The lithostratigraphy of Site 1193 is divided into seven units (Table T3; Fig. F4). Unit I consists of 3.5 m of uppermost Pleistocene light brown to yellow, planktonic foraminifer-dominated grainstone with underlying mudstone and packstone. Below Unit I is 31 m of unconsolidated Pleistocene to uppermost Miocene hemipelagic foraminiferal packstone (Unit II). Unit II overlies a major hiatus, estimated to have occurred from >12 to 5.6 Ma, at the top of a 194-m-thick unit of coarse bioclastic limestone and subordinate dolostone (Unit III). Unit III corresponds to the upper part of the seismically defined Northern Marion Platform (NMP), which is believed to have prograded southeastward in the early to middle Miocene. The diverse biotic assemblage of bryozoans and larger benthic foraminifers, with subordinate mollusks and red algae but almost no coral, indicates temperate to cool subtropical depositional conditions. Immediately below these high-energy, relatively shallow-water deposits (mainly <100 m water depth) is a clay-rich mudstone interval ~20 m thick (Unit IV). Unit IV grades downward into a 136-m interval of fine-grained bioturbated skeletal packstone (Unit V), believed to represent the progradational platform slope that correlates with clinoforms imaged on seismic data. The base of the sedimentary section consists of 146 m of interbedded grainstone and subordinate quartzose sandstones (Unit VI), deposited in a shallow-water setting. The deepest core at Site 1193 (540-549 mbsf) sampled the top of acoustic basement, consisting of hydrothermally altered volcaniclastic deposits of probable basaltic composition (Unit VII).
Unit I consists of light brown to yellow unconsolidated planktonic foraminifer limestone containing subordinate benthic foraminifers and scaphopods (Fig. F4). Also present are rare echinoderm fragments, gastropods, bivalves, ostracods, and arthropod fragments. There is a downward textural change from an upper 2.3-m-thick grainstone interval (Fig. F5) to 0.5 m of mudstone and then a lowermost 0.7-m-thick packstone interval. Bioturbation increases downward from barren at the top to heavy in the packstone. The boundary between Units I and II is marked by a sharp color change from yellow above to light greenish gray below.
This 31.5-m-thick interval of unconsolidated, light olive-gray, skeletal packstone consists of very fine to fine sand-sized planktonic foraminifers in a clay-rich mud matrix (Figs. F4, F6). Bioturbation is heavy, with conspicuous Chondrites. Minor components include benthic foraminifers and crustacean fragments. Minor glauconite is present throughout (<1%) the unit.
Based on differences in color, biota, and dolomitization, Unit III is divided into two subunits (Fig. F4). As a whole, however, this unit consists of 194 m of skeletal rudstone and floatstone with subordinate grainstone, packstone, and clay-rich mudstone. Most of the section is white to red-brown and pink limestone. In some places, it is partly to entirely replaced by a light brown to deep orange sucrosic dolomite (Fig. F4). Most intervals are distinctly bedded by size sorting, horizontal orientation of bioclasts, and varying carbonate mud content.
Bryozoans are the main skeletal components of Unit III; larger benthic foraminifers are common. Subordinate components include bivalve, gastropod, and echinoderm fragments and coralline algae. The latter comprise both discrete fragments of branching forms and rhodoliths. A single specimen of branching hermatypic coral was found at 83 mbsf (interval 194-1193B-8Z-1, 2-4 cm).
Micritic matrix varies widely in abundance resulting in marked porosity changes in Unit III (see "Core Physical Properties"). Porosity has also been reduced by calcite cements.
Subunit IIIA is mainly composed of bryozoan-rich limestone to dolostone showing a rudstone floatstone fabric with a grainstone/packstone matrix. Above 90 mbsf, the cored intervals are nearly pure limestone, but the lower part of this subunit contains alternating layers composed of ~20% to ~100% dolomite (Fig. F4). The uppermost cores of Subunit IIIA include the following facies (from top to bottom):
Within the upper part of Subunit IIIA, four distinctive, irregular surfaces are observed (35.9 mbsf [interval 194-1193B-1R-1, 90 cm], 61.9 mbsf [interval 194-1193C-4R-1, 30 cm], 68.7 mbsf [interval 194-1193B-6Z-1, 82-89 cm], and 86.5 mbsf [interval 194-1193B-11Z-1, 14-18 cm]) (Fig. F11). Several of these surfaces are underlain by reddened coloring suggesting oxidation. The surfaces at 35.9 and 68.7 mbsf are of special note because they are overlain by centimeter-thick accumulations of skeletal grainstone containing rare to abundant planktonic foraminifers and glauconite pellets, both of which are suggestive of reduced neritic sedimentation.
Also worthy of note is a distinctive rock fabric (present in the intervals 63-64 mbsf and 87-88 mbsf) with millimeter- to centimeter-scale layering defined by size sorting and horizontal orientation of bioclasts (Fig. F12). The lowermost of these two intervals contains multiple zones of thick isopachous cement coatings.
The lower part of Subunit IIIA contains at least three intervals consisting of deep reddish brown to orange dolomitized rudstone to floatstone having a finely crystalline sucrosic dolomite texture that preserves recognizable molds of bryozoan and mollusk fragments (Figs. F13, F14).
Subunit IIIB is composed mainly of bioclastic rudstone, grainstone, packstone, and floatstone that may contain a certain amount of dolomite. Rock matrix consists of finer-grained grainstone and packstone. The sediments in Subunit IIIB are broadly similar in composition and fabric to those of Subunit IIIA, but the following differences are noted:
Another distinctive feature of Subunit IIIB is the presence of two intervals with mudstone to floatstone fabric having high clay content. The uppermost of these, which is used to define the top of Subunit IIIB, is light greenish gray and at least 9 m thick (167-176 mbsf). It contains layers of largely intact bryozoan fronds 1-3 cm in maximum dimension, together with benthic foraminifers, bivalves, and echinoids. The bryozoans are most abundant in the uppermost 2 m of this interval (Fig. F16), resulting in a coarsening-upward trend. The mud matrix has been entirely replaced by dolomite, whereas the bryozoans are unaltered. The lower clay-rich mudstone bed (interval 194-1193A-41X-1, 0-40 cm; 220 mbsf) occurs at the top of a fining-upward cycle near the base of Subunit IIIB.
The interval from 186 to 210 mbsf, represented by a series of short core segments, shows a large-scale coarsening-upward trend from grainstone through rudstone. The Unit III/IV boundary is inferred to occur between Cores 194-1193A-42X and 43X; therefore, the nature of this boundary could not be determined.
Unit IV consists of 20 m of greenish gray, clay-rich mudstone containing silt- to very fine sand-sized planktonic and benthic foraminifers and bryozoan fragments, quartz, and glauconite (Figs. F4, F17, F18). Very rare coccoliths are visible in smear slides. Bioturbation is moderate to heavy throughout Unit IV. The lower boundary of this unit is defined by a sharp color change at the base of Core 194-1193A-46X (249.2 mbsf) from light greenish gray to pale olive. However, the lower boundary of Unit IV is gradational in texture as its basal 4 m show a fining-upward trend from very fine grained packstone through wackestone to mudstone.
Unit V is a 135.9-m-thick interval of light olive-gray, skeletal packstone, consisting mainly of fine sand- to silt-sized bioclasts in a clay-rich mud matrix (Fig. F4). Dolomite is common in this unit. Thin section observations indicate that bioclasts are dominantly benthic and planktonic foraminifers with subordinate fragments of echinoderms, bryozoans, red algae, and mollusks (Figs. F19, F20). Quartz sand to silt and glauconite pellets are common. Some intervals are heavily bioturbated. Less bioturbated intervals display current ripples and graded beds up to a few decimeters thick. Concretion-like clusters of coarse celestite crystals with pyrite inclusions are sometimes associated with burrows. The basal contact of Unit V is a surface at interval 194-1193A-62X-5, 77 cm (385.1 mbsf), showing a sharp transition from very fine sand-sized skeletal packstone to underlying coarse-grained skeletal grainstone of Unit VI (Fig. F21).
The 145.9-m-thick Unit VI is coarser than Unit V and is dominated by a grainstone fabric with sandstone beds present in some intervals (Fig. F4). Unit VI is divided into two subunits in order to differentiate a lowermost 2-m-thick interval of conglomerate and sandstone.
Subunit VIA consists mainly of fine- to coarse-grained, poorly to well-sorted skeletal grainstone (Figs. F22, F23) with subordinate beds of quartz sandstone (Fig. F24). Color is mostly light to dark greenish gray, with the interval from 426 to 470 mbsf (Cores 194-1193A-69X to 77X) being brown to reddish yellow. Bioclasts in the grainstone are dominantly benthic foraminifers with minor echinoderm, mollusk, bryozoan, and red algae fragments and minor planktonic foraminifers. Common accessories indicate quartz, glauconite, and phosphate sand-sized grains. Sandstones are rich in calcite bioclasts, glauconite, and phosphate grains and are cemented by isopachous coatings of fine-prismatic calcite.
The deepest core in Subunit VIA (194-1193C-6R; 520-522 mbsf) consists mainly of skeletal grainstone to floatstone, characterized by a high glauconite content (up to 50%) and large oyster shells and bryozoans. The middle part of this interval is finely laminated with bidirectional current ripples (Figs. F25, F26).
Subunit VIB (interval 194-1193C-7R-1, 0 cm, to 7R-2, 54 cm) consists of greenish gray, bioclastic, glauconite-rich, poorly sorted quartz sandstone. Large oyster shells (up to 8 cm long and 2 cm thick) are especially abundant in the upper 45 cm (Fig. F27). The basal 60 cm of this subunit consists of interbedded sandstone and conglomerate with pebble-sized carbonate clasts.
Unit VII consists of volcanics believed to represent regional basement (Fig. F4). The top 0.5 m of the basement, recovered in interval 194-1193C-7R-2, 54-104 cm (531.4-531.9 mbsf), is represented by reddish brown to dark green highly altered basaltic flows (Fig. F28). The rock is highly fractured and cut by calcite-filled veins. Slickensides are present on some fracture surfaces. Thin sections reveal a texture dominated by the effects of low-temperature alteration, forming finely crystalline phyllosilicate and possibly zeolite minerals but preserving areas with relict igneous texture (Fig. F29).
Unit I, which includes the modern seafloor, has been episodically disturbed allowing for cementation and the development of localized hardgrounds. Both Unit I and the hemipelagic sediments of Unit II formed in an open-ocean setting influenced by distal terrigenous influx.
Unit III was deposited in a carbonate platform setting and affected by moderate to strong current energy, as shown by the coarse bioclastic fraction. Unlike equivalent units in Leg 133 (Sites 815, 816, and 826) no evidence of tropical reefal biota was observed at Site 1193. Warm-temperate to cool subtropical environments are suggested by the predominance of both bryozoans and larger benthic foraminifers and the lack of green algae. The larger benthic foraminifers of Unit III are consistent with water depths in the range of 120 m to <30 m (middle to inner neritic zone), as discussed in "Biostratigraphy and Paleoenvironments".
The four irregular surfaces observed in the upper part of Subunit IIIA are interpreted as karst surfaces, recording subaerial exposure. The presence of these surfaces and the greater abundance of red algae and clay in Subunit IIIB suggest a large-scale shoaling-upward trend through Unit III.
Ubiquitous extensive leaching of bioclasts and the presence of vadose silt and possible freshwater cements suggest that Unit III may have experienced meteoric diagenesis throughout the entire interval.
The facies at the top of Subunit IIIA contains a mixture of planktonic foraminifers and biota typical of the underlying shallow-platform carbonates. Therefore, this thin zone may record a transitional final growth stage of the platform. It is uncertain whether the tight cementation of this zone mainly reflects subaerial or submarine exposure. In either case, extended submarine exposure is suggested by the phosphatic coatings on several core pieces (Fig. F5).
In the uppermost mudstone horizon of Subunit IIIB, the benthic foraminiferal assemblage consists exclusively of shallow-water taxa, consistent with a protected setting such as a lagoon or bay. The occurrence of extensively dolomitized horizons in the lower part of Subunit IIIA indicates that this mudstone acted as a laterally extensive aquiclude focusing fluid flow through more permeable layers of the overlying section.
Unit IV contains virtually no micropaleontologic indicators of shallow-water conditions. Its very fine grain size and high clay to silt content are suggestive of distal outer neritic conditions (possibly approaching 200-m water depth) and, thus, are consistent with a location on the seaward slope of a carbonate platform.
Benthic foraminiferal assemblages indicate that Unit V was deposited in outer neritic conditions, but the coarser grain size and lower clay content as compared to Unit IV suggest a more proximal slope setting (>120-m water depth).
Shallow depositional setting is demonstrated for Unit VI by the exclusively shallow-water benthic foraminiferal assemblages (Fig. F4). The frequent occurrences of pelagic foraminifers and glauconite and phosphate grains indicate repeated periods of condensed sedimentation during the depositional history of this unit, possibly corresponding to times of higher relative sea level.
From the interpretations above, a history of geologic events can be proposed for Site 1193: