F-3B: Bioturbated siltstone composed of Cruziana ichnofacies. | ・ F-3B is composed of siltstone dominated by Cruziana ichnofacies. ・ F-3B is moderately well sorted. | ・ No sedimentary structures. | ・ The trace fossils recorded in F-3B are rare Zoophycos? Planolites, Phycosiphon, Chondrites, Thalassinoides, Cruziana, Skolithos, Teichichnus, and Palaeophycos. In cores, these traces are not well preserved. ・ F-3B fugichnia- escape structures are present. | ・ Trace fossils such as Planolites, Thalassinoides, Cruziana, and Palaeophycus are ichnocoenosis of the Cruziana ichnofacies. ・ The Cruziana ichnofacies is commonly characterized by a high diversity of trace fossils associated with a variety of ichnofauna. ・ The present of these trace fossils in F-3B are indicative of distal offshore setting. ・ Conclusion: Distal offshore depositional environment. |
F-4: Dolomitic very fine-grained sandstone | ・ F-4 consist of dolomitic, thin beds (≤1 meter) of very fine-grained sandstone. ・ Thin-section petrography confirms that F-4 is quartz rich, moderately well sorted and dolomitic. ・ F-4 succession shows a coarsening upward trend. | ・ The basal contact of F-4 with lithofacies F-5 is sharp and grades into coarse siltstone grade. ・ No sedimentary structures. | ・ Trace fossils and bioturbation are not present in lithofacies F-4. ・ There are no body fossils preserved in F-4. | ・ The coarsening-upward trend in lithofacies F-4 is interpreted as basinward shoreline shift, which often characterizes a progradational trend. ・ The coarsening upward succession of F-4 is likely to have accumulated in deepening water, particularly in areas that are not adjacent to the shoreline and are characteristic of facies that prograded basinward during a falling stage of regression. ・ Conclusion: Proximal offshore depositional environment. |
F-5: Massive siltstone. | ・ Dark grey to black colored, organic rich, pyritized, massive siltstone. ・ Petrographic examination of F-5 confirms that the grains are sub-angular to sub-rounded. ・ The texture of pyrite in F-5 under reflected light microscopy appears as irregularly rounded “clots” that partly coalesce with one another and partly separated by non-reflective dolomite. | ・ No sedimentary structures. ・ The upper contact of F-5 with the overlying Doig Formation is reminiscent of erosional lag deposit characterized by a Glossifungites-Trypanites surface. | ・ Trace fossils and bioturbation are not present in lithofacies F-5. ・ There are no body fossils pre-served in F-5. | ・ The dark grey to black colored, organic carbon content of F-5 is a result of high nutrient rich sediment source and rapid sedimentation, which enhanced the preservation of organic matter. ・ The composition of detrital dolomite in F-5 is interpreted as post-depositional in origin, rather than in-situ. ・ Pyrite in F-5 is related to post-depositional emplacement caused by the dissolution of organic matter due to diagenesis. ・ The deposition of massive siltstone of F-5 may be related to transport and deposition from suspension, principally enhanced by the influence of waves mobilization of sediment by hyperpycnal, or/and clay flocculation mechanisms. ・ Conclusion: Distal offshore (outer shelf) depositional environment to ramp setting. |