Climatic and tectonic controls on Triassic dryland terminal fluvial system architecture, central North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 29

(A)

Ephemeral
fluvial systems

Overbank sabkha and
aeolian deposits

(B)

Te rminal splay

Minimal biogenic activity

Playa

Halite crust

Fig. 7. Conceptual depositional model for Early Triassic deposition in the central North Sea. The overall setting was arid
and likely devoid of biogenic activity as a result of both a lack of soil moisture and an impoverished terrestrial population
in the wake of the end Permian extinction event. (A) Proximal regions were dominated by channel-confined facies and
associated overbank playa. (B) Distal regions were dominated by wet and dry playa deposits, with isolated aeolian sand
patches and terminal splay sandstones.

sediments (based on palynology). The presence of
rounded and frosted grains has been taken as indic-
ative of reworking of Permian aeolian sandstones
(Mange-Rajetzky, 1995), but these could equally be a
product of fluvial reworking of Triassic aeolianites.

crust fabrics are preserved within some shale
members and aeolian facies are present locally,
together with episodic halite deposition in the
broadly equivalent sections in the Southern
Permian Basin (Aigner & Bachmann, 1992; Geluk,
2005) and as far north as east Greenland until the
Carnian (Surlyk, 1990). Four main facies associa-
tions can be recognised within this upper section.
Interbedded playa and marsh deposits form inter-
vals c. 1 m to 30 m thick, composed of metre-scale
alternations between black mudrocks; rooted, bur-
rowed and stratified heterolithic beds; localised
micrite horizons showing laminar carbonate
cementation and haloturbated, muddy sandstone
intervals (Fig. 9A). This facies association interfin-
gers with marginal Muschelkalk lagoonal facies in
the Anisian part of the section (Fig. 9B). The black
mudrocks are laminated and generally lacking
biogenic traces or sandstone partings. The hetero-
lithic sections show the widespread development

Middle to Late Triassic facies associations

Within a poorly dated interval within the Anisian
Judy Sandstone Member there is a marked change
in depositional character from the dryland deposits
as described above towards widespread evidence
of biogenic activity (Fig. 8) and loss of aeolian
facies. Calcrete also becomes widespread at this
stratigraphic level and is present within palaeosols
as rhizoliths, pedogenic nodules and as ground-
water calcrete. These calcretes were commonly
reworked as allochthonous clasts into fluvial
deposits. Despite this intra-Anisian change in
character towards less evidence of aridity, salt