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Expansion of drainage networks through the headward erosion of tidal creeks is an eco‐geomorphologic response of salt marshes to accelerated sea‐level rise (SLR). This response can counter the negative impacts of an elevation deficit by increasing drainage and encouraging plant health, thereby reducing potential for submergence and marsh platform loss. In the wetlands of Cape Romain, SC, intense bioturbation near creek heads by the common marsh crab Sesarma reticulatum has been found to facilitate sediment erosion and rapid creek growth. This keystone grazer has been recently observed to have increasing influence on landscape evolution throughout the southeast US coast. Here, we compare measurements taken at Sapelo Island, GA, with those previously collected at Cape Romain, to confirm that eco‐geomorphic feedbacks facilitating creek growth at each location are similar, and to compare these processes under differing background conditions. We use sediment cores, precise elevation measurements and historical imagery to compare substrate properties, elevation within the tidal frame, creek growth rates and drainage morphology at both sites. Our results show identical processes; however, the higher elevation of the marsh at Sapelo Island leads to shallower and shorter periods of tidal inundation, explaining the greater soil strength and lower belowground biomass compared with the marsh at Cape Romain. The smaller tidal range at the site in Cape Romain compared with Sapelo Island translates to a proportionally shallower depth of tidal creeks, which therefore requires less erosion to produce headward creek extension. These effects are likely to have contributed to slower growth rates of tidal creeks at Sapelo Island during the past several decades of SLR. Our findings highlight the similarities in process but differences in rates in how marshes are responding to climate‐related stress. [ABSTRACT FROM AUTHOR]

Tidal point bars are commonly developed in coastal plain meandering channels. They form by the same basic processes as fluvial point bars but are further modified by tidal action. This study analyses the sedimentary facies of six active tidal point bars and their relationships. The bars are situated along the Georgia coastal plain, USA, in the lower and upper reaches of the fluvial marine transition and in tidal channels without upstream river input. Based on millimetric logging of 31 cores, nine sedimentary facies were identified, which are proposed to be used for the characterization of tidal point bars in other depositional settings. These bars share common sedimentary facies; however, the internal organization of these facies and their associations differ appreciably in response to complex local tidal processes and fluvial–tidal interactions. The increase in tidal influence results in prominent heterogeneous architectures, with greater concentration of heterolithic stratification (mostly inclined), bioturbation and evidence of flow reversals. In contrast, when freshwater river discharge overcomes tidal stages in the fluvial marine transition bars, structureless coarse‐grained facies with attendant erosional surfaces and decreased bioturbation are predominantly developed. In the lower reach of the fluvial marine transition, along the estuarine turbidity maximum, alternations of fluvial and tidal sedimentation are evidenced by a bimodal facies association, where alternations of gravel lag and muddy facies (massive to heterolithic) dominate. Moreover, despite differences in local hydrodynamics, coarsening‐upward sequences, mostly composed of structureless coarser facies, are consistently distributed along the upper parts of the bars, which may indicate overprinting of regional events such as storm surge‐related floodings in the sedimentological record. This study provides a basis for better identifying the hydrodynamic processes that shape coastal systems, such as estuarine and backbarrier environments. Additionally, those deposits are analogues for certain hydrocarbon reservoirs, thereby increasing knowledge of their facies distribution and aiding production optimization. [ABSTRACT FROM AUTHOR]

Beach‐ridge systems are geomorphological features common in every type of coast and have been widely interpreted as geo‐archives of past sea‐level, climatic, or tectonic changes. These relict morphological elements are well‐known by their facies, architecture, stratigraphy, and evolution. However, the coastal context where beach ridges are formed has never been evaluated. Coastal beach‐ridge systems were classified into four main types corresponding to deltaic strandplains, non‐deltaic strandplains, spits, and barrier islands. Our study consisted of three scales of analysis: (1) the entire beach‐ridge system; (2) beach‐ridge sets; and (3) individual beach ridges. Several beach‐ridge systems having formed in different types of coastal settings are compared by their present characteristics. Geomorphic data generated from processing and interpreting satellite images combined with previous studies are used to quantify multi‐scale attributes of beach‐ridge systems. These attributes include the area, length, width, number of sets, number of ridges per set, set rotation, ridge spacing, and ridge elevation. Our findings demonstrate that significant differences define beach‐ridge systems including deltaic strandplains, large non‐deltaic strandplains, small non‐deltaic strandplains, large spits (cuspate forelands), small spits (flying spits, bay‐mouth spits and tombolos) and barrier islands. A more comprehensive characterization of the factors controlling beach‐ridge variability will improve our ability to recognize the sedimentary record of ancient of these systems. The proposed basic platform can be used to isolated different beach‐ridge types and systems to facilitate future process and morphodynamic studies. [ABSTRACT FROM AUTHOR]