Juha Köykkä - Oulu

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Res Terrae, Ser. A 32, J. <strong>Köykkä</strong>, Sedimentology of the Mesoproterozoic Telemark basin-fills, South Norway: implications for sedimentation processes, depositional environments and tectonic evolution breccias, massive and inversely to normally graded conglomerates, stratified sand- stones and laminated and rippled mudstones, were transported by traction currents, se- diment gravity flows and by suspension. The proximal part of the formation contains blockfield / blockslope accumulations and waning flood-flow cycles. These are over- lain by hyperconcentrated and debris flow deposits, and ephemeral high-energy bedforms. The distal part of the formation contains dune bedforms and channel lag deposits, which indicate waning discharge fluctuations. The paleohydrological calculations from the channel-fill conglomerates and sand- stone bedforms correlate with lithofacies assemblages. The estimation of paleoslope and discharge values support the presence of a fluvial stream rather than an alluvial fan environment. The stream power and water velocity systematically decreases towards the distal parts of the formation. The abundance of waning flood-flow cycles, ephemeral high-energy sedimentary deposits, and hyperconcentrated and debris flow deposits is a possible indicator of pe- riglacial melt waters in basin margin strike-slip fault evolution. This melt water com- bined with abundantly available debris from the non-vegetated high-topographic land- scape. 60
Res Terrae, Ser. A 32, J. <strong>Köykkä</strong>, Sedimentology of the Mesoproterozoic Telemark basin-fills, South Norway: implications for sedimentation processes, depositional environments and tectonic evolution 6 Discussion 6.1 Applicability of the used methods Precambrian rock strata often show a lack of lateral and vertical outcrops, which presents a major problem in lithostratigraphic correlation. The unexposed and sheared contacts between formations are often highly problematic because they may hide some of the information of the strata. To tackle these difficulties, it is important to use of geochemistry as supplementary data and to understand which parts of the sedimentary basin (e.g., proximal vs. distal and axial vs. flank) successions are preserved and ex- posed. The principles of Phanerozoic facies models are mainly based on the basic principles of actualism, the natural law of the limited number of depositional environments, Walther’s Law of vertical successions, and the assumption of the uniformita- rianism of recent analogues in the past. However, when studying Precambrian sedimentary environments, at least two different “hypotheses” of facies models must be taken into account. First, the assumption of Walther’s Law is that the vertical succes- sion of facies may reflect a lateral juxtaposition of depositional environments. Howev- er, this fundamental law only applies when there have been no significant changes in factors that control sedimentation patterns. In other words, it only applies to successions without major breaks in sedimentation, which can be complicated to prove in Precambrian strata. Second, Phanerozoic facies models represent a snapshot of the lateral relationships of sedimentary environments and facies over a limited amount of time. In addition, due to geological, atmospheric and biological differences in the Pre- cambrian, some of the sedimentary basin conditions in the past may not have analogues today, and non-uniformitarian models may have to be used. Thus, it is import to recognize, from the study area facies scheme, what is actually local and what is global. Usually, unit and bed contacts are an important part of facies studies (e.g., sharp, gra- dual) because they can record significant breaks in sedimentation. Although it is diffi- cult to apply a 3D facies architecture analysis to Precambrian strata, lithofacies analysis is a fundamental tool in Precambrian basin analysis because it helps clarify the sedimentation processes at local, regional, and possibly global scales. The lithofacies assemblages and paleohydrological parameters presented in the six papers suggest that 61
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Juha Köykkä - Oulu

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