Within the ~926.6-m-thick succession drilled at Site 1118 eight lithostratigraphic units were recognized on the basis of sediment or rock type, grain size, sedimentary structures, color, smear slides, thin sections, bulk mineralogy (X-ray diffraction [XRD]), and carbonate content, aided by geophysical logs (Fig. F1). Smoothed grain-size trends are shown in Figure F2. No coring took place in Hole 1118A until 205.0 mbsf. However, part of this missing interval (100.0-205.0 mbsf), reconstructed by using geophysical logs, was found to be mainly muddy sediments with rare thin (<15 cm), more sandy layers (see "Downhole Measurements"). The Formation MicroScanner (FMS) images show that the basal unit recovered is a sedimentary conglomerate rather than in situ igneous rock as initially inferred from the limited recovery. Details of the lithostratigraphic units present are as follows:
From 205.5 to 255 mbsf RCB recovery was minimal. Beneath this, recovery was good to excellent (see the core description forms, or "barrel sheets," in the "Core Descriptions" contents list).
Lithostratigraphic Unit I is characterized by a relatively homogenous succession of mainly greenish and grayish silty claystone and clayey siltstones interbedded with graded sandstones and siltstones. Carbonate values of the fine-grained sediments of Unit I vary between 2.4 and 16.2 wt% with a few more calcareous samples being present (35.5 and 72.5 wt% in Cores 7R and 8R; see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). In general, claystones, grayish siltstones, greenish siltstones, and paler siltstones alternate every few centimeters to tens of centimeters. Colors are mainly greenish or grayish in the upper part of the unit. Graded sandstones/siltstones tend to be darker green and greenish gray in color (e.g, Section 12R-5) than the clayey siltstones and silty claystones that are typically pale shades of the same colors. Slightly reddish intervals appear from the middle part of the unit downward (~310 mbsf).
The following lithologies are present:
Greenish gray silty claystone and clayey siltstone form much of the background sediment. Typically, these sediments are calcareous and contain volcanic glass and detrital grains, scattered foraminifers, and rare small (several millimeters) shell fragments. The silty claystones are mainly moderately to highly bioturbated. Small Chondrites burrowing predominates, but larger Zoophycos burrowing is locally present (Fig. F3). Many of the small (<5 mm) burrows are lensoidal in shape. In addition, sulfide reduction spots (with reduction halos) and color mottling are visible.
Smear slides reveal the presence of common nannofossils and planktonic foraminifers together with feldspar, biotite, volcanic glass, and accessory minerals, particularly hornblende (see "Site 1118 Smear Slides"). The XRD analysis of the fine-grained sediment component (claystone and silty claystone) revealed mainly plagioclase, calcite, pyroxene and minor amphibole, illite, smectite?, chlorite, and possible mixed-layer clays. Dolomite and pyrite are found sporadically (Table T3). Below 290 mbsf calcite, plagioclase, and quartz predominate in most samples with minor amounts of clay minerals (i.e., chlorite and illite).
These are similar to the above sediments, but tend to be well laminated, reddish, and exhibit little or no burrowing (Section 9R-1). These intervals range from several centimeters to tens of centimeters in thickness and become relatively numerous below 335.0 mbsf (e.g., interval 180-1118A-14R-7, 79-90 cm), although the reddish colors are always subordinate within Unit I. Smear slides contain nannofossils and planktonic foraminifers together with feldspar, biotite, volcanic glass, and accessory minerals, including inorganic calcite (see "Site 1118 Smear Slides").
Very thin beds and laminae of dark greenish gray siltstones occur throughout the unit. Typically, each has a structureless or laminated silty base several millimeters thick overlain by almost homogenous dark silty claystone. The tops of individual beds are commonly burrowed. Elsewhere, the siltstone is extensively burrowed, obscuring much of the primary structure. The burrows are infilled with clayey siltstone. Smear slides are seen to be similar in composition to the lithologies discussed above (see "Site 1118 Smear Slides").
Throughout the unit there are occurrences of normally graded sandstone as very thin beds and laminae ranging from 0.5 through 3.5 cm thick (average 2 cm). Colors range from dark greenish gray to dark gray. Most beds begin with scoured bases. These bases are mainly subplanar, but are locally irregular. Rarely, isolated fine- to medium-grained sandstone is present in small lobes at the base of individual sandstone beds (e.g., interval 180-1118A-6R-6, 125 cm). In many cases the overlying sandstone bed was not recovered. Where recovered, the fine sandstone grades upward to clayey siltstone, which is usually structureless. Occasionally, planar lamination, ripple, or wavy lamination is present (e.g., interval 180-1118A-6R-1, 38-38.5 cm). This sediment is typically burrowed such that bedding is commonly obscured.
In smear slides the following poorly sorted grains were observed: nannofossils, planktonic foraminifers, sponge spicules, quartz, plagioclase, biotite, calcite, pyrite, accessory minerals (e.g., hornblende), volcanic rock fragments, and detrital organic matter (see "Site 1118 Smear Slides"). Also, rare carbonaceous detritus was noted at the base of a few fine-grained, graded beds. In addition, one impregnated thin section of sandstone revealed quartz, plagioclase, planktonic foraminifers, biotite, basaltic grains (flow banded), glassy basalt, and rare benthic foraminifers set in a clay-rich matrix. Occasional burrows are pyrite filled (see "Site 1118 Thin Sections"). XRD analysis also indicates pyrite in several samples (Table T3).
Soft-sediment deformation was observed in parts of Unit I (see Fig. F4). These structures are intraformational and adjacent to undeformed beds. This contrasts with faulting, folding, and other structural features that follow deposition and partial lithification (see "Structural Geology"). The inferred soft-sediment deformation features were first seen as locally inclined lamination sharply overlain by subhorizontal laminae (e.g., intervals 180-1118A-9R-3, 33-34 cm, and 13R-5, 80-104 cm). Soft-sediment deformation structures then become larger and more extensively developed downhole (Sections 14R-1 through 14R-5; 250-340 mbsf). Fold axes are subhorizontal, and the deformed interval includes several small faults (i.e., interval 180-1118A-14R-1, 60-149 cm). Several of the deformed zones are overlain by small injection structures (intervals 180-1118A-14R-2, 15-45 cm, and 14R-3, 60-95 cm). The highly deformed and folded intervals are separated by less deformed inclined beds of laminated silty claystone and clayey siltstone (Fig. F5). Beneath the zone of deformation, beds are less deformed but show some evidence of sediment dewatering (interval 180-1118A-4R-5, 35-49 cm). In addition, fluid escape pipes were also noted in intervals 180-1118A-15R-3, 46-57 cm, and 16R-6, 51-59 and 82-87 cm.
Unit I accumulated during late Pliocene (to Pleistocene?) time in an inferred middle bathyal water depth (500-2000 m) at an estimated average sedimentation rate of 155 m/m.y. (see "Sediment Accumulation Rate"). The succession was mainly deposited by low-density turbidity currents alternating with hemipelagic mudstone. Flute casts formed by erosion at the head of a turbidity current, or load structures caused by differential compaction of sand and clay, are occasionally preserved at the base of individual beds. The bottom sediment was well oxidized, judging from the common bioturbation. A single interval of high carbonate content (72.5 wt%) combined with elevated organic carbon and sulfur is interpreted as a bioclast-rich interval associated with abundant pyrite (see "Discussion"). These bioclasts were possibly formed in a shallower water (but still pelagic) setting and then redeposited by turbidity currents. Below 330.0 mbsf the rare reddish, less burrowed intercalations are similar to more extensive reddish sediment found in Unit II (see "Lithostratigraphic Unit II") and may indicate times of relatively oxidizing bottom-water conditions. The mineralogy and petrography indicate relatively constant provenance from a basic-acidic volcanic terrain, based on the abundance of plagioclase and feldspar and small lithoclasts of basic volcanic rock seen in thin section. Tectonic instability, manifested by slumping, peaked at ~330.0-340.0 mbsf.
The geophysical logs (triple combo) reveal large-scale trends and variation in the succession (see "Downhole Measurements"). Above the cored interval (0-205 mbsf) alternating clay-rich and more sandy intervals are present. The geophysical logs suggest that the upper interval of minimal recovery (200.0-255.0 mbsf) is relatively clay rich, mainly based on the combined gamma-ray log and neutron porosity logs. The diameter of the borehole decreased here, suggesting the presence of abundant swelling clay. Some mixed-layer clay was detected in the adjacent interval lower in the succession that was recovered. Beneath 205.0 mbsf there is a relatively dense (calcareous?) clay-rich unit, followed from 291.5 to 289.8 mbsf by a more bedded, still clay-rich succession. Possible slumps or slides are imaged on the FMS from 285.5-290.5 mbsf, marked by apparently deformed bedding inclined in variable directions. Below 292.0 mbsf the succession apparently becomes generally more sandy with a pronounced sandy interval ~20 cm thick at 297.0 mbsf. More possible slumps or slides are seen from 308 to 309 mbsf on the FMS images. Below 347.0 mbsf, the succession becomes more clay rich with a carbonate-rich bed (<30 cm) at 363.0 mbsf. A large increase in the K/Th ratio at 376.5 mbsf suggests the presence of sandy volcaniclastic sediment at this level.
Lithostratigraphic Unit II is defined by the presence of distinctive intercalations of reddish silty claystone and clayey siltstone within greenish gray silty claystone, clayey siltstone, siltstone, and sandstone. In addition, some graded sandstone intervals are thicker (>5 cm) than those of Unit I. Furthermore, intervals of soft-sediment deformation were only rarely observed in Unit II. Calcium carbonate values in fine-grained sediment vary from 0.45 to 16.5 wt% and show no systematic variation downhole in Unit II (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). Otherwise, the lithologies present are very similar to those of Unit I and will be summarized only briefly.
The following lithologies are present in Unit II:
Typically, the intervals in which the dominant color is reddish or reddish brown, range from tens of centimeters to several meters thick. Commonly, these intervals are well laminated with relatively little or no bioturbation (Fig. F6). The reddish intervals are interbedded with grayish to greenish sandstones, siltstones, and some claystones (see "Dark Greenish or Grayish Clayey Siltstones"). Individual laminae are thin to thick and defined by subtle color changes. Very rare foraminifers are present. Good examples of well-laminated intervals are as follows: intervals 180-1118A-19R-4, 0-55 cm, and 22R-1, 0-30 cm; Sections 22R-2 and 3; intervals 180-1118A-23R-3, 25-35 cm; 23R-5, 0-89 cm; 24R-7, 20-66 cm; 25R-1, 22-25 cm; 25R-6, 68-124 cm; 25R-7, 0-49 cm; 25R-CC, 0-12 cm; and 26R-1, 0-23 cm; Section 27R-6; and interval 180-1118A-28R-1, 0-108 cm. In addition, Cores 28R and 29R include a number of reddish brown finely laminated intervals 5-20 cm thick.
Examination of smear slides reveals nannofossils, foraminifers, quartz, feldspar, mica, volcanic glass, volcanic rock fragments, and accessory minerals (e.g., hornblende; see "Site 1118 Smear Slides"). Pyrite is relatively rare compared to the darker greenish gray sediments. The XRD analysis of the fine-grained sediment revealed a very constant composition of calcite, plagioclase with minor amphibole, pyroxene, pyrite, and clay minerals (mainly chlorite and illite). Minor mixed-layer clay may also be present (Table T3).
These intervals are subordinate, estimated at 15%-25% of the recovered sedimentary rocks within this unit. Individual beds begin with planar-laminated, ripple- or wavy-laminated siltstone. Locally, starved ripples are present (interval 180-1118A-26R-4, 70-72 cm). The bed bases are sharp and commonly scoured. The upper parts of individual beds are homogeneous, dark gray or greenish gray, grading into silty claystone. The tops of individual beds are burrowed, and burrowing locally extends into the body of the bed above.
Rarely, fluidization and small fluid-escape pipes were noted in the siltstone. These features take the form of thin (<1 mm), wispy vertical linear veins just above the base of individual siltstones. The individual vertical linear vein structures are ~3-5 cm long and ~2-4 mm apart (e.g., interval 180-1118A-25R-3, 60-66 cm). These structures are unusual and were not noted in similar sediments in other holes during Leg 180.
Smear slides of this facies revealed quartz, feldspar, biotite, volcanic rock fragments, accessory minerals (e.g., hornblende), calcite, pyrite, nannofossils, and mainly planktonic foraminifers (see "Site 1118 Smear Slides").
From 415.0 mbsf normally graded sandstones are rarely more than a few centimeters thick. However, occasional thicker beds are present. For example, in interval 180-1118A-23R-4, 0-62 cm, a single sandstone bed (the lower 7 cm) grades into fine-grained sandstone (25 cm thick; Fig. F7), then into siltstone (30 cm thick). Sole marks (flutes and loads) are present at the base of some of these beds (e.g., interval 180-1118A-23R-6, 20-21 cm) and, in addition, low-angle ripple lamination (e.g., intervals 180-1118A-27R-5, 23-25 and 84-86 cm, and 27R-6, 90-92 cm), and wavy lamination (interval 180-1118A-27R-6, 96-98 cm) are locally present in the lower parts of individual beds. The sandstone rarely also shows evidence of fluid injection into overlying siltstone.
Smear slides reveal essentially the same compositions as within the generally finer grained sediments described above (see "Site 1118 Smear Slides"). In addition, thin sections of very fine grained sandstone from the base of normal-graded units revealed the following composition: angular grains of quartz, plagioclase, biotite, rare palagonite, planktonic foraminifers, fresh basaltic grains (with flow-banded feldspar microphenocrysts), rare chloritic grains, and common pyrite, especially within burrows, and planktonic foraminifer tests (Fig. F8; see "Site 1118 Thin Sections").
A zone of inclined lamination and folding was noted in interval 180-1118A-21R-4, 121-131 cm, and a small interval with dewatering structures was observed higher in the same core (Fig. F9) and again in intervals 180-1118A-21R-5, 21-34 and 78-83 cm. A further short interval of contorted and overturned bedding is seen in interval 180-1118A-27R-1, 93-106 cm.
Unit II, of mainly middle Pliocene age, records a continuation of very similar turbiditic and hemipelagic sediment as in Unit I. However, the sedimentation rate was substantially higher at ~435 m/m.y. and the depth of accumulation was reduced to upper bathyal (150-500 m; see "Sediment Accumulation Rate"). Unit II was recognized mainly on the presence of distinctive reddish, mainly fine-grained intervals that are finely laminated and lack all but incipient bioturbation. These intervals are interpreted to record times when bottom waters were relatively oxidizing, resulting in combustion of organic matter, and thus, a relatively unsuitable substrate for benthic fauna. Strong bottom-current activity might have inhibited benthic activity. An alternative explanation is that these sediments were relatively enriched in iron oxide when initially deposited and lacked nutrients. By contrast, the intercalated more greenish gray turbidites and hemipelagic sediments are rich in pyrite, especially in burrows and foraminifers, indicating that subsurface anoxia was developed. Rapid deposition of Unit II is consistent with the presence of fluid-escape structures, although these could have been tectonically triggered.
The XRD and smear-slide data indicate that there is little systematic difference in the provenance of the different sediment types discussed above, or any significant change from Unit I in this regard. The abundance of quartz, plagioclase, and basic volcanic rock fragments points to a mainly volcaniclastic origin, including basaltic rocks. In addition, acidic volcanic glass is a minor component of Unit II. Seafloor conditions were more stable than during the accumulation of Unit I, based on the rarer occurrence of soft-sediment deformation structures.
The geophysical logs indicate a continuation of a very similar muddy succession as in Unit I, including rare medium thickness (<15 cm) sandstone beds, based mainly on the natural gamma-ray and neutron porosity responses (see "Downhole Measurements"). At 287.5 mbsf there is a marked increase in resistivity seen on the FMS images as a bright blotchy image that may reflect increased calcium carbonate content in view of the increased photoelectric response. This enhanced photoelectric effect response might also relate to the increased presence of iron oxide that imparts the distinctive reddish color to Unit II. From 402.0 to 411.0 mbsf an inferred sand interval shows a high Th/K ratio that is interpreted as three main volcaniclastic turbidites (each ~30 cm thick), based on the FMS images. Beneath this, the succession is well bedded, corresponding to the turbiditic deposits cored. At 437 mbsf the succession apparently becomes more claystone rich, but still with sandstone intercalations marked by high thorium, uranium, and potassium log responses.
Lithostratigraphic Unit III is marked by a return to a mainly grayish green succession of sandstones, siltstones, and hemipelagic sediments similar to those of Unit I. Calcium carbonate analyses indicate a downward trend of generally increasing carbonate content from ~3 to 25 wt%. Occasional volcanic ash layer samples exhibit much lower values, and some intervals between 610.0 and 635.0 mbsf have values of 30-35 wt% (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). The lithologies are as follows:
As in Units I and II, silty claystones and clayey siltstones constitute the background sedimentation. These sediments are typically greenish to grayish, burrowed, with rare foraminifers and small shell fragments. The sediments are typically paler colored (e.g., see Section 37R-5) than the two main types of graded sandstones as discussed below. The silty claystone and clayey siltstone are mainly structureless, but are rarely thinly laminated to thinly bedded. Some thin beds and laminae exhibit sharp bases, but some bed bases are diffuse, even where not affected by burrowing (e.g., Section 43R-6). Occasionally, large burrows are elliptical (intervals 180-1118A-42R-6, 78-80 and 86-88 cm). The XRD analysis of the fine-grained sediment revealed a remarkably constant composition with calcite, plagioclase, quartz, also minor amphibole, pyroxene, chlorite, illite, smectite?, and pyrite (Table T3).
Interbeds of siltstone/silty claystone 5-15 cm thick are found throughout Unit III. Typically, several such interbeds are present per section, but up to 10 per section were observed in certain cores (e.g., Section 44R-5). Beds typically begin with several millimeters of well-sorted siltstone and pass up into dark greenish gray structureless, or parallel-wavy-laminated siltstone (Fig. F10), locally with common planktonic foraminifers (e.g., interval 180-1118A-35R-4, 13-50 cm). Most of these very thin beds lack burrowing. Locally, near the top of the unit, some thin-bedded (<3 cm) sandstones are dark reddish brown as in Unit II (e.g., Section 31R-1 and interval 180-1118A-31R-2, 43-65 cm). The tops of individual beds are strongly burrowed (mainly Chondrites type). The burrows are infilled with silty claystone or sandstone rich in ferromagnesian mineral grains. Near the base of the unit, siltstones are occasionally dark yellowish brown (e.g., interval 180-1118A-44R-7, 22-29 cm). Below 640 mbsf graded siltstone/silty claystone couplets become less numerous, whereas thicker bedded, graded sandstones/siltstones increase in relative abundance (see "Sandstone/Siltstone"). Smear slides reveal compositions effectively identical to that of the sandstone/siltstone (see following section; also see "Site 1118 Smear Slides").
The sandstones/siltstones range from medium to fine grained and thin to medium bedded with erosional bases. They are structureless, exhibit normal grading, parallel, wavy (e.g., interval 180-1118A-33R-2, 99-103 cm, and Section 34R-3), or ripple laminated (intervals 180-1118A-33R-1, 104 cm; 37R-2, 28-31 and 75-87 cm). Approximately seven graded sandstone beds occur per core section (e.g., Section 44R-5). Most of the beds are greenish gray; however, near the top of the unit a few sandstone beds are dark reddish brown (e.g., Sections 31R-5 and 6; and intervals 180-1118A-33R-3, 126-139 cm, and 33R-4, 87-89 cm).
In detail, some individual thin beds have a scoured base followed by beds of planar lamination (Fig. F11), followed by beds of ripple lamination (5-7 cm), then followed by structureless siltstone and claystone. Rarely, climbing-ripple lamination is observed with a high angle of climb (Fig. F12). Small (1 cm) basal flutes or load casts are occasionally present (e.g., interval 180-1118A-35R-5, 14-16 cm). A few beds exhibit convolute lamination (e.g., interval 180-1118A-46R-3, 140-144 cm), or small water-escape structures (Fig. F13). The tops of beds are commonly bioturbated, and the tops of the individual graded units are often obscured by intense burrowing. Up to 6-10 graded beds were observed per section in some cores (e.g., Section 36R-5).
Near the base of the unit the thickness of the individual sandstone/siltstone couplets increases to a maximum of ~35 cm. Such sandstones show planar and cross lamination and grade up into silty claystone and siltstone (e.g., interval 180-1118A-45R-6, 53-94 cm). The upper parts of the beds are composed of dark siltstone that is variably burrowed, making the top of individual beds hard to recognize. In addition, near the base of the unit there are occasional intervals of bed amalgamation, including normal-graded sandstone, small-scale climbing-ripple lamination, and clayey intercalations (e.g., interval 180-1118-47R-6, 40-145 cm). Individual cross laminations show differing dip orientations within single core sections.
Many of the sandstone beds are rich in volcaniclastic detrital grains. Also, carbonaceous grains are locally abundant. Smear slides reveal the presence of nannofossils, mainly planktonic foraminifers, quartz, feldspar, plagioclase, mica, volcanic rock fragments, volcanic glass, calcite, and pyrite (see "Site 1118 Smear Slides"). Seven thin sections of fine- to coarse-grained sandstone showed very similar compositions (see "Site 1118 Thin Sections"). Most of the sandstones are relatively well sorted with angular to subrounded grains in different thin sections. Normal grading is clearly seen in some cases. Mineral grains are mainly plagioclase and quartz, with biotite, amphibole, and pyroxene. Rock fragments are abundant mainly of basic volcanic rocks with flow-banded feldspar microphenocrysts, variable occurrences of fresh colorless volcanic glass, also rare palagonite, acidic and chloritic volcanic grains, rare calcite grains (micrite and microspar), and a few shell fragments (Fig. F14). Pyrite is unusually abundant within the matrix as well as in the foraminifers. The matrix is largely fine-grained carbonate.
The basic volcanic rocks are commonly present as small clasts, transitional to matrix (e.g., interval 180-1118A-35R-1, 140-143 cm). In several cases (e.g., interval 180-1118A-34R-3, 61-63 cm) individual laminae are packed with broken and intact planktonic foraminifers and form discrete laminae (interval 180-1118A-44R-4, 29-30 cm). One sample is a mixed carbonate-volcaniclastic sandstone with most of the above mineral and rock grains mixed with abundant derived micritic grains and mainly planktonic foraminifers (interval 180-1118A-43R-7, 63-64 cm). Individual foraminifer tests (commonly pyrite filled) are coated with fine calcite spar.
Thin beds of light gray volcanic ash are found sporadically (e.g., intervals 180-1118A-32R-4, 99-99.5 cm, and 37R-4, 52-57 cm). Most of these ash beds are distinguished by a relatively uniform fine grain size, light gray to yellowish brown color, and low calcium carbonate content (<3 wt%). A further four thin beds (1-5 cm) of sandstone to siltstone were identified as crystal-rich volcanic ash (interval 180-1118A-43R-60, 52-62 cm). Thin volcanic ash laminae also are present in interval 180-1118A-44R-2, 103-112 cm. Smear slides mainly reveal abundant colorless volcanic ash. In addition, one thin section in interval 180-1118A-38R-3, 128-130 cm, was found to comprise bubble-wall colorless glass shards in an isotropic fine glass-rich matrix (Fig. F15, see also "Site 1118 Thin Sections").
These features are rare in Unit III. For example, a small interval of inclined to recumbent folding within structureless silty claystone and overlying planar-laminated sandstone is seen in interval 180-1118A-31R-2, 56-64 cm (Fig. F16). The top of this convolute interval is capped by small dewatering or flame structures (several millimeters long). Additional very small convolute, folded intervals with flame structures are seen in the same section at intervals 180-1118A-31R-2, 71-73, 78-80, 93-97, 109-110, 22-123, and 137-138 cm. Another short interval of inclined lamination was observed in interval 180-1118A-39R-1, 53-56 cm. In one instance, an interval of soft-sediment deformation is marked by "plastically" deformed clasts of silty claystone, including very coarse grained to granule sandstone and shell and organic fragments (interval 180-1118A-40R-1, 105-120 cm). Small sand-injection structures were also noted in interval 180-1118A-47R-6, 63-77 cm.
Unit III accumulated in the middle Pliocene at upper bathyal water depths (150-500 m) at an estimated very rapid average sedimentation rate of 479 m/m.y. In detail, Unit III spans two intervals when accumulation rates are determined as 435 and 485 m/m.y. (see "Sediment Accumulation Rate"). The unit records further turbiditic and hemipelagic sedimentation. However, near the base of the unit (below 640 mbsf) few turbidites are identifiable. In contrast to Unit II, reddish thinly laminated intervals are not developed. Although still sporadic throughout the unit, volcanic glass is more abundant than in Unit II. The provenance of the turbiditic sandstone/siltstone remains little changed from Unit II. However, some sandstones are extremely rich in lithic clasts derived from basic volcanic rocks. Also, some sandstones contain calcium carbonate grains and concentrations of planktonic foraminifers that were probably redeposited from an upslope but still pelagic setting.
In addition, the geophysical logs suggest that much of Unit III is more sandy than above. Individual intervals 1-2 m thick are composed of inferred "radioactive" (i.e., volcaniclastic) sandstone. From 587.0 to 613.0 mbsf the combined density, neutron porosity, and (low) photoelectric log responses suggest the presence of sand that is "nonradioactive" in contrast to that above. Several different provenances of volcaniclastic sandstone are implied (see "Downhole Measurements"). The FMS shows that this interval is well bedded.
Lithostratigraphic Unit IV is marked by the disappearance of regular- graded couplets and the appearance of more variably bedded volcaniclastic sandstones, siltstones, mixed sediments (e.g., sandy silty claystone), and common volcanic ash. Ash-poor fine-grained sediments contain ~20-30 wt% calcium carbonate, whereas volcanic ash is strongly depleted in calcium carbonate and in organic carbon (<4%) (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). The following lithologies are present in Unit IV:
Silty claystones and clayey siltstone differ from counterparts in the overlying units in that they are less regularly bedded and commonly contain admixtures of detrital volcaniclastic grains and volcanic ash (i.e., sandy silty claystone; e.g., Section 56R-5). Some bed bases are diffuse and ill defined (e.g., interval 180-1118A-57R-1, 0-16 cm). Most of the silty claystones and clayey siltstones have a uniform olive green color (dark gray to greenish gray; Fig. F17). In places these sediments contain scattered bioclasts, shell fragments, planktonic foraminifers, and fragments of terrestrial organic matter. Burrows are typically small Chondrites and larger Zoophycos as seen elsewhere. These sedimentary rocks are mainly sparsely burrowed, in contrast to the very strong bioturbation seen in the overlying units (although some intervals are strongly burrowed; Fig. F17). Some burrows are infilled with fine- to medium-grained volcaniclastic sandstone.
Sandstones/siltstones are well developed between 730.0 and 790.0 mbsf. Up to six discrete normal-graded sandstone/siltstone beds occur per section (Fig. F18). The sandstones and siltstones rarely exhibit parallel lamination or wavy lamination (e.g., interval 180-1118A-59R-2, 24-48 cm). Individual beds are mainly sharp based and erosional (e.g., interval 180-1118A-60R-2, 53-56.5 cm), but a few have diffuse bases not only owing to bioturbation (e.g., interval 180-1118A-50R-4, 24-27 cm). The sandstones are medium to fine grained, with concentrations of volcaniclastic grains, including dark ferromagnesian mineral grains (hornblende and biotite) and scattered shell fragments. The sandstone mainly changes abruptly into silty claystone. Some graded beds exhibit parallel, ripple, and wavy lamination (interval 180-1118A-59R-2, 24-48 cm). Also, small (1 cm) load casts are locally present at the base of some beds (e.g., interval 180-1118A-63R-5, 98-98.5 cm). Some of the graded sandstones are very rich in volcanic glass, although they differ from the more homogenous volcanic ash described below. In these sandstones the distinction between volcaniclastic sandstone and volcanic ash becomes difficult.
Three thin sections of sandstone (see "Site 1118 Thin Sections") contain common angular grains of quartz, plagioclase (including large zoned crystals), hornblende, rare pyroxene, common lithoclasts of flow-banded basalt, vesicular colorless glass, and rare acidic extrusive grains. Individual fragments of volcanic glass include (co-magmatic) phenocrysts of hornblende and biotite, planktonic foraminifers, rare fragments of calcareous algae, and shell fragments. Foraminifers are lined with calcite spar overgrowths. One sample (interval 180-1118A-58R-3, 38-40 cm) is rich in biotite laths defining lamination.
This unit comprises numerous variable, intermixed sediment types. Occasional interbeds are greenish clay-rich siltstone with scattered planktonic foraminifers concentrated near the tops of individual beds (e.g., interval 180-1118A-50R-5, 0-24 cm). The sandy siltstone includes admixed detrital grains, foraminifers, and bioclast fragments. In addition, the sandy silty claystone has a high concentration of detrital sand grains most abundant near the base of individual beds (e.g., interval 180-1118A-57R-3, 52.5-73 cm). Sandy silty claystones are also locally rich in bioclasts and foraminifers (interval 180-1118A-63R-5, 101-122 cm). Some beds are sharp based and graded, but others are nearly homogenous with diffuse bed tops and bases, especially where disrupted by burrowing (e.g., interval 180-1118A-57R-1, 124-130 cm).
Smear slides contain quartz, feldspar, plagioclase, biotite, volcanic rock fragments, volcanic ash, calcite, pyrite, nannofossils, foraminifers, and sponge spicules (see "Site 1118 Smear Slides"). In addition, XRD analysis reveals common calcite, plagioclase, quartz, and minor illite, pyrite, amphibole, and chlorite (see Table T3).
Common volcanic ash layers are distinguished by a distinctive pale buff color and are present as laminae to thin beds. Some of the volcaniclastic sandstones are very rich in volcanic glass, as mentioned above. Grain size ranges from very fine through medium to rarely coarse grained. Most have sharp bases and are graded. Some beds are graded and exhibit well-developed parallel lamination (intervals 180-1118A-59R-5, 59-62 cm, and 59R-6, 53-55 cm). Many beds begin with medium, fine, or very fine grained sandstone and pass into siltstone that becomes darker upward merging with greenish silty claystone. Burrowing in the volcanic ash is relatively minor except at the top of some thin beds (Fig. F19).
Examples of very fine grained volcanic ash laminae are seen in intervals 180-1118A-53R-1, 92 cm; 54R-1, 46-47 cm; 56R-1, 34-44.5 cm; 56R-1, 70-70.5 cm; and 56R-5, 26-29 cm. Seven discrete beds of volcanic ash up to 9 cm thick are present in Section 57R-4. Lower in the succession (below 745.0 mbsf) some ash layers are crystal rich (e.g., interval 180-1118A-58R-1, 123-126 cm). Thin beds of volcanic ash in interval 180-1118A-58R-5, 50-51.5 cm, exhibit sharp bases and tops. Volcanic ash is also conspicuous in Sections 59R-5 (as three thin interbeds) and 63R-5 (as five very thin beds), and in intervals 180-1118A-62R-3, 73-75 cm, and 63R-4, 0-9 cm. Furthermore, a small number of composite glass-rich intervals are present as repeated thin beds and laminae showing repeated grading and parallel lamination (e.g., interval 180-1118A-63R-4, 0-9 cm).
Two thin sections of volcanic ash revealed a mixed glassy and detrital origin. In addition to abundant angular shards of colorless volcanic glass and grains of plagioclase, quartz, biotite, and hornblende, lithoclasts of basic and acidic volcanics were observed. Individual fragments of volcanic glass again include phenocrysts of hornblende and biotite (Fig. F20; see "Site 1118 Thin Sections").
In Unit IV these are restricted to small elongate, subvertical sand-filled dewatering structures (e.g., interval 180-1118A-63R-5, 100-122 cm).
Unit IV accumulated in the middle Pliocene at upper bathyal water depths (150-500 m) at an estimated sedimentation rate of ~485 m/m.y. (see "Sediment Accumulation Rate"). Unit IV marks a significant change from the mainly hemipelagic and turbiditic sediments of Units I through III to generally coarser grained sediments with more variable sedimentary structures. Although some beds still show clear evidence of deposition from turbidity currents (grading, partial Bouma sequences, and sharp bases; see above), many others exhibit contrasting features, including sharp bed tops. These features are suggestive of reworking by currents other than turbidites. In addition, there is a relatively greater input of calcium carbonate mainly in the form of micritic matrix and micritic clasts. A number of laminae very rich in planktonic foraminifers were probably redeposited from further upslope, based on the textural evidence. Pelagic carbonate was also redeposited as micritic clasts.
Acidic volcanic glass is abundant in Unit IV. This glass is co-magmatic with biotite and hornblende phenocrysts. Similar crystals associated with volcanic glass fragments are present in abundance in the interbedded volcaniclastic sandstones and siltstones. Thus, the volcanic ash layers and the glass-rich clastic sediments are inferred to relate to the same episode of contemporaneous volcanism.
The geophysical logs must be interpreted with caution because the caliper indicates markedly larger borehole diameter in the lower part of the unit (beneath 740.0 mbsf). However, the logs indicate that Unit IV is sandy, more so than Unit III. From 682.0 to 735.0 mbsf, an interval of very poor recovery, sands of "nonradioactive type" appear to be present, based on the low K/Th ratio. The sandstone intervals show up as "fuzzy" on the FMS, in addition, interbedded with several thin, more claystone-rich intervals. From 735.0 mbsf the succession appears to become more muddy, alternating with more sandstone intervals down to 839.0 mbsf. The sandstone remains of "nonradioactive type" (with low thorium and potassium; see "Downhole Measurements").
Lithostratigraphic Unit V is characterized by variably interbedded, poorly sorted, mixed sandy and silty claystones, siltstones, and cemented sandstones with local lithic fragments. Coarse-grained sandstones rich in bioclasts are present in the lowermost 10 m of the unit. By contrast with Unit IV, primary volcanic ash is minimal. Calcium carbonate values are mainly high, ranging from 10 to 33 wt% (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). The following lithologies are present:
This is greenish gray, burrowed, with scattered volcaniclastic grains. Bedding is irregular with sharp bases and tops to individual beds. Small lithoclasts (<1 cm) of volcanic rock are rarely present (e.g., interval 180-1118A-64R-1, 50-53 cm; and Sections 66R-3 and 67R-CC. Fragments of wood were noted occasionally (intervals 180-1118A-65R-1, 109.5-111 cm; 66R-1, 101.5 and 138.5 cm; 66R-2, 60 cm; and 66R-CC, 6-27 cm). Common concentrates of quartz, feldspar, and ferromagnesian grains are present. Burrows include possible rare Zoophycos (Section 66R-4). Locally, the claystone is admixed with detrital volcaniclastic grains and volcanic ash (Fig. F21). In one case, claystone (rich in volcanic ash) is thickly interlaminated with medium- to coarse-grained volcaniclastic sandstone (Section 66R-CC).
These sediments are moderately to strongly burrowed with scattered shell fragments, detrital grains, and planktonic foraminifers (Fig. F22). Burrows are infilled with siltstone or sandstone, as seen in overlying units. The bases of individual beds are commonly diffuse, and overall, bedding is weakly defined (Section 67R-1). Rare intervals of reverse grading are typically disrupted by burrowing. Elliptical burrows and minor pyrite were observed locally (e.g., interval 180-1118A-65R-4, 99 cm). Lower in the unit (from ~825.0 mbsf) silty claystone is interbedded with fine- to medium-grained sandstone with diffuse intergradational boundaries (e.g., Section 65R-CC). Some beds show sharp bases as well as tops (e.g., interval 180-1118A-66R-5, 14-21 cm).
This sediment is medium to thick bedded, with sharp, scoured bases (e.g., interval 180-1118A-64R-2, 9-12 cm). Colors range from greenish gray to dark gray. Burrowing is extensive with individual burrows being locally infilled with pyritic sandstone. Numerous lithic clasts and bioclasts are present, including foraminifers and shelly fragments. The latter include cross sections of complete thin-shelled bivalves (Section 65R-5). Sparse carbonaceous grains are also present (e.g., Section 64R-1). Parallel and wavy lamination were noted. Sandstone-siltstone commonly grade into siltstone and claystone at the top of individual beds (e.g., interval 180-1118A-64R-2, 9-12 cm), but the contact is often diffuse as a result of extensive burrowing. Commonly, the base of individual graded units was not recovered. The sandstone is mainly well cemented with calcite spar.
In general, the sandstone is mainly fine to medium grained in the upper part of the unit, but is locally coarse grained in the lower part (below ~850 mbsf). This sandstone shows only a very weak bedding. Sand grains are angular, but relatively well sorted (e.g., Section 67R-5).
This is restricted to near the base of the unit. It is dominated by poorly sorted, medium-grained, rarely normally graded, weakly bioturbated calcareous sandstone with common, but scattered, bioclasts including thin shell fragments, planktonic and benthic foraminifers, coralline algae, and coral fragments (e.g., interval 180-1118A-68R-2, 117-118.5 cm; Fig. F23). Granule-sized clay-rich clasts (0.8 cm × 0.2 cm × 0.3 cm) were observed subparallel to each other (e.g., interval 180-1118A-68R-1, 54-74 cm). The orientation of bioclasts defines a weak horizontal bedding. The sandstone locally passes downward into finer grained, more muddy sediment (interval 180-1118A-68R-3, 40-60 cm). A small number of subrounded to rounded pebbles of basic volcanics were noted at the base of the unit (interval 180-1118A-68R-3, 110-115 cm).
A thin section of heterogeneous laminated sandstone (interval 180-1118A-64R-1, 49-61 cm) consists of laminae of different composition (see "Site 1118 Thin Sections"). Graded volcaniclastic laminae are composed of volcanic glass, quartz, feldspar, biotite, and hornblende in a calcite spar matrix. In addition, intercalated laminae are rich in micrite with particles of volcanic glass (as globular fragments).
The above bioclastic-rich sandstone is interbedded with much less calcareous, darker, well-cemented planar-laminated, coarse-grained sandstone, composed of angular quartz, feldspar, and ferromagnesian mineral grains (e.g., interval 180-1118A-68R-3, 60-64 cm). Only rare small bioclasts are present in this sandstone (Fig. F24).
Olive green, weakly calcareous homogenous silty claystone forms a very minor amount of Unit V (e.g., within interval 180-1118A-64R-1, 36-38 cm). The XRD analysis of this fine-grained sediment indicates the presence of calcite, plagioclase, quartz, illite, and minor pyrite and amphibole (Table T3).
Local small-scale subvertical sand-injection structures are present (e.g., interval 180-1118A-64R-1, 60-63 cm). In one case the injected sandstone directly underlies the base of a sandstone bed (e.g., interval 180-1118A-64R-1, 21.5-23 cm). In another case, possible sand injection up a small, steeply inclined fault plane was observed (interval 180-1118A-64R-1, 108-120 cm; see "Structural Geology").
Unit V accumulated mainly in the middle Pliocene. However, the lowest part of the unit (Section 68R-3) accumulated in the latest early Pliocene. Upper bathyal depths are inferred from benthic foraminifers. The sedimentation rate remains high, averaging about 480 m/m.y. (see "Sediment Accumulation Rate"). Unit V is inferred to record well-oxygenated, mixed hemipelagic and turbiditic sediments, but the succession was also influenced by traction currents within a slope setting adjacent to a landmass. The presence of irregular bedding and sharp tops to many units specifically attest to a traction current influence. A vegetated adjacent landmass is inferred from the presence of sporadic wood fragments. A relatively higher input of neritic bioclasts (including coral fragments, coralline algae, and benthic foraminifers) near the base of the unit is indicative of proximity to a carbonate margin.
In addition, the geophysical logs of this short interval suggest that it is sandy, especially toward the base (below 851.0 mbsf), based on the resistivity and gamma logs and that this material is not "radioactive," similar to the sands in Unit III above. A very resistant inferred medium bed of sandstone (<30 cm) is seen on the FMS at 815.0 mbsf (see "FMS Images"). Finally, around 850.0 mbsf there was a marked input of very "radiogenic" sand, as also seen in Unit VI (see "Lithostratigraphic Unit VI").
Lithostratigraphic Unit VI is dominated by a thin interval of packstone/grainstone rich in bioclasts of shallow-water carbonate. The upper contact is marked by an irregular contact between pale packstone/grainstone below and well-cemented calcareous sandstone of Unit V above. The base of the unit is marked by a gradational change from packstone/grainstone to conglomerate in Section 69R-1 (see "Lithostratigraphic Unit VII"). Two calcium carbonate analyses yielded values of ~82 and 91 wt% (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). The following lithology is present:
This is made up of poorly sorted bioclastic fragments (up to 2.5 cm long), including calcareous algae, coral, echinoderm debris, bivalve shells, and benthic foraminifers. The material is well cemented by calcite spar. In places intact rhodoliths are present. The limestone includes wispy, irregular laminae composed of silty clay with detrital grains (Fig. F25). Sand-sized detrital grains are also scattered through the packstone/grainstone as a whole. In addition, rare siliciclastic granules or small pebbles of dolerite and basalt are locally present (e.g., interval 180-1118A-69R-1, 0-9 cm). There are also intervals with rare angular, to subrounded, to rounded pebbles of basalt/dolerite with bioclastic fragments giving rise to ill-defined beds (e.g., Section 69R-1). Some of the bioclasts, especially those composed of aragonite (e.g., coral), are dissolved to form secondary solution porosity.
Thin sections reveal that texturally the limestones are packstone/grainstone (see "Site 1118 Thin Sections"). The main biogenic components are calcareous algae, shell fragments, benthic foraminifers, bryozoans, echinoderm debris, occasional coral fragments (dissolved), and rare small planktonic foraminifers (globigerines). In addition, scattered detrital grains are present (quartz, plagioclase [zoned], hornblende, and biotite). Lithic grains are aphyric basalt, basalt with large feldspar phenocrysts, rare felsic and rare chloritized grains, and micritic clasts. Bryozoans are locally encrusted with calcareous algae. Remnants of a micritic matrix are also present together with a pyrite-calcite spar cement. Pyrite is locally abundant.
Unit VI accumulated during early Pliocene, or earlier, and included reworked benthic foraminifers (see "Benthic Foraminifers"). This limestone is a shallow-water carbonate with coralline algae, coral fragments, echinoderm debris, benthic foraminifers, and other bioclasts. The matrix was originally micritic, but was later dissolved and replaced by calcite spar. This evidence, and the state of preservation of delicate algal material (e.g., as original algal mats) shows that the bioclastic material originally accumulated in a relatively low energy setting, probably a lagoon or embayed area open to marine circulation. In addition, a coastal setting is suggested by admixing with detrital lithoclastic grains of basalt/dolerite. However, there is little evidence of coeval volcanism, in contrast to the overlying units (see sections above).
The geophysical logs, especially the photoelectric effect log, confirm that it is a very carbonate rich interval ~3 m thick from 857 to 860 mbsf. This indicates that the recovered packstone/grainstone is about one-half of that present. Limestone is present down to 860.2 mbsf, followed by sandstone, based on the gamma-ray log. This sandstone corresponds to an interval of very radiogenic sand (with a Th/K ratio of up to 10; see "Lithologic Analysis").
Lithostratigraphic Unit VII is defined by the presence of poorly sorted paraconglomerate composed of basic igneous rock clasts set in a matrix of neritic bioclastic carbonate. The upper contact is seen to be gradational on the FMS log (see paragraph below). The lower contact is a sharp, subhorizontal, planar surface separating sandy limestone above from dolerite below. The measured calcium carbonate content varies from 67 to 84 wt% (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen"). The following lithologies are present:
This is a pebbly, mixed sediment with bioclastic debris, as described above, mixed with mainly subrounded to rounded granules and pebbles of basalt and dolerite together with common quartz, feldspar, and ferromagnesian detrital grains. There is well-developed calcite spar cement. The largest pebble recovered is 6 cm in length (Fig. F26). A small number of intact rhodoliths are preserved (e.g., Section 69R-2). The largest pebbles are preserved in the middle part of the unit (interval 180-1118A-69R-3, 35-65 cm). None of the clast-rich intervals define a clast-supported texture. In addition, individual pebbles exhibit pale alteration rims and are coated with calcium carbonate (Fig. F27).
All of the bioclasts exhibit secondary solution porosity that is not seen in more sandy material. Rare vugs are present (<1 cm × 1 cm) with a lining of drusy calcite. Rare coral fragments are preserved only as internal molds (e.g., Section 69R-CC).
Coarse, to very coarse grained, mixed sandy limestone and calcareous sandstone dominate the lower 1 m of the unit. This includes common poorly sorted, but well-rounded pebbles and granules of dolerite and basalt together with neritic bioclasts, notably calcareous algae, rhodoliths, coral, and shell fragments (Fig. F28). In addition, well-sorted calcareous bioclast-rich medium-grained limestone <10 cm thick rests directly on dolerite beneath (interval 180-1118A-70R-1, 80-87 cm). Several thin layers of wavy-laminated, disrupted algal micrite are present (interval 180-1118A-70R-1, 3-12 cm). Also, just above the contact with the underlying basic igneous rock, two intact pieces of homogenous calcareous algae were recovered (interval 180-1118A-70R-1, 70-80 cm).
Thin sections contain abundant fragments of calcareous algae (locally rounded), shell fragments, benthic foraminifers, echinoderm plates, also rare echinoderm debris, bryozoans, and coral fragments together with rounded fresh aphyric basalt granules, rare chloritized basic and acidic extrusive igneous rock, and detritus, including grains of quartz and feldspar (see "Site 1118 Thin Sections"). Echinoderm spines are lined with prismatic calcite spar. There is a cement composed of blocky calcite spar (Fig. F29). Several thin sections show evidence of a primary micritic matrix replaced mainly by calcite spar.
In addition, XRD analysis of the sandstone contains calcite and subordinate plagioclase, quartz, amphibole, and illite (Table T3).
Unit VII lacks age-diagnostic fossils and can only be said to have accumulated in early Pliocene time, or earlier (see "Biostratigraphy"). This is a mixed sediment composed of detritus of shallow-water carbonate material as in Unit VI (see "Lithostratigraphic Unit VI"), mixed with rounded pebbles and granules of basalt and dolerite, as seen in Unit VIII (see "Lithostratigraphic Unit VIII"). The igneous clasts are inferred to have been rounded and then mixed with shallow-water carbonate. In view of the presence of underlying inferred river conglomerate (see "Lithostratigraphic Unit VIII") it is likely that the conglomerate was supplied fluvially. The probable setting is a coastal area affected by waves or currents. However, the algal mats and a primary micritic matrix is suggestive of a relatively low energy setting, possibly a marine lagoon or embayed area, as inferred for Unit VII. During diagenesis much of this micritic matrix was replaced by sparry calcite. In addition, the base of the unit is marked by a sharp planar, slightly inclined (6º-7º) contact of the unit between well-washed shallow-water carbonate and dolerite. This contact may represent a wave-cut platform (Fig. F30), although FMS interpretation suggests that, alternatively, it may be an artefact of drilling.
The FMS logs confirm that much of Unit VII is conglomeratic, corresponding to the paraconglomerate recovered. The logs additionally show that major spikes in gamma ray, thorium, potassium, photoelectric effect, and velocity are present at 860.2-816.7 mbsf. These are interpreted as a "radioactive" volcaniclastic sandstone. Below 865 mbsf the gamma log was not available, making interpretation more tentative (see "Downhole Measurements"). However, the combined neutron porosity, photoelectric logs, and FMS resistivity logs indicate the presence of a carbonate-rich interval near the base of the unit (869.2-873.1 mbsf) in agreement with the material recovered.
Lithostratigraphic Unit VIII is mainly dolerite as described in "Unbrecciated Dolerite". However, a small number of thin sedimentary intercalations are present. The FMS images are critical in showing that at least from 890 mbsf upward a very coarse conglomerate is present with no intact dolerite (Fig. F30). Details of the recovery are as follows:
Well-lithified calcite-cemented sandstone is found as two pieces ~60 cm beneath the highest location of basalt/dolerite (i.e., within interval 180-1118A-70R-2, 0-14 cm). This sandstone comprises well-rounded bioclastic grains, including calcareous algae together with angular to rounded lithoclasts of basalt/dolerite and black breccia (see paragraph below). The breccia lithoclast has angular grains of basalt/dolerite in a matrix of well-cemented, black, fine-grained sandstone with scattered granules. The lithology of this clast is the same as that of the black breccia described below. A thin section reveals poorly sorted, rounded grains of basalt/dolerite and rare large, altered plagioclase grains set in a chloritic silty matrix (see "Site 1118 Thin Sections").
This material is present ~60 cm lower in the recovered succession beneath clasts of breccia. The black breccia is composed of subangular to subrounded clasts of relatively fresh dolerite/basalt, plus a few outstanding orange, weathered clasts set in a matrix of well-lithified black siltstone with subangular granules of basalt/dolerite. Additional very similar fragments of black breccia and sandstone are seen in the underlying interval (interval 180-1118A-70R-3, 0-50 cm).
In addition, a few pieces of polymict breccia were recovered in the underlying core (intervals 180-1118A-71R-1, 13-15 and 51-61 cm). A thin section of this rock revealed subrounded lithoclasts of basalt and dolerite in very variable states of alteration in a matrix of volcaniclastic silt (derived from basalt), sand-sized basalt and dolerite grains, and rare pyroxene and green chloritic material (Fig. F31; see also "Site 1118 Thin Sections"). A few calcite grains are also present. XRD analysis revealed plagioclase quartz, K-feldspar, and smectite? (Table T3). Another thin section (interval 180-1118A-71R-1, 29-31 cm) is dominated by subrounded granules of very variably altered basalt/dolerite in a matrix of greenish chloritic material (see "Site 1118 Thin Sections"). In Section 72R-1 three intervals of polymict breccia were noted (Fig. F32). Core 74R includes pieces of weathered dolerite that in some cases appear to be derived from conglomerate as the fragments are subangular to rounded. Furthermore, within Section 74R-3 a number of isolated dolerite pieces are present, which are inferred to represent clasts within conglomerate that were disaggregated by drilling.
Additional clasts and sediments were recovered in Core 180-1118A-75R, as follows:
Several individual pieces of basalt are cut by small (2-3 mm) fissures infilled with orange brown sandy siltstone (interval 180-1118A-75R-1, 114-115.5 cm).
Several pieces were recovered of poorly sorted dark brown angular granules of basalt/dolerite with a matrix of sand grains and granules (up to 3 mm in size). These grains show variable weathering and alteration (interval 180-1118A-75R-1, 80-85 cm).
This was encountered as a piece (interval 180-1118A-75R-2, 0.3 cm) of angular to subangular to locally rounded breccia with pebbles and granules of mainly basalt and dolerite in a dark brown clayey siltstone matrix. In addition, three pieces of matrix-supported breccia were recovered lower in the succession (interval 180-1118A-76R-1, 40-57 cm). The matrix-supported breccia contains angular to subrounded clasts of dolerite/basalt within a orange brown sandy and silty matrix showing very variable degrees of weathering of individual grains. The clasts include coarse-grained sandstone composed of subrounded grains and granules (i.e., second-cycle conglomerate clasts). Some of the derived clasts in the primary conglomerate include fragments of basalt/dolerite that have undergone onion-skin weathering and alteration. The matrix of the breccia is cut by small calcite veins.
Several pieces of basalt/dolerite coated with poorly sorted sandy siltstone were recovered (interval 180-1118A-75R-2, 3-10 cm).
One piece of weathered basalt/dolerite was recovered including a mud-filled fissure (interval 180-1118A-75R-2, 28-43 cm). This is infilled with dark brown sandy silty claystone, including scattered small basalt/dolerite clasts in variable states of alteration. In addition, the adjacent basalt/dolerite is very strongly weathered and fissured. Individual fissures (weathering cracks) are infilled with mud. Another piece (interval 180-1118A-76R-2, 113-119 cm) of very weathered dolerite is fissured with an infilling siltstone, sandstone, and granules of orange weathered basalt/dolerite.
The lowest sediment to be recovered (interval 180-1118A-76R-2, 113-119 cm) comprises small pieces (i.e., a drilling breccia) of very altered orange brown silty claystone with small clasts (sand and granule sized) of very weathered basalt/dolerite. Some of these clasts are very well rounded.
An interpretation of Unit VIII is heavily dependent on interpretation of the FMS log data. Also, there is an (excessive) offset between FMS depths and triple-combo depths that complicates comparisons. The gamma-ray log is not available and the neutron porosity log ends at 872 mbsf. Conglomerate appears at 873.1 mbsf. There is a fairly sharp contact between inferred large (tens of centimeters), rounded clasts of basalt/dolerite and overlying limestone at the base of Unit VII. In the cores a sharp planar contact between a piece of grainstone and a piece of basalt/dolerite was observed. This contact was initially interpreted as an original subhorizontal planar contact between dolerite and limestone (i.e., a wave-cut platform?), based on the core recovery alone. The FMS image did not reveal any such planar-sharp contact, but nevertheless, confirms that an abrupt contact exists between conglomerate and limestone.
From 873.5 to 890.0 mbsf the FMS images reveal a poorly sorted conglomerate composed of mainly rounded clasts up to 0.5 m thick. The interstices between these rounded clasts are infilled with smaller (<5 cm) angular to subangular clasts and dark, resistive, presumably finer grained material. In some areas, the conglomerate appears to be matrix supported, but overall this interval is clast supported. The lowest 40 m of the succession, which includes pieces of dolerite and minor sedimentary rock, was not imaged.
Taking account of the critical FMS images, Unit VIII is inferred to represent deposits from a fluvial channel at least 30 m thick draining a hinterland of substantial relief (hundreds of meters at least). The conglomerate was almost entirely derived from basalt/dolerite (locally pegmatitic; see "Igneous and Metamorphic Petrology"). This implies that at least locally, large outcrops of basalt/dolerite existed in the area.
All the clastic material between the recovered dolerite is interpreted as original primary sediment intercalations, including some sediment that filtered into cracks within individual clasts. This material initially accumulated in a highly oxidizing climate, resulting in variable reddening and alteration. Specifically, the fine-grained and poorly sorted sandy sediment with strongly oxidized material is inferred to represent paleosol. Surface oxidation rather than later alteration in response to fluid flow is the probable cause of this oxidation. This, however, excludes the minor hydrothermal veining that took place prior to incorporation of the basalt/breccia as clasts in the conglomerate. Later, the texturally less mature, less oxidized, black breccia and sand were deposited between larger clasts. Finally, the conglomerate was transgressed, resulting in interfingering with neritic grainstone over a narrow interval (~1 m) directly below Unit VII.
Site 1118 was initially part of a tropically weathering landmass with basalt/dolerite locally outcropping (Unit VIII). A rugged hinterland was drained by a river giving rise to a conglomerate-filled channel at least 50 m thick. Weathered volcaniclastic material filtered into interstices and cracks within the conglomerate. Alternatives are that this was part of the Paleogene ophiolitic basement related to the Papuan Ophiolitic Belt, part of the Miocene Trobriand forearc (emergent prior to early Pliocene time), or magmatic rocks related to rifting of the Woodlark Basin. Initially, the interstitial material was lateritic, essentially reworked paleosol, followed by less altered more angular dolerite/breccia debris. Later the conglomerate was transgressed by the sea, resulting in minor interfingering of conglomerate and limestone.
Conglomeratic material derived from the landmass was reworked probably in a coastal setting and mixed with shallow-water-derived carbonate as paraconglomerate (Unit VII). The FMS data suggest that the conglomerate fines upward, presumably as transgression advanced. Corals grew either as fringing reefs or near-coastal patch reefs, although little is preserved at Site 1118. The rhodolithic algae and algal mats developed in a relatively protected shallow-water area, possibly an open-marine lagoon or embayed area. With further transgression in early Pliocene time, terrigenous input diminished and a pure limestone accumulated, still in a shallow, semi-enclosed setting (Unit VI).
The base of the overlying mixed sandstone, siltstone, and volcaniclastic sandstone accumulated in the early-middle Pliocene already at upper bathyal depths (150-500 m). This implies that sudden subsidence took place ushering in very rapid sedimentation (~479 m/m.y.). However, the contact between Units VI and V is sharp and irregular, and it is possible that intervening slope facies were deposited but then removed by currents or slumping. The overlying interval (Unit IV) contains much reworked pelagic carbonate, and it is possible that this too was reworked from a slope setting but at a later time. The mixed sandstone, siltstone, and volcaniclastic sandstone (Unit V) reveals the combined activity of turbidity currents and traction currents. Shallow-water detritus was still being supplied from a neighboring carbonate platform and wood drifted from a landmass.
During the middle Pliocene, at a time of continuing very rapid deposition, subsidence carried the basin to well below wave base and turbiditic and hemipelagic sedimentation ensued (Unit IV). This was a time of explosive volcanic activity, alternatively related to rifting of the pre-existing Trobriand Arc or to (classical) continental rifting to form the Woodlark Basin. Both fine-grained air-fall tuffs and coarser grained redeposited crystal tuff accumulated, related to coeval acidic volcanism.
In all, ~500 m of turbidites and hemipelagic sediments accumulated, initially at upper bathyal depths (Units II, III, and IV) and then at middle bathyal depths (500-2000 m) under very similar conditions (Unit I) during the middle Pliocene to late Pliocene to Pleistocene. However, this was broken by an interval (Unit III) that includes reddish, finely laminated, little-bioturbated sediments that could record an episode of more oxidizing bottom-water conditions, if not simply increased input of oxidized iron. Sporadic input of air-fall tuff continued, but the dominant input of volcaniclastic sediment switched to a copious supply of fresh basic volcanic rock. This epiclastic sediment was derived either from Woodlark rift-related extrusives or from the earlier (Miocene) Trobriand Arc. Associated mixed-layer clay was possibly derived from the Papua New Guinea landmass or the D'Entrecasteaux Islands, as discussed for the nearby Site 1108 (see "Site 1108" chapter). During late Pliocene time deposition slowed from ~435 m/m.y. to ~155 m/m.y., paralleling the trend at the other sites determined during Leg 180. The little-cored initial interval of Unit I may represent muddy sediment rich in swelling clay, based on the geophysical logs and reports of the change in hole diameter through time. Finally, the geophysical logs also suggest that the noncored interval of upper Pliocene? to Pleistocene records continued turbiditic and hemipelagic deposition, as recovered at Site 1109.
Finally, drilling of Hole 1118A revealed additional important information on the nature and history of contemporaneous volcanism related to genesis of the Woodlark Basin as summarized in Figure F33. Analysis of the visual core descriptions shows that volcanic ash has a cumulative thickness of 20.1 m. The total number of ash layers recovered is 611. Of these, 41 are interpreted as primary air-fall tuff and 570 as volcaniclastic sand and silt layers. The latter category includes both reworked contemporaneous volcanic ash and crystal tuff, and also epiclastic (older) volcanic rock debris. The majority of the ash layers are found from 695 to 811 mbsf (Cores 180-1118A-51R through 63R). These are considered to relate to rifting of the Woodlark Basin during the middle Pliocene, but determining whether from Trobriand Arc volcanism and/or from rift volcanism will require shore-based geochemical analysis.