A low-temperature, meteoric water-dominated origin for smectitic clay minerals in the Chicxulub impact crater upper peak ring, as inferred from their oxygen and hydrogen isotope compositions

The origin of carbonates in impact melt‐bearing breccias from Site M0077 at the Chicxulub impact structure, Mexico

“…The clay surrounding these clasts were analyzed via EDS spot analysis and WDS elemental mapping and was discovered to be primarily composed of Si, Mg, and Fe, with lesser amounts of Al and Na (Figure 4). These results closely resemble the Mg‐rich, trioctahedral, smectite group clay mineral, saponite, which is abundant throughout Unit 2 (Simpson et al., 2021). With regard to the geochemical composition of the Type B clast calcite cores, the average total of most minor oxides and chemical elements studied via WDS spot analysis from three separate clasts throughout Unit 2 is below 0.10 wt% except for SiO 2 , SO 3 , MgO, and MnO, which are 0.17, 0.33, 0.43, and 0.96 wt% on average, respectively.…”

“…It was pervasive, though incomplete, and resulted in the Type C calcite attaining a granular texture (e.g., Figure 5c). At Site M0077, clay from the palagonitized glass clasts throughout Unit 2 has been characterized as predominantly the Mg-Fe, trioctahedral, smectite group clay mineral, saponite (Simpson et al, 2021). Our observations suggest that the spaces in which Type D calcite occupies (e.g., vugs, vesicles, fractures, and altered glass cores) were subject to the same fluid and alteration history as the matrix (e.g., Figure 8e-h).…”

“…In the post‐impact sediments directly overlying the impact melt‐bearing breccias at Sites M0077 and Yax‐1, several meters of elevated Mn is observed suggesting up to 2.1 Myr of post‐impact hydrothermal venting (Kring et al., 2020; Rowe et al., 2004). This has been attributed to a meteoric‐groundwater‐dominated hydrothermal system based on numerical modeling, isotopic and fluid inclusion data from the Yax‐1 drill core (Abramov & Kring, 2007; Kring et al., 2020; Lüders & Rickers, 2004; Zürcher et al., 2005), and meteoric δ 2 H and δ 18 O isotopic signatures captured by smectite clays throughout Unit 2 at Site M0077 (Simpson et al., 2021).…”

“…The impact melt-bearing breccia of Unit 2 is 104 m thick and composed of impact glass clasts, now hydrothermally altered via palagonitization (Simpson et al, 2020), and lithic clasts in a matrix dominated by calcite and saponite, with lesser amounts of zeolites, silicates, Al-rich smectite, sulfides, sulfates, and oxides (Gulick et al, 2017;Kring et al, 2020;Simpson et al, 2020Simpson et al, , 2021. The lithic clasts have been divided into five different groups: felsic basement, mafic basement, silica, primary carbonate, and reacted carbonate clasts (Kaskes et al, 2022).…”

“…Since the retrieval of drill core at Site M0077, several studies have discussed the formation and chemistry of some of the observed carbonates. Post‐impact hydrothermal activity and impactite alteration account for much of the carbonate volume in the impact melt‐bearing breccia and are interpreted as derived from meteoric‐dominated groundwater flow as the affected rocks cooled (Kring et al., 2020; Simpson et al., 2021). Carbonate clasts are present throughout the impact melt‐bearing breccia and have recently been described and characterized as “non‐reacted” (clasts bearing sedimentary and biological features) and “reacted” (featureless clasts with a reaction rim of microcrystalline calcite), with both clasts yielding similar geochemical signatures: CaO (∼88 wt%), SiO 2 (<10 wt%), Al 2 O 3 (1–2 wt%), MnO (1–2 wt%), and P 2 O 5 (∼0.3 wt%) (Kaskes et al., 2022).…”