Petrographic and chemical studies of the Cretaceous-Paleogene boundary sequence at El Guayal, Tabasco, Mexico: Implications for ejecta plume evolution from the Chicxulub impact crater
Petrographic and chemical studies of the Cretaceous-Paleogene boundary sequence at El Guayal, Tabasco, Mexico: Implications for ejecta plume evolution from the Chicxulub impact crater
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墨西哥塔巴斯科州埃尔瓜亚尔白垩纪-古近纪边界序列的岩石学和化学研究：对希克苏鲁伯撞击坑喷射物羽流演化的影响
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发表时间：
2021
期刊：
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通讯作者：
T. Salge
中科院分区：
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作者：
T. Salge
对墨西哥塔巴斯科州埃尔瓜亚尔（希克苏鲁伯陨石坑西南 520 公里）白垩纪-古近纪边界序列的喷射物颗粒进行了岩相学和化学联合研究，以评估其在撞击过程中的形成条件和成因关系。在大气传输过程中，硅酸盐喷射物颗粒与热挥发物的反应可能引起了在喷射物沉积物中观察到的蚀变过程，例如硅化和胶结作用。方解石喷射物颗粒的各种微观结构被解释为反映震后条件下不同的热历史。球晶方解石颗粒可以代表在喷射过程中骤冷的碳酸盐熔体。再结晶微观结构可能表明短暂而强烈的热应力。各种聚集体记录了颗粒与颗粒之间的相互作用以及来自下层硅酸盐和上层沉积目标岩性的组分的混合。重结晶方解石与硅酸盐熔体的聚集体表明热钙石组分与沉积物在 ≳750 °C 时固结。增生火山岩是在约 100 °C 的湍流、蒸汽冷凝环境中通过固体、灰烬大小的颗粒聚集而形成的。具有较小粒径的吸积颗粒的同心区域表明与较热环境的反复交换。
我们的结果表明，在部分喷射物羽流塌陷期间，热硅酸盐成分与当地表面衍生沉积物的细小部分混合，后者被前面的喷射物幕所取代。这些过程维持了由气体驱动的热横向基底传输，并伴随着更高水平的湍流羽流。分解的碳酸盐和硫酸盐与 CO2 发生 CaO 的放热逆反应，形成 CaCO3，这可能是羽流演化后期热能长期释放的原因。
A combined petrographic and chemical study of ejecta particles from the Cretaceous-Paleogene boundary sequence of El Guayal, Tabasco, Mexico (520 km SW of Chicxulub crater), was carried out to assess their formation conditions and genetic relation during the impact process. The reaction of silicate ejecta particles with hot volatiles during atmospheric transport may have induced alteration processes, e.g., silicification and cementation, observed in the ejecta deposits. The various microstructures of calcite ejecta particles are interpreted to reflect different thermal histories at postshock conditions. Spherulitic calcite particles may represent carbonate melts that were quenched during ejection. A recrystallized microstructure may indicate short, intense thermal stress. Various aggregates document particle-particle interactions and intermixing of components from lower silicate and upper sedimentary target lithologies. Aggregates of recrystallized calcite with silicate melt indicate the consolidation of a hot suevitic component with sediments at ≳750 °C. Accretionary lapilli formed in a turbulent, steam-condensing environment at ~100 °C by aggregation of solid, ash-sized particles. Concentric zones with smaller grain sizes of accreted particles indicate a recurring exchange with a hotter environment.
Our results suggest that during partial ejecta plume collapse, hot silicate compo nents were mixed with the fine fraction of local surface-derived sediments, the latter of which were displaced by the preceding ejecta curtain. These processes sustained a hot, gas-driven, lateral basal transport that was accompanied by a turbulent plume at a higher level. The exothermic back-reaction of CaO from decomposed carbonates and sulfates with CO2 to form CaCO3 may have been responsible for a prolonged release of thermal energy at a late stage of plume evolution.