INTERPRETED SEDIMENTARY STRUCTURES IN THE LITTLETON FORMATION, BOLTON CONNECTICUT

The Siluro-Devonian transgressive sequence in the Bronson Hill Terrane is interpreted from the metamorphic rocks at Bolton Notch State Park in Bolton, Connecticut. The rocks were described and mapped at a reconnaissance level as part of an initiative of the Connecticut Geological Survey to make the geology of the state parts accessible to the public. The rocks are exposed in a series of cliffs on the right-side-up limb of the overturned Great Hill Syncline. Although the rocks have experienced extensive deformation, the section at Bolton Notch does not appear to be sheared. Foliation and bedding appear coincident.

The Silurian Clough Quartzite, 10-12 m thick, is coarser grained and thicker bedded at its base and grades upward to mica schist. Mica schist and the overlying calcareous Fitch Formation are together 20-25 m thick. The Fitch Formation is overlain with a sharp contact by the Devonian Littleton Formation, ~120 m thick, which contains garnets and staurolites in the lower part and lenses of grey graphic quartzite in the upper part. The quartzite lenses have previously been interpreted as sheared-off noses of isoclinal folds within the Littleton. The lenses however contain graded beds that are all right-side-up. They have erosional bases that appear channel like, on the bottom side of the lenses and are convex downward within the lenses. We interpret these data to suggest that the lenses are submarine channel deposits rather than sheared fold noses. Shearing does not appear intense at Bolton Notch.

Protoliths were quartz sandstone, mud rocks and calcareous mud rocks. Initial sedimentation of what would become the Clough Quartzite took place in near shore marine conditions. Decreasing grain-size and increasing mud content (now schist) suggest deepening conditions. The calcareous content suggest possible fossils in the protolith and deposition in offshore environments. Finally the lens-like sand bodies in the Littleton suggest deeper water submarine channels. Graphite in these sand bodies may have once been hydrocarbons.