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 50

Fennoscandia MNSH Variscan remnants

Tr ade winds
Summer monsoon
Te thys

Central North Sea
Playa

Southern Permian Basin

Salina

cool

Dry phase, endorheic basins

(A)

Moist Te thyan air masses
Summer monsoon

Fluvial expansion

Playa

warm

(B)

Pluvial phase, endorheic basins

Tr ade winds

Fluvial contraction

Moist air

Summer monsoon

Muschelkalk Fm.

cool

(C)

Dry phase, endorheic CNS basin, Permian basin flooded

Incised streams, isolated lakes Exorheic drainage to

marine base level

Reef crisis

(D) Pluvial phase, exorheic fluvial systems

Fig. 20. End-member climatic scenarios. During conditions of general background aridity the central North Sea and
Southern Permian Basin were characterised by widespread playa deposition and seasonal monsoon precipitation (A).
During pluvial episodes (B) the summer monsoon may have intensified, resulting in the basinward expansion of Skagerrak
Formation terminal fluvial systems. Weakened trade winds may have allowed the northward transport of moist Tethyan air
masses, which helped maintain year-round soil moisture and intermittent fluvial transport. During the Middle Triassic
vegetation cover and standing water were maintained through arid episodes (C) as a result of the flooding of the Southern
Permian Basin, which elevated humidity and ground water tables in the adjacent central North Sea. During the major
Ladinian and Carnian pluvial phases (D) large exorheic systems drained off Fennoscandia into the Tethys Sea. This
drainage to an initially lower base level resulted in widespread fluvial incision and sediment by-pass in the Southern
Permian Basin. In the central North Sea this pluvial event is apparently absent, although this is likely to be due to a
combination of fluvial incision, drainage diversion away from the basin centre and a limited dataset biased towards
structural highs which may have become areas of by-pass during this period of lowered base level. MNSH - mid-North Sea
High, CNS - central North Sea.

of sand-prone fluvial facies in the North Sea and
UK Atlantic margin is indicative of a persistent
sediment supply from Greenland, Fennoscandia
and the Scottish Highlands (McKie & Williams,
2009), which contrasts with the marked reduction
in fluvial sand transport seen across southern
Britain, offshore Ireland and the Southern Permian
Basin (Fig. 21). This reduction occurred relatively
rapidly through the Anisian, resulting in the depo-

sition of widespread Keuper and Mercia Mudstone
playa and limited clastic input to the Muschelkalk
seaway. Such a reduction is unlikely to have been
the product of slow denudation processes. Instead
it appears that there was a general reduction in
sediment yield in southern latitudes after the
Early Triassic, whilst fluvial transport was main-
tained further north through much of the Triassic.
Given the continuity of sandy, vegetated fluvial