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C. J. O’Hara

Publications and source records attributed to C. J. O’Hara.

7 recordsLinked to original sources
USGS1984

Glaciotectonic origin of the Massachusetts coastal end moraines and a fluctuating late Wisconsinan ice margin

Late Wisconsinan end moraines on Cape Cod and islands south and west of Cape Cod are believed to be glaciotectonic features formed by advancing ice fronts. Evidence of a glaciotectonic origin includes the stratified drift composition of the moraines, dislocated preglacial and glaciolacustrine deposits, tilted preglacial and glacial beds, folding and thrust faulting, and morphologic similarity to ancient and modern glaciotectonic moraines. Evidence for major ice readvances during over-all general recession includes the moraines themselves, till atop stratified drift, and the numerous basal tills that are inferred to exist beneath Cape Cod Bay. The Thompson Glacier end moraine in the Canadian Arctic Archipelago is considered to be a modern example of how late Wisconsinan end moraines on Cape Cod and the islands were formed. The Thompson Glacier is overriding its outwash plain, displacing outwash deposits forward and upward beyond the ice front. New sheets are added to the base of the moraine, and till is deposited atop the moraine as the ice overrides it. Evidence from Cape Cod and the nearby islands indicates that over-all recession of late Wisconsinan ice was characterized by alternating episodes of ice-front retreat, during which the outwash plains were formed, and of ice-front advance, during which the moraines were built. Retreat of the ice from Cape Cod and the islands may have been similar to the retreat of the Lake Michigan lobe, deposits of which contain evidence of at least 12 moraine-building episodes caused by readvancing ice during the over-all retreat of the late Wisconsinan ice sheet.

Geological Society of America Bulletin↗
USGS1983

Quaternary geology of the Rhode Island inner shelf

Five sedimentary units and three erosional unconformities identified in high-resolution seismic-reflection profiles reveal the stratigraphic framework and Quaternary history of the inner continental shelf south of Narragansett Bay, Rhode Island. Late Tertiary to early Pleistocene rivers eroded the pre-Mesozoic bedrock and the Upper Cretaceous to lower Tertiary coastal plain and continental shelf strata to form a lowland and cuesta having a north-facing escarpment. The lowland and landward flanks of the cuesta were modified by glaciers during Pleistocene time and subsequently were overlain by drift and end moraine deposits of the late Wisconsinan ice advance. During deglaciation, freshwater lakes formed between the retreating ice and end moraines. Prior to sea-level rise, the drift and older deposits were cut by streams flowing south and southwestward toward Block Island Sound. As sea level rose, postglacial valleys were partly filled by fluvial, freshwater-peat, estuarine and salt-marsh deposits. Transgressing seas eroded the sea floor, exposing bedrock and coastal plain outcrops, and deposited marine sediments. ?? 1983.

Rhode Island↗