Geology Reference
In-Depth Information
Fig. 18.21
(
a
) Outcrop impression of the alluvial valley depos-
its of the Gargalluda sandstone complex, a 2 km wide tidally-
infl uenced trunk river alluvial valley exposed 2 km south of Puente
de Montanyana (Fig.
18.10
). (
b
) Lower delta plain embayment
deposits into which the alluvial valley incised at this location.
(1) Well-bioturbated brack-water marls and very-fi ne grained
thin sandstone layers with oysters. (2) Non-bioturbated planar
bedded and laminated very fi ne grained sandstone and siltstone
layers showing rhythmic deposition inferred to have been con-
trolled by tides and possibly indicating neap-spring cyclicity.
(3) Medium-grained fl uvial sandstone bed. (
c
,
d
) Medium-grained
sandstone beds showing (i) increasing to decreasing bottomset
thickness, (ii) increasing to decreasing foreset dip and shape (from
convex to concave), (iii) in places increasing-decreasing organic
particle concentrations, and (iv) occasional reactivation surfaces.
These features interpreted as tidally-infl uenced fl uvial accre-
tionary bedforms resulting from successive fl uctuations in fl ow
regime conditions from lower (during fl ood tidal retardation) to
higher (during ebb tidal drawdown) current velocities (cf. Martinius
and Gowland
2010
) . (
e
) Outcrop image of a mouth bar complex
associated with a lower delta-plain distributary channel in the
Perarrua Fm (Fig.
18.5
) directly east of the town of Salanova
(8 km south of La Puebla de Roda; Fig.
18.10
). (
f
) Mud-draped
ripple-laminated (form)set forming part of the bottomset of a
tabular cross-stratifi ed bed in the upper part of the mouth bar
shown in (
e
) and interpreted to have been formed during bank-
full stage and reversal after fl ood combined with low current
velocities in the channel (cf. Cuevas Gozalo and de Boer
1991
)
internal Pano Fm facies boundaries. Only a short
(approximately 10 km) shelf was present and a number
of tectonically induced relative sea-level changes
controlled sedimentation. These were related to a rela-
tively high rate of subsidence alongside the growing
Mediano anticline. The Pano Fm is divided in two third
order sequences and each of these is further divided in
a number of fourth order sequences (Cuevas Gozalo
1989
; Donselaar
1996a
, Fig. 1.-23).
The Ypresian and Lutetian T-G-A Basin fi ll is
overlain by upper Eocene and Oligocene fl uvial and
alluvial fan deposits mainly sourced from the north
(Puigdefàbregas et al.
1989
) .
18.5.2 Tidally-Infl uenced Fluvial Point-Bars
and Mouth Bars
Tidal infl uence is encountered in fl uvial sandstone
bodies of the Castigaleu, Montllobar and Capella Fms
and two tidally-infl uenced fl uvial point-bar models
with current reversals were proposed (Cuevas Gozalo
