ASTRONOMICALLY FORCED HYDROLOGY OF THE LATE CRETACEOUS SUB-TROPICAL POTOSÍ BASIN

Abstract

Orbital forcings have been shown to pace the Pleistocene ice ages, demonstrating that periodic variations in the latitudinal distribution of insolation amplified by ice-albedo feedbacks can guide global climate. How these forcings operate in the hot-houses that span most of the planet's history, however, is unknown. The lacustrine El Molino formation of the late Cretaceous-early Paleogene Potosí Basin in present-day Bolivia contains carbonate-mud parasequences that record fluctuating hydrological conditions roughly from 73 to 63~Ma. By merging drone-derived imagery and elevation models with measurements of magnetic susceptibility in an unprecedented use of stratigraphic modeling, this study demonstrates that these parasequences exhibit significant cyclicity with periods corresponding to eccentricity (400 and 100 kyr), obliquity (50, 38, and 29 kyr), precession (17-23 kyr), and semi-precession (9-11 kyr). New U-Pb ID-TIMS ages corroborate the corresponding sedimentation rates at two sites, indicating that the Potosí Basin contains evidence for hot-house astronomical forcing of sub-tropical lacustrine hydrology. Global climate simulations of late Cretaceous orbital end-member configurations demonstrate precessional-eccentricity and obliquity driven modulation of basin hydrology. In both cases, the forcings drive long-term shifts in the location of the intertropical convergence zone, changing precipitation in the northern extent of the basin's catchment area. This evidence is the first to be provided for orbital forcing of a Cretaceous lacustrine system and could ultimately result in an astrochronology for timing of the Cretaceous-Paleogene boundary.