Abstract
This work analyzes the distribution of coal-bearing strata in the stratigraphic framework of the Mannville Group (Lower Cretaceous, Western Canada Sedimentary Basin). In the 3rd-order depositional sequence the maximum abundance of coal layers is found in the highstand system tracts (HST), whereas in the 4th-order eustatic sequences, coal deposits distribute similarly in the highstand and transgressive system tracts (TST). These trends have been related to the variation of accommodation space in the basin, which mostly influence the occurrence of favorable conditions for organic matter preservation.Petrographic analyses permit to identify variation in the coal layers composition and to relate them with the stratigraphic dynamic of the basin. The HST is characterized by a low subsidence rate, which induces low levels of the groundwater table, favoring dry conditions in the peat. By consequence, in the HST a higher abundance of inertinite maceral group is observed than in the TST. On the other hand, the TST is characterized by higher subsidence rates, thus more stable groundwater table levels, promoting the organic matter preservation. Therefore, in the TST a higher content of vitrinite and liptinite maceral groups is observed. In correspondence of the maximum flooding surface (MFS), the peat is frequently flooded, with the consequent dilution of the organic matter with terrigeneous sediment, forming carbonaceous shales deposits.By the analysis of the organic matter composition, seven depositional environments for coal were identified, located at different distance from the coast line. Each depositional environment is characterized by a specific organo-facies association, which is the reflex of different environmental conditions in the peat, in terms of water table level, type of vegetation and hydrodynamic processes. The vertical superimposition in a coal package of different depositional environments has been related to high order climatic cyclicity (5th-order transgressive and regressive cycles), which controls the groundwater table fluctuations.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.