The sediments at Site 1003 at the lower slope and Site 1007 at the toe of the slope of the western Great Bahama Bank contained a higher percentage of redeposited beds, namely turbidites and debris flows, than the other sites; therefore, we concentrated our study on these two sites. Slump deposits have not been included here, although Betzler et al. (in press) showed that most slumps can be clearly related to the occurrence of turbidite depositional systems. Within the 1104 m of Neogene sediments at Site 1003 (Sequence Boundaries C to P2), 463 turbidites have been counted with a total thickness of 130.18 m, which represents only 12% of the total sediment thickness. The average turbidite thickness is 28 cm. The sedimentary sequence analyses allowed us to separate these sediments into 16 packages of lowstand and highstand systems tracts (Fig. 4). Sequence q is not included, because the bottom of the Neogene was not reached at Site 1003. A total of 309 turbidites (67%) were shed during high sea level covering a thickness of 77.24 m (59% of the entire turbidite volume). During low sea level, only 154 turbidites were shed (33%) with a total thickness of 52.94 m (41% of total volume) (Fig. 5).
The distribution of turbidite deposits varies greatly from one sedimentary sequence to another (Table 6). Most turbidites were deposited during the late Langhian, Seravillian, and to some extent the early Tortonian (middle Miocene). In the Burgidalian, early Langhian, late Tortonian, Piacenzian, and Pleistocene, only a few turbidites were deposited, whereas during the Messinian and Zanclian, no turbidites were recorded in the cores of the studied sites.
The sediments at the basinal Site 1007 were separated into only 14 packages, because Sequence Boundaries A and B were not recorded and Sequence Boundaries D and E merged (Fig. 6). Within the 1155 m of Neogene sediments, 541 turbidites were counted (Sequence Boundaries C through Q). These turbidites had a total thickness of 51.84 m, with an average turbidite thickness of 10 cm. Only 39% of all turbidites at this site were deposited during sea-level highstand, while 61% were shed during sea-level lowstand. The thickness of the highstand turbidite deposits, however, is 29.90 m, which represents 57% of the total volume (Fig. 5). As is the case with Site 1003, most of the turbidites were shed in the Seravillian (middle Miocene), followed by Burgidalian, late Langhian, early Tortonian, early Messinian, and early Pliocene. Only a few turbidites were recorded in the early Langhian, late Tortonian, and late Messinian. Compared to Site 1003, overall the lowstand turbidites were more abundant except in the late Langhian (Table 7).
The Miocene turbidites can be separated from the background sediment by compositional differences. Figure 7 illustrates the differences in composition between background sediments (Figs. 7A, 7B) and turbidite sediments (Figs. 7C, 7D) at Sites 1003 and 1007. In comparison to the background sediment, turbidite deposits show a higher abundance of shallow-water components including green algae, red algae, shallow-water benthic foraminifers (such as Miliolids), and ooids. The turbidites at Site 1003 on the lower slope show an abundance of intraclasts and mollusks, whereas the turbidites at the toe of the slope (Site 1007) consist mostly of deeper water benthic foraminifers (rotaliids), lithoclasts, and bioclasts. The background sediment consistently contains more deep-water benthic foraminifers, fine-grained muddy particles, and planktonic foraminifers (Table 8, Table 9).
Turbidites deposited during sea-level highstand can be compared to those deposited during sea-level lowstand (Fig. 8, Fig. 9). Highstand turbidites show a higher abundance of shallow-water constituents including green algae, red algae, shallow-water benthic foraminifers (Miliolids), lithoclasts, and intraclasts. The lowstand turbidites are characterized by planktonic foraminifers and micrite.
The composition of highstand or lowstand turbidites at the lower slope is very similar to the toe of the slope. The only difference consists in the number of benthic foraminifers (rotaliids) and bioclasts. During sea-level highstand, a larger number of rotaliids and bioclasts are deposited at the lower slope, while during lowstand, more bioclasts are deposited at the lower slope (Table 10, Table 11).
A comparison of background sediment in lowstand vs. highstand deposits reveals few diagnostic indicators (Fig. 10, Fig. 11). The background sediment deposited during sea-level lowstand (Site 1007) consists of a higher abundance of planktonic foraminifers and lithoclasts, whereas the background sediment deposited during sea-level highstand shows a higher abundance of deep-water benthic foraminifers (rotaliids) and fine-grained, muddy particles. On the lower slope, shallow-water components such as green algae, red algae, ooids, and mollusks characterize sea-level highstands, whereas the same shallow-water components show a higher abundance at the toe of the slope during sea-level lowstands (Table 12, Table 13).