Geologos, 2020, 26, 1
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Item Facies patterns and depositional processes in two Frasnian mixed siliciclastic-carbonate systems in the Cantabrian Mountains, northwest Spain(Instytut Geologii UAM, 2020-04) van Loevezijn, Gerard B.S.; Raven, J.G.M.Relative sea level fluctuations during the Frasnian generated two shallow-marine, mixed siliciclastic-carbonate successions in the Devonian Asturo-Leonese Basin. Each system represents a third-order sequence-stratigraphical unit deposited in the same basin during comparable extreme greenhouse conditions without nearby fluvial entry points. Depositional control on the siliciclastic and carbonate distribution was driven by relative sea level fluctuations, basin geometry, availability of sand and the way sediment was distributed by shelf currents. Early Variscan flexural bending of the continental crust changed the basin shape from a shelf with a gradual profile and low dip (early Frasnian) towards a shelf with a steep depositional dip (late Frasnian). Shelf distribution changed from along-shelf transport (early Frasnian) towards offshore-directed gravity flows (late Frasnian). As a consequence, siliciclastic-carbonate distribution changed from a predominance of skeletal carbonate in the proximal shoreface – foreshore area and siliciclastic predominance distally (early Frasnian), to a distribution pattern with proximal shoreface skeletal carbonates, offshore muddy carbonates and a siliciclastic zone in between where gravity flows distributed the siliciclastic sediment down dip (late Frasnian).Item Crevasse splays within a lignite seam at the Tomisławice opencast mine near Konin, central Poland: architecture, sedimentology and depositional model(Instytut Geologii UAM, 2020-04) Chomiak, LiliannaThe present article focuses predominantly on sandy deposits that occur within the Middle Miocene lignite seam at the Tomisławice opencast mine, owned by the Konin Lignite Mine. As a result of mining activity, these siliciclastics were available for direct observation in 2015–2016. They are situated between two lignite benches over a distance of ~500 m in the lower part and ~200 m in the higher part of the exploitation levels. The maximum thickness of these sandy sediments, of a lenticular structure in a S–N cross section, is up to 1.8 m. With the exception of a thin lignite intercalation, these siliciclastics comprise mainly by fine-grained and well-sorted sands, and only their basal and top layers are enriched with silt particles and organic matter. Based on a detailed analysis of the sediments studied (i.e., their architecture and textural-structural features), I present a discussion of their genesis and then propose a model of their formation. These siliciclastics most likely formed during at least two flood events in the overbank area of a Middle Miocene meandering or anastomosing river. Following breaching of the natural river levee, the sandy particles (derived mainly from the main river channel and levees) were deposited on the mire (backswamp) surface in the form of crevasse splays. After each flooding event, vegetation developed on the top of these siliciclastics; hence, two crevasse-splay bodies (here referred to as the older and younger) came into existence. As a result, the first Mid-Polish lignite seam at the Tomisławice opencast mine is currently divided in two by relatively thick siliciclastics, which prevents a significant portion of this seam from being used for industrial purposes.Item Episkeletozoans and bioerosional ichnotaxa on isolated bones of Late Cretaceous mosasaurs and cheloniid turtles from the Maastricht area, the Netherlands(Instytut Geologii UAM, 2020-04) Jagt, John W.M.; Deckers, Mart J.M.; De Leebeeck, Magda; Donovan, Stephen K.; Nieuwenhuis, EricIsolated bones of three taxa of marine reptiles (Mosasaurus hoffmannii Mantell, Plioplatecarpus marshi Dollo and Allopleuron hofmanni (Gray)) from various levels within the Maastricht Formation (upper Maastrichtian) at the former ENCI-HeidelbergCement Group quarry (Maastricht, the Netherlands) exhibit bioerosional traces and encrustation. Episkeletozoans include dimyid, ostreid and monopleurid bivalves, at least three species of cheilostome and cyclostome bryozoans and two adnate calcareous foraminifera. The bones show biting traces (Gnathichnus pentax Bromley, Linichnus cf. serratus Jacobsen & Bromley and Machichnus isp.), as well as borings. The latter may be referred to Karethraichnus lakkos Zonneveld, Bartels, Gunnell & McHugh, which is here considered to be a junior synonym of Gastrochaenolites isp.Item Petrology and origin of the Lar igneous complex of the Sistan suture zone, Iran(Instytut Geologii UAM, 2020-04) Boomeri, Mohammad; Moradi, Rahele; Bagheri, SasanThe Oligocene Lar igneous complex is located in the Sistan suture zone of Iran, being emplaced in Paleocene to Eocene flysch-type rocks. This complex includes mainly intermediate K-rich volcanic (trachyte, latite and andesite) and plutonic (syenite and monzonite) rocks that belong to shoshonitic magma. The geochemical characteristics of the Lar igneous complex, such as an enrichment of LREE and LILE relative to HREE and HFSE, respectively, a negative anomaly of Ti, Ba and Nb and a positive anomaly of Rb and Th are similar to those of arc-type igneous rocks. Tectonic discrimination diagrams also show that rocks of the Lar igneous complex fall within the arc-related and post-collisional fields and K-enrichment of these rocks confirm the post-collisional setting. Based on geochemical features, the Lar igneous complex magma was derived from partial melting of a phlogopite-bearing, enriched and metasomatised lithospheric mantle source and the magma was affected by some evolutionary processes like fractional crystallisation and crustal contamination.Item The Nowdan anticline of the Zagros orogen as a geoheritage ‘window’ into the late Mesozoic– Cenozoic evolution of the African–Arabian continental margin(2020-04) Habibi, Tahereh; Ruban, Dmitry A.; Yashalova, Natalia N.Geological heritage can contribute to our understanding of the long-term evolution of important sectors of our planet. Cretaceous–Neogene rocks (chiefly carbonates) crop out in the Nowdan anticline of the Zagros orogen. Field investigations have permitted the establishment of 10 key localities (stratigraphical reference sections) that represent these rocks within this anticline, which is a single large geosite. The formations are related to the main phases in the evolution of the northeastern sector of the African–Arabian continental margin. For instance, carbonate rocks of the Asmari Formation mark changes in the affinity of the study area, from the African–Arabian plate to only the Arabian plate, separated in conjunction with Red Sea rifting during the Oligocene. Information on the palaeogeographical changes is really precious to geoscientists and geotourists alike, and contributes to the great value of the Nowdan anticline geosite. Evidence from the latter, as well as from a few other places (i.e., the Mountainous Adygeya geodiversity hotspot in Russia, the North Coast of São Paulo in Brazil and the possible Gondwanan geopark in Namibia) illustrates the necessity of distinguishing a palaeomapping subtype in palaeogeographical characterisation of geological heritage.Item A statistical approach to estimates of geomorphological-morphotectonic diversity for evaluating the scientific value of geosites: a case study from the southeastern Lut desert, Iran(Instytut Geologii UAM, 2020-04) Sadeghi-Farshbaf, Pouya; Khatib, Mohammad Mahdi; Rezaei, NaserThe present study aims to investigate the diversity index (dv-index) of morphotectonic and geomorphological landforms as one of the scientific value indices for evaluation of the geotouristic potential of the southeastern Lut desert using topographic statistical analysis. Scientific index scoring in most models is based on descriptive assessment by geotourists and experts. Statistical analysis of the dv-index in the present study helps experts to base their scoring on scientific methods. The dv-index is controlled by several items. In the present study, we analyse two of these, including the classification of topographic continuity pattern (TCP) and topographic slope position correlation (TSPC). For this purpose, a network of section lines is used to analyse slope continuity. The TSPC analysis is performed by using two parameters of absolute value and slope position. Results for these two evaluated items indicate a score of 1.46 (out of 2) for the dv-index. Given a rating of 5, the score obtained for the two items is a high one. Therefore, an initial estimate of the dv-index indicates a significant scientific value of the study area.