INTRODUCTION

Site 1081 (Fig. F1) (1937.2S, 1119.2E) is the shallow-water (793.8 m) site of the Walvis Ridge/Walvis Basin Group, which includes Ocean Drilling Program (ODP) Sites 1082 and 1083 and Deep Sea Drilling Project (DSDP) Sites 362 and 532 (Shipboard Scientific Party, 1998).

In general, the sediments at Site 1081 consist of clay with varying amounts of diatoms, nannofossils, foraminifers, and radiolarians; below 390 meters below seafloor (mbsf) the sediments are primarily a clayey nannofossil ooze (Shipboard Scientific Party, 1998). Concentrations of calcium carbonate and organic carbon are high to ~77 mbsf (average = 31 and 5 wt%, respectively); between 77 and 230 mbsf, concentrations of carbonate decrease to an average of 8 wt%, but organic carbon concentration remains high (maximum = 8.2 wt%; average = 5.21 wt%) (Shipboard Scientific Party, 1998). Between 230 and 390 mbsf, carbonate concentrations increase to an average of 18 wt% with 3.34 wt% organic carbon (Shipboard Scientific Party, 1998). Below 390 mbsf, carbonate concentrations average 30 wt% with 2.18 wt% organic carbon. Intervals of dolomitized clay are present between 137 and 183 mbsf (Shipboard Scientific Party, 1998). Sedimentation rates for the reported sample set are high, averaging between 70 and 150 m/m.y. (Shipboard Scientific Party, 1998). The oldest sediments are late Miocene in age based on paleontologic data (Shipboard Scientific Party, 1998). A complete magnetostratigraphy for the uppermost 120 mbsf was determined aboard ship (Shipboard Scientific Party, 1998).

Environmental processes affect the magnetic properties of sediments (Hall et al., 1997; Karlin, 1990a, 1990b; Karlin and Levi, 1983, 1985; Karlin et al., 1987; Roberts and Turner, 1993; Torii, 1997), particularly in areas of high productivity with a high organic carbon influx (Bloemendal et al., 1992; Hartl et al., 1995; Mead et al., 1986; Tarduno, 1994, 1995). Of particular concern are diagenetic changes that occur after core recovery (Richter et al., 1999; Roberts et al., 1999; Yamazaki et al., 2000), which affects the integrity of paleomagnetic and rock magnetic records of marine sediments.

In this paper, the following magnetic properties are reported for sediments recovered from Site 1081: remanent intensity variation, magnetic susceptibility, anhysteretic and isothermal remanence acquisition and demagnetization, and hysteresis behavior.

NEXT