Late Holocene Spit Evolution on Centennial Timescales in the Southeast Delaware Bay, USA

• Main Author: Phillip, Ryan Eli
• Format: Thesis
• Language: unknown
• Published: CCU Digital Commons 2018
• Subjects: Centennial; Coastal Geology; Holocene; Sedimentology; Spit; Storms; Geology; The Spit; North Atlantic
• Online Access: https://digitalcommons.coastal.edu/etd/108; https://digitalcommons.coastal.edu/cgi/viewcontent.cgi?article=1160&context=etd

The relationship between barrier spit growth and longshore drift is well established. However, the role of storm activity in spit evolution on an intermediate (centennial) timescale is more of a mystery due to a knowledge gap between decadal-scale shoreline processes and millennial-scale stratigraphic data. Recent studies in the northwestern Atlantic basin using ground-penetrating radar (GPR) and optically-stimulated luminescence (OSL) are providing the opportunity to study centennial-scale shoreline evolution and examine similar age storm activity. Cape Henlopen, Delaware exhibits preserved remnants of a long-term northward-growing spit coastline that evolved from a recurved spit complex, to a cuspate spit, to the present-day simple spit. This location provides ideal late-Holocene spit features on which to collect GPR and OSL data. Within Cape Henlopen State Park, approximately 10 trackline-km of GPR data were collected from the southernmost relict recurved spits to the more northern simple spit for the purpose of revealing the internal architecture and growth patterns of the spits, as well as evidence of storm influence. A total of 8 OSL samples were obtained to find coincidences among the ages of the spit deposits and periods of increased storm activity. GPR analysis exhibits 5 major sedimentary facies: shallow marine, spit platform, spit beach and dune, overwash fan foreset deposits, and modern dunes. OSL ages indicate that spit development began around 2.4 ka, followed by phases of major growth of recurved spits during CE 100 to 500 (1.9-1.5 ka) and then converting to a cuspate foreland around CE 1500 (0.5 ka). Analysis of the OSL dates reveals concurrences between the ages of the spit features and periods of increased storm frequency during CE 0 to 700 (2.0-1.3 ka) and CE 1300 to 1800(0.7-0.2 ka) in the North Atlantic basin which produces evidence that storm activity may have a significant influence on barrier spit evolution on centennial timescales. The results of this study provide both an increased understanding of how barrier spits evolve as well as centennial-scale data to be used for coastal change and hazard management modeling.