Diatomaceous sedimentation in late Neogene lacustrine basins of western Macedonia, Greece

Several lacustrine basins were formed by late Miocene tectonic processes in western Macedonia, Greece. These were occupied by a series of lakes and wetland swamps during the late Miocene and early Pliocene giving rise to diatomaceous claystones, siltstones and diatom-bearing tufa deposits. Diatoms are rare or fragmentary in sandstones and chemical sediments, and are absent in conglomerates. The Fe²⁺-rich phosphate minerals anapaite and vivianite are present in parts of the diatomaceous siltstones. Six major diatom groups were identified using cluster and correspondence analyses, each of which tends to be associated with a particular lithofacies. The floras are indicative of mildly acidic to alkaline water of varying depths. The dominant taxa include Aulacoseira ambigua, A. distans, Cyclotella iris and several of its varieties, C. aegeae, C. castracanei, C. elymaea, C. ocellata, and two unidentified Cyclotella. Fragilariaceae are common, consisting mainly of Fragilaria bituminosa, Pseudostaurosira brevistriata, P. zeilleri, Staurosira construens, Staurosirella leptostauron, and S. pinnata. Locally, chysophycean stomatocysts are common, suggesting more oligotrophic conditions. Nine diatom stages are recognized in the Lower Neogene Series at Kariditsa (Kozani basin), reflecting shallow swamps, small alkaline lakes, and terrestrial settings. The Upper Neogene Series rocks are characterized by Mg-rich carbonates such as hydromagnesite, huntite and magnesite. A detailed stratigraphy was developed for Mio-Pliocene deposits in the Florina basin at Klidi. Parts of this sequence show clear cyclicity in both the sediments and the diatom floras, with shallow-water diatoms repeatedly giving way to taxa indicative of deeper conditions. Larger-scale, shallow-deep cycles are also present and may be related to precession- and eccentricity-forced climate change.