--> Abstract: Carbonate-Slope Failures as Indicators of Sea-Level Lowerings, by H. E. Cook and M. E. Taylor; #91004 (1991)

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Carbonate-Slope Failures as Indicators of Sea-Level Lowerings

COOK, HARRY E., U.S. Geological Survey, Menlo Park, CA, and MICHAEL E. TAYLOR, U.S. Geological Survey, Denver, CO

Occasionally, carbonate-slope failures of such a magnitude occur that immense volumes of material move downslope as submarine slides and boulder-bearing debris flows. These spectacular deposits can be triggered by earthquakes or tsunamis. However, when such deposits are regionally widespread or are on separate lithospheric plates, at times of sea-level lowering, the trigger mechanism is most likely eustatic sea-level fluctuations. We propose that during the initial phases of a sea-level lowering, slope and/or platform-margin collapse can happen, owing to gravitational instability of partially cemented carbonates.

Fragments of the margins of the early Paleozoic proto-Pacific Ocean are found in widely separated terranes, including western North America and southern Kazakhstan (USSR). Coeval carbonate-slope and platform-margin failures occurred in both areas during the Late Cambrian and Early Ordovician. Up to 75-km-long segments of these carbonate slopes and platform margins collapsed and were transported seaward as submarine slides and megabreccia debris flows. These catastrophic events contributed to the development of 500-m-thick carbonate submarine fans and aprons. Slope and platform-margin failures also correlate with solution breccia and faunal disconformities in platform-interior sites. We interpret these widely separated yet coeval mass-transport processes to have happened during rapid o eanward progradation of their respective carbonate margins, in combination with several eustatic sea-level lowerings.

Carbonate-slope and platform-margin failures that resulted from eustatic and relative sea-level lowerings can assist in defining carbonate-sequence stratigraphic boundaries in slope, platform-margin, and shelf-interior environments. Submarine slide, slumps, and sediment-gravity flow deposits of eustatic origin also can help in refining existing sea-level curves.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)