A morpho-tectonic approach to the study of earthquakes in Rome

Rome has the world’s longest historical record of felt earthquakes, with more than 100 events during the last 2,600 years. However, no destructive earthquake has been reported in the sources and all of the greatest damage suffered in the past has been attributed to far-field events. While this fact suggests that a moderate seismotectonic regime characterizes the Rome area, no study has provided a comprehensive explanation for the lack of strong earthquakes in the region. Through the analysis of the focal mechanism and the morphostructural setting of the epicentral area of a "typical" moderate earthquake (ML = 3.3) that recently occurred in the northern urban area of Rome, we demonstrate that this event reactivated a buried segment of an ancient fault generated under both a different and a stronger tectonic regime than that which is presently active. We also show that the evident structural control over the drainage network in this area reflects an extreme degree of fragmentation of a set of buried faults generated under two competing stress fields throughout the Pleistocene. Small faults and a present-day weaker tectonic regime with respect to that acting during the Pleistocene explain the lack of strong seismicity and imply that a large earthquake could not reasonably occur.

Tectonic regime of the area of the Sukhoi Log geological practice in the Middle Devonian and volcanic arcs in the basement of Western Siberia

The article briefly describes current understanding of the tectonic regime of study area. It is related to the field geological practice of students of Industrial University of Tyumen. Study area is located at the western edge of Sukhoi Log town, Sverdlovsk region. The relevance of the work is related to the educational process. Information about the geological structure of the Devonian and Carboniferous formations of study area is collected. Some of the most characteristic outcrops of Paleozoic are described. Actual information about the Ural mountain genesis is given. The list of studied objects includes the outcrop of Eifelian reefal limestones near to the Shata waterfall and the ruins of a volcano. According to other researchers, it is a part of Middle Devonian volcanic arc, which was formed over the subduction zone. Here the Ordovician-Silurian Paleouralian Ocean were subducted under the collage of different-age terrains and paleocontinents (Paleozoic basement of the modern West Siberian Plate). A possible section across the Middle Devonian subduction zone of study area is presented. Similar objects associated with the oil and gas are known in the Pre-Jurassic basement of Western Siberia. The limestones and volcanic massifs exposed near the Sukhoi Log are good natural equivalents of the objects of oil and gas exploration in Western Siberia.

Tectonic Influence on Speleogenesis of Sea Caves on Biševo Island (UNESCO Global Geopark Vis Archipelago, Adriatic Sea, Croatia)

A geological and speleological investigation was conducted in the famous Blue Cave (Modra špilja) and the Monk Seal Cave (Medvidina špilja) on Biševo Island (Croatia) to promote the island’s geoheritage through the new Visitor Centre. The island is mainly composed of Cretaceous to Paleogene neritic carbonates, which form the bedrock, whereas parts of the island are covered with thin Quaternary sediments. The caves are of small dimensions and a simple layout, composed of the main channel and few shorter side channels, all positioned in the tidal zone. Thus, the caves are semi-submerged sea caves located along the coastline. The Blue Cave and the Monk Seal Cave developed within the bedrock limestones and dolostones, respectively, within a zone of left-lateral NNE–SSW striking strike-slip faults that belong to the Biševo fault system. Conjugated discontinuities within the carbonate bedrock indicate a specific strike-slip tectonic regime. Additionally, the host rocks were probably also deformed and fractured during the rise of salt diapirs that characterise this part of the Adriatic foreland. Tectonic and bedding discontinuities form the fragments of the host rock, that combined with the impacts of the strong southern waves, significantly influenced the genesis of the caves.

PECULIARITIES OF FORMATION OF THE LOWER CRETACEOUS TEСTONO-SEDIMENTATION SYSTEM OF THE BLACK SEA MEGADEPRESSION

Based on the analysis of the distribution of structural-material complexes, facial-genetic types and modeling of the history of immersion of the Lower Cretaceous sediments, the spatial-temporal differentiation of the tectonic regime of the Black Sea megadepression in the Early Cretaceous was established. It is shown that the structural and lithologicalfacial features of the Lower Cretaceous tectonic-sedimentation system were determined by the interaction of tectonic and geological-paleooceanographic factors. Thus, the low sea level and the initial phases of activation of sublatitudinal faults in the Hoterivian-Aptian determined the dominant influence of submeridional tectonic faults on the formation of the corresponding structural-facial block zonation. The increase in the area of the basin, the removal of denudation areas in the Late Albian reduced the intensity of terrigenous discharge, and the prolonged activity of sublatitudinal faults led to the formation of sublatitudinal structural-facial zonation. In the subsequent geological history, the tectonic regime was characterized by a complex mosaic-block character, which influenced the heterogeneity of oil and gas lithofluid systems of Cretaceous deposits.

Mariana-type ophiolites constrain the establishment of modern plate tectonic regime during Gondwana assembly

Initiation of Mariana-type oceanic subduction zones requires rheologically strong oceanic lithosphere, which developed through secular cooling of Earth’s mantle. Here, we report a 518 Ma Mariana-type subduction initiation ophiolite from northern Tibet, which, along with compilation of similar ophiolites through Earth history, argues for the establishment of the modern plate tectonic regime by the early Cambrian. The ophiolite was formed during the subduction initiation of the Proto-Tethys Ocean that coincided with slab roll-back along the southern and western Gondwana margins at ca. 530-520 Ma. This global tectonic re-organization and the establishment of modern plate tectonic regime was likely controlled by secular cooling of the Earth, and facilitated by enhanced lubrication of subduction zones by sediments derived from widespread surface erosion of the extensive mountain ranges formed during Gondwana assembly. This time also corresponds to extreme events recorded in climate and surface proxies that herald formation of the contemporary Earth.

Sedimentation across the Paraburdoo spherule layer: Implications for the Neoarchean Earth system

ABSTRACT Large bolide impacts in the Phanerozoic produced global change identifiable in the postimpact sediments. Aside from a few isolated examples, however, evidence of postimpact change associated with Precambrian impacts is sparse. This study used the Neoarchean Paraburdoo spherule layer as a case study to search for impact-induced change in the sediments above the spherule layer. We found possible minor sedimentary changes that may have been due to either a disturbance by bottom currents or changing diagenetic conditions. Contrary to the trends found with several post–Great Oxidation Event large bolide impacts, we found no evidence of shifts in tectonic regime, sediment weathering and deposition, or paleoenvironment induced by the Paraburdoo spherule layer impact, for which the impactor is estimated to have been approximately three times larger than the Cretaceous–Paleogene bolide. This lack of a clear signal of climatic shift may be due to one or more mechanisms. Either the Paraburdoo spherule layer’s deposition in several-hundred-meter-deep water within the Hamersley Basin of Western Australia was too deep to accumulate and record observable changes, or the Neoarchean’s high-CO2 atmospheric composition acted as a threshold below which the introduction of more impact-produced gases would not have produced the expected climatic and weathering changes. We also report minor traces of elevated iron and arsenic concentrations in the sediments immediately above the Paraburdoo spherule layer, consistent with trends observed above other distal impact deposits, as well as distinctive layers of hematite nodules bracketing the spherule layer. These geochemical changes may record ocean overturn of the Neoarchean stratified water column, which brought slightly oxygenated waters to depth, consistent with the observation of tsunami deposits in shallower impact deposits and/or heating of the global oceans by tens to hundreds of degrees Celsius in the wake of the Paraburdoo spherule layer impact. Either or both of these mechanisms in addition to impact-induced shallow-water ocean evaporation may also have caused a massive die-off of microbes, which also would have produced a postimpact increase in iron and arsenic concentrations.

Supplemental Material: Earth’s new tectonic regime at the dawn of the Paleoproterozoic: Hf isotope evidence for efficient crustal growth and reworking in the São Francisco craton, Brazil

Methodology and sample descriptions.<br>