PALYNOLOGICAL CONSTRAINTS ON THE STRATIGRAPHY OF THE MAGOTHY FORMATION (CRETACEOUS), NEW JERSEY AND DELAWARE, AND IMPLICATIONS FOR INTERSTATE AQUIFER CORRELATION

The Upper Cretaceous Magothy Formation consists of heterogeneous sands, silts, and clays deposited in marginal- to shallow-marine environments in the coastal plains of New Jersey (NJ) and Delaware (DE). Magothy sands are important aquifers in both states. This study integrated core analyses and palynology to understand the stratigraphic architecture and regional correlation of the Magothy Formation. A ~100 m-thick, continuous-cored Magothy section at Sandy Hook, NJ records predominantly deltaic deposition. Five members were differentiated by lithology and palynologic content. Upward, these are the Sayreville Sand (Complexiopollis exigua-Santalacites minor Zone, Coniacian), the South Amboy Fire Clay (C. exigua-S. minor Zone), the Amboy Stoneware Clay (Pseudoplicapollis longiannulata-Plicapollis incisa zone, Coniacian), the Morgan Beds (?Pseudoplicapollis cuneata-Semioculopollis verrucosa Zone, Santonian) and the Cliffwood Beds (upper ?P. cuneata-S. verrucosa Zone, Santonian). The underlying Raritan Formation contains an older assemblage (lower Zone IV, upper Cenomanian), suggesting an unconformity. The overlying Cheesequake Formation yielded similar assemblages as the Cliffwood Beds (upper ?P. cuneata-S. verrucosa Zone or Zone CA-2A, lower Santonian). At Dover, DE, the Magothy is 32 m-thick and contains dinoflagellates. The lower two-thirds of the formation is blocky sand; the upper one-third is interbedded lignitic sand and silt. Preliminary palynlogy of split-spoon cores places the Dover section in the ?P. cuneata-S. verrucosa Zone (lower Santonian), correlating it with the upper Magothy Formation in NJ. The Summit Marina corehole 50 km north contains less than 1.5 m of the Magothy Formation; preliminary pollen data indicate the C. exigua-S. minor Zone (Coniacian), correlative with the lower-middle part of the Magothy in NJ. A similar assemblage occurs at an outcrop 5 km west. The Magothy Formation progressively thins southward from Sandy Hook, reflecting increasing distance from a northern deltaic source and truncation under an unconformity. Deposition at Summit Marina represents incised valley fill near the updip limit of the formation and deposition at Dover represents estuarine and nearshore environments further seaward.