Rare Earth and Metal Geochemistry of Land and Submarine Phosphorites in the Baja California Peninsula,Mexico |
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| Authors: | L W Daesslé J D Carriquiry |
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| Institution: | 1. Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Ensenada , Baja California, Mexico;2. Lehrstuhl für Angewandte Geologie, Institut für Geologie und Mineralogie, Friedrich-Alexander Universit?t Erlangen-Nürnberg , Erlangen, Germany walter@uabc.mx;4. Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Ensenada , Baja California, Mexico |
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| Abstract: | The geochemical composition of phosphorites and phosphatic sediments in the Baja California peninsula is studied and used to assess the environment in which phosphogenesis took place. The deposits are classified in three groups: (1) stratified phosphorites, (2) phosphatic sandy sediments from beaches and dunes, and (3) submarine sediments. Some of the elements that might have substituted Ca and PO4 during francolite mineralization were studied by means of ICP-AES. Significant differences are seen in the concentration of these metals (e.g., Cr = 72-406 μg g?1 and V = 17-198 μg g?1), indicating that their concentration is not only controlled by the P2O5 concentration, but also by paleo-environmental conditions existing during francolite precipitation. Shale normalized REE patterns suggest two main environments of formation: (1) a strong negative Ce anomaly (< ? 0.3) and La enrichment (La/Nd ≥ 1) enrichment, suggesting well oxygenated shelf environments and probably lower light REE weathering, and (2) a weak negative Ce anomaly (> ? 0.3) and La depletion (La/Nd ≤ 1) suggesting shallower waters or restricted circulation and probably LREE weathering. |
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| Keywords: | Baja California geochemistry metals phosphate phosphorite rare earth elements sediment |
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