30 th Conference on the Geology of Long Island and Metropolitan New York, April 2023 1 FIRST VERTEBRATE FOSSILS REPORTED FROM CRETACEOUS STRATA ON LONG ISLAND WITH NEW SEDIMENTOLOGICAL DATA & OBSERVATIONS Hart, William Jude & Bennington, J Bret Department of Geology, Environment, and Sustainability, Hofstra University, NY, USA. Summary The geology of Long Island consists primarily of Pleistocene glacial deposits underlain by much older Cretaceous coastal plain layers below sea level. Allochthonous blocks of Cretaceous sediments attributed to the Raritan Formation were incorporated into the Harbor Hill moraine and are exposed in the shoreline cliffs along the necks of northwestern Long Island. The stratigraphy and paleontology of these exposures have been documented in the literature going back over 180 years, including descriptions of pollen (e.g. Sirkin, 1974) and plant fossils (e.g. Hollick, 1894, 1906). However, there are no confidently documented reports of vertebrate fossils in the Cretaceous of Long Island going back to Mather (1843). Herein, we report the first vertebrate remains (a bone fragment and a fish vertebra) to have been recovered from Cretaceous strata on Long Island and include some observations on the sedimentology of the Cretaceous deposits. Stratigraphy Cretaceous deposits identified as the Magothy and Raritan Formations are present in the subsurface beneath glacial deposits under most of Long Island and are part of the Northern Atlantic Coastal Plain Aquifer System (Figure 1) which is also a part of the “Island Series” of both subsurface and exposed formations of Mesozoic & Cenozoic strata that extend as far north as Martha’s Vineyard (White, 1892) while terminating somewhere to the south of the Atlantic Coastal Plain Geomorphic Province (Richards, 1967). Strata correlative to the Magothy and Raritan under Long Island outcrop in central New Jersey. Outcrops on Long Island are limited to cliff exposures along the coast of Long Island Sound (Figure 2) which appear to be allochthonous blocks of sediment excavated and redeposited by glacial advance within the Harbor Hill moraine (Fleming, 1935). This occurred during the most recent Late Pleistocene glacial advance when the sediments were frozen in permafrost. Glaciotectonic deformation of the strata can be observed in folded layering and the strata are discontinuous along the shoreline, overlain and laterally truncated by deposits of Pleistocene outwash and till. Paleontology and Sedimentology Cretaceous plant fossils have been documented for over 150 years from the Cretaceous deposits on Long Island (e.g. Mather, 1843; Hollick, 1906). Plant fossils are common in slabs of hematitic sandstone and siltstone found on north shore beaches and pollen and lignite are found in Cretaceous clays (e.g. Fuller, 1914; Sirkin, 1974). Most of the plant fossils have been found as “float” in small slabs of hematitic siltstone and sandstone (Figure 3) and cannot be confidently attributed to either the Raritan or Magothy formations, although Berry (1915) states that the flora found on the north shore of Long Island is “unquestionably” of Magothy age. The slabs containing the plant fossils were likely reworked during glacial advances from Magothy strata and incorporated into the till and outwash exposed in the beach cliffs, where coastal erosion leaves them as a lag on the upper shoreline. Plant fossils include fragments of lignitic wood (sometimes replaced by hematite and limonite mineral), comminuted plant debris, and impressions of leaves from genera such as Salix (willow), Sassafras, and Viburnum (Hollick, 1894). Pollen from clays outcropping at Garvies Point and Eatons Neck correlate these deposits to the Raritan Formation in