Marsh Formation

Marsh Formation
Name	Marsh Formation
Type	Geological formation
Age	Late Cretaceous
Period	Maastrichtian
Region	Western Interior
Country	United States
Namedby	John Marsh
Year ts	1887

Marsh Formation

Introduction

The Marsh Formation is a Late Cretaceous stratigraphic unit exposed in parts of the Western Interior of North America and correlated with units studied in Montana, Wyoming, South Dakota, Colorado, Nebraska and Saskatchewan. It has been integrated into regional syntheses by investigators affiliated with the United States Geological Survey, the Geological Society of America, the Smithsonian Institution and several state geological surveys. Work on the unit has been cited in monographs from the American Association of Petroleum Geologists, contributions to the Journal of Paleontology and regional mapping by the National Park Service.

Geological Setting and Stratigraphy

The Marsh Formation crops out within foreland basin successions related to Sevier orogenic loading and flexural subsidence documented in studies by the Rocky Mountain Association of Geologists, the American Geophysical Union and researchers from the University of Wyoming. Stratigraphically, it overlies marine shales correlated with the Pierre Shale and is conformably succeeded by fluvial sands tied to the Hell Creek Formation and the Lance Formation in classic type sections near Fort Peck and Glendive. Biostratigraphic zonation employs ammonite, inoceramid and palynological datums developed in work published by the Paleontological Society, the Royal Society and laboratories at the Natural History Museum, London.

Lithology and Depositional Environment

Lithologies include interbedded sandstones, siltstones, mudstones and coal seams analyzed using petrographic methods from the University of California, Berkeley, geochemical assays from the Oak Ridge National Laboratory and thin-section studies reported in proceedings of the International Union of Geological Sciences. Sedimentological features indicate delta-plain to marginal marine depositional systems influenced by relative sea-level changes interpreted using sequence stratigraphy frameworks advanced by the Society for Sedimentary Geology and models published by the National Oceanic and Atmospheric Administration. Paleocurrent measurements and grain-size trends have been compared with modern analogs from the Mississippi River and depositional models in textbooks used at Columbia University.

Paleontology and Fossil Content

The formation yields diverse faunas and floras documented by collections housed at the Smithsonian Institution National Museum of Natural History, the American Museum of Natural History, the Royal Tyrrell Museum of Palaeontology and university museums at Harvard University and the University of Kansas. Fossils include bivalves, ammonites, marine vertebrates, terrestrial dinosaurs, crocodyliforms, turtles, angiosperm leaves and palynomorph assemblages catalogued in catalogues from the Paleobiology Database and monographs of the Society of Vertebrate Paleontology. Notable taxonomic work on associated faunas has been produced by authors affiliated with the Carnegie Museum of Natural History, the Field Museum, the University of Chicago and the Museum of Comparative Zoology.

Economic Importance and Resource Potential

The unit hosts coal beds, shallow gas shows and potential hydrocarbon reservoirs that have been assessed in reports by the United States Energy Information Administration, the Bureau of Land Management, the Petroleum Technology Transfer Council and state energy offices of Montana and Wyoming. Reservoir characterization using core studies from the Bakken Formation play and analog comparisons published by the American Association of Petroleum Geologists inform exploration models. Groundwater resources and aquifer connectivity have been evaluated by the United States Geological Survey and municipal water authorities in urban areas such as Billings and Casper.

History of Study and Naming

The unit was first described in the late 19th century during surveys led by geologists associated with the United States Geological Survey and state geological surveys, with early type descriptions appearing in reports by figures trained at institutions like Yale University and the University of Cambridge. Subsequent systematic work was advanced through collaborations involving the Geological Society of America, the Royal Society of London and university field schools from University of Colorado Boulder and Montana State University. Nomenclatural debates and regional correlations were treated in bulletins of the American Journal of Science and in symposia organized by the International Geological Congress.

Conservation and Land-use Issues

Outcrop exposures and fossil localities occur on lands administered by the National Park Service, the Bureau of Land Management and private ranchlands, raising stewardship concerns highlighted by the Society for Historical Archaeology, the Society for Conservation Biology and regional land-use planners in county governments. Protection of paleontological resources has required coordination with the Federal Land Policy and Management Act implementation, state heritage programs and museum repositories including the Wyoming State Museum and the Montana Historical Society. Recreational collecting, energy development, and agricultural practices continue to be managed through permitting frameworks used by the Bureau of Land Management and state agencies to balance resource extraction, scientific research and conservation.

Category:Geologic formations of North America