Aptian— Albian tectonic pattern of the Basque— Cantabrian Basin (Northern Spain)

Abstract

During the Aptian and Albian thick terrigenous and carbonate successions of sediments up to 5000 m thick, including shallow water rudist limestones (Urgonian facies), were deposited in the Basque– Cantabrian Basin of northern Spain as a result of an intense rift‐related subsidence. Based on criteria from surface and subsurface data, syn‐sedimentary faults, folds, angular unconformities, diapirs and sub‐basins are distinguished within the Urgonian successions. Faults are grouped into N– S, E– W, NW– SE and NE– SW families and most are normal and strike‐slip. Folds are gentle anticlines and synclines related to major faults. The angular unconformities have small hiatuses, poor lateral continuity and they are associated with either folds or tilted blocks. Diapirs are related to the intersection of major basement faults and in at least one instance the diapir was fossilized by Late Albian times. Strong differential subsidence controlled by basement faults determined the division of the basin into many subbasins of different sizes, which acted as depocentres (e.g. Bilbao). Despite the tectonic inversion which affected the basin during the Tertiary and created thrusts in their margins and centre, the present position of the syn‐sedimentary tectonic structures gives approximate clues about the broad structural style and this reveals the original model of basin extension. Features characteristic of strike‐slip identified in different parts of the basin are displaced geological lines, wrench corridors, drag effects, thickness shifts, paired uplifts and basins, vaulting of ‘slabs’, decreasing displacements, horsetail and fault splays, ‘chessboard’, oroflexural bending, pull‐apart geometries, in‐line horst slices, and restraining/releasing bends. Sinistral strike‐slip movements along major NW– SE faults are supposedly responsible for transtension, which characterized the basin particularly during the Albian. In this scenario, the main wrench movements would have concentrated along the Oiz domain (Biscay Tertiary Synclinorium) and is a situation that has more in common with the strike‐slip model proposed by some workers for the western Pyrenees, than with the simple extension models proposed for the northern margin of the Bay of Biscay.

Geologic map of the Basque-Cantabrian Basin and a new tectonic interpretation of the Basque Arc

“…It is customarily assumed that the BCB is a major geological entity that was initiated as a peri-cratonic rift related to Mesozoic opening of the North Atlantic/Gulf of Biscay. It experienced extensive faulting and high subsidence rates during the Cretaceous and was inverted during Tertiary compression related to the Alpine orogeny Rat 1988;García-Mondéjar et al 1996;Cámara 1997;Gómez et al 2002).…”

“…The exceptions are the SE and S outcrops, which present siliciclastic successions of continental to transitional environments, ascribed to the "Escucha Formation". This unit was related to a generalized marine transgression and a less active tectonism than in previous stages (Martín -Chivelet et al 2002;García-Mondéjar et al 2004). Vertical and lateral facies and lithological changes, as well as considerable thickness variation across the BCB, are the rule in this unit, which is likely the most extensively and profoundly studied of the BCB after García-Mondéjar (1979; see Appendix 9).…”

“…López-Horgue et al 2014) also exhibits a considerable internal complexity and remarkable geographical variation. In part, it is associated with instauration of a palaeogeographical organization of the sedimentary basin that perdured up to the Palaeogene (Martín- Chivelet et al 2002;García-Mondéjar et al 2004;Floquet 2004). In the BCB map, the colour assigned to the Albian by the International Stratigraphic Chart was used to represent this unit.…”

The uppermost Albian–lower Cenomanian Bielba Formation of the type-area (Cantabria, northern Spain): facies, biostratigraphy, and benthic Foraminifera

“…1), a basin that formed during the Mesozoic-early Cenozoic through several phases of rifting related to the opening of the Bay of Biscay and the North Atlantic Ocean (Boillot 1986;Rat 1988;García-Mondéjar et al 1996;Martín-Chivelet et al 2002). Rift-related tectonics in the basin during the Late Jurassic-Early Cretaceous created strong structural segmentation into tilted blocks (e.g., Wilmsen 1997) with formation of several sub-basins.…”

Synextensional mid-Cretaceous stratigraphic architecture of the eastern Basque–Cantabrian basin margin (western Pyrenees)

“…Since the area is located at the boundary between the Iberian and Eurasian plates, basin development is intimately linked to the Cretaceous relative motion of these plates, which was governed by the North Atlantic Ocean. This resulted in the opening of the Bay of Biscay during the Mesozoic under extensional to transtensional tectonics (Choukroune and Mattauer, 1978;Montadert et al, 1979;García-Mond ejar et al, 1996) and subsequent convergence and orogenic belt formation due to the northward displacement of the Iberian plate since the Late Cretaceous until the middle Miocene (Srivastava et al, 1990;Roest and Srivastava, 1991;Rosenbaum et al, 2002), which resulted in the inversion of the basin.…”