The Biostratigraphy of the Delaware Limestone (Middle Devonian) of Southwestern Ontario

The Delaware Limestone of Middle Devonian age crops out along two belts in southwestern Ontario. All but one of the major outcrops studied occur in the easternmost of these belts. Examination of thin-sections and polished slabs of 254 samples collected at vertical intervals of one foot from 19 localities has led to delineation of four major microfacies within the formation. The basal quartzose microfacies, characteristically containing well-rounded, quartz sand, is present in the basal two to four feet of the formation. In the northwestern part of the eastern outcrop belt the predominant microfacies above the basal quartzose microfacies is partially recrystallized limestone. The primary microfacies to the southeast at St. Mary\u27s, Ontario, is the biomicrite microfacies. The biomicrite microfacies grades vertically and laterally to the southeast into the burrowed biomicrite and biomicrite microfacies. A total of 128 species have been obtained from the Delaware Limestone in Ontario. Of these, one species of charophyte, 10 species of arenaceous foraminifera, and 19 species of fish are reported for the first time from the formation in Ontario. The characteristic brachiopods, Martiniopsis ? maia (Billings), Brevispirifer lucasensis (Stauffer) and Spinatrypa spinosa (Hall) are discussed in detail. The interiors of M. ? maia and B. lucasensis are described for the first time. With the exception of Tasmanites sp., Astraeospongium spp., Spinatrypa spinosa, Brevispirifer lucasensis, Polygnathus linguiformis linguiformis, Cheiracanthoides comptus, and Onychodus sigmoides, the taxa of the Delaware Limestone are restricted to one or two of the major microfacies. None of the taxa collected occurs at all of the localities sampled. Three biostratigraphic zones are recognized in the Delaware Limestone of southwestern Ontario. From the base of the formation upward they are the Icriodus latericrescens n. subsp. A Zone, the lower spore zone , and the upper spore zone . The two spore zones are informal zones based on the occurrence of two different sizes of spores belonging to the genus Tasmanites. The Icriodus latericrescens n. subsp. A Zone occurs along the eastern outcrop belt from St. Mary\u27s, Ontario, southeastward to Lake Erie. The lower spore zone can be recognized along the entire eastern outcrop belt. The upper spore zone is found only at St. Mary\u27s, Ontario. Only seven of the 128 species (Icriodus latericrescens n. subsp. A, I. angustus, Hexagonaria truncata, Martiniopsis ? maia, Brevispirifer lucasensis, Spinatrypa spinosa, and Spinulicosta spinulicosta) collected from the Delaware Limestone are of use in correlation of the formation with other units in adjacent portions of the United States. On the basis of the occurrence of one or more of the species mentioned above and the reported presence of the Tioga Bentonite, a key marker bed, in the subsurface of southwestern Ontario, the Delaware Limestone outcrops in Ontario are correlated with the lower portions of the Dundee Limestone of Michigan and Ohio, and the Delaware Limestone of central Ohio. The exposed part of the formation is also correlated with the upper Jeffersonville and lower North Vernon Limestones of Indiana, the upper Grand Tower Limestone and lower Lingle Limestone of Illinois, the Seneca Member of the Onondaga Formation and the lower part of the Cherry Valley Member of the Marcellus Formation in New York. Exact correlation of the upper unexposed portions of the Delaware Limestone in Ontario can not be made at this time because the fossils from these rocks have not been studied adequately. The base of the formation transgresses zonal boundaries along the eastern outcrop belt in a northwesterly direction indicating tentatively that the Delaware Limestone may be a time transgressive formation. Adviser: J. A. Fagerstro