Interpretation and analysis of sequence stratigraphy and palynomorph assemblages of Miocene-age sediments in southern Delaware
Date
2016
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Publisher
University of Delaware
Abstract
The Marshy Hope borehole (Nb53-08) sediments encompass the Calvert, Choptank and St. Marys Formations. This interdisciplinary study combines palynomorphs, biostratigraphy and stratigraphic units to interpret depositional environments and constrain correlations between locations in northwest Sussex County.
Sequence stratigraphy is utilized to subdivide core sediments and to correlate to other boreholes in the region. Seven sequences are recognized, including a shaved sequence in the St. Marys, a type previously recognized and described by Kidwell (1988; 1989; 1997). The Calvert Formation is composed of shelfal clay and silt which becomes a coarsening-upward alternation of sand and silt. The overlying Choptank Formation is composed of mostly fine to coarse sands with interbedded silt and clay. The St. Marys Formation is composed of estuarine silts, clays and fine sands punctuated by offshore silts and clays. The Calvert-St. Marys interval is interpreted at this site as a stack of highstand-dominated stratigraphic sequences which shallow-upward overall.
Palynomorphs record the depositional history of Miocene marine sediments in the Marshy Hope area in Delaware. The changes in species and abundance result in distinct biozones which are used to interpret depositional environments and correlate sediments to other sites in southern Delaware.
The flora is dominated by Quercus, Carya, and Pinus. Taxodiaceae/Cupressaceae/Taxaceae (TCT) and “exotic” taxa such as Engelhardia and Symplocos are also present. The Calvert Formation is interpreted as a warm-temperate climate, whereas the Choptank and St. Marys formations are interpreted as a slightly cooler warm-temperate climate. Stratigraphically constrained cluster analysis reveals three different pollen zones based on sample pollen assemblages. Zone 1 is characterized by abundant Quercus, Carya, and low amounts of exotics Engelhardia and TCT. Zone 2 contains relatively low amounts of Quercus and exotic taxa and high abundances of Pinus. Zone 3 is characterized by high abundances of Quercus and exotic taxa such as TCT and Engelhardia. Dinoflagellate cyst identification result in a preliminary dinocyst zonation which includes seven dinocyst subdivisions.
Correlation of this site to Bethany Beach, Delaware is possible through sequence stratigraphic units based on lithologic analysis results and geophysical logs, stratigraphically constrained cluster analysis of pollen assemblages, and dinoflagellate cyst zonation.