THE NAMA-GROUP REVISITED

The Nama Group of southern Namibia is a candidate for the Terminal Pro terozoic Global Stratotype Section and Point (GSSP). Desirable charact eristics of a GSSP include a well-preserved index-fossil assemblage, l ittle deformation or metamorphism, well-constrained. isotopic ages, st able-isotope records and magnetostratigraphic control. The age of the Nama Group sediments is now constrained to between 570 and 510 Ma. Ass uming the Gondwana assembly was nearly complete at this same time, the re is a discrepancy between the previously published Nama poles, a rev ised 550-510 Ma apparent polar wander path for Gondwana and the preced ing supercontinental assemblages of Rodinia and Panottia. For these re asons, the Nama Group sediments were resampled in an effort to evaluat e the potential of detailing the magnetostratigraphy of the Nama Group and resolving the discrepancy between the Nama poles and the APWP of Gondwana. Collectively, both the previous studies of the Nama Group an d this one show a complex series of overprints and no easily discernib le primary direction of magnetization. We therefore urge caution in us ing the Nama Group poles in any tectonic models of the Neoproterozoic- Early Palaeozoic. Specifically, the N1 component of magnetization, pre viously identified as a primary magnetization, was discovered in a you nger suite of samples. Therefore, previous tectonic models that used t he N1 magnetization direction as representative of the time of Nama de position should be revised in light of these recent findings.