. Bulletin. Natural history; Natuurlijke historie. 92 PEABODY MUSEUM BULLETIN 44. Fig. 43. Inferred western interior paleogeograpiiy of the Early Triassic and approximate isopachs (in meters) of Lower Triassic sediments of the Dinwoody and Red Peak formations (modified from Picard and High 1968). terrestrial highs in the north, east, and southeast, including the Uncompaghre Uplift. In places these sediments reach a thickness of 2,000 m (Kummel 1955). At the same time, central Wyoming was home to a broad, shallow, westward sloping, marine shelf (Fig. 43). This shelf witnessed several eastward t
. Bulletin. Natural history; Natuurlijke historie. 92 PEABODY MUSEUM BULLETIN 44. Fig. 43. Inferred western interior paleogeograpiiy of the Early Triassic and approximate isopachs (in meters) of Lower Triassic sediments of the Dinwoody and Red Peak formations (modified from Picard and High 1968). terrestrial highs in the north, east, and southeast, including the Uncompaghre Uplift. In places these sediments reach a thickness of 2,000 m (Kummel 1955). At the same time, central Wyoming was home to a broad, shallow, westward sloping, marine shelf (Fig. 43). This shelf witnessed several eastward transgressive pulses during the Early, and perhaps the Middle, Triassic (CoUinson and Hasen- mueller 1978). The eastern expanse of the Dinwoody Formation, consisting of grey siltstones and shales, represents the first such invasion of the Triassic sea. Lying above the Dinwoody, the rocks of the lower Chugwater reveal a complex history of transgression and regression, and lithofacies indicative of marine shelf, coastal, and tidal flat environments (Picard 1978). As, however, most past attempts have failed to correlate the Alcova Limestone with the normal marine sediments of the miogeosyncline, it has been uncertain whether or not the Alcova represents a similar marine shelf transgression. The uppermost Chugwater, particularly the Popo Agie Formation, is unquestionably of terrestrial—fluvial and lacustrine— origin. These rocks comprise red clays, sands, and conglomerates and are the materials that filled the structural basins of Wyoming during Late Triassic times. By the Late Triassic, the western miogeosyncline had withdrawn. Its departure is marked by an erosional unconformity at the top of the Timothy Sandstone Member of the Thaynes Formation (Carini 1964). PHYSICAL STRATIGRAPHY AND PETROGRAPHY In addition to a synthesis of published data, field studies on the Alcova Limestone were conducted during the summers of 1983, 1989, and 1990. As much of this. Please note that these
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