Mineralogy and geochemistry of altered ash, pelagic clay, and a clay vein in basalt from DSDP Leg 62 Holes

Volcanic ash was recovered from lower Aptian to Albian deposits from DSDP Sites 463, 465, and 466; pelagic clay of the upper Pleistocene to Upper Cretaceous was recovered mainly from Site 464, with minor amounts at Sites 465 and 466. We present X-ray-mineralogy data on pelagic clay and altered volcanic ash recovered from the four Leg 62 sites. In addition, two ash samples from Sites 463 and 465, a pelagic clay from Site 464, and a clay vein from the basaltic basement at Site 464 each were analyzed for major, minor, and trace elements. Our purpose is to describe the mineralogy and chemistry of altered ash and pelagic clays, to determine the sources of their parent material, and to delineate the diagenetic history of these clay-rich deposits. Correlation of chemistry and mineralogy of ash and pelagic clay with volcanic rocks suspected to be their parent material is not always straightforward, because weathering and diagenetic alteration caused depletion or enrichment of many elements.

Clay minerals in Mesozoic and Cenozoic sediments at DSDP Leg 62 Holes

The main tasks of this study were (1) identification of minerals of the clay fraction, (2) identification of clay-mineral associations in relation to stratigraphic intervals, and (3) elucidation of genetic relations of clay minerals with types of sediments and factors of sedimentation. Identification of clay minerals was carried out mainly with an X-ray diffractometer (DRON-I). X-ray diffractograms were prepared by means of CuKalpha radiation, at 35 kW and a current of 20 ma. The scanning rate was 2°/min. Oriented specimens were prepared for the <1-µm fraction (and partly for the <10-µm fraction because of insufficient core material) in three states: air-dried, saturated with glycerine, and heated at 550°C.