Nature and timing of Late Mississippian to Mid-Pennsylvanian glacio-eustatic sea-level changes of the Pennine Basin, UK
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The Pennine Basin of northern England contains a comparatively complete Serpukhovian– Moscovian succession characterized by high-resolution ammonoid zonation and cyclic paralic sedimentation. Two new isotope dilution thermal ionization mass spectrometry zircon ages from a bentonite deposited during the Arnsbergian (mid-Serpukhovian) regional substage and tonstein of earliest Bolsovian (early Moscovian) regional substage have been determined. The weighted mean 206Pb/238U ages of 328.34 ± 0.55 and 314.37 ± 0.53 Ma (total uncertainty), respectively, require modification of the time scale for the Western Europe regional chronostratigraphy. The areal extent of acme ammonoid facies is used as a proxy for the magnitude of 47 discrete flooding events. Incised valleys (major sequence boundaries) are used as a proxy for the magnitude of sea-level falls. The frequency of these events, in the light of the new radiometric dating, indicates the following: (1) there is temporal coincidence between major glaciations in Gondwana and phases of increased frequency of sequence boundaries in the Pennine Basin; (2) high-amplitude flooding surfaces have an average frequency of c. 400 ka; (3) average cycle durations during the Pendleian–early Arnsbergian and Chokierian–Bolsovian, of c. 111 and c. 150 ka, respectively, reflect short-duration eccentricities; (4) multiple flooding surfaces with the same ammonoid assemblages may equate with sub-100 ka precession or obliquity frequencies.