Preservation of Sedimentary Source Rocks in Fluvial Deposits: ABSTRACT

Abstract

Sedimentary rock fragments are abundant in clastic sedimentary rocks of the Rocky Mountain region, but a quantitative basis for interpretation of the provenance of these deposits has not been previously available. Fluvial clastic rocks of the Duchesne River Formation (Eocene-Oligocene?) in northeastern Utah contain fragments of older sedimentary rocks derived from the Uinta Mountains. The source material consists of about 89% terrigenous clastic rocks, 10% carbonate rocks, and 1% chert. In the Duchesne River Formation, sandstone and conglomerate contain approximately 50% quartz grains and 50% rock fragments. Of the rock fragments, clastic sedimentary rocks constitute 35%, carbonate rock fragments 43% and chert fragments 22%. Pebble conglomerate is present and sandstone co tains as much as 38% carbonate rock fragments at a distance of 64 km from the crest of the mountain range (32 km from the nearest flank). These relations indicate that carbonate rock fragments can be transported considerable distances and suggest that clastic sedimentary rock fragments are broken down relatively quickly, leaving the deposit enriched in fragments of carbonate rocks and chert. Differences in proportions of rock fragments in deposits from different source areas, of different grain sizes, in different depositional environments, and after different distances of transport are considered. The quantitative relationship between composition of the source area and the deposit can be applied to provenance interpretations in areas where source beds have not been preserved. End_of_Article - Last_Page 955------------