THE UPPER PART OF THE SUEVITE AND INTERMEDIATE LAYER AT SITE M0077A, IODP-ICDP EXPEDITION 364 INTO THE PEAK RING OF THE CHICXULUB CRATER (YUCATAN, MEXICO)

IODP-ICDP hole M0077A recovered a core into the peak ring of Chicxulub offshore Yucatán composed of 3 main lithological units: 1) Paleogene sediments, 2) suevite/impact melt rocks and 3) granitic peak ring rocks intruded by pre-impact dikes and intercalated with suevites and impact-melt. This abstract examines the geochemistry of the intermediate unit between the impactites to the overlying Paleogene sediments (core 40 R-1). This ~ 80 cm unit is composed of fine laminated clay and carbonate-rich siltstones that may record the K/Pg boundary PGE anomaly. The contacts with the above lying marlstone-dominated Paleogene sediments and the underlying suevite unit are sharp and clearly visible. The upper and finer part of the suevite sequence is composed of carbonate-rich, sand-sized sorted and graded material, which indicate settling and reworking by high-energy processes (seiche, tsunami, slope failure…). This unit contains few altered impact-melt fragments, with elongated shapes and vesicles and many carbonate clasts of various sizes, with well-preserved Maastrichtian foraminifera floating in a fine carbonate matrix. It resembles the suevite found in the hole Yucatan-6, level N13, drilled onshore also in the peak-ring area, which contains feathery calcite - diagnostic for rapidly quenched carbonate liquids - that has not (yet?) been identified in M0077A. Just above the sharp contact, the lowermost part of the intermediate unit (617.30-617.34 mbsf) contains multiple mm-thick layers, clearly enriched in Ni, over a thickness of ~ 1 cm. Based on LA-ICP-MS concentration profiles and EMPA imaging, these Ni-rich layers are linked to the presence of Fe-Ni-Co-Cu-Pb-Zn sulfide mineralizations that are associated with very small (µm) platinum nuggets, but no clear Ir anomalies is detected. These sulfides probably reflect the existence of an impact-generated hydrothermal system, circulating fluids and solid components in the crust and releasing S- and volatile-rich fluids. Focus is now placed on the upper section of the intermediate settling unit, where additional siderophile element enrichments occur. The identification a clear Ir anomaly with chondritic inter-element ratios should reveal the source and processes responsible for the observed elevated concentrations.

Co-authors: IODP-ICDP Expedition 364 Scientists