Kaoline Mapping Using ASTER Satellite Imagery: The Case Study of Kefalos Peninsula, Kos Island

The present work aims to map kaolin occurrences on the Kefalos peninsula, SW Kos Island, Greece, through the elaboration of ASTER satellite imagery. The island of Kos is located on the eastern edge of the South Aegean Active Volcanic Arc (SAAVA) and is characterised by its complex geologic structure. During Plio-Pleistocene, the voluminous eruption of the Kos Plateau Tuff was recorded on Kefalos; the largest quaternary eruption in the Mediterranean. Kaolin is the product of hydrothermal alteration of the Pliocene volcanic rocks with rhyolitic composition. Our study emphasises the usefulness of satellite imagery combined with the Mixture Tuned Matched Filtering (MTMF) technique to detect occurrences of industrial minerals, kaolin-group minerals in this case, either in terms of raw mineral exploitation or by mapping hydrothermal alteration.

Geologic Structure, Mineralogy, and Geochemistry of the Nerunda Gold Ore Field (Northern Transbaikalia)

—We consider the geologic structure of the Nerunda gold ore field located in the Nerunda–Mama ore district in northern Transbaikalia. Gold–quartz low-sulfide formation and ore-bearing carbonate-terrigenous strata and intrusive complexes are briefly described. An ore complex of beresite–listvenite metasomatites hosting carbonate–quartz veins and vein–veinlet zones is characterized. Two stages of ore formation have been recognized. Anomalous geochemical associations and the composition of ore mineralization typical of these stages have been established. Mineralogical and geochemical studies of gold-bearing metasomatites of the Nerunda ore field were carried out. The known geochemical and mineralogical search criteria used for the assessment of the erosion zone level of gold deposits were applied to the geologic conditions of the Nerunda ore field and the Nerunda–Mama gold ore district as a whole. The emphasis was made on the express assessment of the erosion zone level at the early stage of prospecting. We draw a conclusion about the gold potential of the poorly studied ore objects at depth and give guidelines for the following geological prospecting.

Optimum Detailed Standards to Control Non-Point Source Pollution Priority Management Areas: Centered on Highland Agriculture Watershed

The Ministry of Environment in Korea aims to reduce non-point source (NPS) pollution and improve soil water management by expanding NPS priority management areas. Six NPS priority management areas to reduce suspended solids (SS) according to soil loss were chosen as they either constitute serious hazards to the natural ecosystem due to NPS pollutants or they are areas with unusual geologic structure or strata. Although more comprehensive standards are required for effective NPS management, however, no detailed consideration factors and standards are available in the legal provisions. Therefore, in this study, based on the existing six priority NPS management areas and using results from previous studies, we present detailed legal designation standards. We found that the higher the altitude, slope, and field area ratio, the higher the effect of SS on water quality during rainfall. Additionally, there is a high correlation as R2 0.9813 between SS and the habitat and riparian index. These results are useful for establishing detailed standards for areas requiring an NPS management system, future expansion of the NPS priority management area designation, and policymaking and research for reducing NPS pollution in Korea.

River sinuosity describes a continuum between randomness and ordered growth

River channels are among the most common landscape features on Earth. An essential characteristic of channels is sinuosity: their tendency to take a circuitous path, which is quantified as along-stream length divided by straight-line length. River sinuosity is interpreted as a characteristic that either forms randomly at channel inception or develops over time as meander bends migrate. Studies tend to assume the latter and thus have used river sinuosity as a proxy for both modern and ancient environmental factors including climate, tectonics, vegetation, and geologic structure. But no quantitative criterion for planform expression has distinguished between random, initial sinuosity and that developed by ordered growth through channel migration. This ambiguity calls into question the utility of river sinuosity for understanding Earth’s history. We propose a quantitative framework to reconcile these competing explanations for river sinuosity. Using a coupled analysis of modeled and natural channels, we show that while a majority of observed sinuosity is consistent with randomness and limited channel migration, rivers with sinuosity ≥1.5 likely formed their geometry through sustained, ordered growth due to channel migration. This criterion frames a null hypothesis for river sinuosity that can be applied to evaluate the significance of environmental interpretations in landscapes shaped by rivers. The quantitative link between sinuosity and channel migration further informs strategies for preservation and restoration of riparian habitat and guides predictions of fluvial deposits in the rock record and in remotely sensed environments from the seafloor to planetary surfaces.

Decaying Post-Seismic Deformation Observed on the Korean Peninsula Following the 2011 Tohoku-Oki Earthquake

We investigated decaying post-seismic deformation observed on the Korean Peninsula associated with the 2011 Mw 9.0 Tohoku-Oki earthquake using Global Navigation Satellite System (GNSS). The GNSS velocity vectors were estimated in five periods from 2005 to 2019. A co-seismic offset of the Korean Peninsula caused by the 2011 earthquake was inversely proportional to epicentral distances. According to the temporal variations of two components (magnitude and direction) of the GNSS velocity vector with the epicentral distance, the difference between the eastern and western regions for the two components becomes smaller over time. For approximately nine years after the 2011 event, the direction for the crustal movement in South Korea showed a recovery pattern returning to the pre-earthquake motion. In addition, the recovery patterns of the crustal movement were observed differently with the regional geologic structure (e.g., the crustal thickness) and each period. Our estimates of the decay in post-seismic deformation of the Korean Peninsula suggest that post-seismic relaxation will be complete within 5–20 years after the 2011 earthquake. The results suggest that the crustal movement on the Korean Peninsula is gradually recovering to its pre-earthquake motion.

Multistage Evolution of Proterozoic Crust of East Antarctica by the Example of the Filla Terrane (Rauer Islands): New Geological and Isotope Data

—The paper presents new data on the Rauer Islands, one of the unique objects of the East Antarctic Shield. The interest in this area is triggered by its complex geologic structure, including both Archean and Proterozoic fragments of the Earth’s crust, and by its multiphase formation. A detailed scheme of the geologic structure of the area is proposed, new petrologic complexes are revealed, and the stages of tectonomagmatic activity at ~1400–1320 Ma and 1150 Ma are reliably dated. This serves as a factual basis for comparison the study area with other regions of East Antarctica. Based on the geological and isotope data obtained, the Meso–Neoproterozoic Filla Terrane in the area of the Rauer Islands is recognized. It is composed of metamorphic and primarily intrusive rocks, whose protoliths formed in the time interval 1400–950 Ma. Three periods of tectonothermal activity have been established in the Filla Terrane: Mid-Mesoproterozoic (1400–1320 Ma), Meso–Neoproterozoic (1150–886 Ma), and early Cambrian (536–504 Ma). The first period is the formation time of Mesoproterozoic crust, and it is time-correlated with the tectonogenesis phase in the adjacent Rayner province. The second period corresponds to the later phase of tectonothermal activity in the Rayner province. In the Filla Terrane, this period can be divided into two intervals, 1150–1100 Ma and 1010–886 Ma. The former interval is treated as intense crustal growth in the course of granitoid and mantle magmatism. The latter interval is a period of tectonothermal processes accompanied by intense deformations, high-temperature metamorphism, and intrusion of porphyritic granitoids. Apparently, the gap between the first and the second intervals is the time of deposition of the sedimentary protolith of paragneisses, which, together with the surrounding rocks, underwent high-temperature metamorphism and deformations at 950–914 Ma. The synchronous evolution of the Archean block and the Filla Terrane began at least within 1100–1000 Ma. The youngest, early Cambrian period of tectonic activity coincides with the development of local low-temperature mylonite zones and the intrusion of synkinematic pegmatite veins. Thus, the tectonothermal evolution of the Filla Terrane includes almost the same main phases of crustal growth and transformation as the Rayner province. This indicates that the Filla Terrane is a fragment of the Rayner province, which accreted to the Archean terrane at least in the late Mesoproterozoic.

Superimposed Pattern of the Southern Sichuan Basin Revealed by Seismic Refl ection Profi les Across Lushan–Chishui, China

The Sichuan Basin is a typical intracraton superimposed basin. It is rich in oil and gas resources in the different sets of sedimentary sequences. It underwent multistage tectonic evolution, which resulted in different types of prototype basins. However, there are still many different opinions on the types and superimposed patterns of the Sichuan Basin in different geologic periods, which largely affect the understanding of the mechanism of effective oil and gas accumulation and preservation. This paper aims to re-recognize several prototype types of the Sichuan Basin by discussing the prototype basins and their superimposed models to deepen the significance of superimposed basin evolution for hydrocarbon accumulation. The regional geological and drilling data are used for a detailed interpretation of seismic reflection profiles across Lushan–Chishui. Then, five regional unconformities are identified with the equilibrium profiles technique which is used to flatten the formation interface in different geologic periods. Based on the unconformities, the southern Sichuan Basin is divided into six tectonic layers, each of which is regarded as a prototype basin: a pre-Sinian crystalline basement (AnZ), a marine rift cratonic basin (Z–S), a marine intracratonic sag basin (P2l–T2l), a marine–continental downfaulted basin (T3x1–T3x3), a continental depressed basin (T3x4–J), and a foreland basin (K–Q). The different prototype basins are vertically superimposed to form a “layered block” geologic structure of the multicycle basins. Affected by the late-stage tectonic transformation, the geologic structure of vertical stratification underwent a strong transformation, which had a profound impact on oil and gas accumulation with the characteristics of early accumulation and late adjustment.