PALEOCEANOGRAPHIC CHANGES ACROSS THE CENOMANIAN-TURONIAN BOUNDARY (MID-CRETACEOUS) IN CARBONATES OF SOUTHERN MEXICO
Only minor evidence of high-frequency sea-level changes is observed (meter-scale upward shallowing cycles) and systematic facies changes related to M.y.-scale sea-level change (depositional sequences) are absent except for abrupt deepening just above the C-T boundary. Three sections show similar d 13C carb trends over a 60-100 m-thick interval (~0.5 m sampling interval): relatively uniform values positive values (over ~30 m), two abrupt 2-3 negative shifts (<10 m), an abrupt 5-6 positive shift (<3 m), plateau of uniformly higher values (~10 m), a gradual 2-6 decrease (~10 m), followed by relatively uniform values (10+m). The large positive shift correlates to the positive excursion observed globally (OAE-2). d13C org values show significantly more variability, but some of the d13C carb curve trends are observed. TOC values are low (<0.2 wt%) and show no obvious stratigraphic trends. Trace metal abundance anomalies (Co, Ni, Cr, Pb, Zn, Cs, W, Sb, Mo, Ag, Se) across the Mexican C-T boundary are explained by magma outgassing and hydrothermal exchange with seawater during volcanic activity that built the Caribbean oceanic plateau at ~90-94 Ma, supporting a possible link between the global C-T isotope excursion (OAE-2) and large oceanic plateau formation.