The Ocean Drilling Program (ODP) drilled at five sites in the western Atlantic Ocean during Leg 207. The objective of the drilling was to recover samples from the shallow buried Cretaceous and Paleocene sediments on the Demerara Rise off Suriname, South America. These sediments are being studied for a number of paleoceanographic studies of the low-latitude Atlantic off the coast of Suriname (this volume). For this report two sites, Sites 1257 and 1258, were selected for silicoflagellate study because shipboard results suggested these two sites as the only ones with siliceous microfossils of Paleocene–Eocene age.
The Demarara Rise is a predominant submarine plateau located off the coast of Suriname and French Guyana. This plateau stretches 380 km along the coast and is 220 km wide. The depth to seafloor along the depth transect drilled during ODP Leg 207 ranges from 1000 to 4500 m, but most of the remainder of the plateau lies in shallow water of 700 m. Much of this area is covered with 2–3 km of sediments. The Demerara Rise is built on rifted Precambrian continental crust. The plateau was one of the last places to be in contact with West Africa during the opening of the Atlantic Ocean (see Shipboard Scientific Party, 2004).
Site 1257 (9°27´N, 54°20´W; water depth = 2951 m) is located on a terrace on the northwestern Demerara Rise ~400 km from Suriname. This is the second deepest water depth location drilled during Leg 207. Sediments from this area range in age from Miocene to Albian. This area is part of the transform fault that separated from Central America and western Africa. Three holes were drilled at Site 1257.
Site 1258 (9°26´N, 54°43´W; water depth = 3192 m) is located on the western slope of the Demerara Rise ~380 km north of Suriname. This site is the distal and deepest site of the paleoceanographic depth transect drilled across Demerara Rise during Leg 207. The area is located on a ridge of Paleocene sediments cropping out on the seafloor. Three holes were drilled at Site 1258, but only one is studied.
Simple smear slides were first prepared from each sample. Next, to remove carbonate, ~5 cm3 of raw sample was placed into a 100-mL beaker, to which ~6 mL (sometimes more if needed) of 50% HCl was added while over a slide warmer set to low heat. This was left covered with parafilm overnight to complete the dissolution of any carbonate.
The sample was then centrifuged in a 15-mL test tube using distilled water (pH = 8) three times for 10 min each to remove the HCl. Approximately 6 mL (or until bubbling stopped) of 30% hydrogen peroxide was added, and the sample was allowed to sit covered overnight to remove organic material. The samples were again washed via centrifuge three times then wet-sieved into three size fractions: 63 µm, 38 µm, and the pan. Strewn slides mounted in Norland-61 optical adhesive on a 22 mm x 50 mm coverslip were then made for each fraction.
All the slides for each size fraction were completely examined, with all specimens representing more than one-half of a silicoflagellate included in the counts (see Tables T1, T2). This study was done at the Micropaleontology Undergraduate Research Laboratory at the University of Maine at Presque Isle. The microscope work and some of the analyses were conducted by undergraduate students having limited experience with silicoflagellates. Participating students generally have a year of training in micropaleontology and deep ocean drilling and then conduct micropaleontology research as a directed independent project that is closely supervised by the laboratory's director (K. McCartney).
1Power, C.P., and McCartney, K., 2007. Data report: silicoflagellates recovered from Ocean Drilling Program Leg 207 Sites 1257 and 1258. In Mosher, D.C., Erbacher, J., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 207: College Station, TX (Ocean Drilling Program), 1–11. doi:10.2973/odp.proc.sr.207.111.2007
2Micropaleontology Undergraduate Research Laboratory, University of Maine at Presque Isle, Presque Isle ME 04769, USA. Correspondence author: oldiron@mfx.net
Initial receipt: 14 November 2005
Acceptance: 15 March 2006
Web publication:
7 March 2007
Ms 207SR-111