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
settings are characterized by uniform sedimentation suites with thick, well-sorted
sandstone successions, a lack of clear vertical trends, and a lack of mudstone (e.g.,
Soegaard and Eriksson, 1985; Eriksson et al., 1998). It is thought that these tidal and
nearshore environments during the Precambrian were generally high energy and were
wider and shallower than their Phanerozoic counterparts (see Eriksson et al., 1998,
2005; Eriksson and Simpson, 2004).
The Brattefjell Formation is subdivided into three members based on its distinct li-
thofacies assemblages (Fig. 4). As a whole, the Brattefjell Formation consist diagnos-
tic criteria of an ancient tidal influence in a marine nearshore setting. These criteria are
the following: (i) bi-polar sedimentary structures (herringbone); (ii) double mud
drapes; (iii) sandstone foresets bounded by mudstone couplets or mudstone drapes and
re-activation surfaces reflecting flood-ebb cycles; and (iv) alternations of successive
thick and thin bundles reflecting a diurnal variation. Although tidal bundles in the an-
cient rock record can be disturbed by later erosion, the bundle measurements suggest
that at least 16–18 bundles were formed during the neap-spring cycle, which is sugges-
tive of mixed semidiurnal tides. Paper III concludes that in the early stage of the lower
Brattefjell member sedimentation, the regional subsidence caused marine conditions to
cover wider areas, which gave rise to an early stage of transgression and a minor
landward migration of the shoreline, forming shallowing upward stacking pattern
cycles. The paper suggests that these cycles represent autogenic water level changes in
a sedimentation basin caused by regional subsidence water level changes. The lithofa-
cies assemblages are suggestive of subtidal settings, where tidal currents and wave ac-
tions form complex combinations. The sedimentation at the early stage of the middle
Brattefjell member was characterized mainly by tidal sand flats, tidal channels, sand-
bars, and lagoon-estuarine developments likely protected by sandy barrier ridges. An
ebb-dominant bedload transport was widespread over suspensions and sandbars, and
reactivation surfaces were common. A rise of the relative base level during sedimenta-
tion of the middle Brattefjell member deposited interlayered mudstone and sandstone
beds, suggesting alternating deposition from suspension and traction currents. Suspen-
sion settling occurred during tidal slacks, while traction characterized ebb and flood
currents.
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