Depositional environment and provenance of the Gresten Formation (Middle Jurassic) on the southeastern slopes of the Bohemian Massif (Czech Republic, subsurface data)

Abstract

The deposits of the Gresten Formation (Middle Jurassic) obtained from deep wells in the territory of southern Moravia (Czech Republic) have been newly examined with the aim to better describe their provenance and depositional environment. Deposition within a relatively broad flood plain with fluvial/distributive channels, crevasse channels, crevasses splays and coal-swaps have been recognised in the majority of well cores. Open marine deposits are less common. The heavy mineral association is quite stable, with significant dominance of garnet and commonly also with high content of zircon. The mineralogical spectra of garnet types are broad with strong dominance of almandines. The rutiles were mostly derived from metapelites and additionally also from metamafic rocks and pegmatites. The results point to mixed sources from both intensively weathered crystalline rocks of the eastern margin of the Bohemian Massif (primary source) and the older sedimentary rocks -especially from the Moravo-Silesian Paleozoic deposits (recycled source).

Lower Badenian coarse-grained Gilbert deltas in the southern margin of the Western Carpathian Foredeep basin

“…The composition of garnet, rutile and also pebble petrography of the deposits studied significantly differs from similar data obtained for the autochthonous Jurassic beds along the eastern margins of the Bohemian Massif (Nehyba & Opletal 2016. This result indirectly challenges the provenance of carbonate pebbles only from Jurassic beds (see Eliáš 1981;Řehánek 2001 (Menčík 1973;Eliáš 1981;Stráník et al 1999;Řehánek 2001) supposed the source to be from autochthonous (subsurface) Jurassic deposits of the SE margin of the Bohemian Massif.…”

“…These are recognized in the Moravian-Silesian Paleozoic (Culmian) rocks (Otava et al 2000;Čopjaková et al 2002, 2005Čopjaková 2007), PermoCarboniferous deposits (Nehyba et al 2012;Nehyba & Roetzel 2015), Jurassic deposits of both the Gresten and Nikolčice Formations (Nehyba & Opletal 2016;, Paleogene deposits of the Western Carpathian Flysh Zone (Otava 1998;Otava et al 1997;Stráník et al 2007), and also in Eggenburgian and Ottnangian, Karpatian (Francírek & Nehyba 2016) and Lower Badenian deposits of the Carpathian Foredeep itself. However, the distribution of recognized garnet types varies within these deposits.…”

Sedimentological study of the Nikolčice Formation - evidence of the Middle Jurassic transgression onto the Bohemian Massif (subsurface data)

“…A sig nif i cant sim i lar ity can be seen with the gar net spec tra from the un der ly ing Gresten For ma tion (Nehyba and Opletal, 2016;Fig. 14).…”

“…De pos its of the GF were mostly in ter preted as flu vial depos its (Nehyba and Opletal, 2016). Iden ti fi ca tion of some dif ferences in the prov e nance be tween these two for ma tions is in terest ing for palaeogeographic re con struc tion.…”

“…The ex tent of the sed i men tary ba sin formed dur ing the Ju ras sic is in di cated by the con tin u ous se quence of Ju ras sic de pos its in many bore holes from the Austrian bor der in the south-west to wards the Ždánice area in the north-east and has also been in ter preted us ing 3D seis mic data. The whole se quence be gins with Bajocian-Bathonian (Aalenian-Bathonian in Aus tria) de pos its of the Gresten Forma tion with its deltaic and prodeltaic de pos its in Aus tria (Wessely, 1988) and mostly flu vial de pos its in the Czech Repub lic (Nehyba and Opletal, 2016). Then the se quence con tinues af ter trans gres sion with the sand stones of the NF stud ied (Callovian), which usu ally con form ably over lies the Gresten For ma tion.…”