Measuring the Stratigraphic Filter in Ancient Deltaic Deposits

Abstract:

Internal or autogenic sedimentary-system dynamics act as a filter that can dampen or obliterate signals of environmental perturbations, such as changes in climate and tectonics. Additionally, the transfer of material into the sedimentary archive can further degrade environmental signals. Presently we have a poor understanding of the rates, scales, and types of sedimentary processes that influence the stratigraphic filter in natural systems. A set of statistical tools has been developed for estimating the spatial and temporal scales over which the sedimentary filter operates from preserved stratigraphy. These tools, such as the compensation index, have been applied to experimental data and numerical models, with only limited use on outcrop data. Experimental datasets commonly have several orders of magnitude more data than even the most well exposed ancient outcrops; consequently, the ability to confidently use tools in natural systems is limited. Here we present an evaluation of the suitability of the compensation index for measuring and interpreting sedimentary outcrops. In order to constrain uncertainty due to data-set-size limitations, we model the degree to which measurement error, small data sets, and incomplete sampling influence attempts to quantify stratigraphic architecture. We demonstrate the potential for measuring the stratigraphic filter in ancient deposits by evaluating well-exposed deltaic deposits in the Cretaceous Western Interior Seaway that have been interpreted as having different degrees of to wave, tide, and river influence. Ultimately our results underscore how powerful quantitative tools developed in experimental and model datasets must be applied and interpreted with care in ancient deposits where data availability is limited.