Peritidal Carbonate–Evaporite Sedimentation Coeval to Normal Fault Segmentation During the Triassic–Jurassic Transition, Iberian Chain

Abstract

Around the Triassic-Jurassic transition, a major tectonic rifting phase affected the northern part of the Iberian Basin (northeast Spain). Extensive normal faulting resulted in basin segmentation, as reflected by the rapid thickness and facies variation of the syn-rift, shallow-marine to supratidal carbonate-evaporite units. The upper Rhaetian-Hettangian syn-rift units exposed around the locality of Morata de Jalón (northeast Spain) provide good exposures that enable a precise sedimentological and structural analysis. The study of these units was achieved through geological mapping of an area of 10 km 2 , facies characterization, correlation of seven selected logs (vertical thickness from 40 m to 135 m), and measurement of normal faults, fractures and slump folds. The orientation of the major syn-sedimentary normal faults (NW-SE to NNW-SSE) suggests an origin through reactivation of late Variscan faults located within the Palaeozoic basement. However, the orientation of the newly formed faults and joints indicates a main N-S extension direction. The tectonosedimentary evolution of the studied basin can be summarized in two stages:1 at the end of the Triassic, a subsiding salina formed in the downthrown blocks of two normal faults -salina deposits were sourced from marine waters and, also probably, from the weathering of previously deposited evaporite-rich units; 2 during the Hettangian, tectonic reactivation combined with the long-term regional sea-level rise resulted in the formation of a tidal flat complex.These graded, in the areas of greater subsidence, into shallow-marine carbonate platform deposits. Syn-sedimentary fracturing affected the early lithified carbonates, favouring the formation of collapse-breccias in the tidal-flat environment, and limestone rudites (sedimentary breccias and conglomerates) in the subtidal domain, formed and partly transported as submarine debris flows.

Continuity and facies heterogeneities of shallow carbonate ramp cycles (Sinemurian, Lower Jurassic, North-east Spain)

“…2. Following a widespread latest Triassic unconformity (San Román & Aurell, 1992; Aurell et al. , 2007), there was a long‐term sea‐level rise, up to a maximum transgressive peak in the middle Toarcian, bifrons Zone (Aurell et al.…”

Salt tectonics vs. inversion tectonics: The anticlines of the western Maestrazgo revisited (eastern Iberian Chain, Spain)

“…Diagenetic dissolution of evaporite sequences (probably including anhydrite levels) provided ideal conditions for the formation of the widespread Hettangian collapse-breccia (e.g. Aurell et al, 2007;Bordonaba & Aurell, 2002;Gómez et al, 2007;Hernández et al, 1985;Ortí et al, 2017Ortí et al, , 2020. 6.1.3 | Remarks on the 'Jurassic-Early Cretaceous unconformities related to diapiric uplift'…”

“…Around the Triassic-Jurassic transition, intensification of extensional tectonics favoured the localized deposition (up to 200 m) of alternating peritidal limestones and evaporites (Aurell et al, 2007;Ortí et al, 2017Ortí et al, , 2020San Román & Aurell, 1992) or evaporite-dominated units, especially in the area situated close to the boundary with the Cenozoic Ebro basin (Lecera Fm; Bordonaba & Aurell, 2002). Diagenetic dissolution of evaporites contributed to the development of carbonate breccia in most parts of the region (San Román & Aurell, 1992).…”