Geology Reference
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Fig. 18.5 Summary correlation diagram of Ypresian and Lutetian stratigraphy of the present-day Tremp-Graus and Ager Basins
with a focus on the Montanyana Group (modifi ed after Nijman 1998 )
18.3.2 Overfi lled Shelf
1975 ; Dunne and Ferrill 1988 ; Cuevas Gozalo 1989 ;
Donselaar 1996a ; Nijman 1998 ; Poblet et al. 1998 ;
Clevis et al. 2004 ; Figs. 18.1 , 18.2 , 18.7 and 18.8 ) and
acted as a lateral ramp separating shelf from slope and
basin fl oor deposition during Late Ypresian and Lutetian
sedimentation (52 Ma to 43 Ma; Cámara and Klimowitz
1985 ; Puigdefàbregas et al. 1992 ) .
Associated smaller blind thrusts and associated
ramps developed contemporaneously. An example of
such an additional thrust is the Lascuarre reverse fault
system (E of Graus; Fig. 18.9 ), with a NNE-SSW orien-
tation, which acted as the most important sea-fl oor
topographic expression (Cámara and Klimowitz 1985 ;
Puigdefàbregas et al. 1992 ) east of the main oblique
lateral ramp of the Montsec Thrust from 55.8 Ma to
48.6 Ma. It formed the transition from upper delta
plain environments of the Montanyana Group in the
T-G-A Basin on the hanging wall of the lateral ramp of
the Montsec Thrust to contemporaneous lower delta
plain deposition on the shelf margin and mass-fl ow
deposition on the slope (the latter now making up
a signifi cant part of the present-day Ainsa Basin;
Nijman and Nio 1975 ; Cuevas Gozalo 1989 ; Cuevas
Gozalo and de Boer 1991 ; Donselaar 1996a ; Nijman
Tidalites of the overfi lled shelf stage (Table 18.1 ,
Fig. 18.7 ) are represented by facies of the Middle to
Late Ypresian and Lutetian (51.5 Ma to 43 Ma)
Montanyana Group present across the entire T-G-A
Basin (Figs. 18.4 and 18.5 ). The T-G-A Basin most
probably moved to the margin of the tidal amplifi cation
window (cf. Sztanó and de Boer 1995 ; Fig. 18.6a, c ).
As discussed hereafter, this was caused by the devel-
opment of increasingly more pronounced basin-fl oor
topographic features formed as the result of continuing
thrust movement. These had a progressively more
important control on basin morphology, depositional
environments and tidal resonance.
The overfi lled shelf stage resulted from the conver-
sion of the (segmented) underfi lled foredeep of the
T-G-A Basin to a well-defi ned shelf and slope confi gu-
ration as a result of ongoing thrusting and associated
southward thrust-sheet-top basin translation along the
Montsec Thrust as well as shortening along a N-S direc-
tion. The western part of the southward moving Montsec
Thrust further developed into a pronounced northward
curved oblique (NW-SE) blind thrust (Nijman and Nio
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