Sedimentary History of San Juan Basin of New Mexico and Colorado: ABSTRACT

Abstract

The San Juan basin is an ovoid-shaped intermontane basin located in northwestern New Mexico and southwestern Colorado. It is the southeastern part of the Colorado Plateau and as defined in this paper it encompasses about 7,600 square miles within the Point Lookout (Cretaceous) outcrop. Except for the Ordovician and Silurian and possibly Lower Cretaceous which are not present, all rocks of the geological time scale can be penetrated in 15,000 feet or less. Marine conditions prevailed during early Paleozoic time. At the end of Pennsylvanian time, sedimentation of clastics increased from neighboring highlands and a period of transition from marine to continental deposition extended into Permian time. Primarily, continental conditions continued through Triassic and Jurassic time. After a hiatus at the end of Jurassic time, the Cretaceous was deposited in a varied but mainly marine environment. Local movement due to the Laramide Orogeny, caused subsidence of the basin and rising of the surrounding mountains. Large quantities of detrital material filled the basin with Paleocene and Eocene sediments. Most of the basin has not been drilled below the Dakota Formation. Only 19 wells have penetrated the Paleozoics within the Point Lookout outcrop. The density of Paleozoic tests is one well per 400 square miles and most of these tests are near the periphery of the basin. Because of this exiguous well control, most of the deeper sediments of the basin are relatively unknown. None of the deeper tests have been commercial producers. Economic importance of the rocks in the basin is very diverse with oil, natural gas and coal being the main economic resources. End_of_Article - Last_Page 1874------------