Tectonosedimentary framework of Upper Cretaceous –Neogene series in the Gulf of Tunis inferred from subsurface data: implications for petroleum exploration
Abstract: The objective and the main contribution of this issue are dedicated to using subsurface data to delineate a basin beneath the Gulf of Tunis and its neighbouring areas, and to investigate the potential of this area in terms of hydrocarbon resources. Available well data provided information about the subsurface geology beneath the Gulf of Tunis. 2D seismic data allowed delineation of the basin shape, strata geometries, and some potential promising subsurface structures in terms of hydrocarbon accumulation. Together with lithostratigraphic data obtained from drilled wells, seismic data permitted the construction of isochron and isobath maps of Upper Cretaceous–Neogene strata. Structural and lithostratigraphic interpretations indicate that the area is tectonically complex, and they highlight the tectonic control of strata deposition during the Cretaceous and Neogene. Tectonic activity related to the geodynamic evolution of the northern African margin appears to have been responsible for several thickness and facies variations, and to have played a significant role in the establishment and evolution of petroleum systems in northeastern Tunisia. As for petroleum systems in the basin, the Cretaceous series of the Bahloul, Mouelha and Fahdene formations are acknowledged to be the main source rocks. In addition, potential reservoirs (Fractured Abiod and Bou Dabbous carbonated formations) sealed by shaly and marly formations (Haria and Souar formations respectively) show favourable geometries of trap structures (anticlines, tilted blocks, unconformities, etc.) which make this area adequate for hydrocarbon accumulations
Systematic updates of the agglutinated foraminiferal genus Colominella Popescu, 1998: insights from sectioned specimens
Abstract: The occurrence of agglutinated foraminiferal specimens belonging to the Badenian (middle Miocene) genus Colominella Popescu, 1998 was recently documented for the first time in a lower Pliocene succession of the western Mediterranean area. Direct comparisons with topotype specimens of Colominella paalzowi (Cushman 1936), sampled in the Badenian type section of Lăpugiu de Sus (Transylvania), show that the Pliocene individuals from the western Mediterranean morphologically resemble the type species C. paalzowi, but they also differ in possessing a longer biserial chamber arrangement with a higher number of internal chamber partitions, in lacking a clear early triserial stage and in having a more complex microstructure of the agglutinated wall, thereby supporting the idea that the Pliocene Mediterranean specimens represent a new, more highly evolved species. The fact that the Pliocene individuals from the Mediterranean appear to be more evolved with respect to the Badenian specimens from Paratethys represents an interesting evolutionary development of the genus Colominella that also permits the known stratigraphical and geographical range of the genus, previously limited to the middle Miocene (Badenian) of the Paratethys, to be extended.
Genetic aspects of barite mineralization related to rocks of the teschenite association in the Silesian Unit, Outer Western Carpathians, Czech Republic
Abstract: Barite is a relatively uncommon phase in vein and amygdule mineralizations hosted by igneous rocks of the teschenite association in the Silesian Unit (Western Carpathians). In macroscopically observable sizes, it has been reported from 10 sites situated only in the Czech part of the Silesian Unit. Microscopic barite produced by the hydrothermal alteration of rock matrix and also by the supergene processes is more abundant. We examined four samples of barite by mineralogical and geochemical methods. Electron microprobe analyses proved pure barites with up to 0.038 apfu Sr and without remarkable internal zonation. Fluid inclusion and sulphur isotope data suggests that multiple sources of fluid components have been involved during barite crystallization. Barite contains primary and secondary aqueous all-liquid (L) or less frequent two-phase (L+V) aqueous fluid inclusions with variable salinity (0.4–2.9 wt. % NaCl eq.) and homogenization temperatures between 77 and 152 °C. The higher-salinity fluid endmember was probably Cretaceous seawater and the lower-salinity one was probably diagenetic water derived from surrounding flysch sediments during compaction and thermal alteration of clay minerals. The δ 34S values of barite samples range between –1.0 ‰ and +16.4 ‰ CDT suggesting participation of two sources of sulphate, one with a near-zero δ 34S values probably derived from wall rocks and another with high δ 34S values being most probably sulphate from the Cretaceous seawater. All results underline the role of externally derived fluids during post-magmatic alteration of bodies of rock of the teschenite association.
The Campanian–Maastrichtian foraminiferal biostratigraphy of the basement sediments from the southern Pannonian Basin (Vojvodina, northern Serbia): implications for the continuation of the Eastern Vardar and Sava zones
Abstract: Micropalaeontological and biostratigraphical studies included Campanian–Maastrichtian complexes from five oil exploration wells drilled in northern Serbia (Vojvodina): the first is a carbonate-clastic complex and second is a complex containing ophiolites intercalated with hemipelagic and pelagic sediments. Within the studied complexes, rich associations of planktonic and benthic foraminifera, calcareous nannoplankton, palynomorphs, as well as shallow and deep-water fossil detritus were determined. The presence of relatively rich associations of planktonic foraminifera allowed recognition of two biozones: the Globotruncana ventricosa Zone, observed in the sediments of the carbonateclastic complex and the Gansserina gansseri Zone, observed in both complexes. Except biozones, based on documented index species, for some units in both complexes, larger benthic foraminifera species had special biostratigraphical value, and in some of them, the calcareous nannoplankton zones were recognized. The studied complexes represent deep-water formations, generated in oceanic island arc and trough zones. The presence of limestones, which originate from destroyed rudist reefs, is explained by transfer by means of gravitational transport mechanisms of shallow-water sediments to deep-water depositional environments. In this paper, the results of more detailed biostratigraphical and palaeo-ecological studies of foraminifera associations in Campanian–Maastrichtian complexes in Vojvodina are presented. Combined with lithological studies, seven units were determined within the complexes. The obtained results are important as a part of multidisciplinary, regional exploration of both complexes, generated in specific geological conditions, that today constitute a part of the pre-Neogene basement complex in the southeastern part of the Pannonian Basin. The Campanian–Maastrichtian carbonate-clastic complex represents sedimentary cover of the Eastern Vardar Ophiolitic Unit, while the ophiolites intercalated with hemipelagic and pelagic limestones belongs to the Sava Zone.
Constraints on the depositional age and tectonometamorphic evolution of marbles from the Biharia Nappe System (Apuseni Mountains, Romania)
Abstract: Basement rocks from the Biharia Nappe System in the Apuseni Mountains comprise several dolomite and calcite marble sequences or lenses which experienced deformation and metamorphic overprint during the Alpine orogeny. New Sr, O and C-isotope data in combination with considerations from the lithological sequences indicate Middle to Late Triassic deposition of calcite marbles from the Vulturese-Belioara Series (Biharia Nappe s.str.). Ductile deformation and large-scale folding of the siliciclastic and carbonatic lithologies is attributed to NW-directed nappe stacking during late Early Cretaceous times (D2). The studied marble sequences experienced a metamorphic overprint under lower greenschist-facies conditions (316 –370 °C based on calcite – dolomite geothermometry) during this tectonic event. Other marble sequences from the Biharia Nappe System (i.e. Vidolm and Baia de Arieș nappes) show similarities in the stratigraphic sequence and their isotope signature, together with a comparable structural position close to nappe contact. However, the dataset is not concise enough to allow for a definitive attribution of a Mesozoic origin to other marble sequences than the Vulturese-Belioara Series.
Mapping of tecto-lineaments and their influence on sedimentological processes in a GIS environment: a case study of the Iberian trough, Spain
Abstract: The subsurface sedimentary succession of the Iberian Trough, Spain was examined using geophysical techniques (analogue seismic profiles) and inverse distance weighted (IDW) interpolation algorithm implemented in a gvGIS open source software. The results showed that the Late Cretaceous succession is divided into two depositional sequences: DS-1 (Late Albian–Middle Turonian) and DS-2 (Late Turonian–Campanian). From the analogical seismic sections, digital data and quantitative isopach maps for DS-1 and DS-2 were obtained. The new isopach maps obtained for the DS-1 sequence showed that the deeper sectors of the basin were located to the northeast and the proximal ones to the southwest. The palaeoshoreline was inferred to be situated in the N 150 direction. Across and parallel to this direction several blocks were delimited by faults, with a direction between 30 N and N 65. The thickness of the sediments in these blocks varied in direction NW–SE, with subsidence and depocentres in hangingwall and uplift in the footwall. These variations may have been related to active synsedimentary faults (e.g., Boñar and Yugueros Faults). In the DS-2 sequence, a lineament separated the smaller thicknesses to the southwest from the larger thicknesses (up to 1400 m) to the northeast. This lineament had an N170 orientation and it indicated the position of the palaeoshoreline. In the isopach map for DS-2 there were two groups of lineaments. The first showed a block structure that was limited by N 100 –120, they were foundering toward the S and had large thicknesses (depocentres), and rose towards the N, where there were smaller thicknesses. The second group of lineaments had a N 50 – 65 direction and, in this case, they had a similar interpretation as the one in DS-1. The maps obtained are of great help for geologists and permit better understanding of the geological setting and stratigraphic succession of the Late Cretaceous of the Iberian Trough.