Stratigraphic and oxygen isotope evidence for My-scale glaciation driving eustasy in the Early-Middle Devonian greenhouse world
Abstract
Million year-scale (3rd-order) depositional sequences (few 10s to ~100 m-thick) are common in the Devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin. Tectonically driven changes in mid-ocean ridge spreading rates/lengths are too slow to account for the calculated 3rd-order rise/fall rates and typical orbital frequencies (~20- 400 ky) are too fast.
We analyzed oxygen isotopes from conodont apatite to evaluate if Early-Middle Devonian 3rd-order sea-level changes were controlled by paleoclimatically driven ice volume (glacioeustasy) and seawater temperature change (thermo-eustasy). Two successive depositional sequences in the western U.S. (Nevada) and Czech Republic (Prague Basin) were sampled.
The 18O values range from 1.78% to 2.02% (SMOW) and show similar trends across the Emsian-Eifelian boundary.