Geology Reference
In-Depth Information
Fig. 18.20
Paleodrainage pattern of the Castissent Sandstone
and related Corca Fm. across the underlying Castigaleu Fm.
(lower and upper delta plain) and time equivalent Montllobat
Fm. (fl uvial); see also Fig.
18.4
(modifi ed after Nijman
1998
) .
Units A to C correspond to successive fl uvial depositional
cycles.
CSPT
Central South Pyrenean Thrust system including
the Montsec Thrust and its lateral ramps
The Castigaleu Fm is on average 400 m thick and is
formed by a number of up to 12 m thick sandstone
units intercalated with thick fi ne-grained (mud to
very fine sand) intervals (Nijman and Nio
1975
;
van der Meulen
1989
; Puigdefàbregas et al.
1989
) .
Sandstone units, dominantly formed by fluvial
channel fi lls and bars, are interpreted to generally have
a meandering planform style. Commonly, sheet river-
fl ood deposits are conglomeratic in nature. These
channel fi lls intercalate with distributary mouth bars
and interdistributary muddy, brackish bay deposits
(Fig.
18.21a, e
).
Fluvial sandstone units in the distal part of the
Montllobat Fm are up to 6 m thick and occur as
(1) ribbons, (2) tabular bodies with lateral accretion
and (3) lenticularly-bedded sheet bodies. Wide (up to
3 km) incised alluvial valley fi lls are formed by amal-
gamated sandstone complexes (up to 20 m thick)
deposited in trunk rivers on the lower alluvial plain
(Fig.
18.21a
). In places, they are infl uenced by brack
water and tidal processes as a consequence of
having been formed in the fl uvial to tidal transition
zone (cf. Ghosh et al.
2005
; Van den Berg et al.
2007
;
Martinius and Gowland
2010
; Fig.
18.22
).
Alluvial upper and lower delta plain fl uvial facies
of the Capella Fm reach a thickness of approximately
1,000 m. Sediments were deposited in the depression
formed by subsidence on the footwall of the Lascuarre
Fault system and the lateral ramp of the Montsec
Thrust (Fig.
18.9
). Due to the relative high subsidence
rate, a signifi cant volume of fl uvial sediment was
stored in the Isábena Depression (Fig.
18.9
) largely
preventing progradation of the system. Phases of source
area rejuvenation were characterized by an initially
low-relief alluvial profi le allowing tidal processes to
increase their effect on the dominantly muddy lower
delta plain environments (Cuevas Gozalo
1989
) despite
the short shelf.
The Pano Fm (uppermost Montayana Group;
Fig.
18.5
) was deposited as a transgressive coastal
sandstone wedge forming the shallow-marine and
time equivalent continuation of the uppermost part of
Capella Fm (Nijman and Nio
1975
; Nio and Donselaar
1978
; Cuevas Gozalo
1989
; Donselaar
1996a
;
Fig.
18.9
). The Virgen de la Collada ramp, located
between the Mediano anticline and the Lascuarre
reverse fault system (Donselaar
1996a
; Fig.
18.9
),
controlled sedimentation patterns and the position of
