Paleomagnetic study of satyavedu sandstones of cretaceous age from Andhra Pradesh,India

Summary The paleomagnetism of twenty six oriented samples of red sandstones from three different sites located in Satyavedu hills (near 13°30N, 79°55E) and belonging to coastal upper Gondwana formations of India has been studied. These sandstones have been considered to be equivalent of Tirupati sandstones of Lower to Middle Cretaceous age from Godavari valley on stratigraphic considerations. Consistent directions of magnetization were obtained from two different sites after stability tests. Results from one site gave ancient pole position at 26°N, 67°W, very close to that obtained for Tirupati sandstones, thus confirming the geologic correlation. Results from the second site were rejected on account of instability and those from the third site gave pole position at 79°48N, 76°58W. This site appears to have been remagnetized during Pleistocene times when there was large deposition of laterite in the area. Study of magnetic properties of these sandstones revealed that the magnetization was of the nature of CRM and the NRM was carried almost entirely by red coating on silica grains.N.G.R.I. Contribution No. 70-169.     

Mercury content of mussels from the St. Lawrence Estuary and northwestern Gulf of St. Lawrence, Canada

A first survey of the mercury content of intertidal mussels in the St. Lawrence Estuary and part of the Gulf of St. Lawrence shows means values ranging from 0.160 to 0.629 ppm (dry weight). Highest values (grand mean 0.430 ppm) were found in the upper part of the lower estuary, lowest values (grand mean 0.172 ppm) on the north shore of the estuary and Gulf, and intermediate values along the Gaspé Peninsula. The results indicate a decreasing gradient in mercury levels from the mouth of the Saguenay Fjord seaward.     

Paleomagnetic study of late Proterozoic and Early Cambrian rocks in terranes of the Amur plate

New paleomagnetic data are presented for Proterozoic metamorphic and Cambrian terrigenous-carbonate complexes of the southern Far East of Russia (Primor’e and the Amur and Trans-Baikal regions). Taking into account our results obtained previously, the paper presents revised positions of the paleomagnetic pole corresponding to the Riphean-Lower Paleozoic segment of the apparent polar wander path for terranes of the Amur plate (the Argun and Bureya-Khanka orogenic belts) in comparison with poles from the Siberian and North Chinese plates. It is shown that the paleolatitude positions of the Amur terranes were stable in space and time during the interval from the late Riphean to the end of the Early Cambrian: they were located in equatorial zones of the Northern and Southern hemispheres.     

Paleomagnetic poles and polarity zonation from Cambrian and Devonian strata of Arizona

Basal Paleozoic Tapeats Sandstone (Early and Middle Cambrian) in northern and central Arizona exhibits mixed polarity and a low-latitude paleomagnetic pole. Carbonates of Middle and early Late Cambrian age, and directly superposed carbonate and carbonate-cemented strata of latest Middle(?) and early Late Devonian age, are characterized by reversed polarity and high-latitude poles. The high-latitude Middle Cambrian pole, which appears to record a large but brief excursion of the polar wandering path, is considered provisional pending additional work. The Devonian data from Arizona indicate that a shift of the pole to a “late Paleozoic” position had occurred by Middle Devonian time.     

Concentrations and transport of trace metals in the St. Lawrence River

Samples of raw water were collected in the St. Lawrence River during six sampling trips from August 1990 to April 1992. Water samples were analyzed for both dissolved and particulate phases for five trace metals. Partition coefficients (Kd) and metal fluxes were calculated in order to determine metal transport. A mass balance equation was used for the determination of the major metal sources to the St. Lawrence River and an estimation of metal loadings to the estuary was made. Average dissolved metal concentrations were found to be Cd 10 ng/L, Co 74 ng/L, Cu 64 ng/L, Fe 69 µg/L and Mn 700 ng/L. Particulate concentrations were (in µg/g) 1.68 for Cd, 31 for Co, 73 for Cu, 25 mg/g for Fe and 1.69 mg/g for Mn. Co, Fe and Mn were transported essentially in the particulate phase while Cd and Cu were predominantly found in the dissolved phase at 56% and 48% of the total metal concentration respectively. Log Kd values varied from 5.1 (for Cu) to 6.8 (for Mn). In the dissolved phase the major sources were found to be the Great Lakes and the Ottawa River whereas in the particulate phase Québec tributaries appear to be the most important. Industrial inputs are quite important in both the dissolved and the particulate phases for Cd, whereas other sources are very variable, especially for the dissolved phase.     

Distribution and temporal variation of cadmium in the St. Lawrence river basin

Samples of raw water were collected at regular intevals at two transects in the St. Lawremce River and four of its tributaries from March to November 1991 and from April to June 1992. Water samples were analyzed for both the dissolved and the particulate phase for cadmium (Cd), organic carbon, iron and manganese. Mean dissolved Cd concentration was 10±5 ng/L and no spatial variability was observed. Higher concentrations were found during high flow periods, suggesting an uptake of cadmium by phytoplankton during summer. In addition, dissolved cadmium did not appear to be associated with either DOC, dissolved Fe or dissolved Mn. The mean particulate Cd concentration was 1.3±1.1 μg/g, with almost all stations presenting the same concentration except the Yamaska River, which had a concentration of 0.5±0.2 μg/g. Particulate Cd showed a negative correlation with suspended particulate matter and a positive correlation with particulate organic carbon and particulare manganese. Fifty-nine percent of the cadmium was found to be in the particulate phase. Partition coefficients for cadmium (Kd), organic carbon (Kc), iron (KdFe) and manganese (KdMn) were calculated for each sample. Log Kd varied from 3.9 to 5.9, with an average of 5.0±0.4. Log Kd decreased with increasing particulate, matter as did Log Kc and Log KdMn. No significant correlation was found between Log Kd and Log Kc, suggesting that the distribution of cadmium between the dissolved and the particulate phase is not influenced by the distribution of organic carbon. In contrast, positive correlations were observed between Log Kd, Log KdFe and Log KdMn. Cadmium distribution appears to be influenced by Fe and Mn distribution.     

137Cs and 210Po in Pacific walrus and bearded seal from St. Lawrence Island, Alaska

The activity concentration of Cesium-137 ((137)Cs) and naturally-occurring Polonium-210 ((210)Po) were measured in the muscle tissue, kidney and liver of Pacific walrus (Odobenus rosmarus divergens) and bearded seal (Erignathus barbatus) collected by native hunters from the Bering Sea during May 1996. The mean (137)Cs concentrations in muscle, liver and kidney of Pacific walrus were 0.07, 0.09 and 0.07 Bq kg(-1) (n=5, wet weight), respectively, and 0.17, 0.10, and 0.17 Bq kg(-1) (n=2, wet weight), respectively, in bearded seal. In general, (137)Cs tissue concentrations are significantly lower than those previously reported for mammals from other regions. By comparison, (210)Po activity concentrations are more variable and appear to be higher level compared with mammal data from other regions. The mean (210)Po concentration in the muscle tissue, liver and kidney of Pacific walrus (n=5, wet weight) were 28.7, 189, and 174 Bq kg(-1), respectively. This compares with (210)Po concentration values (n=2, wet weight) of 27, 207 and 68 Bq kg(-1) measured in the muscle tissue, liver and kidney, of bearded seal, respectively. Estimated concentration factors--as defined by the radionuclide concentration ratio between the target tissue to that in sea water--were two to three orders of magnitude higher for (210)Po that those of (137)Cs. We conclude from radiological dose estimates that ingestion of (137)Cs in foods derived from walrus and seal will pose no threat to human health. This work has important implications for assessment of risks of Alaskan coastal communities concerned about the dumping of nuclear waste in the Russia Arctic.     

Effects of hypoxia on benthic macrofauna and bioturbation in the Estuary and Gulf of St. Lawrence,Canada

The bottom water in the >300 m deep Lower St. Lawrence Estuary (LSLE) is persistently hypoxic in contrast to the normoxic bottom waters in the Gulf of St. Lawrence (GSL). We photographed the seabed at 11 stations in the Estuary and Gulf of St. Lawrence (EGSL) during the summers 2006 and 2007 and analysed the images to identify bioturbation traces (lebensspuren) and benthic macrofauna. The objective was to identify the environmental variables that influence the density and diversity of benthic macrofauna and bioturbation traces, and the differences that exist among regions with high, medium and low oxygen levels in the bottom water. The bottom water oxygen concentration is the variable that best explains the densities of total-traces as well as surface-traces. However, the density of these traces was higher in hypoxic regions than in well-oxygenated regions. The higher density of traces in the hypoxic region of the LSLE is mainly due to the activities of the surface deposit feeder Ophiura sp., which occurs in large numbers in this region. Possible explanations explored are stress behaviour of the organisms in response to hypoxia and different benthic macrofauna community structures between the hypoxic regions of the LSLE and the normoxic regions of the GSL. In the former, surface deposit feeders and low-oxygen tolerant species dominate over suspension feeders and low-oxygen intolerant species.     

Paleomagnetic study of the Tunguska catastrophe epicenter

The Tunguska catastrophe occurred in the area of the East Siberian magnetic anomaly on June 30, 1908. The epicenter of the explosive destruction of the Tunguska cosmic body (TCB) was above the central neck of a paleovolcano (Mt. Stoikovich). According to the paleomagnetic data available, the bedrocks on the top of Mt. Stoikovich carry remanent magnetization, which is substantially higher than that in rocks from neighboring mountains. Analysis of the results of paleomagnetic measurements of rock samples collected in the vicinity of the Tunguska catastrophe epicenter showed that the destruction of the cosmic body was accompanied by the formation of multidirectional magnetic fields, which provide disturbances spreading over a distance of 25 km from the epicenter. The chaotic distribution pattern of magnetization vectors measured in the soil in the vicinity of the Tunguska catastrophe epicenter confirms the previously expressed assumption that destruction of the TCB was accompanied with multiple discharges. According to this, we can conclude that the matter of the Tunguska cosmic body was dispersed around the epicenter in a zone approximately 25 km in diameter.     

Influence of lithostratigraphy on the retreat of an unconsolidated sedimentary coastal cliff (St. Lawrence estuary,eastern Canada)

This paper investigates the processes involved in unconsolidated cliff recession using LiDAR surveys (2005, 2010 and 2013) and aerial photographs (1964–2012) at Pointe‐au‐Bouleau, on the north shore of the St. Lawrence estuary, in eastern Canada. The high lithostratigraphic variability of the sediments allowed for the identification of stratigraphic and lithological variables that explain the evolution of coastal cliffs. Space‐for‐time substitution was also used to assess how lithostratigraphy controls the evolution of emerged glaciomarine coastal cliffs over decadal to centennial timescales. This case study presents new quantitative data that contributes to a better understanding of the role of sediment architecture, stratigraphy and geomorphology on coastal evolution. The methodological approach includes the development of a new conceptual model suitable for identifying erosion on cliff coastlines. The high spatial resolution methodology (<5 cm) used herein demonstrates the need for further research using LiDAR data in order to quantify the processes involved in the evolution of coastal cliffs. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigating snowpack across scale in the northern Great Lakes–St. Lawrence forest region of Central Ontario,Canada

This study investigates scaling issues by evaluating snow processes and quantifying bias in snowpack properties across scale in a northern Great Lakes–St. Lawrence forest. Snow depth and density were measured along transects stratified by land cover over the 2015/2016 and 2016/2017 winters. Daily snow depth was measured using a time‐lapse (TL) camera at each transect. Semivariogram analysis of the transect data was conducted, and no autocorrelation was found, indicating little spatial structure along the transects. Pairwise differences in snow depth and snow water equivalent (SWE) between land covers were calculated and compared across scales. Differences in snowpack between forested sites at the TL points corresponded to differences in canopy cover, but this relationship was not evident at the transect scale, indicating a difference in observed process across scale. TL and transect estimates had substantial bias, but consistency in error was observed, which indicates that scaling coefficients may be derived to improve point scale estimates. TL and transect measurements were upscaled to estimate grid scale means. Upscaled estimates were compared and found to be consistent, indicating that appropriately stratified point scale measurements can be used to approximate a grid scale mean when transect data are not available. These findings are important in remote regions such as the study area, where frequent transect data may be difficult to obtain. TL, transect, and upscaled means were compared with modelled depth and SWE. Model comparisons with TL and transect data indicated that bias was dependent on land cover, measurement scale, and seasonality. Modelled means compared well with upscaled estimates, but model SWE was underestimated during spring melt. These findings highlight the importance of understanding the spatial representativeness of in situ measurements and the processes those measurements represent when validating gridded snow products or assimilating data into models.     

Deciphering the Holocene evolution of the St. Lawrence River drainage system using luminescence and radiocarbon dating

The St. Lawrence River is an important drainage route for eastern North American fresh waters. Following Late Pleistocene deglaciation, several fluctuations in base level have fine-tuned the evolution of the ancestral St. Lawrence. These fluctuations are hereby dated using K-feldspar infrared stimulated luminescence (IRSL) and radiocarbon. The accuracy of the individual IRSL dates was achieved by properly correcting for thermal transfer and anomalous fading. For each site investigated, widely used statistical approaches in equivalent dose data have been used to establish which age model, the central or the minimum model, would be appropriate to define the “true” depositional age. The chronology of the succession of regional lake levels is based on careful mapping and dating of the regional dunes, beaches and deltaic sediments. A relative time-space evolution history could be drawn, from ca. 8000 years BP to the present time period. Three major fluctuations are documented for the middle to late Holocene. An unexpected finding, from the ages cluster diagram, is that there have been times in the recent past (ca. 1000–4000 years BP) when the river level was lower or at the same elevation as today. The potential for K-feldspar IRSL to accurately date the Holocene lacustrine evolution is critical in the St. Lawrence River modern drainage basin, an environment that might be negatively impacted over the next century.     

Paleomagnetic study of a vertical sequence of traps from Mount Pavagarh,Gujrat, India

The paleomagnetism of 22 flows which range in composition from olivine basalts to rhyolite and in elevation from 450 ft. to 2680 ft., from Mount Pavagarh, situated in Gujrat, India, has been studied. The igneous activity represented by these flows belongs to the Deccan Trap Plateau Basalt Series. Sixteen flows ranging in elevation from 900 to 2680 ft. showed normal magnetization with upward inclination, consistent with the position of India in the southern hemisphere during the period of their eruption. Four flows from elevation 450 ft. to 730 ft. showed intermediate as well as discordant directions. The paleomagnetic results obtained from these flows have been correlated with those of Deccan traps from other areas. The amount of paleosecular variation represented by these flows has been estimated and compared with that from similar vertical sequences of traps studied from other areas. It has been found that the magnitude of paleosecular variation varied during the period of Deccan trap activity. An estimate of continental drift has been made from mean pole position of the several vertical sequences of traps. This indicates that a drift of the Indian landmass of the order of 24° took place during the entire period represented by the Deccan trap activity. The results of paleomagnetic studies of other sedimentary and igneous formations of Cretaceous age are reviewed in the light of recent results on Deccan traps.     

Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, Japan

Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high‐grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote‐amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle‐derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted.     

Paleomagnetic study on the Early Triassic red beds from Jiaocheng,Shanxi Province

Paleomagnetic and rock magnetic study has been conducted on the Early Triassic red beds of Liujiagou Formation from Jiaocheng, Shanxi Province. Hematite was shown as the main magnetic mineral. After eradicating an initial viscous component at room temperature to ~100°C–200°C, thermal demagnetization shows that most samples contain two remanence components, intermediate-temperature remanence component at 250°C–500°C and high-temperature component at 500°C–680°C. The intermediate-temperature component has a negative fold test at the 95% confidence level. And the pole position of the intermediate-temperature component in geographic coordinates is correlated with the Middle Jurassic reference pole of the North China Block (NCB) within the 95% confidence, suggesting that it might be a remagnetization component acquired during the Yanshanian period. The high-temperature component contains both reversal and normal polarities with positive fold test and C-level positive reversal test at the 95% confidence level, which suggests that this high-temperature component can be regarded as primary magnetization. Comparison of this newly obtained Early Triassic paleopole with the coeval mean pole of the Ordos Basin suggests that a locally relative rotation may have happened between the Ordos and the Jiaocheng area of Shanxi Province. This rotation may be related with two faults: one is Lishi big fault separating Ordos from Shanxi and the other is Jiaocheng big fault, which is situated in the southeast of sampling locality and was still in motion during the Cenozoic.     

Effect of stratification on tidal circulation over the Scotian Shelf and Gulf of St. Lawrence: a numerical study using a three-dimensional shelf circulation model

A three-dimensional shelf circulation model is used to examine the effect of seasonal changes in water-column stratification on the tidal circulation over the Scotian Shelf and Gulf of St. Lawrence. The model is driven by tidal forcing specified at the model’s lateral open boundaries in terms of tidal sea surface elevations and depth-averaged currents for five major tidal constituents (M₂, N₂, S₂, K₁, and O₁). Three numerical experiments are conducted to determine the influence of baroclinic pressure gradients and changes in vertical mixing, both associated with stratification, on the seasonal variation of tidal circulation over the study region. The model is initialized with climatological hydrographic fields and integrated for 16 months in each experiment. Model results from the last 12 months are analyzed to determine the dominant semidiurnal and diurnal tidal components, M₂ and K₁. Model results suggest that the seasonal variation in the water-column stratification affects the M₂ tidal circulation most strongly over the shelf break and over the deep waters off the Scotian Shelf (through the development of baroclinic pressure gradients) and along Northumberland Strait in the Gulf of St. Lawrence (through changes in vertical mixing and bottom stress). For the K₁ constituent, the baroclinic pressure gradient and vertical mixing have opposing effects on the tidal circulation over several areas of the study region, while near the bottom, vertical mixing appears to play only a small role in the tidal circulation.