Paleozoic History of Southeastern Colorado

Abstract

Southeastern Colorado was first covered by Paleozoic seas in Late Cambrian time, when coarse clastics (Lamotte sandstone) derived mainly from the north were deposited in front of a low landmass that extended from New Mexico northwestward to the vicinity of Canon City. The seas gradually encroached on this landmass, depositing additional Upper Cambrian (Bonneterre dolomite) and Lower Ordovician (Arbuckle group) rocks farther southwest. Near the close of Early Ordovician time, gentle upwarping raised the central part of southeastern Colorado above sea-level. During Middle and Late Ordovician time, seas lapped upon the eastern and western slopes of this upwarp, depositing the sediments of the Simpson group and the Viola limestone. After the close of Ordovician time, upliftin , probably with some faulting, along the present trend of the Front Range, Wet Mountains, and Apishapa-Sierra Grande uplift, permitted the removal by erosion of most of the Cambrian and Ordovician rocks from that area. In Mississippian time the seas advanced from the Anadarko basin, lapping on the gently sloping landmass. During Meramec time the seas probably completely covered the landmass and at the end of Meramec time began a withdrawal into the Anadarko basin. During Chester time the seas appear to have been restricted to the Hugoton embayment in the southeasternmost part of Colorado. At the beginning of Pennsylvanian time, the seas advanced upon the flanks of the low landmass of eastern Colorado, bringing clastic material from the southeast. Near the end of Morrow time major uplifting accompanied by faulting elevated the Apishapa-Sierra Grande uplift, the Wet Mountains, and the Front Range, which supplied clastic material to transgressing seas during the remainder of Pennsylvanian time. A cross flexure marking the earliest beginnings of the Las Animas arch seems to have developed near the end of Missouri time. During early Permian time the seas gradually covered the Apishapa-Sierra Grande landmass, and during late Permian time the shore line remained fairly stable, until the seas receded at the close of the period.