Primary Phosphatic Oolites from the Lower Cambrian of Spitsbergen

Abstract

Thin sandstones and sandy lenses within the Lower Cambrian Topiggane Shale Member of the Tokammane Formation from Ny Friesland, Spitsbergen (Svalbard), consist of medium to fine sand-size quartz, glauconite, and sparse feldspars and stable heavy minerals which are coated by concentrically laminated phosphate. The general inverse proportionality of the thickness of the phosphatic coatings to the detrital grain size suggests an energy/mass control of the phosphatic coating growth process. Four lines of evidence support a primary origin for the phosphatic oolitic coatings: 1) The detrital grains would be unsupported without oolitic coatings but as oolites they are grain supported; 2) the microscopic details of the concentrically laminated oolitic coatings are exquisitely preserved implying lack of replacement; 3) the guest-host relationships of the phosphate to subsequent diagenesis, involving silica and dolomite, indicate an early formation for the phosphate; and 4) there is a total lack of relict carbonate or textural evidence suggesting a replacement origin for the phosphate. Syntaxial overgrowths on the detrital quartz grains fill pores between the phosphatic oolites and occasionally displace the oolitic coatings but do not replace them. Minor dolomitic cement in burrow structures is exclusively external to the phosphatic oolites and neither displaces nor replaces the phosphate. Underlying and overlying strata, both of which are interpreted as having formed in tidal environments, suggest that the Topiggane Shale was also deposited on the shallow marine, passive margin of the north American plate bordering the Iapetus (Proto-Atlantic) Ocean.