Abstract

Salda Lake in SW Turkey is a highly alkaline (pH > 9) water body with waters enriched in magnesium. Microbial stromatolites along shorelines contain a microflora of diatoms and cyanobacteria with extensive associated biofilms. Together these are responsible for precipitation of hydromagnesite, although distribution is not congruent with either cells or films. Deposition has continued over several thousand years and is independent of both lake volume and the general concentration of lake waters. The lake is rimmed on three sides by serpentinites and on the fourth by dolomite. The bulk of the water entering the lake is meteoric, fed via extensive gravelly alluvial fan deltas (with predominantly serpentinite pebbles) whose total areas and catchments exceed that of the lake. These waters are significantly cooler than surface waters of the lake, and there is no evidence for derivation from hot springs. The magnesium is thought to have been leached from the gravels. Extensive areas of recent sediments accumulating on shorelines have apparently formed by mechanical breakdown of microbialites. Similar deposits form conspicuous terraces in two areas and point to the long-term effectiveness of these processes. Terrace deposits are modified by a variety of subaerial processes, including growth of hydromagnesite cements. No microbial structures are preserved in these, and it is presumed that they are destroyed during reworking. Fine-grained hydromagnesite sediment derived from shorelines and from terraces is suspended in the water column during storms and is probably redeposited as turbidites in the deeper parts of the lake. Sediments of this kind may be a useful analogue for some ancient and economically important stratiform magnesite deposits.

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