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.

Keywords: Baja California; geochemistry; metals; phosphate; phosphorite; rare earth elements; sediment

Document Type: Research article

DOI: 10.1080/10641190802382633

Affiliations: 1: Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada, Baja California, Mexico,Lehrstuhl fur Angewandte Geologie, Institut fur Geologie und Mineralogie, Friedrich-Alexander Universitat Erlangen-Nurnberg, Er 2: Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada, Baja California, Mexico