Geology Reference
In-Depth Information
Fig. 18.4
Summary correlation diagram of Ypresian stratigraphy
of the present-day Tremp-Graus and Ager Basins with a focus
on the Ager Group. The base of the Ypresian is estimated at
55.8 Ma and the top at 48.6 Ma (Luterbacher et al.
2004
) . The
magnetic polarity change from chron C24 to chron C23 occurs
at 52.6 Ma, and the change from chron C23 to chron C22 occurs
at 50.8 Ma (Luterbacher et al.
2004
) . The former change
coincides with a dating of 52.6 Ma for the Plateau Limestone
(López-Blanco et al.
2003
). Unpublished data of the top of a
Turritella
-dominated mudstone interval in the Esdolomada Mbr
(which is on average 180 m thick) occurring 29 m above the
Plateau Limestone at the stratigraphic level of the El Villar
Limestone gives an age of 52.4 Ma which coincides with
top P6 and a maximum fl ooding of the Roda Fm in the Isabéna
valley (confi rmed by Torricelli et al.
2006
) . Following this
data, the Roda Sst Mbr covers approximately 0.9 Ma and the
Esdolomada Mbr covers approximately 1.6 Ma. Note, however,
that López-Blanco et al. (
2003
) , using magnetostratigraphic
data obtained from the Roda Fm (Bentham and Burbank
1996
)
and the magnetic polarity scale of Cande and Kent (
1995
) ,
estimated approximately 400 Ka for the Roda Sst Mbr and
approximately 600 Ka for the Esdolomada Mbr. The allostrati-
graphic subdivision of the Figols Group advocated by Mutti and
his co-workers, based on the philosophy that comparable facies
throughout the basin are combined into groups or depositional
systems (for example, the Figols Group for terrigeneous facies of
mainly deltaic character, the Campodarbe-Montañana Group
for continental facies and the Hecho Group for basin fl oor facies),
is not incorporated. Note that tidal deposits of Maastrichtian age
in the Aren Formation (Tremp Group; Nagtegaal et al.
1983
; De
Boer
1985
and a wealth of recent but unpublished data collected
by Spanish workers) and of Upper Lutetian age in the Sobrarbe
Formation (Campodarbe Group; Hall
1997
; Dreyer et al.
1999
)
are also present but not included in this review
is uncertain but is estimated at up to 60 km (larger than
it is at present after post-Ypresian compression, uplift
and erosion).
In conclusion, the combined Jaca and T-G-A Basin
was within the tidal amplifi cation window (cf. Sztanó
and de Boer
1995
) with favourable average depth and
length for resonant amplifi cation (Figs.
18.3
and
18.6a,
c
), favorable paleobathymetric parameters, but unfa-
vourable depth-width confi guration for development
of amphidromic point(s) as the basin was too narrow.
