Abstract: Goodwin Limestone--Lower Ordovician Shelf/Slope Carbonate Deposits in North-Central Nevada

Michael J. P. Welland, Joseph H. Makurath, Ronald Marchel

Several sections of the Goodwin Limestone (Lower Ordovician) within the Antler orogenic belt of north-central Nevada have been examined. Measurement of approximately 150 m of section in Pete's Canyon, east of Austin, suggests that locally the Goodwin can be divided into two facies. The lower facies is approximately 100 m thick and is composed of two lithologies. Lithology A includes thickly laminated to thinly bedded, poorly sorted calcisiltites and calcarenites; grading is typical of individual beds and laminae. These grade laterally and vertically into lithology B which includes massive units of coarse intraformational conglomerate. Intraclasts are flat pebbles, cobbles, and boulders of lithology A set in a poorly sorted matrix of calcisiltite and calcarenite. The upper facies (approximately 50 m) lacks intraformational conglomerates and is composed of thinly bedded, poorly sorted calcisiltites and calcarenites. These are bioturbated and commonly contain unbroken fossil debris of echinoderms, trilobites, and brachiopods.

The facies succession apparently represents a transition from slope and shelf-edge deposits to continental-shelf sediments. Sections in adjacent ranges show similar facies organization with additional siliciclastic components.

Locally, sections of the Goodwin are allochthonous, suggesting that, regionally, Early Ordovician shelf/slope paleogeography has been modified by tectonic "stacking" of unknown extent below the Roberts Mountain thrust.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC