Seasonal variations in modern speleothem calcite growth in Central Texas, USA by Jay L. Banner, Amber Guilfoyle, Eric W. James, Libby A. Stern and MaryLynn Musgrove
Wednesday, July 18, 2012
Deposits of calcite in caves (speleothems) have served as important paleoclimate proxies, providing detailed information of late Pleistocene and Holocene change. To explore the use of these important proxies, Banner et al. described a series of studies of speleothem growth rates from several sites in three present-day caves and compared these data with measurements of controlling factors (temperature, rainfall, drip rates, drip-water composition, and cave-air composition). The results suggested that growth rate was most closely influenced “by regional temperature effects on ventilation of cave-air CO2 concentrations and/or drip-water CO2 contents,” although local changes in drip rate changed the absolute rates within each cage. The results suggested that “growth-rate variations in ancient speleothems may serve as a paleoenvironmental proxy with seasonal resolution.”
Use of cave deposits as paleoclimate indicators requires that the minerals preserve geochemical tracers of environmental conditions, a factor that may be compromised if minerals are altered. To explore the utility of these features, Frisia et al. examined the genesis, nature (morphology, isotope geochemistry, and mineralogy), distribution, and alteration of aragonite in cave deposits in France. The data revealed that calcite and several habits of aragonite can grow in the same cave system, and that calcite replaced aragonite in less than 1 ka. The results also showed that the “isotope signal of different aragonite habits may reflect conditions of formation rather than climate parameters” and that isotopes in calcite varied markedly, depending on if it were primary or replacing aragonite. In both cases, however, the data highlighted the need for careful integration of geochemical, textural, trace element, and isotopic data for assessing the utility of speleothems to characterize past climate.
Aragonite-calcite relationships in speleothems (Grotte de Clamouse, France): Environment, fabrics, and carbonate geochemistry by Silvia Frisia, Andrea Borsato, Ian J. Fairchild, Frank McDermott and Enrico M. Selmo
Friday, July 13, 2012
Diagenetic processes can either destroy or create porosity; in some cases early events can markedly influence later processes. French et al. describe scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) observations from a Cretaceous succession in Germany and relate these observations to porosity. The data reveal nanofilms of amorphous silica between the detrital quartz grains and a subsequent microcrystalline quartz cement with c axes randomly oriented relative to the grain. These observations lead to a conceptual model for one means of preservation of porosity in deep sandstone reservoirs, wherein the amorphous silica nanofilm inhibits growth of systematically growing quartz that could fill the pores.
Microcrystalline quartz generation and the preservation of porosity in sandstones: evidence from the Upper Cretaceous of the Subhercynian basin, Germany by Marsha W. French, Richard H. Worden, Elisabetta Mariani, Richard E. Larese, Russell R. Mueller, and Chris E. Kliewer
Thursday, July 12, 2012
Many successions of interbedded tide-influenced sandstone and marine shale include complex vertical and lateral facies patterns, and make prediction of lateral variability challenging. Willis and Fitris describe a detailed study of core, log, and seismic data from a Miocene succession in Indonesia, that captures the nature of stratigraphic heterogeneity. The results of this study challenge the notion that sharp-based tidal-influenced sandstone bodies are underlain by lowstand fluvial erosion surfaces and represent incised valley-fill deposits. Instead, this succession is interpreted to reflect a mix of regressive, transgressive, and re-worked shelf deposits, but with trends that are constrained by the sequence stratigraphic framework.
Sequence stratigraphy of Miocene tide-influenced sandstones in the Minas field, Sumatra, Indonesia by Brian J. Willis and Faizil Fitris
Wednesday, July 11, 2012
Many sandy shorelines include sand ridges attached to the shoreface. To explain the evolution and dynamics of shoreface-connected ridges, Son et al. describe observations of sedimentary structures, sediment textures and bathymetry from repeat surveys over the same area in the southern North Sea, and characterize changes in the context of observations and models of tides and waves. The data reveal variability and systematic changes, interpreted to be the result of a combination of tides and waves generated by storms. These data lead to a conceptual model for the variable and dynamic sedimentology and morphology of these ridge-and-trough systems, and their possible ultimate stratigraphic record.
Long-term changes in morphology and textural sediment characteristics in response to energy variation on shoreface-connected ridges off the East Frisian barrier-island coast, southern North Sea by Chang Soo Son, Burghard W. Fleming, Alexander Bartholomä, and Seung Soo Chun
Tuesday, July 10, 2012
A fundamental attribute of many sedimentary rocks, and the basis for many subsequent interpretations, is texture. Yet, consistently and accurately describing texture in many sedimentary systems is challenging due to inherent limitations of many existing classification schemes. In this paper, Farrell et al. propose and describe a new system for textural nomenclature that is objective and broadly applicable to many sedimentary systems. They suggest that use of this system would aid to standardize descriptions and to more directly link to process-based interpretations of sedimentary successions.
Standardizing texture and facies codes for a process-based classification of clastic sediment and rock by Kathleen M. Farrell, W. Burleigh Harris, David J. Mallinson, Stephen J. Culver, Stanley R. Riggs, Jessica Pierson, Jean M. Self-Trail, and Jeff C. Lautier
Monday, July 9, 2012
Sediment gravity currents commonly are invoked as important processes controlling deposition of the deep-marine stratigraphic record. Deposits of these currents, which commonly include the idealized Bouma succession, lack evidence of a dune cross-stratified unit that would be present were deposition merely the result of decelerating flow. Where did they go? Arnott suggests that this absence is the result of elevated concentrations of suspended sediment (high density), which in turn inhibits development of hydrodynamic instability that could lead to development of dunes. This conceptual model explains why dunes, so prevalent in coarse-grained terrestrial and shallow marine deposits, are rare in the deep-marine record.
Turbidites and the case of the missing dunes by R.W.C. Arnott
Monday, July 2, 2012
For the third year in a row, the Impact Factor for the Journal of Sedimentary Research has risen! Based on 2011 ratings, the Impact Factor is 2.331, a rise of more than 32% since 2008. With this increase, JSR remains the highest-rated sedimentology/stratigraphy journal, and presently ranks #5 in the “Geology” subject category.
The Impact Factor (IF) of a journal is a quantitative measure of the impact of a journal, calculated by comparing the average number of citations of recent articles to the number of articles published over a period of time (generally 2 years). It is published online in Journal Citation Reports® as part of the ISI Web of Knowledgesm. The concept has been around for many years (commentary by Eugene Garfield, the originator, is available at at THIS link),
Although we are proud of this increase, we also resist the urge to over-interpret these quantitative metrics. These types of tools have been roundly criticized on several bases. In one recent review, Vanclay (2011) went so far as to suggest that calculating the impact factor has parallels with “the out-dated pseudo-science that attempted to infer human behaviour from measurements of skull morphology….” Similarly, numbers can be easy to abuse, manipulate, or mis-interpret – unintentionally or intentionally. A former department chair once said in reference to the tenure process that “The dean can’t read, but he can count…,” consistent with Smith (2006), who noted that “…people, including scientists, credit numbers with an importance that they deny to words.”
In this sense, we re-iterate the objective of JSR—to provide readers with the best-written, cutting-edge science papers dedicated to advancing the broad field of sedimentary geology. We hope that you, our readers, agree that JSR offers important and interesting contributions—regardless of any quantitative measure of “impact.”
Finally, we close with important words—thanks to those of you who have contributed to the journal, as authors, reviewers, or Associate Editors. Be proud, for this increase is in no small part a reflection of your contributions and efforts to advance sedimentary geology.