Only one lithologic unit was recognized at Site 1144 (Fig. F5). The sediments represent continuous hemipelagic sedimentation of fine-grained, clay-sized terrigenous material, quartz silt, and calcareous nannofossils. APC coring at Site 1144 failed to recover the oxidized sediment layer from the seafloor (see "Composite Section"). Despite the relative homogeneity, we propose a three-part subdivision of the unit based on the abundance of "iron sulfides," pyrite, and siliceous biota, as noted in core description and smear-slide analysis.
The dominant lithology throughout the recovered section at Site 1144 is clay with quartz silt and nannofossils. Other lithologies include clay with quartz silt and sponge spicules, clay with quartz silt and diatoms, clay with silt, silty clay, and clay. These minor lithologies comprise only ~5%-10% of the total sediment recovered. Irregularly shaped white pockets, typically a few millimeters in diameter, are randomly distributed in the structureless clay, sometimes quite densely. These are filled with sponge spicules and particles of recrystallized authigenic and/or biogenic silica.
Subordinate lithologies, such as ash layers and green clay layers, are rare throughout, comprising <1% of the total section. Green clay layers, which are abundant at Site 1143 in the southern South China Sea (see "Lithostratigraphy" in the "Site 1143" chapter), are seldom recognized at Site 1144 (13 layers in Hole 1144A, seven layers in Hole 1144B, and four layers in Hole 1144C). In addition to well-defined green layers, a large number of rather indistinct green clay layers and patches are noted over these same intervals in the three holes at Site 1144. The same relationship of discrete and indistinct layers was also noted for the green clay at Site 1143 (see "Lithostratigraphy" in the "Site 1143" chapter). A single fine sand interval, ~1 mm thick, occurs at 189.39-189.40 mcd in Hole 1144B, but otherwise coarse clastic material is limited to silt-sized material disseminated in the sediment, normally dominated in composition by quartz, feldspar, and, locally, pyrite. Volcanic glass shards and altered igneous rock fragments are minor but frequent components of the silt fraction.
In general, the sediments at Site 1144 were only slightly disturbed by the coring process but were often extremely disturbed over discrete intervals. Disturbance is seen as porous, soupy sediment and as spaces between core segments. These gaps are caused by gas, mainly methane and some hydrogen sulfide in the top three cores (see "Organic Geochemistry").
Bulk X-ray diffraction of one sample per core in Hole 1144A revealed that the mineralogy follows the overall visual homogeneity of the sediment (Fig. F6). A decrease in the quartz content occurs below about 277 mcd, but this may simply reflect the trend toward an increase of finer grained material for the older sediments at this site. Analysis of color indices measured with the spectrophotometer, qualitatively compared with the clay content as determined by smear-slide analysis, indicates that lower values of the L* parameter and higher values of the a* parameter (toward red) correlate with higher percentages of clay.
Subunit IA is distinguished from the rest of the section by the common presence of fine-grained "iron sulfide" (its actual mineralogy to be determined), which is seen as a mild to intense black mottling of the cut core face, whereas pyrite is rare. Opaque material is also noted in smear slides, both in the mottled and normal clay lithologies throughout the upper 283.43 mcd of the drilled section (Fig. F7).
Subunit IB is distinguished from the overlying subunit by a sudden drop in black "iron sulfide" mottling, coinciding closely with a significant increase in the proportion of nannofossils (Fig. F7). Pyrite is observed in modest quantities, usually as a replacement of burrow fills (Fig. F7). This subunit contains the highest proportion of siliceous biogenic debris, principally diatoms and sponge spicules (Fig. F7), noted over the drilled section.
The basal subunit is distinguished on the basis of the high proportion of pyrite, usually present in burrows. Like Subunit IB, the proportion of nannofossils observed in smear slides remains high, and fine-grained "iron sulfides" are present only in minute amounts, whereas siliceous organisms decrease in concentration (Fig. F7).
"Iron sulfide" mottling in the sediments in Subunit IA contrasts with an increase in pyrite in Subunit IC and implies changes in sedimentary and early diagenetic environments. Pyrite is an authigenic mineral that usually forms early during diagenesis and burial of fine marine sediments and is usually found just a few centimeters below the seafloor. The pyrite concretions found at Site 1144 show enrichment in iron and sulfur as a result of local biological activity. In contrast, the "iron sulfide" mottles reflect relative enrichment in iron but a relative deficiency in sulfur, as shown by sulfur analyses of the interstitial water at Site 1144 (see "Inorganic Geochemistry"). The abundance of "iron sulfides" in Subunit IA was likely caused by high organic carbon flux.
The clayey sediment at Site 1144 is completely homogenized by bioturbation. Carbonate content (i.e., nannofossils, foraminifers, and other forms of calcite, biogenic and/or nonbiogenic) varies between 5% and 45%, based on smear-slide observation. In comparison, coulometric analysis of carbonate content ranges from 10 to 20 wt% (see "Organic Geochemistry"). The mismatch reflects the difficulty in estimating carbonate fractions accurately using smear slides as well as the sampling resolution of the chemical analyses, which consider much higher volumes, spaced regularly through the core, whereas the smear slides reflect mineralogic composition of small volumes at specified levels.
Diffuse mottling occurs throughout the sedimentary section. Yellowish olive and brownish olive-gray clay patches, up to 5 cm across, are locally present in moderate amounts but are much reduced compared to the sediments observed at Sites 1143. The patchy appearance is presumed to reflect bioturbation.
Layers of foraminifer ooze with small amounts of pyrite are noted. These layers form a very small proportion of the total section, <0.1%, and are typically <1 cm thick (e.g., 500.00-500.01 mcd; interval 184-1144A-47X-3, 147-148 cm). Sharp bases and normal grading are often, but not always, associated with these intervals. These beds probably represent deposition from turbidity currents.
Volcanic ash layers, ranging from <1 to 6 cm thick, are observed at Site 1144. Eight ash layers are observed in Hole 1144A, six in Hole 1144B, and two in Hole 1144C (Table T5). The ash layers are composed of angular glass shards and volcanic minerals. The thicker ash layers are often light colored, suggesting a composition dominated by high-silica glass as well as small amounts of quartz (<5%). Most of these ash layers have relatively sharp lower boundaries with bioturbated tops. Bioturbation may also result in mixed and/or homogenized sediments of volcanic ash and silty clay. A comparison between Holes 1144A, 1144B, and 1144C reveals that many ashes were seen in only one of the holes. However, one correlative ash layer occurs at 176.07-176.03, 175.05-176.11, and 176.01-176.07 mcd in Holes 1144A, 1144B, and 1144C, respectively. Lack of interhole correlation between the other ash layers may be caused by dispersion of the layers by bioturbation (Fig. F8) or by current redistribution, so that only patches of the thin layers are preserved (Fig. F8).
Nannofossils are abundant throughout Site 1144. Among other microfossils, foraminifers are always recognized in smear slides but are often invisible on the cut core face. A few intervals have common to abundant foraminifers, such as a 1-cm-thick layer at 179.45-179.46 mcd at Section 184-1144A-18H-5, 39 cm, as well as an interval of three to four layers between 456.47 and 456.57 mcd (interval 184-1144A-47X-3, 147 cm, to 47X-4, 10 cm), and a 10-cm-thick interval comprising pockets of foraminifers at 456.47-456.57 mcd (interval 184-1144B-44X-4, 29-39 cm). Sponge spicules, often present as millimeter-scale and irregularly shaped white pockets, are rare to common in all sections of the three holes; these may be interpreted as burrow fills, as representing small (or parts of) individual sponges, or as the result of redepositional processes (Martini and Locker, 1990).
Macrofossils are rare; however, ~1-cm-long gastropods, ~1-cm-long scaphopods, and up to ~1-cm-long pteropods are observed. Wood debris is uncommon but is observed at several intervals in all three holes; individual pieces are as long as 4 cm. Fragments of echinoderms are found only in the shallower intervals of the recovered section.