ABSTRACT Outcrops of Late Cretaceous Gulf Series strata (Woodbine, Eagle Ford, and Austin) in the Dallas area expose middle Cenomanian to the early Campanian (96 to ˜ 83 Ma) rocks, which are well known in the subsurface of the oil-rich East Texas Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set of strata provides a record of the last 50 million years of the Cretaceous. Although both marine and terrestrial vertebrates are known in this interval, the Late Cretaceous record is primarily marine. On this field trip, sites are visited that have yielded sharks, bony fish, turtles, dinosaurs, crocodiles, pterosaurs, mammals, long- and short-necked plesiosaurs, and a classic record of mosasaur evolution.

ABSTRACT The purpose of this trip is to visit an internationally famous Quaternary vertebrate paleontology site, Friesenhahn Cave, on the eastern margin of the Edwards Plateau in the heart of the central Texas Hill Country. This site has a very long history of scientific investigations beginning in the early twentieth century and continuing today. The cave has produced the fossil remains of more than 50 vertebrate taxa, including amphibians, reptiles and mammals. However, the abundant remains of an extinct scimitar cat, Homotherium serum, including juvenile individuals along with hundreds of teeth, cranial, and postcranial elements of juvenile mammoths, Mammuthus cf. M. columbi, make it an especially unique site. Our visit to Friesenhahn Cave will focus on its physical setting, cave sediment stratigraphy, potential age and taphonomy as they relate to the adaptations of Homotherium in the late Pleistocene of central Texas and its relationship to its potential prey, juvenile mammoths. We will also discuss recent studies of the cave itself, and its protection for future investigations by Concordia College.

ABSTRACT This trip follows part of the route taken by E.T. Dumble, R.A.F. Penrose, Jr. (later president of and great benefactor to the Geological Society of America), and R.T. Hill as they surveyed the geology from the vantage point of the Colorado River between Austin and La Grange during the Geological Survey of the State of Texas in April of 1889. This year has particular significance because it is the same year that Penrose joined the Geological Society of America. The river has changed in flow regime, and many outcrops have weathered or been flooded. This trip passes through the primarily Claiborne (middle Eocene) geologic section between Bastrop and Smithville, Texas, and illustrates the difficulties to be faced when retracing historic geological surveys. The group will be using and testing a mobile application developed specifically for this field trip theme.

ABSTRACT This field trip examines exposures of transgressive and highstand marine deposits of the Sabinetown transgression that forms the upper part of the Calvert Bluff Formation of the Wilcox Group in the outcrop belt. The horizon of maximum flood in the Sabinetown transgression at Bastrop contains molluscs and diverse vertebrate fossils characteristic of open marine environments. The highstand deposits coarsen upward and are capped with a well-developed paleosol. These deposits are dated as early Eocene.

Abstract This volume, prepared in conjunction with the 47th Annual Meeting of the GSA South-Central Section, contains four guides that focus on sedimentology and paleontology in Texas. A theme of exploration threads its way through the trips, all of which can trace their roots to the work of early geologic explorers. One trip retraces part of the 1889 Dumble survey that explored the geology along the Colorado River between Austin and La Grange, Texas, while another takes readers to an internationally famous Quaternary vertebrate paleontology site, studied since the beginning of the twentieth century, inside Friesenhahn Cave in the central Texas Hill Country. Another guide visits Paleocene- to Eocene-age sediments derived from the Rocky Mountains and transported via rivers to the Houston Embayment, building out the continental shelf, while a fourth explores Late Cretaceous Gulf Series strata in the Dallas area.

The Main Central Thrust shear zone is the dominant crustal thickening feature in the Himalayas, largely responsible for the extreme relief and mass wasting of the range. Along the Bhagirathi River in NW India, the Main Central Thrust is several kilometers thick and separates high-grade gneisses of the Greater Himalayan Crystallines from Lesser Himalayan metasedimentary rocks. Th-Pb ion microprobe ages of monazite dated in rock thin section from the Greater Himalayan Crystallines are Eocene (38.0 ± 0.8 Ma) to Miocene (19.5 ± 0.3 Ma), consistent with the burial of the unit during imbrication of the northern Indian margin and subsequent exhumation due to Main Central Thrust activity, respectively. However, two samples directly beneath the Main Central Thrust yield 4.5 ± 1.1 Ma ( T = 540 ± 25 °C and P = 700 ± 180 MPa from coexisting assemblage) and 4.3 ± 0.1 Ma (five grains) matrix monazite ages, suggesting Pliocene reactivation of the structure. Hydrothermal monazites at the base of the Main Central Thrust shear zone record Th-Pb ages of 1.0 ± 0.5 Ma and 0.8 ± 0.2 Ma, the youngest ever reported for the Himalayas. These ages postdate or overlap activity along structures closer to the Indian foreland and show that the zone of Indo-Asia plate convergence did not shift systematically southwestward from the Main Central Thrust toward the foreland during the mountain-building process. Instead, age data support out-of-sequence thrusting and reactivation consistent with critical-taper wedge models of the Himalayas.

The Western Anatolia extended terrane in Turkey is bounded by the North Anatolian fault zone to the north, the Lycian nappes to the south. It contains the Menderes massif, one of the post-collisional Alpine metamorphic core complexes. Field data and available radiometric ages suggest that the north-directed Cenozoic extension in the terrane is the product of three consecutive, uninterrupted stages, and that it is still continuing today. The first stage was initiated in the Late Oligocene along a north-dipping extensional simple-shear zone with a listric geometry at depth. The shear zone is named here as the Southwest Anatolian shear zone and marks the southern and southwestern boundary of the Western Anatolia extended terrane. Evidence for the presence of this shear zone includes (1) the dominant top to the north-northeast shear sense indicators in the Menderes massif and (2) a series of Oligocene extensional basins located adjacent to the shear zone that contain carbonate and ophiolitic rock clasts, but no high-grade metamorphic rock fragments. During this stage, erosion and extensional unroofing brought high-grade metamorphic rocks of the Central Menderes massif to the surface by the early Miocene. The second stage of extension produced the north-dipping Alasehir and the south-dipping Büyük Menderes detachment surfaces in the early Miocene. The detachments control the Miocene sedimentation in the Alasehir and Büyük Menderes grabens, containing high-grade metamorphic rock fragments that were already at the surface in the Central Menderes massif in the early Miocene. The third stage of extension may have started ca. 5 Ma, when the North Anatolian fault was initiated. This extensional phase produced faults within the Alasehir and Büyük Menderes grabens and possibly the Kucuk Menderes graben.