Lab 5 - Pennsylvanian Field Trip

Lab 5 - Pennsylvanian Field Trip - FIELD TRIP GUIDE...

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FIELD TRIP GUIDE PENNSYLVANIAN FOSSILS, FACIES AND ANCIENT DEPOSITIONAL ENVIRONMENTS OF NORTH-CENTRAL TEXAS FIELD TRIP GUIDE FOR THE 2010 TEXAS ACADEMY OF SCIENCE MEETING MARCH 4-6, 2010 TARLETON STATE UNIVERSITY EDITOR JOREE BURNETT BO ALLEN BEAUX JENNINGS BEAU BEREND CLIFTON HOLLAND SPENCER BUSCH KAYLI LAGOW CODY CHRISTIAN JAMIE LANE CALVIN CLARY CHANCE MARTIN SHAWN FOYT MICHEAL PRATT TAD GASS ROBERT SCHERMERHORN PATRICK GLEASON LYNN SMITH CHRISTINE GOFFINET MATTHEW WATERMAN DEDRICK HAIL BRITTANY WHITE MARK WIDMER OVERVIEW This field trip guide will concentrate on the Pennsylvanian system of rocks deposited in the North-Central Texas area. These facies were deposited in the Pennsylvanian Period and are named for the coal-bearing rocks found in the state of Pennsylvania. The Pennsylvanian System is divided into five series (oldest to youngest): the Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian. For the purpose of this field trip, the study will be confined to the Desmoinesian and Missourian Series (Middle to Late Pennsylvanian Age), and concentrate on the formations that represent the Strawn Group. The outcrops seen today were worked by Tarleton’s sedimentology class for class field trips, and the class’s interpretations are represented in the guidebook. The interpretations are based on the delta models outlined by Bradshaw, Mazzulo, Brown, Cleaves and Erxleben. INTRODUCTION North Texas was a very active area during the Middle and Upper Pennsylvanian Period. Several tectonic, or mountain building events, were occurring and influencing North Texas. The Amarillo-Wichita-Arkbuckle Uplifts were to the north, along with the southern extension of the Ouachita Uplift to the east, and the Llano-Pecos-Marathon Uplift to the south. These tectonic events allowed for a shallow seaway to extend over the Kern, Val Verde and Midland basins. Large river systems transported loads of sediment from the erosion of the uplands. Throughout the Pennsylvanian, and by the Upper Pennsylvanian, these rivers systems had created a large coastal plain that extended from the Dallas-Fort Worth area westward to north-central Texas. As
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these large river systems entered the shallow seaway, they deposited their sediment loads of sand, silts and clays. These sediments were deposited along the shelf area as fan-shaped delta deposits. The localities that will be seen will each be pertaining to a different section of a fluvial- dominated delta and shallow shelf environment. To envision some of the things we will be seeing, a little bit about deltas needs to be explained. In a delta environment, as the sediment-rich waters from the channel enter the seaway, the velocity decreases, thereby releasing the sands, silts and clays out of suspension. As more and more sediment comes into the sea, the delta builds out (progrades) onto the shelf. On the shelf, at a substantial distance from the incoming channel, prodelta silts and clays are deposited. Prodelta mudstones are generally thick and laminated with very little fossil content,
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Lab 5 - Pennsylvanian Field Trip - FIELD TRIP GUIDE...

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