Dr. Fűköh Levente szerk.: Malakológiai Tájékoztató 27. (Eger, 2009.)

SÁNDOR, R.-SÜMEGI,P.: New preliminary data for evolution of the Holocene Hungarian Mollusc fauna

The second malacological zone formed between the depths of 200-160 cm (9000-7000 BP years). The rheophilous elements decline and disappear in this zone. The first terrestrial elements (Succinea putris, Vallonia puchella, Vertigo antivertigo) emerged in this zone. The Mollusc fauna composition suggests that the Valvata cristata-Bithynia leachi-Bithynia tentaculata paleoassociation developed in this zone. Elements with different ecological requirements (deep and shallow water, open and dense aquatic vegetation) dominated in the same quantity. This phenomenon is explicable with the periodic flood of River Danube. Macrofossil concentration was lower. Typha, Phragmites plants were the major macrobotanical remains. Pioneer mud vegetation and water-crowfoot communities formed in this zone. The water level of the initial phase of this horse-shoe lake was somewhat lower and fluctuating. The third malacological zone formed between the depths of 160-100 cm (7000-3000/ 3500 BP years).The Valvata cristata shells were frequent (more than 50%). The frequency of aquatic (Lymnaea palustris, Pisidium spp., Segmentina nitida), amphibious (Succinea oblonga, Oxyloma elegáns, Carychium minimum) and strongly hygrophilous terrestrial elements (Vertigo antivertigo, Vallonia enniensis) is the highest in this zone. On the basis of radiocarbon dating the first agricultural human populations occupy the territory at this time. Presumably the high quantity of sediment and terrestrial mollusca shell got into the channel derived from the shore, because of human impact. Typha, Phragmites remains were the major peat components, with in combination of Carex elata remains. Remains of water-lily communities detected in this zone. Water table was higher, but water surface was covered by closed plant mat. From 100 cm the aquatic malacofauna changed. Valvata cristata declines, and the frequency of Bithynia tentaculata increased, indicating the eutrophication of water. The xerophilous and mesophilous elemets (Pupilla muscorum, Vallonia costata, Helicopsis striata) emerge among the terrestrial species. Carex elata and Phragmites australis remains were the major peat components and Fe, K rich peat formed on the top of the peat series. Water table is somewhat lower and Caricetum elatae plant community started covering the peatland surface during the last 3000 years. Summary The Red Marsh get well oxygenised, nutrient and carbonate rich surface water since the sediment accumulation have started. Then the paleochannel of the Red Marsh isolated from the flood waters of the Danube and got only underground water since the Early Holocene, when the increased erosion activity, caused by the Holocene neotectonic subsidence of the Solti Plain, got large amount of inorganic sediment to the cannel. Phragmites dominated plant associations emerged only in the Early Holocene. Tussock-hollow forming Caricetum elatae plant association emerged in the fragmented chanell, because of the increasing trophity and improving climate after 3500/30000 year BP. Paleoassociations determined with the help of malacological data form a line of successions with the first fluvial phase appearing as early as 13.000 - 9.000 BP. This faunal assemblage must have been linked to a fluvial system. The appearance of several fluvial species ( Valvata piscinalis, Lithoglyphus naticoides, Planorbis cf. carinatus, Unio cf. crassus, Pisidium amnicum) is also connected to this sandy layers.