Clay minerals in Cenozoic sediments off Cape Roberts (McMurdo Sound, Antarctica) reveal palaeoclimatic history
AbstractThe clay mineral assemblages of the ca. 1600 m thick Cenozoic sedimentary succession recovered at the CRP-1, CRP-2/2Aand CRP-3 drill sites off Cape Roberts on the McMurdo Sound shelf, Antarctica, were analysed in order to reconstruct thepalaeoclimate and the glacial history of this part of Antarctica. The sequence can be subdivided into seven clay mineral unitsthat reflect the transition from humid to subpolar and polar conditions. Unit I (35–33.6 Ma) is characterised by an almostmonomineralic assemblage consisting of well crystalline, authigenic smectite, and therefore does not allow a palaeoclimaticreconstruction. Unit II (33.6–33.1 Ma) has also a monomineralic clay mineral composition. However, the assemblage consistsof variably crystallized smectite that, at least in part, is of detrital origin and indicates chemical weathering under a humidclimate. The main source area for the clays was in the Transantarctic Mountains. Minor amounts of illite and chlorite appear forthe first time in Unit III (33.1–31 Ma) and suggest subordinate physical weathering. The sediments of Unit IV (31–30.5 Ma)have strongly variable smectite and illite concentrations indicating an alternation of chemical weathering periods and physicalweathering periods. Unit V (30.5–24.2 Ma) shows a further shift towards physical weathering. Unit VI (24.2–18.5 Ma)indicates strong physical weathering under a cold climate with persistent and intense illite formation. Unit VII (18.5 Ma topresent) documents an additional input of smectite derived from the McMurdo Volcanic Group in the south.D 2005 Elsevier B.V. All rights reserved.