Geophysical records of dispersed weathering products on the Frasnian carbonate platform and early Famennian ramps in Moravia, Czech Republic: proxies for eustasy and palaeoclimate

摘要: Abstract An exceptionally high sea level in Frasnian times (early Late Devonian) changed many peneplained, cratonised and tectonically undisturbed continental margins of tropical belts into carbonate platforms which became covered by thick banks limestone. The stages marked very pure carbonates developed during partial sea-level highstands since, when the flooding reached its maximum, shoreline was distant conditions for reef growth were good. increased extension emerged, flat, coastal areas coupled with an opposite situation, oscillating fell to momentary minimum accommodation space available accumulation material low. Subaerially exposed surfaces subject weathering products dispersed aeolian or aquatic means form layers these materials trapped carbonates. This overall scenario relating trapping tested at geographically isolated platform a stable only slowly subsiding basement (Eastern Moravia, Czech Republic). amounts limestone documented using combined methods γ-ray logging, spectrometry magnetic susceptibility measuring, i.e. according their radioactivity (K, Th U) magnetism (Fe). Six third-order eustatic cycles have been inferred from data, estimated period 1 Ma. especially Frasnian/Famennian (F/F) transition brought total destruction least strong overlay on this hypothetical background setting. record fluctuations F/F interval is shown oscillations offsets related pronounced hiatuses surfaces. Such rapid fluctuation typical glacioeustatic control, although present estimates maximum amplitudes are larger than realisable glaciation events may be explained combination tectonoeustatic models. Comparison sections between centre periphery substantiates concept that shorelines rapidly prograding. Very low early Famennian depositionary systems extensive narrow ramps positioned out down extinct bank slopes. central parts Eastern Moravian also other world not normally sediments, transgressive onlaps above any crystalline highs observed therefore drowned reefs periphery, emphasised geologists, reflect sliding tectonic subsidence blocks rather rise level.