History, sedimentology, and taphonomy of the carnegie quarry, dinosaur national monument, Utah

摘要

The taphonomy of Dinosaur National Monument is presented based in part on the extensive archival material of Earl Douglass. This material includes unpublished manuscripts, diaries, notes, photographs, and quarry maps, and is supplemented with the petrography of matrix still encasing the original collections, as well as numerous site visits. A new quarry map is presented based on the original Douglass map, historical photographs, and a photo-mosaic of the current quarry face made by the author. Three-dimensionally preserved sand bars (>1.5 m tall), bone distribution and orientation, and generally poorly sorted, conglomeratic, multi-storied, trough-cross bedded sandstones indicate repeated episodes (3-4) of flashy, rapid deposition in a Platte River-like braided system (named the Quarry River) flowing south-southeast. Modeling of the Quarry River using a one-dimensional computer program (HEC-RAS 4.1.0) on a Platte River-like river under a variety of flow conditions revealed possible flow velocities for the Quarry River, as well as the effects on flow of bones on the riverbed. These results are compared against the velocities required to move bone based on various boulder transport equations developed for paleofloods. The forces needed to move weighted casts of bone across a subaqueous sand substrate were determined using a strain gauge. Casts were also used to map turbulent flow around bones to better understand sediment deposition leading to bone burial. Several lines of evidence, including the varying degrees of skeletal disarticulation, strongly suggest non-catastrophic mass mortality during extreme droughts. Due to the lack of sweat glands, most dinosaurs were probably water dependent, thus restricting distance traveled for foraging. To avoid thermal stress, individuals sought refuge in the river and death was primarily by malnutrition and secondarily by disease. Opisthotonous induced by sickness in an ostrich suggests a similar cause in some of the dinosaurs. Postmortem damage to bone by insects is rare and is shown to be due to some unknown osteophagic insect, but not dermestids.