The epiclastic barrier-island system of the Early‒Middle Jurassic in eastern Spain

Abstract

[Background] During the Early-Middle Jurassic, several mainly volcaniclastic submarine eruptions, which followed well marked lineaments, took place in the Iberian Ranges of eastern Spain. Some of these volcanoes were occasionally emerged during sea-level lowstand periods

[Purposes] In this work we aim to present the signs indicating that a huge volcanic pile, located in the Sierra de Javalambre (Teruel, Spain), could have been subjected to emersion, reworking and colonization by flora. We also intend to date the volcanism and to delimit the most likely period of time when emersion, reworking and colonization were produced.

[Methods] The research work was supported by geological mapping, as well as by preparing stratigraphic sections and their palaeontological sampling. Biostratigraphical dating was achieved though taxonimical determination of ammonites, brachiopods, and data from pre-existing palynological studies.

[Results] As a result of the shallow marine and subaerial partial erosion of the volcanic edifice, epiclastic bodies, some of which show large scale cross-bedding and bar geometry, were generated. These bedforms are interpreted as sandwaves constituting a barrier-island system protecting a lagoon on which low-energy sediments, rich in plant remains, together with washover fan facies were deposited.

[Conclusions] An Early Toarcian, Serpentinum Chronozone age for the volcanism is indicated by the brachiopod and ammonite content of infra- and inter-volcanic sediments. However, burial of the volcanic mound by the carbonates of the surrounding platforms ended in the Late Aalenian Bradfordensis Chronozone, about 10 million years after the eruption. This delay was partly due to a significant regional sedimentary gap marked by the hiatus of the Late Toarcian (from the Late Variabilis Chronozone) to the Late Aalenian (Bradfordensis-Concavum chronozones). The emersion of the volcanic pile, the colonization of the emerged islands by continental vegetation and the instauration of the epiclastic barrier-island system occurred between part of the Aalenian Murchisonae and part of the Bradfordensis chronozones. The concurrence of the porous epiclastic lithofacies together with the organic-rich lagoonal sediments could represent an analogue model of an untypical hydrocarbon system located in neritic position, which could probably be applied in other areas of extensive emerged submarine volcanoes present in the geological record.