Thursday, September 4, 2014

Highlights—Proximal Hybrid Flow Deposits

Many deep-sea fan and sheet systems include deposits of rheologically complex sediment gravity currents (“hybrid flows”) with suggestions of turbulent, transitional and laminar flow character, most commonly interpreted to represent deposition in more distal regions. In this paper, Patacci et al. describe a succession deposited as strata that onlap a confining slope. The sedimentology and geometry of these strata illustrate that hybrid flow-associated deposits can occur in proximal settings, and on scales of just 100s of meters, given a confining topography (e.g., onlap) that transforms the flows. This flow hybridization mechanism provides an alternative explanation for the occurrence of clay-rich facies development at the foot of flow-confining seafloor slopes, and may be important for predicting trends in reservoir quality in subsurface analogs.

Wednesday, September 3, 2014

Highlights—Small Incised Valleys

Although incised valleys at or near the highstand shoreline are common on many Holocene (and ancient) continental margins, their dynamics remain poorly understood. To explore these systems, Mattheus and Rodriguez use geophysical and lithologic data and geomorphic analyses to examine the morphology and facies architecture of coastal prism and tributary incised valleys on the Holocene lower coastal plain of North Carolina. The results reveal trends in Holocene coastal evolution in response to sea-level rise and sedimentation, including the observation that incised-valley width is proportional to drainage-basin area. They suggest that distinguishing between valley morphologies in the coastal plain provides insight into the distribution of sandy lithosomes, important for mapping groundwater and hydrocarbon reservoirs.

Tuesday, September 2, 2014

Highlights—Combined Flow Diagrams

Bedforms occur in many depositional systems, and can be influenced by unidirectional, oscillatory, or combined flows. In this paper, Perillo et al. collected experimental data under a wide range of unidirectional, oscillatory and combined flows to address range of unexplored flow conditions (strong unidirectional flows and intermediate oscillation periods) where the bedform geometry, and hence consequent sedimentary structures, have not been explored. Under these flow conditions, ten distinctive bedform states are identified, and the planform and cross-sectional geometry are described. This new nomenclature unifies past research on bedforms in both unidirectional and oscillatory flows, and thus presents a new synopsis of bedforms developed under such flows. This new data and analysis allows proposition of a new unified phase diagram for combined flows.

A new phase diagram for combined-flow bedforms by Mauricio M. Perillo, James L. Best, and Marcelo H. Garcia