TY - JOUR
T1 - Constraining the conditions of phosphogenesis
T2 - Stable isotope and trace element systematics of Recent Namibian phosphatic sediments
AU - Lumiste, Kaarel
AU - Mänd, Kaarel
AU - Bailey, Jake
AU - Stüeken, Eva E.
AU - Paiste, Kärt
AU - Lang, Liisa
AU - Sepp, Holar
AU - Lepland, Aivo
AU - Kirsimäe, Kalle
N1 - Publisher Copyright:
© 2021 Elsevier Ltd
PY - 2021/6/1
Y1 - 2021/6/1
N2 - Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ phosphorites are scarce. In this contribution, we investigate the trace element and sulfur, nitrogen and organic carbon stable isotope composition of Recent in-situ phosphatic sediments off the coast of Namibia. Also, we examine the reliability of different widely used geochemical proxies in phosphatic sediments. Our results suggest a shift from sulfidic to suboxic conditions, coinciding with the maximum in solid calcium phosphate mineral concentration. This shift is accompanied by unidirectional changes in Mo and Re enrichments and TOC abundance. Relatively low pyrite δ34S values (ca −20‰) of phosphatic sediments indicate open system fractionation during phosphogenesis. The initiation of phosphogenesis is also accompanied by negative shifts in sedimentary δ13Corg and δ15N values. Phosphate associated sulfate (PAS) δ34S values are lower than modern seawater sulfate values, suggesting the involvement of chemolithotrophic sulfur oxidation. Our results show a shift in redox conditions from sulfidic to (sub)oxic, coupled with active sulfur cycling are prerequisites for phosphogenesis. Phosphatic sediments show substantial enrichments in U and V highlighting the complexity of using these elements, as well as V/(V + Ni) and V/Cr, as redox proxies particularly in phosphorites and phosphatic sediments.
AB - Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ phosphorites are scarce. In this contribution, we investigate the trace element and sulfur, nitrogen and organic carbon stable isotope composition of Recent in-situ phosphatic sediments off the coast of Namibia. Also, we examine the reliability of different widely used geochemical proxies in phosphatic sediments. Our results suggest a shift from sulfidic to suboxic conditions, coinciding with the maximum in solid calcium phosphate mineral concentration. This shift is accompanied by unidirectional changes in Mo and Re enrichments and TOC abundance. Relatively low pyrite δ34S values (ca −20‰) of phosphatic sediments indicate open system fractionation during phosphogenesis. The initiation of phosphogenesis is also accompanied by negative shifts in sedimentary δ13Corg and δ15N values. Phosphate associated sulfate (PAS) δ34S values are lower than modern seawater sulfate values, suggesting the involvement of chemolithotrophic sulfur oxidation. Our results show a shift in redox conditions from sulfidic to (sub)oxic, coupled with active sulfur cycling are prerequisites for phosphogenesis. Phosphatic sediments show substantial enrichments in U and V highlighting the complexity of using these elements, as well as V/(V + Ni) and V/Cr, as redox proxies particularly in phosphorites and phosphatic sediments.
KW - Phosphatic sediments
KW - Phosphogenesis
KW - Redox
KW - Stable isotopes
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U2 - 10.1016/j.gca.2021.03.022
DO - 10.1016/j.gca.2021.03.022
M3 - Article
AN - SCOPUS:85104295785
SN - 0016-7037
VL - 302
SP - 141
EP - 159
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -