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 lection of commonly associated sedimentary attributes within lithological units. Thus, lithofacies associations represent the basic building blocks of facies models that sum- marize a particular depositional system within the sedimentary environment and basin. According to Walker (1992), the four fundamental purposes and functions of a facies model are that it must (i) act as a norm for comparison, (ii) act as a framework and guide for future observations, (iii) act as a predictor in new geological situations, and (iv) act as an integrated basis for the interpretation of the system it represents. The lithofacies associations can be later grouped to form even bigger lithofacies successions in which a series of lithofacies pass gradually from one to another. To extent the lithofacies analysis to the entire basin, it is necessary to follow the basin analysis workflow, starting with the lithostratigraphic mapping and correlations. The lithofacies analysis usually starts by establishing a facies scheme that encom- passes all the lithological units in the studied area. The lithofacies in these schemes include detailed measurements of different structures, lithofacies logs, outcrop sketches and photographs, additional sample collection, paleocurrents, paleohydrology and ripple-index measurements. The lithofacies classification used in this thesis was designed to be as simple as possible to cover all the necessary information from each lithological unit and to form a fundamental core that was used in every paper. 4.3 Sequence stratigraphy Sequence stratigraphy studies the change in depositional trends and cycles in response to the interplay of accommodation and sediment supply, from the scale of individual depositional systems to entire basin-fills (Catuneanu et al., 2005, 2009; Catuneanu, 2006). Sequence stratigraphy reveals the history of sedimentation in a basin in response to base level cycles, which is the highest level to which sediment successions can be built (i.e., more-or-less sea level). Therefore, sequence stratigraphy assumes a subdivision of the sedimentary pile into sequences, which are stratigraphic units re- lated to cyclic change in the sedimentation through time. A sequence stratigraphic framework includes genetic units that result from the interplay of accommodation and sedimentation, which are bounded by stratigraphic surfaces. Each genetic unit is de- fined by special strata stacking patterns and bounding surfaces, and consists of a tract of correlatable depositional systems (i.e., system tracts). The mappability of system 40
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 tracts and sequence stratigraphic surfaces depends on depositional setting and types of data available for analysis. However, the essence of sequence stratigraphy is the mapping of strata based on an identification of stratigraphic surfaces (e.g., subaerial unconformity, maximum flood- ing surface), which refer to linkages of correlative depositional systems commonly associated with significant lateral changes of facies (Fig. 6). These stratigraphic surfaces mark shifts through time in a depositional regime, and they are created by the interplay between base level changes and sedimentation. Thus, surfaces are also tied to depositional models, and they form the fundamental framework for the genetic interpretation of sedimentary succession. However, in Precambrian sequence stratigraphy, time is largely irrelevant as a parameter in the classification of stratigraphic surfaces (independent of base-level cycle duration). Instead of time, it is rather the record of changes in the tectonic setting that provides the key criteria for the basic subdivision of the stratigraphic record into basin-fill succession separated by first-order sequence boundaries (e.g., Eriksson et al., 2005). Boundaries not expected to correlate to other sequences of other basins, which are likely characterized by different timing and duration. System tract is a linkage of contemporaneous depositional systems, forming subdivision of a sequence. Due to different “schools” in sequence stratigraphy concept, the model-independent approach for the sequence models is the most flexible and suitable for the ancient rock record. Therefore, system tracts can be classified as follows: (i) regressive system tract, including (a) forced regression (regression of the shoreline driven by base-level fall; progradational and downstepping stacking patterns), and (b) normal regression (regression of the shoreline driven sediment supply, during a time of base-level rise at the shoreline or at a time of base-level stillstand; normal regression occurs when sedimentation rates outpace the rates of new accommodation added due to base-level rise at the shoreline; combination of progradational and aggradational depositional trends); (ii) lowstand system tract (accumulates at the stage of early-rise of normal regression; rate of rise outpaced by the sedimentation rate; (iii) transgressive system tract (landward shift of marine or lacustrine system, triggered by a rise in base- level at rates higher than the sedimentation rates; retrogradational stacking patterns; (iv) high-stand system tract (forms during the late stage of base level rise, when the 41
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Juha Köykkä - Oulu

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