediment of early Miocene and late Oligocene age, and diatoms are consistently rare or absent. Radiolarians are present in the lower Miocene–upper Oligocene and in the middle Eocene–upper Paleocene but are absent from the ~110 m thick interval (~130–240 m CSF-A) spanning the Oligocene–Eocene transition. Nannofossils are present and show good preservation continuously across the Eocene/Oligocene boundary interval and through the upper to middle Eocene section. A major unconformity at ~255 m CSF-A is inferred to span the entire lower Eocene and uppermost Paleocene, including the PETM. Below this unconformity, a complete succession of uppermost to middle Paleocene microfossil zones is identified. Benthic foraminifers are generally rare (the “present” category) but increase in abundance in upper Eocene to upper Oligocene sediment (~110–220 m CSF-A). Benthic foraminifer preservation is generally good to very good.

Paleomagnetic results from Site U1406 reveal a series of normal and reversed magnetozones between ~10 and 204 m CSF-A. Magnetozones can be straightforwardly correlated between all three holes, especially below ~66 m CSF-A. We used nannofossil, radiolarian, and foraminifer biostratigraphic datums to correlate the Hole U1406A magnetostratigraphy to chron boundaries C5Dn/C5Dr.1r (17.533 Ma) through C5Dr.2r/C5En (18.056 Ma), C6n/C6r (19.722 Ma) through C6An.1n/C6An.1r (20.213 Ma), C6AAr.3r/C6Bn.1n (21.767 Ma) through C7An/C7Ar (24.984 Ma), C8r/C9n (26.420 Ma), and C10r/C11n.1n (29.183 Ma) through C13r/C15n (34.999 Ma) on the geomagnetic polarity timescale. Hiatuses at Site U1406 are generally co-eval with those recognized at Site U1405, where at least three hiatuses were identified to occur during rapid deposition of the middle Miocene drift deposits. We estimate the age of these hiatuses to range from 0.25 to ~3 Ma. The lower Miocene to middle Eocene succession appears to be stratigraphically complete, at the resolution of shipboard biostratigraphy and magnetostratigraphy, but a significant hiatus occurs between the middle Eocene and uppermost Paleocene. Sedimentation rates are relatively consistent around ~3 cm/k.y. for the lower Miocene to upper middle Eocene but are lower (~0.5 cm/k.y.) through the lower middle Eocene and the Paleocene.

The shipboard splice for Site U1406 is stratigraphically continuous for most of the sediment column, with only four appended cores in the interval covered in all three holes (~0–240 m CSF-A). The splice is mainly based on NGR values, but magnetic susceptibility was also useful below ~200 m CSF-A, where values exceed 20 instrument units. In particular, our splice indicates a stratigraphically continuous record across the Eocene–Oligocene transition between ~215 and 230 m CCSF, including cores from all three holes. Distinct color changes in the upper sediment column at Site U1406 aided real-time stratigraphic correlation between holes, allowing initial offset of coring gaps. From ~25 to 200 m CSF-A, magnetic susceptibility is below the detection limit and GRA bulk density shows an overall increase but few prominent features. Changing from APC to XCB resulted in poor recovery in Holes U1406A and U1406B around 200 m CSF-A. By switching to XCB earlier in Hole U1406C, most of this missing interval was successfully recovered.

Gradients in calcium concentrations, strontium concentrations, and strontium/calcium ratios of pore water suggest that the upper 70 m CSF-A reflects a mature diffusion profile from deep basaltic exchange reactions. Between 70 and 180 m CSF-A, carbonate dissolution contributes to the shape of the pore fluid profiles, indicated by a switch from decreasing to uniform Sr/Ca ratios at 70 m CSF-A. In lithostratigraphic Unit IV, decreasing pore water alkalinity and calcium concentrations are consistent with precipitation of authigenic carbonate from pore fluids. Carbonate overgrowths on benthic foraminifers in the sediments of middle Eocene and Paleocene age in Unit IV are consistent with this interpretation.

The sediment column at Site U1406 is generally carbonate rich (21–92 wt% CaCO₃) with low TOC content (0.01–0.5 wt% TOC) and low headspace gas contents. A prominent increase in carbonate content occurs around 190–200 m CSF-A associated with the Eocene–Oligocene transition, as defined by biostratigraphy and magnetostratigraphy. However, peak values (92 wt% CaCO₃) occur lower in the sediment column at Site U1406 in middle to upper Eocene strata.

Sediment bulk density at Site U1406 increases downhole from 1.4 to 1.9 g/cm³. Grain density averages 2.7 g/cm³, and both porosity and water content show a decreasing trend downhole (from 50% to 80% and from 25% to 60%, respectively), with the lowest values occurring in carbonate-rich sediment (below ~170 m CSF-A). Magnetic susceptibility averages 9 instrument units throughout all holes, but significant peaks occur at ~182, 205, and 235 m CSF-A. P-wave velocity increases progressively downhole from 1500 to 1800 m/s reflecting increased compaction and lithification. Significant peaks in NGR, reflectance, and magnetic susceptibility are observed associated with the Eocene–Oligocene transition.

Site U1407

Background and objectives

Site U1407 is a mid-depth site (3073 mbsl; ~2600 mbsl at 50 Ma) (Tucholke and Vogt, 1979) in the upper end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site was positioned to capture a record of sedimentation ~1.9 km shallower than the largely sub-CCD record drilled at Site U1403. The location above the average late Paleogene CCD should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in background noncarbonate sedimentation. Our primary scientific objectives for drilling Site U1407 were

• To reconstruct the mid-depth CCD in a primarily carbonate-dominated record for the early and middle Eocene;
• To obtain records of the Eocene and Paleocene in carbonate-rich sediments that host abundant foraminifers suitable to the construction of geochemical climate records;
• To evaluate the history of deep water on sediment chemistry, grain size, and provenance; and
• To evaluate biological evolution during Paleogene climate transitions.

Secondary objectives included dating acoustic horizons to better constrain regional sedimentation during the Paleogene and Cretaceous and allow us to anticipate the likely age of the sedimentary sequence at the remaining Expedition 342 sites.

Principal results

After a 120 nmi, 11 h transit from Site U1406 at a speed of 10.9 kt, the vessel arrived at Site U1407 at 0800 h (UTC – 2.5 h) on 7 July 2012. The plan for Site U1407 called for drilling three holes to a depth of ~250 m DSF. A mudline core established water depth for Hole U1407A at 3073.1 mbsl. Cores 342-U1407A-1H through 15H were retrieved using nonmagnetic core barrels and the FlexIt core orientation tool. The first partial stroke was experienced with Core 11H, and the APC was advanced by recovery to Core 15H at 121.9 m DSF. The XCB was deployed for Cores 16X through 35X to a final depth of 308.7 m DSF. Overall core recovery for Hole U1407A was 205.64 m for the 308.7 m cored (66% recovery). This relatively low recovery can most likely be attributed to the high heave and large pitch and roll of the vessel during coring operations.

The vessel was offset 20 m east, and Cores 342-U1407B-1H through 11H were recovered using nonmagnetic core barrels and the FlexIt core orientation tool. A 3 m interval (27.4–30.4 m DSF) was drilled without coring in an attempt to cover a coring gap in Hole U1407A. Based on the recovery of an interval of chert layers in Hole U1407A, the interval from 95 to 127 m DSF was drilled without coring using the XCB. Cores 13X through 28X were then recovered to the final depth of 276.3 m DSF. The recovery for Hole U1407B was 234.54 m over the 241.3 m cored (97% recovery).

The vessel was offset 40 m west, and Cores 342-U1407C-1H through 11H (0–93.0 m DSF) were recovered using nonmagnetic core barrels. A 3 m interval (27.4–30.4 m DSF) was drilled without coring to optimize core overlap in multiple holes. Once again, a 21 m interval (96–117 m DSF) was drilled without coring through the chert layers using the XCB. Cores 13X through 29X were then recovered to the final depth of 261.6 m DSF. Overall recovery for Hole U1407C was 244.4 m from the 237.6 m interval cored (103% recovery). The rig was secured for a dynamic positioning move to the next site at 1915 h on 11 July, ending Site U1407. The overall recovery for Site U1407 was 87%. The total time spent on Site U1407 was 107.25 h (4.5 days).

The downhole sedimentary sequence at Site U1407 consists of a Pleistocene to uppermost Lower Cretaceous column of pelagic sediments overlying reef sediment of late Albian age. The sequence is divided into six site-specific lithostratigraphic units. Unit I is ~8 m thick and composed of Pleistocene foraminiferal nannofossil ooze intermittently interbedded at decimeter scale with foraminiferal sand and clay with nannofossils. Rock fragments of pebble to cobble size and coarse silt- to sand-sized quartz and amphibole are pervasive. Unit II is a ~10 m thick sequence of early Oligocene age composed of clay with nannofossils with disseminated manganese nodules and sulfide patches and intercalated millimeter to centimeter sulfide layers. Unit III consists of ~70 m of middle Eocene nannofossil ooze with foraminifers; sulfide patches and layers are also present. An abrupt downhole change in color from light greenish gray to white marks the contact between Units III and IV and is associated with significant changes in physical proxies and a downhole increase in carbonate content. Unit IV consists of ~20 m of lower Eocene nannofossil ooze with foraminifers. Unit V is composed of Paleocene to Cenomanian nannofossil chalk divided into two subunits (Va and Vb). The contact between Unit IV and Subunit Va was not recovered because of the operations decision to drill without attempting to recover a sequence interpreted to contain well-developed cherts. Subunit Va is composed of ~60 m of Paleocene nannofossil chalk with foraminifers and radiolarians. Subunit Vb is mainly nannofossil chalk or nannofossil chalk with foraminifers and spans the Cenomanian to Campanian over a ~85 m thick sequence. Subunit Vb contains black shales of Cenomanian/Turonian boundary age (OAE 2; ~93 Ma). Unit VI is divided into two subunits (VIa and VIb). Subunit VIa is ~1 m thick and comprises fine-grained, partially silicified and dolomitized calcareous grainstone with horizontal laminations and is of late Albian age. Subunit VIb consists of extremely poorly recovered fossiliferous reef deposits of Albian age.

The biochronology of Site U1407 is based on nannofossils and planktonic and benthic foraminifers throughout the ~300 m thick sequence. Nannofossils, planktonic foraminifers, and smaller benthic foraminifers are present in all but the basal Albian neritic limestone, which contains larger benthic foraminifers and macrofossils. Thin Pleistocene and lower Oligocene intervals overlie an expanded middle Eocene through upper Albian succession. A detailed biozonation of Upper to mid-Cretaceous sediments reveals a condensed sequence that records the Campanian/Santonian, Santonian/Coniacian, Coniacian/Turonian, and Albian/Cenomanian boundaries. Biostratigraphy of black shale recovered at ~230 m CSF-A indicates the presence of Turonian nannofossil Zone UC6 above, and Cenomanian nannofossil Zone UC5/4 below, providing strong evidence that this lithology represents OAE 2. Benthic foraminiferal assemblages support this conclusion, with the black shale dominated by agglutinated species and calcareous taxa that indicate low oxygen concentrations at the seafloor. Radiolarians are abundant and well preserved in the early middle Eocene and the Paleocene but are either absent or age-indeterminate in both the upper Pleistocene–lower middle Eocene and lowermost Paleocene–Cretaceous intervals.

Geochronologic analyses suggest that the late to middle Eocene transition is continuous to the magnetochron level with comparatively high average linear sedimentation rates (2.0–8.7 cm/k.y.). A series of distinct magnetochrons have been identified between Cores 342-U1407A-6H and 10H (and correlative intervals in Holes U1407B and U1407C) that have a biochronology consistent with Chrons C20r through C22r (~43.4–49.4 Ma). The magnetostratigraphy and biochronology suggest that sedimentation rates varied between 2.0 and 8.7 cm/k.y. across the late Eocene–middle Eocene transition. The Chron C25r/C26n boundary is present in Section 342-U1407A-19X-2.

Headspace methane concentrations (1.4–4.12 ppmv) were not above atmospheric levels. Pore water profiles show evidence of compartmentalization with prominent abrupt downhole shifts in Mg, Mn, and K at ~100–120 m CSF-A, suggesting that the unrecovered sequence of cherts acts as an aquiclude. The downhole profile for Mg shows a reversed gradient to the base of the sediment column suggestive of a source of Mg within the highly porous underlying reefal sediment. Carbonate content in the whole sediment column at Site U1407 ranges from 0 to 93 wt%. The most prominent change in carbonate content is a step increase associated with the transition downhole from middle Eocene to lower Eocene sediment (from 59.0 to 82.5 wt% CaCO₃; ~80 m CSF-A). This step correlates with shifts in several proxies (e.g., L*, magnetic susceptibility, NGR, TOC, and TN values). TOC values are typically 0.1–0.5 wt% over this whole interval. Homogeneous to microlaminated organic-rich black shales from Holes U1407A and U1407C are rich in TOC (~4 and 17 wt%, respectively). Organic matter is thermally immature and relatively well preserved, as shown by both the high hydrogen indexes (~600–620 mg hydrocarbons per gram organic carbon) and low T_max values (<415°C). C/N ratios increase as organic carbon concentrations increase. Organic matter is Type II kerogen, derived from algal and microbial primary production.

Sediment bulk density shows a downhole-increasing trend from ~1.5 g/cm³ at the uppermost part of the hole to ~2.2 g/cm³ at the contact between the basal Albian pelagic sediments and the lithified cap of the underlying reef carbonate sediments (~270 m CSF-A). Grain density peaks at the same contact to 2.9 g/cm³ in Hole U1407A. Porosity values are generally highest in the upper ~50 m CSF-A of the sediment column and between ~150 and 175 m CSF-A (~60%), whereas porosity is low in the basal pelagic carbonates (~40%). Magnetic susceptibility measurements decrease from high values (up to 120 instrument units) to 5 instrument units, associated with the downhole transition from the thin veneer of Oligocene–Pleistocene sediment into the underlying Eocene nannofossil ooze. P-wave velocity increases progressively downhole and shows abrupt changes at ~180, 206, 225, and 270 m CSF-A. These changes in P-wave velocity may contribute to development of weak reflections in the seismic reflection profiles crossing the site. NGR shows an overall downhole increase at Site U1407 with multiple superimposed prominent features that are readily correlated among all three holes, such as

• A sharp peak (to ~50 cps at ~10 m CSF-A) at the contact between the Pleistocene cover at the top of the sediment column and the underlying Oligocene clays,
• A downhole step decrease from ~30 to 5 cps (~80 m CSF-A) associated with the step increase in carbonate content across the contact between the middle and lower Eocene nannofossil ooze, and
• A distinctive peak (to ~40–50 cps at ~230 m CSF-A) associated with the Cenomanian–Turonian black shales.

Color reflectance follows a trend similar to magnetic susceptibility, with distinctive peaks in a* and b* and a minimum associated with the black shale sequence that can be correlated among all three holes.

The stratigraphic splice constructed for Site U1407 is stratigraphically continuous from 0 to ~112 m CCSF and ~200 to 312 m CCSF. Part of the gap between these two spliced intervals (~112–133 m CCSF) is attributable to the operations decision to drill without attempting to recover a horizon with well-developed cherts. The interval between 133 and 200 m CCSF is characterized by modest changes in physical properties data sets and proved impossible to splice using shipboard data alone. Both magnetic susceptibility and NGR were used for stratigraphic correlation and construction of the two spliced intervals. These two data sets show clear, correlative features throughout the sediment column. NGR is the most useful data set for correlation from 0 to ~112 m CCSF and magnetic susceptibility is most useful from ~135 to 200 m CCSF, whereas both data series show distinctive features from ~200 to 312 m CCSF. The black shale sequence associated with OAE 2 was successfully recovered in all three holes, although the exact lithostratigraphic expression of this interval differs quite markedly among the three holes.

Site U1408

Background and Objectives

Site U1408 is a mid-depth site (~3022 mbsl; ~2575 mbsl at 50 Ma) (Tucholke and Vogt, 1979) in the shallow end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site is positioned to capture a record of sedimentation ~2 km shallower than the largely sub-CCD record drilled at Site U1403. The location, well above the average late Paleogene CCD, should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in background noncarbonate sedimentation. The site is also intended to sample the core of a small sediment drift for comparison with the age structure and depositional processes of other drift deposits on Southeast Newfoundland Ridge and J-Anomaly Ridge.

Principal results

The vessel arrived at Site U1408 after a 1.46 nmi transit from Site U1407 in dynamic positioning mode, which took 1.75 h at 0.83 nmi/h. The vessel stabilized over Site U1408 at 2045 h (UTC – 2.5 h) on 11 July 2012. Cores 342-U1408A-1H through 20H were retrieved using nonmagnetic core barrels and the FlexIt core orientation tool. Core 14H experienced the first partial stroke, and the APC was advanced by recovery to the APC total depth of 182.9 m DSF. The XCB was deployed for Cores 21X through 27X to the final depth of 246.5 m DSF. The seafloor was cleared at 1045 h on 13 July, ending Hole U1408A. Overall core recovery for Hole U1408A was 243.92 m for the 246.5 m interval cored (99% recovery). The total time spent on Hole U1408A was 38.00 h.

The vessel was offset 20 m east and Cores 342-U1408B-1H through 18H were retrieved using nonmagnetic core barrels and the FlexIt core orientation tool. A 3 m long interval (25.7–28.7 m DSF) was drilled without recovery to optimize coverage of coring gaps in Hole U1408A. Coring was slowed when the FlexIt housing sheared at the overshot connection above the core barrel three times during APC coring in Hole U1408B. Total advance, including the drilled interval with the APC, was 154.5 m. The XCB was deployed for Cores 19X through 26X to a final depth of 217.5 m DSF. The seafloor was cleared at 1700 h on 14 July, ending Hole U1408B. The recovery for Hole U1408B was 224.09 m over the 214.5 m cored (105% recovery). The total time spent on Hole U1408B was 30.25 h.

The vessel was offset 20 m south, and Hole U1408C was spudded at 1905 h on 14 July. Cores 342-U1408C-1H through 19H (0–165.1 m DSF) were retrieved using nonmagnetic core barrels. A 3 m long interval (8.8–11.8 m DSF) was drilled without recovery to optimize coverage of coring gaps in Hole U1408A. Core orientation was performed with Cores 6H through 8H. Again, the FlexIt tool was thought responsible for mechanical trouble, including one mechanical shear at the overshot and one mechanical shear of the APC shear pins. During APC operations, an intermittent electrical fault developed, and coring operations were suspended for 6.5 h while the problem was fixed. The XCB was deployed for Cores 20X through 23X to a final depth of 187.5 m DSF. The recovery for Hole U1408C was 181.52 m over the 184.5 m cored (98% recovery). The total time spent on Hole U1408C was 38.25 h. The drill string was pulled to the surface and the drill floor was secured at 0715 h on 16 July, ending Hole U1408C and Site U1408. The overall recovery for Site U1408 was 106%. The total time spent on Site U1408 was 106.5 h (4.4 days).

The ~250 m thick sedimentary succession recovered in Holes U1408A–U1408C consists of pelagic deep-sea sediments of Pleistocene to late Paleocene age; however, all stratigraphic epoch boundaries (Paleocene/Eocene, Eocene/Oligocene, Oligocene/Miocene) are represented by hiatuses. The succession is divided into four site-specific lithostratigraphic units. Unit I is ~13 m thick and includes sediments of Pleistocene to Oligocene age. These are composed of uppermost brown silty clay followed by decimeter-scale alternations of brownish foraminiferal nannofossil ooze and reddish brown clay. These likely represent Pleistocene glacial–interglacial cycles. Manganese nodules and dropstones are common. The 10 m thick Unit II consists of well-homogenized silty clay with nannofossils and nannofossil clay with silt of Oligocene age. Sand-sized lithoclasts are found in the >63 μm size fraction from Section 342-U1408A-4H-3 (Oligocene nannofossil Zone NP23) uphole. Unit III is 202 m thick and displays a predominantly greenish gray color but also cyclical color changes between greenish gray to dark green and very light gray intervals on a decimeter-scale. Burrowing is mostly of moderate intensity; in particular, Zoophycos, Planolites, and Chondrites burrows are common. Unit IV was recovered only in Hole U1408A and consists principally of whitish and pinkish brown nannofossil chalk. This unit spans parts of the early Eocene and the late Paleocene. Biostratigraphy constrains the Paleocene/Eocene boundary close to the base of Section 342-U1408A-26X-2; however, the PETM was not recovered because of an unconformity.

Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the Pleistocene to upper Paleocene succession recovered at Site U1408. Radiolarians are only present in a short interval of the middle Eocene and upper Paleocene. Thin Pleistocene, upper Miocene, and lower Oligocene intervals overlie a middle Eocene–upper Paleocene succession with significant hiatuses between the Oligocene and middle Eocene (~7 m.y.) and middle and lower Eocene (~3 m.y.) and a minor hiatus or condensed interval around the Paleocene/Eocene boundary. Sedimentation rates are high (~1.49–3.14 cm/k.y.) through the middle Eocene, low through the lower Eocene (~0.08 cm/k.y.), and relatively high through the upper Paleocene (~1.27 cm/k.y.).

Shipboard results reveal a series of normal and reversed magnetozones between Cores 342-U1408A-4H and 25X (~29–220 m CSF-A), between Cores 342-U1408B-5H and 18H (~30–154 m CSF-A), and between Cores 342-U1408C-5H and 19H (~35–165 m CSF-A). These magnetostratigraphies can be correlated between all three holes and consist of lower Chron C17n.3n (~38.3 Ma) through upper Chron C20r (~43.4 Ma). The geomagnetic field transitions from Chron C18n.1n to C18n.1r to C18n.2n are recorded in exceptional detail in all three holes at Site U1408. Chron C20r is continuously recognized downhole to the bottom of the APC-cored interval and continues into the XCB portion, where we recognize the C20r/C21n chron boundary (45.724 Ma). The magnetochronology suggests that sedimentation rates varied between ~1.5 and 3.1 cm/k.y. across the middle Eocene. Sedimentation rates were higher before the MECO (~41.5 Ma) than after it.

Physical properties at Site U1408 largely reflect compaction and calcium carbonate content. Bulk density globally increases downhole from 1.40 to 1.95 g/cm³, but an abrupt step down to ~1.4 g/cm³ occurs at the transition between lithostratigraphic Units I and II. Grain density averages 2.77 g/cm³ in Hole U1408A. Overall in Hole U1408A, water content and porosity show a decreasing trend downhole (from 50% to 25% and 75% to 50%, respectively). P-wave velocity increases progressively downhole from 1500 to 1800 m/s. Color reflectance parameters a* and b* show higher values in Units I, II, and IV and display cyclicity in Unit III (a* averages 0.5 and b* averages –0.35). Magnetic susceptibility drops from ~60 to 10 instrument units at 12 m CSF-A and also cycles regularly around an average value of ~14 instrument units to the bottom of the sediment column. NGR and L* show a relatively low variability and average 25 cps and 55, respectively. Throughout Unit III, variations in magnetic susceptibility, NGR, and L* correlate with calcium carbonate content (with peaks at ~95, 155, and 230 m CSF-A).

A clear signal in magnetic susceptibility resulted in an accurate splice of the three holes at Site U1408. The expression of orbital (most likely precession) cycles between 35 and 220 m CCSF was a particular aid to the correlation. The overall trends and patterns between holes are very similar among the three holes. The splice for the upper 150 m CCSF of the section is quite robust and could be used for high-resolution sampling. However, low variability in magnetic susceptibility between 70 and 80 m CCSF and between 150 and 226 m CCSF creates intervals with a tentative splice. Our correlation results in a growth rate of 13%.

The downhole patterns of alkalinity, manganese, and iron suggest two zones of organic matter degradation within the recovered sequence. Very high concentrations of manganese in the upper 30 m CSF-A coupled with iron concentrations of 0 μm suggest ongoing oxic to suboxic diagenesis driven by microbial reduction of manganese oxides. Below 30 m CSF-A, the reduction of iron oxides is evident from the rapid increase in iron concentrations. The broad peak in iron between 40 and 90 m CSF-A suggests a locus of organic matter consumption within this depth. Increasing alkalinity concentrations beginning at 50 m CSF-A corroborate this interpretation. Relatively high carbonate contents throughout the recovered sequence in Hole U1408A are consistent with the relatively shallow paleodepth of the site throughout the Eocene. Carbonate concentrations are roughly 40 wt% in Unit I and fall to 0–10 wt% in Unit II, which is consistent with low carbonate levels observed in other Oligocene sequences recovered during Expedition 342. In the expanded middle Eocene sequence represented by Unit III, carbonate content ranges from 40 to 50 wt%, with a few peaks up to 80–90 wt%. Carbonate content increases to 90 wt% in Unit IV, which corresponds to lower Eocene sediment. The downhole increase in carbonate content at the Unit III/IV boundary (225 m CSF-A) is typical of the early/late Eocene boundary in Expedition 342 sediment cores. It is possible that the change in carbonate is linked to a change in production, preservation, or dilution by other sedimentary components.

Site U1409

Background and objectives

Site U1409 is a mid-depth site (~3500 mbsl; ~3050 mbsl at 50 Ma) (Tucholke and Vogt, 1979), in the upper mid-depth end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site is positioned to capture a record of sedimentation ~1.5 km shallower than the largely sub-CCD record drilled at Site U1403. Site U1409, therefore, is located well above the average late Paleogene CCD and should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in noncarbonate sedimentation. Site U1409 is a companion site to Site U1410, at which we employ an offset drilling strategy to obtain APC/XCB records through a thicker section of the same sediment drift than would be possible by drilling a single site. Our objective at Site U1409, situated at the edge of the sediment drift, was to penetrate a more condensed middle Eocene sequence than anticipated in the mid-section of the drift, making it possible to penetrate lower Eocene and Paleocene sediments at relatively shallow burial depth (<250 m).

Principal results

The vessel arrived at Site U1409 at 1010 h (UTC – 2.5 h) on 16 July 2012 after a 26.3 nmi transit from Site U1408 that took 3.0 h at 8.8 nmi/h. The pipe trip to the seafloor was interrupted at 2863.3 m DRF for a test of the subsea camera system, which had been damaged at Site U1403, but strong ocean currents led to the early termination of the test. After completing the pipe trip, Cores 342-U1409A-1H through 16H were recovered to 127.0 m DSF using nonmagnetic core barrels and the FlexIt core orientation tool. Core 15H experienced the first partial stroke, and the APC was advanced by recovery to Core 16H. The XCB was deployed for Cores 17X through 26X to 200.1 m DSF. The seafloor was cleared at 0550 h on 18 July, ending Hole U1409A. Overall core recovery for Hole U1409A was 183.33 m for the 200.1 m interval cored (92% recovery). The total time spent on Hole U1409A was 43.5 h.

The vessel was offset 20 m east, and Cores 342-U1409B-1H through 14H were retrieved to 122.5 m DSF using nonmagnetic core barrels and the FlexIt core orientation tool. The XCB was deployed for Cores 15X through 19X to 170.5 m DSF. The seafloor was cleared at 0340 h on 19 July, ending Hole U1409B. The recovery for Hole U1409B was 167.09 m over the 170.5 m cored (98% recovery). The total time spent on Hole U1409B was 22.00 h. The vessel was offset 20 m south, and Cores 342-U1409C-1H through14H (124.2 m DSF) were retrieved using nonmagnetic core barrels. Core orientation was not performed in Hole U1409C. XCB coring continued from Core 15X through 21X to the final depth of 160.8 m DSF. The recovery for Hole U1409C was 160.98 m over the 160.8 m cored (100% recovery).

The drill string was pulled to ~3200 m DRF and the rig prepared for a transit in dynamic positioning mode to Site U1410. Poor weather conditions and high surface currents foiled the recovery of the beacon, which was declared lost at 1515 h on 20 July, ending Hole U1409C. The total time spent on Hole U1409C was 35.50 h. The overall percentage recovery for Site U1409 was 96%. The total time spent on Site U1409 was 101.0 h (4.2 days).

Four site-specific lithostratigraphic units were described in the ~200 m thick sedimentary succession of deep-sea pelagic sediment recovered at Site U1409. Unit I contains alternating brown to reddish brown Pleistocene silty clay and nannofossil ooze with varying abundances of foraminifers and diatoms and occasional layers of muddy sand with foraminifers. Both the Unit I/II and II/III boundaries are erosive contacts. Unit II is a heavily bioturbated, light yellowish brown Oligocene silty clay to nannofossil clay containing manganese nodules, patches of disseminated sulfides, and rare concentrations of faint red oxide horizons. Unit III contains alternating beds of light greenish gray nannofossil clay and white nannofossils ooze. Some intervals are associated with oxide horizons and dampened color contrast between adjacent beds. Unit IV contains lithologies ranging from pinkish white nannofossil ooze with varying abundances of radiolarians and foraminifers to dark brown claystone, siliceous limestone, and chert. The middle Eocene to early Paleocene sediments of Unit IV are divided into three subunits. Subunits IVa–IVc contain pinkish white nannofossil oozes with radiolarians; frequent cherts and highly varied lithologies including pink to dark brown or gray nannofossil ooze to chalk with interbedded chert, siliceous nannofossil limestone, and nannofossil claystone; and pink to pale gray or pale brown nannofossil chalk.

Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the Pleistocene to lower Paleocene succession, although all microfossil groups are absent through a short interval between the Pleistocene and Oligocene. Radiolarians are only present in the uppermost Pleistocene and the lower middle Eocene through upper Paleocene. Thin Pleistocene and Oligocene sequences overlie a middle Eocene through lower Paleocene succession with significant hiatuses between the lower Pleistocene and upper Oligocene (22 m.y. duration) and lower Oligocene and middle Eocene (8.3 m.y. duration). A short hiatus or condensed interval is also identified at the Paleocene/Eocene boundary. The Oligocene is highly condensed and may contain significant hiatuses. Sedimentation rates are 0.68–1.31 cm/k.y. through the middle Eocene, 0.51–1.44 cm/k.y. through the lower Eocene, and ~0.47–1.80 cm/k.y. through the Paleocene.

Magnetochronology reveals a series of normal and reversed magnetozones between Cores 342-U1409A-1H and 13H (~0–115 m CSF-A), between Cores 342-U1409B-1H and 13H (~0–120 m CSF-A), and between Cores 342-U1409C-1H and 13H (~0–115 m CSF-A). These magnetostratigraphies are straightforward to correlate among all three holes and primarily consist of two time intervals. The first interval is from lower Chron C6Cr (~23.9 Ma) through upper Chron C13r (~33.7 Ma), and the second interval is from lower Chron C19r (~42.3 Ma) through upper Chron C22r (~49.4 Ma). Chrons C9n, C9r, and C10n.1n are not observed in any hole at Site U1409, indicating a hiatus at ~27.5 Ma. The C13n/C13r chron boundary (33.705 Ma) is tentatively identified in Section 342-U1409A-5H-2, between Sections 342-U1409B-4H-5 and 4H-6, and in Section 342-U1409C-5H-2. The magnetochronology suggests that sedimentation rates were ~0.3 cm/k.y. through the Oligocene and varied between ~0.5 and ~1.3 cm/k.y. across the middle Eocene. Sedimentation rates were higher before the MECO (~41.5 Ma) than after, similar to results from Site U1408.

Bulk density shows a general increase downhole from 1.40 to 1.95 g/cm³, with a superimposed abrupt step decrease to ~1.5 g/cm³ at the transition between lithostratigraphic Units I and II. Grain density averages 2.75 g/cm³ in Hole U1409A. Overall in Hole U1409A, water content and porosity show a decreasing trend downhole (from 25 to 60% and 45 and 80%, respectively). At ~15 m CSF-A, water content and porosity both show a decrease associated with the major hiatus between the Oligocene and Eocene. P-wave velocity increases progressively downhole from 1500 to 1800 m/s. Magnetic susceptibility decreases from ~120 to 30 instrument units at 18 m CSF-A and remains near constant (~9 instrument units) to the bottom of the sediment column, except for three notable peaks within Unit III at ~50, ~72, and ~90 m CSF-A corresponding to oxide-rich layers. Color reflectance parameters a* and b* show very distinct downhole variation throughout the sediment column. NGR and L* show five major peaks at ~38, 47, 70, 100, and 155 m CSF-A. All of these depths correlate with the major variations in calcium carbonate content.

The stratigraphic splice constructed for Site U1409 is stratigraphically continuous from 0 to ~130 and 150 to 190 m CCSF. From ~130 to 150 m CCSF, poor recovery associated with the change to XCB prevented the generation of a continuous splice. Magnetic susceptibility, which shows clear, correlative cycles, was used for correlation and splice construction from 0 to 130 m CCSF. NGR was most useful for correlation below ~130 m CCSF, where magnetic susceptibility data were noisy as a result of drilling disturbance associated with numerous chert layers. The chert associated with the Paleocene/Eocene boundary was recovered in Cores 342-U1409A-20X and 342-U1409B-18X, and the boundary appears to fall in the core catcher of Core 342-U1409C-21X. However, physical properties in the interval preceding the PETM appear quite different in Hole U1409C compared to Holes U1409A and U1409B.

Headspace methane concentrations (1.79–6.43 ppmv) were not above atmospheric levels. Pore water profiles display evidence of compartmentalization with pronounced abrupt downhole shifts in magnesium, manganese, and potassium at ~125–130 m CSF-A, suggesting that the unrecovered sequence of cherts acts as an aquiclude. Overall, pore water profiles of potassium, calcium, and magnesium are consistent with those resulting from exchange with and alteration of basaltic basement at depth. Potassium and magnesium concentrations decrease and calcium concentrations increase with depth. The downhole patterns of manganese and sulfate suggest two zones of organic matter degradation within the recovered sequence, one above the chert-rich interval and one below. In general, sulfate concentrations are high, consistent with low TOC content. A broad downhole peak in boron concentrations at 59 m CSF-A presumably indicates increased supply from the terrigenous sediment component in Unit II.

Carbonate content in the whole sediment column at Site U1409 ranges from 0 to 93 wt%. As with other sites drilled to date on the Southeast Newfoundland Ridge (Sites U1407 and U1408), the most prominent change is a downhole step increase (50 to 90 wt% at ~100 m CSF-A) in sediments of Zone NP14 age (around the early/middle Eocene boundary). This step correlates with shifts in several proxies (e.g., color reflectance, magnetic susceptibility, NGR, TOC, and TN values) and marks a transition from pelagic chalk sedimentation to clay deposition in the initial stages of sediment drift development. Middle Eocene sediments appear cyclic, with alternating green clay-rich beds and white nannofossil ooze layers with carbonate contents of 40 and 85 wt%, respectively. TOC values are typically 0.1–0.5 wt% throughout the sediment column. Organic matter is thermally immature and relatively well preserved with low T_max values (380°–420°C). Organic matter is a mixture of Type II (algal and microbial) and Type III (land plant/detrital) kerogen.

Site U1410

Background and objectives

Site U1410 is a mid-depth site (~3400 mbsl; ~2950 mbsl at 50 Ma) (Tucholke and Vogt, 1979) in the upper mid-depth end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site is positioned to capture a record of sedimentation ~1.5 km shallower than the largely sub-CCD record drilled at Site U1403. The location, well above the average late Paleogene CCD, should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in background noncarbonate sedimentation. Our primary scientific objectives for drilling Site U1410 were

• To obtain an expanded record of lower to middle Eocene drift sedimentation to compare directly to the relatively condensed record at Site U1409 drilled on the edge of the same drift;
• To capture fine-scale variations in carbonate preservation and lysocline shifts in carbonate-rich sediments that are ~400 m deeper than Site U1408; and
• To evaluate the history of deep water and the CCD on sediment chemistry, grain size, and provenance.

Secondary objectives included the possible recovery of specific Paleogene hyperthermals such as the MECO for comparison with the record of these events elsewhere, particularly Sites U1404, U1406, and U1408 along the Expedition 342 depth transect.

Principal results

The vessel arrived at Site U1410 at 1845 h (UTC - 2.5 h) on 20 July 2012 after a 3.46 nmi transit from Site U1409 in dynamic positioning mode that took 3.5 h at 1.0 nmi/h. The plan for Site U1410 called for drilling three holes to a depth of ~250 m DSF. Hole U1410A (3387.3 mbsl) was spudded at 2125 h on 20 July. Cores 342-U1410A-1H through 16H were recovered to 151.0 m DSF using nonmagnetic core barrels and the FlexIt core orientation tool. Core 16H experienced the first partial stroke. The XCB was deployed for Cores 17X through 28X to a final depth of 259.8 m DSF. The seafloor was cleared at 0500 h on 22 July, ending Hole U1410A. Overall core recovery for Hole U1410A was 256.88 m for the 259.8 m interval cored (99% recovery). The total time spent on Hole U1410A was 34.25 h.

The vessel was offset 20 m east. Hole U1410B (3398.7 mbsl) was spudded at 0650 h on 22 July. Cores 342-U1410B-1H through 18H were recovered to 153.8 m DSF using nonmagnetic core barrels and the FlexIt core orientation tool. The XCB was deployed for Cores 19X through 28X to a final depth of 245.2 m DSF. The seafloor was cleared at 1620 h on 23 July, ending Hole U1410B. The recovery for Hole U1410B was 244.84 m over the 245.2 m cored (100% recovery). The total time spent on Hole U1410B was 35.25 hours.

The vessel was offset 20 m south, and Hole U1410C (3386.9 mbsl) was spudded at 1825 h on 23 July. Cores 342-U1410C-1H through 16H were recovered to 146.8 m DSF using nonmagnetic core barrels. No core orientation was performed in Hole U1410C. The XCB was deployed for Cores 17X through 27X to a final depth of 243.8 m DSF. Recovery for Hole U1410C was 238.81 m over the 243.8 m cored (98% recovery). Recovery for Site U1410 was 740.5 m out of 748.8 m cored (98% recovery). The seafloor was cleared and the vessel was secured for transit at 0915 h on 25 July, ending Hole U1410C. The total time spent on Hole U1410C was 41.00 h.

The sedimentary sequence at Site U1410 comprises four site-specific lithostratigraphic units. Unit I is a ~34 m thick succession of Pleistocene sediment with alternating reddish brown clay, gray to dark brown muddy/clayey foraminiferal ooze with nannofossils, grayish brown foraminiferal sand, and occasional sand- to pebble-sized lithic grains. Unit II is a ~30 m thick succession of clay, clay with nannofossils, and nannofossil clay of late Miocene to Oligocene age. Manganese, present as discrete nodules or disseminated silt- to sand-sized flecks, and disseminated sulfides are common. Sedimentological and biostratigraphic information indicate that Unit II contains multiple hiatal surfaces in addition to the unconformities that define its upper and lower boundaries. Middle to early Eocene Unit III is the thickest of the four units (63–68 m) and contains greenish gray nannofossil clay and greenish nannofossil clay to clayey nannofossil ooze with distinctive 10–25 cm thick bands of light gray to white nannofossil ooze that occur as a secondary lithology. Lithostratigraphic Unit IV is a 48 m thick sequence of white to pinkish white nannofossil chalk with foraminifers and/or radiolarians of middle Eocene to early Eocene age. This unit is divided into two generally similar subunits, with the lower subunit containing several chert beds.

Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the Pleistocene to lower Eocene succession. Short barren intervals occur between thin Pleistocene, upper Miocene, and lower Miocene–Oligocene sequences. Radiolarians are only present in the uppermost Pleistocene and lower Eocene. Thin Pleistocene, upper Miocene and lower Miocene–Oligocene sequences overlie a middle Eocene through lower Eocene succession. Hiatuses or highly condensed intervals occur between the lower Pleistocene and upper Miocene (7.1 m.y. duration), upper and lower Miocene (7.4 m.y. duration), lower Miocene and upper Oligocene (5.4 m.y. duration), and lower Oligocene and middle Eocene (7.4 m.y. duration). The Oligocene is highly condensed and may also contain significant hiatuses.

Shipboard results reveal two series of normal and reversed magnetozones. These zones are observed between Cores 342-U1410A-1H and 4H (~0–33 m CSF-A), between Cores 342-U1410B-1H and 5H (~0–33 m CSF-A), and between Cores 342-U1410C-1H and 4H (~0–32 m CSF-A). The second series is observed between Cores 342-U1410A-8H and 24X (~69–218 m CSF-A), between Cores 342-U1410B-9H and 15H (~69–121 m CSF-A), and Cores 342-U1410C-8H and 14H (~70–118 m CSF-A). These magnetostratigraphies are straightforward to correlate among all three holes and represent two distinct time intervals. The first interval is from Chron C1n (Brunhes; modern) through upper Chron C2An.1n (Gauss; ~2.6 Ma). The second interval is from upper Chron C18n.1n (~39.6 Ma) through upper Chron C21r (~47.4 Ma). The lower part of Chron C20n, as well as Chrons C21n and C21r, have not yet been correlated in the XCB-recovered intervals in Holes U1410B and U1410C. Finally, the geomagnetic field transitions from C18n.1n to C18n.1r to C18n.2n are recorded in exceptional detail in Hole U1410B and show remarkably similar behavior as the same transitions recorded at Site U1408.

The magnetochronology and biochronology suggests that average linear sedimentation rates (LSRs) were ~1.5–2.3 cm/k.y. during the Pleistocene, with higher sedimentation rates during Chron C2 than during Chron C1. Sedimentation rates are 0.2 cm/k.y. through the Oligocene. Average LSRs varied from 1.30 cm/k.y. at the beginning of the middle Eocene to 1.98 cm/k.y. at the end of the middle Eocene. Within the middle Eocene, LSRs peak at 2.63 cm/k.y. during Chron C20n, one chron younger than the interval of peak LSRs at Site U1409. Finally, biochronology suggests sedimentation rates of 0.6 cm/k.y. through the lower Eocene.

The stratigraphic splice constructed for Site U1410 is continuous from 0 to ~256 m CCSF, with the exception of one append at ~226 m CCSF. Correlation during drilling operations was possible because of clear, correlative signals in magnetic susceptibility. Magnetic susceptibility and NGR were used for refining the real-time correlation and constructing the splice. All three holes recorded the prominent lithologic transition from greenish clay to carbonate-rich sediment, characterized by a step change to lower magnetic susceptibility and NGR at ~220–230 m CCSF (across the early middle Eocene). Core 342-U1410A-23X, showing the transitional physical properties data, exhibits clear green to white cycles, which are absent from the equivalent cores in Holes U1410B and U1410C. As a result, we append Core 23X in the splice and add large offsets to Cores 342-U1410B-26X and 342-U1410C-24X (13.3 and 4.8 m, respectively).

Headspace methane concentrations (2.11–6.72 ppmv) were not above atmospheric levels. Pore water profiles display evidence of compartmentalization with prominent abrupt downhole shifts in magnesium, manganese, and potassium at ~220–230 m CSF-A, suggesting that the unrecovered sequence of cherts functions as an aquiclude. Overall, pore water profiles of potassium, calcium, and magnesium are consistent with those resulting from exchange with and alteration of basaltic basement at depth. Potassium and magnesium concentrations decrease and calcium concentrations increase with depth. The downhole patterns of manganese, iron, and sulfate suggest organic matter degradation. Low alkalinity, ammonium, and manganese concentrations and high sulfate concentrations suggest that the influence of organic matter respiration within the sediment column at Site U1410 is modest. The broad downhole peak in boron concentrations at ~30 m CSF-A presumably indicates increased supply from the terrigenous sediment component in lithostratigraphic Unit II.

Carbonate content in the entire sediment column at Site U1409 ranges from 0.7 to 92 wt%. As observed at the other drill sites on Southeast Newfoundland Ridge (Sites U1407–U1409), the most prominent change is a step increase (from 46 to 52 wt% CaCO₃; ~210 m CSF-A) in calcium carbonate content in sediments around the early/middle Eocene boundary (Zone NP14). This step correlates with shifts in several proxies (e.g., color reflectance, magnetic susceptibility, NGR, TOC, and TN values) and marks a transition in time from pelagic chalk sedimentation to clay deposition in the initial stages of sediment drift development. Middle Eocene sediments appear cyclic, with alternating clay-rich beds and white nannofossil ooze layers that have ~30 and 80 wt% carbonate, respectively. TOC values are typically 0.01–0.57 wt% throughout the sediment column. Organic matter is thermally immature and relatively well preserved with low T_max values (380°–420°C). Organic matter throughout the sediment column is a mixture of Type II (algal and microbial) and Type III (land plant/detrital) kerogen.

Bulk density shows a general increase downhole from 1.5 to 2.4 g/cm³. Grain density is ~2.7 g/cm³ in Hole U1410A, and both water content and porosity show a decreasing trend downhole (from 53% to 21% for water content and 76% to 43% for porosity). P-wave velocity increases progressively downhole from 1490 to 1960 m/s. Magnetic susceptibility decreases from ~290 to –2 instrument units, with notable steps at 30 and 45 m CSF-A, but exhibits uniform (–2 to 20 instrument units) values below 45 m CSF-A to the bottom of the sediment column. Color reflectance parameters a* and b* gradually increase from –3 to 3 downhole to 210 m CSF-A. Below 210 m CSF-A, a* and b* increase to 12 and 8, respectively. L* increases downhole from 13 to 91, with steps at 115, 150, and 210 m CSF-A. NGR fluctuates from 21 to 47 cps downhole to 210 m CSF-A, but then decreases from 27 to ~10 cps from 210 m CSF-A to the bottom of the hole. Color reflectance and NGR reflect calcium carbonate content. Thermal conductivity gradually increases downhole from 0.9 to 1.5 W/(m·K).

Site U1411

Background and objectives

Site U1411 is a mid-depth site (~3300 mbsl; ~2850 mbsl at 50 Ma) (Tucholke and Vogt, 1979) in the upper end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect. The site is positioned to capture a record of sedimentation ~1.65 km shallower than the largely sub-CCD record drilled at Site U1403. The location, well above the average late Paleogene CCD, should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in background noncarbonate sedimentation. Our primary scientific objectives for drilling Site U1411 were

• To obtain an expanded record of the upper half of a Miocene(?) to lower Eocene(?) sediment drift to directly compare to the timing and nature of drift development at the Sites U1407 and U1408 drift and the Sites U1409 and U1410 drift;
• To capture fine-scale variations in carbonate preservation and lysocline shifts in Miocene–Eocene carbonate-rich sediments that are ~550 m shallower than the Site U1406 Oligocene–Miocene section; and
• To evaluate the history of deep water and the CCD on sediment chemistry, grain size, and provenance.

Secondary objectives include the possible recovery of the Oligocene/Miocene and Eocene/Oligocene boundaries for comparison with the record of these events elsewhere, particularly Sites U1404–U1406 along the Expedition 342 depth transect.

Principal results

The vessel arrived at Site U1411 at 1115 h (UTC – 2.5 h) on 25 July 2012 after a 19.0 nmi transit from Site U1410, which took 2.0 h at 9.5 nmi/h. The plan for Site U1411 called for three holes to a depth of ~250 m DSF.

Hole U1411A was spudded at 2320 h on 25 July. The first core for Hole U1411A, Core 342-U1411A-1H, with a length of 9.87 m, failed to capture the mudline and the hole was terminated. The seafloor was cleared at 2320 h on 25 July, ending Hole U1411A. Recovery for Hole U1411A was 9.87 m for the 9.5 m interval recovered (104% recovery). The total time spent on Hole U1411A was 12.00 h. The vessel was offset 20 m east and Hole U1411B (3298.8 mbsl) was spudded at 0035 h on 26 July. Cores 342-U1411B-1H through 20H were recovered to 177.4 m DSF using nonmagnetic core barrels and the FlexIt core orientation tool. The XCB was deployed for Cores 21X through 28X to a final depth of 254.2 m DSF. The seafloor was cleared at 1310 h on 27 July, ending Hole U1411B. Recovery for Hole U1411B was 233.94 m over the 254.2 m cored (92% recovery). The total time spent on Hole U1411B was 38.00 hours.

The vessel was offset 20 m south. Hole U1411C (3300.5 mbsl) was spudded at 1505 h on 27 July. Cores 342-U1411C-1H through 2H were recovered to 9.2 m DSF. After recovering Core 2H, the hole was drilled without coring from 9.2 to 100 m DSF in order to save operational time for deeper objectives. After the drilling advance, APC coring continued with Cores 4H through 9H (100–152.2 m DSF). All APC cores were oriented with the FlexIt core orientation tool and recovered using the nonmagnetic core barrels. The XCB was deployed for Cores 10X through 17X to a final depth of 223.9 m DSF. After Core 17X, a medical emergency arose and it was decided to terminate operations and transit to St. Johns, Newfoundland. The seafloor was cleared and the vessel was secured for transit at 0500 h on 29 July, ending Hole U1411C. Recovery for Hole U1411C was 118.62 m over the 133.1 m cored (89% recovery). The total time spent on Hole U1411C was 39.75 h.

Overall recovery for Site U1411 was 91%. The total time spent on Site U1411 was 89.75 h (3.7 days).

At Site U1411, we recovered a 254.5 m thick sedimentary succession of deep-sea pelagic sediment of Pleistocene to late Eocene age highlighted by an expanded record of the Eocene–Oligocene transition. The sedimentary sequence at Site U1411 comprises three site-specific lithostratigraphic units. Unit I is a 13 m thick succession of Pleistocene sediment of alternating gray and reddish brown clayey foraminiferal ooze, gray silty sand with foraminifers, and brown to grayish brown silty clay with foraminifers. Dropstones and sand-sized lithic grains are prominent in Unit I. Unit II is a 198 m thick succession of silty clay, clay with nannofossils, and silty nannofossil clay of early Miocene to late Eocene age. Nannofossil ooze is also present in Unit II but only in the interval immediately above the Eocene/Oligocene boundary. Small blebs of quartz silt on core surfaces, interpreted as ice-rafted siltstone clasts, are very common in the Miocene and Oligocene sediment of Unit II. Nannofossil ooze occurs just above the Eocene/Oligocene boundary, possibly representing the widespread carbonate overshoot observed at other Expedition 342 sites. Unit III is 42 m thick and composed of greenish gray and dark greenish gray nannofossil clay with foraminifers, clayey nannofossil chalk with foraminifers, and clayey foraminiferal chalk. Laminated intervals, some of which are highly concentrated in foraminifers, are common in Unit III and provide evidence for significant reworking and winnowing by currents associated with drift formation.

Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the Pleistocene to upper Eocene succession. A short barren interval occurs between the Pleistocene and lower Miocene–Eocene sequence. Radiolarians are only present in the uppermost Pleistocene. A relatively thin Pleistocene sequence overlies a lower Miocene to mid-Oligocene succession with relatively poor carbonate microfossil preservation, followed by an expanded lower Oligocene through upper Eocene succession with excellent preservation of calcareous microfossils. Average linear sedimentation rates across the Eocene–Oligocene transition are up to ~5 cm/k.y.

Shipboard results reveal two series of normal and reversed magnetozones. The first zone is observed in Core 342-U1411B-2H (~1–11 m CSF-A) and Cores 342-U1411C-1H through 2H (~0–7 m CSF-A). The second series is observed between Cores 342-U1411B-4H and 20H (~20–177 m CSF-A). Part of this second series is observed between Cores 342-U1411C-7H and 8H (~127–143 m CSF-A). These magnetostratigraphies can be correlated between both holes and represent two distinct time intervals. The first interval is from Chron C1n (Brunhes; modern) through upper Chron C1r.3r (~1.2 Ma). The second interval is from lower Chron C8n.2n (~25.9 Ma) through upper Chron C15n (~35.0 Ma). At least four significant conclusions can be drawn from this shipboard magnetostratigraphy:

1. Site U1411 contains a nearly complete and expanded Oligocene record, with average LSRs of 1.53 cm/k.y. and peak LSRs of 3.22 cm/k.y.

2. The C11r/C12n and C12n/C12r chron boundaries are not clearly identified in the shipboard paleomagnetic data, suggesting a hiatus of at least ~0.5 m.y. in the lower Oligocene. This interval also corresponds to a 10 m broad zone of depressed NGR values, a sharp lithostratigraphic contact in Section 342-U1411B-10H-5, and a hiatus inferred from nannofossil and foraminifer biostratigraphic datums.

3. The Eocene–Oligocene transition is highly expanded, with average LSRs of 2.63 cm/k.y. and peak LSRs of 5.02 cm/k.y. The Chron C13n/C13r boundary (33.705 Ma) is recognized in Section 342-U1411B-17H-1 at ~144.15 m CSF-A and Sections 342-U1411C-8H-5 and 8H-6 at ~142.50 m CSF-A.

4. Shipboard paleomagnetic data indicate at least three cryptochrons within Chron C13r. The second and longest of these cryptochrons occurs in the same stratigraphic interval as the first downhole appearance of the Eocene marker foraminifer Hantkenina alabamensis.

The stratigraphic splice constructed for Site U1411 is composed of a series of stratigraphically continuous intervals from 0 to ~20, ~100 to 128, ~128 to 178, ~207 to 226, and ~226 to 236 m CCSF. Coring in Hole U1411A did not recover a mudline, so Hole U1411A was ended after the first core. Hole U1411B spans the thickest sediment column recovered at this site, with a maximum depth of ~269 m CCSF, whereas Hole U1411C has a maximum depth of ~236 m CCSF. The large number of appended intervals in the splice is due to a drilling advance without coring from ~20 to 100 m CCSF in Hole U1411C. As a result, only Hole U1411B recovered this interval. Correlation during drilling for the interval from ~100 to 236 m CCSF was possible based on magnetic susceptibility and GRA bulk density data, though magnetic susceptibility was low from ~100 to 148 m CCSF. Magnetic susceptibility was used for refining the real-time correlation and constructing the splice. The longest continuous intervals in the splice are from ~100 to 128 m CCSF and ~128 to 178 m CCSF; the former covers the Eocene/Oligocene boundary. The appended cores from ~178 to 269 m CCSF are a function of poor XCB recovery in both Holes U1411B and U1411C.

Methane was the only hydrocarbon detected in the headspace samples from Hole U1411B. Methane increases very slightly downhole, with values between 2.11 and 4.12 ppmv. Pore water constituents at Hole U1411B are consistent with consumption of organic matter under oxic to suboxic conditions. However, sulfate concentrations remain high throughout the sequence, indicating that pore fluid diagenesis does not proceed to sulfate reduction. Overall, pore water profiles of potassium, calcium, and magnesium are consistent with those resulting from exchange with and alteration of basaltic basement at depth. Potassium concentrations may be responding to adsorption onto clay particles. As with other sites where the Eocene–Oligocene transition was recovered (Sites U1404 and U1406), carbonate content shows an increase across the transition followed by a decrease in carbonate contents within the lower Oligocene. TOC ranges from 0.01 to 0.50 wt%, with many samples falling below detection limits. TN values generally fall below 0.1 wt%, with slightly lower values at the bottom of Hole U1411B.

Bulk density globally increases downhole from 1.5 to 1.95 g/cm³, but an abrupt step down to ~1.5 g/cm³ occurs at the transition between lithostratigraphic Units I and II between Pleistocene and Miocene sediments. Grain density averages 2.75 g/cm³, and water content and porosity exhibit a decreasing trend downhole (from 55% to 25% and 80% and 45%, respectively) as expected for sediment compaction. P-wave velocity increases progressively downhole from 1500 to 1700 m/s. Magnetic susceptibility drops from ~160 to 30 instrument units at 18 m CSF-A and remains constant downhole other than a small increase at ~140 m CSF-A. Color reflectance parameters a* and b* follow similar trends throughout the hole, but in Units II and III some superimposed peaks appear in b*. NGR and L* show a major peak at ~140 m CSF-A that correlates with the major variation in calcium carbonate content. Almost all the physical properties show a shift or a peak in their values at ~140 m CSF-A associated with the post-Eocene–Oligocene pulse of carbonate deposition.

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