Continuous hemipelagic sediments from Sites 1143 and 1146 were recovered using a combination of advanced hydraulic piston coring and extended core barrel drilling. This report focuses upon the Miocene-age sediments recovered from both sites (5.32 Ma and older). Specifically, sediment samples were examined from the lowermost Pliocene (beginning several cores above the base of planktonic foraminiferal Zone N19/calcareous nannofossil Zone CN10) to the bottom of the drilled holes. For Site 1143 the studied interval is from 182.91 to 512.91 meters composite depth (mcd) (Samples 184-1143A-20H-1, 115-117 cm, through 184-1143C-54X-CC, 43-48 cm). For Site 1146 the studied interval is from 295.17 to 643.11 mcd (Samples 184-1146A-30X-5, 10-14 cm, through 64X-CC, 35-41 cm). In general, three samples per core (~9.6 m) were studied from both sites. Zonal boundaries and primary datums are placed at the average depth of the two samples that constrained them (Tables T1, T2, T3, T4).
Sediment volumes of ~10 cm3 (Site 1143) and ~20 cm3 (Site 1146) were collected; the larger volume was taken for Site 1146 when the processing of Site 1143 samples yielded few foraminifers (on average). All samples were soaked in a mixture of three parts water to one part hydrogen peroxide (initially 40% wt/vol H2O2) and Calgon (adjusting the pH to alkaline) for several days. The mixture was then washed over a 63-µm screen, and the residues were dried in an oven at 60°C. The residues from the >150-µm sieve fraction were examined for the species present (richness), relative abundance, and preservation.
Each sample was first repeatedly split with a microsplitter until a volume of sediment, equivalent to that used for a population analysis (~2000 tests), was obtained and evenly spread onto a picking tray. This smaller but representative sample volume allows for a more accurate visual assessment of species relative abundances and preservation. Abundances were categorized as follows:
Sample preservation was qualitatively estimated by the degree of test breakage and/or dissolution:
To determine species richness and to place zonal boundaries accurately, foraminiferal tests were spread upon a picking tray and examined using a binocular microscope (typically, a minimum of two trays were examined). In some cases a large fraction of the vial or its entire contents were examined (because of low to moderate yields after washing or the scarcity of a marker species). Tests of representative species were mounted on gummed slides. Both authors examined all samples.
The observed species and their relative abundances, as well as sample preservation, are recorded in occurrence tables for each site (Site 1143, Table T1; Site 1146, Table T2). The primary intent of this report is to locate and substantiate the placement of planktonic foraminiferal biostratigraphic zonal boundaries within the two sites by using both primary and secondary marker species. The resulting biostratigraphy provides the basis for a revised age-depth model based on planktonic foraminifers. However, the species ranges presented on the occurrence tables herein (Tables T1, T2) should be considered provisional with the exception of the species used to define the biostratigraphic zones.
The species concepts used to identify the planktonic foraminifers for this report closely follow Kennett and Srinivasan (1983), Chaisson and Leckie (1993), Chaisson and Pearson (1997), and Norris (1998) except where stated in the "Appendix." The notes that follow briefly describe the species observed at both sites and/or provide commentary as to how we differentiated these taxa from other similar species.