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Keywords:

  • Active faulting;
  • carbonate platform;
  • dissolution cavities;
  • hydrothermal calcite;
  • Late Albian;
  • sandstone fills

ABSTRACT A calcite mass more than 1·5 km long and 20 m wide crops outs along the faulted margin of the Albian carbonate platform of Jorrios in northern Spain. The mass contains abundant dissolution cavities up to 7 m long and 1 m high, filled with cross-stratified quartz sandstone and alternating sandstone–calcite laminae. Similar cavities are also present in a 50-m-wide zone of platform limestones adjacent to the calcite mass that are filled with limestone breccias and sandstone. The calcite mass has mean δ18O values of 19·6‰ (SMOW), whereas platform limestones have mean δ18O values of 24·4‰ (SMOW). Synsedimentary faulting of the carbonate margin and circulation of heated fault-related waters resulted in replacement of a band of limestone by calcite. Soon after this replacement, dissolution by undersaturated fluids affected both the calcite mass and the adjacent limestones. Percolating marine quartz sand filled all dissolution cavities, sometimes alternating with precipitating calcite. The resulting cavities and fills, which recall products of meteoric diagenesis, are attributed to a hydrothermal origin based on their geometry, occurrence along the profile and synsedimentary tectonic relationships. The early faulting and diagenesis are related to local extensional tectonism in a large-scale strike-slip setting. Movements occurred during the early dispar/appenninica zone of the Late Albian.