PhD: Landscapes of Extinction and Evolution: The Global Sedimentary Record of Biotic-Abiotic Feedbacks in Mesozoic and Cenozoic River Systems

Amongst many abiotic-biotic feedbacks observable in modern environments, one crucial role is that which plants play in moderating processes and landforms in rivers. Studies into such modern interactions commonly cite a geological observation that ancient rivers left a fundamentally different sedimentary record prior to the evolution of land plants. However, Earth's oldest vegetation was dominated by extinct lineages, with physiological traits and environmental effects that may not fully be analogous to modern flora. The geological record of post-Palaeozoic vegetation controls is poorly understood, but this 250-Ma interval has seen a number of extinctions (e.g., the collapse of lyscopsid-dominated rainforests) and evolutionary events (e.g., the evolution of angiosperms and C4 grasslands) that should be expected to have resulted in shifts in the global ‘behaviour' and sedimentary products of ancient rivers. This research will quantify the sedimentary record during this prolonged and punctuated floral transition: with implications for the underlying role of plants in river processes and the physical-ecological impacts expected when vegetation is modified/removed from modern rivers.
Almost all modern rivers are partly colonized by angiosperms or grasses, providing stability to banks and islands and rerouting water and sediment in channels. Yet both organisms are geologically-recent constituents of Earth: so how were rivers different before they evolved? What florally-induced changes to river processes and habitats are discernible the ancient alluvial record? The geological record of older strata (the interval between ‘pre-vegetation' Earth and the colonization of the earliest land plants) shows that plant evolution did lead to tangible worldwide stratigraphic shifts in the character of the alluvial record. This project will quantify the more recent characteristics of river deposits through the Mesozoic-Cenozoic, identifying shifts in the frequency-distribution of physical-biological alluvial signatures to reveal the underlying interactions between plants and rivers.
The student will be responsible for compiling and managing an holistic database in which the sedimentary characteristics of worldwide alluvial successions are recorded. The nature and dimensions of different sedimentary architectures and bedforms will be documented, alongside data pertaining to varying lithologies and the palaeoecology of different alluvial successions (e.g., trace fossils). The database will be analysed to recognise shifts in the worldwide frequency-distribution of the characteristics of alluvium that may be stratigraphically allied with (and explained by) the evolution of new plant physiologies, documenting concomitant shifts in fluvial processes and river habitats. The database will be used to identify field areas as case studies, from which conceptual models of deposition during different intervals of plant evolution can be constructed using field sedimentological and ichnological techniques (sedimentary logging, architectural analysis, trace fossil characterization). A likely key fieldwork site will be the Bighorn Basin of Wyoming and Montana, in which fluvial sedimentary strata were deposited during various intervals of the Mesozoic and Cenozoic.