Grain size and chemical compositions of bottom sediments from the Amur Bay

Composition of clay minerals in the <0.001 mm size fraction from the uppermost layer of bottom sediments in the northern Amur Bay was determined by X-ray powder diffraction analysis, and enrichment of 33 elements in the <0.001 mm and <0.01 mm size fractions of surface sediments from a number of sites at the marginal filter of the Razdol'naya River were studied by ICP-MS. Fe, U, and chalcophile elements occur in the highest concentrations in sediments from all sampling sites within the filter. The bottom sediments are not enriched in trace, alkali, and alkaline earth elements. Maximum concentrations of chemical elements were found in deposits from the brackish part of the marginal filter, perhaps, because of formation of Fe and Mn (Al) hydroxides. Bottom sediments at the boundary between the brackish and marine parts of the filter contain the lowest concentrations of the examined elements.

Eolian mass-accumulation rates and grain size at DSDP Sites 86-576 and 86-578

The mass-accumulation rate and grain size of the total eolian component of North Pacific pelagic clays at Deep Sea Drilling Project Sites 576 and 578 have been used to evaluate changes in eolian sedimentation and the intensity of atmospheric circulation that have occurred during the past 70 m.y. Eolian deposition, an indicator of source area aridity, was low in the Paleocene, Eocene, and Oligocene, apparently reflecting the humid environments of that time as well as the lack of glacial erosion products. A general increase in eoiian accumulation in the Miocene apparently reflects the relative increase in global aridity during the latter part of the Cenozoic. A dramatic increase in eolian accumulation rates in the Pliocene reflects the increased aridity and availability of glacial erosion products associated with Northern Hemisphere glaciation 2.5 m.y. ago. Eolian grain size, an indicator of wind intensity, suggests that Late Cretaceous wind strength was comparable to present-day wind strength. A sharp decrease in eolian grain size across the Paleocene/Eocene boundary is not readily interpreted, but may indicate a significant reduction in the intensity of atmospheric circulation at that time. Fine eolian grain size and low accumulation rates in the Eocene and early Oligocene are in agreement with low early Tertiary thermal gradients and less vigorous atmospheric circulation. Large increases in grain size during the Oligocene, mid-to-late Miocene, and Pliocene appear to be a response to steepening thermal gradients resulting from increasing polar isolation.