The Aptian Incised Valleys Recorded in the Maestrat Basin (E Iberia)

Carbonate platforms flourished in the Maestrat Basin (E Iberian Plate) during the Aptian recorded two episodes of major sea-level fall. The sedimentary results of lowering sea level during the Aptian were studied in two sub-basins of the Maestrat Basin, namely, Galve (in the western margin) and Morella (in the northern margin). The oldest episode occurred within the Dufrenoyia furcata ammonite zone, during the late early Aptian, whereas the youngest event had an early late Aptian age and occurred around the boundary between the Epicheloniceras martini and Parahoplites melchioris ammonite zones. The sedimentary evidence of such drops in sea level includes erosional, locally incised, subaerial unconformities with paleokarst developed at the platform tops. The amplitudes of sea-level fall are estimated to be in the order of 50 to > 100 m and were measured from the depths of the incised valleys recorded. There are no angular stratal relationships between the truncated sedimentary successions and the incised valley fills. Therefore, these drops in relative sea level are interpreted to be mainly of eustatic origin. The late early and early late Aptian sea-level drops occurred respectively in < 0.9 and < 3 Myr according to the current version of the Geological Time Scale. Such amplitudes (> 10 m) and durations (< 0.9 Myr) of relative sea-level fall and subsequent rise are considered rapid in geological terms, and thus could be the result of glacial eustasy. Nevertheless, clear sedimentological, paleontological, and/or isotopic evidence of significant portions of Earth’s surface covered by extensive ice sheets during the Aptian has not been reported so far.