Variability of the Blazar J1504+1029 on Timescales from Hours to Years

The results of observations of the blazar J1504+1029 (PKS 1502+106, OR 103), obtained in 2000–2018 on the RATAN-600 radio telescope of the Special Astrophysical Observatory at 2.3, 3.9 (4.7), 7.7 (8.2), 11.2, and 21.7 GHz and on the 32-m Zelenchuk and Badary radio telescopes of the Quasar-KVO complex of the Institute of Applied Astronomy of the Russian Academy of Sciences at 5.05 and 8.63 GHz are presented. The long-term variability is studied, as well as variability on time scales from several days to several weeks and intraday variability (IDV). The long-term light curves are correlated at all frequencies and show continuous activity, against which three flares with their maxima in 2002, 2009, and 2018 are distinguished. The time scale for variability of the flare in 2009 is τ_var ≈ 1 year. At 21.7 GHz, the linear size of the emitting region is R ≤ 0.3 pc, its angular size is θ ≤ 0.05 mas, its brightness temperature is T_b ≥ 2 × 1014 K, and the Doppler factor is δ ≥ 5.8. The flare with its maximum in 2018 has a long rising branch at 21.7 GHz: τ_var = 3.2 years, linear size R ≤ 1.1 pc, angular size θ ≤ 0.17 μas, brightness temperature T_b ≥ 2.2 × 10¹² K, and Doppler factor δ ≥ 2.8. Among eleven sets of daily observations of the source over 75–120 days in 2000–2017, variability was detected in eight data sets at two to four frequencies with characteristic time scales of 4–30 days. In seven data sets, the variability is due to one to three cyclic processes with characteristic time scales τ_acf = 4?30^d. The spectral indices of the variable components in different years vary from α_var = ?1.6 to +1.8. In at least four data sets, the variability is due to processes in the source itself. In this case, at 21.7 GHz, the apparent linear size of the emitting region is ≤4000 AU, the angular size is θ ≤ 3.5 μas, the brightness temperature is T_b ≥ 3 × 10¹⁴ K, and the Doppler factor is δ ≥ 14. In the 2004 data set, the variability has an “ anti-flare” form, with the flux density of the variable component falling at high frequencies. Thirty-six successful sessions were conducted on the 32-m telescopes at 8.63 GHz, and 16 at 5.05 GHz. IDV was detected in 17 sessions at 8.63 GHz and in three sessions at 5.05 GHz, with the IDV being detected mainly near flare maxima.

     

Pressure–temperature–time evolution of the Central East Greenland Caledonides: quantitative constraints on crustal thickening and synorogenic extension

Whereas geologists have known for three‐quarters of a century that there was significant crustal thickening in the central East Greenland Caledonides, the crucial role of extensional faulting during Caledonian orogenesis has only been recognized during the past decade. In this paper, new petrographic and thermobarometric observations are presented from migmatitic metasedimentary gneisses of the Forsblad Fjord region (c. 72.5°N). Samples of the Krummedal Sequence, collected from the footwall of the upper of two significant splays of the main extensional fault system in the region—the Fjord Region Detachment (FRD)—enable us to establish a relative sequence of metamorphism. Our pressure (P)–temperature (T) results imply a clockwise loop in P–T space. As recorded by mineral assemblages in the Krummedal gneisses, prograde metamorphism involved a net increase of c. 4 kbar and 250 °C, with peak conditions of c. 10.5 kbar at 785 °C. Early burial and heating was followed by near‐isothermal decompression of 4.5 kbar, a process which is attributed to roughly 18 km of tectonostratigraphic throw on the upper splay of the FRD. Combining data reported here with the published data, it is estimated that the approximate tectonostratigraphic throw along the lower splay of the FRD was c. 16 km. In situ U–Th–Pb‐monazite electron microprobe dating suggests that the earliest phase of metamorphism recorded in the Krummedal Sequence gneisses of Forsblad Fjord occurred during the Caledonian orogeny. Furthermore, the combination of our new data with existing conventional TIMS U‐Pb and ⁴⁰Ar/³⁹Ar data imply that: (1) movement along the uppermost splay of the FRD (c. 425–423 Ma) occurred at maximum time‐averaged slip‐rates equivalent to c. 9 mm of vertical displacement per year; and (2) that the final stages of metamorphism occurred prior to c. 411 Ma, although part of this denudation was likely accommodated on overlying extensional structures that may have been active more recently. There is close agreement between our data and results from the Krummedal Sequence north of the field area (72.5°?74°N), and rocks of the Smallefjord Sequence (75°?76°N) that are suggested to correlate with the Krummedal Sequence. This leads us to infer that the events recorded in the Forsblad Fjord region are of orogen‐scale significance.     

Lognormal field size distributions as a consequence of economic truncation

The assumption of lognormal (parent) field size distributions has for a long time been applied to resource appraisal and evaluation of exploration strategy by the petroleum industry. However, frequency distributions estimated with observed data and used to justify this hypotheses are conditional. Examination of various observed field size distributions across basins and over time shows that such distributions should be regarded as the end result of an economic filtering process. Commercial discoveries depend on oil and gas prices and field development costs. Some new fields are eliminated due to location, depths, or water depths. This filtering process is called economic truncation. Economic truncation may occur when predictions of a discovery process are passed through an economic appraisal model. We demonstrate that (1) economic resource appraisals, (2) forecasts of levels of petroleum industry activity, and (3) expected benefits of developing and implementing cost reducing technology are sensitive to assumptions made about the nature of that portion of (parent) field size distribution subject to economic truncation.     

Aspects of the structural and late thermal evolution of the Redbank Thrust system,central Australia: Constraints from the Speares Metamorphics

We present new data on the field geology and late thermal evolution of the Redbank Thrust system in the Arunta Block of central Australia. Geochronological and field data from the Speares Metamorphics are also used to relate the thermal evolution of the Redbank Thrust system to the structural evolution of the region. We show that several stages in the evolution might be discerned. An originally sedimentary sequence was intruded by mafic intrusions and then deformed during partial melting to form the principal foliation observed in the region (D1). This sequence was then folded during D2 into upright folds with north‐ to northeast‐plunging fold axes. These events are likely to correlate with the Strangways and/or Argilke and Chewings Orogenies known from previous studies. Subsequently, the Redbank Thrust was initiated during D3. This event is recognised by deflection of the host rocks into the shear zone and might therefore have been associated with a component of strike‐slip motion. It occurred probably at or before 1500–1400 Ma. Subsequent north‐over‐south thrust motion in the Redbank Thrust formed the intense mylonitic fabric and folded the mylonitic fabric during D4 into asymmetric folds with shallow fold axes. New ⁴⁰Ar/³⁹Ar K‐feldspar ages from three samples collected from variably deformed branches of the Redbank Thrust and undeformed rocks in the Speares Metamorphics suggest that most parts of the Redbank Thrust system cooled relatively slowly after metamorphism and deformation in the Mesoproterozoic so that the D4 thrusting might have been very long‐lived. Minimum ages of the K‐feldspar age spectra show that the entire region cooled below 200°C by approximately 300 Ma. Apatite fission track ages from nine samples show that cooling through the apatite partial annealing zone occurred during Cretaceous time (ca 150–70 Ma) and modelled cooling histories are consistent with the cooling rates obtained from the K‐feldspar data. They indicate that final exhumation of the Redbank Thrust system occurred probably in response to erosion, possibly driven by rifting around the margins of Australia.     

Sequential sampling to contour an uncertain function

Sampling exploration of uncertain functions to locate critical contour levels is most effective if sampling decisions are made sequentially. A simple sequential exploration strategy, based on pseudo-Bayesian second-moment analysis, is proposed and compared with non-sequential systematic sampling. Repeated application to functions simulated pseudorandomly from stationary random processes on the line and on the plane indicates uniform superiority of the sequential strategy. The method is particularly advantageous when the function of interest,h(X), has an uncertain trend, and in general when the random process that quantifies prior uncertainty onh(X) is highly correlated.     

Timing and nature of fluid flow and alteration during Mesoproterozoic shear zone formation, Olary Domain, South Australia

The development of shear zones at mid‐crustal levels in the Proterozoic Willyama Supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration. Monazite dating of shear zone fabrics reveal that they formed at 1582 ± 22 Ma, at the end of the Olarian D3 deformational event and immediately prior to the emplacement of regional S‐type granites. Two stages of fluid flow are identified in the area: first an albitizing event which involved the addition of Na and loss of Si, K and Fe; and a second phase of calcsilicate alteration with additions of Ca, Fe, Mg and Si and removal of Na. Fluid fluxes calculated for albitization and calcsilicate alteration were 5.56 × 10⁹ to 1.02 × 10¹⁰ mol m^?2 and 2.57 × 10⁸–5.20 × 10⁹ mol m^?2 respectively. These fluxes are consistent with estimates for fluid flow through mid‐crustal shear zones in other terranes. The fluids associated with shearing and alteration are calculated to have δ¹⁸O and δD values ranging between +8 and +11‰, and ?33 and ?42‰, respectively, and ?Nd values between ?2.24 and ?8.11. Our results indicate that fluids were derived from metamorphic dehydration of the Willyama Supergroup metasediments. Fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions. Shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent ‘retrograde’ fluid‐flow event. Thus, the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times, prior to regional granite formation, during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing.     

Low-mature gases and their resource potentiality

In the 80’s of last century, based on the advances in natural gas exploration practice, the concepts of bio-thermocatalytic transitional-zone gas and early thermogenetic gas were proposed, and the lower limit Ro values for the formation and accumulation of thermogenetic natural gases of industrial importance have been extended to 0.3%–0.4%. In accordance with the two-stage model established on the basis of carbon isotope fractionation involved in the formation of coal-type natural gases, the upper limit Ro ...     

Zoned (Cretaceous and Cenozoic) garnet and the timing of high grade metamorphism, Southern Alps, New Zealand

New (garnet Sm–Nd and Lu–Hf) and existing (Rb–Sr, ⁴⁰Ar/³⁹Ar, U–Pb and Sm–Nd) ages and data on deformational fabrics and mineral compositions show for the first time that the garnet growth and ductile deformation in the Alpine Schist belt and Southern Alps orogen, New Zealand are diachronous and partly Cenozoic in age. The dominant metamorphic isograds in the Alpine Schist formed during crustal thickening at a previously unsuspected time, at c. 86 Ma, immediately prior to the opening of the Tasman Sea at c. 84–82 Ma. Obvious changes in the textures and compositional zoning patterns of garnet are not always reliable indicators of polymetamorphism, and fabric elements can be highly diachronous. A detailed timing history for the growth of a single garnet is recorded by a Sm–Nd garnet–whole rock age of 97.8 ± 8.1 Ma for the inmost garnet core (zone 1), Lu–Hf ages of 86.2 ± 0.2 Ma and 86.3 ± 0.2 Ma for overgrowth zones 2 and 3, a step‐leach Sm–Nd age of 12 ± 37 Ma for zone 4, and growth of the garnet rim (zone 5) over the Alpine Fault mylonite foliation during the modern phase of oblique collision that began at c. 5–6 Ma. Plate convergence along the New Zealand portion of the Gondwana margin continued after c. 105 Ma, almost certainly culminating in the oblique collision of a large oceanic plateau (Hikurangi Plateau). The metamorphism of the Alpine Schist at c. 86 Ma is evidence of that hit. The mid‐ to late‐Cretaceous extension that is widespread elsewhere in the New Zealand region is attributed to upper plate extension and slab roll‐back. The effects of the collision with the Hikurangi Plateau may have contributed to the changing plate motions in the region leading up to the opening of the Tasman Sea at c. 82 Ma.     

Dissolved air flotation (DAF) of fine quartz particles using an amine as collector

Experimental studies concerning the dissolved air flotation (DAF) of fine (d_p < 100 μm) quartz particles, using two different flotation cells (setups), are presented. Pure and well characterised quartz samples were treated with a commercial amine as collector prior to flotation and bubbles were characterised by the LTM-BSizer technique. Bubble size distribution showed 71% (by volume) and 94% (by number) of the bubbles having sizes (d_b) lower than 100 μm (i.e. microbubbles). The Sauter and arithmetic mean diameters were 79 μm and 56 μm, respectively, for the bubbles generated at 300 kPa (gauge) saturation pressure (after 30 minute saturation time). Quartz particle size distribution (obtained by laser diffraction) showed a volume-moment diameter of 13 μm. The Rosin–Rammler–Bennett, Gates–Gaudin–Schumann and log-normal distribution functions were well fitted (R² > 0.96) to the bubble size distribution and quartz particle size distribution data. Values of total quartz recovery ranging from 6% to 53% (by mass) were obtained for the DAF experiments under different collector concentrations (up to 2 mg g^− 1), with an optimal collector concentration found at 1 mg g^− 1. These results are significant considering that 27% (by volume) of the quartz particles are ultrafine (d_p < 5 μm), demonstrating the widely-known efficiency of DAF to remove small particles when applied in the field of water and wastewater treatment. The true flotation behaviour, as a function of particle diameter (d_p), exhibits a local minimum when particles are approximately 3–5 μm in size. The results contribute to the discussion in the literature about the existence of such a minimum, which is generally interpreted as a change in the mechanism of particle collection from convection (collision) to diffusion at lower particle sizes.     

Polymetamorphism and isobaric cooling of pelitic schists from the Annex sulphide deposit, Gordonia Belt, South Africa

Abstract Muscovite-poor pelitic schists in the wallrocks of the Proterozoic Annex sulphide deposit, near Prieska, South Africa, contain peak metamorphic assemblages including Crd + Bt + Sil, St + Sil + Bt, Crd + St + Bt and, rarely, Ky + St ° Crd. All rocks include oligoclase, quartz and commonly Fe–Mn garnet, with or without muscovite. Peak assemblages, assigned to M2 regional metamorphism in the Gordonia Belt (Namaqua Province), are syn- to post-kinematic with respect to the main S2 fabric although larger staurolite grains contain S1 inclusion trails. Garnet–biotite thermometry, utilizing corrections for Fe³⁺, Mn, Al^VI and Ti, yields peak temperatures of 571–624°C at pressures of 4.5–6.0 kbar. Consideration of the sympathetic variation of X_Mn in garnet with X_Mg in biotite and the preserved zoning patterns in prograde garnets, together with the inferred prograde transition from kyanite to sillimanite, indicates that heating occurred during mild decompression to the M2 metamorphic peak. Sillimanite and cordierite grew last in the prograde sequence, possibly related to a pulse of thermal metamorphism (M3) that is found along the margin of the Keimoes Suite batholith to the north. Retrograde assemblages, including Ms + Ky + Chl + Qtz (after Crd + Bt), Ky + Ms (after Sil) and Chl + Ms (after St) indicate a period of isobaric cooling (M4a) terminated by rehydration in the kyanite stability field at about 500°C. The size difference between prograde (1–2-mm) and retrograde (0.05–0.1-mm) mineral grains indicates substantial undercooling below equilibrium positions of relevant retrograde reactions prior to rehydration, and explains why cordierite that grew during M2 is almost completely destroyed. Post-M4a regrowth of staurolite and garnet (M4b) is spatially linked to sites of M4a rehydration. It reached temperatures of 510–530°C, remaining within the stability field of kyanite. A best fit of the observed textural history to the Namaqua orogenic cycle involves collision and heating (M2/D2) followed by granite intrusion (M3), rifting (M4a) and renewed heating due to crustal loading during volcanism (M4b). The P–T path for the Annex region is consistent with those derived from elsewhere in the Gordonia Belt and, with modification, to that published already for the nearby Prieska Copper Mines.     

Microbial alteration of natural gas in Xinglongtai field of the Bohai Bay Basin, China

Xinglongtai field has been an important petroleum-producing area of Liaohe Depression for 30 years. Oil exploration and production were the focus of this field, but the gas was ignored. This study examined twenty five gas samples with the purpose of determining the gas genetic types and their geochemical characteristics. Molecular components, stable carbon isotopic compositions and light hydrocarbons were also measured, and they proved that microbial activity has attacked some of the gas components which resulted in unusual carbon isotopic distributions. Propane seems to be selectively attacked during the initial stage of microbial alteration, with abnormally lower con-tent compared to that of butane as well as anomalously heavy carbon isotope. As a consequence, the carbon isotopic distribution among the gas components is partially reverse, as δ13C1<δ13C2<δ13C3>δ13C4. Besides, n-alkanes of C3+ gas components are preferentially attacked during the process of microbial alteration. This is manifested that n-alkanes are more enriched in 13C than corresponding iso-alkanes. As a result, the concentrations of n-alkanes be-come very low, which may be misleading in indentifying the gas genetic types. As to four gas samples, light hydro-carbon compositions display evidence for microbial alteration. The sequence of hexane isomers varies obviously with high content of 2,3-DMC4, which indicates that they have been in the fourth level of extensively bacterial al-teration. So the geochemical characteristics can be affected by microbial alteration, and recognition of microbial alteration in gas accumulations is very important for interpreting the natural gas genetic types.     

Tectonic setting, petrology and geochronology of jadeite + glaucophane and chloritoid + glaucophane schists from north-west Turkey

The north-west Turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble. The depositional age of the blueschist protoliths are probably Palaeozoic to Mesozoic, while the age of the high-pressure/low-temperature metamorphism is Late Cretaceous. Blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices. The metaclastic rocks with regional jadeite and glaucophane, which comprise the lower part of the blueschist unit, make up an over 1000-m-thick coherent sequence in the Kocasu region of north-west Turkey. Rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole + Iawsonite but no garnet indicate lawsonite blueschist facies metamorphism. The blueschist metaclastics in the Kocasu region are practically free of calcium and ferric iron and closely approximate the NFMASH system in bulk composition. Two low-variance mineral assemblages (with quartz and phengite) are jadeite + glaucophane + chlorite + paragonite and chloritoid + glaucophane + paragonite. The metaclastics comprise up to several-metres-thick layers of jadeite schist with quartz, phengite and nearly 100 mol% jadeite. Phase relations in the metaclastics show that the chloritoid + glaucophane assemblage, even in Fe²⁺-rich compositions, is stable in the jadeite stability field. In the NFASH system the above assemblage without the accompanying garnet has a narrow thermal stability field. Mineral equilibria in the metaclastics involving chloritoid, glaucophane, jadeite, paragonite and chlorite indicate metamorphic P-T conditions of 20 ± 2 kbar and 430 ± 30 d? C, yielding geothermal gradients close to 5d? C km^-1, one of the lowest geotherms recorded. Blueschists in the Kocasu region, which have been buried to 70 km depth, are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km. Phengites from two jadeite schists were dated by Ar/Ar laser probe; they give an age of 88.5 ± 0.5 Ma, interpreted as the age of metamorphism. Blueschists and the overlying peridotite bodies are intruded by 48-53-Ma-old granodiorite bodies that were emplaced at 10 km depth. This suggests that the exhumation of blueschists by underplating of cold continental crust, and normal faulting at the blueschist-peridotite, interface occurred during the Late Cretaceous to Palaeocene (88-53 Ma).     

Oxygen Isotope Studies of Epithermal Systems：A Review

Numerous stable isotope studies of whole rocks and mineral separates in epithermal systems indi-cate that even though meteoric waters are dominant components in epithermal systems ,fluids of other origins,such as sedimentary or meta-sedimentary fluids,magmatic waters and even evolved meteoric waters ,may also play a role in the formation of epithermal ore deposits.Usually the more depleted the wall rocks,the larger the size of ore deposits ,and the least depletion degrees in whole rocks for economic mineralization are by about 3.5‰.The depletion in δ^18O in wall rocks,however,may be complicated by the superimposition of low temperature-hydration over high-temperature altera-tion or vice versa,the existence of primary low-^18O and high-^18O magmas ,and alteration by vol-canic gases.The depletion in δ^18O in wall rocks is controlled by the composition and nature of flu-ids,the temperature of fluids,the elevation of rocks at the time of alteration ,lithology,boiling effects of fluids ,and alteration style,as well as by water/rock ratios.In addition ,the fluids re-sponsible for epithermal deposits have experienced positive δ^18O shifts .It seems that when the above complications and controlling factors are well defined,oxygen isotope studies would be a promising and powerful exploration tool.     

Protracted thrusting followed by late rapid cooling of the Greater Himalayan Sequence,Annapurna Himalaya,Central Nepal: Insights from titanite petrochronology

The Greater Himalayan Sequence (GHS) has commonly been treated as a large coherently deforming high‐grade tectonic package, exhumed primarily by simultaneous thrust‐ and normal‐sense shearing on its bounding structures and erosion along its frontal exposure. A new paradigm, developed over the past decade, suggests that the GHS is not a single high‐grade lithotectonic unit, but consists of in‐sequence thrust sheets. In this study, we examine this concept in central Nepal by integrating temperature–time (T–t) paths, based on coupled Zr‐in‐titanite thermometry and U–Pb geochronology for upper GHS calcsilicates, with traditional thermobarometry, textural relationships and field mapping. Peak Zr‐in‐titanite temperatures are 760–850°C at 10–13 kbar, and U–Pb ages of titanite range from c. 30 to c. 15 Ma. Sector zoning of Zr and distribution of U–Pb ages within titanite suggest that diffusion rates of Zr and Pb are slower than experimentally determined rates, and these systems remain unaffected into the lower granulite facies. Two types of T–t paths occur across the Chame Shear Zone (CSZ). Between c. 25 and 17–16 Ma, hangingwall rocks cool at rates of 1–10°C/Ma, while footwall rocks heat at rates of 1–10°C/Ma. Over the same interval, temperatures increase structurally upwards through the hangingwall, but by 17–16 Ma temperatures converge. In contrast, temperatures decrease upwards in footwall rocks at all times. While the footwall is interpreted as an intact, structurally upright section, the thermometric inversion within the hangingwall suggests thrusting of hotter rocks over colder from c. 25 to c. 17–16 Ma. Retrograde hydration that is restricted to the hangingwall, and a lithological repetition of orthogneiss are consistent with thrust‐sense shear on the CSZ. The CSZ is structurally higher than previously identified intra‐GHS thrusts in central Nepal, and thrusting duration was 3–6 Ma longer than proposed for other intra‐GHS thrusts in this region. Cooling rates for both the hangingwall and footwall of the CSZ are comparable to or faster than rates for other intra‐GHS thrust sheets in Nepal. The overlap in high‐T titanite U–Pb ages and previously published muscovite ⁴⁰Ar/³⁹Ar cooling ages imply cooling rates for the hangingwall of ≥200°C/Ma after thrusting. Causes of rapid cooling include passive exhumation driven by a combination of duplexing in the Lesser Himalayan Sequence, and juxtaposition of cooler rocks on top of the GHS by the STDS. Normal‐sense displacement does not appear to affect T–t paths for rocks immediately below the STDS prior to 17–16 Ma.     

Tropical Rain Forest and Climate Dynamics of the Atlantic Lowland, Southern Brazil, during the Late Quaternary

Palynological analysis of a core from the Atlantic rain forest region in Brazil provides unprecedented insight into late Quaternary vegetational and climate dynamics within this southern tropical lowland. The 576-cm-long sediment core is from a former beach-ridge “valley,” located 3 km inland from the Atlantic Ocean. Radio-carbon dates suggest that sediment deposition began prior to 35,000 ¹⁴C yr B.P. Between ca. 37,500 and ca. 27,500 ¹⁴C yr B.P. and during the last glacial maximum (LGM; ca. 27,500 to ca. 14,500 ¹⁴C yr B.P.), the coastal rain forest was replaced by grassland and patches of cold-adapted forest. Tropical trees, such as Alchornea, Moraceae/Urticaceae, and Arecaceae, were almost completely absent during the LGM. Furthermore, their distributions were shifted at least 750 km further north, suggesting a cooling between 3°C and 7°C and a strengthening of Antarctic cold fronts during full-glacial times. A depauperate tropical rain forest developed as part of a successional sequence after ca. 12,300 ¹⁴C yr B.P. There is no evidence that Araucaria trees occurred in the Atlantic lowland during glacial times. The rain forest was disturbed by marine incursions during the early Holocene period until ca. 6100 ¹⁴C yr B.P., as indicated by the presence of microforaminifera. A closed Atlantic rain forest then developed at the study site.     

Pleistocene stratigraphy in the Dellen region, central Sweden

Robertsson, A.-M., Svedlund, J.-O., Andrén, T. & Sundh, M. 1997 (September): Pleistocene stratigraphy in the Dellen region, central Sweden. Boreas, Vol. 26, pp. 237–260. Oslo. ISSN 0300–9483. The Pleistocene stratigraphy in the Dellen region, central Sweden was studied using field observations made during mapping of Quaternary deposits and fabric analyses in excavated sections. The lithostratigraphy was also studied by seismic refraction measurements, analyses of grain-size distribution and organic carbon content. Biostratigraphical methods applied were pollen and diatom analyses. A general outline of the Pleistocene stratigraphy in the area is presented. Three different till beds are identified, the lowermost suggested to have been deposited during the Saalian glaciation and the other two during the Weichselian glaciation. According to the interpretation of the stratigraphy, it is questioned whether the first Weichselian ice sheet did in fact reach the Dellen area. A clayey sediment sequence at Norra Sannas accumulated during an interglacial, probably the Eemian. Most of the interglacial vegetation succession is reflected in the identified pollen flora. An initial phase with a light-demanding forest of Belula and Pinus was followed by immigration of Alnus, Picea and scattered occurrences of Corylus. A freshwater diatom flora was identified dominated by plankton taxa, e.g. Aulacoseira italica, A. distans and Cyclotella spp. In the lower part of the sequence a brackish-marine flora was registered, representing accumulation in a bay of the Eemian Sea. Fine-grained sediments at the Sundson and Vastansjd sites are interpreted as rebedded Eemian sediments according to the pollen flora. An (Early Weichselian) interstadial age is suggested for sediments found at Bjuraker. Dating by the ¹⁴C- and OSL methods was carried out on the interglacial and interstadial sediments, respectively. The ages range from approximately 19000 to 92000 BP. Correlation of interglacial vegetation history with central Finland and other areas is discussed.     

Ecosystem response to Lateglacial and early Holocene climate oscillations in the Great Lakes region of North America

Fossil pollen, plant macrofossils, gastropods, and elemental and stable-isotope geochemistry in a sediment core from Twiss Marl Pond, southern Ontario, Canada, were used to document climate oscillations during the Last Glacial–Interglacial transition (13,000–8500 ¹⁴C BP) and understand their ecological effects. Chronology was provided by AMS ¹⁴C dating and regional pollen correlation. Oxygen isotope (δ¹⁸O) results from mollusc shells, Chara-encrustations and bulk carbonates show a classic climate sequence of a warm Bølling–Allerød (BOA) at 12,500–10,920 ¹⁴C BP, a cold Younger Dryas (YD) at 10,920–10,000 ¹⁴C BP, the Holocene warming at 10,000 ¹⁴C BP, a brief Preboreal Oscillation (PB) at 9650 ¹⁴C BP, and a possible Gerzensee/Killarney (G/K) cooling shortly before 11,000 ¹⁴C BP.Clay sediments at the base of the core contain high herb and shrub pollen and abundant arctic/alpine plant macrofossils, indicating a treeless tundra with severe soil erosion in watershed. During the BOA warm period, authigenic marl began to be deposited, and Picea woodland became established. The establishment of Picea woodland after peaks of δ¹⁸O and of carbonate accumulation suggests a lagged response of upland vegetation to BOA warming. In contrast, the occurrence of warmth-loving aquatics Najas flexilis and Typha latifolia at that time indicates sensitive responses of aquatic plants. The YD cooling is indicated by a 1.5‰ negative excursion in δ¹⁸O, an increase in minerogenic matter and higher concentrations of erosion-derived elements (Al, Na, K, Ti and V). Pollen data show no forest transformation in response to YD cooling, which is attributed to the insensitive nonecotonal vegetation at that time. However, more openings in the forests and increased erosion in the watershed are indicated by a slight increase of herb pollen, high concentrations of erosion elements and a Pediastrum peak. The onset of the Holocene was marked by an abrupt increase of 2‰ in δ¹⁸O and the replacement of Picea woodland by Pinus-dominated forest. The Picea recurrence at 9650 ¹⁴C BP demonstrates sensitive response of ecotonal vegetation to the PB climate oscillation, which is also indicated by 0.4‰ negative excursion of δ¹⁸O. These new results suggest the importance of multiproxy records for reliable paleoclimate reconstruction.Reevaluation and revised chronologies of previously published sites (Gage Street, and Nichols Brook) in the eastern Great Lakes region show their major δ¹⁸O shifts correlative to the YD and PB oscillations as documented from Twiss Marl Pond and nearby Crawford Lake. The sequence and magnitude of climatic oscillations from these sites match in detail with records from the Atlantic Seaboard, suggesting that these oscillations are an expression of broad-scale, probably global, climate change rather than local meltwater-induced climate cooling.     

Long‐Term Sediment Export Estimates from Northern Jordan using Roman Cisterns as Sediment Traps

Roman cisterns served as rainwater storage devices for centuries and are densely distributed in parts of northern Jordan. A major earthquake hit the region ca. A.D. 750 and in a short time many settlements were abandoned. As a consequence, most cisterns were not maintained, and they filled with sediments that today provide a postabandonment depositional record. In two field surveys, we mapped the locations of more than 100 cisterns in the Wadi Al‐Arab basin and selected two for detailed stratigraphic analysis that included ¹⁴C and optically stimulated luminescence dating. Catchment basin area for each cistern was determined by differential GPS. Both cisterns filled with sediments after the great earthquake and consequent abandonment of the region. Calculated sediment volumes are translated to long‐term average sediment export rates of 2.6–6.6 t ha⁻¹a⁻¹, which are comparable to erosion and sediment yield rates from other studies within the Mediterranean region. Our pilot study suggests that this approach can be applied elsewhere to calculate long‐term sediment export rates on hill slopes containing relict cisterns.     

Impact of internal waves on the acoustic field at a coastal station off Paradeep,east coast of India

Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24–25 October 2008. The IW characteristics, viz. period (t _per ), velocity (C _vel ), wavelength (L), and wave numbers (k), are found to be 2.133–34.72 h, 0.135 km h⁻¹, 0.37–6.2 km and 2.70–0.16 cycles km⁻¹, respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E ₀ = 3.34 J m⁻²). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.     

Simultaneous determination of sulfide, polysulfides and thiosulfate as an aid to ore exploration

The interaction of water and sulfide minerals yields dissolved species which can be utilized to trace back the presence of sulfide minerals and associated minerals. Computer modeling and laboratory and field results show that the most characteristic dissolved species are hydrogen sulfide (H₂S, HS⁻), polysulfide ions (S_n²⁻) and thiosulfate (S₂O₃²⁻), derived from the hydrolysis of sulfide minerals. Typical concentration ranges are: 10⁻⁵ – 10⁻⁷ mole/l for hydrogen sulfide, 10⁻⁶ – 10⁻⁹ mole/l for polysulfides and 10⁻⁵ – 10⁻⁸ mole/l for thiosulfate. The chemical reactivity of these species at contact with air makes them difficult to assess unless determined immediately after sampling.These sulfur species can be determined rapidly and accurately in field conditions by simultaneous titration with mercuric chloride employing an Ag/Ag₂S electrode for the determination of the end points.The application to ore exploration is exemplified by the results of the research on roll-type uranium deposits in the southwest of France.