Bighorn Basin Stratigraphic Column Prior to Arriving at Field Camp

Tectonic Setting Tectonostratigraphic Stratigraphy and Orogenic Events Assemblage Quaternary Pliocene c i Neog. Miocene o z Oligocene o n Tatman Fm. e Eocene C Willwood Fm. TSA4 Retroarc foreland segmented Paleogene Paleocene Fort Union Fm. Laramide Orogeny by basement uplifts; non-marine Lance Formation Meeteetse Fm. Mesaverde Fm. n TSA3 i g Upper Cody Shale r Retroarc foreland; a shallow marine to Torchlight Sandstone M Frontier Fm. t Peay Sandstone n e sediments Mowry Shale g r Sevier Orogeny Cretaceous Shell Creek Shale e c i Muddy Sandstone v o Thermopolis Shale n z Lower Sykes Mtn. Fm. (“Rusty beds”) o o Cloverly Fm. Greybull Ss. C s e Nevadan Orogeny TSA2 M Morrison Fm. Transitional to retroarc Upper Sundance “upper Sund.” foreland; shallow Formation “lower Sund.” marine & non-marine Middle Gypsum Spring Fm. clastic sediments Jurassic Lower Triassic Chugwater Formation Dinwoody Fm. Goose Phosphoria Egg Fm. Permian Fm. Ancestral Rockies TSA1 Pennsylvanian Tensleep Sandstone Orogeny Amsden Fm. Darwin Ss. Proximal miogeoclinal strata; mixed carbonate Mississippian Madison Limestone c & siliciclastic sediment; i Darby Fm. Antler Orogeny o dominated by shallow z Devonian o marine & marginal e n l Silurian i marine facies a g Bighorn Dolomite r P Ordovician a M Lander Sandstone e Gallatin v Upper i Limestone s s Gros Ventre Fm. a Middle P Flathead Ss. Cambrian Lower Precambrian Crystalline basement Archean crytalline basement Generalized stratigraphic column for the northern Bighorn Basin, Wyoming, with timing of regional orogenic events and interpretation of tectonostratigraphic assemblages. Modified from May et al. (2013; GSA Bulletin, v. 125, p. 1403-1422), who in turn derived their figure from Fox and Dolton (1996; Wyoming Geological Association 47 Annual Field Conference Guidebook, p. 19-39). The table below indicates exactly what you need to memorize from the Bighorn Basin stratigraphic column prior to arriving at field camp. Specifically, you need to know all the formations listed and the ages as shown in the column on the left (e.g., you need to know that the Cody Shale is Cretaceous in age, but you do not need to know that it is Late Cretaceous). The column of members does not include all subunits that have been defined for the various formations in the Bighorn Basin, just the ones you need to know when you arrive at camp. For the latter, you DO need to know the stratigraphic position within the parent formation as shown in the strat column. For example, you can see that the Greybull Sandstone occurs at the top of the Cloverly Formation, in contrast to the Darwin Sandstone, which is situated at the base of the Amsden Formation. Also note that the Torchlight and Peay sandstones occur near, but not quite at, the top and bottom, respectively, of the Frontier Formation. Age Formation Members Eocene Tatman Fm. Paleocene-Eocene Willwood Fm. Paleocene Fort Union Fm. Cretaceous Lance Fm. Cretaceous Meeteetse Fm. Cretaceous Mesaverde Fm. Cretaceous Cody Shale Cretaceous Frontier Fm. Torchlight Sandstone, Peay Sandstone Cretaceous Mowry Shale Cretaceous Shell Creek Shale Cretaceous Muddy Sandstone Cretaceous Thermopolis Shale Cretaceous Sykes Mtn. Fm. ("Rusty beds") Cretaceous Cloverly Fm. Greybull Sandstone Jurassic Morrison Fm. Jurassic Sundance Fm. Jurassic Gypsum Spring Fm. Triassic Chugwater Formation Triassic Dinwoody Fm. Permian Phosphoria/Goose Egg Fm. Pennsylvanian Tensleep Sandstone Pennsylvanian Amsden Fm. Darwin Sandstone Mississippian Madison Limestone Devonian Darby Formation Ordovician Bighorn Dolomite Lander Sandstone Cambrian Gallatin Limestone Cambrian Gros Ventre Fm. Cambrian Flathead Sandstone Precambrian Crystalline basement.

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