VIRTUAL FIELD TRIP # 6 Sequence Stratigraphy, Evaporite Withdrawl Welds and Brecciation and Dolomitazation in the Edwards Group of West Texas Lafayette Geological Society Spring Field Trip 2003          Our virtual fieldtrip is based upon "Sequence Stratigraphy, Evaporite Withdrawl Welds and Brecciation and Dolomitization in the Edwards Group of West Texas" by Dr. Brian Lock, Dr. James Willis, Barry Wawak, and Francisco Cardona. Click for larger view. Group photo - left to right: Row 1 (top) Francisco Cardona. Row 2 (middle) Kristy Cornell, Mike Lagrange, James Willis, Jill Willis, Kevin Brahm. Row 3 (bottom) (standing) Paul Boroto, Ted Gard, Barry Wawak, (seated) Brian Lock, Natasha Jeansonne, Kerri Borres, Dawn Standridge, Dennis Sullivan. [not pictured] - Javid Zeynalov Click for larger view. Javid Zeynalov, who photographed the group. Ted Gard's Summary of 2003 West Texas Fieldtrip Fifteen people from ULL and LGS toured the Cretaceous Edwards Group roadcut limestone outcrops along I-10 from Kerrville to Iraan, Texas over the 3-day last weekend in March. The group included 10 students of geology (ULL) and 5 LGS members who also think of themselves as students of geology, occasionally. We were ably and sometimes forcefully lead by Drs. Brian Lock and James Willis, who communicated their understanding of the outcrop complexities so well that there were no sustained arguments. We reviewed the Edwards Group stratigraphy and depo environment (lagoonal) and the fate of dissolved gypsum/anhydrite layers in the sequence. This dissolution formed weld contacts of beds that had formerly been separated by evaporite layers. Associated structures of collapse breccias, collapse folds, normal and thrust faults and contorted bedding completed the picture. Other outcrops showed fossil beds, depo cycles and caliche tepee folds, adding spice and interest to the trip. Good exposures, interesting rocks and convenient road pulloffs made it a dream Texas trip. No Texas troopers chased us away from the Interstate stops. A surprise stop involving nontraditional energy emerged when we were invited to view closely the Indian Mesa GE wind turbine generation farm where hundreds of windmills were generating many amps for the power grid. Outa this world! Big thanks to Brian Lock and James Willis for composing and leading the trip and to Barry Wawak for the guidebook and marathon van driving. Many thanks also to all participants and sponsors for supporting this important LGS tradition. Ted Gard Virtual  Fieldtrip  Stops Fieldtrip Leaders Shoaling Upward Cycle Dr. Burt Marl Depo Cycles & Collapse Features More Collapse Features Rudist Caprinids Sinkhole & Paleokarst Parasequences & Oyster Hardground Indian Mesa Windfarm Collapse Features Caliche Deformation, Tepee Structures Kerri's Flora & Fauna People Pictures Click for Larger View. Road Log with Approximate Field Trip Sites. Click for Larger View. Primary evaporite withdrawal welds located within the Fort Terrett Formation of the Cretaceous Edwards Group. Click for Larger View. Interpreted outcrop section showing deformation asociated with collapse pipes formed by gypsum dissolution at depth. Cretaceous stratigraphy of central and west Texas. The base of the Gulfian Series is located at the base of the Woodbine Stage. "Tepees and Other Surficial Deformation Features of Cretaceous Rocks in Central and West Texas, Resulting from Late Cenozoic Caliche Formation," Brian E. Lock, Suk-Joo Choh, and James J. Willis, GCAGS Transactions, Vol. LI, 2001, p. 174. "Reservoir Characteristics and Cretaceous Dolomites, Texas," Brian E. Lock, Francisco J. Cardona, Sequence Stratigraphy, Evaporite Withdrawl Welds and Brecciation and Dolomitization in the Edwards Group of West Texas, Guidebook LGS Spring Field Trip 2003. "Cretaceous stratigraphy, central and west Texas," Brian E. Lock, Francisco J. Cardona, Sequence Stratigraphy, Evaporite Withdrawl Welds and Brecciation and Dolomitization in the Edwards Group of West Texas, Guidebook LGS Spring Field Trip 2003. FIELDTRIP FEATURES & MAPS Early Life on Earth, Stromatolites Wackestones, Grainstones, Brian Lock Depositional cycles, Brian Lock Paleokarst surface, stratiform dolomite, Brian Lock Dolomite lenses, Brian Lock Physiographic Map of Texas Bureau of Economic Geology, Geologic Map of Texas Texas Relief Map - The Johns Hopkins University Applied Physics Laboratory Geologic Maps of Texas - The Walter Geology Library, The University of Texas Barry Wawak's photographs and comments greatly assisted the composition of this virtual fieldtrip. This virtual fieldtrip owes a great deal to James Willis and Ted Gard, who were most generous with their time and their resources. Special thanks to the following fieldtrip members for the use of their excellent fieldtrip photographs: KERRI BORRES (KB) JAVID ZEYNALOV(JZ) BRIAN LOCK (BL) BARRY WAWAK (BW) Lafayette Geological Society thanks CORE LAB PETROLEUM SERVICES for its sponsorship of this fieldtrip & HALLIBURTON for providing beverages.   Web Author: Karen W. Broussard