Journal of Sedimentary Research, 2006, v. 76, 1197–1214 Research Article DOI: 10.2110/jsr.2006.096 HIGH-RESOLUTION STRATIGRAPHY OF AN UNDERFILLED LAKE BASIN: WILKINS PEAK MEMBER, EOCENE GREEN RIVER FORMATION, WYOMING, U.S.A. JEFFREY T. PIETRAS* AND ALAN R. CARROLL 1University of Wisconsin-Madison, Department of Geology and Geophysics, 1215 West Dayton Street, Madison, Wisconsin 53706, U.S.A. e-mail:
[email protected] ABSTRACT: Lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic, tectonic, or geomorphic processes. This unique behavior of lacustrine basins can provide a high-resolution record of geologic processes within the continental setting, far from the globally averaged record of marine strata. The Wilkins Peak Member of the Eocene Green River Formation, in Wyoming, USA, is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions. These lacustrine ‘‘cycles’’ consist of up to four successive facies associations: littoral, profundal–sublittoral, palustrine, and salt pan. Because they comprise disparate facies that may never have been simultaneously deposited in the basin, Wilkins Peak Member cycles are non-Waltherian successions that do not readily equate to any established sequence stratigraphic unit. The completeness of the stratigraphic record in the Wilkins Peak Member varies continuously across the basin. At least 126 cycles are present in the ERDA White Mountain #1 core near the basin depocenter, whereas only about one third as many are recognizable 53 km north, nearer to the basin margin. Cycle boundaries terminate northward by gradual amalgamation into palustrine facies, reflecting the interplay between varying lake levels and a south-dipping deposition gradient.