The Early Carboniferous (Brigantian) Middle Limestone Group of Northumberland represents a prolonged period of rhythmic Yoredale-type deltaic sedimentation. Optical and geochemical analyses were undertaken on the minor Berwick Limestone Cyclothem, a prograding coarsening- and shallowing-upward cycle (parasequence) within the major Oxford Limestone Cyclothem. These indicate an overwhelming dominance of Type III–IV land-plant derived kerogen (woody phytoclasts). The hydrogen index shows a strong negative correlation with the palynologically determined b1ack: brown phytoclast ratio. The total organic carbon content of the fine-grained lithologies increases upwards through the cycle and is positively correlated with silt content, presumably due to the hydrodynamic equivalence and common fluvial source of phytoclasts and silt particles. The 1ath:equant ratio of the black phytoclasts increases upwards through the cycle (i.e. in a proximal direction); this pattern is ‘atypical’ and results from the lath-shaped phytoclasts being larger than the equant ones. The section is marginally mature (about 0.64% vitrinite reflectance); reflectance is correlated with hydrogen index. The distribution of pyrite and siderite is apparently related to sediment accumulation rate, with siderite most common in the interval of probable highest sedimentation in the lower half of the cyclothem above the limestone. The marine flooding surface at the base of the cycle is overlain by black shale, not limestone; the traditional (limestone) base of the cyclothem does not correspond to the true base.
Analysis of the Palaeocene Souris Lignite (northern Williston Basin) using coal petrology and palynology reveals the existence of seven different mire types forming six cycles of varying thickness and composition. The order of mire types within the individual cycles allows an idealized mire type succession to be defined. The principle factor driving the idealized mire type succession is decreasing water depth within the peat-forming environment (terrestrialization), which leads to an increase in species diversity and a change in floral character from ferns→ angiosperms→ gymnosperms. Increases in water depth are the primary agent responsible for the termination of individual cycles in the ancestral Souris mire. Changes in nutrient status of the mire may also promote major changes in the floral assemblage, contributing to cycle termination. Comparison of densinite:ulminite ratios for the central part of the Souris seam shows an overall decrease in the degree of humification south-westward, indicating increased subsidence towards the Williston Basin centre, where seam partings are more common. Fern-rich mire types dominate throughout most of the sampled part of the Souris seam and such mires have been interpreted as representing transitional stages in both modern and Tertiary peat-forming environments. Previous analysis of other parts of the Souris seam has revealed areas dominated by Taxodium forest mires, representing more stable environments. The co-existence of transitional and stable environments suggests that the ancestral Souris mire may have been deposited during the onset of the closing stages of Palaeocene peat formation in the northern part of the Williston Basin.
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