Controls on the stratigraphic framework and paleoenvironmental change within a Holocene estuarine system: Pamlico Sound, North Carolina, USA

Abstract

This study examines the Holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system, at high temporal and spatial resolution, in the context of changing climate, sea level, and hydrodynamics. New data are used to examine two time periods of increased marine influence within Pamlico Sound in northeastern North Carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late Holocene. The study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate, and sea-level change as it interacts with paleotopography. These findings can be used to inform projections of future environmental changes. Estuarine waters occupied paleovalleys in the Pamlico Sound region as early as ca. 7500 cal BP and Pleistocene interfluves separated the paleovalleys from the Atlantic Ocean until ca. 5500 cal BP, when they were flooded by rising sea-level forming the broad, shallow Pamlico Sound. Initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal BP, providing the geomorphic setting for continued estuarine conditions behind the barriers. At ca. 4000 cal BP, an increase in marine influence and sand content is detected in multiple cores, and is correlated to seismic data within the northern Pamlico Sound basin. This change is interpreted to be the result of increased segmentation of barrier islands (thus a greater number of inlets, or wider inlets), which is consistent with a rapid transgression seen in other areas of the U.S. east coast. The segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves. Greater barrier island continuity is evident from 3500 to 1200 cal BP, as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages. At ca. 1200 cal BP, seismic, sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern 3 Pamlico Sound. These changes are interpreted to represent extensive segmentation of the barrier islands during the Medieval Climate Anomaly (MCA). Since ca. cal BP, the Pamlico Sound system has returned to a more restricted state, as inlets have closed. Currently only three major inlets segment the Outer Banks, the barrier island system fronting Pamlico Sound, but warming climate and increasing rates of sea-level rise suggest another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future.

Modeling hydrodynamics of large lagoons: Insights from the Albemarle-Pamlico Estuarine System

“…In Pamlico Sound, the largest bathymetric feature is a long and shallow sand ridge called Bluff Shoal. This stable shoal is the modern bathymetric expression of an inter-stream divide between the paleo Neuse River Valley and the paleo Pamlico Creek Valley which incised during the late Pleistocene (Mallinson et al, 2010;Zaremba et al, 2016). It is 30 km long and 2-3 m deep, oriented north-south across the estuary, and divides Pamlico Sound into two distinct basins (Wells and Kim, 1989) shown in Figure 1.…”

Late Quaternary evolution and stratigraphic framework influence on coastal systems along the north-central Gulf of Mexico, USA

“…Furthermore, these studies do not incorporate how these systems influenced Holocene barrier island morphodynamics and generally lack upland fluvial source mapping. The most complete stratigraphic records of coastal evolution are preserved within fluvial incised valleys in highly dynamic settings (Anderson et al 2014, Mallinson et al 2010, Zaremba et al 2016).…”

“…These geomorphic threshold responses result from forcing mechanisms such as changes in sea level increasing accommodation space by flooding antecedent topography (Rodriguez et al 2004, 2008, Anderson et al 2014 and changes in sediment supply (Raff et al 2018, Rodriguez et al 2018, Odezulu et al 2018. Many studies show the most complete records of coastal evolution are preserved within paleofluvial incised valleys and partially in antecedent shelf deposits (Anderson et al 2014, Mallinson et al 2010, Zaremba et al 2016, Nordfjord et al 2005. Comparing the chronologic evolution of these preserved environments to well-constrained Holocene sea level curves sheds valuable insight toward geomorphic threshold parameters (Milliken et al 2008.…”

“…Comparing the chronologic evolution of these preserved environments to well-constrained Holocene sea level curves sheds valuable insight toward geomorphic threshold parameters (Milliken et al 2008. However, research concerning how the regional stratigraphic framework influences modern coastal geomorphology and sediment supply variability is limited to a few study areas (Riggs et al 1995, Zaremba et al 2016, Mallinson et al 2010, Anderson et al 2016, Belknap and Kraft 1985 and is yet to be constrained for the Mississippi-Alabama (MSAL) barrier island chain.…”

Sedimentary architecture and depositional controls of a Holocene wave‐dominated barrier‐island system

“…Inherited topography, storms and sediment supply As mentioned above, the formation of the barrier-island system began when the rising sea reached the topographic palaeo-high in the Pleistocene landscape. It is well-documented that large-scale palaeo-topographic features, such as headlands and incised valleys, influence coastal evolution, because they exert strong control on sediment erosion, transport, deposition and accommodation space (Belknap & Kraft, 1985;Riggs et al, 1995;Rossi et al, 2011;Cooper et al, 2012;Zaremba et al, 2016). The present study shows that even minor bathymetric highs with elevations exceeding the surrounding areas by only a few (<2) metres can alter wave and tidal dynamics in such ways that these highs become the locus of sediment accumulation and anchor points of barrier islands.…”