IDENTIFYING STRATIGRAPHIC CYCLICITY AT THE SCALE OF CONTINENTS AND BASINS (Invited Presentation)

Many approaches to the study of cyclicity in sediments rely on measurements, such as elemental abundance and grain size, extracted from single stratigraphic sections. Although such approaches are powerful because they provide large sample sizes that are stratigraphically well-ordered, even on short thickness scales, there are many different scales of stratigraphic variability, ranging from individual sedimentary basins to the sedimentary carapaces of entire continents, that are not adequately captured at any one location. Macrostratigraphy yields quantitative data describing spatially-integrated temporal variability in the sedimentary record. Because correlation and analysis of at multiple locations is required for macrostratigraphy, the realized temporal acuity of macrostratigraphy is generally lower than what is possible in analyses of single stratigraphic sections. Nevertheless, siliciclastic sediment transport models indicate that macrostratigraphic quantities can be successfully used to measure basin-scale patterns of sedimentation, which are in turn quantitatively directly related to model forcing parameters. Macrostratigraphy applied to high-resolution stratigraphic sections in the Wilkins Peak Member (WPM) of the Green River Formation identifies a reciprocal relationship between carbonate-rich lacustrine facies and dominantly siliciclastic alluvial facies, with an emergent strong and statistically robust ~100 Kyr signal. Contrary to previous interpretations of Fischer-Assay data derived from individual WPM cores, macrostratigraphy demonstrates that eccentricity-length cycles are not driven by fluctuations in lake water level, but reflect instead basin-scale alternations in siliciclastic-rich alluvial and carbonate-rich lacustrine environments. On the timescales of entire sedimentary basins and on the spatial scales of a continent, macrostratigraphy demonstrates that sedimentation in North America is also cyclic, with oscillations of approximately 60 Myr duration being driven by large-scale marine transgressive-regressive cycles. Thus, over several orders of magnitude in space and time, macrostratigraphic analysis is capable of providing a new framework for discovering cyclicity in the stratigraphic record and testing hypotheses for its origins.