Search Results (6)

The Miné-Akiyoshidai Karst Plateau aspiring UNESCO Global Geopark (aUGGp) in western Japan hosts several geologically significant heritage sites, including the Late Paleozoic Akiyoshi Limestone, the Late Triassic Mine Group, the Late Cretaceous Naganobori copper deposits, and the Akiyoshido Cave and karst plateau. The Akiyoshi Limestone at the Kaerimizu site originated as an atoll reef atop a seamount on an oceanic plate. It preserves approximately 80 million years of ancient marine environments and subduction-related tectonic histories. The Mine Group at the Momonoki site, with its coal-bearing strata, contains fossils of the earliest members of Diptera and Hymenoptera. The Naganobori copper mine at the Naganobori site played a vital role in Japanese society from the 8th to the 20th centuries. Meanwhile, the Akiyoshido site, renowned for its scenic beauty, is one of Japan’s most iconic tourist destinations. Using the IUGS guidelines and geoheritage assessment methodology, we reassessed the value and utilization of these geological heritage sites. The Kaerimizu and Momonoki sites were identified as internationally significant and ideal for scientific research. The Naganobori site was determined to be well-suited for educational purposes with national significance, while the Akiyoshido site was deemed optimal for geotourism with national significance. Full article

This paper studies ten Subbetic (Betic External Zones) stratigraphic sections spanning the Pliensbachian–early Toarcian time interval. Eight lithofacies were distinguished: crinoidal limestones, peloidal limestones, breccias, cherty limestones, nodular limestones, hardground surfaces and condensed levels, marls and marly limestone alternance, and dark marls. The biostratigraphy matches data from ammonite and calcareous nannofossil zonations. In addition, we analyzed C and O isotopes from bulk samples from three of the studied sections in which the lower Toarcian sedimentation crops out. The demise of the Lower Jurassic shallow platform developed in the South Iberian Paleomargin was a complex process driven by rifting, which led to tilted blocks giving way to different sedimentary environments. The tectonic stages occurred in the Sinemurian–Pliensbachian transition (R1), toward the lower part of the Ibex Zone (FO of the Biscutum grande, R2), in the Ibex–Davoei zones boundary (FO of Lotharingius barozii, R3), in the lower–upper Pliensbachian (R4), and in the lower boundary of the NJT4d nannofossil Subzone (R5) (Lavinianum Zone, upper Pliensbachian). After this last phase, sedimentation became pelagic in origin throughout the basin, represented by the sections studied. However, the isotope data show no clear record of the different C-isotopic events, though the Davoei–Margaritatus Event, the late Pliensbachian Event, and the Pliensbachian–Toarcian Boundary Event (PTBE) could be cautiously identified. These geochemical features are explained by the convergence of marine currents from Panthalassa (through the Hispanic Corridor) and Tethys. Full article

Zircon U-Pb geochronology was applied to investigate the provenance, depositional ages, and paleogeography of the southwestern Gondwana in detrital and ash fall sediments from Carboniferous to Jurassic succession of the southern Paraná Basin. Four detrital age populations suggest provenance from local and distal sources located to the south, southeast, and southwest: (i) Archean to Paleoproterozoic zircons from the Rio de La Plata Craton, Nico Peres and Taquarembó terranes; (ii) Grenvillian zircons from the basement of the Gondwanides and Namaqua–Natal belts; (iii) Neoproterozoic grains from the Don Feliciano Belt; and (iv) Phanerozoic populations from Paleozoic orogenic belts and related foreland systems in Argentina, as well as eroded units of the Paraná Basin. The paleogeographic reconstruction indicates an evolution in three distinct stages: (1) a gulf open to the Panthalassa Ocean during the Carboniferous; (2) an epicontinental sea with the rise of the Gondwanides Orogeny during the Permian; and (3) continental deposits controlled by an intra-plate graben system during the Triassic. Permian–Triassic volcanogenic zircons provide constrained maximum depositional ages and attested persistent volcanism, related to the Choiyoi magmatism and effects of the climate change episodes. During the Triassic, the extensional graben system recorded the uplift of the basement through regional northwest and northeast fault systems, and the recycling of Permian zircons, modifying source-to-sink relationships. Full article

Upper Triassic carbonate platforms from the Panthalassa Ocean remain less-understood and less-studied than their Tethyan equivalents. This imbalance is largely due to the poorer preservation state of Panthalassan carbonate rock successions in terms of rock quality and depositional geometries, which prevents good appreciation of depositional systems. In this context, carbonate exposures from Lime Peak (Yukon, Canada) represent an outstanding exception. There, the remains of an Upper Norian Panthalassan carbonate platform are well-exposed, show remarkably preserved depositional geometries and overall superior rock preservation. In this work, we analyse the carbonates from the Lime Peak area with particular attention to the vertical and lateral distribution of biotic assemblages and microfacies at the platform scale. Results demonstrate that the Lime Peak platform was surrounded by a basin with an aphotic sea bottom. The carbonate complex developed in warm waters characterized by high carbonate saturation. The area was also defined by moderate to high nutrient levels: this influenced the type of carbonate factory by favouring microbialites and sponges over corals. During its growth, Lime Peak was influenced by tectono-eustatism, which controlled the accommodation space at the platform top, primarily impacting the internal platform environments and the stability of the slope. Gaining better knowledge of the spatial distribution and dynamics of Upper Triassic organisms and sedimentary facies of Panthalassa in relation to tectono-eustatism lays the first foundations for reconstructing more robust platform models and understanding the evolution of other, more dismantled Upper Triassic Panthalassan carbonate systems through time. Full article

Island ecosystems differ in several elements from mainland ecosystems and may induce variations related to natural selection and patterns of adaptation in most aspects of the biology of an organism. Thylamys elegans (Waterhouse, 1839) is a marsupial endemic to Chile, distributed from Loa River to Concepción. Historically, three subspecies have been described: Thylamys elegans elegans, Thylamys elegans coquimbensis and Thylamys elegans soricinus. For this research, two morphometric approaches and a biomechanical model were used to compare the mandible shapes and biomechanics between two Chilean mouse opossum populations belonging to different subspecies: one from the coastal desert of Chile (T. e. coquimbensis) and the other from the central inland region (T. e. elegans). Additionally, mandibles of insular populations found in the Reserva Nacional Pinguino de Humboldt (RNPH)), from which the subspecies association is unknown, were also included. The results showed that insular populations have differences in mandibular shapes, sizes and biomechanical characteristics compared to continental populations, which may be related to environmental variables like aridity and vegetation cover, prey type, insularity effects and/or the founder effect on micromammals, apart from vicariance hypotheses and other selective pressures. Full article

Marine geoheritage comprises unique geological features of modern and ancient seas and oceans. The Russian Altai (southern Siberia) is a vast and geologically rich area, which was covered by a marginal sea of the Panthalassa Ocean in the Devonian. New geosites representing shallow- and deep-marine depositional environments and palaeoecosystems of submarine volcano slopes are proposed, namely, Melnichnye Sopki and Zavodskie Sopki. They are located near the town of Zmeinogorsk (Altai Region of the Russian Federation). These pieces of marine geoheritage are valuable on an international scale. Special geoconservation procedures are recommended to manage the proposed geosites efficiently. They can be included in a geopark, which is reasonable to create due to the concentration of geological and mining heritage in the study area. Full article