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 25

(A) (B) (C) (D) (E)

Playa

Floodplain
Lacustrine

Channel belt

Floodplain

Terminal splay

3m

Playa

30 m

clay vfs ms clay vfs ms clay vfs ms clay vfs ms

γ

N /D Δ T

Fig. 4. Typical facies architecture of the Skagerrak Formation. (A) Architecture in UK well 22/24d-10. The lower part of
the section comprises playa mudrocks passing upwards into terminal splay deposits and records deposition in a largely
vegetation-free dryland setting. The upper part of the section is dominated by vegetated floodplain deposits containing
calcic palaeosols, interbedded with channel belt sandstones. The uppermost part of the section is playa-dominated, but
with minor lacustrine mudrocks. This uppermost mud-prone interval corresponds to the Julius Mudstone Member,
overlying a near-complete Judy Sandstone member succession. (B) Sedimentary log illustrating a coarsening-upward
cycle ranging from basal playa mudrocks to terminal splay sandstones (UK 22/24b-9). Such facies are typical of the Early
Triassic to Early Anisian). (C) Sedimentary log of fluvial channel sandstones associated with terminal splay sandstones
(UK 22/24a-3), again characteristic of the Early Triassic to early Anisian). (D) Sedimentary log of floodplain deposits with
extensive palaeosol disruption of mud-prone heterolithic units (UK 22/24b-5S1). Palaeosol and root trace disruption is
most common in the Anisian to Norian section in association with fluvial channel sandstones. (E) Sedimentary log of
fluvial sandstones punctuated by minor palaeosol disruption in the upper parts of discrete and amalgamated, multi-
storey channel bodies (UK 22/24a-3).

are commonly interbedded on a scale of metres
to tens of metres, but show a gradual transition in
overall dominance over lateral distances of the
order of tens of kilometres.
Dry playa deposits (Snyder, 1962) typically form
heterolithic intervals 1 m to 20 m thick and are
most common in the Smith Bank Formation, in the
muddy intervals immediately overlying the Bunter
Sandstone and into the lowermost parts of the
Judy Sandstone Member. The heteroliths are
composed of millimetre-scale to centimetre-scale
alternations of very fine-grained to fine-grained
sandstone and mudstone (Fig. 5A), organised
into metre-scale cleaning-upward and coarsening-
upward cycles. Wave-ripple and current-ripple

lamination, dewatering and desiccation fabrics are
common and minor adhesion and salt crust fabrics
(cf. Goodall et al ., 2000) are locally developed.
Burrows and root traces are present but extremely
rare in these deposits, in marked contrast to Middle
and Late Triassic playa deposits. Locally, limited
core data suggest the presence of well sorted,
homogeneous siltstone to very fine-grained sand-
stone (Fig. 5B) which occurs in intervals up to
5 m thick. These intervals lack bedding or internal
stratification, although a very indistinct, irregular,
dish-like, wispy lamination is rarely discernible.
Individual packages of massive siltstone are
separated by thin (<0.1 m), current ripple laminated,
fine-grained sandstones with mud chips.