The Kellwasser event in Moravia

Abstract

The intensive rebuilding of the ecosystems including the gradual extinction of the reef communities which is observed in the late Frasnian and early Famennian ages corresponds to the large restriction of the shelf areas as well as to the increase of humidity. While the nearshore areas were often uplifted and/or destroyed, as concerned their previous stable ecosystem, the frontal margin of the reefoid communities progressed deeper basinwards with some ingressions and consequent replacement by the basinal, both pelagic and benthic communities. The terrigenous phyto-debris, oogonies of Charophyta, fish remains and other indications of rising climatic humidity are noticed from Moravian shelfs.

Additionally to this, the rough evolutionary pattern of these changes appears to be eustatic changes of the sea level. The raising of the anoxic water level in the depression areas accompanied by the extinction of some basinal taxa is supposed to be contemporaneous with the particular transgressions on the reefoid shoals. On the other hand the extinctions of the reefoid communities can be placed into the regression levels. "Black" transgressional (lagoonal, sebkha) horizons occur on the carbonate shoals. However, the particular crisis in the reefoid communities which were under stress of the great eco-factors can be iniciated also by other very fine causes. The main crises of the reefoid communities in Moravia are correlated with the three levels:

• i) near the limits of the Lower and Upper Pa. gigas Zone (top of the Crassioalveolites domrachevi coral Zone)

• ii) at the top of the Upper Pa. gigas Zone (top of the lower Scoliopora denticulata vassinoensis coral Zone)

• iii) in the Middle to Upper Pa. triangularis Zone; always somewhat higher then the "black" crisis of the basinal facies are referred.

The total ceasing of the late Frasnian to early Famennian shallow water corals and stromatoporoids in Moravia was found much higher on profile, at the Pa. crepida Zone (Křitiny HV 105 borehole, Mokrá — Western Quarry).