Three lithostratigraphic units are identified at Site 1095 (Figs. F4, F5; Table T2). The uppermost, Unit I, is mainly composed of clays and silty clays, which are locally biogenic rich, contain scattered ice-rafted debris, and alternate in color between gray and brown. The underlying Unit II is the thickest and is characterized by thick and repetitive sequences of green laminated silt and mud. Ice-rafted debris is scattered throughout Unit II and appears concentrated within bioturbated intervals. Unit III, the lowest identified at Site 1095, is mainly composed of dark greenish gray laminated claystone.
Intervals: Cores 178-1095A-1H through 6H; Core 178-1095C-1H; Core 178-1095D-1H through Section 6H-2
Age: Holocene to late Pliocene (0.00-1.77 Ma)
Depth: 0.0-49.3 mbsf
Unit I is mainly composed of fine-grained brown and dark gray diatom-bearing silty clay, silty clay, and clay, with minor siliceous ooze (Figs. F4, F5). The sediments are indistinctly laminated and extensively bioturbated. Two subunits are identified. Subunit IA consists of alternating diatom-bearing silty clay and clay, probably extending from the present back to marine oxygen isotope Stage 11 at ~7.5 mbsf, by comparison with the results of Pudsey and Camerlenghi (1998). Subunit IB consists of alternating silty clay with sand grains, and clay with silt laminae, down to the top of a coarse-grained unit at 49.3 mbsf (in Hole 1095A).
The biogenic-rich facies of Subunit IA, diatom silty clay and diatom-bearing silty clay, dark grayish brown to brown and olive brown (10YR 4/2, 4/3, 5/3, 6/4; 2.5Y 4/2), are intensely bioturbated and are in five layers, 30-70 cm thick (reduced to 10 cm at the core top; Fig. F6), with gradational burrowed tops and bases. In addition to well-preserved diatoms, these sediments contain foraminifers (most common in the second layer from top) plus rare radiolarians and nannofossils. This facies has low magnetic susceptibility and high values of chromaticity parameters a* and b* (see "Lithostratigraphy," in the "Explanatory Notes" chapter; Figs. F6, F7).
The terrigenous facies of Subunit IA consists of clay with 
1% diatoms and is olive gray and grayish brown (5Y 5/2 and 2.5Y 5/2). It occurs in layers 0.9-1.7 m thick between the biogenic-rich facies. Sedimentary structures include faint, diffuse lamination visible as color contrasts (browner/grayer layers, indistinguishable on the Munsell scale) and minor bioturbation. Scattered sand grains and granules are present from 2 mbsf downward. This facies has high and variable magnetic susceptibility and low values of a* and b* (Figs. F6, F7).
The massive facies of Subunit IB is silty clay with scattered sand grains and granules. This occurs in layers 0.5-2.1 m thick and is mainly grayish brown, gray, and olive gray (2.5Y 5/2, 5Y 4/2, 5Y 5/1). It appears to be almost structureless, although burrow mottling is seen where there are faint color contrasts. The biogenic content is low, but there are a few thin foraminifer-bearing (e.g., interval 178-1095A-5H-1, 86-105 cm; Section 178-1095D-2H-7; and intervals 178-1095D-2H-6, 43-62 cm; 4H, 3-88 and 4-44 cm) and diatom-bearing (e.g., Sections 178-1095D-2H-2 and 3) layers (Figs. F6, F7, F8).
The laminated facies of Subunit IB consists of clay with silt laminae. The clay is dark gray to gray or dark grayish brown (N4/0, N5/0, 5Y 5/1, 5Y 4/2, 2.5Y 4/2). Silt laminae are olive gray (5Y 4/2), 1-10 mm thick, rarely up to 30 mm. The silts have very sharp bases, locally scoured or microburrowed, and are weakly graded with sharp tops (Fig. F9). Silts form 5%-10% of the section, and units of the clay plus silt lithology are 1.3-4.0 m thick. In general, no vertical trends are seen in thickness or number of silt laminae; only two thinning-upward sequences occur (intervals 178-1095A-4H-2, 75-98 cm, and 5H-3, 68-78 cm). Fine to very fine sand occurs locally as graded beds up to 6 cm thick (e.g., Sections 178-1095A-2H-2, 42 and 130 cm; and 5H-2, 95 cm). There are isolated thin (1-3 cm) layers of poorly sorted sand.
In most of Subunit IB, these two facies alternate on a scale of meters (Fig. F7). In the lower part, particularly in Core 178-1095D-5H, thinner cyclic alternations of silty clay with scattered sand grains pass downward to clay containing a few thin silt laminae.
Unit I records deposition from suspension in a low-energy environment, as indicated by the fine grain size, lack of sorting, and absence of sedimentary structures indicating current winnowing. Slow sedimentation of the biogenic-rich facies in Subunit IA and the massive silty clay in Subunit IB allowed complete reworking by benthic burrowing organisms. In the terrigenous facies of Subunit IA, the diffuse nature of the lamination, and the absence of silt laminae or graded-laminated facies, suggests an origin as hemipelagites, which have been influenced by a regime of weak bottom currents (Pudsey and Camerlenghi, 1998). Dispersed sand grains and granules were transported to the area by ice rafting.
Sharp-based, parallel-laminated silt laminae in Unit I are interpreted as distal turbidites (Bouma TD-E divisions; see "Lithostratigraphy" in the "Explanatory Notes" chapter). Their limited occurrence in Unit I, compared with Unit II (see below), is consistent with low input of sediment by turbidity currents and a reduction in deposition rates (Fig. F5). Short depositional coarsening-upward cycles toward the base of Subunit IB record, from the bottom up, distal turbidity current activity (clays with thin silt laminae), which is followed by increasing input of ice-rafted debris accompanied by bioturbation.
The downward disappearance of diatoms from Subunit IA is not yet understood but may reflect long-term (longer than a glacial-interglacial cycle) changes in sea ice cover, or in seawater chemistry and hence dissolution. The presence of rare foraminiferal layers attests to open water conditions, free of ice cover for short periods (few hundred to few thousand years?) during the time span of Subunit IB (Fig. F7).
Intervals: Core 178-1095A-7H to base of Hole 1095A; Cores 178-1095B-1H through 37X; Section 178-1095D-6H-3 to base of Hole 1095D
Age: late Pliocene to late Miocene (1.77-8.93 Ma)
Depth: 49.3-435.5 mbsf
Unit II is characterized by sharp-based, graded, variably laminated fine sands and silts and laminated silty clays, interbedded with massive deposits (Fig. F4). Three distinct laminated lithofacies (L1, L2, and L3; see "Lithostratigraphy" in the "Explanatory Notes" chapter) are identified by the presence or absence of fine sand and silt laminae. The massive facies (M) is characterized by the absence of primary sedimentary structures, except for diffuse grading (Fig. F10). As will be shown below, Facies L1, L2, and L3 are genetically related and part of a facies continuum deposited by muddy turbidity currents (Fig. F11). They are described separately because they tend to occur in different parts of Unit II. Facies M results from hemipelagic sedimentation and intense bioturbation. Diamict deposits (Facies D; see "Lithostratigraphy" in the "Explanatory Notes" chapter) are also recognized but constitute a minor component of Unit II. Sediments of Unit II show an alternation of facies, which develop a cyclic depositional pattern. These cycles occur at several scales from a few meters to many tens of meters and are identified by different facies associations.
The contact between Unit I and the underlying Unit II at Site 1095 is not sharp but occurs over a 10-m-thick interval (e.g., in Cores 178-1095A-6H and 7H). This transitional zone is marked by an upward increase in ice-rafted debris and sand content (see Figs. F4, F5; Table T3) and a reduction in the frequency of laminated silts and fine sands. In Core 178-1095A-7H, several beds of diamict, as much as 85 cm thick, have clasts supported by a silty clay matrix.
Facies L1 accounts for ~10% of the total thickness of Unit II (Fig. F4). This facies consists of repetitive sequences of laminated (<1 cm) to thin-bedded (1-3 cm) fine sand and silt that grades upward into laminated and massive diatom-bearing silty clay (Fig. F10A, F10C). Facies L1 shows a consistent internal structure for each depositional sequence, with four distinct fining-upward divisions (Fig. F11). The lowermost division 1 consists of cross-laminated fine sand/silt with a sharp upper contact with parallel-laminated silt and mud in division 2. Division 2 passes upward into a laminated/graded silty mud component that comprises division 3. Finally, massive silty clay comprises division 4. In some cases, muds contain sufficient diatoms to be classified as oozes. The top division of the sequence shows varying degrees of bioturbation from intense, where primary structure has been destroyed, to absent. Planolites, Zoophycos, Chondrites, and Phycosiphon ichnofacies types can be identified and belong to the Nereites (bathyal) ichnofacies assemblage of Pemberton et al. (1992). Ice-rafted debris is concentrated in bioturbated bed tops (division 4). Basal bed contacts are conformable or erosional.
Facies L2 is the most abundant in Unit II, accounting for ~70% of the total stratigraphic thickness. It consists of repetitive sequences of the three upper divisions of Facies L1 (divisions 2, 3, and 4). Silt beds in division 2 are parallel laminated and have an erosional or sharp lower contact (Figs. F10B, F11). Silt grades upward into overlying laminated or massive diatom-bearing silty clay (divisions 3 and 4). Nereites-type bioturbation is limited to the upper few centimeters of bed tops. This facies is progressively indurated downcore and becomes claystone toward the bottom of Unit II.
This facies accounts for ~10% of the total stratigraphic thickness of Unit II. It consists of repetitive depositional sequences of the thinly laminated (<1 cm) and massive silty clay (divisions 3 and 4, respectively) that are present in the upper parts of Facies L1 and L2 (Fig. F11). Color banding is common, and upward transitions from dark to light hues within the depositional sequences suggest upward grading in grain size. In most cases, this facies is bioturbated and shows ichnofacies characteristic of the bathyal Nereites ichnofacies assemblage (see above). The degree of bioturbation varies from minimal to moderate. A mottled "bioturbate" texture occurs where bioturbation is moderate, which is characteristic of the few-centimeters-thick, overlying "hemipelagic" interval of the sequence. Ice-rafted debris is concentrated in such hemipelagic intervals, and diatoms are present.
Facies M is diatom-bearing homogenous silty clay, largely lacking any distinct internal structure as a result of intensive bioturbation (Fig. F10D, F10E). This facies accounts for ~10% of the deposits of Unit II. In contrast to the rather thin hemipelagic intervals of the laminated facies, the massive facies is present in beds up to 1 m thick and is generally grayish green (5G 5/2), in comparison with the predominantly dark greenish gray (5G 4/1) of other Unit II facies.
Subtle gradations in texture are present within Facies M, and beds may show a gradual upward coarsening from silty clay to sandy, clayey silt beds, or upward fining from clayey silt into silty clay. Ice-rafted debris is more common in Facies M than in any other facies at Site 1095. Ice-rafted terrigenous sand particles, also dispersed in the fine-grained matrix of these facies, may account for as much as 10% of the total composition. Bed tops are typically abrupt and sharply defined; lower contacts are locally blurred by burrowing (typically Planolites).
Diamict is defined as a poorly sorted admixture of clasts (>2 mm in diameter) and matrix (see "Lithostratigraphy" in the "Explanatory Notes" chapter). At Site 1095, diamict is present between 51 and 63.8 mbsf. Gray (5Y 5/1) diamict beds are massive and have a fine-grained silty clay matrix that supports sand- to pebble-sized clasts. They are interbedded with laminated silts and clays (Facies L1 and L2). In Hole 1095A, approximately seven diamict beds range in thickness from 1 to 3 cm (with one 85 cm thick); bed contacts are sharp, but with no evidence of erosion at the base of beds. In Hole 1095D, one diamict bed 34 cm thick is present at 57.1 mbsf. Diamicts and associated laminated sediments are not bioturbated.
Sediments resembling laminated sand, silt, and mud sequences of Facies L1, L2, and L3 within Unit II are well described in the literature as "parallel silt-laminated muds" (Stow and Piper, 1984), "mud turbidites" (Stow and Townsend, 1990), and "thin-bedded turbidites." These facies are characteristic of deep-sea depositional environments dominated by muddy sediment gravity flows (e.g., Pickering et al., 1988; Alonso and Maldonado, 1990). Consequently, Facies L1, L2, and L3 are all interpreted as turbidites (see "Lithostratigraphy" in the "Explanatory Notes" chapter).
Facies M probably results from slow hemipelagic settling of fine-grained particles derived from various sources such as low-density turbid flows, sediment plumes following the pycnocline and transported by geostrophic flows, and biogenic components formed by primary productivity. Bioturbation in this facies is very intense, and normally all original bedding is obliterated or obscured. This indicates low deposition rates and sufficient time to allow infauna to completely mix seafloor sediments. The low carbonate and organic matter content (see "Organic Geochemistry" and "Inorganic Geochemistry") of these sediments indicates well-oxygenated bottom-water conditions and deposition below the carbonate compensation depth. Ice-rafted debris is a more conspicuous component of Facies M than L1 to L3. This may be attributed either to a reduction in the rate of supply of fine-grained sediment relative to the influx of ice-rafted debris or to an increase in the flux of ice-rafted debris (see below).
The beds of diamict that are present between Unit I and Unit II are massive and nonbioturbated and appear conformable with interbedded laminated sediments deposited by turbidites. One possible interpretation of these is that they record episodes of enhanced deposition of debris from floating ice relative to background deposition of mud, such as recorded in Unit II by Facies M (see above). There are important differences, however, between these two facies. For example, Facies M is intensely bioturbated, which is strong evidence of reduced mud deposition and an extended time in which to accumulate ice-rafted debris. Diamicts, however, are nonbioturbated and occur conformably with nonbioturbated laminated silty clays, which indicates a short recurrence interval between successive turbidites and insufficient time to accumulate debris. The alternative suggestion is to invoke a vastly increased flux of ice-rafted debris sufficient to deposit beds up to 85 cm thick. The number and thickness of diamict beds are variable between Holes 1095A and 1095D, offset only 40 m from Hole 1095A, which indicates very local extent. This would appear to rule out a simple ice-rafting origin as this process could be expected to leave a blanket of ice-rafted debris across a large area. The occurrence of diamict as sharply defined beds also argues against a simple ice-rafted debris origin; very abrupt changes in ice-rafted debris are unlikely unless such beds are the equivalent of Heinrich events recorded from the North Atlantic Ocean (e.g., Heinrich, 1988). The depositional context of the diamict facies (conformable with turbidites deposited on a slope) suggests an origin as debrites (debris flows) produced by the local resedimentation and mixing of ice-rafted debris and silty clay.
Interval: Cores 178-1095B-38X through 52X
Age: late Miocene (8.93-10.1 Ma)
Depth: 435.5-570.2 mbsf
A zone of poor core recovery in the lower part of Core 178-1095B-37X (432.0-435.5 mbsf) marks an abrupt change in physical properties from indurated silts and muds of Unit II to lithified siltstones and mudstones of Unit III (see "Physical Properties"). The same facies, however, are present throughout Units II and III, and the distinction between these lithostratigraphic units does not imply a drastic change in the lithology, except in the proportion of the different facies. Unit III can be differentiated from Unit II, however, by the absence of cyclic alternation of facies observed in Unit II, in addition to the sharp change in physical properties. It is likely that the overall depositional setting was maintained, but the environmental factors influencing sedimentation were somewhat different. Core recovery in Unit III is poor below 481 mbsf (Core 178-1095B-43X). Sufficient core was recovered, however, to allow facies description, and it is considered unlikely that poor core recovery is related to a significant change in facies.
Unit III is composed of finely laminated claystone and siltstone, lacking bioturbation (Fig. F12). The laminated facies with siltstone layers show cross and planar lamination typical of turbidite Facies L2 and L3 described above for Unit II (Fig. F12A, F12C). Bioturbation is limited to small-scale Nereites-type burrows at bed tops (Fig. F12B). Ice-rafted debris is scattered throughout (Fig. F12D, F12E; see below). Unit III shows an overall upward fining from dominantly Facies L2 at the base to Facies L3 at the top (Fig. F4).
Smear-slide data provide insight into long-term trends in depositional conditions at Site 1095. This data set has not yet been fully evaluated and related to lithofacies, but several trends are evident in Figure F5. Downhole variation in the biogenic component, in general, is inversely related to sedimentation rate (Fig. F5). In intervals of more rapid sedimentation (such as between ~380 and 220 mbsf), the biogenic component is reduced as a result either of lowered production or dilution by enhanced influx of terrigenous sediment. This same stratigraphic interval is marked by a prominent "first-order" depositional cycle in Unit II, possibly recording progradation along the margin of the Antarctic Peninsula (see "Depositional Cycles in Unit II"). The biogenic component is lower in Unit III and at the base of Unit II during relatively low input of terrigenous sediment.
Throughout the core, the most abundant biogenic component is diatoms, which normally account for 10%-30% but locally reach 60% of the sediment (Table T3; Fig. F5). Sponge spicules are also a common component, whereas radiolarians and silicoflagellates represent only minor proportions in some horizons. Foraminifers are very rare.
In general, the mineralogy of the terrigenous component is dominated by lithic fragments, quartz, and feldspar, except for rare glauconite-bearing silt beds. Glauconite, hornblende, mica, opaque minerals, pyroxene, carbonates, and volcanic glass have been identified.
One of the goals of Leg 178 is to extend knowledge of the glacial history of the Antarctic Peninsula. Ice-rafted debris is a ubiquitous component of Units I, II, and III (Table T3; Fig. F5) and locally a substantial part of the flux of terrigenous sediment to the site. Because of the overall fine-grained nature of sediment at Site 1095, ice-rafted debris is readily identified. It occurs as scattered sand grains and granules, as isolated pebbles (lonestones), and as lenses of granules and sand. Ice-rafted debris lithologies are variable but include volcanic (rhyolite and basalt), volcaniclastic, intrusive igneous (granite and granodiorite), and metamorphic rocks. Most or all can be matched to Antarctic Peninsula sources (see papers in Craddock, 1982; Oliver et al., 1983; and Thomson et al., 1991). In the absence of core X-radiographs, a rough estimate of ice-rafted debris abundance and characteristics has been made from visual examination of split cores.
Scattered sand grains and granules are common in Unit I from 2 mbsf downward. Pebbles as much as 5 cm in diameter are particularly common in Cores 178-1095D-2H, 3H, and 5H and include a variety of volcanic and acid to intermediate plutonic rocks, with rare, low-grade metasedimentary rocks. Most pebbles are subrounded to subangular, the largest being rounded.
In general, the number of ice-rafted pebbles (>0.5 cm diameter) at the top of Unit II in Hole 1095B fluctuates but remains high until 205 mbsf at the base of Core 178-1095B-13H (Table T3). Most of these cores contain sand and granules and from one to three pebbles. Below 205 mbsf until 426 mbsf (base of Core 178-1095B-36X), cores contain sand, granules, and low numbers of pebbles (Fig. F5). Granite and basalt were the only pebble lithologies described from this 221-m-thick interval. In Unit III, below Core 178-1095B-40X, scattered sand and granules are accompanied by gravel clasts representing a wide variety of lithologies (Fig. F12D, F12E).
The changing flux of ice-rafted debris through time at Site 1095 cannot be quantified without further study. It is not possible to identify glacial-interglacial cycles simply on the basis of observed downhole ice-rafted debris abundance because this would disregard changes in the rate of background sedimentation. At times of rapid sedimentation, the flux of ice-rafted debris is diluted. Conversely, reduced sedimentation rates result in concentration of ice-rafted debris unrelated to any change in the ice-rafted debris flux itself. This is clearly demonstrated by low content of ice-rafted debris in rapidly deposited turbidite sequences and enhanced content in bioturbated intervals with low sedimentation rates (e.g., Facies M in Unit II; Fig. F5).
Biogenic-rich facies of Subunit IA are interpreted as interglacial isotope Stages 1-11 because (1) core-top sediment (i.e., Holocene) is biogenic rich, (2) good lithologic correlation can be made with piston cores from this area dated down to Stage 5 by chemostratigraphy (cf. Pudsey and Camerlenghi, 1998), and (3) the diatom Hemidiscus karstenii is absent in the second but present in the third biogenic unit down, which corresponds to isotope Stage 7 (Fig. F6).
Terrigenous facies are interpreted as glacial stage sediments, with perennial sea ice cover inhibiting biogenic production at the sea surface (and hence food supply to the benthos). Glacial terrigenous supply may have been higher than interglacial, as glacial units are thicker despite negligible biogenic input. The lack of bioturbation in the glacial units, despite low sedimentation rates (2 cm/k.y. down to Stage 7) may be explained by the very low food supply to the benthos. The higher abundance of ice-rafted debris downhole from 5 to 10 mbsf is interpreted as more ice rafting instead of less background sedimentation, as the glacial intervals maintain the same thickness.
In the absence of consistent cyclicity in biogenic content of Subunit IB, the relationship of the two facies to glacial-interglacial cycles is not self-evident. We suggest that the massive silty clays with scattered sand grains and intermittent foraminifers and diatoms are interglacial, and the laminated clays with silt laminae are glacial. This is consistent with interglacial, ice-free, open-water conditions allowing biogenic productivity and supporting a burrowing benthic fauna, although microfossils are not generally preserved. It is also consistent with the model of Larter and Barker (1991), which predicts that frequent turbidites are generated at the continental shelf edge during glacials, when the ice sheet is at the continental shelf edge.
Given the similarity of lithofacies within Units II and III (e.g., Figs. F4, F10, F11, F12), a similar depositional setting is indicated. When considered together, these units provide a record very similar to that of an aggrading distal base-of-slope setting in low latitudes. Cross- and parallel-laminated silt-mud turbidites such as those of Unit II are characteristic of distal and interchannel portions of submarine fan lobes and slopes (cf. Nelson and Maldonado, 1990). A likely depositional setting consists of an interchannel environment such as a levee marginal to active distributary channels (Fig. F13; Stow et al., 1990; Alonso and Maldonado, 1990; Nelson et al., 1991), but this must be assessed in the light of other data sets. Facies L1, L2, and L3 clearly represent a facies continuum of muddy turbidites. Transitions from type TC-D-E1-E2-E3 (Facies L1) to type TD-E1-E2-E3 (Facies L2) and TE1-E2-E3 (Facies L3) typically occur downslope and across slope on the lower distal portions of lobes and slopes (Fig. F11).
The stratigraphic distribution of Facies L1, L2, and L3 in Unit II shows recurring patterns giving rise to a broadly cyclic repetition of facies. Typical "coarsening-upward" cycles comprise a lowermost part dominated by L2 and L3 facies. Upward, L1 and L2 facies become dominant. In other cases, the sequence of facies occurs in reverse order (L1, L2 and L3), representing an overall "fining-upward" sequence (Fig. F4). Those intervals within a cycle of a high frequency of TC-D-E turbidites (Facies L1) indicate higher energy conditions and usually a more proximal setting to the sediment source (Fig. F13). Those parts of a cycle dominated by more fine-grained TD-E turbidites record a more distal setting. These trends provide valuable information regarding environmental conditions and overall depositional energy and have been termed "first-order cycles" by Stow et al. (1990). Two such cycles, of 50- to 100-m thickness, can be identified in Unit II (a, b in Fig. F5). The first-order cycles of Unit II, determined from uphole trends in lithofacies types and frequency at Site 1095, correlate approximately with paleomagnetically determined higher depositional rates. Also, the base of the long first-order cycle at 300 mbsf is coincident with an influx of neritic diatoms, which may indicate sediment supply from a more distal environment inshore. Upward in the cycle, as sedimentation rates increase and turbidites become coarser grained (i.e., Facies L1; Fig. F4), diatoms are few and fragmentary (see "Biostratigraphy"). Provisionally, first-order cycles of several tens of meters can be interpreted as recording long-term (0.5-1.5 m.y.) phases of enhanced sediment deposition, reflecting sediment supply trends and changing position and dimensions of feeder channels, lobes, or levees along the margin of the Antarctic Peninsula.
Depositional trends in high-latitude glacial settings cannot be interpreted in terms of changes in sea level, in contrast to lower latitude and temperate margins where relative sea-level change, tectonics, and sediment supply control sedimentation. The advance and retreat of continental ice sheets are considered a major factor influencing deposition on high-latitude margins (e.g., Boulton, 1990; Larter and Barker, 1991), and the "relative erosion level" is the ice-sheet base, rather than sea level. In an alternative view of the Antarctic Peninsula margin, Bart and Anderson (1995) suggested that "ice-sheet expansion across the overdeepened inner and outer shelf may only have occurred during extreme sea-level falls," but this is a question of degree rather than a fundamental difference of interpretation. Tectonics has not been a major factor controlling deposition at Site 1095, since ridge-crest collision occurred in the early Oligocene at this section of the margin (see Fig. F7, in Barker and Camerlenghi, Chap. 2, this volume). Larter and Barker (1991) estimated >1 km subsidence of the outer shelf off Adelaide Island, where ridge-crest collision occurred more recently (at 16.5 Ma). The shelf break has prograded during deposition of S1 and S2 (by as much as 25 km within Lobe 4 [Larter et al., 1997; Barker and Camerlenghi, Chap. 2, this volume]), which implies only limited changes in margin morphology (see also "Site 1097" and "Shelf Transect" [Sites 1100, 1102, and 1103] chapters).
Well-defined, second-order cycles occur within the first-order cycles in Unit II. These cycles are bounded by Facies M, which records episodes of reduced deposition and the accumulation of ice-rafted debris (Fig. F12D). The second-order cycles can also be seen in color and magnetic susceptibility data (Fig. F7). They may be the stratigraphic expression of high-frequency (possibly 40 and 100 k.y.) glacial-interglacial changes in sediment supply along the Antarctic Peninsula continental margin. The absence of second-order cycles in Unit III at Site 1095 may be significant in understanding glacial history.
The low overall intensity of bioturbation through much of Units II and III suggests near-constant deposition rates and short recurrence intervals between successive turbidity current flows, or bottom conditions that did not favor a significant development of bottom-dwelling fauna, such as a reduced nutrient supply or low oxygen content (see "Lithostratigraphy" in the "Site 1096" chapter). The deposits of Unit III show a moderate sedimentation rate of 11 cm/k.y., and most of the deposits of Unit II recorded a rather low mean depositional rate of 6-8 cm/k.y. (Fig. F5), which is close to rates estimated for the same stratigraphic interval penetrated at Deep Sea Drilling Project Site 325 (Hollister, Craddock, et al., 1976). Calculation of the frequency of turbidite events, on the basis of the mean sedimentation rate and thickness of turbidite sequences, yields a recurrence interval of ~0.4-2 turbidity flows/k.y. This frequency should be greater at times of enhanced sediment supply to the margin during the development of the laminated facies and lower for the massive facies. The rate of bioturbation in the deposits thus reflects the interplay between the two controlling factors, sediment supply and oceanographic conditions, during the depositional evolution at Site 1096. Deposition rates decline above the top of Unit II, which is marked by enhanced concentrations of ice-rafted debris and diamict facies. It is likely that much of the terrigenous fine-grained sediment within Unit I was provided to the water column by dilute turbidity flows as suspension clouds and then deposited by weak bottom currents (e.g., Stow et al., 1990; Rebesco et al., 1996; Pudsey and Camerlenghi, 1998).
