Geochemical History of Post-Jurassic Sedimentation in the Central Northwestern Pacific, Northern Hess Rise, Deep Sea Drilling Project Site 464

Abstract

Results describe the chemical composition of post-Jurassic sediments penetrated by Deep Sea Drilling Project Hole 464 (northern Hess Rise), peculiar features in the distribution of chemical components through the section, and modes of their occurrence determined by factor analysis and from the data on mineralogy, lithology, and accumulation rates of sediments and chemical components.Three main stages in the geochemical history of sedimentation in the region are outlined: I. Late Mesozoic stage (Early Albian-Cenomanian). la. Early phase (Late Aptian-Early Albian). This early phase is characterized by accumulation of dark-red and brown, calcareous silica-clay oozes, considerably enriched by volcanogenic (mostly hyalopelite basalt volcaniclastic) material. High accumulation rates of sediments (22.5 mm 10~3yr -1 ) and chemical components are noted. Ib. Late phase (late Albian-Cenomanian). Accumulation of relatively light-colored, calcareous, essentially silicic sediments took place at that time. The amount of volcaniclastic material, iron, and other heavy metals in these sediments is much less than in the early Albian deposits. Relatively high accumulation rates of sediments (17.9 mm 10~3yr~') and of some of the components (SiO 2 , A1 2 O 3 , etc.) were recorded. The obtained data are in good correlation with the model which implies that in the Albian the northern part of Hess Rise was in the equatorial zone, with high biological productivity, while the Pacific Plate moved northward. II. Late Cretaceous (Early Turonian?-Middle Miocene). During that time, relatively local accumulation of fine volcaniclastic material (ash) took place; this material was transformed into clay (montmorillonite-hydromica) enriched by ferric hydroxide, and to a lesser degree by Mnhydroxide and associated heavy metals. III. Late Cenozoic stage (upper Miocene-Pleistocene) was the time of accumulation of clay-silica, mostly radiolarian oozes, in chemical composition and accumulation rates similar to the typical clay-silica sediments of the modern open ocean at depths below the level of carbonate compensation. The outlined stages, phases of geochemical history of sedimentation in the region, represent the evolution of sediment accumulation in the basin.

The origin of black shale-hosted Mn deposits in Paratethyan basins: Constraints from geological events at the Eocene/Oligocene boundary

“…In the terminal Eocene-Oligocene time, the strong global cooling [Savin, 1977] and a relative increase in the surface water density gave rise to the systems of vertical circulation and bottom currents that operate to this day. The bottom currents, when their velocity increased, transported very appreciable masses of nutrients (of initially hydrothermal, halmyrogenic nature), to result in Early Oligocene time in high biological productivity accompanied by massive siliceous and organic-rich deposition [Laliev, 1964;Lisitsyn, 1980;Van Andel, 1976;Varentsov et al, 1981]. Broad development of such siliceous deposits is typical of sedimentation in the Early Oligocene basin of Georgia.…”