Glacio-Eustatic Sedimentary Cycles in Trenton Limestone (Middle Ordovician) of Southern Ontario: ABSTRACT

Abstract

The fully-developed ideal cycle consists of the following, from base to top, always with calcareous clay seams throughout. (a) Coarse, poorly sorted intrabiosparite or biosparite grainstones, in crosscutting (often cross-stratified) lenses, or channelized. In places, grain flow is shown by lobate, steep-sided edges, often smoothed by well-sorted biosparite grainstones. (b) Fine to medium-grained well-sorted biosparite grainstones, parallel or cross-laminated, usually in several thin beds. (c) Very fine-grained, well-sorted, commonly graded biosparite and biomicrosparite packstones and grainstones, with coarser shell fragments concentrated at their bases. (d) Nodular bioturbated biomicrite mudstones and wackestones, alternating with bioturbated calcareous clays. This unit may also contain lenses of poorly sorted biosparite. Units (a) to (c) show abundant evidence of rapid deposition of individual beds, followed by extensive periods of non-deposition, erosion, or both, when the bed surfaces were burrowed by omission-type trace fossil-forming organisms, cemented, and colonized by attached organisms. The abundant and diverse hardgrounds of the Ordovician sequence are concentrated at these horizons. In the more argillaceous sections, subdued cyclicity occurs. The difficulty of explaining these cycles by normal facies changes has led to a glacio-eustatic explanation. Actualistic comparison can be made with the recent Arabian shelf of the Persian Gulf. End_of_Article - Last_Page 1165------------