Other records of seawater chemistry provide supporting evidence for changes in tectonic activity and enhanced continental weathering during the formation of the Great Unconformity. For example, the average 87Sr/86Sr of sea water increased during the Neoproterozoic
(Fig. 4). This long-term signal is attributable to the increasing concentration of 87Sr in continental crust due to the decay of 87Rb, and to the long-term erosion and progressive exposure of 87Sr-rich granitic rocks required to form the Great Unconformity. During the Cambrian,
87Sr/86Sr increased more rapidly to achieve a 900 Myr maximum (that is, a maximum over the past 900 Myr) near the end of the Sauk transgression2, a signal we attribute to enhanced weathering of continental …show more content…
The 900 Myr Cambrian peak in 87Sr/86Sr was not approached again until the recent, possibly indicating enhanced removal of
Phanerozoic sedimentary cover during Cenozoic orogenesis and global climate change15.
Congruent evidence for enhanced weathering of continental crust during the Sauk transgression is provided by eNd, an isotopic tracer with a short oceanic residence time that is sensitive to the mean age of continental crust undergoing chemical weathering. Average seawater eNd declined through the Cambrian to reach a long-term minimumat the peak of the Sauk transgression26 (Fig. 4), reflecting increasingly important input from ancient continental basement rocks as the Sauk transgression progressed from relatively young continental margins into generally older cratonic interiors.
Perhaps the strongest evidence for an increased reservoir and flux of continental chemical weathering products to the global ocean is provided by direct measurements of [Ca21] in evaporite fluid inclusions.
Concentrations of Ca21 in sea water rose precipitously from
(Fig. 4). This long-term signal is attributable to the increasing concentration of 87Sr in continental crust due to the decay of 87Rb, and to the long-term erosion and progressive exposure of 87Sr-rich granitic rocks required to form the Great Unconformity. During the Cambrian,
87Sr/86Sr increased more rapidly to achieve a 900 Myr maximum (that is, a maximum over the past 900 Myr) near the end of the Sauk transgression2, a signal we attribute to enhanced weathering of continental …show more content…
The 900 Myr Cambrian peak in 87Sr/86Sr was not approached again until the recent, possibly indicating enhanced removal of
Phanerozoic sedimentary cover during Cenozoic orogenesis and global climate change15.
Congruent evidence for enhanced weathering of continental crust during the Sauk transgression is provided by eNd, an isotopic tracer with a short oceanic residence time that is sensitive to the mean age of continental crust undergoing chemical weathering. Average seawater eNd declined through the Cambrian to reach a long-term minimumat the peak of the Sauk transgression26 (Fig. 4), reflecting increasingly important input from ancient continental basement rocks as the Sauk transgression progressed from relatively young continental margins into generally older cratonic interiors.
Perhaps the strongest evidence for an increased reservoir and flux of continental chemical weathering products to the global ocean is provided by direct measurements of [Ca21] in evaporite fluid inclusions.
Concentrations of Ca21 in sea water rose precipitously from