THE TEMPLE STREAM FORMATION, WEST-CENTRAL MAINE: DEVONIAN OR SILURIAN?

The Temple Stream Formation comprises a 250-m thick sequence of dark pelitic strata, locally strongly graphitic and sulfide-rich, within the Rumford domain between Farmington and Phillips, west-central Maine. Moench and Pankiwskyj (1988) included this unit within the Devonian Seboomook Group. Alternatively, Solar & Brown (2001) correlate the Temple Stream Formation with the Late Silurian Smalls Falls Formation, implying a significantly different stratigraphy and regional structure. A study of black shales in the Maritime Appalachians found greater geochemical variability across the transect than within stratigraphic sections (Fyffe and Pickerell, 1993). In an attempt to better constrain the age of the Temple Stream Formation, samples have been collected to compare their major and trace element concentrations with fossil-dated samples (e.g., Middle Ordovician Partridge Formation, Late Silurian Smalls Falls Formation, and Early Ordovician Penobscot Formation). Preliminary XRF spectrometry data suggest an inverse correlation between Zr/(Al+Ti), an indicator of grain size, and sulfide content. This is consistent with surface area control on organic carbon preservation and subsequent sulfate reduction. A speculative explanation for the minor calcareous horizons within and above the Temple Stream Formation invokes carbonate precipitation caused by the alkalinity produced during sulfate reduction. An attempt is also underway to construct a Re/Os isochron from Temple Stream samples.