Magnesium isotope evidence for enhanced crustal reworking in lowermost Cambrian sedimentary rocks (Kazakhstan)

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Abstract

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.

Original languageEnglish
Article number109452
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume538
DOIs
Publication statusPublished - 15 Jan 2020

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sedimentary rocks
Kazakhstan
reworking
Precambrian-Cambrian boundary
sedimentary rock
isotopes
magnesium
isotope
oceans
weathering
ocean
chemistry
nutrient budget
weathering rate
water currents
water-rock interaction
metazoan
nutrients
hydrochemistry
global ocean

ASJC Scopus subject areas

  • Oceanography
  • Ecology, Evolution, Behavior and Systematics
  • Earth-Surface Processes
  • Palaeontology

Cite this

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title = "Magnesium isotope evidence for enhanced crustal reworking in lowermost Cambrian sedimentary rocks (Kazakhstan)",
abstract = "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.",
author = "Stammeier, {Jessica A.} and Dorothee Hippler and Oliver Nebel and Martin Dietzel",
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T1 - Magnesium isotope evidence for enhanced crustal reworking in lowermost Cambrian sedimentary rocks (Kazakhstan)

AU - Stammeier, Jessica A.

AU - Hippler, Dorothee

AU - Nebel, Oliver

AU - Dietzel, Martin

PY - 2020/1/15

Y1 - 2020/1/15

N2 - 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.

AB - 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.

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