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Ager and Ainsa Basins (Mascle and Puigdefàbregas
1998 ). The rate of thrusting was highest from the end
of the Paleocene to the Lutetian (Vergés et al. 1995 ;
Millán et al. 1995 ) producing a relatively deep and
wide basin and the broadest expansion of marine
deposits (Puigdefàbregas et al. 1992 ; Burbank et al.
1992 ) . Syntectonic contemporaneous sequences are
present in neighboring basins (Pocoví 1978 ; Martínez-
Peña and Pocoví 1988 ; Vergés et al. 1995 ; Mascle
and Puigdefàbregas 1998 ) . Paleomagnetic data from
the present-day Ainsa Basin, which rotated 30 ° clock-
wise during Montsec Thrust displacement (Poblet
et al. 1998 ), indicates the rotation of the entire thrust-
sheet-top basin (Nijman 1989 ; Poblet et al. 1998 ) .
This complex structural development had a profound
effect on basin morphology and sedimentation pat-
terns and has infl uenced basin-scale tidal current
patterns.
18.3
Tidalites and Paleogeography,
Bathymetry and Fill - Underfi lled
Foredeep Versus Overfi lled Shelf
18.3.1 Underfi lled Foredeep
The underfi lled foredeep stage (Table 18.1 , Fig. 18.3b )
is stratigraphically represented by deposits of the
Ager Group (Figs. 18.4 and 18.5 ; see next section)
and occurred during the early stage of thrust-sheet-
top basin development (Early Ypresian, 55.5 Ma to
51.5 Ma). As discussed hereafter, the associated
and characteristic confi guration of basin morphology
parameters indicate that the basin was within the tidal
amplifi cation window (cf. Sztanó and de Boer 1995 ;
Fig. 18.6a, c ) .
The present-day Tremp-Graus and Ager Basins,
now separated by the Montsec Thrust, formed one
entity, Tremp-Graus-Ager (T-G-A) Basin. The T-G-A
Basin was elongated along an E-W line and connected
to the Atlantic Ocean via the Jaca Basin (Fig. 18.7a ).
A subaerial topographic high, formed by a thrusted
anticlinal system, bounded the T-G-A Basin in the
south (Figs. 18.2 and 18.3b ). In the area east and south-
east of Tremp, the T-G-A Basin was most likely closed
and is referred to as the Gulf of Ager by some workers
(Fonnesu 1984 ; Eichenseer 1988 ; Eichenseer and
Luterbacher 1992 ; Mutti et al. 1994 ; Barberà et al. 1997 ;
Waehry 1999 ). It included a southern limb that likely
extended farther to the east than the present-day
closure (Maestro-Maideu et al. 1991 ; Dreyer and
Fält 1993 ; Dercourt et al. 2000 ; Vincent 1993 ; Olariu
et al. 2008a ; Fig. 18.3b ). Any connection with the
Mediterranean is uncertain and unlikely as it would
generate strong tidal currents for which no support is
found in the sedimentary record. A number of NW-SE
oriented anticlines developed along the central northern
basin margin controlled by the long-lived inverted
Mesozoic fault structures. They developed either as
(i) lateral or oblique ramps (or their associated hanging-
wall anticlines) to S-directed upper cover-thrust sheets
(cf. Muñoz 1992 ) or, alternatively, (ii) linked to the
Bóixols frontal thrust (Cámara and Klimowitz 1985 ) .
It is suggested here that the periodic re-activation of
these structures was expressed by an indented coastline
along the northern basin margin locally forming estua-
ries and/or embayments causing tidal amplifi cation
and ebb-fl ood cyclicity.
18.2.2 Lower Eocene Paleoclimate,
Eustatic Sea Level, and
Stratigraphy
During the upper lower Ypresian, the upper Ypresian
and the Lutetian, the study area was located at a
latitude of approximately 35°N and was characterized
by a warm and stable, sub-tropical to tropical climate
(Early Eocene Climatic Optimum; Zachos et al. 2001 )
and generally warm and arid to semiarid conditions in
the Pyrenees (Haseldonckx 1972 ; Schmitz and Pujalte
2003 ; Pearson et al. 2007 ) .
The Ypresian and Lutetian are periods of pro-
nounced long-term tectonic development (see above)
controlling local relative sea-level changes, that are
likely to have varied spatially and temporally in the
Pyrenean foreland Basin. Egger et al. ( 2009 ) , in con-
trast, concluded that the effects of Paleogene changes
in eustatic sea-level exceeded the effects of regional
tectonic activity in the shelves of the European and
Adriatic Plates as a result of the much shorter magni-
tude and time scales over which these processes oper-
ate. This is illustrated by the occurrence of a
widespread and relative rapid marine transgression
during the lowermost Ypresian (Pujalte et al. 2009 ) .
However, in general and in comparison Alpine tec-
tonic activity in the Pyreneen orogenic zone was much
stronger than elsewhere (Vergés et al. 1995 ; Meigs
and Burbank 1997 ; Capote et al. 2002 ) .
 
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