Middle Devonian (Givetian, Hamilton Group) Ostracoda in two diamond drill cores from Lambton County, southwestern Ontario

Abstract

Analysis of some five hundred ostracode-bearing samples in two diamond drill cores (GSC DD1 Arkona and GSC DD2 Ipperwash) from Bosanquet Township, Lambton County permits more exact understanding of the stratigraphic distribution of Ostracoda in the Middle Devonian (Givetian) Hamilton Group of southwestern Ontario. This allows more precise age determination and stratigraphic correlation of late Middle Devonian Ostracoda in southern Ontario with Middle Devonian ostracode faunas of the Michigan Basin and borderlands in central North America. The ostracode fauna of the Hamilton Group in these drill cores, contained within the Bell, Rockport Quarry, Arkona, Hungry Hollow, and Widder formations and, in GSC DD2, part of the overlying Ipperwash Formation, comprises some 50 genera represented by almost twice that number of species. These are, with few exceptions, synonymous with ostracode faunas previously reported from elsewhere in the Michigan Basin. The palaeocopid ostracode fauna is dominated by species of the suborders Beyrichicopina and Kloedenellocopina and the podocopid ostracode fauna is represented by species of the suborders Podocopina and Metacopina. There are no leperditicopids. This Hamilton Group ostracode assemblage is of latest Middle Devonian age and may be equated, in part, with similar faunas of the Silica Formation of southeastern Michigan northwestern Ohio, the Traverse Group of the northern part of the lower peninsula of Michigan, and Middle Devonian faunas of western New York State. The Hamilton Group ostracodes from southwestern Ontario appear to have evolved during a period of relatively stable environmental conditions and represent lineages of continuous faunal development.