Abstract

Sediments transported from source terrains to depositional sinks carry environmental signals, which may or may not be preserved in stratigraphy. Existing theory suggests that storage thresholds for environmental signals are set by the internal dynamics of sediment transport systems. We test this theory by exploring whether changes in relative sea level (RSL) of various scales produce detectable signals stored in field-scale strata. This field test builds on results from physical experiments where identifiable stratigraphic signals of RSL change were produced only 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, comparing strata of the late Miocene (LM) and early Quaternary (EQ), to study effects of paleo–sea-level change on the dimensions of channelized bodies in the MRD. Calculating dimensionless depth and time scales, we show that the likelihood that EQ channelized bodies store signals of relative sea-level change is higher than that in the LM channelized bodies. Observations lead to interpretations of paleovalleys preserved in the EQ strata, but not in the LM strata, which broadly supports predictions from signal-shredding theory. This study adds field-scale observations that quantify the intermingling of stratigraphic products of internal dynamics with products of RSL change over geologic timescales and underscores the need to appreciate stochasticity in surface processes when building hypotheses related to the stratigraphic record.