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Several methods for the palaeobotanical analysis of inorganic rocks are developed and through the employment of these methods both microfossils and macrofossils have been recovered from certain Upper Ordovician Strata. These fragments are assigned to series, basing such designation upon their sources and individual morphological characteristics. The problematical identity and biological importance of these fragments is discussed, and their practical usage in problems of correlation is considered. / Thesis / Master of Science (MSc)

Late Ordovician Red River strata of southeastern Saskatchewan were deposited in a broad epicontinental sea. In the lower part, the Yeoman and Herald formations comprise two cycles of carbonateevaporite sequences. Although these units possess an overall layer-cake aspect, thickness variations especially in the Herald Formation show that accumulation was affected by syndepositional flexure, differential subsidence and displacement of fault-bounded blocks. The mainly laminated dolomudstones and anhydrites of the Lake Alma and Coronach members of the Herald Formation were deposited under relatively tranquil conditions. These units host different kinds of synsedimentary deformation features, interpreted to have been induced by earthquakes generated because of movements along basement faults thought to have been oriented orthogonally NE−SW and NW−SE. The low-energy environmental setting was conducive to preserving these features, referred to as seismites.<p> The variety of seismites in the Herald Formation is related to the varying rheology of the carbonate or evaporite sediment, as well as shaking intensity. Brittle and quasi-brittle failure is represented by faults, microfaults, shear-vein arrays and pseudo-intraclastic breccias, mostly in dolomudstones which must have been stiff at the time of deformation. Plastic behaviour is recorded by soft-sediment deformation, comprising a family of features that includes loop bedding, folded laminae and convolute bedding. Indeed, these structures in enterolithic anhydrite are more reasonably interpreted as due to deformation than crystal growth, volume expansion and displacement, the more usual explanations. Sediment shrinkage and concomitant fluidization are recorded by dikelets containing injected carbonate mud or granular gypsum, the latter now preserved as anhydrite. Evidence for wholesale liquefaction, however, was not observed. These rheological differences were caused by the primary nature of the sediment plus modifications due to early diagenesis and burial confinement. Shaking intensity is difficult to gauge, but it is presumed that a minimum of VI on the modified Mercalli scale was required to produce these features. Consequently, shaking of lesser magnitude was probably not recorded.<p> The geographic distribution of seismites should reflect the location of basement faults presumed to have been active during deposition, and indeed there is a concentration adjacent to the known location of syndepositonal fault lineaments. In addition, the stratigraphic distribution of seismites records higher frequencies of activity of these same faults. These distributions show that earthquake-induced ground motion was common during deposition of the Lake Alma Member in southeastern Saskatchewan but less so during deposition of the Coronach Member.<p> Seismites serve as proxies for the activity of relatively nearby syndepositional faults making up the tectonic fabric of sedimentary basins. They also point to basement features that, if re-activated, can induce fracture porosity or influence subsurface fluid flow. Syndepositional tectonism undoubtedly had a much more profound influence on many successions than is presently accepted, and its effects are more widespread than currently appreciated.

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The upper Tanglewood Member is the final member of the Lexington Limestone and is well-known for its soft-sediment deformation. This study has confirmed the carbonate-shoal-complex origin of the unit, and detailed study shows that its development took place during five small-scale, sequence-like, fining-upward cycles related to eustasy and tectonics. Four lithofacies are represented in the unit. Facies analysis of each cycle shows that the thickest and coarsest part of each cycle corresponds to previously uplifted basement-fault blocks; the occurrence of thick, coarse facies on the same fault blocks suggests that the blocks continued to experience uplift due to Taconian far-field forces generated on the eastern margin of Laurentia. The upper Tanglewood Member includes six deformed horizons that can be traced into equivalent parts of the Clays Ferry and Point Pleasant formations. Concurrence of four lines of evidence, suggested by Ettensohn et al. (2002d) for interpretation of seismites, indicates that the widespread horizons of deformation are seismogenic in origin. Reactivation of basement structures due to Taconian far-field forces probably induced seismicity on the intra-platform carbonate complex so as to produce soft-sediment deformation. Petrographic investigation indicates that most of the cements in the upper Tanglewood limestones appear to be late diagenetic, fresh-water phreatic cements. Comparing the petrography of deformed and undeformed portions of the same horizon showed no significant differences in terms of cementation, indicating that cementation occurred primarily after deformation. The primary impact of deformation on the microstructure of the unit was the randomization of grain fabric and the increased presence of broken intraclasts.