Basal Cambrian reworked phosphates from Spitsbergen (Norway) and their implications

Abstract

AbstractSeveral phosphatic zones are associated with the oldest remains of shelly fossils on the arctic island of Spitsbergen. The phosphate occurs as reworked nodules and layers associated with a disconformity. A gap in the acritarch biostratigraphic record supports a hiatus associated with the phosphatic zone. Palaeogeographic positions for Svalbard, both (1) as a single unit, and (2) as three isolated parts prior to Caledonian tectonism are consistent with conditions favourable to at least minimal amounts of upwelling. However, upwelling may not have been a prerequisite for development of these phosphate deposits. These phosphates were deposited in a nearshore shelf environmnt which contrasts with the outer shelf setting of many modern and recent phosphate deposits.Geochemistry of the Lower Cambrian phosphates of Spitsbergen varies with the mode of phosphate occurrence. Concretionary phosphate clasts are chemically zoned such that their centres are enriched in P2O5 and CaO and are depleted in A12O3, SiO2, and K2O. Laminated and thinly bedded phosphate shows no chemical zonation within clasts. Phosphate cements are the most pure with respect to calcium phosphate.This thin phosphatic zone of Svalbard is minor when compared with thicker and richer Lower Cambrian phosphate deposits, particularly those in the Soviet Union, Southeast Asia, and Australia. Coupled with the near absence of phosphate in some extensive Proterozoic to Lower Palaeozoic successions (e.g. western North America), this emphasizes the fact that widespread Lower Cambrian phosphate deposition was unevenly distributed. Althouth the Upper Proterozoic and Lower Cambrian are characterized by enhanced phosphogenesis, palaeogeographic position was also apparently critical to deposition of phosphatic sediments.