Organic petrology and depositional environments of the Souris Lignite, Ravenscrag Formation (Palaeocene), southern Saskatchewan, Canada

Posted on:2001-05-17

Degree:Ph.D

Type:Dissertation

University:The University of Regina (Canada)

Candidate:Frank, Michael Clay

Full Text:PDF

GTID:1460390014952864

Subject:Paleoecology

Abstract/Summary:

Various coal petrographic models exist, which suggest to be able to reconstruct the nature of the ancient peat-forming environment. In order to test the validity of these models, the Palaeocene Souris Lignite of south-eastern Saskatchewan was chosen for a study in which the depositional environments and vegetation as derived from these various models, was compared with the palaeoenvironment and vegetation as determined by petrography, palynology and selected chemical trends.; Analysis of the Souris lignite reveals an idealised mire succession of:; top C - Gymnosperm (Taxodium) forest mire ↑ H - Mixed angiosperm/gymnosperm forest mire ↑ G - Angiosperm forest mire ↑ E - Dry Fern mire ↑ D - Wet Fern mire ↑ A - Fern/Burr-reed fen base L - Algae dominated mire ; The principle factor driving the idealised succession is decreasing water depth within the peat-forming environment (terrestrialisation), which causes a change in the characteristic mire vegetation from: Algae→Ferns→Angiosperms→Gymnosperms. The application of previously published petrographic models to the Souris seam reveals that none of the models examined in this study adequately describes the Souris seam.; The main reasons for the failure of the models are ascribed to: (1) Over-simplification of the effects of humification on tissue preservation. (2) The lack of distinction made by some models between the different inertinite macerals and their modes of formation. (3) The inability to recognise rheotrophic mires with low mineral matter contents. (4) The use of post diagenetic processes (e.g. geochemical gelification) in determining depositional environments. (5) Changes in petrographic composition related to floral evolution, geological age, rank increase, and compaction.; While the relationship between petrographic composition and palynology on an individual sample basis is poor, the use of mean petrographic compositions for each mire type (L, A, D, E, G, H, C) does reveal trends in some models which are related to the idealised mire succession. This phenomenon reflects the reduction in the resolution level of the petrographic composition caused by the calculation of mean compositional values.; The sample preparation and preservation techniques developed in this study have proven satisfactory in limiting sample desiccation while still allowing standard polishing and reflected light microscopy techniques, as employed in coal petrographic analyses, to be performed.

Keywords/Search Tags:

Cellrule rty, Tablecell chj, Petrographic, Souris lignite, Depositional environments, Models, Mire

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