13C
values can be used to infer the origin of the organic matter contained within
the sediments and to explore some of the factors affecting its preservation and
accumulation (Meyers, 1994).Site 1085 is located on
the continental rise of southwest Africa at a water depth of 1713 m off the
mouth of the Orange River in the Cape Basin. The site is part of the suite of
locations drilled during Leg 175 on the Africa margin to reconstruct the onset
and evolution of the elevated biological productivity associated with the
Benguela Current upwelling system (Wefer, Berger, Richter, et al., 1998). Three
sediment samples were collected per section from Cores 170-1085A-28H through 45X
(251-419 mbsf) to provide a survey of the sediment record of paleoproductivity
from the middle late Miocene to the early Pliocene (~8.7-4.7 Ma), which is a
period that includes the postulated northward migration and intensification of
the Benguela Current and the establishment of modern circulation off southwest
Africa (Siesser, 1980; Diester-Haass et al., 1992; Berger et al., 1998). Core
170-1085A-30H (270-279 mbsf) had essentially no recovery; this coring gap was
filled with samples from Cores 170-1085B-29H and 30H (261-280 mbsf). The results
of measurements of multiple paleoproductivity proxies are summarized in this
report. Included in these proxies are the radiolarian, foraminiferal, and
echinoderm components of the sand-sized sediment fraction. Opal skeletons of
radiolarians (no diatoms were found) relate to paleoproductivity and water mass
chemistry (Summerhayes et al., 1995; Lange and Berger, 1993; Nelson et al.,
1995). The accumulation rates of benthic foraminifers are useful proxies for
paleoproductivity (Herguera and Berger, 1991; Nees, 1997; Schmiedl and Mackensen,
1997) because these fauna subsist on organic matter exported from the photic
zone. Echinoderms also depend mainly on food supply from the photic zone (Gooday
and Turley, 1990), and their accumulation rates are an additional
paleoproductivity proxy. Concentrations of calcium carbonate (CaCO3)
and organic carbon in sediment samples are fundamental measures of
paleoproductivity (e.g., Meyers, 1997). In addition, organic matter atomic
carbon/nitrogen (C/N) ratios and 13C
values can be used to infer the origin of the organic matter contained within
the sediments and to explore some of the factors affecting its preservation and
accumulation (Meyers, 1994).
1 Diester-Haass, L., Meyers, P.A., Vidal, L., and Wefer, G., 2001. Data report: Sand fraction, carbonate, and organic carbon contents of late Miocene sediments from Site 1085, Middle Cape Basin. In Wefer, G., Berger, W.H., and Richter, C. (Eds.), Proc. ODP, Sci. Results, 175 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/175_SR/chap_01/chap_01.htm> [Cited YYYY-MM-DD]
2 Zentrum für Umweltforschung, Universität des Saarlandes, D-66041 Saarbrücken, Federal Republic of Germany. A.L.Haass@t-online.de
3 Department of Geological Sciences, University of Michigan, Ann Arbor MI 48109-1063 USA.
4 Universite Aix-Marseille, Europole de l'Arbois, BP 80, 13545 Aix en Provence Cedex, France.
5 Fachbereich Geologie, Universität Bremen, D-28334 Bremen, Federal Republic of Germany.
Initial
receipt: 31 January 2000
Acceptance: 24 July 2000
Web publication: 10 January 2001
Ms 175SR-222
