1966. Ph.D.,  420 pp. McMaster University, Hamilton, ON.

THE SEDIMENTOLOGY OF THE MEDINA FORMATION OUTCROPPING ALONG THE NIAGARA ESCARPMENT (ONTARIO AND NEW YORK STATE

Martini, I. P.

Detailed studies of sedimentological sequences, primary sedimentary structure, and textural relationship have provided new information concerning the paleoenvironmental setting of the Lower Silurian Medina Formation outcropping along the Niagara Escarpment in Ontario and New York State.

The analysis of cross bedding and other primary directional sedimentary structures, the determination of quartz grain orientation on more than 150 samples of the Thorold and Grimsby Sandstones yielded a general paleocurrent trend to the North and North-West. The source area of the Medina sand is believed to be the Bald-Eagle, Juniata formations of the Appalachians.

A second line of movement of the paleoflow, in direction South-West and North-East has been detected in part of the New York outcrops, and in the Ontario region. This paleocurrent trend seems to have been related to marine agents reworking a hypothesized submerged deltaic complex. The regional variation of several sedimentological parameters, such as grain size, packing, boron concentrations, faunal assemblages and so on, confirm a mixed environment with a deltaic complex model of sedimentation for the Medina Formation.

Accordingl1y, the primary constructive phase of the Medina delta is believed to be limited to the Lockport-Rochester region and only partially reflected in the sections to the west and east. A shift of the deltaic channel complex resulted in a second area of clastic input in the Niagara- De Cew Falls region where the marine agents were competent enough to redistribute the delta-born sediments to a minor or major degree.

A shallow Silurian sea and a very slow basinal subsidence yielded a complex interfingering of top-set environments varying from a submerged channel sedimentation to tidal flat, as demonstrated by the presence of Lingula shells to high tidal-flat flood-plain settings characterized by a well developed "Burrow zone". The foreset part of the delta may be represented by the sublittoral Cabot Head and Lower Grimsby in the Hamilton area.

The model herein presented does not significantly differ from the one constructed by Fisher (1954) except in stressing a more detaile4 analysis and the introduction of a submerged delta concept.

A detailed study of quartz grain orientation confirms the validity of the appositional fabric as a paleocurrent indicator. The study has also revealed, however, that potential errors (e.g. misinterpretation of the primary surface of deposition) or a generalized analysis

(i.e. assumption of homogeneous population) could lead to geological1y erroneous or irrelevant inferences.

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