UDITA MUKHERJEE, Kyle M. Straub

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 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 detectable signals stored in field scale stratigraphy. This field test builds on results from physical experiments where identifiable stratigraphic signals of RSL change were only produced from RSL cycles with magnitudes and/or periodicities greater than the spatial and temporal scales of the internal dynamics of deltas. Published long term sedimentation rates and sea level reconstructions suggest that the Mississippi River Delta (MRD) should be a good place to study sea level signal storage thresholds. We use publicly available seismic volumes from NAMSS-USGS to study how and if signals of paleo-sea level change are stored in strata of the MRD, comparing strata of the late Miocene (LM) and early Quaternary (EQ). Comparison of the amplitude and period of cycles in these two time periods, constrained by micropaleontological data, predicts storage of RSL signals in EQ strata, but not in the LM strata. This is confirmed as we show that signals of larger amplitude EQ RSL cycles are preserved in the MRD, but smaller amplitude LM signals are not detectable. This study adds field scale observations that quantify the intermingling of stratigraphic products of internal dynamics with products of RSL change over geological timescales.