Palynostratigraphy of the late Cretaceous (Coniacian) magothy formation of Delaware and Maryland
Date
2022
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Publisher
University of Delaware
Abstract
This study examines the palynostratigraphy of the Magothy Formation in the Northern Delmarva Peninsula with the objectives of correlation with the Magothy Formation of New Jersey; documentation of palynomorphs within this interval; assessment of the depositional history and environment of these sediments; and determination of whether the overlying Cheesequake Formation is present in the study area. In northern Delmarva the Magothy Formation is a Coniacian aged deposit consisting mainly of tidally influenced estuarine and fluvial sands and lignitic clays. The lateral continuity of these subsurficial Magothy sand beds remains poorly understood in their updip section around northern Delaware. An improved biostratigraphic understanding of this poorly studied interval may aid future mapping efforts. Additionally, documentation of Magothy Formation palynomorphs from the study area has been lacking. Previous work in central New Jersey has divided the Magothy Formation into three palynostratigraphic zones, but these zones have yet been systematically correlated to Delaware. This study fills that gap with a palynological analysis conducted on Magothy sediments at nine sites across northern Delaware and Maryland to gain a better understanding of the depositional history, distribution, and lateral continuity of the northern Delmarva Magothy Formation. Two continuously drilled wireline cores at Port Penn Delaware and Bohemia River State Park were drilled into the Magothy Formation for the purposes of this project, and field sampling of Magothy Formation outcrops was conducted at Grove Point Maryland and along the Chesapeake and Delaware Canal. Additionally, material from previously drilled core holes and split spoon cores at five sites were examined for palynomorphs. All sites contained Normapolles type angiosperm pollen indicative of a Magothy age (Coniacian). Assemblages from Lums Pond, Summit Marina, Middletown, Woodland Beach, Dover AFB, the Canal Outcrop, and Grove Point were consistent with the presence of the upper Magothy ?Pseudoplicapollis cuneata-Semioculopollis verrucosa (Pc-Sv) zone. The lowermost Complexiopollis exigua - Santalacites minor zone (Ce-Sm), was recognized at Bohemia River and at Dover AFB. The middle Pseudoplicapollis longiannulata- Plicapollis incisa (Pl-Pi) zone was recognized at Port Penn, lower in the Lums Pond core, and in a thin interval in the Bohemia River core. This diversity of observed assemblages across the nine sites in the study reveal a high degree of lateral variability between sites consistent with a paleochannel-fill model of deposition. A pollen assemblage suggestive of equivalence with the Cheesequake Formation was found directly above the Magothy Formation in the Bohemia River core, and assemblages from directly above the Magothy Formation at several other sites are consistent with the presence of this previously unrecognized unit in Delaware. Additionally, a large collection of palynomorph photographs was accumulated for this project to document the local palynology of the Magothy Formation; many of those are here presented in the plates to aid future workers in studying this interval.
Description
Keywords
Coniacian, Germinal, Magothy formation, Normapolles, Palynomorph, Palynostratigraphy