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

Friday, August 22, 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.

Tuesday, August 19, 2014

A Look Back…70 Years: Sand Fleas at the Beach

Organisms interact with their environment, and in many cases, they leave geological evidence.  Seventy years ago, Emery noted and described amphipod burrows (sand fleas) in California beaches.  He went on to suggest that the presence of comparable burrows in ancient successions “should be supplementary indications of a marine beach environment because they require a temporary drying of the beach such as occurs between tides.”  Hmmm.  As we end the summer beach season in the northern hemisphere, JSR PaperClips readers who visit the beach and are hassled by sand fleas may want to take this paper along to consider the geological significance of the things that annoy them. 

v. 14, p. 26–28.

Thursday, August 14, 2014

Highlights—Kenyan Lacustrine Carbonates

Lacustrine depositional systems can include both prolific source rocks and porous reservoirs, yet the controls on spatial variability in these systems are poorly constrained. This study by Hargrave et al. focuses on Plio-Pleistocene to Holocene lacustrine carbonate strata that accumulated along the southeastern margin of Lake Turkana (Kenya), a long-lived extensional basin that preserves a suite of carbonate facies assemblages. Field and laboratory data reveal the complex depositional environments of the carbonate facies of the volcanically mediated, mixed siliciclastic and carbonate system of the South Basin. These observations provide a conceptual model that may be a useful analogue for extensional basins that host economic quantities of hydrocarbons.

Lacustrine carbonates from Lake Turkana,Kenya: a depositional model of carbonates in an extensional basin by Jennifer E. Hargrave, Melissa K. Hicks, and Christopher A. Scholz