FINNEY, STANLEY C., California State University at Long Beach, Long Beach, CA, and CLAUDIO BARTOLINI, University of Texas at El Paso, El Paso, TX

ABSTRACT: The Record of Ordovician Sea Level Changes in Outer Continental Margin Settings of North America

Ordovician rocks exposed in the Ouachita Mountains of Arkansas and Oklahoma and the Marathon region of Texas and Ordovician strata in the Roberts Mountains allochthon of Nevada were deposited in deep-marine basins peripheral to the North America continent. Ordovician rocks in Sonora, Mexico, accumulated in a similar setting. Deposition in all three areas, which were to some extent continuous, was very similar and included black shale, bedded chert, sandstone, and limestone. The sandstone is turbiditic and composed of quartz and/or carbonate grains derived from the North American craton and shelf. The introduction of turbidites into the peripheral basins occurred twice, in the latest Ibexian to middle Whiterockian and in the latest Whiterockian to Mohawkian. Both times are recorded in ll three areas where the sandstones are separated by black shale of middle to late Whiterockian age. The nearly simultaneous, widespread deposition of turbiditic sandstone indicates that the deposition events were initiated by eustatic sea level changes. In some areas, the turbiditic events are recorded by thick (hundreds of meters) sequences of coarse-grained, thick bedded quartzite, quartz arenite, and quartz wacke with interbedded siltstone, shale, limestone, and conglomerate; in other areas, by 1-2 massive 5--10 m thick beds of quartzite; and in still other areas, by thin-bedded siltstone and fine-grained sandstone. Although Ordovician sea level changes may have been simultaneous along the western and southern margins of North America, sandstone deposition was uneven in the periphera basins because turbidites originated from point sources.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.