Date of Award

December 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

John L Isbell

Committee Members

Mark Harris, Lindsay McHenry, Fernando Vesely

Keywords

Dwyka Group, Itararé Group, Kaokoveld, Late Paleozoic Glaciation, Paraná Basin, sediment gravity flows

Abstract

The late Paleozoic Ice Age (LPIA; 362 to 255 Ma) was an icehouse interval that drove substantial changes in Earth’s surficial systems. Numerous paradigms regarding aspects of the LPIA were established throughout ~150 years of research based primarily on the evolving state of knowledge in sedimentology. The near-field lithological evidence for widespread glaciation across sedimentary basins of Gondwana are the building blocks for comprehensive paleoclimatic, biologic, paleogeographic, and ice volume models. Nevertheless, the embodied glacial record from several late Paleozoic Gondwanan depocenters still rely on insufficient and/or outdated sedimentologic and stratigraphic studies, which can lead to misinterpretations in models built on the spatio-temporal distribution of ice-spreading centers. The Paraná epicontinental sea was one of the most extensive late Paleozoic depocenters that encompass the large Paraná Basin in South America and the Kaokoveld fjord network and Huab Basin in Namibia. The eastern and southern margins of the Paraná Basin have at present a relatively well-established glacial-postglacial chronostratigraphic scheme that serves as a foundation for LPIA models. On the contrary, many primary questions remain regarding the LPIA stratigraphic record in the western Paraná Basin and in its Namibian counterparts, though they are widely included in paleogeographic and paleoenvironmental models. This dissertation focuses on unraveling the stratigraphic record in the western Paraná Basin and in the Kaokoveld fjord network through a multiproxy analysis consisting of facies analysis, sediment transport vectors, ichnology, geomorphology, and environmental geochemistry.The first chapter reassess the stratigraphic architecture of the poorly-deciphered Aquidauana Formation in the western Paraná Basin by describing the sedimentological and ichnological aspects of an unusual thick and continuous section. Half of the vertical extent of the Aquidauana Formation was deposited in a subaqueous slope setting by sediment gravity flows without glacial influence. Episodic glacial influence is recorded in a thin interval associated with deposition in a glaciated outer shelf setting. This view contrasts with the dominant interpretations for the Aquidauana strata, which rely on continental glaciers as the main depositional agents. Furthermore, analysis on sediment transport vectors supports the hypothesis of a local westward ice source, contrary to the hypothesis regarding the huge Gondwanan Ice Sheet covering the whole Paraná epicontinental sea. The second chapter focuses on a comprehensive sedimentological and geomorphological analysis for the Orutanda fjord in the Kaokoveld fjord network, bringing new insights on the relevance of paraglacial mass wasting in overprinting glaciogenic deposits. The Orutanda fjord hosts a compelling exhumed record to assess in detail a complete glacial-deglacial cycle and to quantitatively analyze its geomorphology and estimate ice thickness. Although in a depositional setting controlled by glaciers, both the deglacial and postglacial strata are dominated by facies emplaced by gravitational resedimentation processes in fjord-side and fjord-head delta systems. This insight from the Orutanda fjord is key to understanding the role of glaciers versus non-glacial processes in producing the glacial deep-time record. The third chapter investigates the infill of the Engo fjord in the Kaokoveld fjord network through a linked sedimentological, ichnological, geochemical, and geomorphological analysis. While it is a depocenter buried by thick upper Paleozoic glacial strata and modern alluvial and eolian sediment, the Engo fjord hosts a valuable ~80 m thick succession that allowed for a pioneer assessment of the postglacial onset in the fjord network. The postglacial Engo Formation is characterized by a retrogradational, transgressive, tripartite subdivision consisting of estuarine tidal bars and heterolithic-carbonate tidal flats bearing microbialites as well as nearshore sedimentation. Correlations with the well-established analogous depositional context from the once-connected Paraná Basin allowed to constrain the depositional age for the Engo Formation and insert the Namibian fjord network as an important piece when considering the puzzling glacial-to-postglacial turnover in the Paraná epicontinental sea. This research on critical but poorly-comprehended domains of the Paraná epicontinental sea demonstrates that exploration and sedimentologic reassessment of the upper Paleozoic successions are still very necessary to develop a thorough picture of this extensive depocenter during the LPIA. Although this late Paleozoic depocenter hosts strata deposited during an extensive icehouse interval that were influenced by multiple waxing and waning ice-spreading centers, the glacial activity is suggested to have had an essential underlying but not an ultimate role in the genesis of the glacial strata.

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