Analysis of the iron oxide assemblages in the ANDRILL AND-1B drill core, Ross Sea, Antarctica

The AND-1B drill core recovered a 13.57 million year Miocene through Pleistocene record from beneath the McMurdo Ice Shelf in Antarctica (77.9°S, 167.1°E). Varying sedimentary facies in the 1285 m core indicate glacial-interglacial cyclicity with the proximity of ice at the site ranging from grounding of ice in 917 m of water to ice free marine conditions. Broader interpretation of climatic conditions of the wider Ross Sea Embayment is deduced from provenance studies. Here we present an analysis of the iron oxide assemblages in the AND-1B core and interpret their variability with respect to wider paleoclimatic conditions. The core is naturally divided into an upper and lower succession by an expanded 170 m thick volcanic interval between 590 and 760 m. Above 590 m the Plio-Pleistocene glacial cycles are diatom rich and below 760 m late Miocene glacial cycles are terrigenous. Electron microscopy and rock magnetic parameters confirm the subdivision with biogenic silica diluting the terrigenous input (fine pseudo-single domain and stable single domain titanomagnetite from the McMurdo Volcanic Group with a variety of textures and compositions) above 590 m. Below 760 m, the Miocene section consists of coarse-grained ilmenite and multidomain magnetite derived from Transantarctic Mountain lithologies. This may reflect ice flow patterns and the absence of McMurdo Volcanic Group volcanic centers or indicate that volcanic centers had not yet grown to a significant size. The combined rock magnetic and electron microscopy signatures of magnetic minerals serve as provenance tracers in both ice proximal and distal sedimentary units, aiding in the study of ice sheet extent and dynamics, and the identification of ice rafted debris sources and dispersal patterns in the Ross Sea sector of Antarctica.

40Ar-39Ar geochronological studies on rocks at DSDP Leg 58 Holes

The technique of 40Ar-39Ar step-heating dating was applied to three rock samples from core of DSDP Site 443, one sample from Site 445, and four samples at Site 446. All sites were drilled during DSDP Leg 58. At Site 443 (Shikoku Basin), about 116 meters of basalt basement was drilled. Three samples were chosen for dating from different levels in the basalt; two samples are aphyric basalt, and the other is subophitic dolerite. At Site 445 (Daito Ridge), no basement rock was drilled; however, conglomeratic sandstone was cored in the lower part of the hole. 40Ar-39Ar dating was applied to a basalt pebble in the conglomerate. At Site 446 (Daito Basin), the lower cored sequence is clay stone interlayered with 16 basalt sills. Four samples were chosen from sills at different levels.