RPG: Millennial-Scale Paleoclimatic Cycles Expressed in Paleozoic Basinal Marine Sequences

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The proposed research is to investigate the origin and periodicity of rhythmically interbedded limestone-marl couplets in four separate Paleozoic basinal marine sequences. In each of the sequences, the limestone-marl couplets are characterized by decimeter-scale alternations of even-bedded, laminated limestone and marls; well-preserved calcareous fossils in marl layers indicates a primary depositional(versus diagenetic origin) to the interbeds. Spectral analysis of the limestone-marl interbeds will be conducted to determine whether there is a regularly cyclicity to the bedding couplets, and the duration of the cycles will be determined from a range of sedimentation rates calculated for each individual sequence. A planning grant is submitted to study the sedimentologic origin and periodicity pf rhythmically bedded limestone-marl couplets in one of the proposed sequences; the Middle Cambrian of western Utah (Wheeler and Marjum Formations). The emphasis of the pilot project is to develop accurate and time-efficient sampling techniques for generating time series in interbedded limestone and marl facies. In previous studies, time series generated from variations in HCI-insoluble residues has proven to be an accurate method, however it is very laboratory-time intensive. Consequently, three other less-time consuming methods will be tested on the Middle Cambrian couplets determine which technique (s) best reflects the rhythmic nature of the deposits. Specific planning grant activities will include describing and interpreting the sedimentologic and stratigraphic characteristics of the basinal facies, evaluating the lateral continuity of limestone-marl couplets, sampling the best-exposed section for variations in HCI-insoluble residues, magnetic properties, and bed- thickness variations. Results from spectral analysis of the different time series will be compared to determine which time series sampling technique(s) are appropriate for interbedded limestone-marl facies. The cause of millennial-scale paleoclimatic fluctuations is not well understood, however they have been attributed to changes in solar activity or due to the nonlinear response of the climate to precessional (~20,000 yr) orbital forcing. If the periods of such persistent oscillations can be characterized, they offer the potential for developing high-resolution chronostratigraphy, with a greater resolution than Milankovitch cycles, that can be used to calibrate the length of time between absolute datums, variations in sedimentation rates, biologic evolution rates, and the time intervals over which geomagnetic reversals occur.