29-8 The Provenance and Ages of Glacial Sediments from Long Island, NY

Session: Rates, Dates, and Plates: Petrochronological Approaches to Unraveling Tectonometamorphic Histories (Posters)

Presenting Author:

Authors:

Abstract:

The Laurentide Ice Sheet (LIS) terminated on Long Island during the last glacial maximum, constructing the Ronkonkoma and Harbor Hill moraines. Despite a century of mapping, debate persists over ice-flow directions and the bedrock sources that fed these deposits. We present a provenance study integrating detrital zircon U–Pb geochronology with heavy-mineral assemblages from four sites spanning ~130 km E–W across Long Island: Huntington and Caumsett State Park in the west, and Greenport (North Fork) and Hither Hills (Montauk) in the east. We dated 939 sand-sized zircons by LA-ICP-MS and characterized heavy-mineral separates by SEM-EDS/EMPA to link age populations and mineralogy to potential source terranes.

Western localities (Huntington; Caumsett) are dominated by Mesoproterozoic age peaks near ~1.0–1.05 Ga, consistent with Grenvillian sources and recycled zircons from Laurentian-margin metasedimentary rocks of the Manhattan Prong. A small peak ~440 Ma matches peak metamorphism during the Taconic orogeny. Eastern sites yield prominent Late Paleozoic–Early Mesozoic peaks: ~275 Ma (regional Permian plutonism/pegmatites) and ~365–409 Ma (Acadian–Neoacadian magmatism and metamorphism). Jurassic ages near ~190 Ma at Caumsett, Greenport, and Hither Hills are difficult to reconcile with local basement but plausibly derive from the White Mountain igneous province to the N–NE. Heavy-mineral suites are dominated by metamorphic minerals: kyanite, staurolite, rutile, pyroxene and amphibole. Magnetite and tourmaline also occur. The geographic partitioning of zircon age modes and heavy-mineral supports dominant ice flow from the N to NE into both moraines.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.