2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 13
Presentation Time: 8:00 AM-12:00 PM


O'CONNOR, Diane, Dept. of Earth and Planetary Science, Univ. of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720-4767, ALVAREZ, Walter, Department of Earth and Planetary Science, Univ of California, Berkeley, CA 94720-4767 and RITTER, Scott, Dept. of Geology, Brigham Young Univ, Provo, UT 84602, oconnord@eps.berkeley.edu

The Candalaria Formation, long considered to be entirely Triassic in age, is exposed in the Candalaria Hills in western Nevada, southwest of the town of Mina. The Candalaria and underlying Early to early Middle Permian Diablo Formation exposed at this locality rest on Roberts Mountain allocthon sediments and are overthrust by serpentinite melange. The contact between the Candalaria and Diablo Formations is apparently conformable, although they are in fault contact at some localities. A disconformity between them has been inferred, due to their apparent age discontinuity. The open marine marls of the basal member of the Candalaria contain several carbonate units, and two of the three lowest of these units have yielded conodonts from the Jinogondolella nankingensis (early Middle Permian) to Pseudoclarkina bitteri (late Middle Permian) complex, as well as abundant silicious sponge spicules. These units are part of a continuous depositional sequence, and many of the contacts with the adjacent shales and marls are clearly gradational. Probable impressions of the Early Triassic bivalve Claraia have been observed from about 27 to 29 meters above the lowest carbonate unit, and possible Eumorphotis (middle Early Triassic) impressions have been observed at about 35 meters above the lowest carbonate unit. This new information suggests that the lower member of the Candalaria Formation is not entirely Triassic in age, as previously thought, but contains significant Middle Permian, confirming biostratigraphic continuity with the underlying Diablo Formation. In addition, the Candalaria Formation most likely contains a relatively continuous Permian-Triassic boundary section.