Современное напряженное состояние коры Апеннинского полуострова и сопредельных территорий (Центральное Средиземноморье)

This paper discusses models showing the formation of the Central Mediterranean region and the geodynamic setting of the Apennine Peninsula. Cataclastic analysis is used for a repeated reconstruction of the Central Mediterranean region. The catalogue of earthquake focal mechanisms includes 662 events (3.6≤Mb≤6.5) recorded in the study area from 1977 to 2015 (Global CMT, http://www.globalcmt.org; RCMT, http://rcmt2.bo.ingv.it/index.html; Italian CMT dataset, http://rcmt2.bo.ingv.it/Italydataset.html). The reconstruction yielded the directions of principal stresses (including algebraically maximum and minimum ones), locations of domains differing in geodynamic regime, Lode – Nadai coefficients, and orientation of tangential shear stresses acting from the mantle to the crust. By comparing our results to the published data obtained by M.‐L. Zoback’s method, we have identified differences in the orientations of maximum horizontal compression axes at points where the stress ellipsoid takes on its critical values. It is revealed that the strongest earthquakes (M>6) were generated in the areas characterized by the minimum and average relative stress magnitudes.В данной работе рассматриваются возможные модели образования Центрального Средиземноморья и геодинамическая обстановка Апеннинского полуострова. С помощью метода катакластического анализа проводится повторная реконструкция Центрального Средиземноморья. Каталог механизмов очагов землетрясений включает в себя данные Global СМТ (http://www.globalcmt.org), RCMT (http://rcmt2.bo.ingv.it/index.html) и Итальянской базы данных (Italian CMT dataset) (http://rcmt2.bo.ingv.it/Italydataset.html). Каталог составили 662 события с магнитудами 3.6≤Mୠ≤6.5, произошедшие за период с 1977 по 2015 г. Результатом реконструкции является ориентация направлений алгебраически максимальных и минимальных главных напряжений, расположение доменов геодинамического режима и коэффициента Лоде – Надаи, а также ориентация поддвиговых касательных напряжений, действующих со стороны мантии на кору. Проводится сравнение с уже имеющимися данными, которые были получены с помощью методики М.Л. Зобак, найдены отличия в ориентации осей наибольшего горизонтального сжатия в местах, где вид эллипсоида напряжений принимает свои критические значения. По данным об относительных величинах напряжений показано, что формирование наиболее сильных событий (М>6) происходило в областях с минимальными и средними относительными величинами

Неотектоника и тектонические напряжения острова Сахалин

The paper describes the neotectonics of the Sakhalin Island and analyzes the latest and recent tectonic stresses in the study area in order to establish their differences in the Amur and Okhotsk microplates, which boundary is confined to the Tym-Poronaisk fault, the largest NS-striking fault in the Central Sakhalin (Fig. 1). Our map of the structural geomorphological features of the study area (Fig. 2) shows three longitudinal zones: the western and eastern uplifts, and the Central Sakhalin basin between the uplifts. In the Southern Sakhalin, neotectonic stresses were studied by a combination of tectonophysical methods and the method of structural geology (Figures 3 to 6, and Table). Our study shows that the regional axes of maximum and minimum compressive principal normal stresses are primarily of the subhorizontal orientations (Fig. 5, Д). In the Northern and Central Sakhalin, neotectonic stresses were reconstructed by the structural geomorphology method. The compression axes are oriented sublatitudinally, with the NE-trending strike in the Northern Sakhalin (Fig. 7, A), and the extension axes are oriented submeridionally; in the Northern Sakhalin, respectively, they are oriented in the NW direction. The results of our study of neotectonic stresses were used to construct a map of recent geodynamics of Sakhalin (Fig. 7, Б), which shows zones differing in the geodynamic settings of the most recent faulting. According to the analysis of the recent tectonic stress with respect to the earthquake focal mechanisms in the period from 1978 to 2015 (Fig. 8), recent stresses dominating in Sakhalin have mainly the sublatitudinal low-angle orientations of the deviatoric compression axis. The submeridional low-angle orientations of the deviatoric extension axes are observed in the Northern Sakhalin and partly in the north of the Southern Sakhalin (see Fig. 8). The high-angle axes of deviatoric extension are typical of the western and central parts of the Southern Sakhalin, and such extension leads to horizontal compression and reverse faulting. In some areas of the recent stress field, the deviatoric axes of compression and extension have unstable orientations. The latitudinal boundaries of such areas are nearly coincident with the boundaries of the zones that differ in the geodynamic settings of the most recent faulting, which means that these areas and zones are reliably identified. The relative inhomogeneity of the neotectonic and recent stress fields in the Southern Sakhalin does not give grounds to distinguish differences in the state of crustal stresses in the areas located on the sides of the Southern Sakhalin fault. As a consequence, a boundary between the Amur and the Okhotsk Plate in the South Sakhalin cannot be drawn along this fault. It is most likely that this boundary coincides with the Western-Sakhalin fault in the southern areas of the study region. Our data on the Central and Northern Sakhalin does not contradict with the conclusion in [Savostin et al., 1982] concerning this boundary.Охарактеризована неотектоника, новейшие и современные тектонические напряжения Сахалина для установления их различия в Амурской и Охотской микроплитах, граница между которыми приурочена к меридиональному крупнейшему Центрально-Сахалинскому (Тымь-Поронайскому) разлому (рис. 1). Составлена структурно-геоморфологическая карта (рис. 2), на которой выделены три продольные зоны – западная и восточная зоны поднятий, разделенные Центрально-Сахалинской протяженной впадиной. Неотектонические напряжения, изученные комплексом тектонофизических и структурных методов на Южном Сахалине (рис. 3–6; табл. 1), показали, что оси максимальных и минимальных сжимающих главных нормальных напряжений регионального уровня ориентированы преимущественно субгоризонтально (рис. 5, Д). На Северном и Центральном Сахалине неотектонические напряжения восстановлены структурно-геоморфологическим методом. Оси сжатия ориентированы субширотно, с тенденцией северо-восточного простирания на Северном Сахалине (рис. 7, А), а оси растяжения – субмеридионально; на Северном Сахалине, соответственно, они ориентированы в северо-западном направлении. В результате изучения неотектонических напряжений составлена схема новейшей геодинамики Сахалина (рис. 7, Б). На ней показано районирование областей с разной геодинамической обстановкой формирования разломов в новейший этап. Анализ современных тектонических напряжений по механизмам очагов землетрясений, характеризующих события 1978–2015 гг. (рис. 8), показал, что на Сахалине доминируют современные напряжения с субширотной пологой ориентировкой оси девиаторного сжатия и субмеридиональной, также пологой, ориентировкой оси девиаторного растяжения на севере острова и частично на севере Южного Сахалина (рис. 8). Запад и центр Южного Сахалина, включая восточную часть Татарского пролива, характеризуются крутыми осями девиаторного растяжения, обеспечивающего геодинамический режим горизонтального сжатия и развитие взбросовых структур. Широтные границы областей с неустойчивыми ориентировками девиаторных осей сжатия и растяжения современного поля напряжений близки к границам областей с разной геодинамической обстановкой формирования разломов в новейший этап, что подтверждает объективность выделения этих областей. Выявленная относительная однородность неотектонического и современного полей напряжений Южного Сахалина не дает основания различать напряженное состояние коры с разных сторон от Центрально-Сахалинского разлома и, как следствие, не позволяет проводить по этому разлому границу между Амурской и Охотской плитами на Южном Сахалине. Наиболее вероятным представляется то, что на юге района она совпадает с Западно-Сахалинским разломом, а на Центральном и на Северном Сахалине материалы, полученные проведенными исследованиями, не противоречат границе, проведенной Л.А. Савостиным [Savostin et al., 1982]

Geochemical Characterization of Two Ferruginous Meromictic Lakes in the Upper Midwest, USA

To elucidate the role of (bio)geochemical processes that fueled iron and carbon cycling in early Earth oceans, modern environments with similar geochemical conditions are needed. As the range of chemical, physical, and biological attributes of the Precambrian oceans must have varied in time and space, lakes of different compositions are useful to ask and answer different questions. Tropical Lake Matano (Indonesia), the largest known ferruginous lake, and Lake Pavin (France), a meromictic crater lake, are the two best studied Precambrian ocean analogs. Here we present seasonal geochemical data from two glacially formed temperate ferruginous lakes: Brownie Lake (MN) and Canyon Lake (MI) in the Upper Midwest, USA. The results of seasonal monitoring over multiple years indicate that (1) each lake is meromictic with a dense, anoxic monimolimnion, which is separated from the less dense, oxic mixolimnion by a sharp chemocline; (2) below this chemocline are ferruginous waters, with maximum dissolved iron concentrations \u3e1 mM; (3) meromixis in Brownie Lake is largely anthropogenic, whereas in Canyon Lake it is natural; (4) the shallow chemocline of Brownie Lake and high phosphorus reservoir make it an ideal analog to study anoxygenic photosynthesis, elemental ratios, and mineralogy; and (5) a deep penetrating suboxic zone in Canyon Lake may support future studies of suboxic microbial activity or mineral transformation

Photoferrotrophy: Remains of an ancient photosynthesis in modern environments

© 2017 Camacho, Walter, Picazo and Zopfi. Photoferrotrophy, the process by which inorganic carbon is fixed into organic matter using light as an energy source and reduced iron [Fe(II)] as an electron donor, has been proposed as one of the oldest photoautotrophic metabolisms on Earth. Under the iron-rich (ferruginous) but sulfide poor conditions dominating the Archean ocean, this type of metabolism could have accounted for most of the primary production in the photic zone. Here we review the current knowledge of biogeochemical, microbial and phylogenetic aspects of photoferrotrophy, and evaluate the ecological significance of this process in ancient and modern environments. From the ferruginous conditions that prevailed during most of the Archean, the ancient ocean evolved toward euxinic (anoxic and sulfide rich) conditions and, finally, much after the advent of oxygenic photosynthesis, to a predominantly oxic environment. Under these new conditions photoferrotrophs lost importance as primary producers, and now photoferrotrophy remains as a vestige of a formerly relevant photosynthetic process. Apart from the geological record and other biogeochemical markers, modern environments resembling the redox conditions of these ancient oceans can offer insights into the past significance of photoferrotrophy and help to explain how this metabolism operated as an important source of organic carbon for the early biosphere. Iron-rich meromictic (permanently stratified) lakes can be considered as modern analogs of the ancient Archean ocean, as they present anoxic ferruginous water columns where light can still be available at the chemocline, thus offering suitable niches for photoferrotrophs. A few bacterial strains of purple bacteria as well as of green sulfur bacteria have been shown to possess photoferrotrophic capacities, and hence, could thrive in these modern Archean ocean analogs. Studies addressing the occurrence and the biogeochemical significance of photoferrotrophy in ferruginous environments have been conducted so far in lakes Matano, Pavin, La Cruz, and the Kabuno Bay of Lake Kivu. To date, only in the latter two lakes a biogeochemical role of photoferrotrophs has been confirmed. In this review we critically summarize the current knowledge on iron-driven photosynthesis, as a remains of ancient Earth biogeochemistry

Modern state of crustal stresses of the Apennine Peninsula and adjacent territories (Central Mediterranean region)

This paper discusses models showing the formation of the Central Mediterranean region and the geodynamic setting of the Apennine Peninsula. Cataclastic analysis is used for a repeated reconstruction of the Central Mediterranean region. The catalogue of earthquake focal mechanisms includes 662 events (3.6≤Mb≤6.5) recorded in the study area from 1977 to 2015 (Global CMT, http://www.globalcmt.org; RCMT, http://rcmt2.bo.ingv.it/index.html; Italian CMT dataset, http://rcmt2.bo.ingv.it/Italydataset.html). The reconstruction yielded the directions of principal stresses (including algebraically maximum and minimum ones), locations of domains differing in geodynamic regime, Lode – Nadai coefficients, and orientation of tangential shear stresses acting from the mantle to the crust. By comparing our results to the published data obtained by M.‐L. Zoback’s method, we have identified differences in the orientations of maximum horizontal compression axes at points where the stress ellipsoid takes on its critical values. It is revealed that the strongest earthquakes (M>6) were generated in the areas characterized by the minimum and average relative stress magnitudes

Neotectonics and tectonic stresses of the Sakhalin Island

The paper describes the neotectonics of the Sakhalin Island and analyzes the latest and recent tectonic stresses in the study area in order to establish their differences in the Amur and Okhotsk microplates, which boundary is confined to the Tym-Poronaisk fault, the largest NS-striking fault in the Central Sakhalin (Fig. 1). Our map of the structural geomorphological features of the study area (Fig. 2) shows three longitudinal zones: the western and eastern uplifts, and the Central Sakhalin basin between the uplifts. In the Southern Sakhalin, neotectonic stresses were studied by a combination of tectonophysical methods and the method of structural geology (Figures 3 to 6, and Table). Our study shows that the regional axes of maximum and minimum compressive principal normal stresses are primarily of the subhorizontal orientations (Fig. 5, Д). In the Northern and Central Sakhalin, neotectonic stresses were reconstructed by the structural geomorphology method. The compression axes are oriented sublatitudinally, with the NE-trending strike in the Northern Sakhalin (Fig. 7, A), and the extension axes are oriented submeridionally; in the Northern Sakhalin, respectively, they are oriented in the NW direction. The results of our study of neotectonic stresses were used to construct a map of recent geodynamics of Sakhalin (Fig. 7, Б), which shows zones differing in the geodynamic settings of the most recent faulting. According to the analysis of the recent tectonic stress with respect to the earthquake focal mechanisms in the period from 1978 to 2015 (Fig. 8), recent stresses dominating in Sakhalin have mainly the sublatitudinal low-angle orientations of the deviatoric compression axis. The submeridional low-angle orientations of the deviatoric extension axes are observed in the Northern Sakhalin and partly in the north of the Southern Sakhalin (see Fig. 8). The high-angle axes of deviatoric extension are typical of the western and central parts of the Southern Sakhalin, and such extension leads to horizontal compression and reverse faulting. In some areas of the recent stress field, the deviatoric axes of compression and extension have unstable orientations. The latitudinal boundaries of such areas are nearly coincident with the boundaries of the zones that differ in the geodynamic settings of the most recent faulting, which means that these areas and zones are reliably identified. The relative inhomogeneity of the neotectonic and recent stress fields in the Southern Sakhalin does not give grounds to distinguish differences in the state of crustal stresses in the areas located on the sides of the Southern Sakhalin fault. As a consequence, a boundary between the Amur and the Okhotsk Plate in the South Sakhalin cannot be drawn along this fault. It is most likely that this boundary coincides with the Western-Sakhalin fault in the southern areas of the study region. Our data on the Central and Northern Sakhalin does not contradict with the conclusion in [Savostin et al., 1982] concerning this boundary

Biogeochemistry (speciation and isotopes of S and C) in bottom sediments, water and bacterial mats from the White Sea

This publication presents results of microbiological and biogeochemical studies in the White Sea. Material was obtained during a series of expeditions in 1999-2002. The studies were carried out in the open part of the White Sea, in the Onega, Dvina and Kandalaksha Bays, as well as in the intertidal zone of the Kandalaksha Bay. Quantitative characteristics of activity of microbial processes in waters and bottom sediments of the White Sea were obtained. The total number of bacteria was equal to 150000-800000 cells/ml, and intensity of dark CO2 assimilation was equal to 0.9-17 µg C/l/day. Bacterial sulfate reduction was equal to 3-150 mg S/m**2/day, and methane formation and oxidation was equal to 13-6840 and 20-14650 µl CH4/m**2/day, respectively. Extremely high values of intensity of all principal microbial processes were found in intertidal sediments rich in organic matter: under decomposing macrophytes, in local pits at the lower intertidal boundary, and in the mouth of a freshwater brook. Average hydrogen sulfide production in highly productive intertidal sediments was 1950-4300 mg S/m**2/day, methane production was 0.5-8.7 ml CH4/m**2/day, and intensity of methane oxidation was up to 17.5 ml CH4/m**2/day. Calculations performed with account for areas occupied by microlandscapes of increased productivity showed that diurnal production of H2S and CH4 per 1 km**2 of the intertidal zone (August) was estimated as 60.8-202 kg S/km**2/day and 192-300 l CH4/km**2/day, respectively