Late Cretaceous (Turonian-Coniacian) sequence stratigraphy, sea level, and deltaic facies, Magothy Formation, U. S. Middle Atlantic Coastal Plain

The peak hothouse interval of the Turonian-Coniacian (93-87 Ma) is represented on the U.S. middle Atlantic Coastal Plain by sequences of the Raritan/Bass River, Magothy, and Cheesequake Formations deposited on a passive continentalmargin as mixed wave-, tide-, and river dominated deltas. We apply sequence stratigraphy integrated with biostratigraphy to identify and map two major sequence boundaries separating the Raritan/Bass River, Magothy, and Cheesequake Formations and four to five (Mg1, Mg2, Mg3, ?Mg4, Mg5) Magothy sequences using continuous cores, outcrops, and geophysical logs in New Jersey. We extend correlations into New York and Delaware using well logs. The Magothy sequences disconformably overlie the well-dated (>93 Ma) lower Turonian to Cenomanian marine Raritan/Bass River sequences and are disconformably overlain by the marine Cheesequake Formation, which straddles the Coniacian/Santonian boundary. A mid-Turonian hiatus (ca. 93-90 Ma) associated with this major disconformity is a global sequence boundary (K-Tu4) reflecting a similar to 25 m sea-level lowering based on published NJ and Russian Platform backstripping records that indicate this was a major lowering ofGlobalMean Sea Level (GMSL). Higher-order (similar to 1 Myr scale) sequence boundaries bracketing Mg1-Mg5 apparently correlate with global sequences but are only associated with low-amplitude (<25 m) sea-level falls. Mapping of sequences within the Magothy Formation shows the influence of 2 to 3 moderate-sized river sources, with thickening northeastward toward Long Island, New York, and thinning southwestward toward Delaware. Thick northern depocenters contrast with the preceding Potomac Formation (Barremian-early Cenomanian) with thick southern depocenters. This seesawing of basins on the 100-300 km and 2-10+ Myr scales is due to tectonism likely from changes inmantle dynamic topography. The remarkably widespread distribution of Magothy sequences and facies indicates stability of this deltaic depositional system over similar to 4Myr despite low-amplitude (less than 25m) sea-level variations. Widespread facies correlation provides a predictable distribution of aquifer sands and confining-unit clays tied to sea-level changes on complex deltaic facies.

Automated summary

This study utilizes sequence stratigraphy and biostratigraphy to analyze geological samples from New Jersey, identifying and mapping major sequence boundaries of the late Cretaceous period and demonstrating the impact of sea-level lowering. The research reveals that the Magothy Formation is influenced by multiple small to moderate river sources, thickening towards the northeast along Long Island. Overall, the deltaic depositional system remained relatively stable despite low-amplitude sea-level variations.