Becky Rogala Honours Thesis Abstract

Thesis Title: 
A Metamorphosed Evaporite Section from the Sibley Basin, Northwestern Ontario

This study concentrates on a section through a lateral correlative of the cyclic facies contained in the Rossport Formation present in the Noranda drill core NI-92-5.  The location of this drill hole is north of other cored sections and outcrops of the cyclic facies and represents a more basin center environment.  The cyclic facies to the south consists of alternating layers of dolomite and red shale with individual layers, in the approximately 40 m thick assemblage, varying from mm- to dm-scale.  In drill hole NI-92-5 the layering is at a similar scale, but is composed of alternations between what was first thought to be dolomite-rich and gypsum-rich intervals, reflecting wet and dry seasonality in the central playa environment.

S.E.M. and X.R.D. analysis indicate that the sequence was metamorphosed.  The following minerals represent the progression of metamorphic facies, from lower to higher T towards the diabase sill:  talc, tremolite, and pargasite.  Clinochlore and calcite are found throughout the metamorphic series.  The metamorphism masks the primary layering in places.  However, S.E.M. analysis clearly shows the mineralogical layering, reflecting variations in primary geochemical constituents between individual laminae.  ICP-AES analysis also highlights the varying compositions of the sequence.  The pargasite tends to exist in layers with differing K and Na proportions.  The K+ and Na+ ions may reflect the incorporation of KCl and NaCl.  Both of the minerals are found in S.E.M. sections taken near the middle of the sequence.  Nb and Ba show unusual concentrations and fluctuations, and need to be studied further.

Clastic input is variable between individual layers, but shows an increase at the top of the section.  This increase is related to the appearance of sand sheets, which typically mark the end of the cyclic facies in the Sibley Group sediments.  Clastic material becomes slightly enriched in elements denoting a mafic rock source up-section.