engleski

The Megabreccia Facies of the Middle Pleistocene Glacial Deposits of the southwest Croatia ID 3049

The Middle Pleistocene glacial deposits with megabreccia facies occur at many locations at altitudes between 1 m and 800 m a.s.l. within the study area, which includes northern Adriatic islands (Krk, Rab, Pag) and coastal zone of the southwest Croatian mainland (Southern Velebit Mts.(Velika Paklenica) and Northern Dalmatia (Ždrilo, Novigrad Sea coast, Obrovac)). The megabreccias are erosional remnants of terminal, basal and lateral dump moraines. They occur in association with kame-terrace deposits (Baška valley on Krk island and Velika Paklenica) or with proglacial fluvial or lacustrine sediments (Novigrad Sea coast and Ždrilo Cove). Their main characteristic are extra large limestone boulders and megablocks that “float” in the coarse-grained “matrix”. The boulders are commonly 1 to 10 m in diametre, but their maximum size is nearly 25 m. Boulders are subrounded to medium rounded, faceted with rounded keels and usually polished. Many have preserved glacial striae. Their orientation is usually random, although prefered orientation showing push direction has been noticed in Velika Paklenica, Ždrilo and Novigrad Sea coastal section. Some boulders show fossil karren of preglacial karstification. The “matrix” is poorly to well cemented polymict breccia with medium grain size from 9 to 10 cm. Smaller boulders up to 50 cm are also frequent. Crushed or fractured limestone clasts are common. The megabreccias are completely unsorted. During ice retreat this poorly packed sediment was firstly washed out by meltwaters and later filled again with finer sediment. Water trapped in interspaces locally produced calcite cement. Erosional contact with underlying severly disturbed glaciolacustrine sediments is visible at Ždrilo. The basal moraine on Krk island show gradual transition to glaciofluvial deposits of extesive kame-terrace. The primary origin of megablocs may also be result of a major earthquake, and then entrainment by ice.

Croatia; Adriatic; Middle Pleistocene; megabreccia; glaciation

nije evidentirano