USGS Science⌕ Search

Geology topics

S. J. Soulliere

Publications and source records attributed to S. J. Soulliere.

12 recordsLinked to original sources
USGS1986

Minturn and Sangre de Cristo formations of Southern Colorado: A prograding fan delta and alluvial fan sequence shed from the ancestral Rocky Mountains

The Middle Pennsylvania!) Minturn Formation and the Pennsylvanian-Permian Sangre de Cristo Formation of the northern Sangre de Cristo Range form a thick progradational sequence of coarse clastic sediments. These sediments were deposited along the western margin of the central Colorado trough during uplift of the late Paleozoic Uncompahgre highland, a major structural and topographic feature of the Ancestral Rocky Mountains. The Minturn is composed mostly of sandstone and shale deposited by fan deltas that prograded into the central Colorado trough. The Minturn of the northern Sangre de Cristo Range is divisible into a turbidite-bearing facies, a limestone-bearing facies, and a redbed facies. The turbidite-bearing facies is interpreted as deposits of fan deltas that prograded onto the sea bottom below wave base. The limestone-bearing facies is interpreted as deposits of fan deltas that prograded onto a shallow sea bottom above wave base. In this facies, sandstones containing deltaic foresets overlie thin shallow marine limestones and are considered diagnostic of that facies. Both facies contain thick intervals of sandstone and shale interpreted as deltaic and alluvial deposits. Where it onlaps the Uncompahgre highland, the lower part of the Minturn Formation contains quartzose and arkosic redbeds of probable alluvial origin. The continental Sangre de Cristo Formation conformably overlies the Minturn Formation basinward, but it unconformably overlies the Minturn and Precambrian basement near the Uncompahgre highland. The Sangre de Cristo contains two facies. A sandstone facies consists of fining-upward cycles of red conglomeratic sandstone and siltstone interpreted as braided stream deposits on distal parts of alluvial fans. A conglomerate facies (Crestone Conglomerate Member) consists of poorly sorted conglomerates interpreted as debris flow and mudflow deposits and sorted conglomerate and sandstone interpreted as streamflow and sheetflow deposits on proximal parts of alluvial fans. The fan deltas and alluvial fans that deposited the Minturn and Sangre de Cristo formations probably developed in response to faulting and uplift of the Uncompahgre highland. The highland rose at least three times from Middle Pennsylvanian to Early Permian time. Later, during the Laramide orogeny, the faulted boundary between the highland and the central Colorado trough was destroyed by thrusting. The boundary faults were not strike-slip, as shown by the distribution of clasts in conglomerates directly downstream from identical Precambrian rocks that represent part of the highland.

Colorado↗
USGS1984

Measured sections and discussion of the main turbidite member, Middle Pennsylvanian Minturn Formation, northern Sangre de Cristo Range, Custer and Saguache counties, Colorado

Turbidites are sediments deposited by turbid density currents. The turbidites described here are interpreted as prodelta deposits that formed in front of fan deltas and alluvial fans during the uplift of the ancestral Rocky Mountains in Pennsylvanian time. Laterally extensive, lenticular sand bodies deposited by turbidity flows crop out in the Middle Pennsylvanian Minturn Formation in the northern Sangre de Crísto Range, Custer and Saguache Counties, Colo. (figs. 1, 2). One of the turbidite-bearing intervals, informally designated the "main turbidite member," lies 90.6 m above the base of the Minturn; it reaches 150 m in thickness and extends more than 13 km along strike. The internal stratigraphy and sedimentary structures of the main turbidite member are described from the measured sections presented here. The Middle Pennsylvanian Minturn Formation of the Spread Eagle Peak thrust plate (Lindsey, Johnson, and Andriessen, 1983) consists of about 2,000 m of interbedded conglomeratic sandstone, sandstone, siltstone, and lesser amounts of conglomerate, shale, and limestone. The lower 1,500 m of the Minturn is composed mainly of prograding deltaic-alluvial cycles that contain interva1s of prodelta turbidites. The upper 500 m of the Minturn consists of deposits of small deltas and bralded streams interbedded with shallow marine limestones Interpreted as a san-delta deposit (Clark, 1982). Above the Minturn Formation, the Pennsylvanian and Permian Sangre de Cristo Formation consists of more than 1,700 m of coarse conglomerate and sandstone interpreted as an a 11uvialfan deposit (Lindsey and Schaefer, 1984). The main turbidite member is the thickest and most extensive of the intervals of prodelta turbidites in the Minturn Formation. Each turbidite interval is part of a coarsening upward sequence interpreted as a prograding fan delta. A typical prograding cycle consists of prodelta marine shale and siltstone, prodelta turbidite sandstones, delta-front sandstone and conglomerate, and deltaic and alluvial-plain sandstone, siltstone, and shale. Fossils of 1and plants (mostly Calamites, including some in growth position) are locally abundant in deltaic and alluvial sediments of the prograding cycles. The turbidites are regarded as having been deposited offshore from alluvial systems.

Colorado↗