Date of Award

8-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Ying Cui

Committee Member

Sandra Passchier

Committee Member

Matthew Gorring

Committee Member

Alvaro Penteado Crosta

Abstract

The Chicxulub asteroid impact in what is now the Yucatan Peninsula, Mexican Caribbean, coincides with the Cretaceous/Paleogene boundary (K/Pg boundary ~66Ma) and marked the extinction of three-quarters of the species, including the iconic non-avian dinosaurs. The collision created a massive crater, releasing enormous amounts of energy and expelling millions of tons of molten and vaporized materials into the atmosphere. Chicxulub is an ideal case study for massive impact events since it is the only recognized asteroid impact on Earth's history that preserved a globally traceable ejecta layer representing a precise time-stratigraphic marker. Although numerous studies have examined the consequences of this planetary event, crucial information from numerous areas of the globe is missing, and numerous key aspects of understanding asteroid impacts remain poorly constrained. Most available studies have concentrated on the Gulf of Mexico region, North America, and Europe, but our understanding of tropical or southern hemisphere locations is extremely limited. The recent discovery of the Gorgonilla Island K/Pg boundary section in the Colombian Pacific has revealed a virtually continuous and unaltered sequence that records the conditions of tropical seas at the end of the Cretaceous and the beginning of the Paleogene. Recognizing this locality's importance for studying the regional and global effects triggered by the Chicxulub impact, this doctoral project studied the consequences of the planetary event using a multidisciplinary approach at the macro, micro, and nano scales. Supported by international scientific cooperation, the project focused on studying in detail physical evidence from Gorgonilla Island and complementary K/Pg boundary localities from Mexico, the United States, and Spain. At the macro scale (Chapter 1), detailed sedimentological and stratigraphic analysis of the sedimentary succession of K/Pg boundary sections from Colombia and Mexico provided key information about the occurrence, duration, and effects of potential impact-induced earthquakes. Our results suggest that the impact triggered mega-earthquakes of magnitude Mw=11-12 that persisted for years. Spherules from Colombia, the USA (Mississippi and North Dakota), and Spain were extensively analyzed at the micro-scale (Chapter 2) to determine their morphologic and morphometric characteristics and establish their potential origin and transport mechanisms. Our results identified three populations of spherules. The largest spherules (size > 2mm) correspond to rotational forms, originating as molten materials, which were distributed ballistically. The intermediate-sized spherules (size 0.3 - 2 mm) include a mixture of molten and condensed materials that were transported by the rapid expansion of a fast-moving, high-temperature, turbulent cloud. The smallest spherules (size < 0.3 mm) represent the globally distributed fireball layer, composed of materials condensed from a vapor plume after the Chicxulub impact. The pristine ejecta materials preserved at Gorgonilla, the best preserved in the world known to date, were extensively analyzed at the nano-scale (Chapter 3) using different electron microscopy techniques. Our results show a heterogeneous composition varying depending on the spherules' size, shape, and structure, revealing contributions from both the target rock and the asteroid. For the first time, the occurrence of nanostructures co-localizing Pt, Co, Ni, and Pb, and Cu, Os, and Zn, offers evidence of asteroid contribution beyond the fireball layer and the K/pg clay, and could represent the preservation of quasicrystals in Chicxulub-derived deposits. The conclusions from this doctoral research extend beyond Chicxulub and help improve our understanding of the mechanisms governing the release of energy, the dispersion of materials from the crater, and the nature of impact spherules during massive asteroid impacts.

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