INFLUENCE OF LAKE BASIN MORPHOLOGY ON CLIMATE-SEDIMENT TRANSFER FUNCTIONS: EARLY EOCENE WILKINS PEAK MEMBER, GREEN RIVER FORMATION, WYOMING

Abstract

Lacustrine strata are often among the highest-resolution terrestrial paleoclimate archives available. The manner in which climate signals are registered into lacustrine deposits varies, however, as a function of complex sedimentologic and diagenetic processes. The retrieval of reliable records of climatic forcing therefore requires a means of evaluating the potential influence of changing sedimentary transfer functions. Here, we use high-resolution X-ray fluorescence core scanning of the Wilkins Peak Member of the Green River Formation to characterize the long-term evolution of transfer functions in an ancient lacustrine record. Our analysis identifies a shift in the frequency distribution of Milankovitch-band variance between the lower and middle Wilkins Peak Member across a range of temporally calibrated elemental intensity records. Spectral analysis of the lower Wilkins Peak Member shows strong short eccentricity, obliquity, precession, and sub-Milankovitch−scale variability, while the middle Wilkins Peak Member shows strong eccentricity variability and reduced power at higher frequencies. This transition coincides with a dramatic decline in the number and volume of evaporite beds. We attribute this shift to a change in the Wilkins Peak Member depositional transfer function caused by evolving basin morphology, which directly influenced the preservation of bedded evaporite as the paleolake developed from a deeper, meromictic lake to a shallower, holomictic lake. The loss of bedded evaporite, combined with secondary evaporite growth, results in reduced obliquity- and precession-band power and enhanced eccentricity-band power in the stratigraphic record. These results underscore the need for careful integration of basin and depositional system history with cyclostratigraphic interpretation of the dominant astronomical signals preserved in the stratigraphic archive.