William E. Frerichs

Paleobathymetry, paleotemperature, and tectonism

Paleobathymetric trends of Cenozoic sedimentary sections from widely separated geographic areas show striking similarities. In areas examined, early and middle Eocene and middle Oligocene to middle Miocene ages are intervals of deeper water sedimentation and warm oceanic temperatures. Late Eocene to early Oligocene and the late Miocene to Holocene ages are intervals of shallow-water deposition, colder oceanic temperatures, and glaciation. Some large-scale tectonic cycle, possibly related to convection cells and a phase change, may be responsible for these observed trends.

New Planktic Foraminiferal Data Documenting Coniacian Age For Laramide Orogeny Onset and Paleooceanography in Southern Mexico

A Late Cretaceous flysch comprising the 2600‐m‐thick Mexcala Formation records the initial local pulse of the Laramide Orogeny on the southern arm of the Mexican fold‐thrust belt in northeastern Guerrero State. We identified 15 planktic foraminiferal species from 35 productive shale samples that demonstrate that the Mexcala is assignable to the Dicarinella concavata biozone. Thus, in agreement with evidence from northern Mexico, the Laramide onset in southern Mexico occurred during Coniacian time. Paleozoogeographic interpretation of our faunas shows an oceanic connection with the Caribbean, and that the southern margin of the North American Plate in northern Guerrero must have been isolated from the Coniacian–early Santonian Pacific Ocean.

Distinguishing middle Late Cretaceous tectonic events from regional sea-level change using foraminiferal data from the U.S. Western Interior

Foraminiferal data from seven stratigraphic sections between the Utah-Wyoming thrust belt and western Kansas record 13 correlatable paleoecologic events between Coniacian and early Campanian time, and provide a framework for interpreting tectonic timing and regional sea-level changes. At least three events are synchronous within available biostratigraphic resolution. We infer that the events are regionally isochronous and result from short-term ( That the 13 paleoecologic events are observed across the foreland basin indicates that from western Kansas to the Sevier thrust belt the rate of change of sea level was sufficiently rapid to exceed the rate of sea-floor sedimentation in the case of sea-level rise, and the maximum rate of basin subsidence in the case of sea-level fall. The recognition of these events suggests that correlatable sea-level changes that are found within and beyond the flexural wavelength of foreland basins can be used to distinguish tectonic events from regional sea-level changes. The recognition of relatively short-term subsidence events indicates that tectonic events can occur in foreland basins on time scales similar to third-order (or possibly higher) eustatic sea-level changes. Although this study examines only data from the U.S. Western Interior, the technique of using high-resolution subsidence analysis to identify asymmetric subsidence promises to aid in identifying the tectonic component of subsidence in other foreland basin settings.

Tectonic implications of variations in sea floor spreading rates

Abstract Changes in sea floor spreading rates and directions are related in time to periods of worldwide uplift indicating that sea floor spreading episodes and tectonic cycles may be driven by the same basic mechanism.

Paleobathymetric trends of neogene foraminiferal assemblages and sea floor tectonism in the Andaman Sea area

Abstract Three Miocene and two Pliocene samples recovered from the floor of the Andaman Sea indicate a tectonic history for the sea floor which is similar to the surrounding islands. Benthonic Foraminifera from the Miocene samples indicate that the sediments were deposited in water depths significantly deeper than the depths from which they were dredged. Benthonic Foraminifera in the Pliocene samples, however, indicate depths of deposition similar to the water depths from which they were dredged. The similarity of paleobathymetric histories for the Andaman Sea and surrounding islands suggests that an uplift, probably beginning in the Middle Miocene and culminating in the Pliocene, has affected the entire region. Sediment accumulation and contemporaneous rates of sedimentation suggest that the Andaman Sea may not be older than the Miocene, and that the regional uplift may have been initiated at the same time as the sea-floor spreading.