TRACE FOSSILS FROM EARLY SILURIAN MUDSTONES OF THE SPRAGUEVILLE FORMATION, NORTHEAST MAINE, USA

The Early Silurian Spragueville Formation is well exposed in three regions of northeastern Maine: Presque Isle–Mapleton, Caribou, and Fort Fairfield. This formation comprises a sequence of thinly interbedded and interlaminated medium-gray silty pelites and light-gray silty limestones or calcareous siltstones. The Spragueville Formation has an estimated thickness of 760 to 1,130 m. Graptolites, ostracods, brachiopods, trilobites, and conodonts are some of the fossils found in this formation. Several authors have reported the presence of biogenic sedimentary structures as a distinctive characteristic of the Spragueville Formation (White, 1943; Boucot et al., 1946; Pavlides 1965, and Roy, 1970). This study will describe and interpret the biogenic structures in the context of ichnospecies and ichnofacies. A local detailed stratigraphic study of the Spragueville Formation is underway on a set of large outcrops. These exposures contain a variety of trace fossils at the meso-scale. Horizontal and vertical burrows are generally preserved as positive and negative semireliefs at the tops and bottoms of the beds. Interstrata structures, such as dwelling burrows, and “escape traces” are also present. The degree of bioturbation in the formation is variable. Ichnofabric indexes range from a few discrete isolated specimens to more complex ichnofabrics that destroy all remnants of original bedding. Preliminary analysis of well-preserved specimens allows identification of Rusophycus, Teichichnus, Planolites, and Arthrophycus ichnospecies. This assemblage would be associated with the Cruziana ichnofacies. Base on this information and the stratigraphy, we interpret Spragueville Formation as deposited in an offshore sedimentary environment.