Magnetostratigraphy of the impact breccias and post‐impact carbonates from borehole Yaxcopoil‐1, Chicxulub impact crater, Yucatán, Mexico

Abstract

Abstract-We report the magnetostratigraphy of the sedimentary sequence between the impact breccias and the post-impact carbonate sequence conducted on samples recovered by Yaxcopoil-1 (Yax-1). Samples of impact breccias show reverse polarities that span up to ~56 cm into the postimpact carbonate lithologies. We correlate these breccias to those of PEMEX boreholes Yucatán-6 and Chicxulub-1, from which we tied our magnetostratigraphy to the radiometric age from a melt sample from the Yucatán-6 borehole. Thin section analyses of the carbonate samples showed a significant amount of dark minerals and glass shards that we identified as the magnetic carriers; therefore, we propose that the mechanism of magnetic acquisition within the carbonate rocks for the interval studied is detrital remanent magnetism (DRM). With these samples, we constructed the scale of geomagnetic polarities where we find two polarities within the sequence, a reverse polarity event within the impact breccias and the base of the post-impact carbonate sequence (up to 794.07 m), and a normal polarity event in the last ~20 cm of the interval studied. The polarities recorded in the sequence analyzed are interpreted to span from chron 29r to 29n, and we propose that the reverse polarity event lies within the 29r chron. The magnetostratigraphy of the sequence studied shows that the horizon at 794.11 m deep, interpreted as the K/T boundary, lies within the geomagnetic chron 29r, which contains the K/T boundary.

Impact melt sheet formation on Mars and its implication for hydrothermal systems and exobiology

“…At Chicxulub, trace metals and sulfide mineralization occur within the first 25 m of Tertiary sediments overlying the Cretaceous/Tertiary (K/T) boundary impact melt breccias (Yaxcopoil-1 core), which indicates nearby hydrothermal venting into the deep marine waters of the crater Rowe et al, 2004). As noted by Rowe et al (2004), this venting extends well through sediments containing the 29R/29N magnetic reversal (Rebolledo-Vieyra and Urrutia-Fucugauchi, 2004) and the Danian P1c foraminifera zone (Arz et al, 2004), and into sediments containing the Danian P2 foraminifera zone (Arz et al, 2004). The base of the Danian P2 foraminifera zone is dated to ∼3.5 myr after the K/T boundary (Berggren et al, 1995), suggesting that the hydrothermal system at Chicxulub, like Sudbury, may have lasted 3-4 myr.…”

Reconstruction of the Chicxulub ejecta plume from its deposits in drill core Yaxcopoil-1

“…A reduced thickness of magnotochron R29 in the "Tertiary" 2 section overlying the Upper Sorted Suevite (Rebolledo-Vieyra and Urrutia-Fucugauchi, 2004) and missing early Paleocene foraminiferal biozones (Arz et al, 2004;Keller et al, 2004;Smit et al, 2004) indicate a gap in sedimentation. Moreover, the reconstruction of the infi lling history of the crater from geophysical data (Bell et al, 2004) suggests a gradual fi lling of the crater basin that would not be expected if the basin had been fi lled by tsunami-like backfl owing seawater immediately after the impact (Goto et al, 2004;Tuchscherer et al, 2004a).…”

Volume 364: Chicxulub: Drilling the K-Pg Impact Crater

“…The earliest Cenozoic sediments indicate gravity flows and resurge deposits formed part of the initial crater fill (Goto et al, 2004;Whalen et al, 2008Whalen et al, , 2013 and contain geochemical evidence for long-lasting hydrothermal venting into the ocean (Rowe et al, 2004;Zürcher and Kring, 2004). Unfortunately, its location on a steep slope meant studies of the post-impact section were plagued by coarse-grained redeposited carbonates and lithification, and the very basal Paleocene appears to be missing (Arz et al, 2004;Smit et al, 2004;Rebolledo-Vieyra and Urrutia-Fucugauchi, 2004;Whalen et al, 2013). The 100 m thick melt-rich impactite sequence is complex and composed of six distinct units (Claeys et al, 2003;Kring et al, 2004;Stöffler et al, 2004;Wittmann et al, 2007), which were modified by post-impact hydrothermal circulation .…”