Secondary Calcium Carbonate Research Articles

Effects of grain size and seawater salinity on magnesium hydroxide dissolution and secondary calcium carbonate precipitation kinetics: implications for ocean alkalinity enhancement

Abstract. Understanding the impacts that mineral grain size and seawater salinity have on magnesium hydroxide (Mg(OH)2) dissolution and secondary calcium carbonate (CaCO3) precipitation is critical for the success of ocean alkalinity enhancement. We tested Mg(OH)2 dissolution kinetics in seawater using three Mg(OH)2 grain sizes (<63, 63–180 and >180 µm) at three salinities (∼36, ∼28 and ∼20). While Mg(OH)2 dissolution occurred more quickly the smaller the grain size, salinity did not significantly impact measured rates. Our results also demonstrate that grain size can impact secondary CaCO3 precipitation, suggesting that an optimum grain size exists for ocean alkalinity enhancement (OAE) using solid Mg(OH)2. Of the three grain sizes tested, the medium grain size (63–180 µm) was optimal in terms of delaying secondary CaCO3 precipitation. We hypothesise that in the lowest-grain-size experiments, the higher surface area provided numerous CaCO3 precipitation nuclei, while the slower dissolution of bigger grain sizes maintained a higher alkalinity and pH at the surface of particles, increasing CaCO3 precipitation rates and making them observable much more quickly than for the intermediate grain size. Salinity also played a role in CaCO3 precipitation, where the decrease in magnesium (Mg) allowed secondary precipitation to occur more quickly, similar in effect size to another known inhibitor, i.e. dissolved organic carbon (DOC). In summary, our results suggest that OAE efficiency as influenced by CaCO3 precipitation depends not only on seawater composition but also on the physical properties of the alkaline feedstock used.

A closer look at clasts and groundmass: Micromorphological features in sediments with archaeological significance in Obishir and Katta Sai complexes (Central Asia)

The aim of this study is to investigate the relationship between coarse and fine material in sediments at four archaeological sites in Central Asia, which share a common characteristic of coarse clasts dispersed within a silty matrix. By using micromorphology and grain size analysis, the study aims to understand the microscale processes that have affected the geogenic material and, by extension, the potential impact on the archaeological assemblages. The four sites studied are Obishir-1, Obishir-5, Katta Sai 1, and Katta Sai 2, which are located at the toe or along a slope in Kyrgyzstan and Uzbekistan. The study focuses on the micro-features occurring on the surfaces of pebble-sized clasts and identifies four typical features: loamy cappings, loamy coatings, secondary calcium carbonate accumulations, and cracks. The processes related to these features are identified as alteration of the mineral grains, frost action, redeposition, and pedogenetic and anthropogenic processes. The study concludes that the primary contact between the two components has been disrupted in most cases, and suggests that the findings can be used to analyze site formation and post-depositional processes at archaeological sites. Furthermore, analogies with gravel-sized artifacts can be drawn, particularly with regard to secondary calcium carbonate accumulation.

A carbon-sink in a sacred forest: Biologically-driven calcite formation in highly weathered soils in Northern Togo (West Africa)

Soil organic matter (OM) is a source of fertility for food provisioning and a means for climate mitigation. A high pedodiversity observed over very short distances due to both past and present land use, such as in Western Africa (Northern Togo), makes this a crucial issue. In particular, some small spots covered by sacred forests (forêts sacrées) of high cultural value in this area are extremely biodiverse, calcareous and high in OM in contrast with the non-calcareous, poor OM, overgrazed woody savannah and agricultural surroundings. The objectives of our work were to understand this pedodiversity and the process of CaCO3 formation in the soil under the highly biodiverse forest using morphological, micromorphological, chemical and mineralogical soil analyses. The results show a high degree of weathering of the gneiss parent material, presence of plinthite gravels, dominance of 1:1 clays, formation of swelling clays in the imperfectly drained soils, and low OM content. The presence of palygorskite, although in traces, suggests drier intervals and is consistent in this context with the extreme wet and dry climate conditions in the region. In the OM rich soils under forest, bio-calcification takes place in the form of CaCO3 needles, micrite hypocoatings around biopores and calcified cells. Oribatid excrements are associated with calcite and organic matter in the sacred forest soil, indicating that litter recycling has played an important role in the formation of calcite. We hypothesize that the high biological activity releasing CO2, formation of HCO3– and precipitation of CaCO3 due to the Ca2+ released by the recycled organic matter and weathering of plagioclases, lead to different forms of secondary calcium carbonate in the sacred forest soils. The high oxalate content of the vegetation in the sacred forest suggests that calcium carbonate formation, possibly via the oxalate-carbonate pathway, may also have played a role in calcite precipitation in these in organic matter rich soils. The parent material of these soils is not calcareous, meaning that these are not lithogenic carbonates, thus making them an important carbon sink. The soil characteristics indicate a high potential for development of the soils of the area in both agricultural yields and in potential carbon sequestration relevant to global change policies.

Micromorphological features of soils formed on calcium carbonate\u2013rich slope deposits in the Polish Carpathians

Seven soil profiles developed on calcium carbonate–rich slope deposits in the Polish Carpathians were studied in order to: i) determine the micromorphological features of heterogeneous soils formed in a carbonate depositional environment, and ii) track primary and secondary calcium carbonate forms and their distribution in such stratified soils. Three cases of soils with different arrangements of calcium carbonate were distinguished, controlled mostly by slope processes. For instance, the increasing content and random distribution of angular and subangular rock fragments found in the overall soil matrix and the irregular coarse: fine size limit suggested different intensities of accumulation and mixing of soil material transported along the slope. Slope processes, together with the calcium carbonate content, mineralogical characteristics and texture influenced the type and arrangement of the bfabric pattern. The calcium carbonate distribution within the soils, besides the obvious inheritance from parent material, was governed by the translocation and mixing of deposits on slopes. The climatic conditions prevailing in the area favour the development of secondary forms of calcium carbonate. However, only three of the seven studied profiles contained pedogenic forms of calcium carbonate, yet they were distributed randomly. The occurrence, distribution and preservation of secondary carbonates depended on the content of primary calcium carbonate and soil features such as texture. The transported material down the slope may indicate a very low content of primary calcium or lack thereof, hence its pedogenic forms could not be created.

Quantification of diagenetic transformation of continental margin sediments at the Holocene time scale

Early diagenesis processes in the Bay of Biscay have been studied previously on short interface cores. In order to complete the data base and to characterize anoxic biogeochemical processes that affect Quaternary deposits, 1–3 m long gravity cores were collected at 150, 550, 1000 and 2000 m water depth on the continental slope of the south-eastern part of the Bay of Biscay. The aim of this work was to determine how a recorded signal could be changed in the several thousand-year situation of the Holocene period. For that, we determined radiocarbon and 210Pb dating, sedimentological characteristics, and the vertical distribution of particulate and pore water biogeochemical compounds. The sediment consists of a muddy facies deposited continuously during the Holocene. Results show that the distribution of redox sensitive compounds follows the well-established depth sequence of diagenetic reactions governed by the preferential use of the electron acceptor for the bacterially mediated oxidation of organic matter. Mineralization of organic matter occurs down to the bottom of the cores studied, indicating that Holocene sediment of the Bay of Biscay are in a transient state and they keep on being diagenetically transformed today. Effects of anoxic processes on buried sediments were estimated from fluxes induced by chemical gradients in pore waters. Anoxic processes consume up to 3.6 mg particulate organic carbon (POC) per g of dry sediment. They yield also precipitation of secondary calcium carbonate, which represent up to 5% of total buried carbonates. Early diagenetic reactions, which affect proxies commonly used in paleo-oceanography, such as POC, carbonates, phosphorus, or manganese, should be quantified in order to distinguish the part of a sedimentary record being the result of past environmental conditions from that due to post-depositional diagenetic processes. Diagenesis of Holocene deposits also contributes to a low, but significant fraction of N and P flux to the Bay of Biscay sea water.

Effects of carbonate on the structure and properties of loess and the corresponding mechanism: an experimental study of the Malan loess, Xi’an area, China

The structural, physical and morphological characteristics of loess will change as a result of the dissolution of mineral components, mainly carbonate, when it is exposed to acid rain, industrial acid leakage or other acidic environments. This study investigates the physical and structural characteristics of the Malan loess, Xi’an area, China, after carbonate dissolution. The presence of carbonate is determined by scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. The loess was soaked with 0.2 mol/L acetic acid. The degree of degradation of the loess, carbonate and other minerals was determined by the abundances of elements in the solution. Microstructural analysis combined with the loess characteristics of adsorption, water stability, compressive yield stress and shear strength are used to explain the changes in the soil structure after carbonate dissolution. The results show that bonds in the cementation are irreversibly lost during the remoulding process, and additional bonds are destroyed with the removal of large amounts of carbonate, causing the skeletal particle surface area, specific surface area, adsorption capacity and water stability to decrease. The compressive yield stress and cohesion of the soil are considerably more sensitive at higher water contents. Calcium carbonate is the main carbonate component in the loess, and the secondary calcium carbonate connects the skeletal particles by coating and bridging; the strong cementation stops the particles from dispersing in water. The change in strength and deformation of the soil change its microstructure, which indicates that the secondary calcium carbonate affects the soil structure and stability by reducing the aggregate wettability and changing the mechanical strength of the soil aggregate. This paper will contribute to elucidating the formation and destruction of loess.

Chemical weathering indices applied to soils developed on old lake sediments in a semi-arid region of Turkey

Climate is a major influence on weathering processes affecting soil parent materials. Important contributors to soil formation in arid and semi-arid climatic zones are the diurnal cycles of solar heating and cooling that cause mechanical or physical disintegration of rock or parent materials, and wind-blown sands that score and abrade exposed rock surfaces. By using the Soil Taxonomy classification system, the initial aim of this study was to carry out a pedological evaluation for four soil profiles, classified as Xeric Haplocalcid and Xeric Haplocambid, formed on different parent materials (limestone, marl and old alluvial deposits) under the same conditions, including topography and vegetation, in a semiarid region. The second stage was the exploration of the similarities and differences in the classifications resulting from either the pedogenic processes, or from other factors, by determining the degree of soil weathering using geochemical data. To achieve this, soil samples were collected from the horizons to investigate their mineralogical, geochemical and physiochemical properties. The study also considered other features, such as the pedogenic evolution of soils, through the use of weathering indices, namely the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Base/R2O3 Ratio, Weathering Index of Parker (WIP) and Plagioclase Index of Alteration (PIA). The results clearly showed that soil development at the Altınova State Farm at Konya in the Central Anatolia region of Turkey is due to slow pr ogressive weathering. For this case, the main indicators are secondary calcium carbonate illuviation and weak structural development with a weathering ratio of silicon to aluminium greater than two in all profiles.

Changes in the geochemical parameters of karst lakes over the past three decades – The case of Plitvice Lakes, Croatia

One of the major reasons for the increase in global air temperature since the early 20th century is considered to be the increase in the atmospheric CO2 concentration. Karst relief is considered an important carbon sink, but it can also be a natural source of carbon and CO2 emission. Aquatic systems in karst areas facilitate carbon exchange between the karst and the atmosphere, often through groundwater geochemical carbonate rock dissolution (carbon sink) and in the form of secondary calcium carbonate precipitation (possible carbon source).The protected area of Plitvice Lakes National Park, located in the karst region of Croatia, was chosen as a case study on karst geochemical processes. The lakes are also specific for their authigenic calcite precipitation in the form of tufa barriers and lake sediment. Physical and chemical data (temperature, pH, Ca2+, HCO3−, Mg2+ and CO2 concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and Mg/Ca ratio) from water samples collected at 8 locations (2 springs, 2 rivers, and 4 lakes) from 1981 to 2014 were studied.The data were not collected systematically, so long-term changes have been mostly assessed through comparison between parameters from two selected periods (1981–1986 and 2010–2014) and through temporal correlations for each observed parameter in each calendar month.For the 33 years studied, an increase in air and water temperature, Ca2+ and HCO3− concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and a decrease in the Mg/Ca ratio were observed. No statistically significant change was observed for pH or CO2 and Mg2+ concentrations. Average discharge rates did not display any significant change over the past three decades, however there was a change in their seasonal distribution.The significant increase in Ca2+ and HCO3− concentrations at lake locations were primarily caused by an increase in Ca2+ and HCO3− values in the water of the springs. Simultaneously, Mg2+ concentrations remained constant, which indicates higher levels of limestone (calcite) dissolution than dolomite dissolution. One of the reasons for this could be higher air/soil temperatures, resulting in higher soil CO2 production, which appears to result in the higher dissolution of calcite exclusively. An increase in HCO3− concentrations at the springs implies that karst groundwater is a carbon sink. Furthermore, the fact that the spatial decrease in HCO3− concentration in downstream waters was the same during the 1981–1986 and 2010–2014 periods implies that the entire observed karst lake system itself is a carbon sink.Temporal and spatial changes in SIcalc and IRcalc values in surface waters were mainly attributed to an increase in the intensity of bioactivity, which is in turn connected with an increase in water temperature.

Characterization of sulfur products on CaO at high temperatures for air and oxy-combustion

Oxy-coal combustion is a novel technology that seeks to reduce carbon dioxide emissions from electricity generating units, but the unique combustion environment could potentially affect the manner in which the flue gas and fly ash interact. Of particular interest is the ability of fly ash to reduce SOx emissions, a source of concern in implementing oxy-coal technology. This study seeks to examine the way SOx interacts with calcium oxide, an important fly ash metal oxide, under a variety of flue gas conditions and temperatures. Using DRIFTS and XRD, the major products under the various reaction conditions were analyzed. The dominant sulfur containing product was found to be calcium sulfate. However, a secondary calcium carbonate product was formed under certain oxy-fuel conditions. Additionally, EDX was employed to examine the temperature dependence for sulfur retention.

Carbon dioxide in scree slope deposits: A pathway from atmosphere to pedogenic carbonate

A continuum of carbon, from atmospheric CO2 to secondary calcium carbonate, has been studied in a soil associated with scree slope deposits in the Jura Mountains of Switzerland. This approach is based on former studies conducted in other environments. This C continuum includes atmospheric CO2, soil organic matter (SOM), soil CO2, dissolved inorganic carbon (DIC) in soil solutions, and secondary pedogenic carbonate. Soil parameters (pCO2, temperature, pH, Cmin and Corg contents), soil solution chemistry, and isotopic compositions of soil CO2, DIC, carbonate and soil organic matter (δ13CCO2, δ13CDIC, δ13Ccar and δ13CSOM values) have been monitored at different depths (from 20 to 140cm) over one year. Results demonstrated that the carbon source in secondary carbonate (mainly needle fiber calcite) is related to the dissolved inorganic carbon, which is strongly dependent on soil respiration. The heterotrophic respiration, rather than the limestone parent material, seems to control the pedogenic carbon cycle. The correlation of δ13Corg values with Rock-Eval HI and OI indices demonstrates that, in a soil associated to scree slope deposits, the main process responsible for 13C-enrichment in SOM is related to bacterial oxidative decarboxylation. Finally, precipitation of secondary calcium carbonate is enhanced by changes in soil pCO2 associated to the convective movement of air masses induced by temperature gradients (heat pump effect) in the highly porous scree slope deposits. The exportation of soil C-leachates from systems such as the one studied in this paper could partially explain the “gap in the European carbon budget” reported by recent studies.

Paleoclimatic interpretations of buried paleosols within the pre-Illinoian till sequence in northern Missouri, USA

Northern Missouri preserves shallow buried paleosols ranging in age from Early to Late Pleistocene that are developed in six pre-Illinoian tills beneath Illinoian (MIS 6) and Wisconsinan (MIS 4-2) loess. The morphology of these paleosols changes with age, reflecting a changing climate during the Pleistocene, and cosmogenic-nuclide burial dates of the respective sola provide age control on the timing of these changes.The depth to secondary calcium carbonate nodules within the weathering profiles increases with younger age, indicating a transition to moister conditions during the Pleistocene, and these nodules are absent entirely within the modern soils. After approximately 0.4Ma, the sola became distinctly redder, even as the time available for pedogenesis became shorter, culminating in the bright red Sangamon Geosol (MIS 5). This trend is consistent with increasing interglacial temperatures and/or precipitation. Finally, erosion rates determined from cosmogenic-nuclide concentrations within the sola also increase systematically with younger age. This increase may be due to some combination of changing climate, more-frequent glaciations and the deposition of a thick cover of unconsolidated glacial sediment above the stable residuum-dominated preglacial landscape.

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

Abstract. Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineralization processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeochemical cycles of both Ca and C.

Interaction of chemical and structural components providing defences to sea pansies Renilla reniformis and Renilla muelleri

Chemical and structural defence mechanisms are reported to co-occur in both terrestrial and marine systems. Among benthic marine organisms, the common co-occurrence of secondary metabolites and calcium carbonate (CaCO3) in soft corals provides an opportunity for testing synergistic interactions between these traits. Defensive properties of crude extracts, chemical fractions and CaCO3 sclerites from two sympatric species of soft corals, Renilla reniformis and R. muelleri, from Guanabara Bay, southeastern Brazil, were examined against fishes. To evaluate a potential interaction (secondary metabolites versus sclerites), both crude extracts and sclerites were evaluated as isolated defences and in combination in field assays against generalist fishes during the austral summer of 2007. While neither sclerites nor crude extracts from R. reniformis deterred feeding when offered individually in artificial food, both traits from R. muelleri offered individually provided effective defence. For both species, however, the combination of secondary metabolites and sclerites significantly deterred feeding, indicating that these traits are more effective in combination than in isolation.

An Ultrastructural Approach to Analogies between Fungal Structures and Needle Fiber Calcite

Needle fiber calcite (NFC) is an ubiquitous terrestrial secondary calcium carbonate mineral often associated with calcitic nanofibers. NFC's origin has been debated for a long time and a fungal origin is often proposed. Fungi are known to be involved in mineral weathering and production of metal oxalate, but little information exists regarding the genesis of other minerals, such as calcite. In this study, a comparison of similar ultrastructural characteristics of fungal hyphae and NFC has been performed to highlight analogies between both features. These analogies clearly demonstrate the probable close relationship between fungal filaments (hyphae and rhizomorphs) and NFC and its associated nanofibers.

A natural analogue study of CO2 -cement interaction: Carbonation of calcium silicate hydrate-bearing rocks from Northern Ireland

Natural analogues of Portland cement can provide insights into carbonation processes operating over timescales of interest to performance assessments of CO2 storage. Two such sites in Northern Ireland (Scawt Hill and Carneal Plug) have been investigated, where carbonation reactions of naturally-occurring cement minerals can be observed. Here, partially hydrated larnite-rich nodules have been reacting with atmospheric CO2 or dissolved bicarbonate ions at low temperatures over the last 10–20 thousand years. This has produced rims of carbonate minerals around hydrated low-temperature calcium silicate (CSH) minerals enclosing residual cores of primary high-temperature metamorphic calcium silicates and calcium aluminates (dominated by larnite, and often accompanied by wollastonite, spurrite, paraspurrite, brownmillerite, bredigite, andradite-grossular) with carbonation proceeding progressively from the outer margins of the nodules. Calcite and scawtite are the dominant secondary calcium carbonate minerals, but vaterite and aragonite have also formed. The carbonation produces dense, low-porosity carbonate rims. This is associated with a reduction in volume, accompanied by shrinkage and microfracturing of the underlying residual poorly crystalline CSH gel and its silica-rich alteration product, which has created significant secondary porosity in the altered material. Although some secondary calcium carbonate reaction products may partially mineralise the fractures, they do not seal the fractures completely, allowing further ingress of CO2/bicarbonate. That said, the ingress rate has not been sufficient to completely carbonate the nodules, even after several thousand years. Uncertainties remain in terms of quantifying carbonation reaction rates and the CO2/ HCO3-flux, and further work is needed to understand these potentially very useful analogues.

Surface geochemical expression of bedrock beneath thick sediment cover, Curnamona Province, South Australia

ABSTRACT An increasing requirement for the discovery of new mineral deposits is the ability to detect mineralization through thick cover. Large areas of the southern Australian Curnamona Province are prospective for Pb–Zn and Cu–Au mineralization; however, much of the prospective basement is covered by 10–150 m of Cenozoic fluvial, alluvial and lacustrine sediments. Soil surveys were conducted at the Kalkaroo Cu–Au–Mo deposit and Polygonum multi-element prospect. The major challenge to exploration at both sites is the 40–150 m thickness of transported cover. The objective was to determine whether any surface geochemical method could be used to detect mineralization under such conditions. The range of methods examined included those where some success was indicated in previous surveys in the region. Soil samples were collected from 10–25 cm depth and from the zone of high soil moisture loss as indicated by the presence of secondary calcium carbonate and sulphate (60–300 cm). Samples were treated using aqua regia and the partial extractants weak cyanide, sodium hydroxide, magnesium chloride and the proprietary method MMI-M. Conductivity and pH measurements were made on all samples. A Chinese variant of the electrochemical CHIM technique was also tested over the Kalkaroo deposit. A consistent response to the mineralized zone at the Kalkaroo deposit is double-peak anomalies for Mo. Less regular double-peak anomalies are also present for U and Au, and for soil conductivity. The two survey lines with electrochemical CHIM results show mainly high-contrast, one-point anomalies over mineralization. The significance of these is still to be established. Soils collected over the Kalkaroo and Polygonum prospects contain Ag concentrations that vary coincidently with changes in underlying basement lithology. Relatively high Ag concentrations in soils over the Polygonum prospect show a spatial relationship to underlying mineralized zones. Although no single technique used in this study was identified as a reliable exploration tool, survey results add support to the contention that partial extraction geochemistry of soils in the region may reflect mineralization and/or underlying bedrock trace metal content through as much as 150 m of transported cover.

Microstructural, geochemical and geomechanical properties of caliche deposits from the Adana Basin, Turkey

The 1998 Ceyhan (Adana, Turkey) earthquake caused major damage to construction on caliche formations. Caliche (a heterogenous secondary calcium carbonate deposit formed in arid and semi-arid regions) is widespread in the Adana area. The paper distinguishes three types of caliche: massive, containing vegetation remains and containing gravel. The porosity, water absorption and unconfined compressive strength of these three groups of caliche were determined. The compressive strengths are low compared to caliches in other areas—an important consideration as Adana is the fourth largest city in Turkey.

Bryophytes and lichens of a calcium-rich spring seep isolated on the granitic terrain of Mt. Katahdin, Maine, U.S.A.

Abstract An unexpected concentration of calcicole mosses and lichens has been discovered at and near a small spring seep on the granite headwall of the North Basin of Mt. Katahdin, Piscataquis County, Maine. Water samples from the spring were circumneutral and high in calcium ion content, whereas other springs, ponds, and streams on the mountain tested acidic and low in calcium. Because the Katahdin granite contains no primary carbonate minerals, it is suggested that the source of calcium enrichment in the North Basin spring water is secondary calcium carbonate (calcite) precipitated in cavities and fractures near the base of the upper Katahdin granite and its subsequent dissolution and mobilization by percolating groundwater. Plagioclase, epidote, and other calcic minerals in the granite supply the primary calcium ions. The moss calcicoles grew in small discontinuous patches on wet humified peaty soil over alpine bedrock ledges in communities having floristics and water chemistry similar to lowland rich ...

AMS dating on glacial tills at the source area of the Urumqi River in the Tianshan Mountains and its implications

Using accelerating mass spectrometry (AMS) dating method, a dating has been made on the primary calcium carbonate in tills and secondary calcium carbonate coating on till gravel and the roche moutonnee formed since the Last Glaciation at the source area of the Urumqi River valley in the Tianshan Mountains, northwestern China. The results reveal that the carbonate content in the tills in this noncarbonate area is high enough to date by AMS, that the carbon in the coatings on the newly exposed roche moutons and in the modern till is modern carbon and so the14C dating results in the ancient till can represent the actual ages of the till formation, and that the warm period during the Holocene began as early as 6 500 a B. P. and lasted to 1 800 a B. P.

Results of Significance Testing at 41DW269 Dewitt County, Texas

Site 41DW269 was tested by Texas Department of Transportation (TxDOT) archeologists in July of 1997. The investigations were conducted in the right-of-way of a proposed bridge replacement project on DeWitt County Road 122 at its crossing of Clear Creek. The investigations at Site 41DW269 consisted of mechanical trenching for archeological prospection and stratigraphic evaluation of the site, and the manual excavation of two 1 x 1 m test units and two shovel tests. Site 41DW269 is a multi-component terrace site with cultural deposits ranging in age from the Early Archaic through the Late Archaic. Two discrete alluvial fills, both containing cultural material, underlie the terrace. Unit 1 forms the core of the terrace and consists of a dark brown, sandy to silty loam to clay loam containing abundant secondary calcium carbonate. Unit 2 consists of a very dark grayish brown to black loam that represents a veneer of more recent overbank deposits that is approximately 1.0 to 1.2 m thick. In addition, two younger alluvial fills (Units 3 and 4) are present across the stream and at the base of the cutbank forming the northern site boundary. Testing of the site revealed two clearly distinct prehistoric cultural strata within deep alluvial deposits, and a single pit-like feature. The first cultural deposit is associated with Unit 1, and consists of a sparse assemblage of mineralized bone and lithic material extending from approximately 120-180 cm below the present ground surface. On the basis of a single radiocarbon age and a diagnostic Guadalupe tool, this component is believed to date to the Early Archaic. The second cultural deposit is associated with the upper veneer, and extends from approximately 10 cm to 110 cm below the surface. Although this deposit could not be subdivided based on the limited excavation data, it contains a cultural debris associated with Late Archaic and possibly Middle Archaic occupations Due to the deep and stratified nature of the deposits and the diversity of artifactual assemblages at the site, 41DW269 is considered eligible for inclusion in the National Register of Historic Places and for designation as a State Historic Landmark.