'Cape capture': Geologic data and modeling results suggest the Holocene loss of a Carolina Cape

Abstract

For more than a century, the origin and evolution of the set of cuspate forelands known as the Carolina Capes-Hatteras, Lookout, Fear, and Romain-off the eastern coast of the United States have been discussed and debated. The consensus conceptual model is not only that these capes existed through much or all of the Holocene transgression, but also that their number has not changed. Here we describe bathymetric, lithologic, seismic, and chronologic data that suggest another cape may have existed between Capes Hatteras and Lookout during the early to middle Holocene. This cape likely formed at the distal end of the Neuse-Tar-Pamlico fl uvial system during the early Holocene transgression, when this portion of the shelf was fl ooded ca. 9 cal (calibrated) kyr B.P., and was probably abandoned by ca. 4 cal kyr B.P., when the shoreline attained its present general confi guration. Previously proposed mechanisms for cape formation suggest that the large-scale, rhythmic pattern of the Carolina Capes arose from a hydrodynamic template or the preexisting geologic framework. Numerical modeling, however, suggests that the number and spacing of capes can be dynamic, and that a coast can self-organize in response to a high-angle-wave instability in shoreline shape. In shoreline evolution model simulations, smaller cuspate forelands are subsumed by larger neighbors over millennial time scales through a process of 'cape capture.' The suggested former cape in Raleigh Bay represents the fi rst interpreted geological evidence of dynamic abandonment suggested by the self-organization hypothesis. Cape capture may be a widespread process in coastal environments with large-scale rhythmic shoreline features; its preservation in the sedimentary record will vary according to geologic setting, physical processes, and sea-level history. ABSTRACTWater depth (m) 180 25 60 1

Instability and finite-amplitude self-organization of large-scale coastline shapes

“…Finally, comparisons between model results and the shapes of sandy coastlines (and the sandy shores of lakes and bays) in nature (e.g. figure 7), and the relationship between those shapes and the wave climates [10,13,32], are consistent with the notion that the simple interactions in the model provide the basic explanation for a variety of coastline morphologies and behaviours.…”

Rollover, drowning, and discontinuous retreat: Distinct modes of barrier response to sea‐level rise arising from a simple morphodynamic model

“…Regardless of the formation mechanism, substantial evidence demonstrates that many barrier systems have migrated landward over the last few thousand years through overwash processes, maintaining themselves even as the sea level slowly rose [ Leatherman , ; McBride et al, ]. For instance, along the Atlantic coast of the United States, barrier complexes likely formed as global sea‐level rise slowed to less than 10 mm/yr at the end of the early Holocene, approximately 7000 years ago [ Engelhart et al , ; Thieler and Ashton , ], and have been transgressing landward since. Offshore of modern barrier complexes of New Jersey and New York, geologic evidence suggests that in the early Holocene, barriers existed many kilometers seaward of their current position [ Stuiver and Daddario , ; Stahl et al , ; Rampino and Sanders , ].…”

Submerged shoreline preservation and ravinement during rapid postglacial sea-level rise and subsequent “slowstand”

“…There is, however, a limited range of contemporary and historical sea-level and geomorphic contexts of modern shorelines against which to test these models. Most studies to date are on low-gradient, coastal plain settings, particularly of the eastern United States (e.g., Engelhart et al, 2009;Thieler and Ashton, 2011), which are not representative of all contemporary shorelines. Stratigraphic evidence from submerged shorelines on the continental shelf holds the potential to elucidate the response of the entire littoral zone (shoreface through barrier to back-barrier) as it migrates up profile under a range of sea-level and geomorphic scenarios.…”