THE PRETORIA SALTPAN - A 200,000 YEAR SOUTHERN AFRICAN LACUSTRINE SEQUENCE

The Pretoria Saltpan is a circular crater 1130 m in diameter and is si tuated some 40 km N of Pretoria (lat. 25-degrees 34'30''/long. 28-degr ees 04'59''E). A recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sedim ents (chiefly organic muds, underlain below 30 m depth by micrites) wh ich rest upon a further 61 m of coarse clastic debris. Granite bedrock was encountered at -151 m. Broad sedimentary zones correspond with ma jor phases in the evolution of the crater lake. Superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales. C-14 age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m/2000 yr, suggesting that the lacustrine sequence may span almost 200,000 yr. Over this period major environmental changes are apparent from sedimentological, chemical, mineralogical and isotopic analyses o f the core and studies of the pollen spectra and diatom assemblages pr esent within it. This long continental sequence is therefore providing a high-resolution palaeoenvironmental record for southern mid-latitud es over much the same period as is covered by the Vostok ice-core in A ntarctica.