Field-testing Autogenic Storage Thresholds for Environmental Signals in the Strata of the Mississippi Delta

Abstract:

Sediments transported from source terrains to depositional sinks carry environmental signals, which may or may not be preserved in stratigraphy. Recently developed theory suggests storage thresholds for environmental signals are set by the internal (autogenic) dynamics of sediment transport systems. For the first time, we explore this theory by testing whether changes in relative sea level (RSL) of various scales, produce signals stored in field scale stratigraphy. This field test builds on results from physical experiments that deduced that only RSL cycles with greater magnitudes and/or periodicities than the spatial and temporal scales of the autogenic dynamics of deltas produce signals that get stored in marginal marine stratigraphy. Published long term sedimentation rates and sea level reconstructions suggest that the Mississippi delta should be a good place to study sea level signal storage thresholds. We use publicly available seismic cubes from NAMSS-USGS to study how and if signals of paleo-sea level change are stored in strata of the Mississippi River Depocenter. Specifically, we compare strata of the late Miocene and Pleistocene. Comparison of the amplitude and period of cycles in these two time periods, constrained by micropaleontological data, suggest storage of signals of RSL change in Pleistocene strata, but not in the strata deposited during the Miocene. We focus on statistics of paleo-channels and valleys interpreted in the 3-D seismic volumes. Specifically, we characterize distributions of channel body widths and depths to quantify the type of RSL signals being stored in the basin’s strata. These features are interpreted through use of attributes like variance and root mean square amplitude. The difference in amplitude of the RSL change could also influence other stratigraphic characteristics like grain-size and sediment partitioning between the shelf and the deeper marine. To identify if signals of RSL change are housed in these attributes, ongoing and future work will examine maps of root mean square seismic amplitudes, wireline log attributes, and isopach maps.