[MIS11-07] IODP/ICDP Expedition 364: Using Geophysical Data to Map Suevite and Impact Melt in the Chicxulub Impact Crater
★Invited Papers
キーワード：impact crater, Chicxulub, IODP
IODP/ICDP Expedition 364 drilled one hole (M0077A) into the Chicxulub peak ring, recovering core from depths 505.7-1334.7 m below the seafloor. From bottom to top, the core consisted of ~587 m of shocked granitic target rocks, ~25 m of impact melt rock, ~104 m of suevite, and ~112 m of post-impact sedimentary rock. Analyses of core material, combined with numerical modeling, reveal details of impact and post-impact processes including: 1) The shocked granitic target rocks originated from 8-11 km depth and traveled both outwards and inwards during crater excavation and collapse; during this time these rocks experiences pervasive fracturing. 2) The impact melt rock and lowermost suevite were deposited rapidly by outward flowing melt with possible melt-water interaction (MWI). 3) The majority of the suevite, the uppermost 90 m, was deposited as a resurge deposit formed through settling and seiches in the flooded crater. 4) The lowermost sedimentary rock records the first day of the Cenozoic, and includes evidence for tsunami transporting material from distant shorelines and for impact-generated fires.
We can use geophysical data to map units with distinct physical properties from hole M0077A throughout the Chicxulub impact crater. We utilized the full-waveform inversion (FWI) method to produce high-resolution velocity models of the upper 1.5-2 km on a grid of two-dimensional seismic reflection profiles. A prominent feature in the FWI velocity images is a layer of low-velocity rocks at a depth just below the K-Pg boundary that is associated with the suevite resurge deposit at hole M0077A. The resurge deposit is fairly uniform in thickness (175-190 m) in the annular trough, peak ring, and central basin. The peak ring is identified by elevated topography and low seismic velocities associated with the shocked and fractured granitic target rock. The peak ring is narrower and more elevated in the west near hole M0077A, and is wider and deeper in the east. These differences may be related to pre-impact heterogeneity, as water depth and sediment thickness (deeper water and thicker sediment to northeast) varied with azimuth around the impact site. The top of impact melt is identified in the annular trough and central basin by a low frequency reflector and high seismic velocities. The thickness of material between the base of the suevite resurge deposit and the top of melt is much greater in the central basin than in the annular trough; upwarped features above the melt sheet in the central basin may be possible hydrothermal upflow zones.
We can use geophysical data to map units with distinct physical properties from hole M0077A throughout the Chicxulub impact crater. We utilized the full-waveform inversion (FWI) method to produce high-resolution velocity models of the upper 1.5-2 km on a grid of two-dimensional seismic reflection profiles. A prominent feature in the FWI velocity images is a layer of low-velocity rocks at a depth just below the K-Pg boundary that is associated with the suevite resurge deposit at hole M0077A. The resurge deposit is fairly uniform in thickness (175-190 m) in the annular trough, peak ring, and central basin. The peak ring is identified by elevated topography and low seismic velocities associated with the shocked and fractured granitic target rock. The peak ring is narrower and more elevated in the west near hole M0077A, and is wider and deeper in the east. These differences may be related to pre-impact heterogeneity, as water depth and sediment thickness (deeper water and thicker sediment to northeast) varied with azimuth around the impact site. The top of impact melt is identified in the annular trough and central basin by a low frequency reflector and high seismic velocities. The thickness of material between the base of the suevite resurge deposit and the top of melt is much greater in the central basin than in the annular trough; upwarped features above the melt sheet in the central basin may be possible hydrothermal upflow zones.