Preliminary age assignments were based on planktonic foraminifer, calcareous nannofossil, and larger benthic foraminifer biostratigraphic analysis from core catcher samples, augmented by selected samples within cores to refine placement of datum levels and assemblage boundaries. Sample position, group abundance, group preservation, species frequency, and age or zone of each fossil group are recorded in the ODP database. The timescale and datum ages of planktonic foraminifers and nannofossils follow those of Berggren et al. (1995b). The larger benthic foraminiferal associations and ranges in northern Australia relative to Neogene planktonic foraminiferal zones as determined by Chaproniere (1981, 1984) and modified by Chaproniere and Betzler (1993) were also used.
Shipboard analysis focused primarily on the determination of key datum levels, which provided age control points. As many of the datums do not coincide with traditional zonal boundaries, it was more accurate and convenient to directly report the datums and their corresponding ages rather than translating them into fractional or multiple zones.
Smear slides were prepared directly from nonindurated sediments. For indurated or semi-indurated samples, a spatula was used to grind the samples and only the fine fractions were used to make slides. Slides were examined in a Zeiss light microscope at a magnification of 400× or 1000×, depending on the size of the nannofossils.
Calcareous nannofossil preservation was assessed using the following criteria:
The total relative abundance of calcareous nannofossils for each sample was estimated as follows:
Nannofossil abundances of individual species were recorded as follows:
The foraminifer-based ages were primarily determined by the use of the Berggren et al. (1995b) zonation scheme in association with the tropical Neogene planktonic foraminifer "N-zonation" scheme of Blow (1969), with additional modifications by Kennett and Srinivasan (1983) and Bolli and Saunders (1985) (Fig. F8).
Sample preparation methods varied according to the degree of lithification. Most samples were ultrasonically agitated in a 10% hydrogen peroxide solution and were then washed over a <63-µm sieve. Semilithified samples were manually disaggregated into smaller pieces, sonicated, and sometimes heated in a 10% hydrogen peroxide solution. All samples were oven dried at ~60°C and then sieved into <1-mm, <250-µm, <150-µm, and >150-µm fractions. The <250-µm and <150-µm fractions were used for the examination of planktonic foraminifers. Planktonic foraminiferal abundances were quantitatively estimated using the following categories:
Preservation quality was described as follows:
The whole-sample fractional volume of planktonic foraminifers was described as follows:
Selected larger benthic foraminifers provided limited biostratigraphic resolution within platform intervals that lacked planktonic foraminifers and nannofossils. Larger foraminifers were identified at the genus level and, when possible, to species using washed core catcher samples supplemented by visual observation of half cores. Thin sections provided verification of generic and species-level identifications. Table T3 provides the range estimates of selected taxa from Chaproniere (1981, 1984), modified by Chaproniere and Betzler (1993) and Betzler (1997). Betzler (1997) documented the extension of the upper range of Lepidocyclina howchini into the late Miocene on the Queensland Plateau. This range of L. howchini is in agreement with shipboard biostratigraphy provided by planktonic foraminifers and nannofossils in association with seismic stratigraphy. Detailed shore-based analysis of disaggregated specimens and thin sections will be required to document precisely the upper range of L. howchini on the Marion Plateau.
Core catcher samples provided the principal source of data for paleoenvironmental interpretations. Lithologic variations necessitated the use of flexible preparation and analysis criteria. In lithified sections, interpretations were augmented by visual examination of whole cores and of thin sections prepared for sedimentological analysis (see "Lithostratigraphy and Sedimentology").
Sample preparation methods varied according to the degree of lithification, as noted under "Planktonic Foraminifers". Approximately 300 mg of sample was evenly distributed onto a black gridded picking tray and examined. The whole-sample fractional volume for principal constituents was described as follows:
Preservation quality was described as follows:
Paleobathymetric estimates using benthic foraminifers utilized a modification of van Morkhoven et al.'s (1986) depth zonations to determine outer neritic and upper bathyal depths, and Hallock's (1999) zonations of larger benthic foraminifers (Table T4). The following bathymetric ranges were used:
All sites are in <400 m water depth. Inner and middle neritic depths were assumed to have been within the euphotic zone and were subdivided based upon the taxa and robustness of larger benthic foraminifers.
Depositional settings were interpreted based upon paleobathymetric (Table T4) and sediment constituent (Table T5) assessment. Platform environments were characterized by carbonate sedimentation in euphotic environments of inner to middle neritic depths, predominantly bryozoan-, red algal-, or coral-dominated facies and a significant component of larger benthic foraminifers. Periplatform environments were interpreted when carbonate bioclastic sediments of neritic origin dominated deposition in subeuphotic environments. Periplatform environments were further divided into "proximal" and "distal" based on the texture of the neritic constituents and the prevalence of sediments of pelagic origin. Proximal periplatform sediments are characterized by a wide size range of transported neritic material, generally with minor components of planktonic and outer neritic/upper bathyal benthic foraminifers. Distal periplatform sediments are characterized by silt to very fine sand-sized neritic carbonate debris mixed with planktonic foraminiferal tests and debris and conspicuous, although generally not abundant, outer neritic to upper bathyal benthic foraminifers. Hemipelagic sediments are dominated by planktonic foraminiferal tests, with conspicuous outer neritic/upper bathyal benthic foraminifers. Terrigenous sediments, ranging from coarse quartz and lithic fragments to clays, are occasionally found in all depositional settings.