No abstract

Deposition of regressive successions and coeval positive trend in the oxygen stable isotope record in relatively deep marine successions of the upper Pliensbachian of western European basins have been related to a cooling interlude within the warm greenhouse conditions of the Pliensbachian. Sedimentological, cyclostratigraphic and chemostratigraphic analyses carried out in two upper Pliensbachian successions exposed in the Iberian Chain (Obón and San Pedro localities, Spain) allowed the characterization of the imprint of this cooling interlude on the relatively shallow areas of the Iberian carbonate ramp. The upper Pliensbachian succession is characterized by skeletal limestones and encompasses proximal mid-ramp to proximal outer-ramp facies, in which resedimentation and reworking by storm-induced flows controlled the accumulation of bioclastic debris. Two orders of high-frequency, metre-scale sequences have been identified: bundles of beds, and deepening-shallowing sets of bundles. According to the age calibration (previous biostratigraphic data and new strontium isotopes data) and correlation with nearby sections, these A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2 sequences are suggested as formed in tune with the short-term and long-term eccentricity Milankovitch cycles. The isotopic data from brachiopod shells and belemnite rostra indicate progressively increasing δ 18 O and slightly decreasing δ 13 C trends for the uppermost PliensbachianSpinatum Zone, reflecting the influence of cooling conditions. However, facies analysis reflects that the expected coeval long-term regression was interrupted by a tectonically driven transgressive event in the uppermost part of the Spinatum Zone.

A detailed facies and sequential architectural analysis has been carried out along the wedge-shaped shallow marine cross-bedded oolitic-siliciclastic Ricla Member (Kimmeridgian, Northern Iberian Basin). The obtained results are based on fieldwork along the 4x1 km continuous outcrops with the use of high-resolution photomosaics and drone-made videos, which have led to a precise and extensive facies reconstruction. Three main facies that are laterally related (A to B to C) in down-dip direction have been differentiated, which correspond to the topset, foreset and bottomset parts of a sloping depositional surface. Sedimentation was controlled by sweeping drift and downwelling storm-induced currents causing avalanching processes, with the deep action of oscillatory currents. The sedimentary architecture consists in 5 successive units composed by several sub-units, arranged according to different stacking patterns, which reflect the sedimentary response to wave-base oscillations superimposed to the regressive part of a third-order transgressiveregressive cycle. The sedimentological features indicate that this unit, which has been 2 previously interpreted as a dune complex fit with an infralittoral prograding wedge model, as it is observed in geographically close and stratigraphically similar units. The Ricla Member is therefore regarded as an example of a well-exposed grain-supported unit with broad potential application to other prograding grain-dominated lithosomes that do not conform to the traditional sand shoal model.