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 79

Palaeosol assemblage 1 (PA1) thin horizons (0.2 m to 0.4 m). Vertisols with slick-

ensided surfaces are rare (<5%) within PA1.
Within the unit L10 a transition takes place from
PA1 to PA2, with vertisols comprising up to 15%
of the total floodplain succession (Fig. 11). Reworked
carbonate nodules indicate that some alluvial mud
with calcrete has been eroded. PA1 is dominated
by compound pedocomplexes (Fig. 11).

Palaeosol assemblage 1(PA1) correlates entirely
with FSA1 and occurs in the allostratigraphic
units L12 to L10 in the lower part of the Lunde
Formation (Fig. 3). It comprises red or reddish-
brown mudrocks with up to 50% to 60% sand and
silt. The content of clays (<2 µm) is relatively low.
The floodplain units are composed dominantly of
laminated mudrocks (MF1) and unstratified, struc-
tureless mudrocks (MF2), both facies with entisols/
inceptisols (Table 6, Fig. 12).
In PA1, intervals with thin (<2 m) entisols/
inceptisols are commonly mixed with laminated
beds and capped by laminated mudrocks or sheet-
flood sandstones. Small-scale sand-filled desicca-
tion cracks occur infrequently. Scattered calcrete
nodules, nodular carbonate horizons, vertically
stacked calcrete nodules, rhizocretions, root struc-
tures and burrows are common, but not abundant.
The percentage of carbonate nodules reaches 20%
to 30% of the total mudrock volume within a few

Palaeosol assemblage 2 (PA2)

In PA2, within L09 to L05, floodplain successions
constitute approximately 45% to 50% of the total
rock volume (Figs 6, 8 and 13). Red and reddish-
brown laminated mudrocks (MF1) and entisols/
inceptisols (MF2) dominate, but high chroma
vertisols (in MF3) are also common (Table 6).
Individual palaeosol horizons can be up to
4 m thick before they are succeeded by stratified
mudrocks or sheet-flood sandstones. Reworked
mudrocks (MF5) are also present in L09 to L05, as
reworked mud aggregates and reworked carbonate

Lithostrat.

Pedo-
complexes

Vertical trends

Allostrat

Gp. Fm.

Disappearance
of carbonates

S4

4

S5

L01

L02

3

L03

L04

L05

L06

2

L07

L08

L09

L10

1

Increase

L11

L12

Very common (>50) Rare (5-15%)

Cumulative

Fig. 11. Stratigraphic distribution of
mudrock facies MF1-5 and pedocom-
plexes in the Lunde and Raude forma-
tions. PA = palaeosol assemblage.

Common (40 - 50%)
Moderate (15 - 30%)

Very rare (<5%)

Compound Composite