Serra Gelada (Alicante, Spain)

Evidence and implications of a paleo-island setting during the Jurassic-Cretaceous transition

Abstract

This study revisits the uppermost Jurassic-lowermost Cretaceous succession of Serra Gelada (Alicante, SE Spain) based on new field observations and petrographic analyses. It is the second publication presenting and discussing results and interpretations of the PhD thesis of the first author, defended forty years ago. Several previous interpretations, including the identification of mud-mound facies, tectonic breccias, and hardgrounds, are reassessed.

The Tithonian-lower Berriasian limestones are reinterpreted as deposits formed in very shallow-marine environments, ranging from subtidal to intertidal settings and strongly influenced by microbial activity. A major outcome of this study is the recognition of a genuine paleokarst system comprising dolines, caves, chimneys, and chaotic collapse breccias. These features record a significant phase of subaerial exposure during the late Berriasian-early Valanginian and indicate that Serra Gelada formed a small paleo-island, most likely uplifted through salt tectonics involving Triassic evaporites. During the Valanginian transgression, wave erosion produced an abrasion surface across the karstified rocky substrate, while marine sediments progressively infilled the cavities and fractures, ranging from microscopic to decimetric scale. In addition to collapse breccias, coloured micritic infills help visualize repeated episodes of fracturing, cementation, and sediment percolation from the Valanginian to the earliest Aptian. These processes are interpreted in relation to the extensional tectonic phase that affected the External Zones of the Betic Range. Petrographic and cathodoluminescence analyses reveal a complex cement stratigraphy recording successive stages of early marine cementation, meteoric-phreatic diagenesis with limited marine mixing, and later burial diagenesis.

This revised interpretation provides a more robust reconstruction of the geological evolution of Serra Gelada and contributes to a better understanding of the paleogeographic evolution of the Prebetic domain during the Jurassic-Cretaceous transition.