MILANKOVITCH BASED CORRELATION AND TIMING OF DEPOSITIONAL CYCLICITY ACROSS THE LOWER CRETACEOUS PLATFORM, NE MEXICO

High-frequency, upward-shallowing carbonate cycles are recognized and correlated using lithology and facies-based rock magnetic studies within cyclic and noncyclic sedimentary sections in the Cupido Formation of northeastern Mexico. Magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) variations, which encode high-frequency climate fluctuations, were collected at ~5kyr intervals from two age equivalent stratigraphic sections at Sierra del Fraile. Power spectrum analysis of MS and ARM data suggests that the cycles were controlled by eccentricity and obliquity climate changes. Measured sections from the peritidal-facies dominated Garcia Canyon section and the subtidal-facies dominated Chico Canyon section are comparable in stratigraphic thickness and reveal consistent accumulation rates despite their varied depositional environments. Magnetic results indicate that the stratigraphies, which are bounded by a chronostratigraphically significant sequence boundary and a relatively isochronous regionally transgressive boundary, represent ~2.65 Ma. Magnetic mineral properties indicate that the Garcia and Chico stratigraphic sections, which were originally separated by ~25 km, both contain a fine-grained magnetic mineral population, suggesting a common regional source, possibly atmospheric dust. In addition, Garcia also contains a coarser grained magnetic mineral population within the fine-grained matrix that is most likely derived from a local watershed source. Further rock magnetic analysis of the grain size, grain distribution and composition of the magnetic minerals from each depositional environment will elucidate whether the magnetic variability results from detrital inputs (e.g., wind- or waterborne grains) or the result of internal controls (e.g., carbonate dilution, cementation, or biogenetic magnetite). These investigations will further elucidate how climate is encoded in sedimentary rocks which is an important step for understanding what controls the timing and rates of processes producing high-frequency cyclicity in marine sediments. Additionally ARM measurements, which are insensitive to variations in carbonate content, serves as a robust tool for measuring magnetic variations within carbonate stratigraphies.