Ecostratigraphic Expression of Holocene Parasequence Boundaries in Incised Valleys Along Delaware Bay: Response to Rapid Sea-Level and Climate Change

Ronald E. Martin¹, Eduardo Leorri², and Peter P. McLaughlin^3
1Geological Sciences, University of Delaware, Newark, DE
²Facultad de Ciencia y Tecnología, Universidad del País Vasco/ EHU, Bilbao, Spain
³Delaware Geological Survey, University of Delaware, Newark, DE

Ecostratigraphic datums provide high-resolution stratigraphic frameworks when standard biostratigraphic datums are absent. Benthic foraminiferal assemblage zones of the incised valley of St. Jones Estuary (western Delaware Bay, USA) delimit rapid sea-level fluctuations during the Holocene. These sea-level fluctuations appear to reflect parasequence boundaries which appear correlative with previously-documented rapid climate changes of large regional (North Atlantic basin) and worldwide significance: 6000-5000, 4200-3800, 3500-2500, 1200-1000, and 600 cal years BP. Following postglacial sea-level rise, modern subestuaries and marshes in the region began to develop between 6000 and 4000 years BP, depending on their proximity to the mouth of Delaware Bay and coastal geomorphology. Initial sediments were fluvial in origin, with freshwater marshes established around 4000 years BP. The subsequent sea-level transgression occurred sufficiently slowly that freshwater marshes alternated with salt marshes at the same sites to around 3000 years BP. Locally another two transgressions are identified at 1800 and 1000 years BP respectively. Marine influence increased in the estuaries until 600 years BP (Little Ice Age), when regression occurred. Sea-level began to rise again during the mid-19th Century at the end of the Little Ice Age, when marshes became established.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas