Climate and Bedrock Controls on Sediment Supply to the Paleogene Gulf Coast, Texas, U.S.A.

Abstract

Along the Gulf Coast, the quality of Cenozoic sandstone reservoirs depends on burial depth but is also strongly tied back to the mineral composition of sand at the time of deposition. To understand the controls on sand composition, we analyzed the mineralogy and geochemistry of sandstone and shale from the onshore Wilcox (late Paleocene-early Eocene), Yegua-Jackson (late Eocene), and Vicksburg-Frio (Oligocene) groups in southeastern Texas. In the Wilcox Group, inorganic indices related to chemical weathering were closely tied to oceanic delta-O-18, an indication that continental weathering was coupled to global temperatures in North America. Subsequently, sediment composition increased in maturity as global climate warmed and weathering intensity increased across the Paleocene-Eocene transition, resulting in sharply quartz-enriched sands deposited in the Upper (early Eocene) Wilcox compared to the Lower and Middle (late Paleocene) Wilcox formations. This compositional shift is not related to a change in bedrock availability (through tectonism, volcanism, and/or an evolving catchment), because a variety of provenance indicators are stable across the Paleocene-Eocene boundary. On the other hand, sediment composition in the Yegua-Jackson and Vicksburg-Frio groups reflects both provenance and climate/weathering changes across the Eocene-Oligocene transition. Provenance indicators using rare-earth elements (REE) in shale point to an influx of mafic-sourced sediment that peaked during deposition of the Vicksburg formation (earliest Oligocene). This compositional trend coincides with changing tectonic and volcanic styles in western North America as the Cretaceous-Eocene Laramide orogeny came to a close. At the same time, chemical maturity in the shales, as well as mineralogical maturity in coeval sandstones, declined as global climate cooled and weathering intensity decreased across the late Eocene-early Oligocene transition. Along the Texas Gulf Coast, reservoir quality generally declines through the late Paleogene in parallel with global cooling and post-Laramide tectonism.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019