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Early Cretaceous events in southeastern Spain
Bruno R.C. Granier

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-07 02:50 PM – 03:10 PM
Last modified: 2018-12-15

Abstract


In southeastern  Spain, the upper Jurassic carbonate platform did not end with the Tithonian, but with the Berriasian (Granier, 2019). The sections studied in the Alicante comprise Sierra de Fontcalent (Rasplus & Fourcade, 1987), i.e., a basinal section, Busot (Granier et al., 1995), i.e., a slope section, and three platform sections: Cabezon de Oro, Puig Campana and Sierra Helada (Granier, 1987, 2007, 2019; Granier & Perthuisot, 2009).

A forced regression at the start of the Valanginian was followed by a healing phase (sensu Posamentier & Allen, 1993). It marks the abrupt change from a rimmed carbonate shelf to a mixed siliciclastic-carbonate non-rimmed shelf passing to a ramp system. The associated deposits form a thick sigmoidal sedimentary wedge, hence the 175-meter-thick lower Valanginian section at Sierra de Fontcalent (Rasplus & Fourcade, 1987), with basinal onlaps against the slope beyond the shelf break. On the platform itself, transgressive facies, known as the “Calcarénites à Pseudocyclammines” (Granier, 1987, 2007, 2019; Granier & Perthuisot, 2009) or the upper member of the Sierra del Pozo Formation, are characterized by swaley and hummocky (SCS and HCS) cross-stratifications. The microfacies is commonly represented by a “lithoclastic floatstone with a grainstone matrix, a mixture of carbonate allochems and terrigenous sand or silt” (e.g., Granier, 2007, Fig. 2). The siliciclastic material, which is free of clay, is derived from material stored for millions of years on the southern shore of the Iberian Meseta. Consequently, it did not impede the working of the carbonate factory and the growth of small coral patches.. In conclusion, in southeastern  Spain, this first major Valanginian transgression did not lead to a genuine drowning.

At Sierra de Fontcalent, i.e., the basinal section, most lower Cretaceous units above the lower Valanginian are condensed: 8 m for the upper Valanginian, 7 m for the Hauterivian (glauconitic), and 21 m for the lower Barremian (glauconitic). At Cabezon de Oro, Puig Campana and Sierra Helada, i.e., the platform sections, the whole upper Valanginian to Barremian interval is reduced to a 0.5 to 2 m thick interval with ferruginous oolite and glauconite (Granier, 1987, 2007, 2019; Granier & Perthuisot, 2009) due to hiatuses and extreme condensation.  The hiatuses and condensation are the mark of sedimentary starvation. All these sites were then located within the aphotic zone (with limited carbonate production) and the potential siliciclastic supply from the Iberian Meseta was not reaching these distal areas. On one hill of the Busot village, below the castle ruins ("Castillo árabe"), the ferruginous oolite, which is a few meters thick, contains mostly Hauterivian and Barremian ammonites.  By contrast, on another hill, below a chapel ("Ermita del Calvario") and less than 200 meters away, a 65 meter section consisting only of Hauterivian strata - dated by ammonites - was measured. This anomaly corresponds to the infill of a scar resulting either from a slope collapse or most probably from the growth a synsedimentary fault. The sediments are bioclastic wackestones with benthic foraminifers and calcareous algae, mostly reworked material from the shallower and slightly older sediments. There is no evidence for turbidity current (as it is the case in most Tithonian - Berriasian Vocontian sections in France) but rather for traction currents (with rolling, creeping and saltating grains). In their muddy matrix Granier et al. (1995) reported the striking occurrence of numerous free Calpionellids. The sedimentary features listed above exclude a reworking of these fragile tiny amphoras.

In addition to the Busot paleofault, there are other arguments for a distensive tectonic activity and the related block-faulting that are responsible for basinal starvation. For instance, Granier (1987) documented microscopic sedimentary dikes and sills in the ferruginous oolite at Cabezon de Oro. However, the most striking evidence comes from Sierra Helada with a local hiatus corresponding to the Berriasian-Barremian interval.  Additionally, spectacular macroscopic sedimentary sills and breccias affect the Tithonian limestones. They are post-early Valanginian in age, a dating that is inferred  because few lithoclasts derived from the “Calcarénites à Pseudocyclammines” are found in the sedimentary infills.

To summarize, the three-fold geological story comprises:

1) a pre-Valanginian episode marked by the ending of the Jurassic carbonate platform (first event),

2) an early Valanginian episode marked by significant sea level falls and rises, i.e., forced regressions and major transgressions or drownings,

3) a late Valanginian to early Barremian episode marked by significant distensive tectonic activity (last events) in the whole area.