Integrated sequence stratigraphy and chemostratigraphy of the Middle Cambrian succession in eastern Nevada and western Utah
Robyn A. Howley
University of Nevada, Las Vegas, Department of Geoscience
Las Vegas, Nevada
Cambrian radiation and evolution of marine organisms is one of the most important events in Earth history, however the record of this event relies heavily on exceptional preservation of fossils within restricted basins along ancient passive margins. One such restricted basin is the Middle Cambrian House Range Embayment (HRE) in Nevada and Utah. To understand the environmental and chemical controls on the living habitats and preservation potential of early animals, I propose an integrated sequence and chemostratigraphic study of the passive-margin succession surrounding the HRE. Shallow-water shelf deposition was interrupted during the Middle Cambrian by a deep-water embayment, the HRE, which extended eastward across Nevada into western Utah. The HRE affected both shelf deposition and local seawater chemistry for nearly 10 my but a complete understanding of its evolution and relationship to the surrounding shallow-water platform is not available. This study aims to test the following hypotheses: (1) Sediment deposition within the HRE was primarily controlled by both high- and low-frequency sea-level changes that also affected the adjacent shallow-water platform; (2) The shallow-water platform and HRE both record the same secular d13C curve; and (3) Anoxic conditions prevailed in the HRE during deposition of the Wheeler Formation as identified by negative d34S values in pyrites. The results of this study will provide data for deciphering the combined effects of sea-level change and local tectonics on stratigraphic development, spatial geometries, and isotopic excursions on this ancient carbonate platform and for analyzing the sedimentologic and chemical requirements necessary for exceptional fossil preservation.
AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid