A.G. Fischer | USGS Science

USGS1986

Rhythmic bedding in Upper Cretaceous pelagic carbonate sequences: Varying sedimentary response to climatic forcing

Rhythmic bedding is a prominent feature of North American and European Upper Cretaceous pelagic carbonate sequences deposited in epicontinental and continental-edge settings. Such bedding rhythms can result from variations in carbonate productivity, terrigenous dilution, redox conditions, or bottom currents. Each type of bedding cycle is expressed differently in the stratigraphic record but probably was caused by climatic cycles that are linked to variations in the Earth's orbital characteristics (Milankovitch cycles). Thus, pelagic carbonates of Cretaceous age acted as particularly sensitive recorders of orbitally induced changes in climate. Documentation of these bedding rhythms will permit detailed chronostratigraphic and lithostratigraphic correlations and will further illuminate depositional processes in Upper Cretaceous carbonate sequences.

Geology↗

USGS1970

Geological history of the western North Pacific

A considerable portion of the abyssal floor of the western North Pacific was already receiving pelagic sediment in late Jurassic time. Carbonate sediments were later replaced by abyssal clays as the basin deepened and bottom waters became more aggressive. The resulting facies boundary, which can be recognized on seismic profiles, is broadly transgressive; it ranges in age from mid-Cretaceous in the western Pacific to Oligocene in the central Pacific. Cherts are encountered at and below the major facies boundary and appear to have been formed by postdepositional processes.

Science↗