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

Friday, August 29, 2014

Highlights—Tectonic-Influenced IVFs

Stratigraphic architecture in fluvial-deltaic systems are responsive to eustasy and tectonics. To assess the role of each in stratigraphic heterogeneity, Rasmussen examines a complex Miocene incised valley fill system at the margin of the North Sea. Study of outcrops and boreholes, and integration with seismic data, reveal a marine-to-fluvial succession, with a shift from braided to meandering fluvial style, interpreted to form a compound incised valley fill. The results reveal that the valley fill is a result of both eustatic change and tectonics, and that tectonics results in a different morphology and distinct distribution of lithology than occurs in most eustasy-controlled incised valleys.

Wednesday, August 27, 2014

Highlights—Sediment Processing

Sediment size distribution is a fundamental descriptor of stratigraphic successions and can provide unique genetic information in certain situations. To assess protocols and utility of integrated grain size and grain type information for analysis of marine sediment, Flores-Aqueveque et al. explore the impact of pretreatments that isolate individual components. Comparing fluxes estimated from processed samples with the unprocessed samples suggest up to 58% difference, and that the filtered samples offer more accurate characterization of fine-grained marine successions.

Using image-based size analysis for determining thesize distribution and flux of eolian particles sampled in coastal northernChile (23° S) by Valentina Flores-Aqueveque, Sandrine Caquineau, Stephane Alfaro, Jorge Vald├ęs, and Gabriel Vargas

Monday, August 25, 2014

Highlights—Speleothem Diagenesis

With the increasing recognition of the value of speleothems as high-resolution paleoclimatic archives has come the recognition of the possible influence of diagenetic processes that may modify their geochemical signatures. This paper by Perrin et al. provides criteria for distinguishing primary and secondary features in aragonite and calcite speleothems from study of the Pont-de-Ratz Cave (France). Combining analysis of mineralogical, textural and geochemical data at different scales, results highlight the importance of diagenesis in vadose speleothems and the large variety of potential syn- and post-formational modifications of spelean precipitates in cave environments. The coupled petrography and geochemical identify the nature and origin of the diverse spelean materials, information that must be assessed before extracting reliable paleoenvironmental and geochronological information.

Aragonite–calcite speleothems: identifying originaland diagenetic features by Christine Perrin, Laurent Prestimonaco, Guilhem Servelle, Romain Tilhac, Marion Maury, and Patrick Cabrol