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Geology topics

D.J. Bottjer

Publications and source records attributed to D.J. Bottjer.

4 recordsLinked to original sources
USGS2010

Rhythmic bedding produced in Cretaceous pelagic carbonate environments: Sensitive recorders of climatic cycles

Various types of rhythmic bedding are prominent features of Cretaceous pelagic carbonates. These bedding rhythms are the primary depositional result of variations in carbonate productivity, terrigenous dilution, redox conditions and/or the energy of bottom currents. Each bedding cycle type is different in its expression in the stratigraphic record but ultimately was caused by rhythmic climatic variations related to variations in receipt of solar insolation as the result of the earth's orbital characteristics, the so‐called Milankovitch cycles. Stratigraphic sequences may contain a single bedding cycle type or a composite of several types. Although sediment type and sedimentary structures were influenced by variations in local climatic, oceanographic, tectonic, and diagenetic parameters, pelagic carbonate environments during the Cretaceous were particularly sensitive recorders of orbitally induced changes in worldwide climate.

Paleoceanography↗
USGS1998

Paleomagnetic evidence that the central block of Salinia (California) is not a far-traveled terrane

New paleomagnetic results from Late Cretaceous (75–85 m.y.) red beds on the central block of Salinia indicate that Salinia was located within 6° (in latitude) of its current cratonal North American position during the Late Cretaceous (after correction for Neogene San Andreas Fault transport). The red beds formed as alluvial-fan overbank deposits with hematite cement deposited directly on Salinian granites in the La Panza Range. Paleomagnetic analysis shows two components of magnetization in the red beds, a low-blocking-temperature present-day overprint residing in goethite and a high-blocking-temperature (>600°) component residing in hematite. The hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis. The bedding-corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions. Twenty-three Class I sites (α 95 < 20°) have an average hematite direction with inclination =54.4° and declination = 18.2° (α 95 = 6.1°) after structural correction. These paleomagnetic data suggest that Salinia resided at about 35°N latitude during the Late Cretaceous, within 6° of its current location adjacent to cratonal North America. By contrast, a summary of paleomagnetic data from the Peninsular Ranges terrane and the Sur-Obispo terrane, which are currently outboard of Salinia, shows northward transport of these terranes of 12° to 22° relative to their current locations in North America since the Cretaceous. The offsets increase systematically away from the craton with the most outboard Sur-Obispo terrane (which is composed of accretionary prism and distal forearc material) showing the largest degree of northward translation.

California↗
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↗