SEDIMENTARY STRUCTURES- A LOVE AFFAIR WITH MOVING SAND; INSIGHTS FROM THE WORK OF ROBERT H. DOTT JR

Occam’s razor was never so sharp as when Bob Dott’s curiosity was focused on a new setting for studying the processes and products of moving sand. From early papers on “mechanical limestones” to scores of other publications, he focused on sedimentary processes, and sedimentary structures – and used these as a foundation for regional tectonic syntheses. Repeatedly, his articles, and those with his students and colleagues, meticulously crafted arguments buttressed by quantitative data and field examples, which cautioned against oversimplification by attributing sedimentary structures to specific depositional environments based on data which were only “consistent with”, but not diagnostic. One recurrent interest included the interplay of sediment cohesion, plasticity and liquefaction. In these he and his students elucidated convolute lamination, subaqueous gravity flow dynamics, the origin of dish structures, soft sediment deformation from slumping, and deformed/contorted cross bedding in many settings. Following on his interest in gravity driven flows, he and his students demonstrated that tractive flow occurred in conglomeritic gravity flow deposits in and adjacent to submarine canyons in Oregon and southern Chile. Driven by the need for better paleocurrent data, Dott quantitatively demonstrated the advantages of using trough axis-orientation, and the pitfalls of not recognizing cross stratification types. Two additional significant contributions with his students include the recognition of storm-produced Hummocky Cross Stratification types -which has become a foundational concept in facies recognition in shore line sequences. And secondly, advances in understanding diagnostic eolian sedimentary structures of adhesion ripples and climbing translatent strata has provided the basis for much refined analysis of mixed eolian, fluvial, and littoral sandstones. Together, this diverse array of new knowledge Bob Dott, his students, and colleagues have generated about sedimentary structures has strengthened of our field, and our understanding of the processes which shape the Earth.