DATING HITHERTO UNFOSSILIFEROUS TURBIDITES IN THE SILURIAN SANDSTONE SEA, CENTRAL AND EAST-CENTRAL MAINE: A GLIMMER OF HOPE

Large areas of central and east-central Maine are underlain by low-grade turbidites whose age, correlation, and paleogeographic relationships have been obscured for decades by the near-total absence of fossils. Recent detrital zircon U-Pb SHRIMP dating constrains the maximum ages for some units but ambiguity remains because analytical error in many instances spans the range of the short Silurian stages. Samples were collected from turbidites in the Central Maine/Aroostook-Matapedia and Fredericton trough depocenters, and from selected units thought to be pre-Silurian components of the Miramichi terrane.

200-250 grams of dark gray to black mudstone, siltstone, or slate from each site were broken into 1 cm pieces for processing that included solution in hydrofluoric acid for up to a month, heavy liquid separation, and several stages of decanting and swirling the organic residue to concentrate particulate matter. Despite their chlorite- and sub-chlorite metamorphic grade, nearly all samples contain thermally matured organic matter, typically dark gray to black inertinitic particles with no recognizable organic features. Some samples, however, contain sparse, poorly preserved trilete spores (50-100µ), chitinozoan fragments (~50µ) and sphaeromorph acritarchs (<50µ). Although the concentration of these particles is low, the samples show potential for biostratigraphic determinations at the Period to Epoch level.