Geology Reference
In-Depth Information
Fig. 18.11
(
a
) Strongly simplifi ed geological sketch map of the eastern sector of the present-day Tremp-Graus Basin and the Ager
Basin. (
b
) Geological sketch map of the present-day Ager Basin (modifi ed after Mutti et al.
1985b
)
18.4.2 Tidal Bars of the Alveolina Limestone
subdivided into two members (the Pallaresa and
Collada members; Dreyer and Fält
1993
; Fig.
18.4
)
and tidal deposits occur in both members (Ghibaudo
1975
). The Pallaresa member is comprised of offshore
siltstone intervals which may be up to 45 m thick, and
six laterally continuous tide-infl uenced and - domi-
nated sandstone bodies deposited in deltaic, estuarine
and tidal shelf settings which may be up to 32 m thick
(Fig.
18.12
). The Collada member is interpreted to have
accumulated in a coastal plain to tidal fl at environment
(Dreyer and Fält
1993
; Dreyer
1994
) . Sediments were
shed from an extensive topographic high to the south
(the developing Sierras the Marginales thrust system)
and to the east. The formation was deposited during
active pulsating thrust-sheet development, resulting in
a number of high-frequency relative sea-level changes
(Mutti et al.
1988
). The highest relative subsidence
occurred in the eastern part of the basin, where the
Ametlla depocentre was located. Water depths, how-
ever, increased westward (Dreyer and Fält
1993
) .
During deposition of the Ametlla Fm, the eastern clo-
sure of the T-G-A basin was (signifi cantly) nearer to its
present-day position (Dreyer and Fält
1993
) .
The combined effect of the relatively rapid eustatic sea
level rise at the start of the Early Ypresian (Pujalte
et al.
2009
) and southward displacement of the Bóixols
Thrust and associated lateral or oblique ramps resulted
in NW-SE oriented anticlines and synclines along the
central-northern margin of the T-G-A Basin. Two anti-
clines developed near Serraduy (Fig.
18.10
; the Roda
and Coll de Vent anticlines; Eichenseer
1988
; Vincent
2001
; López-Blanco
1996a,
b
) with a syncline in
between (the Serraduy-Sis syncline; López-Blanco
et al.
2003
). This area became the locus for an approxi-
mately NE-SW oriented warm-water and southward
opening narrow coastal embayment ('Serraduy Bay'
of Unit 2 in the upper part of sequence V of Eichenseer
1988
) , typifi ed by strong tidal currents, during the
relative sea-level rise. Deposits formed in this embay-
ment are part of the Alveolina Limestone Mbr of the
Serraduy Fm (Fig.
18.4
). Shallow-water carbonate
banks and reefs developed particularly on the fl ank of
the Roda anticline (Pool
1983
; Eichenseer
1988
) . The
embayment was dominated by WSW directed
