Cores and thin sections from platform facies at Sites 1193 and 1196 and from associated periplatform sediments at Sites 1194, 1197, and 1198 revealed a continuum of Lepidocyclina/Amphistegina-dominated LBF assemblages (Figs. F18, F19). Four assemblages were distinguished using morphologic trends in Lepidocyclina (Nephrolepidina) lineages (after Chapronière, 1980) and some notable trends in other taxa. A fifth assemblage represented a distinctly different facies. These assemblages occurred sequentially, indicating temporal stages in platform development. This conclusion is supported by biostratigraphic data provided by nannofossil and planktonic foraminifers (Shipboard Scientific Party, 2002).
Assemblage A, which includes components of Chapronière's (1980, 1981) LF Associations 1–5, was found in a range of neritic facies (<150 m) associated with basement flooding sequences seen at Sites 1193–1197. Nannofossil dates support LBF biostratigraphy, indicating latest Oligocene–early Miocene for basement flooding. O. complanata was the dominant LBF in sediments rich in terrigenous muds and oyster fragments. Lepidocyclinids, both Lepidocyclina (Eulepidina) spp. and Lepidocyclina (Nephrolepidina) spp., were typically the most conspicuous LBF in carbonate facies, whether the dominant biota were bryozoans or red algae. Lepidocyclina (Nephrolepidina) spp. were characterized by primitive nonstellate morphologies.
Assemblage B was found in platform facies at Sites 1193 and 1196 and in corresponding slope sediments at Sites 1197 and 1198. This assemblage was characterized by circular-concentric (nonstellate) Lepidocyclina (Nephrolepidina) spp., as well as by abundant Amphistegina, Cycloclypeus, and Operculina. Miogypsinids, when present, were predominantly ovate forms. The predominance of nonstellate Lepidocyclina (Nephrolepidina) indicated late–early Miocene deposition, as some stellate morphologies were observed.
Assemblage C, found at Site 1196 (lithologic Subunit IIA at 183–326 mbsf; Shipboard Scientific Party, 2002), was characterized by Flosculinella, Austrotrillina, soritids, and smaller miliolid foraminifers. This was biostratigraphically and paleoenvironmentally the most definitive assemblage. Both LBF and nannofossils indicate middle Miocene age. The assemblage was characteristic of very shallow (<12 m), somewhat restricted environmental conditions, including seagrass meadows. Red algal–dominated sediments containing Assemblage B occurred below the Assemblage C interval at Site 1196, whereas red algal and coral facies containing Assemblage D occurred directly above.
Assemblage D is characterized by mixed concentric and stellate morphologies of Lepidocyclina (Nephrolepidina) spp., as well as by very modern appearing Amphistegina spp. Miogypsinid morphologies were distinctively vermiform, rather than the ovate morphologies seen in Assemblage B. Intervals characterized by this assemblage were interpreted to be middle Miocene in age (Figs. F18, F19).
Assemblage E was found at Site 1196 in the uppermost platform facies and in corresponding periplatform sediments at Sites 1193, 1194, 1197, and 1198. Amphistegina spp. dominates the LBF assemblage, although stellate lepidocyclinids were the distinctive component. Planktonic foraminifers and nannofossils indicated that this assemblage occurred in late Miocene (~8–11 Ma) periplatform sediments at Site 1198; overlying pelagic deposition was dated at 7.5–8.6 Ma at Site 1194.