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  1. The Green River Formation preserves an extraordinary archive of terrestrial paleoclimate during the Early Eocene Climate Optimum (EECO; ~53-50 Ma), expressing multiple scales of sedimentary cyclicity previously interpreted to reflect annual to Milankovitch-scale forcing. Here we utilize X-ray fluorescence (XRF) core scanning and micro X-ray fluorescence (micro-XRF) scanning in combination with radioisotopic age data to evaluate a rock core record of laminated oil shale and carbonate mudstone from Utah’s Uinta Basin, with the parallel objectives of elucidating the paleo-environmental significance of the sedimentary rhythms, testing a range of forcing hypotheses, and evaluating potential linkages between high- and low-frequency forcing. This new assessment reveals that the ~100 μm-scale laminae – the most fundamental rhythm of the Green River Formation –are most strongly expressed by variations in iron and sulfur abundance. We propose that these variations reflect changes in redox state, consistent with annual stratification of the lake. In contrast to previous studies, no support was found for ENSO or sunspot cycles. However, millimeter to centimeter-scale rhythms—temporally constrained to the decadal to centennial scale—are strongly expressed as alternations in the abundance of silicate- versus carbonate-associated elements (e.g., Al and Si vs. Ca), suggesting changes in precipitation and sediment delivery to the paleo-lake.more »Variations also occur at the meter-scale, defining a ~4 m cycle interpreted to reflect precession. We also identify punctuated intervals, primarily associated with one phase of the proposed precession cycle, where Si disconnects from the silicate input. We propose an alternate authigenic or biogenic Si source for these intervals, which reflects periods of enhanced productivity. This result reveals how long-term astronomical forcings can govern the response of the system to shorter-term processes, yielding insight into decadal to millennial scale terrestrial climate change in the Eocene greenhouse earth.« less