The Úrkút Manganese Ore Formation is a Jurassic geologic formation in Hungary. It covers the Early Toarcian stage of the Early Jurassic, and it is one of the main regional units linked to the Toarcian Anoxic Events. Different fossils heve been recovered on the locations, including marine life such as Ammonites Fish and terrestrial fossils, such as Palynomorphs and fossil wood. Úrkút (17´38'E and 47´05'N) and Eplény (17´55'E and 47´12'N) are the main deposits of the Formation. Are related to the Bakony Range, an ancient massif that was uplifted gradually and exposed to a long period of erosion, where the deposits of Úrkút appear to be a basin inclined gently to the north, while the highest point to the south is the basalt mass of Kab Mountain. Eplény region consists of a broad N-S trending open valley between fiat-topped, small hills.
Geology The Urkut Area is part of the Bakony Tectonic Block, with the abundant presence of faults dividing the region into several segments. The terrain where the Manganese Ore is developed is characterised by a high fracturation, where the Jurassic beds and shale lent themselves readily to deformation, with minor folds, faults and shear zones. During the geological evolution of the Bakony range a series of principal fractures were active repeatedly, yielding to vertical as well as horizontal forces that ultimately produced the structural make-up controlling the present topographic configuration of the area. The Jurassic sediments, along the other Mesozoic aged strata were deposited in a branch of a Geosyncline, connected with the Alpine coeval biota. On the Triassic-Jurassic boundary Kimmerian movements take place, as evidenced by the change observed on the texture of the local Calcareous sediments, interpreted as a gradual rising of the sea bottom. To the end of the Lower Jurassic, on the Toarcian, there are several records of another series of pulses from Kimmerian movements, that resulted in partial emergence, which dates the beginning of Karst development on the Csirda Mountain. However, marine sedimentation continued over most of the region and the sea became more widespread. On this time a global sea transgression occur, where on the Úrkút basin shallow-water sediments accumulated near the margins, and with progressive deepening of the sea bottom until the end of late Liassic time, sediments of correspondingly deeper water were deposited. Due to a cut-off of water circulation there were a series of changes on the local development of the basin, which led to the accumulation of the manganese minerals. The Éplény Area shows a structure and geological development with minor differences from those of Úrkút, being considered overall identical. However, it suffered minor deformation during the late Kimmerian movements, and instead of the Austrian movements, the Subhercynian and Laramide movements produced important structures. After the Pyrenean and Savian movements, the Éplény area started to sink slowly and to receive marine sediments, emerging later on the Middle Miocene. The manganese ore group of beds appears in an absolutely different way according to evolution in Eplény, where while in Úrkút 4 beds can be divided, in Eplény, the 3 beds appear usually with sharp boundary, in reduced thickness.
Stratigraphy
The oldest formations on the Úrkút basin are referred to the Upper Triassic Dolomite range and the Dachstein Limestone of Raetian age. After the deposition of the Triassic rocks a series of Jurassic strata successions have overlain the older deposits, with its lowermost contact found on the uppermost strata of the own Dachstein Limestone, developing a lower Liassic sequence that is a white, yellowish-gray or pink, dense Limestone resembling that of the Dachstein. Over it, there is a series of younger liassic strata and a Crinoid-Brachiopod and Rhynchonellatan bearing reddish Limestone, that resembles the Sinemurian Hierlatz Limestone of the Csárda Mountain, that is the last unit under the coeval Manganese deposits from there. Late Pliensbachian strata is composed by nodular and cherty red limestone with abundant ammonites and brachiopods, that belong to the Isztimér Formation. On the uppermost Pliensbachian strata there is a series of beds that consists of greenish-gray limestone and marl, which also contain crinoids and brachiopods, being the last unit under the Manganese Ore. The Upper Liassic (Toarcian) sequence is composed mostly by the Úrkút Manganese and the Éplény Limestone (Late Toarcian-Aalenian), and starts with thick-bedded, gray, Radiolaria-bearing, argillaceous marl containing several intercalations of manganese carbonate, or rarely, manganese oxides, with the top of the sequence being a brown to purple nodular Limestone with light green spots. Middle Jurassic overlaying these deposits, being mostly a series of cherty Marlstone containing the genus Posidonomya and several types of Radiolaria. The Late Jurassic strata is vanished locally, with the Cretaceous sedimentation starting with several continental beds with Bauxite and accompanying Laterites. Finally, on the Tertiary, the Lower Eocene continental clay and bauxite are overlain by gray carbonaceous clay and sandstone, with the Jurassic beds and manganiferous beds eroded.
Lithology
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