Non-calcareous Sediments Research Articles

Organic matter variations in the deep marginal basin of the Western Tethys and links to various environments in isotopic Albian–Cenomanian Boundary Interval

In the latest Albian–lowermost Cenomanian, the palaeoenvironments along the northern margin in the Carpathian domain of the Western Tethys were characterized by deep basins with floors below the calcium compensation depth, which were filled with flysch and hemipelagic sediments. On the other hand, the terrestrial areas surrounding the Western Tethys to the north were covered by a diverse flora of gymnosperms and experienced an increase in the diversity of angiosperms; the latter was characterized by a rapid spread in most terrestrial environments. The flysch/hemipelagic succession of the Silesian Basin (the Polish part of the Outer Carpathians) contains a sedimentological record of organic-rich accumulation that is related to the carbon isotope excursion, known as the Albian–Cenomanian Boundary Interval (ACBI); its older part corresponds to Oceanic Anoxic Event 1d (OAE1d). Organic matter (OM) records from these noncalcareous sediments are characterized by the occurrence of both terrigenous and marine organic compounds, and an increase in their accumulation intensity occurred during OAE1d, similar to other Western Tethyan areas and their northern surroundings. Quantitative analyses of the OM compounds using petrographic and chemical methods indicate that the majority were redeposited from land and estuarine environments; however, the OAE1d strata (Alternans Level) and the lower part of the post-OAE1d black shale succession are also enriched in OM of marine origin. This enrichment is interpreted as the result of enhanced surface water productivity, most likely related to redistribution of nutrients from coastal areas during the sea level rise of the KAl8 eustatic cycle. OAE1d was also the period in which the degradation of OM took place under reducing conditions in the bottom waters (although they were not anoxic), which was possibly caused by poor ventilation. A high proportion of terrigenous/estuarine OM compounds redeposited in the Silesian Basin is characteristic, especially for the post-ACBI black and dark grey shales. A large amount of this OM type has undergone relatively rapid degradation as it has settled from the shallows through a well‑oxygenated water column in the epi-, meso- and bathypelagic zones. Some terrigenous OM came from forest fires that occurred in the catchment area and supplied material to the Silesian Basin.

Simultaneous determination of mercury and organic carbon in sediment and soils using a direct mercury analyzer based on thermal decomposition–atomic absorption spectrophotometry

The purpose of this work was to study the feasibility of using a direct mercury analyzer (DMA) to simultaneously determine mercury (Hg) and organic matter content in sediment and soils. Organic carbon was estimated by re-weighing the sample boats post analysis to obtain loss-on-ignition (LOI) data. The DMA-LOI results were statistically similar (p<0.05) to the conventional muffle furnace approach. A regression equation was developed to convert DMA-LOI data to total organic carbon (TOC), which varied between 0.2% and 13.0%. Thus, mercury analyzers based on combustion can provide accurate estimates of organic carbon content in non-calcareous sediment and soils; however, weight gain from moisture (post-analysis), measurement uncertainty, and sample representativeness should all be taken into account. Sediment cores from seasonal wetland and open water areas from six oxbow lakes in the Mississippi River alluvial flood plain were analyzed. Wetland sediments generally had higher levels of Hg than open water areas owing to a greater fraction of fine particles and higher levels of organic matter. Annual loading of Hg in open water areas was estimated at 4.3, 13.4, 19.2, 20.7, 129, and 135ngcm−2yr−1 for Beasley, Roundaway, Hampton, Washington, Wolf and Sky Lakes, respectively. Generally, the interval with the highest Hg flux was dated to the 1960s and 1970s.

Living on the good soil: relationships between soils, vegetation and human settlement during the late Allerød period in Denmark

The immigration of woody plants, especially Betula (tree birch), is examined in relation to geomorphological regions in a compilation of Late-glacial plant macrofossil records from Denmark. The immigration of trees led to a large ecological transformation of the landscape and had a major effect on the flora and fauna available to Palaeolithic people. We show that soil type was a controlling factor in the development of vegetation during the Allerød and Younger Dryas periods. Following the first immigration of trees during the Allerød period, woods became established in the eastern part of Denmark, where ice advances from the Baltic had deposited calcareous and clayey sediments. The western and northern parts of Denmark that are characterised by more sandy and non-calcareous sediments remained treeless throughout the whole Late-glacial period. Finds from the Bromme Culture are concentrated in the region which was wooded, suggesting that the regional variable environment allowed local adaptations using the diverse resources available.

What do results of common sequential fractionation and single-step extractions tell us about P binding with Fe and Al compounds in non-calcareous sediments?

Correct identification of P forms together with their main Fe and Al binding partners in non-calcareous sediments is of crucial importance for evaluation of P cycling in water bodies. In this paper, we assess extraction methods frequently used for this purpose, i.e., a sequential five-step fractionation (water, bicarbonate buffered dithionite solution (BD), NaOH, HCl, nitric-perchloric acid), ascorbate extraction (pH ∼7.5), and oxalate extraction (pH ∼3), directly on a range of laboratory prepared Fe and Al minerals enriched with adsorbed P. Extraction selectivity and efficiency for particular P, Fe and Al forms were also verified by specific combinations of these extraction methods applied on freshwater sediment samples. In the sequential fractionation, BD was highly effective in dissolving both amorphous and crystalline Fe (hydr)oxides and the associated P, while neither FeS nor Al (hydr)oxides were dissolved. The following NaOH extraction effectively dissolved both amorphous and crystalline Al (hydr)oxides. The high solubilizing power of BD and NaOH to dissolve crystalline Fe and Al oxides that have only a small P-sorption ability prevents the use of resulting Fe/P and Al/P ratios as simple predictors of total P sorption capacity of sediments and soils. Ascorbate non-selectively extracted small proportions of FeS and amorphous Fe and Al (hydr)oxides, but significant amounts of adsorbed P, which hinders its use for the characterization of P forms in non-calcareous sediments. Similar nonselective characteristics were found for oxalate extractions. As oxalate extracts most of the adsorbed phosphate, it is not possible to use it unambiguously to determine specific Fe/P and Al/P ratios of active complexes. However, this method is convenient (and more selective than NaOH step in the sequential fractionation) for the determination of amorphous Al (hydr)oxides.

Effect of magnesium on charophytes calcification: implications for phosphorus speciation stored in biomass and sediment in Myall Lake (Australia)

We examined the effect of magnesium (Mg) on the charophytes calcite (CaCO3) encrustation and assessed whether charophytes, growing on non-calcareous sediments in the Myall Lake, a poorly flushed shallow coastal lake with salinity of 2–3 PSU, could function as an effective nutrient sink for phosphorus (P) in a similar manner to charophytes growing on calcareous sediments of the freshwater calcium (Ca)-rich hardwater, i.e., through the formation of Ca-bound P. Our results showed that high Mg in the Myall Lake water reduced the calcification in charophytes. Likewise, the addition of Mg into the tap water also produced the same effect. The inhibition of the calcite formation decreased significantly the percentage of Ca-bound P formation in the charophyte biomass as well as in the sediment. However, the inability of charophytes in Myall Lake to precipitate calcite does not reduce the plant beds' capability to act as a P nutrient sink. Instead of Ca-bound P, a large percentage of less bioavailable non-reactive organically bound P (NaOH–P: 40–65%) fraction in the biomass, together with the plant’s slow decomposition rate, will lead to burial of dead organic matter and an incomplete mineralization process. In particular, detritus of the charophyte plants’ thalli is relatively more resistant to mineralization. This mechanism was supported by the result of sedimentary P fractionation in which the refractory P and non-reactive organic P fractions accounted for at least 80% of the total P.

Ichnology of the Cretaceous Oceanic Red Beds (Outer Western Carpathians, Czech Republic)

Ichnology of the Cretaceous Oceanic Red Beds (Outer Western Carpathians, Czech Republic)Large differences in the intensity and overall character of bioturbational structures were found in five facies containing hemipelagic red beds. Red beds (CORB) of the Godula facies of the Silesian Unit and their equivalents (mostly not red) in the Kelč facies of the Silesian Unit and the CORB in the non-calcareous sediments of the Rača Unit display a very low degree of bioturbation. The CORB facies of the Rača Unit, containing calcareous intercalations, displays a very high degree of bioturbation as expressed by a high ichnofabric index. They contain trace fossilsChondrites, Zoophycos, Planolites, Thalassinoides, Palaeophycus, TeichichnusandPhycosiphon.The supply of food obviously acted as the controlling factor. The "calcareous" facies of the CORB of the Rača Unit has a considerably higher proportion of sand-dominated interbeds and also carbonates than the non-calcareous facies. This (especially the presence of carbonates) suggests a relative proximity of food-rich environments and an easy transport of nutrition-rich substrate by turbidite currents into the basin directly, not only by periodical fall-out of dead plankton (which is probably responsible for the rhythmicity of poor colonization horizons in weakly bioturbated units).

Fractionation of sediment phosphorus revisited: II. Changes in phosphorus fractions during sampling and storing in the presence or absence of oxygen

The purpose of this study was to evaluate the sensitivity of a phosphorus (P) fractionation procedure on sampling practices and other sources of error in the characterization of the chemical status of P in noncalcareous sediments rich in humic compounds and iron (Fe). We investigated the effects of nitrogen gas (N2) shielding on the stability of various P fractions during sampling and various periods of sample storage on both oxic and reduced sediments. In addition, we studied storage‐induced changes in preserved or unpreserved extracts from different fractionation steps. Sampling and storage conditions were critical factors in P fractionation studies. During sampling, sample storage, and extraction, the N2 atmosphere (atm) protected samples from oxidation and consequent changes in P forms, especially in the redox‐sensitive form. Long‐term storage without N2‐shielding caused the most drastic changes in oxic sediment, whereas the reduced sediment protected with N2 experienced only minor changes. Extracts preserved with acid can be stored for at least 1 week without significant changes. The extraction results of P and other elements obtained with both oxic and reduced sediment samples supported the biogeochemical basis of the fractionation procedure, demonstrated by the behavior of Fe and Fe‐bound P in sediment originating from and treated in different oxygen (O2) conditions. Despite a few shortcomings, with careful laboratory work and avoidance of sample oxidation during sampling and storage, the fractionation procedure and working practices used seem to provide reliable results and valuable information on the chemical character of sediment P.

Carbon Dioxide Emissions from Exhumed Petrocalcic Horizons

The second largest pool of terrestrial carbon is soil CaCO3 In addition to being an important sink of atmospheric CO2, soil carbonate is potentially an important source of atmospheric CO2 The cemented form of soil carbonate—the petrocalcic horizon—develops in geomorphically stable soil in arid, semiarid, and some subhumid climates. In many of these dryland areas, such as the Chihuahuan Desert of North America, erosion has stripped away overlying soil and exhumed the petrocalcic horizon, thereby exposing it to a weathering zone above the calcification zone where it normally forms. This research tested the hypothesis that soil type 1 (eroded Aridisols with exhumed petrocalcic horizons) will emit more CO2 than soil type 2 (noneroded Aridisols with petrocalcic horizons) or soil type 3 (Entisols formed in sandy, noncalcareous sediments). We tested this hypothesis by comparing the amount of CO2 and the δ13C of CO2 released from the three soil types. Using a randomized complete block design, CO2 emissions were measured using NaOH and soda lime traps from June 2002 to October 2003. Neither the NaOH traps nor soda lime traps detected any statistical difference in cumulative CO2 emissions from the three soil types at the α = 0.05 level. Moreover, the isotopic analysis of CO2 did not match the isotopic values of pedogenic carbonate, nor were there any statistical differences (α = 0.05) in δ13C of CO2 among the three soil types. We conclude, therefore, that exhumed petrocalcic horizons are not actively emitting CO2 at a rate significantly greater than adjacent soils, and thus carbon stored in petrocalcic horizons can be considered a recalcitrant reservoir within the decadal timeframe pertinent to carbon sequestration policies.

Pátek, Levousy a Chlumčany – významné fosiliferní středopleistocénní lokality na pravém břehu Ohře mezi Louny a Libochovicemi [Pátek, Levousy and Chlumčany – important mid-pleistocene localities on the right bank of the Ohře River between Louny and Libochovice

Due to a complete predominance of non-calcareous fluvial sediments in the Czech Republic, any find of fossil malacofauna is always considered as rare. The present work describes three localities in the Ohře river area, which contain, especially in the case of the Pátek locality, very abundant mid-Pleistocene malacofaunas. They were mainly collected in the floodplain fine-grained loam and back swamp deposits but also in sandy gravels. The molluscan thanatocenoses from localities near the Pátek village indicate the interglacial maximum (with up to 25 forest species s.l.), which developed directly on a 30 m thick river terrace dating back to the period, during which the Ohře river established its present-day easterly course. The fossil molluscs from the Levousy locality come from floodplain loam deposits as well as from the underlying sandy terrace gravels. The species distribution, nevertheless, indicates only a transitional glacial-interglacial period. The somewhat higher morphologic position of the locality, as well as that of another section at Chlumčany, and complete predominance of local late Cretaceous material indicates that the Ohře river did not flow to the east yet during the accumulation of the floodplain deposits with molluscs, but still to the north, towards Bílina. The terrestrial malacofauna from the Chlumčany section came from floodplain marls, particularly from sandy tufa deposits in the alluvium, which contains no forest-biotope elements, but the presence of the species Columella columella – distinct representative of our „coldest“ loess deposits – is an absolute surprise, since the peak of production of the sandy tufa deposits has always been associated with climate optima of the interglacials and of the Holocene.Therefore, the described malacofaunas come from a boundary period, during which the Ohře river did not use its present-day valley (Levousy and Clumčany) yet. Then, from the oldest time span, it took up for the first time its eastward course. Stratigraphy of the localities cannot be determined with a reasonable certainty in regard to the current controversial situation in Pleistocene chronology both in the northern foothills of the Alps and in the area of the „classic“ localities belonging to the continental ice-sheet region in northern Germany (Kovanda 2005a). Altogether 12 mid-Pleistocene species of small mammals were found in thanaotocoenoses at localities Pátek and Levousy. Ostracod assemblages analysis was also undertaken (11 species in 8 samples were determined)

Test of experimental set-ups for electrodialytic removal of Cu, Zn, Pb and Cd from different contaminated harbour sediments

Electrodialytic removal of heavy metals from different harbour sediments was investigated. Electrodialytic remediation experiments in laboratory scale were made with calcareous and non-calcareous harbour sediments. Two different experimental set-ups were used for the study, one with stirring of the sediment slurry, the other without stirring. The removal of heavy metals was highest in the non-calcareous sediment, where 94% Cd, 91% Zn and 73% Cu were removed after 24 days. The highest removal obtained for the calcareous sediment was 81% Cd, 76% Zn, 75% Pb and 53% Cu after 21 days, with stirred sediment slurry. Electrodialytic experiments without stirring of calcareous sediment gave high removals (84% Zn, 58% Pb and 48% Cu), but there were problems with precipitations in the sediment, which limited the removal. The stirred experiments gave the highest removals of heavy metals and the voltage was the most stable in these experiments, and thus, the stirred set-up is the best choice for experimental set-up. The order in which the heavy metals were removed from the harbour sediments was Cd>Zn>Pb>Cu.

The micropaleontological character of anomalous calcareous sediments of late Pliocene through early Pleistocene age below the CCD in the northwestern North Pacific Ocean

Calcium carbonate was preserved more than 1 km below the modern calcite compensation depth (CCD) at ODP Site 1179 over several short intervals around 2.5–2.4, 1.65 and 0.9–0.7 Ma. This anomalous preservation resulted from a combination of increased production of planktonic foraminiferal tests at the sea-surface and increased rate of sedimentation to the sea floor. The abundance of dinoflagellate cysts in calcareous sediments records intense plankton blooms, and the preservation of oxidation-susceptible round brown Brigantedinium cysts in foraminifer-rich samples supports the theory of rapid burial. The rise in sea-surface productivity was driven by enhanced flux of continentally derived limiting nutrients, consistent with the pollen evidence of continental aridification, cooling, and an increase in wind strength. The abundant pollen, dominated by steppe herb and montane–boreal conifer taxa, contrasts with lower pollen concentrations dominated by temperate-subtropical deciduous tree and Taxodium-type pollen in non-calcareous sediments.

The micropaleontological character of anomalous calcareous sediments of late Pliocene through early Pleistocene age below the CCD in the northwestern North Pacific Ocean

Calcium carbonate was preserved more than 1 km below the modern calcite compensation depth (CCD) at ODP Site 1179 over several short intervals around 2.5–2.4, 1.65 and 0.9–0.7 Ma. This anomalous preservation resulted from a combination of increased production of planktonic foraminiferal tests at the sea-surface and increased rate of sedimentation to the sea floor. The abundance of dinoflagellate cysts in calcareous sediments records intense plankton blooms, and the preservation of oxidation-susceptible round brown Brigantedinium cysts in foraminifer-rich samples supports the theory of rapid burial. The rise in sea-surface productivity was driven by enhanced flux of continentally derived limiting nutrients, consistent with the pollen evidence of continental aridification, cooling, and an increase in wind strength. The abundant pollen, dominated by steppe herb and montane–boreal conifer taxa, contrasts with lower pollen concentrations dominated by temperate-subtropical deciduous tree and Taxodium -type pollen in non-calcareous sediments.

Enhanced attenuation of septic system phosphate in noncalcareous sediments.

Review of phosphate behavior in four mature septic system plumes on similar textured sand has revealed a strong correlation between carbonate mineral content and phosphate concentrations. A plume on calcareous sand (Cambridge site, 27 wt % CaCO3 equiv.) has proximal zone PO4 concentrations (4.8 mg/L P average) that are about 75% of the septic tank effluent value, whereas three plumes on noncalcareous sand (Muskoka, L. Joseph, and Nobel sites, <1 wt % CaCO3 equiv.) have proximal zone phosphate concentrations (<0.1 mg/L P) that are consistently less than 2% of the effluent values. Phosphate attenuation at the noncalcareous sites appears to be an indirect result of the development of acidic conditions (site average pH 3.5 to 5.9) and elevated Al concentrations (up to 24 mg/L), which subsequently causes the precipitation of Al-P minerals such as variscite (AlPO4 x 2H2O). This is supported by scanning electron microscope analyses, which show the widespread occurrence of (Al+P)--rich secondary mineral coatings on sand grains below the infiltration beds. All of these septic systems are more than 10 years old, indicating that these attenuation reactions have substantial longevity. A field lysimeter experiment demonstrated that this reaction sequence can be readily incorporated into engineered waste water treatment systems. We feel this important P removal mechanism has not been adequately recognized, particularly for its potential significance in reducing P loading from septic systems in lakeshore environments.

Phosphorus characterization in sediments impacted by septic effluent at four sites in central Canada

Characterization of phosphorus (P) enriched solids was undertaken in the sediments below four mature septic system infiltration beds, where previous monitoring of phosphate (PO 4) concentrations in the groundwater had indicated that substantial retention of P was occurring in the vadose zone. At each site, zones of sediment P enrichment were identified by an acid extraction procedure. Acid extractable sediment P concentrations were found to be 2–5 times higher than background values, within narrow discrete zones generally 10–30 cm in thickness, located within one meter of the infiltration pipes. Back scattered electron images of the P enriched zones indicated that the P solids occurred as distinct authigenic grains (up to 300 μm diameter) and as grain coatings. Microprobe analyses indicated predominantly Fe–P in calcareous sediments (Cambridge and Langton) and Al–Fe–P in non-calcareous sediments (Muskoka and Harp Lake). Porewater analyses indicated that the zones of P accumulation were closely associated with zones of redox change characterized by the conversion of effluent NH 4 + to NO 3 −. The data suggests that a substantial amount of the septic derived P is being attenuated by mineral precipitation reactions that occur rapidly after the effluent encounters subsurface sediments. Reductive dissolution of ferric (oxy)hydroxide minerals as a consequence of reducing environments near the infiltrations pipes, the release of Fe 2+ in solution and subsequent conversion of Fe 2+ to Fe 3+ may promote the precipitation of ferric or ferrosoferric PO 4 minerals. In sediments with limited buffering capacity (calcite deficient), the decrease in pH resulting from effluent oxidation may cause Al (oxy)hydroxide dissolution and subsequent precipitation of Al–P rich phases. These precipitation reactions appear to have the capacity to immobilize a substantial amount of septic derived P (25–99% at these sites) for a considerable period of time.

Pleistocene agglutinated foraminifera from the Lomonosov Ridge and Amundsen Basin, Arctic Basin. Initial report on piston cores 2177-5 (KAL) and 2176-3 (KAL)

Noncalcareous Pleistocene sediments of the Central Arctic Ocean contain sparse benthic foraminiferal assemblages consisting entirely of agglutinated taxa. Deep water agglutinated foraminifera are studied from two piston cores collected from the Lomonosov Ridge and Amundsen Basin [Cores PS 2177-5 (KAL) and 2176-3 (KAL)]. Core PS 2177-5 (KAL) contains an assemblage of 10 species, dominated by Cyclammina pusilla Brady, and is interpreted to reflect a bathyal environment with variable organic flux and nutrition levels. Core PS 2176-3 (KAL) in the Amundsen Basin yielded a very depauperate benthic foraminiferal assemblage. It is assumed that the environment was inhospitable for agglutinated foraminifera.

The effect of acidification, liming and reacidification on macrophyte development, water quality and sediment characteristics of soft-water lakes

Rapid expansion of Juncus bulbosus L. and the concomitant suppression of isoetid plant species has often been observed in acidifying soft water lakes in Western Europe. Experimental studies have shown that this mass development of J.bulbosus was caused by changes in the carbon and nitrogen budgets in these ecosystems. Acidification leads to temporarily strongly increased carbon dioxide (CO2) levels in the slightly calcareous sediment and to accumulation of ammonium as a result of a reduced nitrification rate in acidifying waters. Many acidifying Scandinavian soft water lakes, however, have a well developed macrophyte vegetation. It is suggested that this is related with the non-calcareous sediments of these lakes. After liming, however, mass development of J. bulbosus and/or Sphagnum spec. has been observed in Swedish and S.W. Norwegian lakes. From field experiments it has become clear that part of the lime is deposited on the sediments leading to an increase of mineralisation rates, CO2 production, sediment pore water levels of phosphate and ammonium and to a decrease of the nitrate concentrations in the sediment. These changes have been earlier observed in acidifying West European waters. Rooted species like J.bulbosus can only benefit from the higher nutrient levels in the sediment when the CO2 level of the water layer is relatively high as this species is adapted to leaf carbon uptake. It is demonstrated that gradual reacidification by the acid water from the catchments and the increased flux of carbonic acid from the limed sediments to the overlying water leads to increased CO2 levels in the water layer of the limed lakes already a few months after liming.

Characterization of Wind Erosion Sediments in the Red River Valley of North Dakota

AbstractWind erosion is a serious problem in the Red River Valley of North Dakota. Wind erosion sediments were characterized to evaluate their potential as nonpoint source pollutants for surface water and shallow groundwater. Thirty‐four sites from the South Dakota border to the Canadian border were sampled to measure physical and chemical characteristics of displaced sediment and field soils. Collected sediments originated from fields with soils having silt loam, silty clay loam or silty clay textures. Sediments had &gt;98% water‐stable aggregates and average NO−3‐N levels of 105 mg kg−1. Calcareous sediments (22 samples) were significantly higher in pH, NO−3‐N and electrical conductivity (EC), while noncalcareous sediments (12 samples) were higher in P and K. Soils from sugar beet (Beta vulgaris L.) and small grain fields tended to have higher NO−3‐N levels than fields with other crops or cropping practices. Agricultural chemical residues were detected and identified at two sample sites. A comparison of displaced sediments with field soils showed significant increases in NO−3‐N, P, K and EC in the sediments and a significant reduction in pH. Nearly 96% of the NO−3‐N could be leached out of the sediments in an initial leaching. Wind erosion sediments have the potential to be nonpoint sources of NO−3‐N and salinity for surface and groundwater.

Smectite-Illite Transition in Barbados Accretionary Wedge Sediments: Tem and Aem Evidence for Dissolution/Crystallization at Low Temperature

AbstractSediments from depths to 670 m in the Barbados accretionary complex and transecting the décollement zone have been studied by transmission and analytical electron microscopy (TEM/AEM). The sediments consist of claystone and mudstone intercalated with layers of volcanic ash. Smectite comprises the bulk of the noncalcareous sediments and forms a continuous matrix enveloping sparse, irregular, large grains of illite, chlorite, kaolinite and mixed-layer illite/chlorite of detrital origin at all depths. The detrital origin of illite is implied by illite-smectite textural relations, well-ordered 2M polytypism, and a muscovite-like composition. K is the dominant interlayer cation in smectite at all depths, in contrast to the Na and Ca that are normally present in similar rocks.Deeper samples associated with the décollement zone contain small (up to 100 Å thick) illite packets included within still-dominant subparallel layers of contiguous smectite. AEM analyses of these packets imply illite-like compositions. Selected area electron diffraction (SAED) patterns show that this illite is the 1Md polytype. Packets display step-like terminations like those seen in illite of hydrothermal origin. The data collectively demonstrate that smectite transforms progressively to illite via a dissolution-recrystallization process within a depleting matrix of smectite, and not by a mechanism of layer replacement. This illite seems to form at depths as shallow as 500 m and temperatures of 20°-30°C, which is in marked contrast to the much higher temperature conditions normally assumed for this transformation. This implies that the high water/rock ratios associated with the décollement zone are significant in promoting reaction.

Hydrochemical aspects of the negro river, patagonia, argentina

AbstractWater samples collected in the Negro River drainage basin (Patagonia, Argentina) during two different field trips—the first in May 1972 and the second in January 1973—were analysed for the major dissolved inorganic constituents. Q‐mode factor analyses demonstrate that two factors account for over 98 per cent of the variance in both sample suites. They represent: a) the direct influence of solution of evaporites and associated carbonate rocks in an arid environment‐type; b) the influence of the weathering products of metamorphic, igneous rocks, and varied non‐calcareous sediments. R‐mode factor analyses of the two sets of data suggest that although the main mechanisms controlling water chemistry were essentially the same, the principal sources of dissolved solids differed significantly in each separate occasion. Further, the major mechanisms controlling its water chemistry are within a wide spectrum of the so‐called ‘rock dominance’.

The influence of chironomus plumosus larvae on the exchange of dissolved substances between sediment and water

4th instar Chironomus plumosus larvae (about 1000·m−2) were added to tubes containing sediment and overlying water. At a temperature of 20°C the larvae greatly increased the trasnport of silica, phosphorus and iron from the sediment to the water. Oxygen concentrations did not influence the exchange of silica. For two non-calcareous sediments the exchange of phosphorus and iron was much higher under anaerobic than under aerobic conditions while the difference was small for sediment from a hardwater lake. Exchange of inorganic nitrogen was little influenced by added chironomid larvae.