John Robert Parker HBSc thesis abstract

Thesis Title: 
The Structure and Environment of Deposition of the Finmark Metasediments, Thunder Bay, Ontario

The Finmark metasedimentary belt is situated west of Thunder Bay, Ontario.  Metasedimentary rocks predominate and form part of the Shebandowan-Wawa greenstone belt where they overlie a Keewatin succession of metabasalts.  The metasediments form interlayered sandstone-siltstone-mudstone sequences which alternate with thick deposits of cross-stratified sandstones.  The interlayered sequences contain many of the primary sedimentary structures characteristic of tidal flat deposits.

The rocks in the area have undergone very low grade greenschist metamorphism and are structurally complicated.  Reversals of top directions and the presence of both easterly and westerly plunging minor folds, suggest that one or more episodes of folding have occurred.  The attitude of cleavage within the area does not vary considerably, indicating that it may have developed after one or more episodes of folding.  Numerous left lateral displacements and the intrusion of mafic dikes have contributed to the structural deformation in the area.  One continuous section of outcrops have remained stratigraphically upright and were used to determine the depositional environment of the metasediments.

The sedimentary rocks are composed of feldspar, rock fragments, quartz, and some mafic minerals.  Modal analysis has revealed that most of the sandstones in the area are arkosic arenites.  The rock fragments are felsic to intermediate and predominantly volcanic, with lesser amounts of igneous and sedimentary rock fragments.  The volcanic clasts have been derived from the Lake Shebandowan metavolcanics which are part of a calc-alkaline suite of rocks.  Therefore, the metasediments probably represent immature detritus from proximal volcanic centers.