Magnesium isotope evidence for enhanced crustal reworking in lowermost Cambrian sedimentary rocks (Kazakhstan)
| Autor: | Dorothee Hippler, Oliver Nebel, Martin Dietzel, Jessica Alexandra Stammeier |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
010506 paleontology
Radiogenic nuclide Proterozoic Ocean chemistry Ocean current Geochemistry Paleontology Weathering 010502 geochemistry & geophysics Oceanography 01 natural sciences Gondwana Phanerozoic Sedimentary rock Ecology Evolution Behavior and Systematics Geology 0105 earth and related environmental sciences Earth-Surface Processes |
| Zdroj: | Palaeogeography Palaeoclimatology Palaeoecology |
| Popis: | The transition from the Proterozoic to the Phanerozoic Eon was accompanied by the rise of metazoan life, a key and unique biogeochemical milestone in Earth's history. Concomitant continental re-organization and collision were associated with enhanced continental reworking and changes in global ocean currents, with profound impacts on continental weathering rates, riverine run-off and associated changes in the ocean nutrient budget. The causal relationship between the geological re-organisation of continents and the biologic evolution of marine life, however, remains elusive. In this study, we investigate phosphatic shallow-water sedimentary successions from Kazakhstan, which host key marker horizons from the Precambrian-Cambrian (Pc-C) boundary. We show that a rapid change (over ca. 3 Myrs) towards heavier stable Mg isotope compositions of the phosphatic sedimentary deposits in Kazakhstan, which we consider representative for contemporaneous ocean chemistry, co-varies with changes in radiogenic Sr isotope signatures. We propose that ocean chemistry at the Pc-C boundary, represented through this co-variation, was strongly affected by continental re-organization and associated weathering, which, in analogy, would have affected ocean nutrient levels. A rapid reversal of isotope compositions towards signatures similar to those prior to the isotope excursion likely reflects the fading influence of weathering and a buffering of water-rock interactions during oceanic spreading. We conclude that, based on the positive, coupled 87Sr/86Sr- δ26Mg isotope spike in ocean water chemistry, a link between Gondwana re-organization at the Pc-C boundary and the marked change in marine fauna seems plausible. |
| Databáze: | OpenAIRE |
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