Abstract A phenomenon unique to fine-grained sediment is its ability to alter the physical characteristics of the overlying water column. Although the present state of research recognizes many aspects of fine-grained seabed and water column interactions, this study documents how an energetic sandy, shallow marine system can autogenically transition to a system capable of accumulating fine-grained bedforms to clinoforms. To understand these transitional processes this study examines the lithostratigraphy and depositional history of the Suriname portion of the Guiana Coast (French Guiana, Suriname, and Guyana). Four major lithologic facies (Pre-Holocene silty clay; peat-rich silty clay; sandy mud; silty clay with cheniers) were derived from the Late Holocene sea level rise and influx of sediments emitted from the Amazon River. Since approximately 6000 BP, ~10 to 20% of Amazon-derived sediments bypass the Amazon shelf and are transported northwestward toward the study area. Along the Suriname coast (~900 km from the Amazon), however, significant mud accumulation did not commence until 3000 to 3500 BP. Suspended sediments can travel this distance in less than 1 month. A migrating (1.5 km/yr) mud bank could travel the 900 km from the Amazon mouth in 600 years or, after formation of a 400-km-wide subaqueous Amazon delta (by 1200 BP), migrate the remaining 500 km by 4500 BP, still 1000 to 1500 years prior to the time period during which radiocarbon dates indicate significant mud accumulation began. Consequently, either there was a major hiatus in sediment transport and accumulation between 6000 BP to 3000 BP or some other transport process other than suspension or mud-bank migration-controlled initial mud accumulation. Assuming steady-state conditions, lateral accretion rates from 6000 BP to 3000 BP equate to 0.3 to 0.4 km/yr. These rates, which are similar to migration rates cited by previous studies for the trailing edges of mud banks in French Guiana, may reflect postmigration erosion of the initial mud banks. Whether there is an erosional overprint or some other process, this lateral accretion rate is an indicator of the amount of fluid mud necessary for ‘mud to beget mud.’ More general prerequisites necessary for a shallow marine setting to autogenically form fine-grained clinoform-scale accumulations are, first, a single large source of muddy sediments (a major river) and, secondly, unidirectional transport processes to concentrate and continuously supply mud sediments to the system.

The enormous and growing scale of human intervention in coastal processes is driven by a short-sighted societal desire to protect property in the face of shoreline recession. Underpinning this effort in both the design of engineering interventions and the amelioration of their impacts is the application of numerical models that purport to simulate and predict coastal processes. Coasts are complex systems in which (1) waves, currents, tides, and wind operate on a (2) finite or changing volume of sediment of specific character (3) within a particular geological context. Feedbacks exist within and between these three domains, and all are temporally and spatially variable. The simplifications and assumptions involved in reducing this complexity to equations and numerical models cause a deviation from reality such that models are unable to provide realistic predictions of coastal behavior. Nonetheless (and despite criticism from geologists), models have become entrenched in coastal engineering practice and are now a standard weapon in society's assault on the world's coasts. In this paper, we chart the development of several widely used models, highlight their shortcomings, and speculate on why they remain in use. The disconnect between reality and the mathematics of coastal process models is extreme, and a fundamental reassessment is required.