Clemens, S.C., Kuhnt, W., LeVay, L.J., and the Expedition 353 Scientists
Proceedings of the International Ocean Discovery Program Volume 353
S.C. Clemens, W. Kuhnt, L.J. LeVay, P. Anand, T. Ando, M. Bartol, C.T. Bolton, X. Ding, K. Gariboldi, L. Giosan, E.C. Hathorne, Y. Huang, P. Jaiswal, S. Kim, J.B. Kirkpatrick, K. Littler, G. Marino, P. Martinez, D. Naik, A. Peketi, S.C. Phillips, M.M. Robinson, O.E. Romero, N. Sagar, K.B. Taladay, S.N. Taylor, K. Thirumalai, G. Uramoto, Y. Usui, J. Wang, M. Yamamoto, and L. Zhou2
Keywords: International Ocean Discovery Program, IODP, Expedition 353, JOIDES Resolution, Site U1447, Indian monsoon, monsoon, Bay of Bengal, Andaman Sea, paleoclimate, paleoceanography, Miocene, Pliocene, Pleistocene, Holocene, Ninetyeast Ridge, Indian Ocean, salinity, orbital, millennial, centennial, abrupt climate change
The Andaman Sea is situated between the Andaman Islands and the Malay Peninsula (Figure F1). The Andaman-Sumatra island arc system results from the oblique subduction of the Indo-Australian plate beneath the Eurasian plate (Singh et al., 2013). Stretching and rifting of the overriding plate during the early Miocene (~25 Ma) resulted in two distinct plates (Sunda and Burma) separated by an active spreading center (Curray, 1991, 2005) located in the deepest portion of the Andaman Sea. An accretionary wedge complex scraped off the subducting slab lies west of the spreading center, forming a series of shallower basins associated with back-thrust faulting within the accreted sediments (Figure F2). The Andaman Sea drilling sites are within the Nicobar-Andaman Basin, bounded on either side by the Diligent and Eastern margin faults.
Runoff into the Andaman Sea is dominated by the Irrawaddy and Salween Rivers (Varkey et al., 1996), supplying a combined 30.8 × 1010 m3 of water during June, July, and August. Comparison with the winter (December, January, and February) discharge of 2.8 × 1010 m3, indicates strong seasonality with a dominance of summer (92%) over winter (8%) runoff. Terrigenous sediment supply to the Andaman Sea is dominantly from the Irrawaddy and Salween Rivers (Colin et al., 1999, 2006) with contributions from the Indo-Burman-Arakan mountain ranges as well as the Andaman Islands (Awasthi et al., 2014). However, by virtue of proximity, Little Andaman Island is likely a dominant source of terrigenous materials to International Ocean Discovery Program (IODP) Site U1447. Analysis of Andaman Sea surface sediments indicates that foraminifers are abundant and well preserved shallower than ~1800 meters below sea level (mbsl) (>100,000 individuals/g) and decrease to <100 individuals/g deeper than 3000 mbsl (Frerichs, 1971).
Site U1447 is located at 1391 mbsl, ~45 km offshore Little Andaman Island within a basin on the eastern flank of a rise separating north-south–oriented basins associated with the Eastern Margin and Diligent fault zones. Seismic sections (Figure F3) indicate ~740 m of sediments overlying an accretionary wedge complex. Sedimentation rates at Site NGHP-01-17 (Collett et al., 2008; Flores et al., 2014) suggest that the base of this site will be late Miocene in age. A series of hard reflectors from 0.30 to 0.38 s two-way traveltime (TWT) below the seafloor is interpreted as an interval of coarse sediments.
The objective at this site is to recover Miocene to Holocene sediments from multiple holes in order to reconstruct changes in surface water salinity and runoff associated with summer monsoon rainfall at tectonic to suborbital timescales. Sites U1448 and U1447 will constitute the middle (10°N) portion of a meridional salinity transect that includes sites on the northeast Indian margin (19°N) and is anchored by IODP Site U1443 at 5°N.
Site U1447 consisted of three holes (Table T1), ranging in depth from 24.4 to 738.0 m drilling depth below seafloor (DSF). Overall, 108 cores were recorded for the site. A total of 451.27 m of core over a 444.3 m cored interval was recovered using the advanced piston corer (APC) system (102% recovery). The cored interval with the half-length advanced piston corer (HLAPC) system was 67.8 m with a core recovery of 69.12 m (102%). The cored interval with the extended core barrel (XCB) system was 409.2 m with 395.15 m of core recovered (97%). The overall recovery percentage for Site U1447 was 99%. The total time spent on Site U1447 was 6.1 days.
Hole U1447A was spudded at 2320 h on 15 January 2015. Core 353-U1447A-1H was used to estimate the seafloor depth at 1390.9 mbsl. The APC system was used for Cores 1H through 29H. The HLAPC was deployed for Cores 30F through 44F. Cores 45X through 88X were cut with the XCB system. Downhole temperature measurements using the third-generation advanced piston corer temperature tool (APCT-3) shoe were taken on Cores 4H, 7H, 10H, and 15H. The Icefield MI-5 tool was used to obtain orientation data for Cores 3H through 29H. After coring operations, the hole was displaced with heavy mud and the pipe was pulled from the hole. The pipe cleared the seafloor at 1705 h on 20 January.
A total of 29 APC cores were taken over a 261.0 m interval with a total core recovery of 268.69 m (103% core recovery). The HLAPC system was used for 15 cores over a cored interval of 67.8 m with 69.12 m recovered (102%). A total of 44 XCB cores were cut over a 409.2 m interval with 395.15 m of core recovered (97%). Total core recovery for Hole U1447A was 99%.
The vessel was offset 20 m south of Hole U1447A, and Hole U1447B was spudded at 2045 h on 20 January 2015. Cores 353-U1447B-1H through 3H were recovered and sampled for high-resolution pore water chemistry. The pipe was pulled from the hole and cleared the seafloor at 2220 h.
The vessel was offset 20 m east of Hole U1447B, and Hole U1447C was spudded at 2300 h on 20 January 2015. Cores 353-U1447C-1H through 18H were cored with the APC system to a total depth of 160.9 m. A 2 m drilled interval (353-U1447C-31) extended from 16.4 to 18.4 m DSF. Cores 4H through 16H were oriented using the Icefield MI-5 tool. At the end of coring operations, the pipe was pulled from the hole and cleared the seafloor at 1405 h on 21 January. The remaining drill pipe was tripped during the 9.4 nmi transit to Site U1448.
Sediments recovered from Holes U1447A–U1447C are principally composed of Late Pleistocene to late Miocene hemipelagic clays with a significant biogenic component, as well as a large number of calcitic turbidites, of Late Pleistocene to late Miocene age, comprising four distinct lithostratigraphic units (I–IV) (Figure F4). Unit I is 126 m thick and comprised of Late Pleistocene greenish gray clayey nannofossil ooze with foraminifers and foraminifer-rich nannofossil ooze with clay. Unit II is 193 m thick, comprised of Late Pleistocene to late Pliocene greenish gray clayey nannofossil ooze with foraminifers, foraminifer-rich nannofossil ooze with clay, and clayey calcareous ooze with varying proportions of foraminifers. This unit is also characterized by the presence of numerous thin to thick light gray beds of foraminifer-rich or bioclastic carbonate fragments of sand–silt size, interpreted as turbidites because of the presence of normal grading and coarser grain size compared to the surrounding hemipelagic sediment. Unit III is 180 m thick, comprised of early Pliocene to late Miocene greenish gray clayey nannofossil ooze to calcareous ooze with varying amounts of glauconite. Unit IV is composed of late Miocene greenish gray–gray clayey nannofossil ooze with glauconite or biosilica, biosilica-rich clay with varying proportions of glauconite and nannofossils, and nannofossil-rich clay with biosilica. The observed lithologic differences between units are principally the result of variations in biosilica abundance (predominantly diatoms and sponge spicules), turbidites, and nannofossils (Figure F5). Lithologic descriptions are based primarily on sediments recovered from Hole U1447A, supplemented with observations from Hole U1447C.
- Intervals: 353-U1447A-1H-1, 0 cm, through 14H-CC, 3 cm; 353-U1447B-1H-1, 0 cm, through 3H-CC, 15 cm; 353-U1447C-1H-1, 0 cm, through 15H-CC, 30 cm
- Depths: Hole U1447A = 0–126.00 m core depth below seafloor, Method A (CSF-A); Hole U1447B = 0–24.45 m CSF-A; Hole U1447C = 0–133.54 m CSF-A
- Age: Late Pleistocene
- Major lithology: clayey nannofossil ooze with foraminifers and foraminifer-rich nannofossil ooze with clay
- Minor lithology: volcanic ash and foraminifer-rich and/or bioclastic sand/silt
Unit I is a ~126 m thick succession of light greenish gray (GLEY 1 5/10Y) clayey nannofossil ooze with foraminifers and foraminifer-rich nannofossil ooze with clay (Figures F4, F6, F7). Calcareous nannofossils make up ~30%–50% in smear slide samples, followed by foraminifers (10%–30%), clay (10%–40%), and biosilica, which is dominated by sponge spicules and diatoms (~10%) (Figure F8). Physical property data is relatively invariant within Unit I, although there is a minor decrease in b* downhole (see Physical properties). Two thick (93.5 and 20 cm) turbidites composed of sand and bioclastic sand, respectively, are present in sediments from Unit I (intervals 353-U1447A-2H-1, 0–93.5 cm, and 9H-6, 7–29 cm) (Figure F9). Two light gray vitric ash layers (6 and 63 cm thick) are also present in Unit I (intervals 3H-3, 21–27 cm, and 12H-5, 42–105 cm). A bioclastic sand from interval 353-U1447B-1H-4, 38 cm, also contains lithic fragments, including a fragment of serpentinite (Figure F10). A 5.5 cm thick light gray ash at 16.21–16.26 m CSF-A (interval 353-U1447B-3H-1, 130.5–136 cm) is tentatively identified as the Late Pleistocene Toba ash event but was not observed in Holes U1447A or U1447C. Drilling disturbance is minor with only occasional horizontal cracks.
Figure F9. Minor lithologies, Site U1447. A. Volcanic ash. B. Gray volcanic ash with clay. C. Light gray bleb of volcanic ash with glauconite. D. Very dark gray volcanic ash. E. Thick turbidite with coarse sand, shell fragments, and foraminifers. F. Bioclastic sandy blebs and thin bioclastic turbidite layers. G. Dark patches of plant debris.
- Intervals: 353-U1447A-14H-CC, 3 cm, through 45F-1, 32 cm; 353-U1447C-15H-CC, 30 cm, through 18H-CC, 22 cm
- Depths: Hole U1447A = 126.00–329.12 m CSF-A; Hole U1447C = 133.54–162 m CSF-A
- Age: Late Pleistocene to late Pliocene
- Major lithology: Clayey nannofossil ooze with foraminifers, foraminifer-rich nannofossil ooze with clay, and clayey calcareous ooze
- Minor lithology: foraminifer-rich sand/silt and bioclastic sand with authigenic carbonate and foraminifers
Unit II is a ~193 m thick succession of greenish gray (GLEY 1 4/10Y to GLEY 1 5/10Y) clayey nannofossil ooze with foraminifers, foraminifer-rich nannofossil ooze with clay, and clayey calcareous ooze with varying proportions of foraminifers (Figures F4, F6, F7). Between 170 and 300 m CSF-A, the proportion and preservation of calcareous nannofossils and foraminifers decreases and the proportion of authigenic carbonate increases (Figure F8). The biosiliceous component within Unit II is predominantly composed of sponge spicules with virtually no contribution from other biosiliceous organisms. There is a minor downhole decrease in b* and L* and an increase in natural gamma radiation (NGR) and magnetic susceptibility (MS) within Unit II (see Physical properties). Numerous light gray (2.5Y 7/2) calcitic turbidites are observed in Unit II, composed of foraminifer-rich sand to clay and bioclastic sand with authigenic carbonate and foraminifers, varying in thickness from 1 to 80 cm (Figures F9, F11). The frequency of turbidites and the percentage of each core composed of turbidites increases downhole, peaks between 160 and 220 m CSF-A, and then decreases downhole until the last turbidite is observed at 329.12 m CSF-A (interval 353-U1447A-45X-1, 29–32 cm), marking the base of the unit (Figure F11). Variations in the frequency and number of turbidites per meter is inversely correlated with nannofossil and clay abundance, whereas authigenic carbonate content positively correlates with turbidite frequency (Figures F8, F11). Smear slide observations demonstrate that Unit II turbidites between 130 and 144 m CSF-A are dominated by foraminifers (Figures F8, F11), whereas calcareous bioclasts are the dominant component deeper than 144 m CSF-A, with quartz content increasing between 260 and 297 m CSF-A (Figure F11). Comparison of X-ray diffraction (XRD) data from the bioclastic turbidites and surrounding nannofossil ooze shows an increase in aragonite and high-Mg calcite within the calcitic turbidites (Figure F10). Drilling disturbance is minor with only occasional horizontal cracks observed.
- Interval: 353-U1447A-45F-1, 32 cm, through 62X-2, 0 cm
- Depth: Hole U1447A = 329.12–489.80 m CSF-A
- Age: late Pliocene to late Miocene
- Major lithology: clayey nannofossil ooze and clayey calcareous ooze
- Minor lithology: clayey nannofossil ooze with foraminifers, clayey calcareous ooze with glauconite, nannofossil ooze with clay, and volcanic ash
Unit III is a ~182 m thick succession of greenish gray (GLEY 1 5/5GY to GLEY 1 5/10GY) clayey nannofossil ooze or clayey calcareous ooze with varying glauconite abundance, further characterized by a complete absence of biosiliceous components (Figures F6, F7, F8). Within the clayey nannofossil ooze, faint color variations from dark gray (GLEY 1 3/5GY) to lighter gray (GLEY 1 5/5GY), or more brownish gray (GLEY 1 5/10Y), are common. The composition of the different colored oozes is very similar, except for slightly higher foraminifer content in the brownish gray intervals. Deeper than 425 m CSF-A, calcareous nannofossil content increases up to 60% with a corresponding decrease in the proportion of clays, reflected in a downhole decrease in NGR (Figure F5; see Physical properties). Authigenic carbonate is more common near the top of the unit (~350–425 m CSF-A) and decreases in abundance downhole. A key characteristic of Unit III is the absence of any biosiliceous components, including the sponge spicules that were ubiquitous in Units I and II (Figure F8); indeed, the base of Unit III is defined by the occurrence of the first sponge spicule-bearing interval in Section 353-U1447A-62X-2. Rare volcanic ashes are preserved as pale blebs (interval 53X-6, 3–8 cm) or thin dark gray beds (interval 54X-1, 7–12 cm) (Figure F9). No turbidites were observed in Unit III. Drilling disturbance is slight to moderate, with frequent biscuiting, coincident with the change to XCB coring at the top of the unit.
- Interval: 353-U1447A-62X-2, 0 cm, through 88X-CC, 83 cm
- Depth: Hole U1447A = 489.80–740.46 m CSF-A
- Age: late Miocene
- Major lithology: clayey nannofossil ooze with glauconite, biosilica-rich clay with nannofossils, and nannofossil-rich clay with biosilica
- Minor lithology: volcanic ash
Unit IV is a ~182 m thick succession of greenish gray (GLEY 1 5/5GY to GLEY 1 5/10GY) clayey nannofossil ooze with glauconite, biosilica-rich clay with nannofossils, and nannofossil-rich clay with biosilica (Figures F6, F7, F8). Unit IV is considerably richer in biosilica than Units I–III, with biosiliceous content increasing with depth, reflecting an increase in both the proportion of sponge spicules and diatoms (Figure F8). Foraminifers are a more minor component of the sediment relative to Units I–III. Unit IV is divided into two subunits: Subunit IVb is distinguished from IVa by a substantial increase in biosilica downhole, particularly diatoms, which reach a maximum at the base of the hole between Cores 353-U1447A-84X and 88X. The b* values increase strongly downhole, peaking in Subunit IVb, whereas NGR values steadily decrease as the amount of biosilica increases (Figure F5). MS values peak in Subunit IVb between 630 and 670 m CSF-A. One volcanic ash was noted at interval 74X-1, 11–17 cm. No turbidites were observed in Unit IV. Drilling disturbance in this unit is slight to severe, most commonly present as biscuiting (Figure F6).
- Interval: 353-U1447A-62X-2, 0 cm, through 71X-CC, 25 cm
- Depth: Hole U1447A = 489.80–585.33 m CSF-A
- Age: late Miocene
- Major lithology: clayey nannofossil ooze with glauconite and nannofossil-rich clay with glauconite
Subunit IVa is a ~77 m thick succession of greenish gray (GLEY 1 5/5GY to GLEY 1 5/10Y) clayey nannofossil ooze with glauconite. There are subtle color variations from brownish gray (GLEY 1 5/10Y) to greenish gray (GLEY 1 5/10GY) throughout Subunit IVa. Sponge spicules are present (~7%), and diatoms are rare, whereas the proportions of clays and nannofossils are similar to one another throughout (30%–40%) (Figure F8). The first diatoms outside of the Late Pleistocene appear downhole at the base of Subunit IVa. Drilling disturbance in Subunit IVa is slight to severe, most commonly present as biscuiting and with some cracks (Figure F6).
- Interval: 353-U1447A-72X-1, 0 cm, through 88X-CC, 83 cm
- Depth: Hole U1447A = 585.33–740.46 m CSF-A
- Age: late Miocene
- Major lithology: biosilica-rich clay with nannofossils and nannofossil-rich clay with biosilica
- Minor lithology: clay with biosilica, biosilica-rich clay with glauconite, and volcanic ash
Subunit IVb is a ~155 m thick succession of greenish gray (GLEY 1 6/5GY to GLEY 1 6/10Y and GLEY 1 4/10Y to GLEY 1 6/10Y) biosilica-rich clay with nannofossils. Biosilica content increases downhole, dominated by diatoms and sponge spicules and matched by a concurrent increase in b* and decrease in NGR (Figures F5, F8) (see Physical properties). There are faint color variations from brownish (GLEY 1 6/10Y) to greenish (GLEY 1 6/10GY) gray, and from lighter (GLEY 1 7/5GY) to dark greenish gray (GLEY 1 5/5GY), throughout. Brown patches with more abundant foraminifers and green patches with more abundant glauconite are common throughout Subunit IVb (Figure F8). Heavy bioturbation is visible throughout Subunit IVb in the form of mottling and burrows of various sizes and morphologies. Drilling disturbance in Subunit IVb is moderate to severe, most commonly present as biscuiting and with some cracks.
Calcareous nannofossils are abundant (50%–90% of sediment particles) or common (10%–50%) throughout Hole U1447A. Their preservation is generally very good to moderate, except in Samples 353-U1447A-22H-CC and 23H-CC (202.69 and 211.88 m CSF-A), which contained poorly preserved overgrown nannofossils.
Foraminifers are dominant to abundant and very well preserved throughout the Pliocene and Pleistocene in Hole U1447A with a few exceptions in the turbiditic interval of lithostratigraphic Unit II, where preservation decreases to moderate or poor and/or abundance decreases to common. Foraminifers are dominant to abundant in most Miocene sediments as well, though abundance decreases to common or few in samples where diatom abundance is high. Preservation in the Miocene continues to be good with only two exceptions where moderate preservation accompanies low foraminifer abundances in Samples 353-U1447A-78X-CC and 88X-CC (651.57 and 740.44 m CSF-A, respectively).
Diatoms are sporadically present from 0 to 566 m CSF-A in Hole U1447A. Their abundance varies downcore between abundant and few between Samples 353-U1447A-71X-2W, 70–71 cm, and 88X-CC (576.67 and 740.44 m CSF-A). Valve preservation ranges from good to poor, and valves are better preserved whenever abundance is higher than common.
The age model for Hole U1447A was established by combining calcareous nannofossil, planktonic foraminifer, and diatom datums with paleomagnetic reversal datums. The oldest calcareous nannofossil sample studied (Sample 353-U1447A-88X-CC) contained Discoaster hamatus, suggesting an age greater than 9.53 Ma. The oldest planktonic foraminifer datum encountered is the first occurrence (FO) of Neogloboquadrina acostaensis (9.83 Ma) in Sample 86X-CC. Globorotalia limbata is found in Sample 87X-CC, suggesting that the basal age of Hole U1447A is between 9.83 and 10.66 Ma. The oldest diatom datum is the FO of Thalassiosira burckliana (between 719.87 and 721.31 m CSF-A), suggesting that the bottom of Hole U1447A is slightly older than 9.1 Ma.
Calcareous nannofossils were examined in all core catcher samples from Hole U1447A. Additional split core samples from Hole U1447A were examined to refine the depth of biostratigraphic datums once they were defined between two core catcher samples. Semiquantitative species abundance estimates for all core catcher samples are shown in Table T2. Pleistocene to middle Miocene nannofossil assemblages are typical of tropical/subtropical paleoenvironments and include common Florisphaera profunda, Gephyrocapsa spp., Reticulofenestra spp., Sphenolithus spp., Discoaster spp., Helicosphaera spp., Calcidiscus spp., and Umbilicosphaera spp. This permitted the construction of a relatively high resolution stratigraphy using this fossil group (Table T3; Figure F12). In Samples 353-U1447A-22H-CC (202.69 m CSF-A) and 23H-CC (211.88 m CSF-A), the presence of abundant abiogenic carbonate particles (of detrital or authigenic origin) and a high degree of overgrowth of nannofossils prevented identification to species level. In all other samples studied, overgrowth of nannofossils was not significant under the light microscope and etching was minor, allowing species-level identification. Reworked species are few to common from the top of the hole to Sample 37F-CC (299.78 m CSF-A), below which they are few, rare, or not found (Table T2).
Table T2. Semiquantitative calcareous nannofossils abundance counts from core catcher samples, Hole U1447A. Download table in .csv format.
Table T3. Calcareous nannofossil datums, Hole U1447A. Download table in .csv format.
Well-preserved calcareous nannofossils are present throughout the Pleistocene (approximately 0–300 m CSF-A) and Pliocene (approximately 300–470 m CSF-A) sedimentary section of Hole U1447A. All Pleistocene marker species defined by Martini (1971) and Okada and Bukry (1980) were found (Table T3) (Biostratigraphy in the Expedition 353 methods chapter [Clemens et al., 2016a] for zonal schemes used; all ages cited in the text and figures are those of Gradstein et al., 2012). Emiliania huxleyi, which delineates the base of Zone NN21 (0.29 Ma), is present in Sample 353-U1447A-6H-2W, 140 cm (44.2 m CSF-A), and in all shallower samples studied based on shipboard scanning electron microscope work.
The onset of the dominance of E. huxleyi among the Noelaerhabdaceae could not be determined because this species is common down to Sample 353-U1447A-5H-CC (41.65 m CSF-A), just above where its FO was recorded. The last occurrence (LO) of Pseudoemiliania lacunosa, dated at 0.44 Ma, occurs between Samples 8H-CC and 9H-CC (midpoint depth = 74.81 m CSF-A). Reticulofenestra asanoi is present in Samples 13H-CC through 16H-CC (116.47–145.52 m CSF-A). Similar to other IODP Expedition 353 sites, the only large (>5.5 µm) Gephyrocapsa coccoliths found were present in the Late Pleistocene and belonged to the species Gephyrocapsa oceanica. Other well-defined Pleistocene events at Site U1447 are the FOs of Helicosphaera sellii, Calcidiscus macintyrei, Discoaster brouweri, Discoaster triradiatus, and Discoaster pentaradiatus (Table T3; Figure F12). We note that in Hole U1447A, D. triradiatus is rare where present; therefore, limited confidence can be placed in the exact depths of its LO at 1.95 Ma.
The Pliocene/Pleistocene boundary (2.59 Ma) is placed just below the LO of D. pentaradiatus (2.39 Ma), which occurs between Samples 353-U1447A-37F-CC and 38F-2W, 100 cm (299.78 and 301.89 m CSF-A). The LO of Sphenolithus species (3.54 Ma) occurs between Samples 48X-CC and 49X-3W, 50 cm. Reticulofenestra pseudoumbilicus (>7 µm) was found in Sample 50X-CC (381.10 m CSF-A) and deeper. Discoaster asymmetricus was almost entirely absent from the Site U1447 assemblage.
The Miocene/Pliocene boundary (5.33 Ma) occurs between Samples 353-U1447A-59X-CC and 60X-2W, 110 cm (468.89 and 470.19 m CSF-A), based on the LO of Triquetrorhabdulus rugosus (5.28 Ma) and the FO of Ceratolithus acutus (5.35 Ma) in this interval. The LO of Discoaster quinqueramus (5.59 Ma) also occurs between the same samples. Reticulofenestra rotaria, which occurs in Subzone CN9c (Bown, 1998) (5.94 to 6.91 Ma based on the calibrated ages of Gradstein et al., 2012), was present in Samples 68X-CC through 71X-CC (556.47–585.31 m CSF-A). The FOs of D. quinqueramus (8.12 Ma) and Discoaster berggrenii (8.29 Ma) occurred between Samples 78X-2W, 84 cm, and 79X-CC (645.84 and 653.89 m CSF-A). Minylitha convallis occurs in Sample 82X-CC (682.47 m CSF-A) and deeper. The oldest sample studied for biostratigraphy (Sample 88X-CC; 740.44 m CSF-A) contains D. hamatus, suggesting an age greater than 9.53 Ma.
Planktonic foraminifer biostratigraphy of the Pleistocene to late Miocene section of Site U1447 was based on the shipboard study of core catcher samples from Hole U1447A with the addition of a single sample from Section 353-U1447A-47X-1W. Planktonic foraminifer distribution in Hole U1447A is shown in Table T4. The absolute ages assigned to biostratigraphic datums listed in Table T5 follow the references given in Table T2 in the Expedition 353 methods chapter (Clemens et al., 2016a).
Table T4. Semiquantitative planktonic foraminifer abundance counts from core catcher samples, Hole U1447A. Download table in .csv format.
Table T5. Planktonic foraminifer datums, Hole U1447A. Download table in .csv format.
Planktonic foraminifer percentage is consistently high (mean = 93.6%) in the Pliocene and Pleistocene, though two samples in the turbiditic interval (Unit II) show considerably lower values: 47.5% in Sample 353-U1447A-22H-CC (202.69 m CSF-A) and 68.1% in Sample 31F-CC (267.28 m CSF-A). Planktonic foraminifer percentage is more variable in the Miocene, as it and the total number of foraminifers per 10 cm3 decreases as diatom abundance increases. The planktonic/benthic ratio, reported as percentage planktonic foraminifers of the total foraminifer population, and the number of benthic foraminifers and total foraminifers found in a 10 cm3 sample are based on examination of the >150 µm size fraction of core catcher samples.
Pleistocene planktonic foraminifer assemblages were recovered from Samples 353-U1447A-1H-CC through 34F-CC (3.35 to 285.36 m CSF-A). Foraminifers are dominant and very well preserved with few exceptions in the turbiditic interval where preservation decreases to moderate or poor and/or abundance decreases to abundant or common. Planktonic assemblages are dominated by the tropical to warm subtropical species Globigerinoides ruber, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globigerinoides sacculifer.
The LO of G. ruber (pink) in Sample 353-U1447A-4H-CC (32.26 m CSF-A) places these sediments in Zone PT1b. The top of Zone PT1a is located at the LO of Globorotalia tosaensis in Sample 11H-CC (98.79 m CSF-A). The LOs of Globigerinoides obliquus in Sample 18H-CC (164.54 m CSF-A), N. acostaensis in Sample 24H-CC (221.22 m CSF-A), and Globigerinoides fistulosus in Sample 26H-CC (240.08 m CSF-A) define Zone PT1a. The LO of Globoturborotalita woodi in Sample 35F-CC (290.24 m CSF-A) defines the base of Zone PL6.
Pliocene planktonic foraminifer assemblages were recovered from Samples 353-U1447A-35F-CC through 60X-CC (290.24–478.51 m CSF-A). Foraminifers are dominant to abundant and very well preserved except where preservation decreases to moderate in the turbiditic interval. G. sacculifer, G. ruber, Globigerinoides extremus, Dentoglobigerina altispira, Globigerinoides trilobus, and N. dutertrei dominate Pliocene samples.
The LO of G. limbata is found in Sample 353-U1447A-35F-CC (290.24 m CSF-A), marking the top of Zone PL5. The LO of Globoturborotalita decoraperta in Sample 35F-CC (290.24 m CSF-A) and the FO of G. fistulosus in Sample 45X-CC (333.08 m CSF-A) further define Zone PL5. The LO of D. altispira in Sample 47X-1W, 20–24 cm (343.02 m CSF-A), defines the upper boundary of Zone PL4. The LO of Sphaeroidinellopsis seminulina in this same sample marks the top of Zone PL3, such that Zone PL4 is not represented in these sediments. The LO of Pulleniatina primalis within Zone PL3 is in Sample 47X-CC (352.87 m CSF-A). The upper boundary of Zone PL2 is marked by the LO of Globorotalia margaritae in Sample 51X-CC (391.33 m CSF-A), and the LO of Sphaeroidinellopsis kochi in Sample 52X-CC (401.24 m CSF-A) marks the top of Zone PL1.
Samples 353-U1447A-61X-CC through 88X-CC (488.02–740.44 m CSF-A) contain Miocene sediments. Foraminifers are dominant to abundant in most samples, though abundance decreases to common or few where diatom abundance is high. Preservation is good with only two exceptions where moderate preservation accompanies low foraminifer abundances in Samples 78X-CC and 88X-CC.
The planktonic foraminifer assemblage is dominated by G. trilobus, G. obliquus, and G. extremus. Globorotalia menardii appears sporadically as a common to abundant member of the assemblage. The LO of Globoquadrina dehiscens in Sample 353-U1447A-61X-CC (488.02 m CSF-A) identifies Zone M14, and the FO of Globorotalia plesiotumida in Sample 80X-CC (663.29 m CSF-A) identifies Zone M13b. The M14/M13b boundary could not be resolved. The FOs of G. extremus in Sample 83X-CC (692.15 m CSF-A) and Globorotalia juanai in Sample 84X-CC (700.08 m CSF-A) mark these samples as part of Zone M13a. The FO of N. acostaensis (Zone M13a; 9.83 Ma) is found in Sample 86X-CC. G. limbata is found in Sample 87X-CC, suggesting that the basal age of Hole U1447A is between 9.83 and 10.66 Ma. Sample 88X-CC (740.44 m CSF-A) contained few foraminifers, and an age diagnosis was not possible.
In order to define the sediment age and paleoenvironmental conditions, core catcher samples and samples from selected split core sections from Hole U1447A were investigated. The sampling resolution was high, and the number of samples studied for each core varied between 2 and 6. The distribution of diatoms in Hole U1447A is shown in Table T6. The absolute ages assigned to biostratigraphic datums listed in Table T7 follow the references given in Table T3 in the Expedition 353 methods chapter (Clemens et al., 2016a). Figure F13 shows the age/depth plot for Site U1447 (also shown are calcareous nannofossils and foraminifer datums).
Table T6. Semiquantitative diatom abundance counts from core catcher and split core samples, Site U1447. Download table in .csv format.
Table T7. Diatom datums, Site U1447. Download table in .csv format.
The diatom community at Site U1447 is highly diverse and mainly consists of species typical of warm to temperate low-latitude ocean waters. High-productivity water species, including Thalassionema nitzschioides var. nitzschioides and Cyclotella striata, tend to dominate when total diatom abundance is higher than “few” in the uppermost 53 m. Accompanying components of the diatom assemblage are warm and temperate species including Azpeitia nodulifera, Shionodiscus oestrupii, and Alveus marinus. Deeper than 556.11 m CSF-A in Hole U1447A, T. nitzschioides and Thalassiothrix spp. dominate, whereas T. burckliana, Nitzschia porteri, Paralia sulcata, Actinoptychus senarius, and Azpeitia nodulifera fa. cyclopa are secondary components.
Diatoms are useful for age estimation deeper than 556.11 m CSF-A in Hole U1447A. The co-occurrence of Nitzschia reinholdii and N. porteri between Samples 353-U1447A-72X-2W, 76 cm, and 74X-6W, 66 cm (587.56 and 612.9 m CSF-A), delimits this interval to a subzone of the Nitzschia miocenica Zone (see Table T3 in the Expedition 353 methods chapter [Clemens et al., 2016a]). The LO of N. porteri (6.8 Ma) was observed between Samples 71X-CC and 72X-2W, 76 cm (585.31 and 587.56 m CSF-A). Close to this bioevent, the FO of N. reinholdii was found between Samples 74X-6W, 66 cm, and 74X-CC (612.90 and 614.87 m CSF-A). The LO of T. burckliana (7.85 Ma) was found between Samples 79X-2W, 80 cm, and 79X-3W, 76 cm (650.01 and 651.47 m CSF-A): this bioevent divides the N. porteri Zone (NTD11) into Subzones a and b. The LO of Thalassiosira yabei (8.6 Ma) defines the boundary between the N. porteri (NTD11) and T. yabei (NTD10) Zones and was found between Samples 82X-2W, 76 cm, and 82X-CC (673.81 and 682.47 m CSF-A). Finally, the FO of T. burckliana between Samples 86X-CC and 87X-2W, 45 cm (721.29 and 723.15 m CSF-A), defines the boundary between Subzones a and b of the Thalassiosira yabei Zone. This event suggests that the bottom of Hole U1447A is slightly older than 9.1 Ma.
Age-depth relationships for Hole U1447A based on biostratigraphy for the three fossil groups studied (calcareous nannofossils, planktonic foraminifers, and diatoms) show good agreement (Figure F13). A few paleomagnetic reversals were also determined at Site U1447 (see Magnetostratigraphy). The match between biostratigraphic datums and magnetochron boundary datums is very good. Based on linear fits including all data, sedimentation rates in Hole U1447A are relatively high in the Pleistocene (on average 12 cm/ky linear sedimentation rate [LSR]) and moderate in the Pliocene and most of the Miocene (on average 6.5 cm/ky LSR). The sedimentation rate deeper than 700 m CSF-A decreases to about 3.3 cm/ky; however, only limited confidence can be placed in this observation, as it is based on few data points (Figure F13). A number of unconformities with possible short-term stratigraphic hiatuses are indicated in Figure F13 by the co-occurrence of three or more successive biostratigraphic events within the same stratigraphic interval (e.g., 290, 340, 470, and 650 m CSF-A). Some of these events are associated with observed lithologic changes or features (see the Expedition 353 summary chapter [Clemens et al., 2016b]).
The geochemistry of Site U1447 mainly reflects the anaerobic processes of sulfate reduction and methanogenesis associated with microbial degradation of organic matter. The organic carbon content ranges from 0.1 to 2.0 wt% (average = 0.8 wt%). Sulfate declines rapidly from 28 mM at the sediment/water interface to nearly zero at approximately 20 m CSF-A. Alkalinity peaks at 20 m CSF-A, consistent with the production of bicarbonate during sulfate reduction. A gradual increase in dissolved Ba concentration with depth suggests ongoing barite dissolution and potential deep sulfate reduction. Changes in the concentrations of other elements and ions (Fe, Mn, Ca, B, ammonia, and Sr) in interstitial water can be readily explained by microbially mediated chemical reactions and their effects on pH, alkalinity, and mineral dissolution and precipitation. Headspace methane concentration peaks at 125 m CSF-A, abruptly decreases below the peak, and is consistently low to the bottom of the hole. High methane/ethane ratios suggest that the methane is mostly of biogenic origin (methanogenesis). Carbonate content varies significantly between 9 and 55 wt%.
Headspace gas samples were taken at a frequency of one sample per core in Hole U1447A as part of the routine environmental protection and safety-monitoring program (Table T8). Methane concentration increases from around 2 parts per million (ppm) in the upper 22 m CSF-A to a peak of 345 ppm at 69 m CSF-A, followed by a larger peak of 1065 ppm at 125 m CSF-A, before decreasing to <140 ppm from 144 m CSF-A until the bottom of the hole (Figure F14). Heavier hydrocarbons such as ethane and propane were not detected. Void gas analysis indicates a trace amount of ethane, but the methane/ethane ratio is higher than 14,000 (Table T9), which suggests that methane is of biogenic origin. Ethane and hydrogen sulfide were also detected in void gas samples. In Hole U1447B, headspace gas samples were taken at a frequency of one per section as part of high-resolution geochemical studies in the uppermost 25 m (Table T8). Methane concentrations are low throughout (<2 ppm), consistent with results from Hole U1447A.
Table T8. Headspace methane concentrations, Site U1447. Download table in .csv format.
Table T9. Void gas methane, ethane, and hydrogen sulfide concentrations, Hole U1447A. Download table in .csv format.
Calcium carbonate, inorganic carbon, and total organic carbon (TOC) contents were determined on sediment samples from Hole U1447A (Table T10; Figure F15). CaCO3 concentration ranges between 9 and 55 wt% and is highest in the upper part of lithostratigraphic Unit II, which corresponds to carbonate turbidites, and lithostratigraphic Subunit IVb (Figure F15). TOC ranges between 0.1 and 2.0 wt% and is highest within lithostratigraphic Unit II.
Table T10. Calcium carbonate and carbon contents, Hole U1447A. Download table in .csv format.
Hole U1447A was analyzed for pore water chemistry at a relatively coarse resolution of one sample per core for all cores. Hole U1447B was sampled for high-resolution geochemistry at a resolution of one sample per section (150 cm) for three cores (i.e., the top 25 m CSF-A). Most whole-round samples for pore water squeezing were kept under N2 before and during extraction of interstitial waters, and some additional samples were taken using Rhizon samplers (Table T11).
Table T11. Interstitial water chemistry, Holes U1447A and U1447B. Download table in .csv format.
Concomitant with a sharp drawdown of sulfate in the uppermost 20 m, alkalinity increases (Figure F16; Table T11). Although sulfate is below detection from ~20 m CSF-A downhole, Ba increases sharply from a few micromolar at ~11 m CSF-A to ~67 µM at ~21 m CSF-A. Alkalinity peaks at ~34 mM at 30 m CSF-A, slowly decreases to ~11 mM at 190 m CSF-A, and varies between ~11 and 14 mM for the rest of the sediment section. The alkalinity change deeper than 20 m CSF-A is more difficult to explain but is likely related to the varying production-consumption balance of various anaerobic microbial processes.
Ammonium increases from 0.4 mM at the top of Hole U1447B to 5.8 mM at 200 m CSF-A in Hole U1447A (Figure F16). The ammonium increase rate in the uppermost 30 m is roughly twice as fast as that deeper than 30 m CSF-A. Dissolved Mn concentration decreases rapidly from 0 to ~21 m CSF-A from 31 to 4.27 µM, consistent with microbial reduction of Mn oxides in the uppermost sediments (Figure F16; Table T11). Although dissolved Fe decreases from 12 to ~3 µM within the uppermost 20 m of the sediment column, it varies between ~2 and 51 µM in the remaining sediment column, probably reflecting variable amounts and dissolution of residual Fe oxides in sediments. When associated with sulfate reduction and production of hydrogen sulfide, soluble Fe is scavenged by sulfide and converted to sulfide minerals and eventually pyrite. Calcium concentration decreases from around 10 mM near the sediment/water interface to ~2.5 mM at ~20 m CSF-A then increases with depth with a break in slope at ~250 m CSF-A. The drop in Ca concentration in the uppermost 20 m is most likely related to the production of bicarbonate with sulfate reduction and carbonate precipitation. Magnesium is highest at ~4 m CSF-A and gradually decreases to a minimum of 30 mM around 200 m CSF-A. Deeper than 200 m CSF-A, Mg increases to ~36 mM at ~300 m CSF-A before decreasing to around 30 mM toward the bottom of the hole.
Boron concentration decreases from around 550 µM at 0 m CSF-A to 350 µM at 100 m CSF-A (Figure F16; Table T11) before peaking at around 550 µM near 200 m CSF-A. Deeper than 200 m CSF-A, B decreases with depth and fluctuates between 296 and 380 µM. Interestingly, Li, Si, and Sr all show similar downhole patterns with a peak around 300 m CSF-A, followed by a trough and increase to a flat-topped peak deeper than 600 m CSF-A. The minimum and maximum concentrations of Li, Sr, and Si are 15, 66, and 408 and 107, 326, and 1260 µM, respectively (Figure F16; Table T11).
Paleomagnetic measurements were conducted on archive-half sections for all three holes at Site U1447 with alternating field (AF) demagnetization up to 10 mT (Figures F17, F18). Discrete samples taken from the working-half sections of Hole U1447A (N = 200) were also analyzed with AF demagnetization between 40 and 80 mT (Table T12). Characteristic remanent magnetization (ChRM) of these discrete samples was calculated using the principal component analysis (PCA) technique. In addition, anhysteretic remanent magnetization (ARM) was acquired and measured on a selection of discrete samples from Hole U1447A for preliminary insight into depth variations in Site U1447 sediment bulk magnetic properties.
Table T12. Summary of discrete sample measurements, Hole U1447A. Download table in .csv format.
Cores 353-U1447A-2H through 29H and 353-U1447C-4H through 15H were oriented using the Icefield MI-5 tool. Therefore we have obtained “true” declinations between 3.30 and 260.2 m CSF-A for Hole U1447A and 18.4 and 133.45 m CSF-A for Hole U1447C (Figures F17, F18). For some cores, the orientation tool was not stable before shooting, and the orientation pick is somewhat subjective (Table T13). Nonetheless, the true declinations reasonably concentrate around 0 (360°) downhole to ~90 m CSF-A for both holes, indicating normal magnetic polarity. Deeper than ~90 m CSF-A, scatter in declination starts to increase, introducing uncertainty in polarity determinations. Declination data between ~140 and 220 m CSF-A from Hole U1447A seem to concentrate around 180°, and we argue that this interval shows reversed polarity. Inclination after 10 mT becomes steeper deeper than ~90 m CSF-A for both Holes U1447A and U1447C, suggesting more severe drilling-related overprint. Similar to the section measurements, discrete samples revealed reasonable ChRM downhole to ~90 m CSF-A (Sample 353-U1447A-10H-6W, 80–82 cm [87.78 m CSF-A]), but PCA did not work well for deeper samples. Most of the natural remanent magnetization was lost during the first few demagnetization steps (up to 10–15 mT), with a significant drilling-related vertical overprint (Figure F19). Cores 353-U1447A-26H through 28H (230.5–254.88 m CSF-A) revealed a clear remanence pattern from both archive halves (Figure F17) and discrete samples. Both measurements indicate positive (normal) polarity for these depth ranges. For HLAPC and XCB cores, large drilling overprints prevent any determination of magnetostratigraphy.
Table T13. Summary of core orientation picks, Site U1447. Download table in .csv format.
Although many discrete samples did not show good results from PCA, we observe that the remanence direction during AF demagnetization often concentrates around a single point for each sample (after the first few steps of demagnetization) before the direction becomes scattered at high AF steps (Figure F19B). In addition, the remanence measured on samples from the same APC core often migrates toward a common direction. To investigate the significance of this direction, we plotted the depth variation in the remanence directions of discrete samples after 10 mT demagnetization (Figure F20). The declination data concentrate around 0° (360°) shallower than Sample 353-U1447A-13H-3W, 50–52 cm (119.09 m CSF-A), close to 180° deeper than Sample 16H-4W, 100–102 cm (137.68 m CSF-A), and back to 0° (360°) deeper than Sample 26H-2W, 80–82 cm (232.71 m CSF-A). As expected, this pattern is similar to trends in section measurements, albeit with less scatter. Note that the reliability of these declinations in determining a magnetostratigraphy is debatable because stepwise AF demagnetization shows variable ChRM stability within discrete samples.
We construct two classes of magnetostratigraphy for Site U1447 using two sets of data with different reliability (Table T14). The first (Class 1) utilizes archive-half measurements and PCA directions of discrete samples, whereas the second (Class 2) uses inclination and declination from discrete samples after 10 mT demagnetization to the same interval where the Class 1 magnetostratigraphy was inconclusive (Figure F20). Class 1 should be considered as more conservative, as it is based on the same methodology used at other sites during Expedition 353.
Table T14. Summary of magnetostratigraphy, Site U1447. Download table in .csv format.
ARM (0.05 mT direct current field, 80 mT AF) was acquired on a selection of discrete samples taken from the working halves of Hole U1447A. ARM broadly measures relative changes in the concentration of ferrimagnetic minerals, where increases in the concentration of finer grained particles will increase ARM values much greater than an equivalent change in coarser grained particles. A significant decrease in ARM values for Hole U1447A at 10 m CSF-A (Figure F21) suggests either a decrease in the input, or the removal, of fine-grained ferrimagnetic minerals. A similar decrease is observed in magnetic susceptibility (see Physical properties) and is likely a response to early diagenesis (see Geochemistry). The decrease in ARM values at this depth (10 m CSF-A) is similar to what we see at IODP Site U1445 in the Mahanadi basin (see Paleomagnetism in the Site U1445 chapter [Clemens et al., 2016c]). From 10 to 240 m CSF-A, ARM is fairly stable and then it begins to increase to a peak value at 310 m CSF-A, approximately coinciding with lithostratigraphic Unit III. The increased and less stable ARM values deeper than 240 m CSF-A may be related to a lack of biosilica (see Lithostratigraphy) that could be diluting the magnetic record.
Standard physical property measurements were collected at Site U1447 with the addition of thermal infrared (IR) scanning of cores on the catwalk for the detection of temperature anomalies that could possibly be related to gas hydrate. Data from Hole U1447B are presented but are not discussed, as the hole was dedicated to high-resolution geochemistry. Overall, we were able to identify four physical property (PP) units based on significant changes with the physical property data sets: Units 1 (0–200 m CSF-A), 2 (200–320 m CSF-A), 3 (320–570 m CSF-A), and 4 (570–730 m CSF-A) (Table T15). In general, data from both Holes U1447A and U1447C are in good agreement.
Table T15. Physical property units, Site U1447. Download table in .csv format.
Gamma ray attenuation (GRA), MS, P-wave velocity (VP), and NGR measurements were acquired on all whole-round sections using the Special Task Multisensor Logger (STMSL), the Whole-Round Multisensor Logger (WRMSL), and the Natural Gamma Radiation Logger (NGRL). Whole-round sections from Hole U1447A were logged on the STMSL (5 cm resolution) and WRMSL (at 5 cm resolution) before being taken to the core rack for thermal equilibration (~19°C). For Hole U1447C, alternate sections were run on the STMSL (Sections 1, 3, 5, and 7) and WRMSL (Sections 2, 4, 6, 8, and CC). We measured alternate sections in Hole U1447C to maximize logging efficiency in order to assist the stratigraphic correlation process. The P-wave logger (PWL) produced unreliable data; therefore, it was disabled for the remainder of Hole U1447C. Following thermal equilibration, sections were logged on the NGRL. Approximately 10 cm3 sediment samples were collected from the working halves of Sections 2, 4, and 6 from Hole U1447A for moisture and density (MAD) analyses. The archive-half sections were used to collect color reflectance and point MS data on the Section Half Multisensor Logger (SHMSL) and red, green, and blue (RGB) data on the Section Half Imaging Logger (SHIL). The data presented in this report were conditioned to remove outliers related to endcaps, voids, and foam spacers (see Physical properties in the Expedition 353 methods chapter [Clemens et al., 2016a]). We summarize statistics (minimum, maximum, and mean) of all measured parameters downhole for Holes U1447A–U1447C for comparison (Table T16).
Table T16. Minimum, maximum, and mean statistics of measured physical properties data, Holes U1447A–U1447C. Download table in .csv format.
STMSL and WRMSL MS values recorded for Hole U1447A vary between 1.0 and 50 instrument units (IU) (Figure F22; Table T16). Occasional values >50 IU were recorded in PP Unit 4. The top of PP Unit 1 (0–200 m CSF-A) is characterized by moderate variability in the upper ~150 m CSF-A, which then decreases to the end of the unit boundary (Figure F22). In PP Unit 2, MS values increase steadily downhole to the boundary of PP Unit 3, where MS variability is fairly steady to ~500 m CSF-A. Deeper than ~500 m CSF-A, MS decreases with small fluctuations. MS values increase around 650 m CSF-A and again at the end of the hole. The STMSL and WRMSL track measurements agree well, but the SHMSL point measurements are significantly offset to higher values deeper than 490 m CSF-A; however, the overall trend is similar to the whole-round variability in Hole U1447A. Hole U1447B was a short geochemistry hole (Figure F23) and its physical property data are not being discussed here. The downhole trend and cyclicity in MS in Hole U1447C broadly agrees with Hole U1447A (Figures F22, F24).
NGR counts range from ~6.49 to 57.57 counts/s with an average of 32.13 counts/s in Hole U1447A and from 15.22 to 39.08 counts/s with an average of 31.04 counts/s in Hole U1447C. NGR data show long-term cyclic variability downhole, possibly related to changes in continental input or clay concentrations (Figure F22; see Lithostratigraphy). The downhole trend and cyclicity in NGR counts in Hole U1447C broadly agrees with Hole U1447A (Figures F22, F24).
The bulk density at Site U1447 was measured using (1) the GRA method using the STMSL and WRMSL that provides bulk density estimates from whole-round sections from Holes U1447A–U1447C (Figures F22, F23, F24) and (2) MAD measurements on discrete samples that provide a second, independent measure of bulk density and the dry density, grain density, water content, and porosity from Hole U1447A only (Figure F22). The density data from MAD and GRA show good agreement, and the overall trend in GRA data between Holes U1447A and U1447C are in good agreement.
For Hole U1447A, the GRA bulk density values range from ~1 to 1.96 g/cm3, whereas MAD bulk density ranges between 1.35 and 1.89 g/cm3 in Hole U1447A. The mean MAD bulk density is 1.71 g/cm3 (bulk) and 1.09 g/cm3 (grain) with a minimum dry density of 0.61 g/cm3 and a maximum dry density of 1.54 g/cm3. The porosity values vary significantly downhole and range between 44.1% and 77.3% (Figure F22).
Generally, density increases with a corresponding decrease in porosity with depth, mainly due to sediment compaction (e.g., until PP Unit 2). We observe a general decrease in MAD density and a corresponding increase in porosity, indicating changes in sediment composition, in PP Units 3 and 4 (see Lithostratigraphy). A gap in coring occurred at ~570 m CSF-A, at the bottom of the PP Unit 3. Both Holes U1447A and U1447C whole-round density data agree downhole.
Spectral reflectance was measured on all archive halves using the SHMSL. There are slight color variations downhole in Holes U1447A, U1447B, and U1447C (Figures F25, F26, F27). L* values range between 28 and 56.8 with an average value of 40.08 (Table T16). Reflectance a* and b* values range between −0.6 and 9.9 (average = −0.17) and between −6 and 9.9 (average = 1.58), in Holes U1447A and U1447C, respectively. The reflectance b* trend decreases in PP Unit 1 and then increases until end of the Unit 1 boundary. In PP Unit 2, b* decreases and then increases again in PP Unit 3 and continues to increase until ~730 m CSF-A (Figures F25, F26, F27).
The SHIL data (RGB) were recorded from the surface of the split archive halves prior to drying. The raw RGB data averages are R = 47.37, G = 46.96, and B = 41.78 in Hole U1447A (Figure F28). Hole U1447B and U1447C RGB data are shown in Figures F29 and F30. We summarize variability in RGB statistics (minimum, maximum, and mean) in Table T16.
Standard downhole temperature measurements were made at the sediment/water interface and then on Cores 353-U1447A-4H, 7H, 10H, and 15H using the APCT-3 (Table T17). Using the depth-related temperature change, the geothermal gradient is ~27.3°C/km (Figure F31).
Table T17. Downhole temperature data from the APCT-3, Hole U1447A. Download table in .csv format.
Based on the overall trends within individual physical property data sets, we divided Hole U1447A into four units. The changes in bulk density and porosity reflect changes in sediment composition. We observe similar trends in all physical property data between Holes U1447A and U1447C. Long-term cyclic variability in NGR values may reflect periodic changes in lithogenic input.
A composite scale (CCSF-A) and a splice (CCSF-D) were constructed for Site U1447 using Holes U1447A and U1447C (as defined in Stratigraphic correlation in the Expedition 353 methods chapter [Clemens et al., 2016a]). Splicing among these holes enabled us to construct a continuous stratigraphic sequence to ~147 m CCSF-D (Tables T18, T19; Figure F32). Hole U1447B, dedicated to geochemical sampling on board the ship, was short and not used in splicing; however, we tied it to the same composite scale as Holes U1447A and U1447C.
Table T18. Vertical offsets applied to cores in order to align structure in adjacent holes, Site U1447. Download table in .csv format.
Table T19. Splice intervals, Site U1447. Download table in .csv format.
We selected the core with the best mudline recovery (Core 353-U1447C-1H) to anchor the composite depth scale and defined the top as 0 m CCSF-A. The CCSF-A scale for Site U1447 (see Table T18) is based on correlation of RGB color data and secondarily on MS and on NGR data. RGB green was utilized in correlations for Site U1447. MS and NGR were measured on whole-round sections, whereas RGB was measured on archive-half sections (see Physical properties for details). The R, G, and B components of the RGB triplet are highly correlated to each other because, on the first order, all are measures of the reflectivity of the sediment. The small differences between R, G, and B can be expressed as ratios such as red/green, red/blue, or green/blue. However, ratios were not employed in our correlation due to lack of time (see the Expedition 353 methods chapter [Clemens et al., 2016a]). Reflectance spectroscopy data (i.e., L*, a*, and b*), which can produce information similar to RGB ratios, were not used for correlation due to inconsistent variability from hole to hole resulting from low-quality wavelength spectra collected by the Ocean Optics USB4000 spectrophotometer on the monotonously dark sediments of Site U1447.
A combination of Holes U1447A and U1447C cover the stratigraphic section to ~147 m CCSF-D. When constructing the splice, we tried to minimize inclusion of disturbed intervals and avoid whole-round sampling intervals (notably from Hole U1447A) as much as possible. Selected splice intervals are listed in Table T19. Postcruise, the splice interval tables were modified using the Splice-File-Fixer program to ensure that each depth has been assigned the correct sample ID. Both the affine and the corrected splice interval tables were uploaded into Laboratory Information Management System (LIMS) during the first postcruise meeting in June 2015. The core top depths in the affine tables were not corrected and hence may be slightly incorrect in a range of <2 cm. However, the offsets are correct.
Reliance on RGB, which sometimes has a fuzzy character due to cracks and defects of the split core surface, precluded, in places, the definition of unique correlation features and general trends were used instead, reducing the accuracy of the splice to the decimeter range. As a result, correlation should be viewed with caution deeper than ~112 m CCSF-A, notably if high-resolution sampling is planned. Onshore X-ray fluorescence scanning, color reflectance rescanning, and bulk δ18O should provide better means of correlation.
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Clemens, S.C., Kuhnt, W., LeVay, L.J., Anand, P., Ando, T., Bartol, M., Bolton, C.T., Ding, X., Gariboldi, K., Giosan, L., Hathorne, E.C., Huang, Y., Jaiswal, P., Kim, S., Kirkpatrick, J.B., Littler, K., Marino, G., Martinez, P., Naik, D., Peketi, A., Phillips, S.C., Robinson, M.M., Romero, O.E., Sagar, N., Taladay, K.B., Taylor, S.N., Thirumalai, K., Uramoto, G., Usui, Y., Wang, J., Yamamoto, M., and Zhou, L., 2016a. Expedition 353 methods. In Clemens, S.C., Kuhnt, W., LeVay, L.J., and the Expedition 353 Scientists, Indian Monsoon Rainfall. Proceedings of the International Ocean Discovery Program, 353: College Station, TX (International Ocean Discovery Program). http://dx.doi.org/10.14379/iodp.proc.353.102.2016
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1Clemens, S.C., Kuhnt, W., LeVay, L.J., Anand, P., Ando, T., Bartol, M., Bolton, C.T., Ding, X., Gariboldi, K., Giosan, L., Hathorne, E.C., Huang, Y., Jaiswal, P., Kim, S., Kirkpatrick, J.B., Littler, K., Marino, G., Martinez, P., Naik, D., Peketi, A., Phillips, S.C., Robinson, M.M., Romero, O.E., Sagar, N., Taladay, K.B., Taylor, S.N., Thirumalai, K., Uramoto, G., Usui, Y., Wang, J., Yamamoto, M., and Zhou, L., 2016. Site U1447. In Clemens, S.C., Kuhnt, W., LeVay, L.J., and the Expedition 353 Scientists, Indian Monsoon Rainfall. Proceedings of the International Ocean Discovery Program, 353: College Station, TX (International Ocean Discovery Program). http://dx.doi.org/10.14379/iodp.proc.353.107.2016
- F1. Andaman Sea map with location of Site U1447.
- F2. Summary sketch showing the subduction zone through the back-arc basin to ~40 km depth.
- F3. Seismic lines showing location of Site U1447.
- F4. Lithostratigraphic summary, Site U1447.
- F5. Lithostratigraphic summary with selected physical property and geochemical data from Holes U1447A–U1447C.
- F6. Main lithologies, Site U1447. A. Clayey nannofossil ooze with foraminifers. B. Foraminifer-rich nannofossil ooze with clay. C. Clayey nannofossil ooze with glauconite. D. Clayey nannofossil ooze with glauconite, with minor drilling disturbance. E. Biosilica-rich clay with nannofossils.
- F7. Photomicrographs of the main lithologies, Site U1447. A. Foraminifer-rich nannofossil ooze with clay. B. Authigenic carbonate-rich nannofossil ooze with foraminifers. C. Clay with nannofossils. D. Biosilica-rich clay with nannofossils. E. Volcanic ash. F. Bioclastic sand.
- F8. Smear slide data, Holes U1447A and U1447C.
- F9. Minor lithologies, Site U1447. A. Volcanic ash. B. Gray volcanic ash with clay. C. Light gray bleb of volcanic ash with glauconite. D. Very dark gray volcanic ash. E. Thick turbidite with coarse sand, shell fragments, and foraminifers. F. Bioclastic sandy blebs and thin bioclastic turbidite layers. G. Dark patches of plant debris.
- F10. XRD analyses, Site U1447. A. Serpentinite (lizardite) fragment from a coarse-sand bioclastic turbidite. B. Foraminifer-rich nannofossil ooze with clay. C, D. Bioclastic sand turbidite.
- F11. Turbidite abundance, thickness, and composition over the upper 400 m CSF-A, Hole U1447A.
- F12. Summary of biostratigraphic events identified in Hole U1447A.
- F13. Biostratigraphic- and magnetostratigraphic-based age-depth plot, Hole U1447A.
- F14. Headspace methane concentrations and void gas methane, ethane, and hydrogen sulfide concentrations, Hole U1447A.
- F15. Calcium carbonate and TOC contents, Hole U1447A.
- F16. Interstitial water chemistry profiles, Holes U1447A and U1447B.
- F17. Downhole variations in declination, inclination, and intensity, Hole U1447A.
- F18. Downhole variations in declination, inclination, and intensity, Hole U1447C.
- F19. A–B. Representative stepwise AF demagnetization results, Hole U1447A discrete samples.
- F20. A. Class 1 depth variations of PCA declination and inclination from discrete samples compared with section data for Hole U1447A. B. Class 2 depth variations in declination and inclination from discrete samples after 10 mT AF demagnetization.
- F21. Depth variation in mass-normalized ARM, Hole U1447A.
- F22. Physical properties showing downhole variability in magnetic susceptibility, density, porosity, and NGR, Hole U1447A.
- F23. Physical properties showing downhole variability in magnetic susceptibility, density, and NGR, Hole U1447B.
- F24. Physical properties showing downhole variability in magnetic susceptibility, density, and NGR, Hole U1447C.
- F25. L*, a*, and b* data, Hole U1447A.
- F26. L*, a*, and b* data, Hole U1447B.
- F27. L*, a*, and b* data, Hole U1447C.
- F28. SHIL RGB color data, Hole U1447A.
- F29. SHIL RGB color data, Hole U1447B.
- F30. SHIL RGB color data, Hole U1447C.
- F31. Downhole temperature data, Hole U1447A.
- F32. Core alignment shown using (A) RGB blue, (B) NGR, and (C) MS profiles, Holes U1447A–U1447C.
- T1. Site U1447 core summary.
- T2. Semiquantitative calcareous nannofossils abundance counts from core catcher samples, Hole U1447A.
- T3. Calcareous nannofossil datums, Hole U1447A.
- T4. Semiquantitative planktonic foraminifer abundance counts from core catcher samples, Hole U1447A.
- T5. Planktonic foraminifer datums, Hole U1447A.
- T6. Semiquantitative diatom abundance counts from core catcher and split core samples, Site U1447.
- T7. Diatom datums, Site U1447.
- T8. Headspace methane concentrations, Site U1447.
- T9. Void gas methane, ethane, and hydrogen sulfide concentrations, Hole U1447A.
- T10. Calcium carbonate and carbon contents, Hole U1447A.
- T11. Interstitial water chemistry, Holes U1447A and U1447B.
- T12. Summary of discrete sample measurements, Hole U1447A.
- T13. Summary of core orientation picks, Site U1447.
- T14. Summary of magnetostratigraphy, Site U1447.
- T15. Physical property units, Site U1447.
- T16. Minimum, maximum, and mean statistics of measured physical properties data, Holes U1447A–U1447C.
- T17. Downhole temperature data from the APCT-3, Hole U1447A.
- T18. Vertical offsets applied to cores in order to align structure in adjacent holes, Site U1447.
- T19. Splice intervals, Site U1447.