"Varve" counting vs. tephrochronology and 137Cs and 210Pb dating: a comparative test at Skilak Lake, Alaska

Article Abstract:

Sedimentation rates in Skilak Lake were measured using (super)137-Cs and (super)210-Pb instead of counting 'varves'. These two radionuclides gave lower estimates than those based on varve counts. Tephrochronologic dating agree with the radioisotopic estimates, implying that Skilak Lake rhythmite layers are not annual varves. The results suggest that varve dating may be less accurate than was previously thought, and that sunspot and climatic data from previous research on Skilak Lake must be reevaluated.

Evaluation, Alaska, Natural cycles, Geology, Radioactive dating, Radiometric dating

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Retreat of the front in a prograding delta

Article Abstract:

Delta front retreat will occur after a period of progradation given a constantly rising sea level and a steady input of sediment. The zone in question is designated by the slope-break line marking the interface of subaerial and subaqueous areas. A model is developed to challenge the standard theory of the negative effect of a sea-level change on the rate of horizontal shoreline movement. The results suggest that tectonic or paleoclimatic factors need not be invoked to explain coastline retreat.

Analysis, North Sea, Deltas

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Interbasinal cyclostratigraphic correlation of Milankovitch band transgressive-regressive cycles: correlation of Desmoinesian-Missourian strata between southeastern Arizona and the midcontinent of North America

Article Abstract:

Cyclostratigraphic analysis is used to determine the pattern and causes of Horquilla limestone deposition in southeastern Arizona. Data from the Gunnison Hills and the Dry Canyon section of the Whetstone Mountains were used for the correlations, which had better resolutions than biostratigraphy. Platform carbonates best evince eustasy and are sensitive to base-level changes. Horquilla Limestone cyclicity is predominantly eustatic because of the tectonic stability of the Pedregosa shelf.

North America, Stratigraphic correlation, Geology, Stratigraphic, Correlation (Geology), Stratigraphy

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