Fluid inclusion evidence for impact-related hydrothermal fluid and hydrocarbon migration in Creataceous sediments of the ICDP-Chicxulub drill core Yax-1

Abstract

Fluid inclusions studies in quartz and calcite in samples from the ICDP-Chicxulub drill core Yaxcopoil-1 (Yax-1) have revealed compelling evidence for impact-induced hydrothermal alteration. Fluid circulation through the melt breccia and the underlying sedimentary rocks was not homogeneous in time and space. The formation of euhedral quartz crystals in vugs hosted by Cretaceous limestones is related to the migration of hot (>200 degrees C), highly saline, metal-rich, hydrocarbon-bearing brines. Hydrocarbons present in some inclusions in quartz are assumed to derive from cracking of pre-impact organic matter. The center of the crater is assumed to be the source of the hot quartz-forming brines. Fluid inclusions in abundant newly-formed calcite indicate lower cyrstallization temperatures (75100 degrees C). Calcite crystallization is likely related to a later stage of hydrothermal alteration. Calcite precipitated from saline fluids, most probably from formation water. Carbon and oxygen isotope compositions and REE distributions in calcites and carbonate host rocks suggest that the calcite-forming fluids have achieved close equilibrium conditions with the Cretaceous limestones. The precipitation of calcite may be related to the convection of local pore fluids, possibly triggered by impact-induced conductive heating of the sediments.