Juha Köykkä - Oulu

Res Terrae, Ser. A 32, J. Köykkä, 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 prin-
ciples of actualism, the natural law of the limited number of depositional environ-
ments, Walther’s Law of vertical successions, and the assumption of the uniformita-
rianism of recent analogues in the past. However, when studying Precambrian sedi-
mentary 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 succes-
sions without major breaks in sedimentation, which can be complicated to prove in
Precambrian strata. Second, Phanerozoic facies models represent a snapshot of the lat-
eral 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 analo-
gues 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 analy-
sis is a fundamental tool in Precambrian basin analysis because it helps clarify the se-
dimentation processes at local, regional, and possibly global scales. The lithofacies as-
semblages and paleohydrological parameters presented in the six papers suggest that
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