(Table 1) Biostratigraphic datums of ODP Leg 133 sites

We use benthic foraminifers to reconstruct the Neogene paleobathymetric history of the Marion Plateau, Queensland Plateau, Townsville Trough, and Queensland Trough on the northeastern Australian margin (Ocean Drilling Program Leg 133). Western Queensland Plateau Site 811/825 (present depth, ~938 m) deepened from the neritic zone (0-200 m) to the upper bathyal zone (200-600 m) during the middle Miocene (~13-14 Ma), with further deepening into the middle bathyal zone (600-1000 m) occurring during the late Miocene (~7 Ma). A depth transect across the southern Queensland Plateau shows that deepening from the outer neritic zone (100-200 m) to the upper bathyal zone began during the latest Miocene (~6 Ma) at the deepest location (Site 813, present depth, 539.1 m), whereas the shallower Sites 812 and 814 (present depths, 461.6 and 520.4 m, respectively) deepened during the late Pliocene (~2.7 and ~2.9 Ma). At Marion Plateau Site 815 (present depth, 465.5 m), water depth increased during the late Miocene (~6.7 Ma) from the outer neritic to the upper bathyal zone. Nearby Site 816 (present water depth, 437.3 m) contains Pliocene upper bathyal assemblages that directly overlie middle Miocene shallow neritic deposits; the timing of the deepening is uncertain because of a late Miocene hiatus. On the northern slope of the Townsville Trough (Site 817, present depth, 1015.8 m), benthic foraminifers and sponge spicules indicate deepening from the lower upper bathyal (400-600 m) to the middle bathyal zone in the late Miocene (by ~6.8 Ma). Benthic foraminiferal faunas at nearby Site 818 (present water depth, 752.1 m) do not show evidence of paleobathymetric change; however, a late Pliocene (~2-3 Ma) increase in downslope transport may have been related to the drowning of the Queensland Plateau. Site 822 (present depth, 955.2 m), at the base of the Great Barrier Reef slope, deepened from the upper bathyal to the middle bathyal zone during the late Pliocene (by ~2.3 Ma). Queensland Trough Site 823 (present depth, 1638.4 m) deepened from the middle bathyal to the lower bathyal (1000-2000 m) zone during the late Miocene (~6.5 Ma). Benthic foraminiferal faunal changes at these Leg 133 sites indicate that rapid deepening occurred during the middle Miocene (~13-14 Ma), late Miocene (6-7 Ma), and late Pliocene (2-3 Ma) along the northeastern Australian margin.

Nannofossil biohorizons for ODP Leg 133 sites

Paleontological studies conducted subsequent to the completion of Leg 133 led to refinements of the biostratigraphy for the Leg 133 sites. These biostratigraphic refinements bear on the calculations of sedimentation rates and on the age-depth plots prepared for the Initial Reports volume for Leg 133. To make available the revised data to anyone who may wish to make use of it, the revised biostratigraphic information is presented here in tabulated form. Revised age-depth plots also are presented for all of the sites to facilitate comparison of sedimentation rate curves and to identify intervals where significant changes have been made based on post-cruise studies. The revised age-depth plots include calcareous nannofossils only, and the revised data have been taken from thechapters contributed for this volume (Gartner et al., 1993, doi:10.2973/odp.proc.sr.133.213.1993; Wei and Gartner, 1993, doi:10.2973/odp.proc.sr.133.216.1993). Planktonic foraminifer biostratigraphy revisions became available subsequently and could not be readily incorporated. The age-depth plots for Sites 812 through 818 were made with the (ADP) program provided to ODP by Dave Lazarus.

Pleistocene sedimentology of ODP Hole 133-820A from the northeastern Australian margin

A principal objective at Site 820, situated on the outer shelf, upper slope of the northeastern Australian continental margin, was to test the relationships between changes in Pleistocene sea level and sedimentary packages produced on a mixed carbonate-siliciclastic continental margin. To this end, we have examined the downcore distribution of grain size, magnetic susceptibility, and calcium-carbonate content throughout Hole 820A and, in particular, the top 35 meters below the seafloor (mbsf). These data are compared with variations in the oxygen-isotope signal defined for the same hole and are interpreted as indicating sea-level oscillations. The distribution of sand, mud, calcium carbonate of the mud fraction and total sample, and magnetic susceptibility during the last 20,000 yr defines the position of a sea-level regression (41,000-18,000 yr B.P.), a lowstand, early (18,000-9,400 yr B.P.) and late transgressions (9400-900 yr B.P.), and a highstand (4900 yr to the present). The regression is seen first in a high-carbonate content peak. Calcium carbonate constituents mainly comprise skeletal carbonate grains, with abundant planktonic and benthic foraminifers, and lime muds. The lowstand is characterized by a maximum abundance of the sand fraction, which contains dominantly skeletal carbonate grains and a minor abundance of lithoclasts. Sand-sized terrigenous sediments are proposed to have bypassed the continental shelf during a lowstand of sea level. Sedimentation rates throughout the regression and lowstand are low (3.0 cm/k.y.). The early transgression, marked by highest values in magnetic susceptibility, displays a rapid increase in sedimentation rate that coincided with an increase in terrigenous mud. Highest sedimentation rates of 82.3 cm/k.y. occurred during the late transgression, with increasing percentages of lime-mud. A decrease in noncarbonate constituents in the mud fraction during the late transgression and highstand of sea level is thought to be the result of restricted inner-shelf sedimentation of terrigenous sediments. The same relationship is also seen in the major sea-level oscillation, which is interpreted as isotope stage 6.