Site 1197 is located on the downcurrent, windward margin of the SMP. Site 1197 is ideally positioned to observe the shedding of periplatform sediments from the carbonate growth phases of the southern platform. Site 1197 penetrated a 656.1-m-thick sediment package and recovered material from acoustic basement, which consists of volcaniclastic sediments and basalt. Core recovery at this site was ~100% from 0 to 59.6 mbsf, extremely poor (~0%) between 59.6 and 175.0 mbsf, poor (~10%) from 175.0 to 377.1 mbsf, and variable from 377.1 mbsf to the bottom of the hole. Sediments are unlithified in the upper interval with increased lithification below the hardground surface at 59.6 mbsf that separates hemipelagic drift deposits of lithologic Unit I from the last periplatform sediments of Unit II (Table T3).
The lithostratigraphy of Site 1197 has been divided into six units on the basis of changes in sedimentary texture, grain size, skeletal content, color variations, and the degree of bioturbation. Other criteria for distinguishing these units include changes in siliciclastic content (mostly as clays) and the presence of dolomite within the carbonate fraction (Fig. F3). The dominant lithologies throughout are skeletal packstone and grainstone with significant changes in grain size and fluctuations in the pelagic vs. neritic content. The intervals with abundant neritic skeletal grains indicate increased shedding from the adjacent carbonate platforms of the Marion Plateau.
Unit I is a homogeneous unit of white to pale yellow, unlithified skeletal packstone and grainstone rich in planktonic foraminifers, with minor amounts of bivalve fragments and echinoderms, rare scaphopods and pteropods (Fig. F3). Sponge spicules are common and, along with clays, contribute to the siliceous component of the sediment. Smear slide analysis confirms that only traces of silt-sized quartz and mica are present. Foraminifer fragments are abundant, but calcareous nannofossils are only of minor importance. X-ray diffraction (XRD) analysis indicates that aragonite is present above 43 mbsf, increasing in abundance upcore to a value of 21 wt% just beneath the seafloor.
Characterization of Unit II is hindered by extremely poor recovery, totaling just 0.8% for the entire 115.4-m drilled interval (Fig. F3). Seismic data indicate that the sediments of lithologic Unit II belong to a prograding package of clinoforms and therefore are likely to contain coarse-grained periplatform detritus shed from the SMP (see "Seismic Stratigraphy"). The upper boundary to this unit is marked by a hiatus with a maximum duration of 0.5 m.y. (see "Biostratigraphy and Paleoenvironments"), defined by a distinctive hardground surface.
The uppermost 0.42 m of Unit II is extremely well lithified, with available pore spaces tightly filled by calcite microspar cements. The surface of this unit has a 3- to 4-mm-thick, reddened hardground cap with a high phosphate content (Fig. F4). Borings are associated with this interval (Fig. F5), as is the selective dissolution of turret-shaped gastropods resulting in molds as long as 15 mm. Both of these features were infilled with either fine phosphatic silt or micrite. Color changes progressively downcore in this interval from reddish brown to brownish yellow to yellowish white. This color change was accompanied by a marked decrease in lithification and less pervasive micrite cements. Beneath the upper 0.42-m interval, the sediments are characterized by an increase in porosity and the presence of weak, fine-grained dolomite cements (rhombic crystals). This friable skeletal grainstone is probably responsible for the low recovery in this interval.
The remainder of lithologic Unit II is composed of dolomitized white skeletal grainstone rich in foraminifers (planktonic foraminifers and larger benthic foraminifers, particularly Amphistegina sp.) and coralline algae branch fragments (in the matrix groundmass) (Fig. F6). Operculina sp. and Lepidocyclina sp. are present along with rare echinoderm, bryozoan, and bivalve remains. Dolomite occurs as fine- to coarse-grained interparticle cement as confirmed by XRD analysis (see "Geochemistry") (Fig. F3).
The top of Unit III is defined by a significant unconformity (see "Biostratigraphy and Paleoenvironments"). The sediments of this unit are characterized by dolomitized white to light gray, friable skeletal grainstone (Fig. F3). As with Unit II, recovery in this interval was poor. Larger benthic foraminifers, mainly Lepidocyclina sp., are the principal constituent and comprise almost the entire grainstone texture in some instances (Fig. F7). Other larger benthic foraminifers (Operculina sp. and Amphistegina sp.) are also present in the recovered sediments. Planktonic foraminifers and smaller benthic foraminifers are minor to abundant in the matrix, so the grainstone often appears to have a strongly bimodal sorting. Imbrication of foraminifer grains can be observed in many of the small pieces that were recovered along with a crude parallel lamination (Fig. F8). Many large lepidocyclinids show considerable damage to the test structure as compared to the smaller and more robust amphisteginids. Fragments of coralline algae are also an important contributor to skeletal allochems, whereas echinoderms and bivalves are of minor importance. Dolomite concentrations are often high (Fig. F3) (see "Geochemistry"). Glauconite is present mainly as infillings of foraminifers, becoming more common toward the base of this unit. Unit III represents the upper part of a progradational package as seen on seismic data (see "Seismic Stratigraphy"). The base of Unit III is characterized by an abrupt decrease in the presence of coarse neritic detritus and a decrease in the degree of dolomitization (Fig. F3).
Light gray, olive, and greenish gray fine skeletal packstone/grainstone and silt-sized grainstone/packstone characterize Unit IV (Fig. F3), which is distinguished from the overlying Unit III and underlying Unit V because of its fine sediment grain size. Coarse neritic detritus, particularly visible larger benthic foraminifers, are far less abundant in this interval. The majority of components are indistinct silt-sized skeletal particles whose identification can only be resolved in thin section (Fig. F9). This thick package of sediments is divided into two subunits based on changes in carbonate mineralogy, the degree of bioturbation, and the presence or absence of repetitive/cyclic intervals within the succession. Core recovery increases downcore within Unit IV.
Subunit IVA is characterized by a partially to highly dolomitized, pale yellow to light gray, silt-sized or fine skeletal packstone and grainstone rich in planktonic foraminifers. Planktonic foraminifers are poorly preserved and are often overgrown by dolomite cements. Larger benthic foraminifers, including Lepidocyclina sp., are common locally but not as abundant as in Unit III. Smaller benthic foraminifers, bryozoans, and echinoderm fragments are rare. Glauconite is a minor accessory component, often infilling intraskeletal porosity within foraminifers. Bioturbation ranges from rare to common throughout the unit but is not as abundant as in the underlying Subunit IVB. A further distinction of Subunit IVB is a marked downcore decrease in the abundance of dolomite (Fig. F3).
Subunit IVB marks a change to darker colored lithologies, with a slightly reduced calcium carbonate content resulting from increased siliciclastic input (Fig. F3). Planktonic foraminifers are common, as are smaller and larger benthic foraminifers. Bivalves, bryozoans, and small fragments of coralline algae are rare. Glauconite is low to moderately abundant, often infilling the tests of larger benthic foraminifers or occurring as pellets. As with Subunit IVA, sediments are fine-grained sand- to silt-sized skeletal packstone and grainstone with light gray to olive color. However, finer-grained or muddier skeletal wackestone and mudstone are often present. The skeletal composition of these fine-grained limestones is difficult to distinguish because of their small size, fragmentation, and/or abrasion. Throughout Subunit IVB, there is a noticeable increase in the intensity of bioturbation as compared to Subunit IVA. Dolomitization is greatly reduced or absent (Fig. F3).
Repetitive alternations of darker and lighter colored intervals ranging in thickness from a few tens of centimeters to a few meters is the most obvious feature of Subunit IVB (Fig. F10). Such alternations are also seen in calcium carbonate data (Fig. F3) as a result of fluctuations in siliciclastic detritus, particularly clays, as confirmed by XRD analyses (see "Geochemistry"). The darkest intervals of these cycles contain up to 41% noncarbonate minerals. Bioturbation, mainly caused by Chondrites may mask the original depositional contacts in these cycles (Fig. F11).
Other small-scale sedimentary packages 10-20 cm thick are observed more sporadically throughout Subunit IVB, characterized by a distinct fining-upward trend and overall coarse texture. These packages are interpreted as turbidites (Fig. F12). The basal interval of each turbidite package is usually 5-10 cm thick and comprises a graded coarse grainstone with abundant visible larger benthic foraminifers plus subordinate bryozoans and fragments of coralline algae. The upper part of the package typically shows a well-developed parallel lamination.
Unit V is composed of white to light greenish gray skeletal grainstone and packstone, rudstone, and floatstone rich in larger benthic foraminifers. This abrupt change to lighter-colored lithologies is clearly observed in the color reflectance data (see "Core Physical Properties"). Large-sized lepidocyclinid foraminifers, up to 8 mm long, are the dominant skeletal component, along with other larger foraminifers and fragments of coralline algae, which are at times almost as abundant as the foraminifers (Fig. F13). Bivalve, echinoderm, and bryozoan remains are also commonly observed. Glauconite is abundant (typically 15%-25%), both as isolated pellets and infillings of intraskeletal porosity. Usually ~50% of the larger foraminifers show evidence of glauconite infilling and abrasion, whereas the remainder are freshly preserved. Fine- to coarse-grained quartz sand (up to 30%) is common to abundant in the basal interval of Unit V (646.7 to 656.1 mbsf) as was confirmed by XRD analyses (see "Geochemistry"). Well-developed parallel lamination and primary horizontal orientation of elongated (foraminifer) skeletal clasts are common in the skeletal packstone and grainstone. Small 10- to 30- cm-thick fining-upward intervals of coarse grainstone are seen throughout this unit, often capped by thin 0- to 5-cm darker-colored intervals of parallel-laminated finer-grained packstone (Fig. F14).
A distinctive greenish gray skeletal floatstone (Fig. F15) containing small oysters, pectenids, and abundant large bioclasts of massive celleporiform bryozoans (up to 25 mm in size) is present in the lowermost 0.35 m of Unit V (at 656.4 to 656.1 mbsf; Core 194-1197B-64R). The matrix is composed of larger benthic foraminifers, bryozoans, echinoderms, and coralline algae fragments. Cobbles and pebbles of basalt and other volcanic rocks are included in the basal floatstones that immediately overlie Unit VI.
Unit VI is characterized by multicolored pebble- to cobble-sized volcaniclastic sediments that represent acoustic basement. Two subunits are distinguished: a ~10.5-m-thick series of volcaniclastic sediments and an underlying, thin interval of basalt.
Subunit VIA consists of a highly altered, matrix-supported volcaniclastic breccia with coarse (up to 12 cm) angular clasts of light gray basalt derived from the underlying basement. Small dark red-colored pebble clasts (4-10 mm in size) and larger subangular to subrounded clasts (typically 5-50 mm in size) are also likely to be highly altered material of volcanic origin (Fig. F16). Thin section analysis indicates that bioclastic material is absent. Octahedral dark reddish black metallic crystals are observed within the matrix and are tentatively identified as sphalerite.
Highly altered, light to medium gray basalt with olivine and plagioclase phenocrysts (1-3 and 2-4 mm in diameter, respectively) set in a groundmass of fine crystalline plagioclase was recovered at the base of Hole 1197B (interval 194-1197B-65R-1, 129-142 cm). Rare vesicles up to 1 mm in diameter are present. The rock appears to be highly weathered, with the original mineralogy such as olivine crystals being altered to iddingsite. Only a small interval of this basalt was recovered, and it is uncertain whether this rock is in situ basement or a large breccia clast.
The majority of sediments recovered at Site 1197, particularly in the interval from 59.6 mbsf to the top of the acoustic basement at 601.7 mbsf were deposited on the proximal slope of the SMP resulting in a reworked faunal assemblage of foraminifers, coralline algae, and other skeletal detritus derived from a neritic platform environment. Discussion of the depositional history for Site 1197 is given below.
The age and origin of the thin interval of olivine basalt observed at the base of Site 1197 (Subunit VIB) is uncertain, but it is interpreted as originating from basalt flows related to synrift tectonic activity. The surface of this flow was most likely exposed for a significant period of time and then covered by a veneer of volcaniclastic breccias (Subunit VIA) that accumulated from debris flows related to an alluvial fan or as slope colluvium. This surface likely maintained a significant paleorelief. Similar basaltic igneous rocks were encountered at Site 1198; however, no overlying volcaniclastic sediments were recovered. Unit VI represents the acoustic basement at Site 1197.
Initial flooding of the basement is recorded by an interval of skeletal floatstone rich in oysters with their paired valves still attached. This implies limited reworking across a shallow neritic platform in water depths <30 m. The upper 50 m of sediment in Unit V is coarse skeletal packstone to fine rudstone, indicating either deposition in an open shelf environment at depths of <100 m or, possibly, transport and deposition in a proximal periplatform setting (see "Biostratigraphy and Paleoenvironments"). Small- to medium-scale graded bedding and the strong laminar fabric of many of the deposits suggest deposition from unidirectional gravity flows, probably slope-proximal turbidites, related to shedding in a periplatform setting.
The very fine skeletal packstone, grainstone, and wackestone sediments of Unit IV indicate deposition in a hemipelagic through distal periplatform setting. Thin section analysis confirms that many of the fine skeletal particles are fragmented neritic grains from coralline algae and benthic foraminifers (Fig. F9). Clay content generally increases upward between 600 and 480 mbsf and likely indicates a progressive deepening through this interval, possibly followed by a broad shallowing from 480 mbsf to the top of Subunit IVB, where clay content gradually declines. Distinctive color-banded intervals are recognized within Subunit IVB with slight fluctuations in textural composition and clay content. Small-scale fining-upward intervals with well-preserved parallel lamination are characteristic of deposition from turbidites. Calciturbidites are enriched in coarse skeletal detritus such as larger benthic foraminifers transported from the platform margin. These turbidites are probably unrelated to the cyclicity producing the color-banded intervals discussed previously.
The absence of clays and the presence of fine-grained skeletal particles of neritic origin, including larger benthic foraminifers, is typical of Subunit IVA and indicates deposition in a periplatform setting at water depths of ~200 m (see "Biostratigraphy and Paleoenvironments"). The fine grain size and massive character of this subunit is surprising because it forms the basal part of an inclined, prograding slope package, as seen on seismic profiles (see "Seismic Stratigraphy"). However, the overall coarsening-upward trend is consistent with progradation of slope deposits.
The range of sedimentary structures and abundance of reworked larger benthic foraminifers filled by glauconite (particularly Lepidocyclina sp.) within Unit III imply reworking from the nearby SMP. Larger benthic foraminifers usually live in the euphotic zone (~50-100 m) but have been transported to a proximal periplatform environment with depths of ~150 m or greater (see "Biostratigraphy and Paleoenvironments"). The upper boundary of Unit III is loosely constrained because of poor core recovery, but nonetheless shows a marked nondepositional hiatus (see "Biostratigraphy and Paleoenvironments"). The seismic profile (see "Seismic Stratigraphy") indicates that this horizon is also a downlap unconformity between two prograding seismic sequence packages, likely to represent the boundary of the middle and late Miocene platform growth phases.
Similar to Unit III, the sediments of Unit II often show rudimentary laminations, perhaps indicating deposition from unidirectional currents. The abundance of Amphistegina sp. in particular, along with fragments of coralline algae, is reminiscent of the Subunit IA and IB facies encountered at Sites 1196 and 1199 on the SMP (see "Lithostratigraphy and Sedimentology" in the "Sites 1196 and 1199" chapter). The main difference here is the mixing with planktonic foraminifers (Fig. F6), which enables the dating of these periplatform sediments. The adjacent SMP (observed at Sites 1196 and 1199) likely drowned in the latest Miocene, terminating neritic supply to the slopes. This platform demise is recorded by a relative increase in the amount of planktonic foraminifers in the uppermost part of Unit II in addition to the formation of an indurated hardground with a thin phosphatic cap. The base of Unit II is defined by a significant hiatus (see "Biostratigraphy and Paleoenvironments") and is coincident with a prominent downlap and unconformity surface on seismic profiles (see "Seismic Stratigraphy"). All evidence suggests that Unit II sediments were shed contemporaneously with the growth of the SMP.
A 60-m-thick series of skeletal grainstone and packstone rich in planktonic foraminifers was deposited in an upper bathyal hemipelagic setting above the hardground surface. Mineralogical analyses show that aragonite is present from ~43 mbsf to the modern seafloor with abundance increasing upward. This indicates that aragonite is being produced in the environment, either from organisms living on the seafloor at this location or more likely from shedding and neritic supply related to a distal platform area. It is also likely that aragonite dissolution increases downcore. An identical trend in aragonite concentration vs. preservation can be recognized at Site 1198 on the western side of the SMP (see "Lithostratigraphy and Sedimentology" in the "Site 1198" chapter).