U-Pb calcite dating of fossil eggshell and its impact on continental terrestrial sedimentology

Since the 1920s, palaeontological efforts in the Gobi Basin of Mongolia have sought to elucidate the evolutionary history of fossil vertebrates within a Northeast Asian setting. As a result of the past century’s paleoscientific efforts, a plethora of Mesozoic and Cenozoic vertebrates have been described, not limited to Oviraptor philoceratops, Protoceratops andrewsi and Velociraptor mongoliensis. However, markedly different to this is the lack of complimentary geological context, which has rendered many globally significant biostratigraphic and paleogeographic linkages tenuous at best. One of these key sites is that of Tel Ulaan Chaltsai, a fossil egg and nest bearing locality that has cryptically been placed both within the Early and the Late Cretaceous by different researchers. Therefore, Tel Ulaan Chaltsai offers a crucial opportunity to resolve temporal uncertainty and for the first time place it within a meaningful stratigraphic context. This thesis employed novel methodologies including a non-traditional geochronometer, ergo U-Pb calcite age dating of fossil eggshell. Within Data Chapter One, we evaluated the reliability of elemental mapping coupled with LA-ICP-MS U-Pb calcite age dating of dinosaur eggshell recovered from Tel Ulaan Chaltsai against dinosaur eggshell from the Mussentuchit Member (Utah, USA.) which has been temporally well-constrained by ashfall zircon geochronology. Our results indicate that sediments of Tel Ulaan Chaltsai were deposited near to an age of 75.35 ± 0.74/1.5 Ma. Based on the resulting temporal placement within the Campanian, coupled with regional lithostratigraphic frameworks, Tel Ulaan Chaltsai can be confidently placed within the Baruungoyot Formation. Additionally, elemental mapping indicated post-depositional uptake of uranium (U) in the Mussentuchit Member fossilized eggshells, as well as a geochemical signature related to the Cretaceous Oceanic Anoxic Event 2, but nearly syndepositional uptake within the Tel Ulaan Chaltsai fossilized eggshells. In addition, Data Chapter 2 attempts to reinvestigate the sedimentological and geochemical aspects of Tel Ulaan Chaltsai to better place the locality into one of Zones 1-4 of the Baruungoyot Formation in corroboration with Eberth (2018). Sedimentologically, Tel Ulaan Chaltsai is interpreted to be an intensly aridifed fluvial floodplain, composed of stacked calsisols interbeded by sheetfloods and crevasse splays, with sediments hydraulically reworked by bed-load-rich ephemerally flowing meandering channel belts. Coupled with 88Sr elemental mapping of the Tel Ulaan Chaltsai eggshell samples that reflected an aridifying continental paleoenvironment, the Tel Ulaan Chaltsai sediments align with the lower Baruungoyot Formation. This represents not only the first uppermost post-rift sequence to be radiometrically calibrated within the Eastern Gobi Basin, but also the first assignment of the Tel Ulaan Chaltsai to a sedimentary formation in over three decades. Additionally, 88Sr elemental mapping of the Mussentuchit Member eggshell samples reflect a primary signature of the paralic paleoenvironment within which the sediments were deposited.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Venter, Kira Elisabeth

Advisor dc:contributor.advisor

• Tucker, Ryan T.

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135626

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135626