Chicxulub crater post-impact hydrothermal activity - evidence from Paleocene carbonates in the Santa Elena Borehole

Abstract

Active hydrothermal systems develop in impact structures formed in marine settings, associated with convective processes involving hydrothermal fluids and seawater. Here we investigate hydrothermal activity in the Chicxulub crater, which was formed by a large impact on the Yucatan carbonate platform in the southern Gulf of Mexico at the Cretaceous/Tertiary boundary. The post-impact cover carbonate sediments carry a record of convective hydrothermal activity, which allow investigating on characteristics and timing/duration of the processes. We present the major and trace element geochemistry of basal Paleocene carbonate sediments (304-332 m depth) in the Santa Elena borehole located south of the crater rim outside of the main basin. Hydrothermal activity is evidenced in the major oxides and trace elements, enriched in the first 10 m above the impact breccia-carbonates contact. Basal limestones present high concentrations of silica, magnesium, aluminum, potassium and iron, with similar variation patterns in the other oxides and the trace element data. The geochemical data are consistent with element enrichment associated with hydrothermal input and less likely to result from other processes like diagen-esis or detrital contributions. The relative contents of major oxides remain constant in the next twelve meters of the section above 322 m, with CaO around 50 % wt and SiO2 and MgO around 2 % wt and similar pattern in other oxides and trace elements. Considering location of the study site away from the central zone, the geochemical anomalies may arise from convective activity on the underlying impact breccia sequence and input to the water column associated with the distal hydrothermal vent sources in the central area. Concentration in Fe, K and Al is suggestive of a step pattern, also observed in the trace elements (Zn, V, Cr, Ni, Cu, Zr and Rb). After cessation of the active hydrothermal phase after ~1 Ma following the impact, intermittent hydrothermal venting may have operated for an extended time.