Geological Survey of Denmark and Greenland Bulletin 19 ... - Geus

and Qaarsut (Fig. 22). Its wider distribution is not known
due to lack of exposures.
Type section. The eastern slope of J.P.J. Ravn Kløft constitutes
the type section (Figs 22, 51A). The base of the
type section is located at 70°45.18´N, 52°55.08´W.
Reference sections. Reference sections are found in stream
exposures just east of Ikorfat, at Slibestensfjeldet and at
Vesterfjeld (Figs 22, 51B, 52).
Thickness. The thickness of the Ravn Kløft Member is
about 450 m in the type section, thinning both towards
the east and the west (Midtgaard 1996b). The basal pebbly
sandstone varies in thickness from less than 2 m to
a maximum of 56 m. The overlying deposits are c. 400
m thick in J.P.J. Ravn Kløft.
Lithology. A variety of lithologies and sedimentary facies
are present in the Ravn Kløft Member. The member is
tripartite, comprising a lower pebbly sandstone unit, a
middle unit of mudstones, heteroliths and fine-grained
sandstones with coarsening-upward or fining-upward
depositional patterns, and an upper unit of thick-bedded
medium- to coarse-grained sandstones interbedded
with mudstones and heteroliths (Fig. 50B; Midtgaard
1996b). The lower unit (c. 35–62 m on Fig. 51A) includes
a c. 3 m thick conglomeratic sandstone with rounded pebbles
and large clasts of coaly mudstone, fossil wood and
mudstone, interpreted as a channel lag. This is overlain
by pebbly coarse-grained sandstones with large-scale
cross-bedding, followed by coal-bearing mudstones with
beds consisting of small Scaidopityoides leaves (Midtgaard
1996b). The cross-bedding indicates unidirectional northward
sediment transport.
The middle unit (c. 62–340 m on Fig. 51A) comprises
a variety of facies. Coarsening-upward successions
comprise laminated mudstones, heterolithic sandstones
and hummocky cross-stratified sandstones, which locally
are capped by trough cross-bedded sandstones, mudstones
with root horizons and thin coal beds. Wave-ripple
crests are oriented ESE–WNW. Comminuted car -
bonaceous debris is abundant. Fining-upward successions
comprise medium- to coarse-grained, well-sorted
sandstones with cross-bedding, double mud-drapes, and
abundant reactivation surfaces. They are overlain by heteroliths
with current and wave ripple cross-lamination
followed by black, laminated mudstones. Synaeresis
cracks are common.
The upper unit (c. 340–400 m on Fig. 51A) of the
Ravn Kløft Member consists of thick, erosively based
bodies of greyish sandstone alternating with dark heterolithic
mudstone. The sandstones are fine- to coarsegrained
or conglomeratic, and dominantly cross-bedded.
Foresets are often oversteepened and large-scale soft-sediment
deformation structures are very common (Fig.
52). Composite sandstone bodies may be up to 60 m thick
(Fig. 50), and may extend laterally for at least 8 km. The
cross-bedding indicates sediment transport to the
NE–N–NW. The sandstone bodies alternate with thinly
interbedded rippled sandstones, laminated mudstones
and heteroliths containing abundant rootlets and plant
fossils, thin coal beds and palaeosols at certain levels.
Fossils. A brackish-water dinocyst assemblage dominated
by Nyktericysta davisii has been identified in a number
of the mudstone beds. The pollen Rugubivesiculites rugosus
has its first stratigraphical occurrence within the member
(Fig. 29).
Depositional environment. The lower unit of the Ravn
Kløft Member is interpreted as a basal fluvial valley-fill
conglomerate overlain by fluvial sandstones deposited
by unidirectional northward-flowing currents. The middle
units are interpreted as interbedded deltaic and tidal
estuarine deposits, and wave-ripple crestlines suggest an
ESE–WNW-oriented coastline. The overlying single to
multi-storey sandstone bodies represent a variety of fluvial
styles from slightly sinuous single channels to braided
rivers with multiple channels and northward palaeocurrents.
The presence of rootlets, vitrinite lenses and local
coal beds in the floodplain sandstones and mudstones
indicates the existence of a range of sub-environments
from subaerial floodplain to shallow-water swamps or
ponds adjacent to the fluvial channels. The fluvial sandstones
show an increasing tendency up-section to amalgamate
and form thick, multi-storey sandstone sheets
(Midtgaard 1996b).
Boundaries. The lower boundary of the Ravn Kløft
Member is the same as for the Atane Formation. The
thickness variation of the lower fluvial sandstones of the
Ravn Kløft Member suggests that the base had a relief
of nearly 55 m on a regional scale (Midtgaard 1996b).
The upper boundary is placed at the top of a c. 60 m
thick, amalgamated multi-storey fluvial sandstone sheet
which is abruptly overlain by a succession of interbedded
mudstones, heteroliths, sandstones and thin coal
seams referred to the Kingittoq Member (Fig. 50).
Geological age. Based on the palynomorphs, the Ravn
Kløft Member is assigned a Late Albian – Early Ceno -
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