Ecostratigraphic approaches, sequence stratigraphy proposals and block tectonics: examples from epioceanic swell areas in south and east Iberia

An ecostratigraphic approach is proposed here as a supplementary tool to sequence stratigraphic interpretations mainly based on lithology. As a case study, six sections were selected with condensed ammonitico-rosso facies of Early Tithonian age (Albertinum/Darwini Chron) within an epioceanic fringe. This fringe clearly differs in its ecologic, sedimentary, and tectonic frameworks from better documented epicontinental environments. In the studied sections, “short distance differences vs. long distance similarities” have been evaluated by comparing features of macro and microfacies in the ammonitico-rosso facies and by the analyses of 1239 megainvertebrates which were recorded bed-by-bed. Sixteen average faunal spectra containing anywhere from 50 to 150 specimens were analyzed. The ecostratigraphic interpretation is made by considering the ammonites/other megainvertebrates ratio, the assumed ecology and taphonomy for selected ammonite groups, the depositional dynamics, and proposed short-term sea-level changes and local tectonics. The trends observed in the composition of megainvertebrate faunal spectra are explained by ecospace changes caused by eustasy (shared trends in long-distance correlations) and by relative sea-level changes due to the combined action between tectonics and eustasy (counteractive trends in short-distance correlations).