Date of Award
Master of Science in Geology
Application of standard geologic photointerpretive techniques to a series of offshore photographs of the Block Island cliffs has shown significant correspondence with previous stratigraphic field studies. Constant scale while mapping and a vertical exaggeration for the final profile were achieved with the aid of a Zoom Transfer Scope.
Photogeologic unit boundaries were defined by: the nature of bedding visible in the photographs, the extent of different erosional and drainage patterns on the cliff face, changes in texture of the cliff face, tonal variations, and variations in clast size.
Five photogeologic units have been defined on the northern cliffs of the island by using the above criteria. Their boundaries correspond closely with those of units defined in the field by previous workers and observed in field work for this study. These include a basal out-cropping Cretaceous unit, the Raritan Formation; and Pleistocene units equivalent to two members of the Montauk Drift of Sirkin (1976) and the New Shoreham Outwash and New Shoreham Till of Sirkin (1976).
Nine photogeologic units, representing six depositional stages, were identified on the southern cliffs of the island. These six stages are equivalent to the three members of the Montauk Drift of Sirkin (1976), his New Shoreham Outwash and Till, and channel gravel deposits laid down during the final stages of glacial retreat (Sirkin, 1976). Where Sirkin provided unit thickness or outcrop locations, there is also agreement with photointerpretive results.
Comparison of the photointerpretation with other, still earlier stratigraphic studies was limited by the fact that the mapping (Hoodworth and Wigglesworth, 1934) was in less detail than the present photogeologic study or was of a reconnaissance nature (Hansen and Schiner, 1964) in which stratigraphic control based on well logs was more similar to the present photogeologic study than their reconnaissance mapping of the cliffs.
Barrett, Jonathan Rodman, "PHOTOGRAPHIC INTERPRETATION OF THE STRATIGRAPHY OF BLOCK ISLAND, RHODE ISLAND" (1977). Open Access Master's Theses. Paper 2018.