EXPLORING THE INFLUENCE OF BED SEEPAGE ON THE FORMATION OF RIPPLE CROSS-LAMINATION DURING WANING FLOW

Accurate interpretation of sedimentary structures is a basic task of geologists and an area of basic research in sedimentology. Such interpretations make up the basis for reconstructing the flow behavior and configuration of ancient sediment routing systems. For example, in the case of turbidity currents, which are notoriously challenging to observe, vertical sequences of sedimentary structures and grain size trends are a primary source of information for reconstructing sand delivery to deep water basins. During rapid deposition from a turbidity current, water trapped in underlying pore space may escape upward, as the deposit begins to consolidate. This fluid motion may continue for relatively long periods of time (hours) and generates dewatering structures (e.g., pillar, dish). Although controversial, upward directed seepage (dewatering) may reduce bedload transport, and therefore, may influence the occurrence and geometry of sedimentary structures that appear in the upper portion of a Bouma Sequence, possibly including ripple cross-lamination and planar bedding, which represent an important moment in a turbidity current- the end of turbulent working of bed materials, and thus the cessation of sand delivery by a turbidity current. However, possible influences of a seepage flux on the generation of these sedimentary structures is unknown. To address this gap in knowledge, we will conduct a novel set of physical sedimentological experiments using a bench-scale annular flume. This set of experiments is specifically designed to explore how modest dewatering of a recent deposit may drive reduction of bedload and therefore influence 1) the climb angle of ripple cross-lamination and 2) the transition of ripples to planar beds during overall waning flow conditions. If valid, these hypotheses will add depth and context to future interpretations of sedimentary structures generated near terminal sand transport by turbidity currents.