THE GULF OF CÁDIZ CONTOURITE LABORATORY: VARIABILITY IN SEDIMENT COMPOSITION OVER THE PAST 200 KY

Integrated Ocean Drilling Program Expedition 339 drilled contourite deposits in the Gulf of Cádiz and West Iberian margin. These recovered sedimentary successions provide key data for examining the development of the Mediterranean Outflow Water and the subsequent evolution of a complex contourite depositional system. In this study, we investigate MOW variability using mineralogy as a proxy. The major terrigenous mineral phases at Sites U1387 and U1389 were identified to define sediment composition and interpret its provenance. Temporal changes in sediment composition are analyzed over the last glacial/interglacial cycle, in order to identify changes in sediment provenance, continental weathering regimes, and/or dispersal patterns.

The shipboard age model was used to assign sediment ages (a constant sedimentation rate of 25 cm/ky for Site U1387 and 40 cm/ky for Site U1389). The samples investigated range from Recent to 200 ka, with a sampling interval of ~4 ky. Randomly mounted pressed powder samples were examined using x-ray diffractometry to identify bulk mineralogy. Semiquantitative mineral abundances in each sample are estimated by comparing the ratio of a mineral’s selected peak area to that of the 4.26 Å quartz peak. These values are compared with respect to Marine Isotope Stages.

Preliminary results show that the primary mineral phases include: quartz, calcite, dolomite, aragonite, feldspar, and a variety of clay minerals. This composition is consistent with adjacent onshore lithologies, and is also consistent with shipboard XRD results. No strong link between mineral phases and glacial/interglacial phases is detected. Average ratio values are generally higher during interglacial cycles.