Obolus Sandstone

The coquina bed of Recent Discinisca tenuis (Sowerby) near the coastline at Liideritz, Namibia has been referred to as a modern analogue of Estonian Upper Cambrian Obolus sandstone (Hiller, 1993). A collection of 10 valves of subfossil Discinisca tenuis from Liideritz was kindly given for the study by Dr Lars Holmer (Uppsala University) and Miss Mari-Ann Motus (Institute of Geology at Tallinn Technical University). 

Our example deals with the Upper Cambrian obolids from the Obolus Sandstone in Estonia and NW Russia (Puura, 1996). As these fossils have been in the centre of the studies of fossil linguloid mineralogy, we give a brief oudine on the evolution of ideas (see Nemliher and Puura, 1996 for the historical review). 

Table 2.4 Apatite lattice parameters of linguloids from Obolus Sandstones, Upper Cambrian, Estonia and NW Russia (from Nemliher and Puura, 1996)...

The diagenetic scenarios controlling the precipitation of other minerals must also influence the precipitation of authigenic apatite. Therefore, we can only point to general trends (1) during fossilization skeletal apatite tends to lose hydroxyl ions, and (2) enrichment with precipitated apatite is common. At the same time, quantitative lattice parameter data from our Obolus Sandstone example cannot be directly used as reference data for different geological settings. 

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