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Abstract: Correlation and Paleoenvironmental Analysis of the Early Cretaceous King Lear Formation in NW Nevada

MARTIN, AARON J., Rice University, Dept. of Geology and Geophysics, Houston, TX

Major tectonic features of the Cretaceous period of the western U.S. Cordillera include a magmatic arc and the back arc Sevier Thrust Belt. At present erosional levels, the remains of the magmatic arc consist almost exclusively of plutonic rocks; Cretaceous supracrustal rocks within the arc are extremely rare. The Black Rock Desert region of northwest Nevada contains one of these rare exposures of Cretaceous supracrustal strata within the arc, the King Lear Formation (KLF) exposed in the central Jackson Mountains (JM), and correlative units exposed in the neighboring Krum Hills (KH).

Field work that I conducted last summer in the JM, including measurement of stratigraphic sections and field mapping, has characterized the central JM outcrops of the KLF. The KH outcrops, however, have never been carefully mapped, measured, and described. My work in the central JM demonstrates that a cobble conglomerate member of the KLF represents braided stream deposits filling an elongate half-graben that opened during the Early Cretaceous. Analysis of clast lithology shows that greater than 80% of the clasts were derived external to the arc and the JM, probably from the nearby Golconda Allochthon. If this member of the KLF correlates with the KH outcrops, then the KH rocks could represent a part of the feeder system to the basin in the JM. This possibility is intriguing because the KH outcrops would allow the detailed reconstruction of the Early Cretaceous paleogeography of this region. Specifically, the source region, feeder system, and depositional basin would all be well located relative to each other. The KH exposures are crucial to this reconstruction because they could be the missing link between the source area and the depositional basin for the KLF.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid