Submarine Conditions Research Articles

Rb–Sr and Sm–Nd isotope systematics and geochemical studies on metavolcanic rocks from Peddavura greenstone belt: Evidence for presence of Mesoarchean continental crust in easternmost part of Dharwar Craton, India

Linear, north–south trending Peddavura greenstone belt occurs in easternmost part of the Dharwar Craton. It consists of pillowed basalts, basaltic andesites, andesites (BBA) and rhyolites interlayered with ferruginous chert that were formed under submarine condition. Rhyolites were divided into type-I and II based on their REE abundances and HREE fractionation. Rb–Sr and Sm–Nd isotope studies were carried out on the rock types to understand the evolution of the Dharwar Craton. Due to source heterogeneity Sm–Nd isotope system has not yielded any precise age. Rb–Sr whole-rock isochron age of 2551 ± 19 (MSWD = 1.16) Ma for BBA group could represent time of seafloor metamorphism after the formation of basaltic rocks. Magmas representing BBA group of samples do not show evidence for crustal contamination while magmas representing type-II rhyolites had undergone variable extents of assimilation of Mesoarchean continental crust (>3.3 Ga) as evident from their initial ε Nd isotope values. Trace element and Nd isotope characteristics of type I rhyolites are consistent with model of generation of their magmas by partial melting of mixed sources consisting of basalt and oceanic sediments with continental crustal components. Thus this study shows evidence for presence of Mesoarchean continental crust in Peddavura area in eastern part of Dharwar Craton.

Permafrost (Cryolithozone) of the Russian Arctic Shelf

The problem of age nonuniformity of the permafrost of the Russian Arctic shelf is considered in this paper. It is assumed that recent permafrost exists on the present-day shelf in addition to the cryolithozone, which was formed under subaerial conditions during shelf draining in the Late Pleistocene, was flooded during the subsequent transgression, and exists as a relic zone. It is considered whether permafrost can be formed immediately under submarine conditions. The mechanism of bottom soil freezing and ice formation, based on constant natural transformations in seabed sediments, is proposed. The proposed mechanism is confirmed by analyzing certain sections of the bottom sediments of shelf and of the Pleistocene marine plains (ancient shelves) composed of dislocated sequences with massive ice beds. On the basis of a ground massive ice genetic analysis different geological development as well as different transgressive and regressive regime of the Russian Arctic western and eastern sectors was revealed. The glacial cover limited distribution in the Russian North and its absence on the Russian Arctic and Subarctic plains to the East of the Kanin Peninsula were noted.

Architecture of Upper Cretaceous rhyodacitic hyaloclastite at the polymetallic Madneuli deposit, Lesser Caucasus, Georgia

AbstractThis study focuses on a well-exposed section of the Artvin-Bolnisi zone located in the open pit of the Madneuli ore deposit, Lesser Caucasus, Georgia. Detailed field and petrographic observations of the main volcano-sedimentary lithofacies of its Upper Cretaceous stratigraphic succession were carried out. Whole rock geochemistry studies support the interpretation of intense silicification of the rocks, and supports our petrographic studies of samples from the Madneuli open pit, including lobe-hyaloclastite described in detail during this study. A particular focus concerned lobe-hyaloclastite exposures in the Madneuli open pit, singled out for first time in this area of the Lesser Caucasus. Two types of hyaloclastite are recognized at the Madneuli deposit: hyaloclastite with pillow-like forms and hyaloclastite with glass-like selvages. The petrographic description shows a different nature for both: hyaloclastite with glass-like selvages represented by devitrification of volcanic glass, which is replaced by quartz and K-feldspar overgrowth of crystals in the groundmass and elongated K-feldspar porphyry phenocrysts. Perlitic cracks were identified during thin section observation. The Hyaloclastite with pillow-like forms consists of relicts of volcanic glass and large pumice clasts replaced by sericite. Key observations are presented in the case of lobe-hyaloclastite and their immediate host volcano-sedimentary environment to constrain their depositional setting. A paleoreconstruction of their environment is proposed, in which hyaloclastite record the interaction of magma emplaced in unconsolidated volcano-sedimentary rocks associated with a submarine rhyodacite dome, emplaced during several magmatic pulses. Our study shows that the predominant part of the host rock sequence of the Madneuli polymetallic deposit was deposited under submarine conditions, which is in agreement with volcanogenic massive sulfide models or transitional, shallow submarine magmatic to epithermal models that were proposed by previous studies.

FORMATION AND EVOLUTION OF THE RUSSIAN ARCTIC CRYOLITHOZONE (ON THE SHELF AND THE CONTINENT) IN THE PLEISTOCENE-HOLOCENE

The paper addresses age nonuniformity of the permafrost of the Russian Arctic shelf. It has been widely accepted that recent permafrost exists on the present-day shelf, which was formed under subaerial conditions during shelf draining in the Late Pleistocene, was flooded during the subsequent transgression, and now exists as a relic zone. However, there is also modern permafrost forming under submarine conditions. The paper considers the mechanism of its formation. The author suggests a mechanism that involves bottom soil freezing and ice formation due to constant natural transformations in seabed sediments. The proposed mechanism is supported by analyzes of certain sections of the bottom sediments of shelf and of the Pleistocene marine plains (ancient shelves) composed of dislocated sequences with massive ice beds. Analysis of the massive ground ice genesis identified different geological history as well as different transgressive and regressive regime of the Russian Arctic western and eastern sectors. The glacial cover has limited distribution in the Russian North and was absent on the Russian Arctic and Subarctic plains to the East of the Kanin Peninsula.

The Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland)

Five sections from the Kielce Region of the Holy Cross Mountains and one core from a borehole drilled in the nearby western Mesozoic Margin reveal the best recognized beds from the Devonian/Carboniferous boundary interval. In four sections: Ruda Strawczyńska, Bolechowice IG 1, Zaręby IG 2 and Kowala, the Devonian/Carboniferous boundary is located within a continuous series of deep-water carbonates, whereas in the two remaining: Ostrówka Quarry and the Jabłonna IG 1 borehole, the Devonian/Carboniferous boundary interval contains stratigraphic gaps resulting from lack of deposition in submarine conditions. The biostratigraphic position of the analyzed uppermost Devonian and lowermost Carboniferous beds is determined by assemblages of conodonts, microspores and deep-water ostracodes of the Thuringian ecotype. The lithology and biostratigraphic position of particular beds in the Devonian/Carboniferous boundary interval of the Kowala section from the western part of the Holy Cross Mountains resemble those in a succession of equivalent age from the Rhenish Massif. Both areas are characterized by similar lithological horizons and changes of biotic assemblages within the same conodont zones. Strata and fauna from the uppermost Famennian are influenced by the global regressive Hangenberg Event.

Estimating primaries by sparse inversion of the 3D curvelet transform and the L1-norm constraint

In this paper, we built upon the estimating primaries by sparse inversion (EPSI) method. We use the 3D curvelet transform and modify the EPSI method to the sparse inversion of the biconvex optimization and L1-norm regularization, and use alternating optimization to directly estimate the primary reflection coefficients and source wavelet. The 3D curvelet transform is used as a sparseness constraint when inverting the primary reflection coefficients, which results in avoiding the prediction subtraction process in the surface-related multiples elimination (SRME) method. The proposed method not only reduces the damage to the effective waves but also improves the elimination of multiples. It is also a wave equationbased method for elimination of surface multiple reflections, which effectively removes surface multiples under complex submarine conditions.

Intraplate mafic magmatism, degasification, and deposition of mercury: The giant Almadén mercury deposit (Spain) revisited

The giant Almadén mercury deposit (Spain) is hosted by the Lower Silurian Criadero Quartzite; in turn this ore-bearing rock unit is cross-cut by the so-called Frailesca unit, a diatreme body of basaltic composition. The geochemical characteristics of the Silurian to Devonian Almadén District volcanic units indicate that these rocks originated from an enriched, evolving mantle source that ultimately yielded basanites–nephelinites to rhyolites, through olivine-basalts, pyroxene-basalts, trachybasalts, trachytes, very scarce rhyolites, and quartz-diabases. The Silurian intraplate alkaline volcanism developed in submarine conditions which triggered widespread hydrothermal activity resulting in Hg ore formation and pervasive alteration to carbonates. The δ18O, δ13C, and δ34S isotopic signatures for carbonates and pyrite suggest different sources for carbon and sulfur, including magmatic and organic for the former and magmatic and sea water for the latter. The most important and efficient natural source of mercury on Earth is by far the volcanic activity, which liberates mercury via quiescent degassing and catastrophic (Plinian) events when eruptions can overwhelm the atmospheric budget of Hg. Thus, we suggest that CO2 degasification and coeval distillation of mercury from the volcanic rocks fed the huge hydrothermal system that led to massive deposition of mercury at Almadén. Build up of Hg0gas in magmatic chambers during waning rifting in the Late Ordovician, followed by renewed volcanism in the Early Silurian, would have resulted in massive degasification of the accumulated mercury. Part of this mercury went into the Criadero Quartzite leading to formation of the huge Almadén deposit and others (e.g., El Entredicho) along the same stratigraphic level. Progressive depletion of the deep seated magmatic Hg stock would have resulted in a drastic reduction in ore deposit size after the Lower Silurian when smaller deposits formed (e.g., Las Cuevas).

Geochemistry and Origin of Banded Iron-Formation from the Granulitic Terrain of North Arcot District, Tamil Nadu, South India

Banded iron formations (BIF) form an important part of the Archean supracrustal belts of South India. Major, trace and rare earth elements (REE) chemistry of the banded iron formation of Kavuthimalai-Vediyappanmalai area, North Arcot district, Tamil Nadu region are utilized to compare with other world BIF and explore that this a separate type of Tamil Nadu type. The petrographic observation and the study of REE indicates that this BIF are derived from mantle through hydrothermal solutions and fumarolic activity in submarine conditions with an age of approximately 3800 m.y. old.

East Sakhalin island arc paleosystem of the Sea of Okhotsk region

It has been established that volcanic rocks of the Schmidt, Rymnik, and Terpeniya terranes are fragments of the compound Early to Late Cretaceous-Paleogene East Sakhalin island arc system of the Sea of Okhotsk region. This island arc paleosystem was composed of back-arc volcano-plutonic belt, frontal volcanic island arc, fore-arc, inter-arc, and back-arc basins, and the Sakhalin marginal paleobasin. The continental volcanic rocks dominate in the back-arc volcano-plutonic belt and frontal volcanic island arc. The petrochemical composition of basalts, basaltic andesites, andesites, and trachytes from the frontal island arc formed in submarine conditions are typical of oceanic island arc or marginal sea rocks (IAB). The petrochemical composition of volcanic rocks from the island arc structures indicates its formation on the heterogeneous basement including the continental and oceanic blocks.

The Water Chemistry of Shallow Ponds around Wapusk National Park of Canada, Hudson Bay Lowlands

Understanding the structure and function of ecosystems in Canada's national parks is essential in fulfilling the Parks Canada Agency's mandate to manage for ecological integrity. Wapusk National Park is representative of the Hudson Bay Lowlands and small lakes and ponds make up a considerable component of the landscape. The Hudson Bay Lowlands have experienced relatively recent isostatic rebound from submarine conditions, hence proximity to the coast was found to be a major factor in determining the concentration of dissolved salts in pond water. It was observed that the ionic composition of the water in ponds throughout much of the park is consistent, indicating that most of the ponds are an expression of surface water maintaining little connection to groundwater. The prevalence of permafrost throughout much of the park is likely the reason for this stability. Ponds within the park also show considerable variability in the amount of dissolved organic carbon (DOC) they contain. DOC shows a strong north-south and east-west trend. Ponds in the northeast of the park have lower DOC values while ponds in the southwest of the park have higher levels of DOC. Changes in DOC within the park appear to be driven by changes in the terrestrial vegetation surrounding the ponds. Climatically mediated changes in northern tree line and permafrost are likely to cause the greatest alteration of aquatic habitats in Wapusk National Park. The paucity of background data makes it impossible to assess the amount of change that may have already occurred in the park. This research provides the first landscape-level study for the area and shows that there are distinct limnological patterns over this landscape that are likely to be sensitive to climate change and should be readily detectable with ongoing monitoring.

Oligocene climate changes controlling forced regression in the eastern North Sea

In this paper we investigate the Early Oligocene (Rupelian) high-angle clinoform complex from the western part of the Norwegian–Danish Basin. The study consists of an integrated analysis of 3D seismics, petrophysical well logs and micropaleontological data. A series of erosional features and geometry of prograding units, e.g. the high-angle clinoform complex, interpreted as a forced regressive unit, is identified. The proposed depositional model accounts for lithological variations, climate-induced sea-level fluctuation and depositional environment. The characteristic high-angle clinoform complex has been estimated to be of Late Rupelian age. Paleoenvironmental reconstruction of the unit (based on dinocyst analysis) suggests that the deposition of the succession took place in submarine conditions. Presence of a cold-water dinoflagellate Svalbardella within the unit containing high-angle clinoforms suggests that the unit was deposited during one of the Oligocene glacial maxima (the most probably the Oi2 cooling event).

ON THE SEDIMENTARY PROCESSES OF THE FLYSCH DEPOSITS FORMING OF THE UKRAINIAN CARPATHIANS

On the base of sedimentological investigations the lithodynamic types in the flysch deposits of the Ukrainian Carpathians were destinguished. These types represent the different sedimentary processes in the submarine conditions. Flysch deposits contain three groups of the lithodynamic types, namely, the deposits of the subvertical «particle by particle» sedimentary flow ( hemipelagites or pelagites ); gravitites (turbidites with Bouma’s structure, the products of grain-flows and debris-flows); contourites

The Obolon impact structure, Ukraine, and its ejecta deposits

Abstract— The Obolon impact structure, 18 km in diameter, is situated at the northeastern slope of the Ukrainian Shield near its margin with the Dnieper‐Donets Depression. The crater was formed in crystalline rocks of the Precambrian basement that are overlain by marine Carboniferous and continental Lower Triassic deposits. The post‐impact sediments comprise marine Middle Jurassic (Bajocian and Bathonian) and younger Mesozoic and Cenozoic deposits. Today the impact structure is buried beneath an about 300‐meter‐thick sedimentary rock sequence.Most information on the Obolon structure is derived from two boreholes in the western part of the crater. The lowest part of the section in the deepest borehole is composed by allogenic breccia of crystalline basement rocks overlain by clast‐rich impact melt rocks and suevites. Abundant shock metamorphic effects are planar deformation features (PDFs) in quartz and feldspars, kink bands in biotite, etc. Coesite and impact diamonds were found in clast‐rich impact melt rocks. Crater‐fill deposits are a series of sandstones and breccias with blocks of sedimentary rocks that are covered by a layer of crystalline rock breccia.Crystalline rock breccias, conglomeratic breccias, and sandstones with crystalline rock debris have been found in some boreholes around the Obolon impact structure to a distance of about 50 km from its center. Those deposits are always underlain by Lower Triassic continental red clay and overlain by Middle Jurassic marine clay. The K‐Ar age of impact melt glasses is 169 Ma, which corresponds to the Middle Jurassic (Bajocian) age. The composition of crater‐fill rocks within the crater and sediments outside the Obolon structure testify to its formation under submarine conditions.

Specific features of massive sulfide ore formation under submarine conditions at various depths

Specific features of massive sulfide ore formation under submarine conditions at various depths

How and to what extent does the emergence of orogens above sea level influence their tectonic development?

AbstractGeodynamic modelling indicates that the emergence of initially submarine convergent orogens above sea level can have a significant influence on their subsequent tectonic development. This is because of two effects. First, surface uplift under submarine conditions, and the resulting decrease in gravitational loads, tends to reactivate deformation in the uplifting part of the submerged orogen. Second, an increase in the rate of erosion associated with the emergence of land can cause increased exhumation rates, reduced thrust‐front advance rates, narrowing of the orogen width, and a shift from slow deposition in piggyback basins to rapid deposition in the foredeep. These effects result from the ability of erosion to perturb mass balance at the orogen‐scale. Based on these results, I hypothesize that the emergence of initially submerged orogens such as the Alps and Taiwan played a direct role in explaining major changes in orogen dynamics and basin evolution that are known to occur in these examples.

Geochemical features of the Okhotsk Sea Cenozoic volcanism

Cenozoic volcanic rocks were discovered on major rises of the inner Okhotsk Sea. In this paper, these rocks are geochemically typified, and the geodynamic conditions of their formation reconstructed. For this purpose, mineralogical and geochemical analyses as well as radioisotope age determinations were carried out. The radioisotope age determinations show that the Cenozoic volcanic rocks were formed during the Paleogene–Pleistocene. Within this period, Eocene and Plio-Pleistocene volcanic complexes are particularly prominent. Mineralogical and geochemical analyses show that the rocks belong to the calc-alkaline volcanic series. The Eocene volcanic rocks were formed under subaerial conditions, whereas the Plio-Pleistocene volcanics were formed under submarine conditions. The results of the study suggest that the Okhotsk Sea Basin was formed during the destruction of the Asian continental margin, the Eocene volcanism reflecting subaerial, the Plio-Pleistocene volcanism submarine stages of the Okhotsk Sea evolution.

Transport and emplacement of ignimbrites and resedimented volcaniclastics from Gutai Mts., Eastern Carpathians, Romania

Gutâi Mts. had started to be built up in Middle Miocene, ca. 15.4 Ma ago. A series of explosive events developed starting with a major magmatic explosion and caldera collapse responsible for large volumes of ignimbrites. Successive explosions followed caldera collapse triggering a series of pyroclastic currents that underwent subsequent reworking. Mass flow has been the main transport mechanism recorded by the sedimentary structures of either ignimbrites or post-ignimbrites volcaniclastics. Multiple ignimbrite units resulted from subaerial mass flows, successively emplaced by progressive aggradation from the basal layer of a density-stratified pyroclastic current. The overlying sequence is composed of different volcaniclastics of pyroclastic origin interlayered with mudstones. They preserve the original composition of ignimbrites, but lack the evidence of hot-state deposition, recording the emplacement from more or less dilute mass flows. A syn-eruptive stage of resedimentation is suggested prior to emplacement in submarine conditions, determined by the transformation of gas-supported pyroclastic currents into water-supported mass flows after transition from subaerial to submarine conditions. The syn-eruptive resedimented volcaniclastics may be correlated with the ignimbrite-type subaerial pyroclastic flows, but they show different degrees of fluidization due to the impact of submarine environment.

The pre-Callovian stratigraphic gap in the Central Balkanids: a key for the interpretation of other Early-Middle Jurassic gaps in Bulgaria

The pre-Callovian stratigraphic gap in the Central Balkanids is distributed in the Etropole, Teteven, Troyan, Kazanluk, Gabrovo and Turgovishte Districts. To the west (village of Gintsi, Sofia District) and to the east (the section of well R-3 Yunak, District of Yarn a) of the gap uninterrupted Bathonian-Callovian rock successions exist. In its western and eastern parts the pre-Callovian stratigraphic gap is a diastem. In these localities the gap embraces minimum duration. In the western diastem the duration of the gap is from the Late Bathonian to the Early Callovian. In the eastern diastem the duration of the gap is probably in the framework of the Late Bathonian. In many localities where the gap is diastem the boundary between the basement and the cover is marked by hardgrounds. In its central part (Troyan, Kazanluk and Gabrovo Districts) the pre-Callovian stratigraphic gap is with much longer duration. This is caused by the intensive submarine washout of the earlier deposited Middle and Lower Jurassic sediments. In limited localities the Callovian from the cover lies directly even above Upper Triassic rocks. Almost everywhere the cover of the gap is represented by condensed Middle-Upper Callovian micritic limestones. They are rich of ammonites. The main microfacies type is mudstone/wackestone with filaments from thin-shelled bivalves. It is correlated with the Standard Microfacies Type 3 (SMF 3) - "pelagic mudstone and wackestone". It is formed in the lower part of the deep sublittoral, which is in consent with the ba thymetric interpretations based on the characteristics of the respective faunal spectra. The Callovian limestones in conditions of uninterrupted sedimentation show similar microfacies characteristics. In the localities where the pre-Callovian gap is a diastem, the conclusions for the microfacies characteristics and for the faunal spectra of the Bathonian sandy bioclastic limestones are similar. The microfacies type is bioclastic-lithoclastic packstonelrudstone, which can be attributed to some extent to the SMF 4 - "bioclastic-lithoclastic packstone". It may be supposed that the features of this texture direct to a more shallow parts of the deep sublittoral. Almost the same characteristics have the Bathonian limestones and marls in conditions of uninterrupted sedimentation. In general, the pre-Callovian gap is realized in submarine conditions, which are connected with the deep sublittoral. There are four stages in the transition between normal sedimentation and submarine gap: normal sedimentation (in which biostratigraphic superposition is traceable) → slow sedimentation (condensations) → submarine stratigraphic gaps (as a result of non-deposition - diastems) → submarine stratigraphic gaps (as a result of submarine washout).

In situ mobile subaquatic archaeometry evaluated by non-destructive Raman microscopy of gemstones lying under impure waters

A series of laboratory simulations have been made in order to evaluate the credibility of carrying out physico-chemical analysis of cultural heritage items by Raman spectral fingerprinting using a mobile Raman microscope in situ under natural impure water in subaquatic or submarine conditions. Three different kinds of gemstone (zircon, microcline and sodalite) were successively placed under different kinds of impure water into which a low power microscope objective was immersed to eliminate the normal aerial pathway between the objective and the object to be analysed. According to the nature of the impurities (inorganic or organic, dissolved or suspended, transparent or coloured) the results obtained variously gave Raman band intensities stronger than, similar to or weaker than those of spectra obtained without water, i.e. in air. The significant point is that after only minor spectral treatment the less good spectra nevertheless yielded exploitable data with most, if not all, of the key Raman bands being detected. Thus the problems of fluorescence or peak absences under water are of a similar degree of magnitude to the other problems inherent with the Raman spectroscopic technique in aerial conditions, e.g. relative peak intensities varying with crystal orientation; peak positions varying with chemical composition. These results indicate that even if at certain sites of submerged cities or sunken ships, the combination of animal, vegetal, mineral and microbial impurities join together to inhibit or hinder the success of subaquatic or submarine archaeometry, there will certainly be other sites where such activity is indeed credible.

Effects of regional slope on viscous flows: a preliminary study of lava terrace emplacement at submarine volcanic rift zones

To understand how large submarine lava terraces form and why they are not commonly observed on land, we developed an isoviscous gravity flow model on an inclined surface to simulate the evolution and emplacement of lava flows under submarine conditions. By solving this preliminary model using a finite difference method, we are able to quantify how lava viscosity, pre-existing topographic slope, effusion rate, and lava volume affect meso-scale lava morphology. Our simulations show that, in general, high lava viscosity, gentle regional slope, and low effusion rate favor the formation of large terraces, but environmental conditions also play an important role. A gravity flow spreads more slowly underwater than subaerially. We also conclude that for low viscosity basaltic lava, the cooling of the lava body is one of the most critical factors that affect its shape. This study shows that the isoviscous model, though oversimplified, provides a quantitative tool to relate lava morphology to eruption characteristics. To gain a better understanding of the controls on submarine lava terrace formation, future models must take into account the temporal and spatial variation of lava viscosity, especially the effects of a brittle outer shell.