Inversion of an extensional-ramp basin by a newly formed thrust: the Cameros basin (N. Spain)

Abstract

The Cameros basin (Iberian Chain) was developed under a very subsident extensional regime during the latest Jurassic-Early Cretaceous. Its sedimentary fill constitutes a megasequence of more than 5000 m of vertical thickness which contains six depositional sequences. Most of the sediments are continental (alluvial and lacustrine) with only minor marine intercalations. A lateral accretionary geometry at the basin scale shows a SSW-NNE migration of the depocentre and an onlap to the north of the sedimentary sequences on the Mesozoic substratum of the northern boundary of the basin.The overall Mesozoic structure of the basin, as seen from field studies and seismic profile interpretation, is a gentle WNW-ESE synclinorium 30-70km wide and 150kin long. Extension in the pre-basin Mesozoic rocks is very small. The basin boundaries are defined by an unconformity of the basin filling rocks on the former Mesozoic substratum; it is bounded only locally by major faults at surface. The basin is interpreted as an extensional-ramp basin produced over an S-dipping ramp in a blind, flat-lying extensional fault some kilometres deep in the basement. The extensional displacement on the fault produced a synclinal basin which progressively widened with time. The depocentres of the successive depositional sequences were always located above the ramp and migrated to the north, inside the basin, as a result of the hangingwall displacement to the south. From a computer-modelled cross-section, we estimate the total displacement on the extensional fault to be about 33 km. This extension, in the hangingwall, would have taken place in the Pyrenean basin, north of the Cameros basin.Tertiary compression (Palaeogene to Lower-Middle Miocene) inverted the basin by means of a newly formed E-W north-directed thrust. Overthrusting in the Tertiary Ebro basin fill, this new fault formed in the Keuper beds, in a weakness zone with uniform dip within the extensional hangingwall (about 30 km in cross-section). During the deformation it expanded to the north and south until it branched to the Iberian sole thrust, which might coincide with the Mesozoic extensional sole fault. Although this thrust produced a slight (2-3 km) inversion of the basement-Mesozoic cover unconformity, its maximum displacement was of about 28km. Pre-basin Mesozoic rocks overlie the thrust surface and are overlain by the basin-filling rocks. A south-directed imbricate-fan thrust system developed in the southern margin. The total shortening was about 38 km, leading to the complete inversion of the basin.

Exhumation of the Sierra de Cameros (Iberian Range, Spain): constraints from low-temperature thermochronology

“…Ar -Ar and K -Ar ages for peak temperatures are approximately 100 Ma (Goldberg et al 1988;Casquet et al 1992). During the Tertiary the basin underwent tectonic inversion related to Alpine compression that produced folding and exhumation of the whole Mesozoic basin The Cameros Basin sediments were thrusted 25 -30 km north along the Cameros thrust over the Tertiary molasse of the Ebro Basin (Guimerà et al 1995;Casas-Sainz & Gil-Imaz 1998). During the Palaeocene and Eocene, the Sierra de Cameros was the source area for the detrital sediments that were deposited in the Ebro Basin, in particular for its westernmost part (the Rioja Trough) where they reach a maximum thickness of 5 km (Muñoz-Jiménez & Casas-Sainz 1997).…”

“…In a second model Mas et al (1993) and Guimerà et al (1995) (Fig. 2b) interpreted the Cameros Basin as a sag basin that formed on a ramp of an extensional, subhorizontal fault located several kilometres deep in the Variscan basement.…”

Micro-Sized Dolomite Inclusions in Ferroan Calcite Cements Developed During Burial Diagenesis of Kimmeridgian Reefs, Northern Iberian Basin, Spain

“…1), a rapidly subsiding extensional and continental basin developed during the Late Jurassic and Early Cretaceous, which was filled from the Tithonian to middle Albian by up to 5 km of fluvial and lacustrine deposits with rare marine incursions Guimerá et al 1995;Arribas et al 2003). These deposits overlie up to 1.5 km of Triassic and Jurassic rocks Guimerá et al 1995). The basin-fill succession embodies a large cycle or megasequence overlain by an intra-Albian unconformity that corresponds to the base of the Upper Cretaceous post-rift megacycle Salas et al 2001).…”

“…The basal portion of the Upper Cretaceous megacycle consists of upper Albian sandstones overlain by large Upper Cretaceous carbonate-platform deposits García et al 2004). The Cameros Basin was subsequently tectonically inverted during Paleogene to middle Miocene alpine contraction (Guimerá et al 1995;Mas et al 2003).…”

Depositional Depth of Laminated Carbonate Deposits: Insights From the Lower Cretaceous Valdeprado Formation (Cameros Basin, Northern Spain)

“…1), which is the northwesternmost basin of the Iberian Mesozoic Rift System (Mas et al 1993;Guimerà et al 1995). The Cameros Basin was formed during Late Jurassic to Early Cretaceous intraplate rifting in Iberia as a consequence of the opening of the North Atlantic Ocean.…”