Friday, May 31, 2013

Highlights—Lacustrine-Paralic Genetic Stratigraphy

Sequence stratigraphy uses regionally correlative surfaces to subdivide a succession of strata; in nonmarine strata, marine flooding units can provide important tie points.  In this study, Ielpi documents several marine bands in late Miocene lacustrine-paralic deposits of the Northern Apennines and illustrates their use in basin and sedimentologic analysis.  The data reveal that low-frequency sequences bounded by major marine incursions are regionally correlative and respond to regional high-amplitude base level fluctuations; in contrast, nested high-frequency sequences are noncorrelative and respond to local low-amplitude base level fluctuations. The results are interpreted to underscore the role of differential subsidence in the generation of asymmetrical sequence architectures and the alternation between hydrologically balanced and underfilled phases in high-accommodation and low-topography settings.

Thursday, May 30, 2013

Highlights—Impact of the Impact

The nature of the Cretaceous-Paleogene boundary, and the events recorded in that interval, remain the subject of considerable debate.  Here, Yancey and Liu describe sedimentologic and stratigraphic data from twenty sections along the Brazos River and from nearby cores.  The data include a dominance of mass flows and tempestites that include impact ejecta, and are interpreted to represent the record of mass flows and numerous great storm events associated with the Chicxulub impact, followed by a return to normal conditions.  The data suggest that tsunami waves are not a pronounced influence, contrary to previous interpretations.

Thursday, May 23, 2013

Highlights—Limestone Clasts, Back in Black

Subaerial exposure surfaces in carbonate successions throughout the geologic record include blackened clasts, but the origin of these clasts has remained the subject of debate.  In this contribution, Miller et al. describe the distribution, microstructure, and diagenesis of blackened clasts in the Neogene succession of Australia.  The results illustrate that the clasts are colored by organic carbon, interpreted to be formed in shallow the subsoil (B-C soil horizon) by a complex mix of dissolution and trapping of soil-derived organic matter by rhizogenic calcification.  The results illustrate the complex genesis of these features and the climatic conditions under which they form.

Friday, May 17, 2013

Highlights—Changing Depositional Regimes and Sandstone Variability

Marginal marine depositional systems vary markedly across strike, but along-strike variability is less commonly explored.  Painter et al. describe study of a 14-km long outcrop window of the Cretaceous Sego Sandstone Member (Mesaverde Group, Upper Cretaceous), and compare the sedimentology and stratigraphy with the well-studied Book Cliffs region.  The results illustrate three sequences of roughly similar thickness to the Book Cliffs, but that this area included more tidal and fluvio-deltaic systems.  The spatial and temporal changes in depositional systems are interpreted to reflect changes in paleogeography, and the authors suggests that comparable changes in subsurface analogs would lead to changes in reservoir quality, continuity, and geometry.

Thursday, May 16, 2013

Highlights: 2013 Honorary Member: Dale Leckie

In shelf regions, geostrophic currents, or flows in which the pressure gradient force is balanced by Coriolis forces, result in water motion at a low angle to the shoreline.  These currents have been interpreted to represent important mechanisms for cross-shelf transport.  In this paper, SEPM Honorary Member Dale Leckie and Krystinik (1989) summarized paleocurrent information from a number of ancient progradational shoreface successions to test the interpretation of the importance of these deposits.  Systematic analysis of 8 formations from North America and Europe revealed a predominance of currents oriented offshore at angles between 70-90 degrees,  a result interpreted to reflect a lack of record of geostrophic currents on the sedimentary record preserved in these successions.  So…the answer to the question in their title was interpreted to be… “no.”

Is there evidence for geostrophic currents preserved in the sedimentary record of inner to middle-shelf deposits? by Dale A. Leckie and Lee F. Krystinik, Journal of Sedimentary Research, v. 59, p. 862-870.

Wednesday, May 15, 2013

Highlights: 2013 James Lee Wilson Award: Kyle M. Straub

Many sedimentary systems include channelized bodies.  These channels can be distributed randomly or can preferentially fill topographic lows at the time of deposition (termed compensational stacking).  Exploring the stacking patterns of meter- to km- thick channelized packages from river delta to deep-water minibasins in six separate basins, award winner Kyle Straub and others (2009) described a suite of measurements that suggest that stacking patterns of channelized deposits are midway between the random and the compensational end-members.  They interpreted the results to reflect that channel depth is a fundamental length scale that controls stratigraphic architecture across a range of depositional environments, and hence can be used to better constrain geologic models.

Compensational stacking of channelized sedimentary deposits, by K.M. Straub, C. Paola, D. Mohrig, M.A. Wolinsky, and T. George, Journal of Sedimentary Research, v. 79, p. 673-688, DOI: 10.2110/jsr.2009.070.

Tuesday, May 14, 2013

Highlights: 2013 Pettijohn Medalist: J.A.D. (Tony) Dickson

Secular changes in seawater chemistry, including the Mg/Ca ratio, control the preferred abiotic carbonate precipitate from aragonite to calcite and back.  In this paper, Pettijohn Medalist winner Tony Dickson (2004) empirically tested hypotheses regarding these controls using the composition of Mg-calcite rich echinoderms through the Phanerozoic.  The data revealed low Mg/Ca ratios in the Jurassic and Cretaceous, and highs during the Cambrian, late Carboniferous to Triassic, and today; trends broadly follow proposed first-order Mg/Ca raios from geochemical models and fluid inclusions.  These results were interpreted to represent independent confirmation of the general first-order trends derived from other means.

Echinoderm skeletal preservation: Calcite-aragonite seas and the Mg/Ca ratio of Phanerozoic oceans by J.A.D. (Tony) Dickson. Journal of Sedimentary Research, v. 74, p. 355-365.

Monday, May 13, 2013

Highlights: 2013 Twenhofel Medalist, Paul Enos

Primary depositional intergranular pore systems markedly impact porosity and permeability, influence diagenetic processes and control recovery of resources in many reservoir and aquifer systems.  In this pioneering study, Twenhofel Medalist Paul Enos and Sawatsky (1981) explored the depositional aspects of porosity and permeability by documenting their change in different Holocene carbonate sediment textures.  The results indicated that carbonate mud-rich sediment (fine wackestone) includes the highest porosity (with up to 70%); mud-free grainstone includes 40-50% porosity.  The results provided information on the baseline initial conditions of sediment porosity, for comparison with changes in porosity with compaction and diagenesis.  

Pore networks in Holocene carbonate sediments by Paul Enos and L.H. Sawatsky
Journal of Sedimentary Petrology, v. 51, p. 961-985.

Friday, May 10, 2013

Highlights—Tufas and Paleoclimate

As rapidly precipitating freshwater carbonate accumulations that form in equilibrium with ambient water, tufas represent potential sources of high-resolution paleoenvironmental records.  To critically examine the use of tufa isotopic records in such reconstructions,  Osácar et al. examine a 12-year record of a modern tufa system, comparing water δ18O with δ13C and δ18O signatures in the precipitates.  The data illustrate that these tufas mimic seasonal temperature changes, but that the pattern is complicated by changes in the isotope record of precipitation.  These results are interpreted to illuminate the complex interaction of factors operative at several different type scales (seasonal and annual) that must be evaluated to accurately understand the isotopic record of ancient tufa systems.

Wednesday, May 8, 2013

Highlights—Hydrographs and Hyperpycnites

Hyperpycnites are deposits of a distinct style of flow that represents a mix of sediment and water that is denser than the water into which the mix flows; these types of deposits commonly are interpreted in the context of fluvial discharge into standing bodies of water.  Here, Saitoh and Masuda test conceptual and experimental models of hyperpycnal flow deposits by exploring spatial variability in subaqueous flood deposits in cores from a lake in Japan with limited wave or tide reworking.  The results clearly indicate that a single flood event can produce multiple eposides of waxing and waning flow, and the nature and controls on spatial variability in the sedimentology of the resultant deposits.  The results suggest the absence of a direct correlation between paleo-flood frequency or intensity and the sedimentary record.

Tuesday, May 7, 2013

Highlights—SEPM Medalists

Each year, SEPM honors a group of medalists for their outstanding contributions to sedimentary geology.  This week, we start a series to honor some of the recipients by providing “Highlights” of their contributions to JSR. 

The 2013 awardees include:

Twenhofel Medalist: Paul Enos. The highest award of SEPM Society for Sedimentary Geology. This award is in recognition of "Outstanding Contributions to Sedimentary Geology."
Shepard Medalist: J. Casey Moore. The Francis P. Shepard Medal for Marine Geology is awarded in recognition of "Excellence in Marine Geology."
Pettijohn Medalist: J.A.D. (Tony) Dickson. The Francis J. Pettijohn Medal for Sedimentology is awarded in recognition of "Excellence in Sedimentology."
Moore Medalist: Kenton Stewart Wall Campbell. The Raymond C. Moore Paleontology Medal is awarded in recognition of "Excellence in Paleontology."
James Lee Wilson Award: Kyle M. Straub. The James Lee Wilson Award is bestowed in recognition of "Excellence in Sedimentary Geology by a Young Scientist."
Honorary Member: Dale Leckie.  Honorary Membership in the SEPM Society for Sedimentary Geology acknowledges excellence in professional achievements and extraordinary service to the Society.

Medals and awards will be presented to the awardees at the 2013 President's Reception and Awards Ceremony, during the SEPM Annual Meeting held in Pittsburgh, PA on Tuesday, May 21, 2013 in the Omni William Penn hotel.

To all recipients, congratulations on your honor!