Thin sections, prepared shipboard during Leg 194 and subsequently from shipboard-requested samples, were examined with the goal of comparing assemblages between platforms. LBF were identified using petrographic optical microscopy based upon previously published criteria (Cole, 1954, 1957a, 1957b, 1963; Chapronière, 1980, 1981, 1984; Betzler, 1997; others). Data collection included identification of LBF and selected associated smaller foraminifers and paleoenvironmental interpretation based on foraminiferal assemblages (Chapronière, 1975, 1981; Betzler and Chapronière, 1993), LBF shapes and mineralogies (e.g., Hallock and Glenn, 1986; Hallock, 1999), and other available sedimentological data (Shipboard Scientific Party, 2002). Biostratigraphic analyses included interpreting ages of assemblages using age ranges of key taxa from the literature and by utilizing planktonic foraminiferal and nannofossil ages from Leg 194 cores (Shipboard Scientific Party, 2002). Paleoenvironmental analyses included comparing the LBF assemblages with existing models (e.g., Hallock and Glenn, 1986; Betzler and Chapronière, 1993; Hottinger, 1997; Hallock, 1999; Hohenegger, 1999; others).
Basement volcanics, or terrigenous sediments and larger clasts interpreted as near basement, were reached at Sites 1193, 1194, 1197, and 1198 (Shipboard Scientific Party, 2002). LBF (Figs. F4, F5, F6) occurred in inundation sequences above acoustic basement in sediments ranging from meters-thick, oyster-rich muds containing Operculina complanata (Defrance) (Fig. F4) that graded into more carbonate-rich facies at Sites 1193 (Fig. F5A) and 1197 (Fig. F6C), to a few centimeters of LBF-rich sediments lying between basement and overlying pelagic units at Sites 1194 (421 meters below seafloor [mbsf]) (Fig. F5D) and 1198 (506 mbsf) (Fig. F6D). Although basement was not reached at Site 1196, the sediments in the deepest interval penetrated (643–672 mbsf) were dark sandstones with O. complanata as a biotic component. The oldest sediments retrieved at Site 1195 (517 mbsf) also contained a diverse LBF assemblage (Fig. F5B).
The oldest LBF assemblages encountered are characteristic of latest Oligocene and earliest Miocene (~24–20 Ma) LF associations (LF 1–3), which have been previously described from Australia and New Zealand by Chapronière (1975, 1980, 1984). This range is consistent with nannofossil ages available for the bases of these cores (Shipboard Scientific Party, 2002). Characteristic LBF taxa (Figs. F4, F5, F6) include Amphistegina bikiniensis (Todd and Post), Lepidocyclina (Eulepidina) ephippioides (Jones and Chapman), Lepidocyclina (Nephrolepidina) sumatrensis (Brady), and O. complanata (Chapronière, 1981). Arrangements of equatorial chambers in Lepidocyclina (Nephrolepidina) indicate relatively primitive circular-concentric patterns (i.e., nonstellate morphologies) as indicated by Chapronière's (1980, 1981) F-parameter values <2, which are also indicative of latest Oligocene to early Miocene age.
At Site 1193, ~100 m of mixed siliciclastics and carbonates, biotically characterized by bryozoans and LBF representing LF 1–3 assemblages, were penetrated. Samples 194-1193A-75X-CC (456 mbsf) through 83X-CC (513 mbsf) and 194-1193C-5X-CC (515 mbsf) through 8X-CC (544 mbsf) include both coarse bioclastic and terrigenous clastic sediments, the latter generally increasing downhole (Shipboard Scientific Party, 2002). The LBF assemblages indicate inner to middle neritic water depths for most of this interval. Reworked glauconite and phosphate-infilled bioclasts are common (Fig. F5A, F5C). Nannofossils constrain the age of this interval to 23–18 Ma (Shipboard Scientific Party, 2002), indicating that the cumulative deposition rate was on the order of 20 m/m.y. This interval also represents seismically defined Megasequence A (Shipboard Scientific Party, 2002). A 50-m interval of similar glauconite- and phosphate-infilled bioclasts, including LBF (Fig. F5B), was also found just above basement at Site 1197. Nannofossils indicated age as ~18–19 Ma (Shipboard Scientific Party, 2002).
Following deposition of an interval of arkosic sandstone at ~450–430 mbsf (base of seismic Megasequence B) (Fig. F2), carbonate deposition at Site 1193 abruptly increased as siliciclastic input declined. Nannofossils date this change at ~18.5 Ma. Bryozoan and LBF components increase uphole as percent carbonate increases, with imbricated grainstones and packstones (Fig. F7) dominated by Lepidocyclina (Nephrolepidina) praehowchini (Chapronière) and diverse other LBF (LF 6 of Chapronière [1981]) found at 390 mbsf at the top of lithologic Unit VI (Fig. F2). The continued prevalence of nonstellate lepidocyclinid morphologies (F-parameter < 2.5) is indicative of early Miocene deposition (Chapronière, 1980, 1981).
Evidence of increasing paleodepth at ~18 Ma is seen at all the sites, except Site 1196. At Site 1193, imbricated lepidocyclinid grainstones are succeeded by >150 m of calcareous silt and very fine carbonate sands with bioclastic fragments (Fig. F8), as well as foraminiferal assemblages that indicate deposition at subeuphotic, probably outer neritic depths (>150 m) for ~23 m.y. An accumulation rate of >50 m/m.y. indicates active upslope production, downslope transport, and deposition at this location. At Sites 1194, 1195, and 1198, LBF-rich grainstones or packstones immediately above basement are overlain by similar very fine bioclastic carbonates. Although the basal shallow-water sequence is thicker at Site 1197, it too is abruptly overlain by fine-grained carbonates (~600 mbsf).
Rapid inundation is particularly evident at Site 1198, where a red algal/foraminiferal boundstone consisting of large, very thin foraminifers bound by thin red algal crusts (Fig. F6D) lies upon olivine basalt at 513 mbsf. The carbonate unit is topped by a phosphatic hardground. The LBF assemblage is dominated by L. (E.) badjirraensis and Cycloclypeus eidae, which are the characteristic taxa of LF 5 (Chapronière, 1981, 1984), again indicating deposition in the early Miocene (~18–19 Ma).
At Site 1196, the rapid rise in sea level in the late early Miocene did not overwhelm shallow-water carbonate deposition dominated by red algae, stony coral, and LBF. Rather, combined with subsidence, sea level rise provided accommodation space for accumulation of ~300 m of shallow-water carbonates through the early Miocene (Fig. F3). One calcareous nannofossil date of 24.6–24.2 Ma in Sample 194-1196A-70R-1, 133 cm (664 mbsf), in apparently deltaic facies (Shipboard Scientific Party, 2002), constrains the maximum age of the platform. Extensive dolomitization severely limits biostratigraphic and paleoenvironmental interpretation of most of the interval between ~330 and 620 mbsf. However, a Miogypsina-rich facies at 383–393 mbsf (Fig. F9A, F9B) has a very similar assemblage to that seen at 340 mbsf at Site 1193 (Fig. F7), as well as in transported sediments in Samples 194-1197B-53R-5, 92 cm (557 mbsf) (Fig. F9C), and 194-1198B-26R-5, 48 cm (443 mbsf) (Fig. F9D).