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21.
Ioan Seghedi Alexandru Szakács Emilian Roşu Zoltán Pécskay Katalin Gméling 《Central European Journal of Geosciences》2010,2(3):321-328
Bontâu is a major eroded composite volcano filling the Miocene Zârand extensional basin, near the junction between the Codru-Moma and Highi?-Drocea Mountains, at the tectonic boundary between the South and North Apuseni Mountains. It is a quasi-symmetric structure (16–18 km in diameter) centered on an eroded vent area (9×4 km), buttressed to the south against Mesozoic ophiolites and sedimentary deposits of the South Apuseni Mountains. The volcano was built up in two sub-aerial phases (14–12.5 Ma and 11–10 Ma) from successive eruptions of andesite lava and pyroclastic rocks with a time-increasing volatile budget. The initial phase was dominated by emplacement of pyroxene andesite and resulted in scattered individual volcanic lava domes associated marginally with lava flows and/or pyroclastic block-and-ash flows. The second phase is characterized by amphibole-pyroxene andesite as a succession of pyroclastic eruptions (varying from strombolian to subplinian type) and extrusion of volcanic domes that resulted in the formation of a central vent area. Numerous debris flow deposits accumulated at the periphery of primary pyroclastic deposits. Several intrusive andesitic-dioritic bodies and associated hydrothermal and mineralization processes are known in the volcano vent complex area. Distal epiclastic deposits initially as gravity mass flows and then as alluvial volcaniclastic and terrestrial detritic and coal filled the basin around the volcano in its western and eastern part. Chemical analyses show that lavas are calc-alkaline andesites with SiO2 ranging from 56–61%. The petrographical differences between the two stages are an increase in amphibole content at the expense of two pyroxenes (augite and hypersthene) in the second stage of eruption; CaO and MgO contents decrease with increasing SiO2. In spite of a ～4 Ma evolution, the compositions of calc-alkaline lavas suggest similar fractionation processes. The extensional setting favored two pulses of short-lived magma chamber processes. 相似文献
22.
Katalin Báldi László Benkovics Orsolya Sztanó 《International Journal of Earth Sciences》2002,91(3):490-504
A quantitative paleobathymetric study of Badenian foraminifera was carried out from Tekeres-1 and Tengelic-2 boreholes, north of the Mecsek Mts., SW Hungary. Paleobathymetric data, based on plankton/benthos ratio provided input for the analysis of the subsidence history. The biostratigraphic framework is mainly provided by calcareous nannoplankton (zones NN5-NN7). Changes in sedimentation rates are also considered, partly calculated from number of benthos per unit sediment, and partly estimated from the changes of lithofacies. Relative sea-level changes are calculated from changes of paleowater depth and coeval sedimentary thickness. The result is examined as the sum of accommodation space created by subsidence and eustasy. In that period of time eustatic changes were about an order of magnitude smaller than changes created by movements of the basin floor. According to our model in early Badenian (up to the half of NN5 nannozone) a very rapid transtension-related subsidence of about 500 m occurred. This was interrupted by a short period of uplift of minor magnitude at about the first third of NN5 zone; thereafter, subsidence continued and the basin floor reached its deepest position. Still within the NN5 nannozone (Early Badenian) a significant uplift occurred, terminating the life of the deep basin. The Late Badenian (NN6) is characterized by a relatively small rate of subsidence and presumably quiet tectonism. During this period bathymetric changes are thought to be controlled primarily by eustatic changes. The first uplift - only interrupting subsidence - is regarded as the result of the change of the local stress field because of convergence along the curvature of strike slip faults. The second uplift, which stopped the subsidence of the basin floor is thought to be of a regional character and is attributed to the compression generated between Tisza and Alcapa tectonic units. 相似文献
23.
Katalin Báldi 《International Journal of Earth Sciences》2006,95(1):119-142
Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys.
The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply
(organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and
benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified
accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian
(13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked
out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian
period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin.
Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested
to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with
the cooler period following it. 相似文献