6. Rotational kinematics of the Boltaña anticline - Instituto Geológico ...

Boltaña kinematics Mochales, 2011
Relative deeper siliciclastic sediments evolving towards deltaic facies (Yeba Fm, Van Lunsen, 1970)
conformably overlie the previous carbonate shelf. In the core of the Boltaña anticline, this unit
includes a lower member with marls, siltstones and bioturbated sandstones and an upper member with
bioclastic sandy limestone bed followed by two shallowing-upward sequences of marls, siltstones and
sandstones. The entire Yeba Fm probably represents an important paleogeographic change to a more
pronounced control in the foreland margin sedimentation by the orogenic geometry (Barnolas et al.,
2011). The Yeba Fm includes the Ilerdian-Cuisian boundary (Mochales et al., 2011). The thickness of
this unit is difficult to measure due to the transitional character of its upper part; an estimate of 170 m
has been found for the entire Yeba Fm in the Ara River section (Figures 3 and 4).
Cuisian: The second main carbonate platform in the
Eocene (Barnolas et al., 2011) corresponds to the
Boltaña Fm (Barnolas et al. 1991), Early-Middle Cuisian
(Ypresian) in age, 550 m thick in the Ara River section
(Mochales et al., 2011). Barnolas et al. (1991)
differentiated three units: lower and upper Boltaña
members separated by a double level of limestones with
abundant Assilina (Ascaso Mb of Van Lunsen, 1970)
indicative of a marine transgression (Barnolas and Gil-
Peña, 2001). The lower Boltaña Fm corresponds to a
mixed shelf (siliciclastic and shallow carbonatic)
cropping out in the Boltaña and Mediano anticlines. It is
made up of shallowing-upwards sequences with
siliciclastic base (marls, siltstones and cross bedded,
bioturbated sandstones) including Assilina, Nummulites
and Discocyclina whereas its top is shallower, formed by
sandy limestones with abundant Alveolina. The upper
Boltaña Fm presents progressively deeper, shallowingupward
sequences, acquiring therefore a retrogradational
character (Barnolas and Gil-Peña, 2001). Its top contains
distal ramp carbonates with abundant slump scars and
micritic limestones (Figures 3 and 4).
Figure 3. Simplified stratigraphic log where the main units
dealt in this work are distinguished.
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