Strontium isotope stratigraphy (SIS) dating of the Bathonian regression in western Tethys (Mallorca island)

Abstract

The Sr-isotope stratigraphy (SIS) method has been applied to a Middle Jurassic section of Mallorca (Coves d’Arta) to improve its age control. The Middle Jurassic stratigraphy of this section, more than 220 m thick, is unique in the Mallorca island due to the existence of slope mudstones (Sa Talaia mudstones) evolving upward to a shallow oolitic platform (Coves d’Arta limestones). These slope mudstones and oolitic platform prograde over slope deposits of the Cutri Formation, without any evidence of unconformity in between. The age of this distinctive progradation to a shallow oolitic platform in Coves d’Arta is still unresolved due to the scarcity of age diagnostic fossils through the studied succession and the ambiguity of the previous information, despite being crucial information for the paleogeographic reconstructions of the Middle Jurassic of the Balearic Domain and therefore of the Western Tethys. New age estimates using the SIS method throughout the Coves d’Arta succession has allowed to obtain 87Sr/86Sr values ranging from 0.706976 to 0.707082, supporting an age compatible with the Early–Late Bathonian (~ 168.3–166.1 Ma) for the analysed portion of the succession (Upper Member of the Puig d’en Pare Formation to the transition to the Coves d’Arta limestones). This age has important implications for improving the stratigraphic position of other stratigraphic Jurassic units (i.e. Cutri Formation) and for the paleogeographic reconstruction of the Middle Jurassic of Mallorca. In consequence, the toe of slope resedimented oolitic bodies (i.e. Cutri Formation), which deposited in large areas of Mallorca (Serres de Llevant Domain), changed laterally, toward marginal highs, to shallow Bahamian oolitic platforms (Coves d’Arta limestones), which end in a regressive phase of a Middle Jurassic (Bathonian) platform—slope system. This Bathonian regressive sequence is compared with others recognized along Tethyan basin that began at the end of the Bajocian and culminated in the Middle–Late Bathonian.