COMPOSITIONAL VARIATION IN EARLY PALEOZOIC SANDSTONES FROM NORTHERN MAINE

Detrital compositions of sandstones ranging from Cambrian(?) to Devonian age in northern Maine reflect changing sources and tectonic settings through time. Along the northwestern geographic boundary of Maine, mature quartz arenites from the Cambrian(?) Group de Rosaire indicates that these were most probably derived from an interior cratonic source. An unnamed tectonic mélange to the southeast of, and adjacent to the Rosaire contains sandstone blocks of two distinctly different compositions. One group of blocks from the tectonic mélange reflects a source from a stable cratonic interior, while another group of blocks from this mélange are richer in both feldspar and lithic grains suggesting a different source for this sand. The Saint Daniel Formation/mélange has been recognized to be a complex unit that changes character along strike. In northern Maine, and adjacent areas, blocks from an olistostromal portion of the Saint Daniel are quartz – rich. These blocks are interpreted not to have an arc as a source for the sand.

Middle to early Late Ordovician rocks from northernmost Maine suggest the source of sand was from an eroding arc, but younger well dated shallow water environments of late Late Ordovician age reflect a range of sources from a stable craton through “uplifted basement” to an eroding arc. These composition changes not only demonstrate the changing sources and tectonic environments but stress the importance of understanding late Ordovician environments in this region.

To the southeast, in the Munsungun inlier, Late Ordovician sandstones and conglomerates demonstrate that this region was characterized by an active volcanic arc. Sandstones from the early Late Ordovician Munsungun Lake Formation are quartz poor with variable proportions of feldspar and lithic grains. Conglomerates from the Late Ordovician Rowe Lake Formation have clasts which are overwhelmingly fine grained felsic volcanics.

The Silurian is not well preserved in northern Maine, but prominent sandstone bodies of Early Devonian age have been characterized as a westerly prograding deltaic complex. Composition of sandstones from these rocks do not reflect an active or dissected arc source. Rather these sands reflect a nonvolcanic source despite their close association with rhyolite which stratigraphically overlies or is interbedded with them in several areas.