Terrance R. Foster HBSc thesis abstract

Thesis Title: 
An Archean Pyroclastic and Epiclastic Sequence, Wawa-Abitibi Greenstone Belt
Terrance R.

Detailed study of the sequence has indicated that it is characterized by intimately interbanded pyroclastic and epiclastic facies rock units.  The predominantly felsic (rhyolitic) to intermediate compositions of most of the rock units within the sequence indicate that, assuming a single source of rock material, that rock material was derived from an active volcano.  Primary depositional structures indicate that the sequence was deposited in a subaqueous environment of the flank of that volcano.

The presence of planar laminated and bedded ash flow tuffs, a planar laminated base surge deposit and an adjacently overlying coarse, felsic volcanic breccia indicate that the sequence was deposited as a result of intermittent periods of volcanism which probably varied from effusive to explosive in nature.  The presence of interbedded turbidite sediments and a graded, probably channelized conglomerate unit supports the intermittent nature of the volcanic activity.  Considered collectively, these facies indicate that the depositional environment of the sequence was analogous to a submarine fan environment.

The pyroclastic facies within the sequence have been compared to other similar deposits.  The planar laminated base surge deposit and overlying volcanic breccia have been interpreted to have been deposited simultaneously as two distinct facies of a single pyroclastic flow.  This interpretation is supported by the physical characteristics of the two units and grain size and composition analyses which were done on representative samples from these and all other pyroclastic units within the sequence.