MILANKOVITCH-BASED CORRELATION AND TIMING OF DEPOSITIONAL CYCLICITY ACROSS THE EARLY CRETACEOUS PLATFORM, NE MEXICO: CLIMATE VARIATIONS ENCODED BY ROCK MAGNETICS

Variations in rock magnetic parameters provide an objective, rock-type independent tool for high-resolution stratigraphic correlation that is unmatched by traditional stratigraphic methods. Anhysteretic remanent magnetization (ARM) allows sub-meter, millennial- scale correlation between cyclic peritidal inner shelf and less cyclic mid-shelf carbonates of the Cupido Formation and the lithologically homogeneous basinal lime mudstones of the San Angel Limestone in northeast Mexico. Spectral analysis of ARM data records variations in the concentration of fine-grained ferromagnetic minerals, which fluctuate at frequencies predicted by Milankovitch orbital rhythms (405kyr, 123kyr, 51.2kyr, 39.4kyr, 22.5kyr, 18.6kyr). Accumulation rates of 6-8 cm/kyr for ~1.7Ma suggests uniform subsidence across the Early Cretaceous rimmed carbonate platform. Magnetic mineral composition, grain size distributions, and grain shapes from digested platform and basinal samples are consistent with fine detrital magnetite in atmospheric dust. Prevailing winds and the proximity of the Cretaceous basin to an African aeolian source supports the rock magnetic encoding of orbitally modulated changes in wind intensity or source area aridity fluctuating at precessional time scales across the platform. Inner shelf deposits also contain a coarser, possibly fluvial signal related to watershed runoff variation. ARM measurements offer great potential to correlate depositional environments basin wide, calibrate the pace of depositional processes, and investigate high-frequency orbitally driven climate change in carbonates throughout geologic time.