Stony Creek Granite Gneiss on Beach
Photo by Sandy Richard
Click photo for larger size.
Continental glaciers have created nearly all of the glacial features on the surface of Long Island. However, geologists have not reached a consensus concerning many of the finer details of Long Island's geological development. They do, however, agree that the glaciers moved in a general southerly direction in the Long Island region, bringing a mixture of rocks, sand, and other sediment to Long Island from source areas to the north, including Long Island Sound and Connecticut. Various geologists have, in fact, correlated some of the boulders on Long Island with bedrock units that are located, at least in part, in Connecticut.
The stretch of beach at Wildwood State Park, on Long Island's North Shore, contains numerous boulders of a wide range of sizes that are composed of material that matches the type of bedrock in south-central Connecticut. Two of the types that are easily recognized in this material are the Stony Creek Granite Gneiss and the New Haven Arkose. Both of these units contain an abundance of pink feldspar, however the arkose is a sedimentary rock, while the granite gneiss is metamorphic, meaning it was altered by intense heat and pressure. The abundance of feldspar in the arkose is evidence of burial through rapid sedimentation where it was formed, since felspar particles alter to clay if they are exposed to moist weather for long periods. Bedrock composed of Stony Creek Granite Gneiss is located in a region known as the Avalonian terrane, which ranges north to Canada, south to Georgia, and to parts of Europe, and represents a former microcontinent. During a continental collision known as the Acadian Orogeny around 400 million years ago, this landmass joined what eventually became the supercontinent Pangaea, later on in geologic time when the forerunner of the Atlantic closed. New Haven Arkose occurs as bedrock in the Hartford Basin, which forms a valley that is oriented north-south through central Connecticut and southern Massachusetts, and is a rift that dates back to when Pangaea broke apart 200 million years ago. As this occurred, and the Atlantic Ocean formed and widened, as it continues to do today, parts of the Avalonian terrane remained as part of North America, while other portions remained with Europe.
Arkose
Photo by Sandy Richard
Click photo for larger size.
Both the Stony Creek Granite Gneiss and New Haven Arkose source areas are situated almost due north of Wildwood State Park. Jessica L. McEachern and Daniel Davis, in
Boulder Distribution at Wildwood State Park: Implications for Glacial Processes, state that:
Many erratics have been found at Wildwood State Park, situated on the north shore of Long Island. The park rests atop 50-foot bluffs overlooking the beach. Boulders have been found in this area, as well as on the beach. The dominant lithology of these boulders is granite and granite gneiss, which is similar to rocks found in southeastern Connecticut known as the Avalonian Terrane. These rocks are part of a unit of rock dipping southward underneath Long Island Sound and Long Island itself. It is thought that these boulders are the same type of rock belonging to this unit.
Stony Creek Granite Gneiss
Photo by Sandy Richard
Click photo for larger size.
J Brett Bennington and Tim Young reported on a survey of boulders that they conducted at eight locations on the North Shore of Long Island in their article,
Determining the Direction of Ice Advance... Basin Erratics. They note that:
The maximum percentage of HB (Hartford Basin) erratics found was 4.3% at Wildwood State Park.
Stony Creek Granite Gneiss on Beach
Photo by Sandy Richard
Click photo for larger size.
The attached KMZ file contains map overlays showing the extent of Stony Creek Granite Gneiss and New Haven Arkose in Connecticut, the Quaternary Geologic Map of Connecticut and Long Island Sound Basin showing the direction of ice movement, and placemarks for the locations of Stony Creek Quarry and Wildwood State Park.
Additional InformationField Trip "Hartford Basin, Connecticut"Google Earth Community: Connecticut Geologic Map OverlayGoogle Earth Community: Wildwood State ParkGoogle Earth Community: Glacial Erratic - Stony Creek Granite GneissStony Creek QuarryBedrock Geological Map of ConnecticutLinks to complete
Quaternary Geologic Map of Connecticut and Long Island Sound and detailed informationAdditional photos taken at Wildwood State Park
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