Kimmeridgian palaeogeography and basin evolution of northeastern Iberia
Abstract Two sedimentary basins were developed during the Kimmeridgian in the northeastern part of Iberia: the Basque-Cantabrian Basin, to the northwest, and the Iberian Basin, to the east. These basins were mainly filled by carbonates deposited in a shallow epicontinental sea that was connected to the open marine realms of both the North Atlantic and the Western Tethys respectively. During the Late Jurassic, they were temporarily linked by means of the Soria Seaway. The uppermost Oxfordian to lowermost Tithonian of northeastern Iberia consists of two depositional sequences. Sequence J3.5 spans latest Oxfordian to early late Kimmeridgian times; Sequence J3.6 spans the late Kimmeridgian and early Tithonian. During Sequence J3.5 coralgal reefs were developed in the sedimentary domains of the Basque-Cantabrian Basin and the Soria Seaway, whereas the marginal areas of the Iberian Basin were dominated by oolitic shoals with variable siliciclastic influence. Outer ramp areas, located in the central and eastern part of the Iberian Basin, were dominated by carbonate muds and marls. During the late Kimmeridgian-earliest Tithonian shallow reefal and oolitic facies prograded over the micritic outer ramp facies. The sedimentation areas were reduced, and Sequence J3.6 was only deposited in the Iberian Basin. Most of the western margin of the Iberian Basin and the southern areas of the Soria Seaway were covered by reefal facies during this sequence. Major transgressive events in the Iberian Basin took place in the latest Oxfordian-early Kimmeridgian, and in the middle late Kimmeridgian, whereas eustatic falls in sea level are recognised at the onset of the late Kimmeridgian and at the Kimmeridgian–Tithonian transition. These events have also been described in other West European basins. Synsedimentary extensional tectonics is also evident, and has been related to the onset of the Late Jurassic-Early Cretaceous rifting stage. Synsedimentary normal faulting resulted in the presence of several troughs and highs within the basin. The tectonic uplift of the western basin margin explains the progressive basinwards shift of the shorelines, as observed in the Iberian Basin towards the end of the Jurassic.