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doi:10.2204/iodp.proc.317.104.2011

Lithostratigraphy

Four holes were drilled at Site U1352, reaching a total depth of 1927 m core depth below seafloor (CSF-A; unless otherwise noted, all depths in this section are reported in m CSF-A) and spanning the Holocene to late Eocene. APC drilling was used in Holes U1352A and U1352B to 297 m and in Hole U1352D for the entire cored interval. XCB drilling was used in Hole U1352B to 822 m (total depth), and RCB drilling was used in Hole U1352C.

The succession was divided into three lithologic units (Table T2; Figs. F3, F4). Recovery was variable, ranging from an average maximum of 103% in Subunit IA (Holes U1352A, U1352B, and U1352D) to 38% in Subunit IIA (15% in Hole U1352B and 43% in Hole U1352C). Subunit IB had an average recovery of 97%, whereas recovery for Subunit IC averaged 45% (15% in Hole U1352C and 60% in Hole U1352B). The remaining units occur only in Hole U1352C, where Subunit IIB averaged 53% recovery, Subunit IIC averaged 67%, and Unit III averaged 54%.

Unit I spans the Holocene to middle Pliocene and contains predominantly mud-rich sediment consisting of calcareous sandy mud; interbedded sand, mud, and clay; massive sand; mottled sandy mud; homogeneous mud; shelly mud; and marl.

Although the boundary between Units I and II was placed at 710 m, the lithologic transition between Units I and II is gradual, reflecting a progressive change in water depth to deeper slope depositional environments. Unit II spans the middle Pliocene through early Miocene and contains hemipelagic to pelagic sediment consisting of calcareous sandy mud, sandy marls, chalk, sandy marlstone, and sandy limestone, with minor amounts of calcareous mudstone and sandstone. Unit II contains a gradual progression from uncemented calcareous sandy mud and marl to lithified marlstone and limestone. Notably, this unit generally lacks clay-sized material, except in discrete mudstone beds present in the lower half of the unit. Glauconitic laminae and layers also occur in the lowermost part of this unit. Packages of recumbent and isoclinal folds, tilted beds, contorted strata, and fluid escape features are present within the middle portion of Unit II.

A hiatus representing ~12 m.y. occurs at the base of Unit II at 1853 m, where there is an abrupt change to lithologic Unit III, which is composed of hemipelagic to pelagic foraminifer-bearing nannofossil limestone of early Oligocene to late Eocene age. Except for minor abundances of quartz and clay minerals, Unit III lacks siliciclastic components. This unit is correlative with the onshore Amuri Limestone.

Site U1352 represents a late Eocene to early Oligocene and nearly complete Neogene continental slope sedimentary record dominated by pelagic to hemipelagic sedimentation with minor traction and gravity-flow sediments. The gradual downhole transition in lithofacies from more siliciclastic rich Pleistocene to Holocene muddy facies into pelagic limestones and glauconitic marls and marlstones appears to reflect the transition seen on seismic profiles from an upper-slope location on a clinoformal margin with a sharp shelf-slope break in the Pleistocene to Holocene toward a toe-of-slope to basin-floor position on a more ramplike margin in the Miocene (Lu and Fulthorpe, 2004).

Like those at other Expedition 317 sites, the lithologic units defined at Site U1352 exhibit gradual changes downhole, making definition of unit boundaries difficult. Lithologic units (Table T2) were defined primarily by their lithologies and, importantly, by the repetitive assemblages of facies that occur in each unit. The boundaries between units and subunits were chosen based on these criteria and not, in general, on correlation to any other data set (such as whole-round physical property measurements or downhole logs). However, in intervals of relatively poor recovery, such data sets were used in conjunction with lithologic logs and percentages to determine the locations or depth ranges of unit boundaries. Note that downhole logs exist only for the uppermost 487 m of Hole U1352B and for the uppermost 207 m of Hole U1352C because of hole cave-in below these depths (see "Downhole logging").

Description of lithologic units

Unit I

• Intervals: Cores 317-U1352A-1H through 5H; 317-U1352B-1H through 81X; and 317-U1352C-2R to Section 11R-1, 92 cm

• Depths: Hole U1352A: 0–43.11 m (total depth); Hole U1352B: 0–710.78 m; and Hole U1352C: 574.7–709.32 m

• Age: Holocene to mid-Pliocene

Unit I is divided into subunits according to the occurrence of two sandy lithologies. The first subunit boundary (IA/IB) is placed at 98 m, below which sharp-based, thin gray sand beds are absent. The second subunit boundary (IB/IC) is placed at 447 m to mark the first downhole occurrence of thick gray-green calcareous muddy sand beds, which become sandy marls with >30% carbonate content toward the base of the unit.

Subunit IA

• Intervals: Cores 317-U1352A-1H through 5H and 317-U1352B-1H to Section 11H-4, 23 cm

• Depths: Hole U1352A: 0–43.11 m (total depth) and Hole U1352B: 0–98.41 m

• Age: Holocene to Pleistocene

Subunit IA is dominated by homogeneous mottled and interbedded mud facies that generally contain a few percent of very fine sand, often with thin clay-rich intervals (Figs. F5, F6). Sand beds occur either as thin, very fine to fine, dark gray, sharp-based beds on a scale of a few centimeters or as thin to thick, sharp-based, shelly, greenish very fine to fine muddy sand or sandy mud (Fig. F7). The mud is gray and sometimes mottled or color banded and has either abundant shells (including Tawera, Chlamys patagonica delicatula, and other bivalve, gastropod, barnacle plate, bryozoa, and worm tube fragments) or is devoid of shells (especially in intervals of interbedded mud, sand, and clay). The alternation between shelly and nonshelly mud beds occurs on a scale of 10–40 m. Deformation occurs in the uppermost 20 m of Subunit IA, including normal faulting (interval 317-U1352A-2H-2, 0–50 cm) and folding (intervals 2H-4, 99–130 cm, and 317-U1352B-2H-3, 10–57 cm) (Fig. F8). The ichnofabric index ranges from 1 to 5 but is typically moderate to complete (3–5) in the mud intervals. The thin gray sand beds are generally not bioturbated, although sand-filled burrows sometimes extend a few centimeters below their sharp basal contacts (e.g., Section 317-U1352B-5H-3, 102 cm).

Subtle changes occur within this subunit. At the top of Hole U1352A and in Cores 317-U1352B-1H through 7H there is a marked alternation between green calcareous muddy sand or sandy mud facies and thicker beds composed of gray clay-rich mud beds alternating with sharp-based, thin dark gray sand beds with sand-filled burrows below (Fig. F9). The boundaries of these beds are very distinct, although they are often deformed by drilling (Fig. F8). Below Core 317-U1352B-7H the boundaries of the clay, mud, and thin sand beds are no longer distinct, but individual beds can still be identified. The lack of distinct bedding contacts is presumably the result of increased bioturbation. Below Section 317-U1352B-11H-3, green sand beds are less common, and the thin gray sand beds that occur frequently within the interbedded mud and clay above are absent. Section 317-U1352B-11H-3 also marks a change in magnetic susceptibility logs, with an apparent baseline shift from higher to lower values across the Subunit IA/IB boundary.

Mineralogy from smear slides in Subunit IA shows that the dominant detrital components are quartz, feldspar, rock fragments, mica (dominated by muscovite; see "Site U1352 smear slides" in "Core descriptions"), ferromagnesian minerals (e.g., hornblende), and dense minerals (e.g., epidote and zircon). The authigenic fraction is dominated by pyrite in the upper part of the succession and by microcrystalline carbonate in the lower part of the succession and in cemented zones. The percentage of carbonate components is generally characterized by a wide range of values in Subunit IA, with especially high values in smear slides taken from localized yellow patches within the muddy units (partly cemented burrow fills). The carbonate content of smear slides appears to decrease downhole from the mudline and then increase toward the base of Subunit IA (Fig. F10). Rock fragments observed in this subunit represent a range of lithologies, including grains of siltstone, sandstone, and foliated metamorphic rocks (phyllite and schist), as well as indeterminate rock fragments. Biogenic components are composed dominantly of foraminifers, nannofossils, and undifferentiated or highly altered, abraded, or fragmented bioclasts.

A thin section of a burrowed lithified concretion in interval 317-U1352B-2H-2, 32–34 cm, contains subequal amounts of quartz, feldspar, sedimentary to metasedimentary rock fragments, and mica grains locally suspended in a micritic to clay-rich matrix. The shallow depth of this concretion (10 m) suggests a very early precipitation of authigenic carbonate, perhaps in association with methanogenesis.

X-ray diffraction (XRD) analyses of samples selected from the dominant lithologies show that in Subunit IA peak intensities of quartz and total clay are relatively high, whereas calcite is largely zero (Fig. F11; see also XRD in "Supplementary material"). In this subunit, the micas (muscovite/biotite) and chlorite have relatively low, constant peak intensities with depth relative to their intensities in the rest of the hole. Plagioclase is variable and is not correlated with quartz, as it is at Site U1351, and hornblende is relatively low. Siderite is present in trace amounts, but no appreciable pyrite or dolomite was observed.

Subunit IB

• Interval: Sections 317-U1352B-11H-4, 23 cm, to 53X-1, 18 cm

• Depth: 98.41–446.88 m

• Age: Pleistocene

Subunit IB is dominated by gray to greenish gray and dark greenish gray mud containing rare to locally abundant shells; these shells become less abundant and occur as broken fragments with depth. Decimeter-thick, greenish gray, calcareous very fine to fine sand, sandy mud, and muddy sand are intercalated with the mud, the latter typically forming fining-upward packages. Shells are also commonly associated with the basal boundaries of green calcareous muddy sand beds. These sharp basal surfaces of greenish gray calcareous sandy mud or muddy sand beds are often clustered, occurring as frequently as three times in one core (e.g., Cores 317-U1352B-16H, 23H, and 28H), separated by thicker uninterrupted gray mud beds. Burrows often extend ~50 cm below the base of the graded sand beds. Shells include bivalves (including Chlamys patagonica delicatula), gastropods, echinoid spines, serpulid tubes, coral (Flabellum), and foraminifers. The alternating lithologies change below a sharp-based green sandy marl in Section 317-U1352B-37X-2, becoming dominated by color-banded mud with only very thin green sandy layers. The green sandy layers at the base of each fining-upward succession become increasingly calcareous throughout Subunit IB. Below Core 317-U1352B-35H, very dark greenish gray, poorly sorted very fine to medium sandy marls first appear. These become more frequent with depth, as indicated by smear slide data. Calcareous nodules occur throughout this subunit and are relatively common below 350 m. The ichnofabric index ranges from no bioturbation to heavy bioturbation (1–4), and identifiable traces include Thalassinoides.

Smear slide analysis of Subunit IB reveals components similar to those found in Subunit IA, although with higher carbonate percentages (Fig. F10). The highest carbonate values occur close to the base of Subunit IB, between 380 and 440 m. Smear slide data through Subunit IB document an increase in siliceous biogenic components (diatoms, siliceous sponge spicules, and other minor siliceous debris) in tandem with increasing carbonate content (Fig. F10) to a depth approaching 300 m. Below 300 m, siliceous components are less common, although they are present throughout the remainder of Subunit IB. Below ~205 m, micrite is a common component in smear slides. Below 350 m, concretions or nodules are relatively common; notably, this depth also coincides with the start of an increasing trend in calcium concentration in interstitial water analysis (see "Geochemistry and microbiology").

Thin sections of lithified intervals in Subunit IB have variable lithologies (see "Site U1352 thin sections" in "Core descriptions"). The most numerous stratigraphic examples are concretions similar in texture to those found near the top of Subunit IA (intervals 317-U1352B-16H-4, 130–134 cm; 17H-4, 69–72 cm; and 21H-1, 0–2 cm; Fig. F12A). These concretions contain bioturbated, micritized marlstone (muddy limestone) with sparse, angular silt- to sand-sized terrigenous components, organic debris, and bioclasts (including echinoderm fragments); degraded and micritized foraminifers; and molds of dissolved mollusks. Localized concentrations of pyrite were found within burrows and moldic pores. Lower in Subunit IA, the lithified intervals are more variable and lithification appears to be related to a combination of compaction and cementation rather than micrite formation within the matrix. Some samples are foraminiferal limestones (e.g., Sample 317-U1352B-35H-2, 40–41 cm [294.7 m]) having textures that vary between grain (foraminifer) and matrix supported (e.g., Sample 42X-5, 5–7 cm [347 m]; Fig. F12C). Textural variations in the latter sample are related to bioturbation, and platy fossil fragments show no preferred orientation. This sample also contains evidence of significant compaction. Additionally, glauconite is more prevalent, occurring as a pale green fill in foraminifer tests, as well as in darker green discrete lobate pellets, alteration products of biotite, and likely some epigenetic glauconite in the matrix. The lowermost thin section in the subunit is of a matrix-rich, burrowed marlstone containing a mixture of diagenetic and compactional features.

The interval from 280 to 300 m contains some unusual lithologies in the cores, including a >3 m thick bed of shelly sand that was partly liquefied during the coring process (Sections 317-U1352B-32H-5 through 33H-1) and a sandy marl bed (Sections 36H-2 through 37X-2). In addition to high values of carbonate content, estimates from smear slide and XRD data reveal marked fluctuations in mica, quartz and feldspar, glauconite, and clay between 250 and 300 m (Figs. F10, F11). As at Site U1351, the relative intensity of the calcite peak correlates with the total calcium carbonate concentration determined by coulometry, indicating that calcite is the dominant carbonate mineral. However, minor amounts of Mg calcite and aragonite based on peak heights were also observed, always co-occurring with calcite (e.g., Sample 317-U1352B-32H-CC, 53–55 cm).

XRD data show a distinct mineralogical transition within Subunit IB (Fig. F11). Quartz content determined from XRD analysis is significantly lower (p = 0.05 for this and other t-tests and correlations) below the Subunit IA/IB boundary, which is matched by a decrease in sand content, as seen in smear slides. Additionally, quartz content decreases significantly within Subunit IB below ~250 m; this trend is also observed in smear slides. Plagioclase remains fairly constant within this subunit, but, in contrast to Subunit IA, a significant correlation (N = 40) exists between quartz and plagioclase. Total clays remain relatively high with no apparent depth trends, as also seen in smear slides, but mica and hornblende increase significantly below the Subunit IA/IB boundary, with the increase in mica supported by smear slide observations. Calcite peak intensity also significantly increases below the Subunit IA/IB boundary, supported by both coulometry and smear slide observations. Pyrite and siderite peak intensities are highest in Subunit IB, especially below 250 m. Dolomite was infrequently observed, with peak highs close to detection limits.

Subunit IC

• Intervals: Section 317-U1352B-53X-1, 18 cm, through Core 81X and Core 317-U1352C-2R to Section 11R-1, 92 cm

• Depths: Hole U1352B: 446.88–710.78 m and Hole U1352C: 574.7–709.32 m

• Age: Pleistocene to mid-Pliocene

The top of this subunit was placed at the top of a 6.5 m thick bed of sandy marl, marking the top of an interval of ~40 m where this lithology is dominant. Below this, core recovery in Hole U1352B dropped dramatically, with the recovered intervals containing homogeneous mud (largely lacking in shells), calcareous sandy mud and sandy marl, and sandy marlstone. Many of these sandy mud and sandy marl beds fine upward. Recovery from Hole U1352C (starting at 574.7 m) was also poor; however, the cores from this hole contain largely lithified intervals, generally of very fine sandy marlstone (with scattered small shells, including foraminifers). Bioturbation is particularly evident in the sandy marlstones (ichnofabric index of 1–4, where sediments without recognizable depositional structures were recorded as 1). Poor recovery in Hole U1352B may be caused by the intermittent presence of lithified layers composed of thick sandy marlstone between layers of unlithified sandy marl and homogeneous mud.

The quartz, feldspar, and mica mineralogy in Subunit IC, as estimated from smear slides, is similar to that of Subunits IA and IB, with higher and more variable average carbonate concentrations and therefore lower percentages of other minerals (Fig. F10). The presence of shells in the muddy sediments and sedimentary rocks below ~575 m is extremely rare. All mineral percentage estimates are highly variable throughout Subunit IC, which distinguishes this subunit somewhat from Subunits IA and IB and Unit II. This high variability is also reflected in XRD data (Fig. F11). Glauconite is more common toward the top of Subunit IC and decreases in concentration downhole. The proportion of siliceous bioclasts increases toward the base of the subunit before dropping markedly in the unit below.

Seven thin sections were prepared from Subunit IC. One thin section (Sample 317-U1352B-72X-CC, 27–29 cm) contains micritic limestone/marlstone and is compositionally and texturally very similar to concretions observed at the top of the hole in Subunit IA, which is likely attributable to downhole contamination. Three other thin sections show slightly different microfacies from those described in Subunit IB: Samples 317-U1352B-54X-4, 4–6 cm (~459 m); 65X-1, 14–17 cm (~563 m); and 317-U1352C-4R-5, 52–54 cm (~600 m). In general, these microfacies are finer grained and better sorted and have a smaller, better sorted population of bioclasts. The sand fraction is mainly quartz, feldspar, mica, chlorite, and dense minerals. These samples have variable amounts of calcareous matrix and no distinct lamination, and they are somewhat homogenized by bioturbation, with rare large (centimeter scale) discrete burrows.

The low core recovery in Subunit IC hampered a detailed analysis of depth trends in XRD mineralogy (Fig. F11). In general, this subunit can be characterized as having no clear trends with depth in the minerals discussed above, although there is a notable increase in the variance of all these minerals. Quartz, total clays, and micas co-vary and appear to be inversely related to calcite content. Interestingly, quartz and plagioclase are not well correlated, as was also the case in Subunit IB. Calcite has the highest peak intensities of Unit I within this interval, which is also supported by both coulometry and smear slide observations. Pyrite and siderite peak intensities are highly variable, and dolomite was not observed.

Unit I/II boundary

As at other Expedition 317 sites, the Unit I/II boundary is transitional. All of Subunit IC represents a transition between Unit I and Unit II lithologies, marked by increasing percentages of carbonate and decreasing amounts of clay (Fig. F11), although the noncalcareous homogeneous mud common in Subunits IA and IB occurs as deep as Core 317-U1352B-74X. The Unit I/II boundary was placed at the bottom of Core 317-U1352B-81X (and at the base of Section 317-U1352C-11R-1) at the base of calcareous muddy sand where (1) an abrupt change of baseline occurs in magnetic susceptibility and gamma ray whole-round measurements (see "Physical properties"), (2) the chemistry of interstitial water analyses shows a local peak (see "Geochemistry and microbiology"), and (3) the analysis of XRD mineralogy data shows a major shift in composition from clay-dominated to carbonate-dominated lithologies. When total clays are normalized to calcite to account for carbonate-dilution effects, clay content decreases notably downhole beginning at 709 m (Fig. F13). Similar increases in magnetic susceptibility and natural gamma ray data were observed at the same depth (see "Physical properties"). Below this depth, sediments are carbonate dominated and clay content only occasionally increases.

Unit II

• Intervals: Cores 317-U1352B-81X through 94X and Sections 317-U1352C-11R-1, 92 cm, to 140R-2, 47 cm

• Depths: Hole U1352B: 710.78–822.13 m (total depth) and Hole U1352C: 709.32–1852.63 m

• Age: middle Pliocene to early Miocene

Unit II is dominated by homogeneous calcareous sandy mud or sandy marl (uncemented intervals) and sandy marlstone (cemented intervals) throughout Holes U1352B and U1352C. Subtle differences in Hole U1352C allow for unit subdivision based on the presence of dark muddy intervals (noncalcareous), current-generated structures, and laminated sandstone beds in Subunit IIB, as opposed to the more thorough degree of bioturbation present in Subunit IIA and the presence of glauconite-rich beds in Subunit IIC (Fig. F14).

Subunit IIA

• Intervals: Cores 317-U1352B-81X through 94X and Sections 317-U1352C-11R-1, 92 cm, to 61R-1, 30 cm

• Depths: Hole U1352B: 710.78–822.13 m (total depth) and Hole U1352C: 709.32–1189.30 m

• Age: middle Pliocene to early Pliocene

Subunit IIA is dominated by dark greenish gray to greenish gray homogeneous sandy marlstone along with the less lithified sandy marl recovered in Hole U1352B. Subordinate lithologies such as calcareous very fine sandy mud, muddy sand, mud, and mudstone were recovered from both holes. The partially to fully lithified sandy marl and sandy marlstone were heavily bioturbated, and Chondrites, Helminthopsis, Terebellina, Scolicia, Planolites, Zoophycos, and Thalassinoides ichnogenera were identified in the lithified layers. The ichnofabric index for Hole U1352B cores is generally 1 (partly because drilling overprint obscured the ichnofabric), but in Hole U1352C it ranges between 1 and 5 (typically 3–4). Distinct bedding planes are not visible; however, in some intervals the overprinting of shallow and deeper trace fossils (e.g., Thalassinoides over Chondrites) suggests erosion or other changes at the sediment/water interface (Fig. F15). Shells are extremely rare or are absent in the lower part of Subunit IIA and include fragments of bivalves, brachiopods, and foraminifers. Small ovoid crystalline calcareous fragments or "blebs" first occur in Core 317-U1352C-38R. Calcareous concretions occur sporadically throughout the subunit.

Although variable, carbonate content is more uniform in Subunit IIA than it is in overlying units, and estimated percentages from smear slide observations range generally between 10% and 40% (Fig. F10). Rare outliers, estimated from smear slide observations at >70% (chalk or limestone) carbonate, occur in discrete, paler (light greenish gray) intervals (note that coulometry analyses are not generally available from these minor lithologies). The percentage of carbonate components appears to increase downhole in the uppermost 200 m of Unit II, and values below 900 m seem to fall largely between 30% and 60% carbonate based on smear slide estimations (15%–50% based on coulometry data; Fig. F10). Mica percentages from smear slide and XRD data appear in general to be higher than values in Unit I, whereas clay concentrations are lower. Both glauconite and siliceous bioclastic material become extremely rare with depth. The percentage of ferromagnesian minerals is generally very low throughout Subunit IIA.

Subtly different facies, such as paler greenish gray layers, begin to appear at ~1026 m (Core 317-U1352C-44R) and become more common with depth. These paler intervals, also bioturbated, are generally more cemented and occasionally contain >70% carbonate (estimated from smear slide observation), placing them in the chalk or limestone classification (Fig. F15). The dominant lithotype continues to be dark greenish gray very fine to fine sandy marlstone, but the pale layers give the rock a color-banded appearance in some places (e.g., Core 317-U1352C-44R). In addition to these paler layers, sandy laminae, sand lenses, and wavy or ripple laminae are occasionally present in the cores, increasing in frequency downhole.

Thin sections from Subunit IIA contain distinctly microburrowed marlstone facies. Although the overall composition is marlstone to sandy marlstone, lighter trace-fossil fills and laminae observed in cores were seen in thin section to be arkosic, micaceous, and bioclastic siltstone to fine sandstone that is variably cemented by carbonate or that contains calcareous matrix. Darker burrow fills are mainly calcareous marlstone, a combination of carbonate (nannofossils and/or micrite) and clay with traces of organic matter. Minor terrigenous components include phyllite lithic fragments, glauconite, and dense mineral grains. A few samples contain higher percentages of siliceous debris, including diatoms and sponge spicules, the latter locally concentrated in burrows (e.g., Sample 317-U1352C-11R-2, 21–23 cm). Some samples contain a higher proportion of clay and organic-rich matrix (e.g., Sample 317-U1352C-40R-3, 2–3 cm). Diagenesis is limited to carbonate cementation and pyrite formation as both pore-filling cement and grain replacement, as well as replacement of opaline sponge spicules by birefringent chert/quartz.

Based on XRD analysis, the mineralogy of Subunit IIA is similar to that of Subunit IC, with relatively moderate to high amounts of quartz, micas, and plagioclase feldspars relative to the remainder of the succession (Fig. F11). These mineral groups have no overall trend with depth but do have pronounced variability with depth in this subunit. Total clays are highest near the top of the subunit and decrease from 660 to ~800 m within Hole U1352B. Hornblende is relatively low and variable. Calcite is lowest near the top of the subunit and increases slightly from 660 to 800 m, below which it has no trend with depth but reveals the same pattern of variability shown by silicate minerals, with the relative amount of silicates inversely proportional to the amount of calcite (significant at p = 0.05). The micas (muscovite/biotite) and chlorite are highly positively correlated (R = 0.92), and quartz and the micas are positively correlated, with a stronger correlation between quartz and chlorite (R = 0.4). Plagioclase and quartz abundances do not correlate in Subunit IIA, as was also the case in Subunit IC. XRD mineralogy and smear slide observations agree well, with both showing fluctuating trends in micas and sand, a relative decrease in clays, and an increase in carbonate content near the top of the subunit.

Subunit IIB

• Interval: Sections 317-U1352C-61R-1, 30 cm, to 123R-1, 142 cm

• Depth: 1189.30–1693.92 m

• Age: early Pliocene to late early Miocene

Darker gray and brown lithologies appear in the succession below 1170 m (Fig. F15). Sandy marlstone is the dominant lithology, along with subordinate dark gray, centimeter-thick, bioturbated very fine sandy mudstone beds and centimeter-thick, horizontally laminated fine sandstone. Based on smear slide observations, the latter lithologies are calcareous to noncalcareous but are uniformly less calcareous than the sandy marlstone. The Subunit IIA/IIB boundary was placed at the base of an irregular surface that separates lighter (above) from darker (below) very fine sandy marlstone. Below this boundary, distinct dark brown mudstone beds are more common and are associated with more frequent sandstone beds, wavy laminations, ripples, and sand lenses. Ferromagnesian minerals disappear from smear slides below Core 317-U1352C-62R (1204 m) and are below detection in XRD analyses from approximately Core 317-U1352C-59R (1170 m) and below.

Subhorizontal wavy laminae marked by millimeter-thick, brownish very fine sandy mudstone are increasingly more frequent downcore, becoming prominent from Core 317-U1352C-70R downhole. Below Core 317-U1352C-110R, these laminae are frequently intercalated with lighter gray sandy marlstone, which sometimes gives the rock a dark–light pin-striped appearance (Fig. F15F–F15G). Millimeter-diameter white calcareous blebs were observed throughout the marlstone. Light blue-gray sand-filled burrows are common within the marlstone, particularly in the lower portion of the subunit. Bioturbation is abundant throughout Subunit IIB, ranging between 1 and 5 (mostly 3–4) on the ichnofabric index, and includes traces of Zoophycos, Planolites, Chondrites, Thalassinoides, Paleophycus, Helminthopsis, Terebellina, Scolicia, and Teichichnus.

The Pliocene/Miocene boundary occurs within Core 317-U1352C-73R, probably either at the top or the base of a distinctive paler calcareous unit, the sharp top of which occurs at Section 73R-2, 33 cm (1276.83 m), and the sharp and bioturbated base of which occurs at 73R-4, 20 cm (1279.7 m) (see "Biostratigraphy").

In Sections 317-U1352C-88R-1 through 88R-4 (1371–1376 m), 94R-CC through 95R-1 (1437–1439.5 m), and 105R-2 through 106R-5 (1528–1541 m), variable stratification attitudes, folding, shells, and a greater proportion of carbonaceous material mark several distinct stratigraphic intervals containing mass-transport complexes (slumps) that often include internal planar surfaces that divide areas with different deformation characteristics or bedding angles (Fig. F16).

The common occurrence of dark brown muddy layers stops in Core 317-U1352C-90R (1392 m), although these layers continue to occur sporadically downhole, and a notable change in mineralogy occurs at ~1400 m, as indicated by XRD analyses (Fig. F11). These changes may be associated with a hiatus observed in Core 317-U1352C-91R that is possibly associated with a highly carbonate rich layer at 1409.12 m (Section 91R-7, 73 cm), where the faunal age changes (between Sections 90R-CC and 91R-CC) from latest Miocene to early late Miocene (upper Kapitean to lower Tongaporutuan, ~5.30–11.01 Ma; see "Biostratigraphy").

Carbonaceous material is rare near the top of Unit II, appears more frequently below 1400 m in association with the slumped material mentioned above, and appears again in greater concentration in dark brownish gray layers in Cores 317-U1352C-110R and 111R (1575–1590 m). Glauconite is a common constituent below Core 317-U1352C-105R, where a graded bed has a glauconitic basal layer.

A banded appearance becomes evident in Core 317-U1352C-113R (1603 m) and below. Distinctly wavy, darker gray layers (laminae to thin beds) alternate with greenish gray very fine sandy marlstone layers (Fig. F15). The darker layers are commonly finer and have the appearance of incipient stylolites (although little dissolution appears to have occurred across these surfaces). This banding increases in intensity with depth, and glauconite begins to appear at low concentrations in the marlstones in Core 317-U1352C-117R.

The major minerals of Subunit IIB, as indicated by XRD analyses, are similar to those of Subunit IIA, with the exception of hornblende, which was not observed apart from trace amounts in two samples, and quartz, which decreases significantly in this unit, especially below 1400 m (Fig. F11). Micas (and chlorite) and plagioclase gradually decrease from the top of the subunit to 1400 m and then increase notably to a maximum for this subunit at ~1550 m, below which they decline throughout the remainder of the subunit. Total clays are also higher within this subunit, especially in the uppermost part. Below 1580 m, clays were not detected by XRD. As in Subunit IIA, micas and chlorite are positively correlated and total clays and calcite are inversely correlated; however, there is no correlation between total clays and micas, micas and quartz, or quartz and plagioclase.

Thin section observations show that Subunit IIB contrasts with the overlying subunit in having more matrix in its upper part and mainly a sandy marlstone lithology and some marlstone lithologies. No other difference in the types or ratios of components between Subunits IIA and IIB were observed. Siliceous sponge spicules, organic debris (plant matter), and phosphatic debris (fish remains and fecal pellets?) are also present. In the upper part of Subunit IIB, the matrix is a mixture of nannofossils and clay that changes to micrite and clay below Section 317-U1352C-78R-1 (1314 m). Most samples are bioturbated, but original laminations composed of alternating matrix-rich and well-sorted matrix-poor laminae are locally preserved. The latter are slightly coarser and are carbonate cemented locally by poikilotopic calcite crystals (Sample 317-U1352C-90R-1, 0–3 cm). Sand and silt grains are generally angular.

Differential compaction is evident between more competent cemented zones (usually better sorted burrow fills) and less competent muddy zones. Longer mica flakes are bent and fractured across more competent grains. Evidence for pressure solution is more pronounced within and below Sample 317-U1352C-95R-6, 39–42 cm (1447 m), where glauconite and phosphatic and organic debris are more common. In particular, compaction (fracturing and interpenetration) and truncation (press-solved boundaries) of foraminifers were observed. Dark seams visible in the core were shown to be created by aligned and compacted platy organic matter, which organic geochemical analyses indicate to be of terrestrial origin (see "Geochemistry and microbiology"). The irregular and stylolitic appearance of the seams is a result of differential compaction around more competent grains, as well as some apparent pressure solution. Note that the more calcareous samples below this interval (e.g., Cores 317-U1352C-114R, 116R, and 118R) show evidence for pressure solution only where minor organic matter is present.

Opaline siliceous sponge spicules are variably preserved and locally replaced by silica (chert) and microcrystalline calcite. In some samples (e.g., Cores 317-U1352C-70R and 89R), all three phases, original opal, and secondary chert or carbonate are present. Carbonate cement is present throughout as intraparticle filling of foraminifer chambers and as interparticle filling in better sorted grainstone/siltstone/sandstone laminae and burrow fills. Zeolites were observed as pore-filling cement in foraminifer chambers in thin sections from Cores 317-U1352C-112R and 113R. Zeolite crystals are locally encased by later carbonate cement, indicating that they were an earlier diagenetic process.

Subunit IIC

• Interval: Sections 317-U1352C-123R-1, 142 cm, to 140R-2, 47 cm

• Depth: 1693.9–1852.6 m

• Age: early Miocene

Subunit IIC is characterized by thin, intercalated glauconitic sandstone interspersed with sandy marlstone and sandy limestone and, less frequently, with mudstone lithotypes (Fig. F17). Sandstone first occurs as a minor lithology in Core 317-U1352C-115R, and highly glauconitic sandstone first occurs in Core 123R (top of the subunit). Thereafter, these glauconitic layers become common, and the background sandy marlstone also becomes glauconitic.

The marlstone consists of greenish gray, well-sorted very fine to fine sandy marlstone. A glauconitic, bioturbated section at 317-U1352C-125R-5, 134 cm (1714.34 m), was estimated by smear slide analysis to contain >70% carbonate, making this interval glauconitic sandy limestone. The sandy marlstone in Core 317-U1352C-126R changes to greenish gray, well-sorted very fine to fine sandy limestone (i.e., >70% carbonate) by Core 132R and remains limestone to the base of the subunit. Stylolites are more common with depth and are marked by millimeter-thick muddy layers. A subordinate lithology consists of dark greenish gray very fine sandy calcareous mudstone. Bioturbation ranges between an ichnofabric index of 1 and 5 and includes Zoophycos and Rosselia forms.

Glauconitic sandstones become more common with depth to the base of the subunit. They consist of moderately to well-sorted, very fine to fine (mostly very fine), planar- to ripple-laminated calcareous glauconitic sandstone. Ripple sets are <2 cm thick, and the units themselves are typically <10 cm thick, although one thicker unit (44 cm) occurs in Core 317-U1352C-135R. In the same core, the glauconitic sandstones include both bedding-parallel (i.e., in situ beds) and glauconitic sandstones that truncate bedding and burrows (i.e., sedimentary dikes and sills; Fig. F17). The latter units generally appear to be subhorizontal but also occur at a high angle to stratification. They also bifurcate around centimeter-thick sandy limestone units. In both types of glauconitic sandstone, planar lamination is common. In the glauconitic sandstones that cut primary stratification, two colors of sandstone occur: light blue-gray and dark greenish gray. These layers also contain small clasts of the surrounding limestone. Beginning in Core 317-U1352C-139R, pyrite nodules as large as 1 cm in diameter occur.

Thin sections (see "Site U1352 thin sections" in "Core descriptions") from this subunit are mainly glauconitic calcareous sandstone and glauconitic sandy marlstone at the top of the subunit, transitioning to foraminifer micritic limestone at the base of the subunit. Glauconite occurs as pellets, altered bioclasts, and altered mica grains. Phosphatic fish remains and fecal pellets are locally present in minor amounts. The matrix is a mix of micrite with an indeterminate amount of admixed clay minerals, and the proportion of matrix changes within a sample because of the presence of darker laminae and burrow fills. At the top of the subunit, the darker laminae are arguably depositional features enriched in organic matter and clay minerals. Downsection, these pass to striking dark bands that crosscut the limestone fabric and are composed of glauconitic calcareous sandstone to sandy marlstone. Some of these crosscutting laminae fork, and others taper and pass laterally into stylolites.

Authigenic phases are mainly carbonate (as intraparticle and interparticle cement) and pyrite. Diagenesis includes patchy silicification, and low-birefringence sulfate(?) cement is present in Samples 317-U1352C-135R-5, 38–41 cm, and 137R-2, 58–60 cm (Fig. F12E, F12F).

Evidence for compaction includes grain fracturing, interpenetration, deformation of micrite-filled burrow margins, pressure solution, development of dark seams, and stylolites. The darker intervals (laminae/burrow fills) are associated with organic matter, which appears to enhance pressure solution, creating darker seams and leading to the formation of stylolites. The amount of organic matter essentially declines downhole throughout the subunit, and below Section 317-U1352C-137R-2 there is less compaction or pressure solution and little evidence for stylolitization of the limestone lithologies.

The mineralogy of Subunit IIC from XRD analyses is substantially different from that of other portions of this unit. All silicates decrease significantly, and carbonate increases between Subunits IIB and IIC. As in Subunit IIB, there is no detectable total clay content, with the exception of Sample 317-U1352C-136R-3, 127–129 cm (1816.86 m), which also contains elevated quartz and mica (Fig. F11). Also similar to Subunit IIB, micas and chlorite are positively correlated, but no correlation exists between total clays and calcite, total clays and micas, micas and quartz, or quartz and plagioclase.

Unit II/III boundary

The boundary between Units II and III is an abrupt lithologic change from glauconitic sandy limestones and marlstones in Unit II to clean foraminiferal limestone in Unit III. The boundary coincides with the Marshall Paraconformity, which represents some 12 m.y. of missing time at this locality (see "Biostratigraphy"). The unconformity occurs as a zone of rubble (apparently mostly blocks of the underlying limestone) in interval 317-U1352C-140R-2, 44–48 cm.

Unit III

• Interval: Section 317-U1352C-140R-2, 47 cm, through Core 148R

• Depth: 1852.6–1924.3 m (total depth)

• Age: early Oligocene to late Eocene

Lithologic Unit III consists of white, cemented, fine-grained slightly sandy or silty (a few percent) limestone. This unit was recovered largely in pieces as long as 10 cm. Bioturbation is common throughout and includes abundant Zoophycos burrows, together with Chondrites and Planolites. Ichnofabric index values range between 1 and 5. Stylolites are very common and are better developed than in Subunit IIC. Medium gray siliceous nodules as large as 5 cm in diameter occur sporadically throughout the unit. Color differences include slightly darker intervals and burrow fills as well as a purple coloration that is associated with burrows or appears as circular or curved features. Pyrite nodules in Unit III are associated with burrow fills or stylolites. Below Core 317-U1352C-147R, well-laminated, light greenish gray very fine sandy marlstones occur in beds as thick as 3 cm and may contain pyrite specks or fragments. These marlstone beds appear to occur more frequently downhole.

Smear slide and thin section observations show that the limestone matrix is recrystallized with preserved fabric, suggesting that the original composition was a foraminifer-bearing nannofossil ooze, with a few percent (generally silt sized) grains of quartz and feldspar. Of the seven thin sections prepared from Unit III, six are composed of foraminifer micritic limestone. The stylolites are marked by concentrations of mainly opaque minerals (including pyrite; Figs. F12, F18), but they also contain clay, silt-sized quartz, and organic matter and are oriented at several different angles in the cores, commonly crosscutting each other. They have variable amplitudes, although they are better developed at the top of the section, where they exhibit higher amplitudes, thicker clay seams, and distinct crosscutting relationships. In contrast, the amplitude becomes very low in the muddy limestone below the Oligocene–Eocene unconformity (Cores 317-U1352C-147R and 148R). One stylolite in Sample 317-U1352C-146R-3, 21–24 cm, appears to have had a later dilational phase with intra-stylolite precipitation of microcrystalline carbonate and sulfate(?). The same sample contains a partly silicified bioclast, and some chert nodules and patches are present. In this section (Sample 317-U1352C-145R-1, 36–37 cm) the siliceous rocks appear to be silicified equivalents of the limestone, having been replaced by microquartz/chalcedony (chert) and opal-CT (porcellanite).

The mineralogy of Unit III from XRD analyses is notably different from that of the overlying units at this site and is dominated by carbonate minerals (calcite) with only a minor amount of quartz below 1900 m.

Downhole trends in sediment composition and mineralogy

The composition and mineralogy of Site U1352 is generally comparable to the other Expedition 317 sites. However, because of more complete core recovery, deeper penetration, and the subsequent collection of older strata, several distinct downhole changes in the concentration and relative proportions of components and mineralogy can be recognized between the three lithologic units. Primarily, carbonate concentrations increase and clay content decreases with depth in the hole.

Unit I is a clay-rich unit, composed primarily of quartz, clay, feldspar, rock fragments, mica, hornblende, rare dense minerals, carbonate, and siliceous bioclasts. Quartz and feldspar content is relatively invariant within Unit I, with somewhat higher plagioclase peak intensities within Subunit IC. A distinct feature of Unit I is the co-varying changes between total clay content, total micas, chlorite, and ferromagnesian minerals. Subunits IA and IB have relatively high total clay and ferromagnesian content, with increasing mica and chlorite peak intensities with depth. Subunit IC has distinctly lower ferromagnesian and total clay peak intensities and higher mica and chlorite peak intensities. Glauconite is relatively low throughout Unit I but becomes relatively more prevalent between 250 and 500 m, occurring as fossil infills, often within cemented layers or concretions. Dolomite and siderite were occasionally observed, but peak intensities are close to the limit of detection (see XRD in "Supplementary material").

Overall, the depth trends in calcite peak intensity follow smear slide and bulk CaCO₃ concentrations. Within Unit I, calcite concentrations are lowest in Subunit IA, although there are local patches of high authigenic microcrystalline carbonate concentrations, abundant large shells and shell fragments, and concretions that occur as shallow as 10 m, indicating early precipitation of authigenic carbonate. Micrite becomes increasingly common below 205 m, and concretions or nodules (marlstones to fossiliferous muddy limestones) become common below 350 m, corresponding to an increasing calcium concentration in interstitial water analysis. Subunit IC, below 450 m, has a higher carbonate concentration, which is due to both high volumes of calcareous microfossils and also higher concentrations of authigenic carbonates. In contrast with the other three sites, Site U1352 has high proportions of siliceous biogenic components, with relatively elevated concentrations at ~300 and ~575 m, below which siliceous fragments become abruptly less common.

The Unit I/II boundary at 710 m coincides with a downhole shift from clay-dominated to carbonate-dominated lithologies, which corresponds to changes in magnetic susceptibility and gamma ray measurements and interstitial water chemistry. Below this point, the sediments are significantly dominated by carbonate components (p = 0.05, N = 74), and Unit II is subdivided largely according to the presence or absence of other noncalcareous lithologies. Total clay from XRD is significantly lower in Unit II relative to Unit I (p = 0.05, N = 74). Carbonate concentrations increase gradually downhole through Unit II, whereas hornblende and siliceous bioclasts become rare and clay concentrations also decrease. Below ~800 m, depth trends become less obvious, but the mineralogy remains highly variable. An increase in carbonaceous material at ~1375, 1439, and 1535 m corresponds to lithologies interpreted as mass-transport deposits. A decrease in quartz peak intensities coinciding with an increase in mica and plagioclase occurs at 1400 m, associated with a decrease in the number of dark muddy layers occurring downhole. These changes may be associated with an unconformity that is possibly associated with a carbonate-rich layer at 1409 m, representing ~5 m.y. of Miocene time missing. Below this point, previously rare carbonaceous material becomes more common and glauconite content begins to increase below 1550 m, whereas mica and plagioclase decrease from this point and clays were not detected below 1580 m. Pressure solution is evident in samples below 1440 m and is often associated with minor concentrations of organic matter. Some replacement of siliceous bioclasts by secondary chert or carbonate occurs, and carbonate cement is common, especially in better sorted sandy layers and burrow fills.

A notable change in composition and mineralogy occurs below 1700 m and the transition into Subunit IIC, where the concentration of silicate minerals decreases significantly and carbonate content increases. Clay content was not detectable, except for a few isolated intervals that also contain elevated quartz and mica in rare muddy layers. The content of glauconite increases downhole, although much of this is associated with discrete layers that are interpreted as intrusions from below.

Unit III comprises recrystallized limestone, probably originally a foraminifer-bearing nannofossil ooze, with a few percent of generally silt-sized grains of quartz and feldspar. Total clay, total micas, chlorite, and ferromagnesian minerals were not observed in Unit III. Below 1900 m, pyrite is associated with thin-bedded very fine sandy marlstones, which increase in frequency downhole. Stylolites are well developed in the upper part of this unit and decrease in frequency and amplitude downhole.

Correlation with wireline logs

Only a short interval of downhole wireline logging data could be obtained from Hole U1352B because of a blockage at ~500 m within Subunit IC, presumably from hole cave-in. The caliper tool indicated that the hole above this point was very wide (washed out) (see "Downhole logging"), but a few narrow sections provided points at which caving material could accumulate. In Hole U1352C, the triple combo tool string was blocked at ~200 m. However, enough downhole logging data were acquired to allow some correlation to Unit I lithology (Fig. F19). In addition to the limited downhole logging data, good core recovery over most of the drilled interval at Site U1352 makes it possible to compare lithologic trends to other physical property data (e.g., magnetic susceptibility) acquired from whole-round measurements. Note that the mineralogy of the sediments (feldspar and mica in the sand fraction and quartz in the clay fraction) reduced the ability of gamma ray logging data to unambiguously resolve sand-to-mud transitions (see "Lithostratigraphy" in the "Site U1351" chapter for further discussion). Also, the hole was enlarged, so gamma ray logs should be used with caution (see "Downhole logging").

In Subunit IA, the lithology alternates between an interbedded sand/clay/mud lithology and calcareous, often shelly, green muddy sands. The green sandy beds correlate with low values of magnetic susceptibility measured on the recovered cores and also with low values on the downhole gamma ray log. Mud beds or interbedded lithologies have relatively high magnetic susceptibility and gamma ray values. A particularly high peak in magnetic susceptibility occurs between 58 and 61 m (Cores 317-U1352B-6H through 7H).

In Subunit IB, the succession alternates between homogeneous mud intercalated with green sand. The green sand beds are again calcareous and rich in shells. As in Subunit IA, the sand beds in Subunit IB have low magnetic susceptibility and gamma ray values; however, some low values in the downhole gamma ray data (e.g., 255–265 m) do not apparently correlate with lithologic beds and may relate to mineralogical differences within the mud beds or with conditions in the hole.

The lithology of Subunit IC is characterized by more frequent and more highly calcareous beds of green sand and gray or green mud. The sand beds contain shell fragments, biogenic clasts, and calcareous concretions. The low magnetic susceptibility and gamma ray values correspond to calcareous sand beds, as above; however, a relatively high value of magnetic susceptibility between 630 and 668 m does not correspond to any observed lithologic change in the cores, although it does correspond to a peak in clay and mica concentrations, observed in XRD analyses, as well as a minimum in calcite concentrations (Fig. F11; also see "Physical properties").

No downhole logging data are available for Units II and III. Physical property measurements done on the cores, including magnetic susceptibility and natural gamma radiation (NGR), show trends associated with lithologic changes within Units II and III (see "Physical properties"). Magnetic susceptibility shows another peak at the Unit I/II boundary at ~710 m and then decreases gradually until ~810 m, where there is an abrupt upward baseline shift in the readings and an increase in variability of the measurements, although there is no obvious change in lithology. Below 900 m, variability in magnetic susceptibility and NGR decreases, concurrent with an increase in recovery that is possibly related to increasing carbonate content or cementation. Peaks in magnetic susceptibility and NGR occur at 1200 m (near the Subunit IIA/IIB boundary) and 1440 m, and another upward baseline shift occurs between 1450 and 1500 m (poor core recovery over this interval means the exact location of this shift is unknown). The peaks correspond to lost recovery intervals and to peaks in clay and mica concentrations in XRD measurements and quartz and feldspar contents in smear slide data, possibly indicating that these layers are less cemented, more terrigenous rich layers.

Below 1500 m, NGR and magnetic susceptibility trends decrease steeply, probably related to the rapidly increasing carbonate content of the sediments in the lower part of Subunits IIB and IIC. The Marshall Paraconformity at the Unit II/III boundary shows up as a dramatic downward shift and decrease in variability of both magnetic susceptibility and NGR as a result of the homogeneous and almost purely calcareous nature of the sediments below the boundary.

P-wave velocity measured on the cores shows a relatively stable average value downhole to 1500 m (within Subunit IIB), where the measured velocity increases to ~1700 m (at the base of Subunit IIB), and then remains stable until ~1770 m before increasing until ~1820 m (just above the Unit II/III boundary; see "Physical properties"). A slight downward trend may be present in the bottommost 50 m of core, possibly related to the increasing clay content in the Eocene limestone at the base of the hole. It appears from these trends that velocity is directly related to the carbonate cement content of the sediments, which increases downhole to the Oligocene–Eocene unconformity within Unit III.

Description of lithologic surfaces and associated sediment facies

Sedimentary package description

A major objective of Expedition 317 was to understand how eustasy, climate, and tectonics influence sedimentation in the Canterbury Basin, with a particular emphasis on assessing how these large-scale forcing mechanisms interacted to create stratal packages and the surfaces that bound them, as resolved in seismic reflection profiles (Lu and Fulthorpe, 2004). To this end, we developed a very generalized classification of the different types of lithologic contacts and their associated deposits to aid in core-seismic integration and possible correlation with onshore strata of equivalent age. The classification scheme used here reflects the general changes in lithology of the different lithologic units and applies to all drilled sites. In Unit I at Site U1352, the uppermost 50 m of strata (Subunit IA) contains both centimeter-scale and meter-scale interbedding that reflects lithologic changes, whereas the lower 50–450 m (Subunit IB) generally contains sharp contacts that separate different lithologies and that are associated with discrete, thicker (1–6 m) beds. Poor recovery within the lower part (450–710 m; Subunit IC) hampered evaluation of the presence of surfaces and their associated sediments within that interval. From 710 to 1852 m in Unit II, the sediment is characterized by calcareous cemented lithologies that contain large-scale (6 m thick) and small-scale (5–30 cm thick) sedimentary packages bounded by sharp basal surfaces. Discrete contacts and their associated lithologies are recognized by changes in grain size, texture, color, bioturbation, and carbonate content.

Based on these large-scale trends and the characteristics of the sediments, distinct contacts and facies associations were defined as sedimentary packages, which may potentially vary acoustic impedance and therefore be resolvable in seismic reflection data. These classifications are greatly simplified for the expedition report, and postcruise analyses will permit better definition of sedimentary packages and improve their correlation to seismic data. Broadly, contacts and facies associations were classified based on grain size (muddy sand, sandy mud, sandy marl, marl, or clay), bed thickness, the nature of the basal and upper contacts, and the amalgamation of thinner (centimeter thick) beds with discrete contacts that form meter-thick or thicker packages (Figs. F20, F21).

Type A contacts and facies associations are characterized by a sharp contact that commonly separates thick lithologies above and below. The lithology above the contact can be as thick as 6 m (Fig. F20). Specific examples include thick, dark greenish gray calcareous fine to medium muddy sand or sandy mud in sharp contact with underlying greenish gray mud. The basal contacts of the overlying greenish gray sandy lithology are sharp and lightly to heavily bioturbated, whereas their upper contacts tend to be gradational. When their lower contacts are heavily bioturbated, discrete burrows can be tracked 100 cm beneath the contact. Shells and shell fragments are present in the greenish gray muddy sand and sandy mud deposits within the uppermost 150 m of Holes U1352A and U1352B. These become rare in Hole U1352B from 150 to 250 m and are generally absent from the deeper lithologies, except in a bed near 372 m where they are abundant. When shells and shell fragments are present, they are as long as 3 cm and are abundant within the greenish gray sands immediately above the basal contact. Shells and shell fragments can be present below the basal contact in the greenish gray mud, but the position of these shells is most likely the result of burrowing disturbance because they seem to be closely associated with greenish sand-filled burrows. Mass wasting deposits (as thick as 15 m) found in Unit II from ~1370 to 1550 m are a second example of Type A contacts and deposits. These deposits have a sharp upper and lower contact, soft-sediment deformation features, and medium to coarse sand layers, with generally lower bulk density than the adjacent strata (e.g., Sections 317-U1352C-94R-6 through 94R-7 and Cores 105R and 106R; Fig. F16).

Type B contacts and facies associations represent amalgamation packages of thinly bedded but distinctly contrasting lithologies (e.g., sand, mud, and clay interbedding and sandstone–marlstone and marlstone–limestone alternations). These contrasting lithologies also form meter-thick packages (Fig. F20). The individual beds are thin (1–5 cm), have decimeter-scale spacing, and commonly have sharp basal contacts. When sand is present, it is normally graded. Because of the sharp contrasts in lithology and the thickness of these packages, these types of deposits may be resolvable in seismic reflection profiles.

Type C contacts and facies associations are always sharp and separate contrasting lithologies, for example sand and mud or sandstone and marlstone. Because of this sharp contact in lithology, these surfaces have the potential to create reflections in seismic profiles. However, the thickness of any beds associated with these contacts could not be clearly delineated on board ship (e.g., muddy sand layers fining upward into sandy mud), and additional shore-based analyses are required to establish the relative importance of each in terms of its potential to generate a seismic reflection (Fig. F20).

Table T3 lists the occurrence of each of the three types of contacts and their associated sediments at Site U1352. Type A contacts and associated facies are more common in Unit I than they are in Unit II. Type B contacts and facies associations are more common in the uppermost 50 m of Unit I and throughout Unit II, where they consist of more heavily cemented mudstone and marlstone, marlstone and sandstone, and marlstone and limestone beds within homogeneous sandy marlstone. Within Unit I, Type B contacts and facies associations are packages of interbedded sand and mud or mud and clay (e.g., 26, 34, and 98 m) or several decimeter-thick muddy sand beds that are closely spaced (e.g., 148, 159, 331, and 338 m). Type C contacts and facies associations are found throughout Holes U1352B and U1352C and represent a range of lithologic contacts. Within Unit I, these sedimentary packages tend to comprise fining-upward muddy sand that sharply overlies mud; within Unit II, they comprise beds with distinctly different carbonate contents and/or degrees of cementation. An additional example is the Unit II/III boundary between sandy limestones and limestone.

Description of significant surfaces

Because of time restrictions on board ship, surfaces were only examined close to the predicted depths of seismic sequence boundaries; therefore, the lithologic surfaces identified here are implicitly linked to the predicted occurrences of sequence boundaries identified on the seismic (Lu and Fulthorpe, 2004). A similar approach was used on board ship during ODP Legs 150 and 174A, the objectives of which were also to study sea level changes. Postcruise study will attempt to clarify the exact relationship of all lithologic surfaces and facies associations to sea level changes and seismic stratigraphy. The numbering system used in the site chapters, tables, and summary diagrams comprises a hole-specific prefix and a surface designation (e.g., U1352A-S1) that links each surface to a seismic sequence boundary; therefore, these lithologic surfaces and associated sediments are thought to be correlative between sites across the transect.

The following section contains a brief description of each surface identified at Site U1352, as summarized in Table T4. In contrast to the situation at Site U1351, the identification of significant surfaces at this site was complicated by the common presence of more than one lithologic package per core near the predicted depths of seismic sequence boundaries (Lu and Fulthorpe, 2004). In these situations, the significant surface has generally been assigned to the lithologic package that was thicker and best preserved, but the other surfaces identified nearby are also mentioned.

Surfaces U1352B-S1 and U1352D-S1

A Type A contact and its associated facies, designated U1352B-S1, is tentatively placed at Section 317-U1352B-7H-6, 96 cm (64.20 m) (Table T4). A second sharp, angular dipping contact is present above (62.50 m). This surface is similar to that at 64.20 m, but the former is less burrowed, contains fewer shells and shell fragments, and has thinner beds that grade upward into greenish mud. Note also that from 75 to 93 m there are several intervals of muddy sand beds 25, 86, and 88 cm thick in Cores 317-U1352B-9H, 10H, and 11H, respectively. A lithologic surface of similar character, U1352D-S1, was observed at Section 317-U1352D-8H-3, 88 cm (64.38 m).

Surface U1352B-S2

A Type B contact and its associated facies, designated U1352B-S2, is tentatively placed at Section 317-U1352B-16H-5, 5 cm (147.22 m) (Table T4). The sediments associated with this contact contain a 5 cm thick cemented layer at Section 317-U1352B-16H-4, 128 cm (146.96 m). A second Type B contact is present at 146 m. The overlying sedimentary package is 30 cm thinner than the sedimentary package beneath, and the contacts above and below are gradational into gray mud. Surface U1352B-S2 is therefore tentatively positioned in the sharp contact of the thickest sand bed at 147.22 m.

Surface U1352B-S3

Surface U1352B-S3 is tentatively positioned at a sharp contact at Section 317-U1352B-23H-1, 130 cm (200.00 m). A second sharp contact is present at Section 317-U1352B-23H-6, 80 cm (207.00 m). Note that muddy sand beds 4–27 cm thick are present in most sections of Cores 317-U1352B-24H and 25H.

Surface U1352B-S4

Surface U1352B-S4 is tentatively placed at Section 317-U1352B-28H-4, 7 cm (250.20 m) and is defined by a sharp contact that separates gray mud below from sandy mud above. This Type A contact and facies associations is thin (<1 m) relative to other packages. Two other intervals of sandy mud were also observed between 246 and 249 m. It should also be noted that sand beds as thick as 88 cm are present in Sections 317-U1352B-27H-4 through 27H-7, indicating that these sandy intervals extend several meters below the selected contact.

Surfaces U1352B-S5 and U1352B-S5.1

Two potential Type B surfaces and their associated sediments are designated as surfaces U1352B-S5 (Section 317-U1352B-51X-1, 131 cm [428.81 m]) and U1352B-S5.1 (Section 53X-5, 30 cm [453.00 m]). The latter is associated with an unusually thick (6.5 m) bed of very fine sandy calcareous mud.

Surface U1352B-S6

Lithologically, the depth interval from 475.5 to 484.2 m is very unusual. From the base up, it contains a 15 cm thick bed of very fine sandy mud that fines upward. The basal contact at 484.2 m that separates the sand above from the mud beneath is heavily bioturbated for 15 cm below the contact. A second sand bed (4.15 m thick) is present from 478.10 to 482.20 m. This muddy very fine sand is calcareous and terminates in a sharp basal contact at 482.2 m. Heavy bioturbation is present for 45 cm beneath the contact. Surface U1352B-S6 is positioned at the base of the thickest sand associated with the sharp contact at Section 317-U1352B-56X-5, 70 cm (482.20 m).

Surface U1352C-S9

Surface U1352C-S9 is located within a more calcareous interval within the marlstones defined as chalk. This interval contains a sandy chalk bed from 990.25 to 990.56 m and several 2–5 cm thick chalk-rich intervals between 1026 and 1034 m. The sandy chalk bed has a sharp, scoured contact at Section 317-U1352C-40R-3, 5 cm (990.56 m), that separates it from marlstones above and chalky marlstones beneath. This contact is designated as surface U1352C-S9.

Surface U1352C-S10

A series of Type B contacts with silty sand beds with planar bedding, ripple laminations, shell fragments, and rip-up clasts are present between 1112.50 and 1113.00 m. The contact at Section 317-U1352C-53R-1, 90 cm (1113.00 m), is designated as surface U1352C-S10.

Surface U1352C-S11

An unusually thick (3 m), very calcareous deposit with sharp basal and upper contacts is present between 1276.50 and 1279.80 m (Fig. F22). This deposit is present within Sections 317-U1352C-73R-2 and 73R-4, where the Pliocene/Miocene boundary was identified. Surface U1352C-S11 was placed at the base of the deposit at 1279.8 m.

Surface U1352C-S12

A succession of Type A/B facies deposits found from 1400 to 1438 m documents an increase in laminations and other current structures, such as planar beds and ripples, as well as an increase in grain size and sand beds interpreted as stronger current activity (Fig. F15). Additionally, slump deposits are present between 1371 and 1438 m (Fig. F16). The base of a slump deposit (Section 317-U1352C-94R-7, 60 cm [1938.20 m]) was selected as surface U1352C-S12.

Surface U1352C-S13

One of the most notable surfaces, U1352C-S13, is linked to the Marshall Paraconformity (Fig. F18). This surface is present at Section 317-U1352C-140R-2, 48 cm (1852.64 m), and is marked by a limestone gravel bed that separates glauconitic silty limestone above from limestone beneath. The gravel bed is composed of ~5–10 cm long subrounded limestone fragments having weathered surfaces.

Discussion and interpretation

Interpretation of Unit I

Subunit IA

Seismic reflection profiles indicate a series of downlapping reflectors in this interval, as described by Browne and Naish (2003), who interpreted these as a series of lowstand delta front deposits. The lithologies and sedimentary structures of Subunit IA are consistent with this interpretation. We interpret the sharp-based, dark gray sand to be a product of sediment gravity flows fed by such deltas (gravity flow in this context implies downslope mass transport, not a specific type of transport). The slumped and faulted intervals observed in the uppermost 20 m of both Holes U1352A and U1352B may be related to high rates of sediment supply in delta or pro-delta settings.

Subunit IA is characterized by dark gray muds as well as sharp-based, gray and greenish sand beds. The greenish sand beds are calcareous, and in part siliceous, with abundant to common macrofossils often concentrated into layers. This, together with the sharp-based and fining-upward character of the beds, suggests deposition from gravity flows. The background mud observed in the cores throughout this subunit probably formed through hemipelagic deposition in slope settings or areas removed from major point sources of sediment input from either westerly or southerly source areas.

The gray sand beds in this subunit have compositions consistent with derivation from low-grade zeolite and prehnite-pumpellyite graywacke rocks (Torlesse Terrane) of the Canterbury region. This subunit differs from other units, which appear to have a predominantly schist-derived provenance. For example, XRD data indicate that chlorite is low throughout Subunit IA but increases markedly at 100 m, which is consistent with a change from a dominantly Torlesse provenance in Subunit IA to an increased Otago Schist provenance in Subunit IB (Fig. F11). Grains within the subunit are both well rounded and angular—a bimodal transport history suggesting that the well-rounded grains may be recycled or were rounded in a high-energy beach setting and mixed with less rounded, fluvially transported sediment before being transported offshore.

Subunit IA, characterized by an overall high siliciclastic content, corresponds to the past ~0.25 m.y. (see "Biostratigraphy"), a time period of pronounced glaciation in the Southern Alps (Suggate, 1990). The relatively high concentration of quartz and feldspars within clay-rich intervals might be a glacial rock-flour signature (Heiden and Holmes, 1998; Peuraniemi et al., 1997), and the input of Torlesse-derived material implies that glaciers that originated from the Southern Alps were a dominant sediment source for this subunit.

Subunit IB

The interbedded greenish sands that occur in dark gray muds are typically sharp based and fine upward and are interpreted as sediment gravity flows. Similar sands were interpreted as contourites in Subunit IIB at Site 1119, but because we lack evidence of coarsening- and then fining-upward trends, we prefer to suggest that these sand beds represent either downslope mass transport from shallower areas rich in carbonate or are winnowed condensed intervals. For example, one such sand interval found in Sections 317-U1352B-32X-5 through 32X-CC contains abundant shells that likely represent a sediment gravity flow originating from a shallow-marine setting. XRD analyses show that total clays are lowest and calcite is highest in the calcareous, olive-green muddy sands, which may indicate that these units formed during periods of minimal hemipelagic sediment input or during periods of enhanced traction transport and erosion that winnowed out the clay component. Lastly, the noted decrease in quartz and mica content at ~250 m corresponds to ~0.8 Ma (see "Biostratigraphy"), which is during the mid-Pleistocene climatic transition from high- to low-amplitude eustatic sea level change (Clark et al., 2006).

Similarly, we suggest that the homogeneous mud, which has a relatively high total clay concentration, represents mostly hemipelagic deposition in upper slope settings based on micropaleontological evidence for an upper slope depth of deposition (see "Biostratigraphy").

Subunit IC

Coulometry and smear slide data indicate higher carbonate content in Subunit IC than in the overlying Subunit IB interval. The fine-grained sediments are interpreted to be hemipelagic sediments deposited with a large amount of pelagic carbonate components. Small to moderate proportions of terrigenous sand (10%–35%) may have been derived from downslope mixing or along-slope sand supply, but the better sorting and fine-grained nature of the sand fraction, including a high percentage of bioclasts, suggest considerable transport. Occasional clay-rich muddier units indicate episodic increases in terrigenous supply. Micropaleontological evidence (including the presence of reworked microfauna) supports an interpretation of drift sedimentation in a slope setting for this subunit. This interpretation is consistent with the seismic line in a strike perspective between Sites U1352 and 1119 that shows a series of small drifts at this stratigraphic level (seismic Line EW00-01-19).

Interpretation of Unit II

Unit II is distinguished from Unit I in that it is dominantly calcareous and is composed of sandy marlstone with minor components of limestone and sandy mudstone.

Subunit IIA

Subunit IIA is interpreted to have been deposited in a hemipelagic to pelagic setting largely removed from clastic sediment sources, although the very fine to fine sand, mica, and clay were probably derived from upslope terrigenous sources or along-slope sediment supply, as suggested by the variable mineralogy within this subunit. The sandy sediments are interpreted as thin traction deposits, formed during the reworking of some of the sand into planar-laminated and ripple-laminated beds. We interpret the marlstone as largely drift deposits, consistent with the seismic profile between Sites U1352 and 1119 (seismic Line EW00-01-19). The more calcareous lithologies may represent condensed intervals formed during periods when sediment was starved on these drifts. The increased frequency of chalky intervals in the lower part of Subunit IIA may relate to a slower rate of sedimentation at the base of a clinoformal package of sediment.

Subunit IIB

The alternation of light-colored marlstone with darker colored mudstone and sandstone layers indicates an alternation of dominant processes from more quiescent periods of pelagic deposition to periods of increased sediment supply and current activity. The overall downhole decrease of silicate minerals in this subunit is a continuation of the transition to a more carbonate rich (pelagic) environment with less terrigenous sediment input.

This subunit contains numerous types of bedding structures that may have formed from a combination of transport and diagenetic processes. The common thin, brown, wavy lamination that causes the pin-striped appearance of the lower part of the unit could be (1) original burrows, (2) primary ripple lamination, (3) stylolitic laminae, or (4) a combination of the above. These laminae appear to become better defined and more pervasive with depth, and lower in the subunit some of the white calcareous blebs are dissolving about their margins and forming white trails into the laminae. Thin section observations indicate that the brown wavy laminae are composed of organic matter and associated clay-rich material deposited in laminae and reworked in burrows that have undergone pressure solution, in effect a combination of the proposed mechanisms above.

The sharp-based nature of the darker sandstones and mudstones suggests increased current activity and rapid deposition of these beds. It is probable that the mudstone represents increased deposition of continent-derived material (clay, organic material, etc.). The horizontally and ripple-laminated sandstone beds were deposited by traction currents, probably also sourced from continental areas or, less likely, from reworking of the sand component of the marlstones. Smear slides indicate a considerable amount of organic matter (as much as 10%) in the lower portions of the subunit, implying that a landmass was not too distant from the depocenter. Perhaps the mudstone intervals represent periods of lower sea level, when land-derived sediment was prevalent, whereas the marlstone might represent hemipelagic sedimentation during periods of reduced sediment input from the continent, possibly during rising and high sea level. In general, we interpret these sediments to represent largely hemipelagic to pelagic deposition removed from major sources of sediment (except during lowstands), consistent with a sediment-drift setting.

Intervals of soft-sediment deformation recorded in the lower portion of Subunit IIB may reflect instability caused by sediment loading, seismic triggering, and/or topography within the drift deposits or adjacent submarine highs (the "Endeavour High" of Field and Browne, 1989). These slumped intervals have higher quartz, clay, mica, and feldspar contents, supporting the interpretation that these deposits were formed by mass movements originating closer to shore. The association of a graded sandstone-mudstone turbidite at the top of one of these mass flow units suggests that subsequent mass flows were concentrated into bathymetric lows, which formed by the evacuation of the mass-transport complex that preceded it.

A prominent variance in mineralogy occurs within this subunit, as indicated by the interval of higher mica and chlorite content between ~1470 and 1570 m. As opposed to other sections at this site where micas and quartz/clay positively co-vary, the rise in mica content does not correspond to a similar rise in quartz or clay minerals but does increase along with plagioclase. Smear slides and thin sections from these same intervals reveal the presence of altered basaltic fragments, plagioclase, and zeolites, suggesting that chlorite may be authigenic rather than detrital and may have formed from alteration of mafic volcanic fragments. This depth interval corresponds to ~10–13 Ma (see "Biostratigraphy"), when the mafic volcanic fields at Banks and Otago peninsulas formed (McDougall and Coombs, 1973; Coombs et al., 1986; Sewell, 1988; Sewell et al., 1992).

Subunit IIC

The marlstones and limestones in this subunit are predominantly fine grained, suggesting pelagic to hemipelagic deposition in a deepwater setting with only a small terrigenous sediment supply. Micropa- leontology suggests deposition in a lower bathyal setting (see "Biostratigraphy"). The horizontally laminated nature of the intercalated glauconitic sandstone beds implies some form of traction deposition. In these instances, the sandstone may represent reworking of sediment from areas enriched in glauconite, such as sediment-starved highs. Although this is probably true for some of the observed layers, many of the sandstone layers, especially those in the lower part of the subunit, clearly crosscut primary stratigraphic features and are interpreted as diapiric in nature, both dikes and sills. Examples of this exist in the core where vertical or near-vertical glauconitic sandstone bodies fed into or were fed from subhorizontal glauconitic sandstone. Other core examples show thinner glauconitic sandstones branching from thicker equivalents with a dendritic-type morphology. Some diapiric sandstones show fragments of the surrounding carbonate lithology within them, implying that these fragments were broken off the surrounding walls during emplacement. Accounts of diapiric sandstones at Oamaru (Lewis, 1973) and southern North Island (Browne, 1987) indicate that similar diapiric features occur nearby in similar lithotypes. We suggest that the source of the glauconitic sandstone is the Oligocene Kokoamu Greensand, which should occur stratigraphically below these limestones (but was not recovered in the core) and immediately above the Amuri Limestone (Unit III), based on the nearby exploration well Clipper-1. Sediment loading and/or mild tectonic warping may have caused the upward injection of the glauconitic sand into Subunit IIC (e.g., Jolly and Lonergan, 2002).

Interpretation of Unit III

We interpret Unit III to have accumulated as pelagic foraminifer-bearing nannofossil ooze. The faint purple bands and rings noted in the cores may be related to disseminated fine iron sulfide within the limestone, as described in similar facies recovered from the Ontong Java Plateau during ODP Leg 130 (Lind et al., 1993). These color bands are interpreted as a possible alteration of volcanic ash or other impurities in the limestones. Foraminifer and nannofossil studies reported here (see "Biostratigraphy") suggest a lower bathyal depth between 1000 and 1500 m water depth.

This unit is correlative to the regionally extensive Amuri Limestone, which is widespread throughout South Island and lower North Island, New Zealand. Regional studies suggest that deposition may occur in either shelf (van der Lingen et al., 1978) or bathyal (Edwards et al., 1979) settings. Seismic reflection profiles suggest that Site U1352 was situated slightly seaward of the shelf during the early Oligocene but that the margin was a broad ramp at that time with no clear shelf/slope break. This is consistent with the interpretation made by Field and Browne (1989) that the Amuri Limestone was deposited in an outer shelf to slope paleoenvironment.

Interpretation of lithologic surfaces and associated sediment facies

Hole U1352B

The identified lithologic surfaces and their associated sedimentary packages (Types A, B, and C) are in some instances near the predicted depths of seismic sequence boundaries (Lu and Fulthorpe, 2004), allowing a tentative correlation of lithology to seismically defined surfaces (Figs. F22, F23; Table T4; see also Table T4 in the "Site U1351" chapter). The sharp and often heavily burrowed basal contacts of some of these packages suggest that erosion and/or sediment bypass are associated with the formation of the discontinuity. The lithologic surfaces from Site U1352 differ from those of Site U1351 in that they are composed of several Type A sedimentary packages per core (~9 m intervals) instead of just one event, as was observed at Site U1351. Multiple sedimentary packages can potentially provide a stronger impedance contrast and stronger seismic reflections on the seismic lines. This should be further investigated during postcruise study.

Surface U1352B-S1 is tentatively correlated to seismic sequence boundary U19, which is predicted at 68 m. Of the two depositional events present, surface U1352B-S1 is correlated to the thicker sand bed at 64.16 m and to U19. Surface U1352A-S1 has a similar age range as U1352B-S1 and was identified in interval 317-U1352A-3H-1, 0–70 cm.

Surface U1352B-S2 is a Type B contact and associated facies and is tentatively placed at 147.3 m and correlated with U18, which has a predicted depth of 142 m. Surface U1351B-S2 has a similar age range as U1352B-S2 and was identified in Holes U1351A and U1351B at 27.75 and 31.00 m, respectively (see Table T4 in the "Site U1351" chapter).

Surface U1352B-S3 is tentatively positioned at a sharp contact at 200 m. The Type A contact and associated facies designated U1352B-S3 correlates to U17, predicted at a depth of 195 m. Surface U1352B-S3 has a similar age range as U1351B-S3 (see Table T4 in the "Site U1351" chapter).

Surface U1352B-S4 is tentatively placed at 250.20 m and correlated with U16, which has a predicted depth of 249 m. Again, as in previous surfaces, the lithology indicates three depositional events associated with this interval. Surface U1352B-S4 has the same age range as U1351B-S4 (see Table T4 in the "Site U1351" chapter).

Surface U1352B-S5 at 428.81 m is correlated to U15, which has a predicted depth of 428 m. Surface U1351B-S5 is also tentatively correlated to U15.

Surface U1352B-S5.1 at 453.20 m is tentatively correlated to U14, which has a predicted depth of 448 m. A lithologic surface correlative to U14 was not found at Site U1351, probably because of a recovery gap between 97 and 113 m over the predicted depth of U14 at Site U1351 (103 m).

Surface U1352B-S6 is tentatively positioned at the base of the thickest of two sand beds associated with a sharp contact at 482.20 m. This surface is correlated with U13, which has a predicted depth of 500 m. The sediments from 485.10 to 504.40 m are composed of gray homogeneous mud and had good recovery, except for intervals of cementation between 489 and 492 m. The series of sand beds associated with this contact provides evidence of sediment transport. Surface U1352B-S6 has a similar age range as U1351B-S6, where sand beds and evidence of sediment reworking also make the placement of the Pleistocene/Pliocene boundary in that core questionable (see Table T4 in the "Site U1351" chapter).

U12 and U10 were not found at Site U1352. A Type A contact and facies association, U1351B-S7, is present in Core 317-U1352B-81X at 710.65 m. This lithologic surface and its facies association is tentatively correlated to a seismic surface that could potentially be the continuation of U12. U12 could not be traced from Site U1351 to U1352, so at this point this interpretation is based on the lithology only and not on a seismic surface.

U11 has a predicted depth of 769 m, but a corresponding lithologic surface was not located near this depth. U10 is absent. The Type A surface U1351B-S7 is present in Section 317-U1351B-22X-1 (171.4 m) and tentatively correlated with U12.

Hole U1352C

Several cores in this hole have distinctive lithologies that could be identified as Type A or Type B surfaces. These surfaces, although rare, are important and have been tentatively linked to U9 and U8 (U1352C-S9 [990.60 m] and U1352C-S10 [1113.00 m], respectively). Sediments from 1113 m to the base of the hole at 1924 m include notable events associated with hiatuses and mass flows, also classified as Type A and Type B contacts and facies associations. These events have been tentatively linked to U7 and U6 and to the Marshall Paraconformity. These surfaces and associated sediments are named U1352C-S9 to U1352C-S13. Sediments that could be interpreted as representing U5 and U4 were not recovered at Site U1352.

Surface U1352C-S9 is tentatively linked to U9, which occurs at a predicted depth of 970 m, based on increased calcareous content and a sandy chalk bed. Because of its high calcareous content, the deposit associated with this lithologic surface may represent late high-stand episodes of condensation. This lithologic surface was not directly identified at Site U1351 because sediments near the predicted depth of U9 (312 m) were not recovered.

Surface U1352C-S10 and its associated facies is a Type B lithologic contact positioned at 1113 m and tentatively correlated to U8, which occurs at a predicted depth of 1136 m. The depth at which U8 is predicted at Site U1351 (394 m) was not recovered because of recovery gaps between 394 and 400 m. U1352C-S10 cannot be correlated to the shelf Site U1351.

Surface U1352C-S11 is a Type A contact and facies association. As a result of its sediment composition, sharp boundaries, and age, the base of this deposit is tentatively correlated to U7, which occurs at a predicted depth of 1251 m. The predicted depth interval for U7 at Site U1351 is 614 m; however, this surface was not identified at Site U1351 because of poor recovery from 611 to 620 m.

Surface U1352C-S12 was chosen at the base of a slump deposit at 1438 m. This lithologic surface closely corresponds in depth with U6, which occurs at a predicted depth of 1428 m. The corresponding U6 interval at Site U1351, at the predicted depth of 895 m, was not recovered.

Based on age and lithologic relations, U1352C-S13 is correlated to the Marshall Paraconformity (observed at 1852.6 m), which correlates to the predicted depth of seismic reflector "Green" at 1824 m. A gravel bed marks this lithologic surface, which suggests that the gravels were derived from the limestone beneath and were reworked prior to deposition of the overlying sediment. It is likely that these reworked limestone blocks were derived from the weathered top surfaces of the underlying chalky limestone and that a layer of unconsolidated glauconitic sand between the rubbly surface of the underlying limestone and the coherent glauconitic limestone above exists in the subsurface but was not recovered by coring. This interpretation is based on the exposures onshore of a similar (though shorter duration) unconformity (e.g., Fulthorpe et al., 1996). The unconsolidated glauconitic sediments or rubbly top surface of the limestone would provide a strong impedance contrast, leading to the strong seismic signal of the Marshall Paraconformity sequence bounding unconformity. U1352C-S13 correlates with a hiatus between the upper Miocene (18–19 Ma) and upper Oligocene (30–32 Ma), and its recovery was a very important goal of the expedition. There are no major lithologic features at 1647 m, the originally predicted depth for the Marshall Paraconformity.

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