Geology Reference
In-Depth Information
Table 18.1
Summary of the characteristics of the underfi lled foredeep and overfi lled shelf stage of the Tremp-Graus-Ager Basin.
See text for discussion
Underfi lled foredeep
Overfi lled shelf
Chronostratigraphic
period
Early Ypresian (55.5 Ma to 51.5 Ma)
Late Ypresian to Lutetian (51.5 Ma to 43
Ma)
Basin shape
Narrow and elongate, closed in the E, open to the
Atlantic Ocean in W
Narrow and elongate, closed in the E, open
to the Atlantic Ocean in W
Basin width (total marine
section)
50 km
40 km
Basin length (total marine
section)
200 km
150 km
Estimated water depth in
present-day
Tremp-Graus and Ager
Basin area
Up to 60 m on average
0 to 20 m on average
Sea-fl oor morphology
Shelf fl oor typifi ed by gentle ridges and swells
above blind thrust-related ramps and faults.
Indented northern basin margin. Signifi cant shelf
area present. Slope located in present-day Ainsa
Basin area.
Almost no shelf present (delta and alluvial
plain). Present-day Ainsa Basin locus of
structurally fi xed, narrow and steep shelf
platform-to-slope transition, and slope.
Length of (marine) shelf
Approximately 50 km
Approximately 20 km decreasing to 5 km
Nature of main basin
fi lling processes on
shelf
Dominantly shallow marine siliciclastic deposition
along basin margin in inner parts, with gradual
transition to central basin pelagic deposition and
basinmargin fringing carbonate margins in
present-day Jaca Basin area
Extensive alluvial and lower delta plain with
relatively narrow delta front. Major shelf
slope collapse and basin fl oor turbidites in
present-day Ainsa and Jaca Basins with
carbonate platform along margin.
Position of tidalites in
basin
1) Narrow sea; 2) on platform shelf in front of
(detached or attached to) deltas; 3) estuaries
and embayments
Subaquous delta top along indented shoreline
in inshore part of channels and embayments
Type of tidal deposits
1) Tidal dunes in embayment in front of Gilbert-
type delta lobes; 2) offshore compound tidal dune
fi elds on narrow shelf; 3) detached or attached
delta-front tidal bars
1) Tide-infl uenced mouth bars and point bars
in meandering channels; 2) interdistributary
bay deposits; 3) tidal inlets and back-barrier
lagoons
Examples
Alveolina Lst (Serraduy Fm), Roda Fm, Baronia
Fm and Ametlla Fm
Castigaleu and Montllobar Fms (Lower
Montanyana Group) and Capella and Pano
Fms (Upper Montanyana Group)
than 3 km of displaced, mainly Upper Cretaceous
limestones and Maastrichtian and Paleocene deposits
of the Tremp Group. These were deposited in the
authochtonous South Pyrenean Foreland Basin when it
was not broken-up and partly displaced. The Montsec
Thrust carries a Lower Eocene allochtonous
thrust-sheet-top basin (or piggyback basin cf. Ori and
Friend
1984
, see also Ricci Lucchi
1986
) named the
(present-day Tremp-Graus Basin). The remaining
autochtonous part of the Pyrenean Foreland Basin is
the present-day Ebro Basin (Fig.
18.1
).
As a consequence, the western part of the south-
ward-moving Montsec Thrust developed as a north-
ward curved oblique blind thrust with associated faults
(cf. Dunne and Ferrill
1988
) and acted as a lateral ramp
separating shelf and slope deposition during Ypresian
sedimentation. The formation of secondary blind
thrusts, associated with the Montsec Thrust, is
expressed as near-surface subtle, low-amplitude,
gentle
folding in intrabasinal areas (de Boer et al.
1991
;
López-Blanco et al.
2003
; Clevis et al.
2004
) .
The southward moving Montsec Thrust sheet,
including the present-day Tremp-Graus Basin,
became incorporated into the cover of the next devel-
oping thrust, the Sierras Marginales, when this was
initiated in the early Lutetian and overthrusted to
form several smaller imbricated thrust units and
thrust-sheet-top basins; the connected Tremp-Graus,
