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N. M. Ratcliffe

Publications and source records attributed to N. M. Ratcliffe.

At least 19 recordsLinked to original sources
USGS1999

Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

Middle Ordovician (late Arenigian - early Caradocian) conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the Pinney Hollow Formation in the Eastern Cover sequence near West Bridgewater, Vermont. These are the first reported fossils from the metamorphic cover sequence rocks east of the Green Mountain, Berkshire, and Housatonic massifs of western New England. The conodonts are recrystallized, coated with graphitic matter, thermally altered to a color alteration index (CAI) of at least 5, and tectonically deformed. The faunule is nearly monospecific, consisting of abundant Periodon aculeatus Hadding? and rare Protopanderodus . The preponderance of Periodon and the absence of warm, shallow-water species characteristic of the North American Midcontinent Conodont Province suggest a slope or basin depositional setting. The conodont-bearing carbonaceous schist is traceable 3 km southeast to the Plymouth area, where it had been designated the uppermost member of the Plymouth Formation, previously regarded as Early Cambrian in age. The age and structural position of the carbonaceous schist above dolostones of the Plymouth Formation but below the Pinney Hollow Formation (upper Proterozoic and Lower Cambrian?) suggest that this unit may be correlative or time transgressive with the Ira Formation, which underlies the Taconic allochthons in the Vermont Valley. Such a correlation supports the concept of placing the western limit of the root zone of the Taconic allochthons beneath the Pinney Hollow Formation. An approximate absolute age assignment for the conodont-bearing rock is between 470 and 454 Ma. This suggests that dynamothermal metamorphism during the Taconian orogeny on the east flank of the Green Mountains was younger than early Caradocian, which is in accord with the middle Caradocian age of the Ira Formation west of the Green Mountain massif.

Vermont↗
USGS1996

Preliminary bedrock geologic map of the Vermont part of the 7.5 x 15 minute Mount Ascutney and Springfield quadrangles, Windsor County, Vermont

Bedrock in the Vermont part of the Mount Ascutney and Springfield quadrangles consists largely of, from west to east, Middle Proterozoic gneisses in the core of the Chester Dome, pre-Silurian metasedimentary, metavolcanic, and meta-igneous rocks as a cover sequence immediately above the dome, Silurian and Devonian metasedimentary and metavolcanic rocks of the Connecticut Valley sequence, and Ordovician to Silurian and Devonian metasedimentary rocks informally referred to as the New Hampshire sequence. In addition, the rocks are intruded by granitic dikes of the Devonian New Hampshire Plutonic Suite and, at Mount Ascutney, the Cretaceous White Mountain Plutonic - Volcanic Suite. The primary purpose of this report is to present preliminary results on the stratigraphic and structural relationships in the Connecticut Valley and New Hampshire sequence rocks.

Vermont↗