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William McMahon

William McMahon

Research Student

N297 /Downing Street

Office Phone: +44 (0) 1223 334173

Research Interests

My research is focused on sedimentary processes operating prior to the evolution of terrestrial vegetation, a time where only cryptobiotic films and crusts inhabited the terrestrial realm. Understanding these entirely non-uniformitarian sedimentary environments requires extensive fieldwork and detailed analysis of rocks in order to identify the specific controls on sedimentation. 

 The Palaeozoic greening of the continents by land plants was one of the most important events in Earth history, and had a significant effect on the preserved alluvial rock record. Alluvial successions deposited in the absence of land plants are typically characterised by sand-bodies with high lateral continuity. This seemingly monotonous sedimentology has favoured their attribution to relatively simple depositional processes. However, detailed analysis of numerous Precambrian and Cambrian fluvial successions worldwide demonstrates an underappreciated spectrum of preserved depositional architectures representing a range of fluvial styles.

 Sedimentary Characteristics of Alluvium deposited by Unvegetated Rivers - The sedimentary architecture of multiple pre-vegetation alluvial successions spanning over 2 billion years of Earth history are being assessed as part of one of the largest studies on pre-vegetation terrestrial sedimentation conducted to date. Results have revealed markedly varied depositional processes operating within predominantly low-sinuosity rivers.

Land Plants Forced Mud Retention on the Continents - One similarity all studied pre-vegetation alluvial successions have is a distinct paucity of mudrock.  An exhaustive analysis of the entirety of Earth’s preserved Archean-Carboniferous alluvial sedimentary record demonstrates a tangible characteristic of the global rock record: a unidirectional upsurge in the physical proportion of mud retained on land after the terrestrialization of vegetation. The shift is best interpreted to reflect the ways physical and chemical processes were transformed on the surface of a greening planet.

Microbial Matground influence on Prevegetation River Functioning - Before land plant evolution, non-marine microbial mats formed the only continental biota. The sedimentological influence of these matgrounds has been explored through a critical understanding of the ways in which microbial mats may effect sedimentation, coupled with partial modern analogues and case studies from the Proterozoic and Cambrian sedimentary records. Results indicate that the surficial cohesion provided by matgrounds did not exceed thresholds for reworking by hydrodynamic processes thus having little of no effect on preserved sedimentary architecture.

 

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