Geology Dry Mesa Quarry

graph showing relationship of dinosaur bone volume dry mesa fluvial channel flow velocity

the dry mesa dinosaur quarry of western colorado yields 1 of diverse upper jurassic vertebrate assemblages in world. fossil assemblage deposited within poorly sorted sandstone bed stratigraphically situated in lower portion of upper brushy basin member of morrison formation. bone accumulation, consisting of thousands of bones, consequence of 2 cataclysmic events, drought, , flash flood. in dry mesa area, severe drought resulted in mass mortality of dinosaurs , other vertebrates. these animals attracted remnant water hole of dry lake t oo dichi lake bed died of starvation , dehydration. mass mortality produced considerable accumulation of disarticulated vertebrate remains. subsequently, short-lived flash flood traversed dry lake beds. quarry sandstone bed 2 meter thick, 121 meter wide, poorly sorted pebble-rich sublitharenite. channel sandstone shows abundant trough cross-stratification , possible antidune bedform composed of gravel , sand indicates flow velocities high 200 cm/s (5 miles/hour). measured bone volumes can equated flow velocities. these calculated bone volume velocities in agreement flow velocities determined grain size , bedforms. river flow direction, based upon bedform orientations , bone elongation statistics, east-northeast. geologic , taphonomic characteristics indicate short transport distance bone accumulation (richmond , morris, 1999).