Thickness distribution of reddish brown clay in the western North Pacific

Abstract

Thickness and stratigraphy of reddish brown clay were compiled from lithologic descriptions of various types of cored surface sediments in the western North Pacific. Thin brown clays usually overlie gray clay in hemipelagic depositional environments and the thickness of the brown clay increases offshore, as results of the decreasing rate of sedimentation of terrigenous organic matter. The hemipelagic gray clay disappears in pelagic environments and several tens of meters of pelagic red clay overlies the basement sedimentary sequences of bedded chert and chalk in the pelagic seafloor. In the boundary region of the hemipelagic and pelagic sequences at the outer open floor of the trench basin, the pelagic facies of the red clay-bedded chert-chalk assemblage underlie the hemipelagic gray clay. This stratigraphy might indicate subduction of pelagic facies below the hemipelagic sequences.