Application of Microfossils to Production-Scale Problems in Ground-Water: Aquifer Biostratigraphy of the Cretaceous and Miocene of Delaware and New Jersey, Middle Atlantic Coastal Plain, U.S.A.

Peter P. McLaughlin¹, Peter J. Sugarman¹, Kenneth G. Miller³, Richard N. Benson⁴, James V. Browning³, and Gilbert J. Brenner^5
1 Delaware Geological Survey, Newark, DE
² New Jersey Geological Survey, Trenton, NJ
³ Rutgers University, Piscataway, NJ
⁴ University of Delaware, Newark, DE
⁵ State University of New York, New Paltz, New Paltz, NY

Aquifer geology investigations face many of the same challenges as production geology studies, chief among them delineating the fine-scale stratigraphy of aquifers (analogous to reservoirs) and confining beds (analogous to seals). The petroleum industry has seen biostratigraphy become an integral part of reservoir studies, especially when integrated with sequence stratigraphy; biostratigraphy holds equal promise for ground-water applications. Recent coring in Delaware and New Jersey, combined with existing logs and cuttings, allows us to reinterpret the distribution and connectivity of Cretaceous and Miocene aquifers using biostratigraphy and sequence concepts, which has significantly improved understanding of the stratigraphic constraints on ground water resources of this populous region.

Heterogeneous facies and the lack of marine marker beds complicate correlation in non-and marginal-marine Cretaceous deposits. Pollen and spores are keys to stratigraphic interpretation. In the non-marine Barremian to lower Cenomanian Potomac Formation, biostratigraphy supports log correlation of two sandy aquifer-prone intervals separated by a finer-grained confining layer. In the marginal marine upper Turonian (?) to lower Santonian Magothy Formation, biostratigraphy indicates that aquifer-quality sands are variably developed in three sequences in central New Jersey; to the south in Delaware, this formation is an incised valley fill of variable thickness. In the Miocene, aquifer sands are developed at the tops of coarsening-upward, marine, highstand systems tract packages. Multi-fossil group biostratigraphy and strontium isotopes indicate that lower Miocene aquifers are developed in five sequences, three of which are aquifers regionally. The middle to upper Miocene framework is more complex and microfossil control more limited (pollen).