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doi:10.2204/iodp.proc.324.102.2010 PaleontologyCalcareous microfossils (nannofossils, planktonic foraminifers, and benthic foraminifers) were examined for core catcher samples as well as for additional section-half samples. Preliminary age assignments were based on biostratigraphic analyses of calcareous nannofossils and planktonic foraminifers. Paleobathymetric interpretations were based on benthic foraminifer assemblages. Where possible, the preservation, abundance, and zonal assignment of each microfossil group were entered into the LIMS database through the DESClogik software. The timescale used for this study is that constructed for Leg 198 (Shipboard Scientific Party, 2002a) (Fig. F4). This timescale is based chiefly on Gradstein et al. (1995) and Channell et al. (1995) for the Cretaceous part. For planktonic foraminifer biochronology, modifications to the Leg 198 timescale were made on the base of the Leupoldina cabri Zone (120.5 Ma) and the base of the Rotalipora globotruncanoides Zone (98.9 Ma), according to Leckie et al. (2002). Calcareous microfossil datumsAge assignments for Cretaceous calcareous nannofossil and foraminifer datums (FO = first occurrence or datum base; LO = last occurrence or datum top) are from Erba et al. (1995), Bralower et al. (1997), Premoli Silva and Sliter (1999), and Leckie et al. (2002). Cretaceous datums are graphically presented in Figure F4 and listed in Tables T2 and T3. The ages of a few Cenozoic calcareous nannofossil datums are estimated following Leg 198 (Shipboard Scientific Party, 2002a). Calcareous nannofossilsCalcareous nannofossil zonal scheme and taxonomyThe zonal schemes of Sissingh (1977; CC zones [modified by Perch-Nielsen, 1985]) and Burnett (1998; UC zones) are used for the Late Cretaceous, and those of Roth (1978, 1983; NC zones) for the Early Cretaceous. For the Jurassic/Cretaceous boundary interval, subdivisions proposed by Bralower et al. (1989; NK and NJK zones) are applied. The zonation used is presented in Figure F4. For consistency with the results from Leg 198, nannofossil taxonomy follows Bown (1999). Full taxonomic lists can be found therein. The zonal scheme of Bukry (1973, 1975 [modified by Okada and Bukry, 1980]) is used for the few stratigraphic alignments of Cenozoic calcareous nannofossils. Methods of study for calcareous nannofossilsCalcareous nannofossils were examined in smear slides prepared from raw sediment samples. Slides were observed using standard light microscope techniques, under crossed polarizers, transmitted light, and phase contrast at 1000x magnification. Estimates of the abundance of calcareous nannofossils are
Preservation of calcareous nannofossils are
ForaminifersPlanktonic foraminifer zonal scheme and taxonomyThe zonation used for Cretaceous planktonic foraminifers (Fig. F4) is based on Caron (1985), Sliter (1989), Robaszynski and Caron (1995), Premoli Silva and Sliter (1999), and Leckie et al. (2002). Cretaceous taxonomic concepts of planktonic foraminifers selectively follow those of Michael (1972), Robaszynski et al. (1984), Caron (1985), Nederbragt (1991), Boudagher-Fadel et al. (1997), Bellier and Moullade (2002), Moullade et al. (2002), Verga and Premoli Silva (2003a, 2003b, 2005), and Petrizzo and Huber (2006). Benthic foraminifer taxonomy and paleodepth estimationIn this study, identification of benthic foraminifers is made at the genus level. The benthic taxonomic concepts selectively follow Luterbacher (1973), Sliter (1977, 1980), Gradstein (1978), Loeblich and Tappan (1988), Bolli et al. (1994), Widmark (1997), and Holbourn and Kaminski (1997). Cretaceous paleodepth interpretation is based on Sliter and Baker (1972), Sliter (1977, 1980), Nyong and Olsson (1984), Koutsoukos and Hart (1990), Sikora and Olsson (1991), Jones and Wonders (1992), and Holbourn et al. (2001). The bathymetric terminology follows Sikora and Olsson (1991):
Methods of study for foraminifersAmong pelagic carbonate samples (~1–2 cm3), soft ooze sediments were spray-washed on a 63 µm sieve without any chemical reaction steps, placed in an ultrasonic bath for <1 s, and oven-dried at <50°C. Chalks and limestones were cut into small pieces, soaked in a 3% hydrogen peroxide solution, wet-sieved at 63 µm, sonicated for a few seconds, and oven-dried at <50°C. Indurated or incompletely disaggregated samples were further processed through the glacial (=100%) acetic acid technique (Ando et al., 2009, and references therein) as follows: each sample was oven-dried at ~80°C, soaked in glacial acetic acid for a few hours, quickly transferred to a 63 µm sieve, and washed thoroughly with tap water. The sample was then kept in a beaker full of water until cessation of the chemical reaction, followed by screen-washing and oven-drying. For mudstones (~3–5 cm3), each sample was oven-dried at ~80°C and soaked in kerosene for a few hours. After removing excess kerosene, the sample was immersed in boiling water and wet-sieved at 63 µm. Foraminifer picking and identification were made on the >150 µm size fraction under a stereomicroscope. For pre-Albian samples with smaller planktonic foraminifer test sizes and/or low-abundance benthic foraminifers, the >125 µm fraction was used. For samples with high foraminifer abundance, the sieved fraction was evenly spread on a gridded picking tray, and both planktonic and benthic foraminifers were picked together from the grid transect (~200 specimens). Further collection of benthic foraminifers was made on the entire picking tray. The following categories were used for description of both planktonic and benthic foraminifer abundance:
The preservation status of foraminifers was estimated as | |||
