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Duration and Paleoenviroments of the E Marker, Bridger A, Southwest Wyoming

Jimmy Wilhelm

A unique occurrence of alternating layers of caddisfly cases and micro-laminated carbonate encrusting fossil trees occurs in the lowermost Bridger Formation member. These factors suggest a lacustrine paleoenvironment of significant duration. The encrusted fossil trees occur in an ostracodal oolite. The trees often have root systems, but did not grow in situ as there is no evidence of paleosol in the ostracodal oolite, or in the underlying silty sandstone. The ooids grade into oil shale basinwards over a distance of 5 km. Lateral facies associations suggest a lacustrine paleoenvironment. Furthermore, the alternating layers of micro-laminated stromatolite and caddisfly cases may indicate a minimum duration of the transgression of Lake Gosiute, since many temperate caddisflies are univoltine, and the similar diameter of the cases suggests that they the cases represent yearly pupation events.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013