Late Triassic to Early Jurassic climatic change, northern North Sea region: impact on alluvial architecture, palaeosols and clay mineralogy - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 86

Stratigraphy Alluvial features Pedogenic features Mudrock mineralogy

Dominating
climate type Pedo

complexes

Quartz/
Feldspar

Goethite/
hematite

33/12-2
GR-log

Sm+ML+ka/
chl+ill

M TST Stream Type CDP Palaeosol

0 100 0 100 0 100 0 100

Dunlin Gp

0

Nansen Fm

S1

S2

Humid

100

Monsoonal
braided
streams

S3

S4

Semihumid -
humid

200

S5

300

Semiarid -
Semihumid

Small
meandering
streams

400

500

Large
meandering
streams

600

700

800

Semiarid

Ephemeral
Braided
streams

900

1000

Arid/Semiarid

Alke Fm

1100

Fig. 15. Summary of trend variations through the Lunde Formation and the Statfjord Group in the Snorre Field. Stratigraphy
and reference well as in Fig. 3. CDP = channel deposit proportion, Sm = smectite, ML = mixed layer clay minerals,
ka = kaolinite, chl = chlorite, ill = illite.

increase upwards through the Lunde Formation,
then decrease and disappear up through the Statfjord
Group (Fig. 15).
In addition to distinct vertical trends in the
mudrock mineralogy (Fig. 15), there is also an
increasing content in the clay fraction of mud-
stones upward through the Lunde Formation and
of organic-rich mudstone in the upper part of the
Lunde Formation and the Statfjord Group. The
Lunde Formation is characterised by a polymin-
eralogical suite of clay minerals, varying in an
apparent rhythmic pattern. At the boundary
between the Lunde and Raude formations the
ratio of smectite + mixed layer and smectite + kao-
linite to chlorite + illite increases abruptly, with

smectite dominating in units S5 to S3 and kaolin-
ite in S1 (Figs 14 and 15). The increasing goethite/
hematite ratio upwards from ULF corresponds to
a change in mudstone colour from reddish-brown
to mottled greenish-grey. There is a very strong
correspondence in the stratigraphic positions of
trend changes in alluvial features, pedogenic
features and mudrock mineralogy (Figs 3 and 15).
The trend variation in architectural style and
sandstone : mudstone ratio established within the
Lunde Formation and the Statfjord Group in the
Snorre Field area has been used for correlation
within the Tampen Spur area (Fig. 16). The recorded
trends reflect the response of various processes
and mechanisms that controlled the alluvial