Magnetostratigraphy of the middle Miocene La Muela section: a chronostratigraphy across the central Ebro basin lacustrine units

During the early Miocene, the Ebro Basin evolved as an endorheic depression bounded by the Pyrenees, the Iberian Range, and the Catalan Coastal Ranges. In its central sector, extensive and laterally continuous lacustrine systems developed under variable climatic conditions, including warm-humid phases such as the Miocene Climatic Optimum. The La Muela section is composed of lacustrine sediments from the southern margin of the Ebro Basin’s central lake. The La Muela section documents significant geochemical changes in the lake system, beginning with mudflat environments, followed by evaporitic conditions, and subsequently a return to carbonate-dominated deposition. The well-exposed outcrops and the possibility to correlate this record with other sectors of the basin make it an ideal site for reconstructing environmental variations of the complete system and understanding its geochemical changes. Achieving an accurate correlation between the different sedimentary records requires very fine time correlation lines.
To address this correlation problem, we present a local magnetostratigraphy for the La Muela section based on the analysis of 155 samples distributed over a thickness of 190 meters. A correlation with the Global Geomagnetic Polarity Timescale allows us to propose a new chronology that includes the early to middle Miocene transition. By means of basin-wide magnetostratigraphic correlations, we determine local sedimentation rates across the different sectors. Finally, we discuss the timing and relevance of the major compositional changes in the lacustrine settings, which, constrained by isotopic records, reveal the environmental evolution of the basin.