Naslov
Tectonic controls on alluvial deposition in the earliest syn-rift phase (South Pannonian Basin System, Croatia)

Autori
Pavelić, Davor ; Avanić, Radovan ; Kovačić, Marijan

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Abstracts Book / Pena dos Reis, Rui ; Callapez, Pedro ; Dinis, Pedro - Coimbra : Universidade de Coimbra, 2004

Skup
23rd IAS Meeting of Sedimentology, Sedimentology and Society

Mjesto i datum
Coimbra, Portugal, 15.09.2004. - 17.09.2004

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
tectonic controls; alluvial deposition; Pannonian Basin; Croatia

Sažetak
The Pannonian Basin System was formed as a result of continental collision of the European plate (Tisia-Moesia) with the African plate. Formation of its southern part began during Ottnangian time (Early Miocene) by continental rifting. The syn-rift phase lasted until the Middle Badenian (Middle Miocene), and resulted in the formation of elongated half-grabens characterized by large sediment thicknesses strongly influenced by tectonics and gradually increasing volcanism. The Lower Miocene sedimentary complex of the south Pannonian Basin System, i.e. North Croatian Basin, unconformably overlies pre-Miocene basement, and is represented by fresh-water deposits which belong to the earliest syn-rift phase of basin evolution. Deposition of the lower part of the fresh-water complex occurred in alluvial environments while the upper part was characterized by lacustrine sedimentation. Alluvial deposits have been measured at the Kalnik, Medvednica and Požeška Mts.. The main characteristics of these deposits the domination of coarse-grained over fine-grained sediments, conspicuous variation in grain size, very rapid lateral and vertical facies alternations, occurrences of red beds and a lack of fauna. The sediments form many small fining- and rarely coarsening-upward cycles. These cycles are typical of alluvial fans and braided rivers as a consequence of the autocyclic process on the surface. The deposits are divided into eleven facies: 1. Bcn ; massive breccia, clast-supported: rock-fall, 2. Gmu ; massive conglomerates, matrix-supported: plastic debris flow, 3. Gmi ; massive conglomerates, matrix-supported, rare clast-supported: pseudoplastic debris flow, 4. Gc ; massive conglomerates, clast-supported: main fan-trench, longitudinal bar, 5. Gp ; planar cross-bedded conglomerates, clast-supported: tranverse bar, 6. Ge ; pebble to granule conglomerates, lenses: stream flows, crevasse channel, 7. Sh ; fine- to coarse grained sandstones, horizontal lamination: upper flow regime, 8. Sr ; fine- to coarse grained sandstones, cross-lamination: lower flow regime, 9. Se ; fine- to coarse grained sandstones, lenses: crevasse splay, 10. F1 ; siltstones, massive, brown colour: flood plain, abandoned channel, 11. F2 ; siltstones, scattered granules, calcrete, reddish colour: palaeosol. Kalnik Mt.. The conglomerate bodies interpreted as longitudinal and transverse bar deposits, and the lack of sediments deposited by gravity flows suggest a pebbly braided river in the upper part of the succession. The lower part of the succession is characterized by dominant flood plain over channel deposits indicating deposition in the lower alluvial plain of the braided river. The unusually thick flood plain deposits could be attributed to rapid subsidence of the basin by tectonic influences, when the possibility of erosion of fine-grained deposits is minimal. Medvednica Mt.. The domination of coarse-grained deposits accumulated on longitudinal bars, pedogenic occurrences and the lack of fossils suggest a pebbly braided river. Alluvial deposits are sharply overlain by lacustrine limestones indicating tectonic deepening of the basin. Požeška Mt.. The association of sediments deposited by rock-fall and debris flow mechanisms with deposits of longitudinal bars, flood-plains and palaeosol indicates deposition in alluvial environments, relatively close to the source area, probably in the alluvial fan. The predominance of sediments deposited by traction in the fan succession seems closer to the braided alluvial fan. One of the measured sections shows a fining-upwards megacycle which is expressed by a general decrease in fragment size in the coarse-grained deposits and the occurrence of thick calcretes near the top of the megacycle, followed by gradual decreasing of the conglomerate unit thickness. This megacycle is interpreted as the result of normal faulting along the active margin of the subsiding basin. The deposition of rock-fall breccias also indicates the very high intensity of tectonic activity, and trapping of coarse-grained clastics near the steep slopes in the proximity of the source area.

Izvorni jezik
Engleski

Znanstvena područja
Rudarstvo, nafta i geološko inženjerstvo

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