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Seven exceptional paleontological graptolite sites of Silurian age located in the Srednogorie Zone (the Svoge Unit and the Lyubash-Golo Bardo Unit) and the Moravo-Rhodope Zone (the Morava Unit) of the Alpine Orogenic Belt in Western Bulgaria are described. The graptolitic deposits include predominantly thin-bedded shales referred to 4 formal lithostratigraphic units in the Svoge Unit, and one informal lithostratigraphic unit in both the Lyubash-Golo Bardo and Morava units. This article provides a historical review of the foundation and description of the graptolite sites thus providing a better understanding of their historical value for stratigraphy and the geological evolution of this area during the Silurian. An analysis of their geotourism potential and geoconservation value, according to the new indicative criteria highlighting the specific characteristics of fossil sites, is also given. [ABSTRACT FROM AUTHOR]

Palaeozoic (Silurian and Devonian) bedded cherts from the Balkan Terrane in western Bulgaria occur in three tectonic units: Svoge, Lyubash-Golo Bardo, and Morava. The Silurian and Devonian ages of the chert-bearing lithostratigraphic successions have been determined by conodonts and graptolite macrofauna. The silica source and depositional settings of the cherts have been interpreted based on the received mineralogical, petrographic, and geochemical (major, trace, and rare earth elements) data. The presence of radiolarian tests, the Si/Si+Al+Fe+Ca ratios, and Al–Fe–Mn diagram plotting at the non-hydrothermal field, testify that the source of silica in the studied rocks is mostly biogenic or both biogenic and terrigenous in origin. Differential thermal analysis results suggest that the Silurian and Devonian siliceous rocks were presumably formed in predominating anoxic oceanic conditions and only sporadically in oxic waters. The MnO/TiO2 ratio and received Al2O3, Fe2O3, TiO2, Lan, and Cen contents indicate that the studied cherts have been deposited in continental margin environments. Most probably, they have been formed in slope and outer-shelf settings on the passive margin of northern peri-Gondwana. [ABSTRACT FROM AUTHOR]

Two diorite to monzodiorite sills are recently found among the Silurian sedimentary succession near to Asaritsa peak, West Stara Planina Mountain. Several levels with diagenetic metalliferous nodules occur within shale interval in the sediments. The magmatic rocks are affected by strong propylitic to sericitic alteration (chlorite, sericite, albite and quartz) and only relicts of the rock-forming minerals (feldspar, biotite and clinopyroxene) are observed. The bodies are crosscut by thin quartz veins and disseminated pyrite is observed. The chondrite normalized spidergrams show patterns similar to orogenic rocks, with very high peaks of Th and U and depletion in Sr and Ti. The zircon U-Pb geochronology reveals that the magmatic crystallization is during the Carboniferous period -- 326.4±3.2 Ma, with low content of xenocryst most probably from the sedimentary basement. The magmatic activity coincides with the Variscan orogeny formed during the late Paleozoic and most probabaly is related to the evolution of the alkaline Buhovo-Seslavtsi Pluton which is situated just to the south, at a direct proximity. The different composition of the pyrite from the sills and the diagenetic nodules from the sediments is most probably due to their different genesis. While the alterations of the nodules can be attributed to metasomatic processes related to the magmatic activity. [ABSTRACT FROM AUTHOR]

Five conodont zones (falsiovalis, rhenana, triangularis, marginifera, and praesulcata) were recognized within the Upper Devonian carbonate sequence in the Preslavtsi 2 well from the Moesian Terrane in NE Bulgaria. Microfacies study indicates a climate change (from the Subtropical Arid to the Warm Temperate Climatic Zones) recorded in the Frasnian--Famennian succession. Thus, during the Givetian and early Frasnian, sedimentation took place in an arid tidal flat setting, where microbial mats and lagoon carbonates have been formed. In the late Frasnian, a transgression, followed by a rapid regression was recorded that are presumably related to the Late Devonian Kellwasser event. At the beginning of the Famennian, a climate change has occurred and various shallow- and open-marine carbonates have been formed under warm temperate climate conditions. [ABSTRACT FROM AUTHOR]

As part of a cross-border cooperation program project between Bulgaria and Greece (Interreg), the geotourism potential of the municipality of Madan has been assessed. The assessment was made of the possibilities for the conversion of abandoned mine workings into tourist sites. Eight (8) geotopes are described and the creation of 2 geo-trails is proposed. [ABSTRACT FROM AUTHOR]

Paleozoic (Silurian and Devonian) cherts from Western Bulgaria occur in three tectonic units: Svoge, Lyubash-Golo Bardo and Morava. The SiO2 content in these rocks varies from 76.06% to 96.02%. The silica source and depositional settings of the cherts have been interpreted based on the received geochemical major element data. The calculated Si/(Si+Fe+Al+Ca) ratio and Al-Fe-Mn diagram plotting at non-hydrothermal field suggest that most of silica in the cherts is biogenic or both biogenic and terrigenous in origin. On the other hand, all studied siliceous samples plot into the field of the continental margin sediment environments on the Fe2O3/TiO2 vs. Al2O3/(Al2O3+Fe2O3) diagram. The calculated MnO/TiO2 ratio also indicates deposition in continental shelf or slope environments. [ABSTRACT FROM AUTHOR]

Geochemical studies of different Paleozoic intervals composed of bedded cherts, revealed in the western parts of the Srednogorie and Morava-Rhodope zones are presented: Saltar Fm; the lower and middle part of Katina Fm; the lowest part of Parchar Fm, and Tumba Fm. To determine whether the different bedded cherts intervals are hydrothermally affected, triangular diagrams of the A-F-Mn ratio were used. The low content of Fe compared to Al gives grounds to claim that the Pre-Varisian Paleozoic bedded cherts in Bulgaria are not associated with endogenous processes. [ABSTRACT FROM AUTHOR]

Two sandstone samples from the upper and lower parts of the Ordovician succession of the Svoge Unit were analyzed in order to determine their detrital zircon U-Pb age spectra using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Multi-dimensional scaling statistical technique allowed a reliable objective identification of the potential source areas in North Africa and paleogeographic reconstructions were made. Both samples indicate a close proximity to the Trans-Saharan Belt provenance, which is the most probable source of the detrital component. [ABSTRACT FROM AUTHOR]

The Late Devonian (372-359 million AD) is a time of prolonged climate instability with catastrophic disturbances to global marine ecosystems at the Frasnian-Famennian (F/F) and Devonian-Carboniferous (D/C) boundaries. Global atmospheric CO2 content and climate change in the middle Paleozoic, especially in the Late Devonian, coincide with major events of extinction of organism groups. Anoxic intervals were documented within the Kellwasser event near the Frasnian/Famennian boundary (F/F), the Annulata event in Famennian and the Hangenberg event near the Famennian/Tournaisian boundary (D/C). [ABSTRACT FROM AUTHOR]

The Silurian-Lower Devonian succession in the Değirmentaş-Halevikdere section (E Taurides) shows considerable lithostratigraphic similarities to the three-partite subdivision, initially documented in the same stratigraphic interval in Saxo-Thuringia and later in other peri-Gondwanan terrains. The Llandovery-Wenlockian part of the studied section (ca. 40 m) is characterized by black graptolitic shales. The Llandoverian part is dominated by radiolarian ribbon cherts (ca. 20 m). The Rhuddanian Akidograptus ascensus, Parakidograptus acuminatus, and Cystograptus vesiculosus biozones have been recognized in its lower part, while in the upper part of the succession, the lowermost Telychian Rastrites linnaei Biozone has been documented. The Telychian Spirograptus turriculatus and Streptograptus crispus biozones, as well as the Sheinwoodian Cyrtograptus rigidus/Monograptus belophorus Biozone, have been identified within this succession. Graptolites of the Homerian (Colonograptus deubeli + Col. praedeubeli and Col. ludensis biozones) are only found in the Pekmezkoy and Gurleşen areas, in the black shales, immediately before the first ocher-colored limestone, which is characteristic for the Ockerkalk Formation in the Thuringian facies. The dominantly ocher-colored shale-limestone alternation in the Değirmentaş-Halevikdere section is ca. 50 m in thickness. The lower Ludlowian part is enriched by nautiloids, while in the Pridolian part crinoids are abundant. It is covered by 60-m-thick black shales and siltstones, corresponding to the Upper Graptolite Shale Formation in the Thuringian. The Silurian-Devonian boundary is located in the lower part of this unit on the basis of lobolith findings. The depositional model proposed here accounts for the migration of the considered peri-Gondwana terrains from high to low paleogeographic latitudes that has triggered changes not only in the ocean water thermohaline circulation but also in the wind-driven downwelling or upwelling systems. These changes are responsible for the progressive transition from an oxic regime to an anoxic one in the deep oceanic depositional environments (outer continental shelf, slope, and ocean basin settings) and the deposition of light and dark sediments there. [ABSTRACT FROM AUTHOR]

The Karadere area to the east of Safranbolu in NW Anatolia is one of the very few localities in Turkey where the contact between the Cadomian basement and the Lower Palaeozoic transgressive succession is well exposed. The Ordovician graptolite Rhabdinopora flabelliformis (Eichwald) ssp. was found in the basal part of the Bakacak Formation, indicating an Early to early Late Tremadocian age for the beginning of the Palaeozoic transgression in the Zonguldak terrane. A few metres above this occurrence, another horizon contains Paradelograptus cf. antiquus (T. S. Hall), which mainly ranges into the Late Tremadocian. Higher up in the Ordovician succession, a new graptolite bed confirms an early Darriwilian (Dw1) age for the middle part of the Karadere Formation with the occurrence of the biozonal index Levisograptus austrodentatus (Harris & Keble) and the first record of Tetragraptus cor (Strandmark) in the area. The palaeobiogeographic distribution of these Karadere fossils is in agreement with a peri-Gondwanan affinity of the Zonguldak Terrane of the Pontides, NW Anatolia, during the Early-Middle Ordovician. [ABSTRACT FROM AUTHOR]

The Istranca Crystalline Complex in NW Anatolia and SE Bulgaria includes structural units that differ in lithostratigraphy, metamorphism, age and structural position. They are collectively named as the 'Istranca nappes' comprising from bottom to top the Sarpdere, Mahyadağ and Doğanköy Nappes. The Sarpdere Nappe consists of Lower Triassic arkosic metasandstones with slate interlayers, followed by Middle to Upper Triassic carbonates and an alternation of Upper Triassic clastics and carbonates. The Mahyadağ Nappe comprises a low-grade metamorphic Late Paleozoic- Triassic carbonate-siliciclastic sedimentary succession. The Doğanköy Nappe includes Precambrian?-Paleozoic metasediments, intruded by Late Carboniferous-Early Permian calc-alkaline granitoids. Its Triassic cover comprises metaclastics and metacarbonates. The Istranca nappes were juxtaposed at the end of the Triassic and transgressively covered by Lower Jurassic coarse clastics, followed above by Middle to Late Jurassic carbonates, black shales and carbonate-siliciclastic sedimentary succession. The phosphate concretions in black shales yielded radiolarian assemblages indicating Late Bajocian-Early Bathonian, Early Bathonian and Early Kimmeridgian ages. These nappes and their Jurassic cover are unconformably overlain by the Cenomanian-Santonian volcano-sedimentary successions intruded by Santonian-Campanian Dereköy-Demirköy intrusive suite. The preliminary data suggest that the Variscan basements of the Mahyadağ and Sarpdere Nappes were juxtaposed prior to the Triassic and overridden by the Doğanköy Nappe of possible Rhodopean origin from S to N during the Cimmerian compressional events [ABSTRACT FROM AUTHOR]

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