MULTI-BASIN BIOAPATITE RECORDS OF CARBONIFEROUS SEAWATER SR ISOTOPIC COMPOSITION

Seawater Sr isotopic composition has been used as a chronostratigraphic correlation tool and as a proxy for long-term variations in global climate and tectonics throughout the Phanerozoic. The Carboniferous was a time of extensive glaciation, major global tectonic reconfiguration, and a series of climatic and oceanic perturbations, and thus these events should be recorded in Carboniferous seawater ⁸⁷Sr/⁸⁶Sr. The existing seawater Sr isotopic record, reconstructed from bulk carbonate and brachiopod calcite, however, remains moderately resolved, limiting its chronostratigraphic and proxy potential. The resolution of the existing record reflects biostratigraphic uncertainties in multi-basin records, limited temporal resolution, and variable degrees of diagenetic alternation.

Here we present high-resolution ⁸⁷Sr/⁸⁶Sr records of conodont apatite integrated with detailed conodont biostratigraphy from the Naqing section, south China of the eastern Paleotethys Ocean region and Donets Basin, Ukraine of the western Paleotethys. The carbonate slope succession of Naqing provides a continuous depositional records, whereas the Donets Basin provides a U-Pb calibrated, short-eccentricity record of a fluvial-deltaic to shallow-marine carbonate succession. The newly acquired ⁸⁷Sr/⁸⁶Sr data show an overall rise through the Pennsylvanian beginning with a nadir in the middle Visean to the apex in the middle Bashkirian, followed by a decline in earliest Gzhelian. Our records show previously unrecognized changes in rise rate of ⁸⁷Sr/⁸⁶Sr as well as superimposed with 1–2 myr fluctuations in Bashkirian to the early Gzhelian. Notably a Sr isotope plateau characterizes late Bashkirian through first half of Moscovian, coinciding with a major periods of Pennsylvanian glaciation recorded in the Donets onlap-offlap curves. Comparison of conodont ⁸⁷Sr/⁸⁶Sr values with diagenetically screened micrite and brachiopod values exhibits variable differences, with greatest discrepancies between coexisting micrite and conodont. The new high-resolution seawater Sr isotope curve, when integrated with contemporaneous sea level, glaciation history, and δ¹³C and δ¹⁸O records, provides new insight into the interplay between climate and tectonics during the late Paleozoic ice age.