Wednesday, March 19, 2014

Highlights—Pangean Systems

Much of the geologic history of equatorial Pangea in the Late Triassic is recorded in widespread redbed successions. This contribution by Atchley et al. examines one of these alluvial successions (the Late Triassic Chinle Formation) by calibrating sedimentological and pedogenic features to a high-precision geochronology, to assess relations among cyclic alluviation, climate shifts and biological turnover. The resulting age model and associated stratigraphic and paleoclimatic record represents a markedly refined constraint on the character of the Chinle Formation. These data reveal the history of cyclic environmental change and corresponding biotic turnover, and its temporal correlation to the Late Triassic tectonic history and physiographic evolution of western Pangea. As such, the results shed light on the previously undetected balance among life, paleogeography and tectonism within the Late Triassic of the southwestern United States, and may be broadly comparable to other sedimentary and ecologic systems.

A linkage among Pangean tectonism, cyclic alluviation, climate change, and biologic turnover in the Late Triassic: the record from the Chinle Formation, southwestern United States by Stacy C. Atchley, Lee C. Nordt, Stephen I. Dworkin, Jahandar Ramezani, William G. Parker, Sidney R. Ash, and Samuel A. Bowring

Wednesday, March 12, 2014

Highlights—Experimental Channels

The distribution and connectivity of channel sandstone bodies is a function of a complex suite of variables.  To understand conditions associated with changes in channel course due to lateral gradients in subsidence (“channel steering”) in basins with lateral subsidence gradients, Straub et al. quantify patterns in an experimental basin as the ratio of tectonic tilting to channel mobility varied over four stages.  The results reveal the importance of lateral gradients in subsidence rates relative to lateral mobility of channels in determining channel attributes.  The results also predict situations in which the strength and duration of pulsed tilting events are sufficient to steer channels, and suggest that pulsed events must be strong enough and long-lived enough to produce comparable cross-basin to down-basin transport slopes.  These insights document the broadly important role of interacting tectonics and subsidence in determining surface processes and stratigraphic architecture of channel systems.

Friday, March 7, 2014

Highlights—Garnet to the Source

Detrital garnet compositions provide a means to directly link sediment to the specific source rocks from which they are derived. In this paper, Hietpaset al. applied Mahalanobis distances, measured on canonical discriminant functions, as a metric to differentiate garnet compositions among potential sediment provenances. These metrics, applied to ~2,300 detrital garnet compositions isolated from modern river alluvium, successfully linked ~94% of the detrital grains to the source rocks from which they were derived. These results and methods illustrate a robust objective means to readily assess the complex, multi-dimensional detrital mineral chemical analyses. The method is also applicable to provenance studies relying on major and trace elements of other detrital mineral species. The results illustrate a means to constrain the lithology of source rocks and regional sediment provenance trends, insights valuable for understanding the unroofing history recorded in the stratigraphy of depositional basins.

Monday, March 3, 2014

Reviewer Comments: Linear Space and Long Fingers

The latest suite of JSR reviews has included a number of “gems.”  As always, we appreciate the humor that reviewers bring to the process, intentionally or unintentionally.  Comments include:

“Basically reflux as generally used to describe fluid flow (rather than indigestion!) refers to….”

“The veracity of this statement if difficult to evaluate in linear space.” [Editor’s Note: Huh?]

“Figures 4, 5, and 6 are overly redundant.” [as opposed to un-overly redundant?]

“The authors present some interesting and NEW data and interpretations, but the manuscript in its current version is something I wouldn't accept from a grad student as a class assignment.”

And this one really gave us pause: “The provenance of these voluminous clastics have been widely debated, with most long fingering the Ancestral Rocky Mountains…” 

Ouch!  Poor Ancestral Rocky Mountains!