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doi:10.2204/iodp.proc.342.111.2014 LithostratigraphyAt Site U1410, we recovered an ~260 m thick sedimentary succession of deep-sea sediment of Pleistocene to early Eocene age. The full sequence of lithostratigraphic units was only recovered in Hole U1410A. Holes U1410B and U1410C were terminated at 244.25 and 243.27 meters below seafloor (mbsf), respectively. The sedimentary sequence at Site U1410 comprises four lithostratigraphic units (Figs. F4, F5, F6, F7, F8, F9; Table T2). Unit I is an ~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 lithics (Fig. F5A, F5B). Unit II is an ~30 m thick succession of clay, clay with nannofossils, and nannofossil clay of early Miocene to Oligocene age (Figs. F5C, F5D, F6B). Manganese, present as discrete nodules or disseminated silt- to sand-sized flecks, and disseminated sulfides are common. Sedimentological and biostratigraphic information indicates that Unit II contains multiple hiatal surfaces in addition to the unconformities that define its upper and lower boundaries. Middle to upper Eocene Unit III is the thickest of the four units (63–68 m thick) and contains greenish gray to greenish nannofossil clay to greenish clayey nannofossil ooze with distinctive 10–25 cm thick bands of light gray to white nannofossil ooze (Figs. F5E, F6C). Lithostratigraphic Unit IV is a 48 m thick sequence of white to pinkish white nannofossil chalk with foraminifers and/or radiolarians of early Eocene age (Figs. F5F, F5G, F6D). This unit is divided into two subunits, with the lower subunit containing several chert beds. Hole U1410A is the deepest hole and thus contains the thickest record of Unit IV. Coring in Hole U1410C recovered only 47 cm of the upper part of Subunit IVb. No part of Subunit IVb was recovered from Hole U1410B (Table T2). Lithostratigraphic units and boundaries are defined by changes in lithology (as identified by visual core description and smear slide observations), physical properties, color reflectance (L*, a*, and b*), and biogenic content (calcium carbonate and silica) (Fig. F4). The lithologic differences observed between units are primarily attributable to varying abundances of nannofossils, diatoms, radiolarians, and foraminifers (Figs. F7, F8, F9). Lithologic descriptions are based on sediment recovered from Hole U1410A and refined with observations from Holes U1410B and U1410C. The Unit I/II boundary is a sharp contact between banded brown to gray Pleistocene sediment and underlying greenish gray clay of late Miocene age. The basal boundary of Unit II is also sharp and corresponds to a temporal hiatus between overlying lower Oligocene clay and nannofossil clay and underlying middle Eocene sediment that alternates between white nannofossil ooze and dark green nannofossil clay. The Unit III/IV boundary is defined by the transition from alternating green nannofossil clay and white nannofossil ooze to pinkish white, carbonate-rich nannofossil ooze with foraminifers and radiolarians. Unit I
Unit I is an ~34 m thick succession of Pleistocene sediment with reddish brown (5YR 5/3) to dark greenish gray (10Y 4/1) clay, gray (N6 and 10YR 5/1) and dark brown (5Y 4/2) to dark greenish gray (10Y 4/1) muddy/clayey foraminiferal ooze with nannofossils, and grayish brown (2.5Y 5/2) foraminiferal sand (Fig. F5A, F5B). Sediment in the uppermost interval of Unit I (0 to ~12 mbsf) contains radiolarians and diatoms of varying abundances (Figs. F6, F7, F8, F9). These siliceous components are found only in Units I and IV and further distinguish Unit I sediment from that of underlying Unit II. The upper half of Unit I (0 to ~15 mbsf) contains discrete layers and patches of coarse sand– to small pebble–sized lithics, which are clearly ice-rafted debris. The sediment of Unit I is heavily to completely bioturbated throughout, with the exception of some sandy layers that are only slightly bioturbated. The Unit I/II boundary is defined by a sharp contact between brown and gray Pleistocene sediment and underlying greenish gray clay and dark greenish gray nannofossil clay of late Miocene age in the upper part of Unit II. This contact, which occurs in Cores 342-U1410A-4H, 342-U1410B-5H, and 342-U1410C-4H (~34 mbsf), is expressed as a decrease in magnetic susceptibility from ~150 instrument units (IU) in Unit I to <20–50 IU in Unit II (Fig. F4) and a decrease in bulk density (see “Physical properties”). Core 342-U1410C-4H contains a thin (<5 cm) interval of lithogenic sand that directly overlies a sharp contact. This is likely a winnowed deposit that formed during the >5 m.y. duration of the unconformity that separates Units I and II. Unit II
Unit II is an ~30 m thick succession of clay, clay with nannofossils, and nannofossil clay of late Miocene to Oligocene age (Fig. F4). Colors range from light olive-gray (5Y 6/2) to olive-gray (5Y 6/2), greenish gray (10GY 5/1 and 10Y 6/1), and dark greenish gray (5G 4/1) for the clay and greenish gray (5GY 5/1 and 10Y 5/1) to dark greenish gray (10GY 4/1) for the nannofossil clay (Fig. F5C, F5D). The abundance of foraminifers decreases substantially compared to overlying Unit I, and siliceous biogenic components are absent (Figs. F6, F7, F8, F9). Minor lithologies and accessories include centimeter-scale manganese nodules, disseminated manganese as small dark flecks, dark green glauconite-rich horizons, and dark gray to black concentrations of sulfides. Sulfide mineralization is typically associated with burrows, creating a mottled appearance. Small (1 mm to <1 cm) concentrations of angular, silt- to very fine sand–sized quartz (confirmed by shipboard X-ray diffraction [XRD] analysis) are present throughout Unit II as discrete patches/blebs or, more rarely, as discontinuous lenses within the nannofossil clay (Figs. F5D, F10). We hypothesize that this angular quartz is ice-rafted debris that was subsequently reworked and concentrated by bioturbation. Sharp contacts define the upper and lower stratigraphic boundaries of Unit II in all holes and coincide with abrupt changes in color and lithology (Fig. F4). Additionally, prominent surfaces within Unit II typically associated with sediment containing abundant glauconite and/or manganese directly below are observed separating distinct intervals. For example, a sharp surface at Section 342-U1410A-5H-4, 43 cm, separates overlying upper Miocene nannofossil clay from underlying lower Miocene nannofossil clay with silt. Although the lithologies across this surface are generally similar, there is a temporal gap of as much as 7 m.y. (see “Biostratigraphy”). Additional surfaces within Unit II likely represent other hiatuses that further biostratigraphic investigation could potentially resolve. Unit III
Unit III is a 63–68 m thick succession of predominantly dark greenish gray (5GY 5/1) to greenish gray (10Y 5/1 and 10Y 6/1) nannofossil clay to greenish gray clayey nannofossil ooze (Figs. F4, F5E, F6B, F6C, F7, F8, F9). Distinctive 10–25 cm thick bands of light gray (10Y 7/1 and 10Y 8/1) to white (N 8) nannofossil ooze occur as a secondary, interbedded lithology (Figs. F5E, F6B, F6C). The white nannofossil ooze and greenish gray clay are differentiated by physical properties including color reflectance (L*), magnetic susceptibility, natural gamma radiation (NGR) (Fig. F11), and carbonate content, which varies from ~30 wt% in the dark layers to ~80 wt% in the light layers (Fig. F4). The frequency of the lighter colored, more nannofossil rich bands is variable throughout Unit III, with some cores containing no light-colored bands and other cores displaying a strikingly rhythmic banded appearance (e.g., Core 342-U1410A-12H; Fig. F11). Intervals of alternating greenish gray nannofossil clay and white nannofossil ooze of middle Eocene age were also recovered at Southeast Newfoundland Ridge Sites U1407 and U1408, all in Unit III. A similar succession, although diminished in its visual appearance, was also recovered in Oligocene–Miocene age sediment at J-Anomaly Ridge (e.g., Site U1405). Bioturbation is moderate to heavy throughout Unit III, with Zoophycos, Planolites, and Chondrites burrows mottling both the greenish gray and white sediment. Green horizons with elevated concentrations of glauconite and chlorite occur throughout the light greenish gray beds of Unit III, but these are conspicuously absent from the white nannofossil oozes. The concentration of green horizons is higher in the uppermost portion of the light greenish gray nannofossil clay intervals immediately underlying the white/green contacts. Section 342-U1410A-17X-2 contains a 14 cm thick (153.13–153.27 mbsf) conglomerate with foraminiferal sand matrix (Fig. F12). The clasts are 0.5 to >5 cm in size and composed of the dominant nannofossil clay and clayey nannofossil ooze lithology that is observed throughout Unit III. Examination of calcareous nannofossils sampled from a clast and from the foraminiferal sand matrix indicates an age of nannofossil Subzone NP15b (middle Eocene) for both (see “Biostratigraphy”), which is consistent with the age of the sediment directly under and overlying the conglomerate bed (Fig. F12). We interpret the conglomerate to record erosion, reworking, and winnowing during a period of intensified bottom-current energy. The conglomerate bed in Section 342-U1410A-17X-2 is overlain by an ~11 m thick, internally chaotic interval containing several sharp surfaces, commonly at high angles, that juxtapose lighter clayey nannofossil ooze against darker nannofossil clay. This interval is similar in sedimentary characteristics and age (calcareous nannofossil Subzone NP15b) to an interpreted slump deposit in nearby Site U1409 (see Fig. F16 in the “Site U1409” chapter [Norris et al., 2014d]). Erosion and reworking during the phase that created the conglomerate lag deposit could have produced a relatively rough seafloor topography, which subsequently promoted mass wasting and other soft-sediment deformation in the overlying deposits. The Unit III/IV boundary is defined by the transition from interbedded gray and white nannofossil clay and ooze to pinkish white, carbonate-rich nannofossil chalk with foraminifers and white nannofossil chalk with radiolarians. The carbonate content of sediments decreases at the Unit III/IV boundary from an average of ~90 wt% in Unit IV to an average of ~50 wt% in Unit III. Unit IV
Unit IV is a 48 m thick sequence of dominantly nannofossil chalk with foraminifers and/or radiolarians of early Eocene age. Unit IV is divided into two lithologically similar subunits on the basis of the occurrence of interbedded chert at 245.07 mbsf in Hole U1410A (Fig. F4). The chert-rich Subunit IVb was recovered only in Hole U1410A. Unit IV is distinguished from overlying Unit III primarily by the abrupt change in lithology from greenish gray nannofossil clay to white nannofossil chalk, a change that is apparent in most physical property measurements (see “Physical properties”). A significant increase in siliceous biogenic components, especially radiolarians, further distinguishes Unit IV from overlying Unit III, which is essentially barren of siliceous microfossils (Figs. F6, F7, F8, F9). Subunit IVa
Subunit IVa is a 20–34 m thick succession of white (N8) to pinkish white (7.5YR 8/2 and 7.5YR 8/3) nannofossil chalk with foraminifers and radiolarians (Fig. F5F). Subtle changes in color, from pinkish white to reddish brown (5YR 4/3), occur at the centimeter to decimeter scale in some parts of the succession. Intervals of slightly brighter pink nannofossil chalk are more abundant in radiolarians. Heavy bioturbation, evidenced by faint mottling, occurs throughout Subunit IVa. Underlying Subunit IVb is distinguished by the first occurrence of chert. Subunit IVb
Subunit IVb is a 14 m thick nannofossil chalk with foraminifers and/or radiolarians distinguished from Subunit IVa by several thin (<5 cm) brown (7.5YR 6/4) chert layers. Coring of Subunit IVb in Holes U1410B and U1410C was not attempted because of the significantly slower drilling encountered in Hole U1410A as a result of the chert layers. The brief recovery of this subunit in Hole U1410C is incidental. SummaryThe sedimentary sequence at Site U1410 comprises four lithostratigraphic units. Unit I is an ~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 lithics (Fig. F5A, F5B). Unit II is an ~30 m thick succession of clay, clay with nannofossils, and nannofossil clay of late Miocene to Oligocene age (Fig. F5C, F5D). Manganese, present as discrete nodules or disseminated silt- to sand-sized flecks, and disseminated sulfides are common. Sedimentological and biostratigraphic information indicates that Unit II contains multiple hiatal surfaces in addition to the unconformities that define its upper and lower boundaries. Middle to lower Eocene Unit III is the thickest of the four units (63–68 m) and contains greenish gray to greenish nannofossil clay and greenish clayey nannofossil ooze with distinctive 10–25 cm thick bands of light gray to white nannofossil ooze (Fig. F5E). 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. The lithostratigraphy of Site U1410 strongly resembles that of Sites U1408 and U1409 in terms of the appearance, lithology, degree of bioturbation, and sedimentary succession of units for Units I–III and, to a lesser degree, Unit IV. We observed three lithostratigraphic commonalities among all sites drilled to date on the Southeast Newfoundland Ridge (Sites U1407–U1410). They include
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