DETRITAL ZIRCONS AND SEDIMENT DISPERSAL ACROSS THE MARATHON FORELAND, WEST TEXAS, USA

Analyses of detrital zircons from sandstones within the Pennsylvanian–Permian synorogenic turbidites and associated upward-shallowing facies in the Marathon thrust belt and foreland provide for interpretation of sediment provenance and dispersal patterns. Samples from the Lower Permian Road Canyon Formation and Upper Pennsylvanian Gaptank Formation, as well as published data from the Middle Pennsylvanian Haymond Formation, represent a vertical succession. Each sample has two main modes of detrital-zircon ages, which vary in age range and relative abundance upward. The younger mode spans ages of 553–323 Ma (peaks at 523 and 418 Ma) in the Haymond, 718–340 Ma (peaks at 618, 557, and 481 Ma) in the Gaptank, and 724–316 Ma (peaks at 640, 588, 522, and 348 Ma) in the Road Canyon. The older mode spans ages of 1339–974 Ma (peaks at 1247 and 1123 Ma) in the Haymond, 1194–936 Ma (peak at 1064 Ma) in the Gaptank, and 1188–983 Ma (peaks at 1124 and 1064 Ma) in the Road Canyon. Each sample has scattered grains between the two main modes, as well as scattered grains between the older mode and 2131 Ma (minor peak at 2072–2044 Ma) and a minor peak at 2726–2685 Ma. In the younger mode, the range of ages of older grains increases upward. The older mode is dominant in the Haymond, but the younger mode increases in abundance upward and is dominant in the Road Canyon. Two Haymond samples are described as quartzolithic arenites with feldspar and volcanic grains. The upper Gaptank sample is subarkose containing subrounded 0.1–0.2 mm undulose quartz, plagioclase and microcline cemented by calcite. The lower Road Canyon sample is chert arenite containing 0.05–0.1 mm subangular chert, undulose quartz, and minor clay matrix cemented by euhedral dolomite. The ages of zircons are consistent with a supply of sediment from basement and volcanic rocks of the Coahuila terrane in the interior of the Ouachita orogen within the Marathon salient. Comparison with detrital-zircon populations suggests that Marathon sediment dispersal extended to the Delaware basin and across the Wichita and Arbuckle basement uplifts into the Anadarko basin. Similar detrital-zircon populations indicate that synorogenic clastic sediment in the Fort Worth basin and part of the Arkoma basin in the Ouachita foreland had the same or a similar sediment source as that of the Marathon foreland.