Unusual Depositional Architecture of Foreland Basin Deposits - a case study of Carpathian Foredeep Basin (Neogene)
| Authors | |
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| Year of publication | 2006 |
| Type | Article in Proceedings |
| Conference | Abstracts of the 17th International Sedimentological Congress - Volume B |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | foreland basin- depositional architecture |
| Description | All major architectonical elements of the foreland basins are conventionally considered to accumulate due to flexural subsidence of the foreland plate with typical regional orogenward thickening on the basinal scale [1]. The distinctive geometry of the Early Langhian (Lower Badenian according the Central Paratethys stages) deposits reflects that flexural subsidence was not the major generator of accommodation space formation. Deposits are located in the central parts of the basin in some distance both from the passive and active basin margins. Areas with their maximum thickness are situated in the axis of the basin forming almost symmetric depression with SSW-NNE orientation. Similarly significant oblique seismic termination surface cutting Neogene basin fill can be followed in seismic reflection profiles in the middle parts of the basin. This surface limited a broad depression and its upper part is filled with Lower Badenian deposits. Lithofacies study allows us to distinct 15 lithofacies and 4 facies associations/depositional environments (i.e. coarse-grained deltas, coastal, lagoonal deposits and basinal/shelf deposits). Two of these depositional environments strongly dominate. The coarse-grained deltas are the first one. Their maximum thickness is about 175 m. Deltas are located along both basin margins. Gravels are polymict and the composition of pebble and cobble extraclasts varied for each delta body. Provenance studies (pebble analyses, heavy mineral associations, garnet chemistry, monazite dating) allow detailed recognition of source areas for individual delta bodies and confirm the provenance from both/opposite margins of the basin. Abundant presence of intraclasts (sometimes several m in diameter) reflects cannibalisation of the older basin infill. Delta foresets with deposition of gravity flows represent the prevalent preserved part of deltas. The second dominant depositional environment is the basinal one. Their maximum thickness of about 600 m. Deposition in outer shelf conditions prevailed (hyperpycnal and hypopycnal currents). Several lithofacies differ in the content of silt and clay fraction, shell debris, intensity of bioturbation and sedimentary structures. Clastic coast and lagoonal deposits are restricted both areally and in thickness. Similar situation is with the occurrence of red algal limestones. Recognised horizons of distal air fall tephra were product of acidic calc-alcaline source volcanism of volcanic arch with source in Carpatho-Pannonian area (MiddleRhyolite tuff). Location of the basin, distribution and character of the deposits can all be explained by transtensional and transpresional regime. It reflects the tectonic development of the Carpathian orogenic wedge where original NNW and NW oriented compression change its orientation towards NNE and NE during Upper Karpatian and Lower Badenian. The new accommodation space formed in the central parts of the foreland basin whereas its older and marginal parts were deformed and eroded. Final compressional deformation influenced the shape of the basin. Depositional architecture, facies study and paleoecological results reveal the existence of 4 order cycles within studied deposits directed by combination of tectonic activity and eustatic sea-level changes. |
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