Halten Terrace Lower and Middle Jurassic inter-rift megasequence analysis: megasequence structure, sedimentary architecture and controlling parameters - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 238

Pre-rift drainage
rift-marginal

Rift-marginal
Antecedent
axial

Rift-marginal
Antecedent
transverse

Transfer
zone

Rift-marginal
Antecedent
transverse

N

150km

Tilje progradational segment Tofte-Ile progradational segment Garn progradational segment

Fig. 13. Conceptualised Gross Depositional Environments (GDEs) for the regressive segments of the Halten Terrace Lower
and Middle Jurassic megasequences. Note (1) the inherent contrasts in GDEs for the Tilje, Tofte, ile and Garn megase-
quences, despite overall gross similar sequence development and (2) similarities between the gross overall infill style,
despite variations in lithologies (e.g. Tilje and Garn megasequences) and basin physiographies and depositional systems
(see discussion in text). Blue colouring represents shelfal environments and central parts of embayments, light yellow
represents inner shelf/offshore transition zone and embayment margins, yellow represents shorelines and estuaries, orange
represents deltaic distributaries, estuarine and fluvial channels, green represents delta-plain and floodplain environments,
whereas lighter brown represents alluvial fans, braidplains and fan-deltas.

source areas. in other cases there was a change into
a predominantly longitudinal drainage, sediment
dispersal and outbuilding character, e.g. as inferred
for the Tilje megasequence (Fig. 13). in parallel
there was, commonly, a change in basin physiog-
raphy from more open-coast to semi-protected
embayments or straits, often with an increased
current or mixed tide-wave influence on deposi-
tional facies. These stratigraphic changes in infill
patterns probably represent an increasing rate of
structuring of the receiving basin or depositional
area (Fig. 12B; see also Ravnås & Steel, 1998;
Ravnås et al ., 2000). As a corollary, the postulated
relative sea falls responsible for the marked basin-
ward shift in facies belts were probably tectonic in
origin and related to tectonic uplift of the basin
margin and hinterlands (cf. Steel, 1993) as well as
initial, renewed structuring of the basin itself (cf.
Ravnås et al ., 2000).
There are also notable differences between the
various regressive segments, both in terms of over-
all sedimentary architecture, outbuilding styles

and directions, as well as in their contained archi-
tectural elements (Figs 2 and 13). These differences
are predominantly related to differences in basin
topography and physiography during deposition.
The much thicker normal regressive part in the
Tilje and Tofte-ile megasequences suggests out-
building into a deeper basin with higher subsidence
rates. Predominance of longitudinal or axial infill
appears to reflect changes from early stage, open
and sediment-under-filled to late stage, increas-
ingly confined and sediment-balanced conditions,
often reflecting transitions from normal to forced
regressive situations. The basin energy regime also
seems to follow similar trends; wave influence was
predominant during the normal regressive state,
whereas tide influence gradually increased and
was locally the main reworking process during the
late stage normal regressive and the forced regres-
sive to lowstand states. in addition, reworking by
continuous and strong shelfal currents appear to
have been common during peak regressive state
(e.g. during the Tofte-ile and locally also the Garn