T176 Advancements in Energy Geology: The Best of American Association of Petroleum Geologists Technical Talks 2018

Tuesday, 24 September 2019
8:00 AM - 12:00 PM
Room 127ABC, North Building

XENOCONFORMITIES IN THE GREEN RIVER FORMATION

Paper number: T176-2
Program: Technical Sessions
Time: 8:05 AM – 8:20 AM

Authors

  • Alan Carroll Presenting Author
    Univ Wisconsin - MadisonDepartment of Geoscience, Madison, AZ
  • Michael Smith
    Northern Arizona University, Flagstaff, AZ

Abstract

Lacustrine and associated terrestrial strata commonly exhibit abrupt, basin-scale changes in lithofacies, stratigraphic packaging, biota, geochemistry, and economic resource potential. Unlike conventional stratigraphic successions that may be interpreted to record lateral migration of coexisting depositional environments (Walther’s Law), these transitions record discrete episodes of comprehensive paleoevironmental change. Carroll (2017) proposed the new term xenoconformity, defined as a stratigraphic surface or gradational interval that records a fundamental, abrupt, and persistent change in sedimentary facies across basinal to global scales. The Eocene Green River Formation (GRF) contains multiple xenoconformities, each of which is expressed as a sudden change in lacustrine sedimentary facies association (“lake type”) across an entire depositional basin. For example, the Wilkins Peak Member in Wyoming contains numerous Na-carbonate evaporite beds, has relatively low organic matter enrichment, and lacks any fossil evidence for lacustrine macrofauna. It is separated by a xenoconformity from the overlying Laney Member, which lacks bedded evaporite minerals but is relatively enriched in organic matter and contains a diverse lacustrine macrofauna. A growing body of provenance evidence has demonstrated that the GRF lakes drained much of the frontal cordillera and foreland of the western U.S., and that episodic drainage reorganizations within this large watershed exerted an important control on the balance between accommodation and sediment+water supply in downstream lakes. For example, the Wilkins Peak/Laney transition is accompanied by a dramatic increase in carbonate 87Sr/86Sr ratios, recording capture of new, more radiogenic river water that reduced the salinity of Eocene Lake Gosiute. Smith et al. (2014) proposed that early Eocene drainage networks evolved in response to localized thermal uplift and magmatism, caused by the progressive rollback of the Farallon plate beneath the western U.S. Many questions remain, but it has become clear that Green River Formation lakes were sensitive recorders of landscape evolution at the sub-continental scale. More broadly, watershed evolution exerts a first order control on lacustrine paleoenvironmental records and economic resources.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-331497

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.