Geology Reference
In-Depth Information
Fig. 18.7
Sketch of the inferred paleogeography and water
depths of the T-G-A basin sea during the overfi lled shelf stage
of the Lutetian. The
dotted line
indicates the position of the
basin axis. (
a
) The Montanyana system at initial progradation.
Alluvial fans along the northern basin margin and a fl uvial
system in the eastern and central parts of the T-G-A Basin.
A relatively large delta front area existed with interdistri-
butary bays and mouth bars. (
b
) The Montanyana system
at advance progradation. River systems dominated and
extended out almost to the shelf break fi lling-up the shelf area.
Only a narrow delta front area remained (modifi ed after Nijman
1998
)
1998
; Poblet et al.
1998
; Clevis et al.
2004
; Figs.
18.7
and
18.8
). It also prevented the formation of well-
developed clinoforms (Puigdefàbregas et al.
1989
) .
Later, from 48 Ma to 43.5 Ma (Early Lutetian), the
Mediano anticline (Figs.
18.7
and
18.9
) developed
over the propagating Montsec oblique blind thrust,
approximately 20 km to the west of the Lascuarre fault
system, causing further steepening of the slope, over a
time span of 5.5 Ma (Garrido-Megías
1973
; Nijman
and Nio
1975
; Poblet et al.
1998
) . In between, the
Isábena Depression developed (Cuevas Gozalo
1989
;
Fig.
18.9
).
During Middle to Late Ypresian and Lutetian, the
eastern and central parts of the T-G-A basin had begun
to be progressively fi lled with alluvial and deltaic
sediments from the north and east towards the west.
As a consequence, water depths in the early stages
of infi ll are estimated to have been approximately 20 m
