Thursday, January 9, 2014

Highlights—A Look Back…60 years: Climate Cycles

In December 1953, color television broadcasts were first approved by the U.S. Federal Communications Commission.  Soon thereafter, the first color television sets went on sale for the bargain price of more than US $1,000 (present day: US $7,850).  Journal of Sedimentary Petrology readers found a way to break free and read a paper by Werner Bruckner that examined links between cyclic strata and climate change—a topic still of considerable interest today. Bruckner offered numerous insights, including the now-classic line, “When a detailed study of limestones is made, their interpretation becomes more difficult.”   Overcoming the challenges, he proposed a conceptual model wherein climatic oscillations (changes in temperature) influenced the saturation state of calcium carbonate, which led to cyclicity. He further proposed that the utility could include “correlating formations and climatic events over distances of continental size.”

Cyclic Calcareous Sedimentation as an Index of Climatic Variations in the Past: Werner D. Bruckner, Journal of Sedimentary Petrology, v. 23, p. 235-237.

Monday, January 6, 2014

Highlights—Run River, Run

Sediments record the mechanisms of transport and deposition, but the details of the precision and accuracy of interpretations of processes from the preserved record remains ambiguous. To explore this concept in a fluvial system, Draut and Rubin analyzed relations between grain-size progression in suspended sediment and flood deposits from controlled, dam-release floods in the Colorado River through Marble-Grand Canyon.  The results revealed that for these simple floods, most deposits show inverse grading that reflects coarsening suspended sediment (a result of fine-sediment-supply limitation). But eddy-scale variability creates some profiles with normal grading, a pattern that does not reflect grain-size evolution in the flow as a whole. The results are interpreted to suggest that systemwide grain-size evolution in modern or ancient depositional systems requires sampling enough deposit profiles that the standard error of the mean of grain-size-change measurements becomes small relative to the magnitude of observed changes. Collectively, the results reveal that, with sufficient sampling, fluvial deposits can faithfully reveal paleo-sediment flux and discharge.