Dean, Christopher David; (2019) Untangling the web of life: reconstructing spatial patterns in the palaeoenvironment, palaeoecology and taphonomy of the Western Interior Seaway. Doctoral thesis (Ph.D), Imperial College London.

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Abstract

A central goal of palaeontology is determining trends in diversity through deep time, but our un- derstanding of these patterns is hampered by bias in the fossil record, arising from taphonomic, geological and anthropogenic causes. These factors can be further exacerbated by environments which are unqiue to the past. Epicontinental seas - shallow, continent covering oceans - were common throughout the Phanerozoic and contain the majority of our available fossil record. Their unique environmental conditions have led to the suggestion that their depositional pro- cesses, palaeo-community structure and taphonomic biases could be driven by different variables than those of otherwise time-equivalent shelf margin settings. Understanding this variation in both time and space is essential for bridging the gap in understanding between these environ- ments and the modern. In this thesis, a series of case studies attempt to understand the spatial patterns in palaeoenvironment, palaeoecology and taphonomy of the Western Interior Seaway, an epicontinental sea from the late Cretaceous of North America. A new method of estimat- ing palaeobathymetry using numerical tidal modelling reports that the seaway was deeper than previously suggested in the mid-Campanian, with tides within the 'Utah Bight' amplified by resonance effects. Analysis of palaeocommunity structure reveals that palaeobiogeography of molluscan fauna varies between the Cenomanian-Turonian and the lower Campanian; the for- mer exhibits a latitudinal gradient whilst the latter shows a homogeneous central seaway. As such, previous suggestions of distinct sub-provinces of fauna can be better explained by other palaeobiogeographic patterns. Differences in sampling probability between calcitic and aragonitic molluscs at varying depths suggest that preferential aragonite bias can be expressed spatially, potentially influencing the perceived range size of aragonitic organisms due to differences in between-site preservation. These studies show that it is important to understand the inherent spatial heterogeneity of the geological record to adequately analyse diversity patterns through time.

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