Calcareous Crusts Research Articles

Chemical cleaning of soiled deposits and encrustations on archaeological glass: A diagnostic and practical study

Abstract The aim of this study is practically to establish a chemical strategy for cleaning soiled deposits and encrustations on archaeological glasses. Investigations were performed on a series of Roman glass samples (Fragments and complete objects) coming from different excavations in northern Jordan. The chemical composition of the glass samples was determined by X-ray fluorescence spectrometer (XRF) analysis technique, whereas X-ray powder diffractometer (XRD) and Energy dispersive X-ray (EDX) methods were used to determine the mineralogical and elemental composition of the soiled deposits and encrustations on the glass surfaces. Furthermore, Scanning Electron Microscopy (SEM) examination and optical assessment were performed before and after cleaning glass. The glass samples were subjected to different cleaning protocols such as Calgon (Sodium hexametaphosphate), ethylenediaminetetraacetic acid (EDTA) at different pH values, citric and tartaric acids and piranha solution (a solution of sulphuric acid and hydrogen peroxide). Sepiolite poultices soaked by chemical agents were the most suitable methods used for applying chemical solutions on the glass surface. It can be concluded that EDTA is generally accepted as the most effective chelating agents recommended for cleaning encrustations on durable glass. It was more effective and safe at neutral pH with low concentrations around 5 to 7%. The calcareous crusts can safely be removed by using a piranha solution. Citric and tartaric acids appeared a moderate efficiency on cleaning weathered and stable glass. Calgon has a tendency to damage corroded and iridescent surfaces, and should be avoided when cleaning weathered glass.

Secondary calcification of paddy soils in southern china: Morphological and substantive characteristics

Secondary calcification processes have been studied in three paddy soils (Anthrosols or Aquazems) of southern China. It is shown that the soils’ amendment with lime powder and the periodic ponding of rice paddies with carbonate-rich water lead to the considerable transformation of the initial soils. The general properties of these soils and their morphological, micromorphological, and mineralogical features have been analyzed, and isotopic studies of the carbonate concentrations have been performed. The studied soils differ in the degree of their secondary calcification. The presence of lithogenic and pedogenic carbonates in the soils has been proved. Among the pedogenic carbonates, younger and older concentrations can be distinguished. The major feature of the carbonate concentrations in the studied soils is the coprecipitation of calcium and iron in the clay soil matrix. In general, the studied soil profiles display the initial stages of calcification. At the same time, there are certain analogies between the process of calcification in the paddy soils and the formation of thick accumulative calcareous crusts in some soils of northeastern China.

The dynamics of the restoration of mechanical damage to colonies of the scleractinian coral Porites lutea under conditions of competition with algal settlers for substratum

Natural and anthropogenic catastrophes in the last decades of the 20th century and at the beginning of the new century have evoked significant changes in the biological diversity of coral reefs, viz., the mortality of hermatypic scleractinian corals that are replaced by communities of marine algae and seaweeds. In this connection, the study of the dynamics of algal colonization of a newly formed substratum and competition for the substratum between hermatypic corals and algae is of topical interest. This paper describes the results of investigations conducted in 2003 at the Sesoko Marine Biological Station of Ryukyu University (Okinawa, Japan). Colonies of the massive scleractinian coral Porites lutea were sampled from a fringing reef of Sesoko Island. Damages were inflicted on the upper portions of the colonies, the damaged coral fragments were placed in aquaria and maintained for six months under different light intensities in the absence of herbivorous and corallivorous animals. The experiments showed that under bright (70–90% of incident photosynthetically active radiation, PAR0) and under moderate light (20–30% of PAR0), the damaged parts of colonies of about 25 cm2 were overgrown by newly formed polyps within six months. Under dim light (2–5% of PAR0), this period was not sufficient for recovery from lesions. During the first month, the recovery rate of colonies was the highest and depended on the physiological state of the corals and light intensity: in bright and moderate light it was two times and more higher than under low light. During the subsequent months, the recovery rate was significantly lower and depended mainly on the degree of overgrowth of dead portions with algae and on their species composition. Under bright and moderate light, algal colonization of damaged colonies started with the settling of colonial and filamentous diatoms, cyanobacteria and green algae, followed by the formation of the algal turf community. Communities of red calcareous crusts and fleshy algae were mainly formed on damaged corals under low light. A comparison of experimental results showed that damaged colonies maintained in aquaria in the absence of herbivorous and corallivorous animals recovered 1.5 times faster than in the sea. We hypothesize that herbivorous fish have a negative rather than positive influence on the recovery of damaged colonies.

DISTRIBUITION OF CRUSTOSE CORALLINE ALGAE (CORALLINALES, RHODOPHYTA) IN THE ABROLHOS REEFS, BAHIA, BRAZIL

ABSTRACT The crustose coralline algae have an important structural role in coral reef crests, as observed for some Atlantic reefs. In this work the distribution and abundance of crustose coralline algae and their relation to other benthic reef organisms were described for the Abrolhos Archipelago. The quantification of sessile organisms was made by SCUBA diving along replicated transect lines in different habitats and sites. Anovas were performed to test differences on algae abundance among sites and habitats. Coralline crusts did not show significant differences on abundance among sites (Anova, p>0,05), neither other benthic organisms (Anovas, p=0,634 invertebrates, p=0,767 filamentous algae, p=0,581 foliose algae, p=0,070 leathery algae and p=0,616 non calcareous crusts). Invertebrates and filamentous algae were the most abundant organisms on all sites and most habitats, contrasting with the low cover of coralline algae. In sheltered sites and on reef base it was observed a trend for an increase of fleshy foliose algae and leathery algae, contrasting with wave exposed sites. The distribution of coralline growth forms was characterized by a higher abundance of flat in relation to branched thalli. Branched coralline crusts are apparently more abundant within cryptic reef areas, not necessarily because of light limitation, but probably due to less herbivore pressure.

LANDFORM DEVELOPMENT ALONG THE MIDDLE COURSE OF THE KUISEB RIVER IN THE NAMIB DESERT, NAMIBIA

The hyperarid to arid Namib Desert extends along the west coast of southern Africa. The Kuiseb River is one of the major ephemeral rivers originating in the interior highland, and crosses the Namib Desert. Fluvial terraces are well developed along the middle reaches of the Kuiseb River near Gobabeb, and are classifi ed into four surfaces: upper (H), middle 1 (M1), middle 2 (M2), and lower (L). Layers of calcrete are founded on the M1 and M2 surfaces, and gypcrete layers are founded on the H surface. Dead tree matter, buried by dune sand on the L surface, dates to 300±60 years BP and 550±50 years BP. The calcareous crusts on the M1 surface date to 5,300±60 years BP and 6,450±50 years BP, and those of the M2 surface date to 22,070±260 years BP. The presence of calcrete suggests that the ground water level was higher when the M1 and M2 surfaces were formed than it is at the present time. Tree size distribution on the L surface demonstrates that the L surface was also formed during a relatively wet period. It may be concluded, therefore, that these fluvial terraces record the humid periods of ca 22 ka, 5-6.5 ka, and 300-600 years BP in the catchment area of the Kuiseb River. The presence of a water-soluble gypsum crust on the H surface suggests that the paleohydrologic environment of these terrace-forming periods probably involved increased rainfall in the interior highland east of the desert.

The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)

AbstractThe island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd.

Calcium Carbonate Precipitation by Bacterial Strains Isolated from a Limestone Cave and from a Loamy Soil

To study the role of calcifying bacteria in monument protection, 31 calcifying bacterial strains were isolated from natural habitats: 64% were of the genus Bacillus , 16% of the genus Arthrobacter , and 2 of the remaining isolates were identified as Kingella and Xanthomonas . The ability to form CaCO 3 crystals, the extent of the precipitation, and the type of crystals formed were determined at incubation temperatures of 4, 22, and 32°C. The highest of these temperatures favored CaCO 3 formation. Most of the bacteria precipitated CaCO 3 in the form of calcite. This activity was strictly controlled by the growth of microbial colonies on a solid substrate. The role of the calcifying bacteria in natural precipitation of carbonates is discussed. Further experiments are in progress in order to select the most suitable bacterial strains for a controlled production of calcareous crusts.

Construction and destruction of carbonates by marine and freshwater cyanobacteria

The global carbonate cycle has been controlled and maintained by life processes for at least 3.5 billion years. Within the exogenic carbonate cycle and in very different environments cyanobacteria appear in ‘key positions’ in that they actively and passively influence carbonate cycling. In the carbonate cycle, cyanobacteria play an important and sometimes decisive role. Cycling of carbon and carbonate is linked to biological processes. Some build up specific carbonate structures, some destroy carbonate substrates and others do both simultaneously. All these processes take place from the high mountains down to the sea in various terrestrial and freshwater as well as marine environments. The photosynthetic activity of cyanobacteria, their extracellular polymeric substances and possibly also their adherent heterotrophic bacteria are responsible for the construction of various carbonate structures and the ability to penetrate carbonate material. Boring activity of euendoliths results in biological corrosion and disintegration of carbonate surfaces. Grazing organisms on carbonate surfaces colonized by epi- and endolithic cyanobacteria produce specific biokarst forms and specific grains which can contribute to nearshore sedimentation. Biological corrosion and abrasion together constitute bioerosion. The results of all these processes are calcareous crusts, typical traces and biokarst forms which in many cases have a high fossilization potential, and therefore can be powerful ecological, palaeoecological and facies indicators in recent as well as in fossil environments.

Construction and destruction of carbonates by marine and freshwater cyanobacteria

The global carbonate cycle has been controlled and maintained by life processes for at least 3.5 billion years. Within the exogenic carbonate cycle and in very different environments cyanobacteria appear in ‘key positions’ in that they actively and passively influence carbonate cycling. In the carbonate cycle, cyanobacteria play an important and sometimes decisive role. Cycling of carbon and carbonate is linked to biological processes. Some build up specific carbonate structures, some destroy carbonate substrates and others do both simultaneously. All these processes take place from the high mountains down to the sea in various terrestrial and freshwater as well as marine environments. The photosynthetic activity of cyanobacteria, their extracellular polymeric substances and possibly also their adherent heterotrophic bacteria are responsible for the construction of various carbonate structures and the ability to penetrate carbonate material. Boring activity of euendoliths results in biological corrosion and disintegration of carbonate surfaces. Grazing organisms on carbonate surfaces colonized by epi- and endolithic cyanobacteria produce specific biokarst forms and specific grains which can contribute to nearshore sedimentation. Biological corrosion and abrasion together constitute bioerosion. The results of all these processes are calcareous crusts, typical traces and biokarst forms which in many cases have a high fossilization potential, and therefore can be powerful ecological, palaeoecological and facies indicators in recent as well as in fossil environments.

A study on micro-fungi in arid areas. Notes on stress-tolerant fungi

ABSTRACT Severe selectivity by extreme environments was investigated in mitosporic fungi with regard to their adaptive responses to high temperature, and to high levels of sunlight and evapo-transpiration. A homogeneous group of graminicolous dematiaceous hyphomycetes was removed from sand dunes in the torrid climate of the Namib Naukluft Park, from arid, clayey soil at Etosha pan and from calcareous crusts in the Namib Desert Park: all of them produce darkening conidiophores and deeply pigmented spores. The size and colour of reproductive structures were recorded and compared with bibliographic data. Results are consistent with a uniform morpho-functional response by these fungi to stress conditions.

Facies Variation, Diagenesis, and Exploration Potential of the Cretaceous Rudist-Bearing Carbonates of the Arabian Gulf

The Cretaceous rudist-bearing carbonates of the Arabian Gulf region are proven exploration targets for hydrocarbons and form the reservoirs of a number of giant fields, including Bu Hasa, Fateh, Fahud, Idd El Shargi, Rumaila, Shaybah, and Shah. Rudist buildups occur in three principal formations: (1) Aptian Shuaiba, (2) Cenomanian Mishrif, and (3) Maastrichtian Simsima. A regional subaerial unconformity marks the upper boundary of each of these formations. Associated with the rudists that dominate the Shuaiba Formation are calcareous algal crusts, foraminifera, and echinoid plates, which accumulated in mudstone, packstone, and carbonate sands. These rudists are mainly caprinids, with a lesser number of caprotinids, monopleurids, and requienids, deposited in a normal-marine shallow-shelf setting. The Mishrif Formation contains mollusk fragments, bioclastic packstones to grainstones, miliolid and nonrudist bivalves in muddy limestones, and rudist (mainly radiolitids and caprinids) conglomeratic floatstones, with fragmented rudists mixed with wackestone lithoclasts. The Mishrif sediments accumulated as a progradational, low-energy leeward margin formed in marginal slope, shoal-backshoal, and lagoonal settings. The Simsima Formation consists of bioclastic grainstone to packstone, and dolomitic lime mudstones to wackestone. These are rich in bioclastic grains (Loftusia, rudist and rudist debris, coral, and foraminifera) deposited on a restricted to semirestricted shallow-marine shelf that was exposed to moderate energy conditions. The excellent reservoir porosity and permeability of the rudist deposits and their associated sediments are the products of primary and secondary diagenesis. Freshwater leaching during post-Aptian, post-Cenomanian, and post-Maastrichtian erosion enhanced the secondary moldic porosity. Fracturing locally improved porosity and permeability. Other porosity types that occur include interparticle, intraparticle, vuggy, growth framework, shelter, intercrystalline, and karstic. Because of their favorable depositional and postdepositional conditions, the Cretaceous succession of rudists in this region contains many giant oil fields.

Separating the grazing effects of periwinkles and amphipods on a seaweed community dominated byFucus Distichus

Abstract In situ caging experiments showed that both littorinid snails and gammarid amphipods exerted minimal effects on the suite of algae comprising the canopy of littoral fringe tide pools dominated by Fucus distichus. In the absence of grazers, the Fucus canopy was dramatically reduced by fatal endophyte infections. Among the 10dependent variables making up the algal species and forms at the substratum level below the canopy, 3 were highly affected by grazing. The germlings of F. distiehus were greatly reduced by littorinids. Gamrnarids also reduced germling cover, but were less effective. In addition, the two grazer guilds interactively reduced the cover of algae belonging to the Uniseriate functional form at the substratum level. Sheet/Tube form algae were reduced in cover only by littorinids. Other forms, including calcareous crusts, thalli of Chondrus crispus and 3 Cladophora species were unaffected by grazing. There was no indication of food resource partitioning between littorinids and gammarids.

Quaternary deposits on the South Barbados accretionary prism

A study of recent Quaternary deposits of the South Barbados prism has been carried out over a limited area close to the Venezuela margin. 3.5 kHz lines, submarine photographs and many piston and gravity cores have been collected throughout this area during the cruise of the Caracolante II. The detailed morphology of this area comprises a jumble of microbasins and mud diapiric highs: In the basins, the predominant deposits are sandy and muddy turbidites. On the tops of the highs, the diapiric mud is a mixture of Late Miocene, Pliocene and Quaternary sediments. These muds are clearly identified by their high content of smectite and sometimes by the presence of muddy gravels with a diagenetic calcareous cement. On the seafloor, the muds are often covered by an indurated crust on which deep-sea communities are frequently observed. The three major factors controlling sedimentation on the prism are tectonics, sea-level variations and sediment sources. Tectonics play the major role, being responsible for the mud diapiric processes, the fluid circulation throughout the deposits and the triggering of gravity flows on the steep slopes of the diapiric highs. As a consequence, significant inputs of diapir mud supply the deposits of the adjacent basins, and local calcareous crusts, linked to the upward fluid migration, occur on the seafloor at the tops of the diapirs. Sea-level variations and continental sediment sources partly control the character of the deposits in the ponded basins. During the Holocene, the sediment flux was low (1.7–3.7 g cm −2 ∗ 10 −3 yrs) and the deposits were composed of fine-grained particles comprising equally biogenic calcareous and continental material. The continental material is provided by the Orinoco and the Amazon rivers. During the last glacial period, the flux was much higher (8.5–19 g cm −2 ∗ 10 −3 yrs) as a consequence of a huge increase in coarse-grained terrigenous material introduced by the Orinoco river.

Patterns of organizations of intertidal and shallow subtidal vegetation in wave exposed habitats of central Chile

Wave-exposed rocky intertidal habitats of central Chile exhibit zonation of algal morphologies rather than strict patterns of species zonation. In low shore areas, there is a vertical sequence of perennial belts of calcareous crusts, kelp-like forms and expanded cushions or non-calcareous crusts. The calcareous crusts are represented by species of Mesophyllum, the kelp-like forms include Lessonia nigrescens and Durvillaea antarctica, while the cushions are represented by Gelidium chilense and G. lingulatum and the noncalcareous, expanded crusts by Codium dimorphum. Thin and thick blades, represented by Iridaea laminarioides, Ulva rigida and Porphyra columbia and filamentous forms including Ceramium rubrum, Centroceras clavulatum and Polysiphonia spp. are more patchy than the lower, perennial belts. They may, however, form distinct temporal monocultures at upper intertidal levels. Upper and lower limits of the various zones are set by interactions of several factors, the relative importance of which can change seasonally. When some of the factors restricting species distribution are experimentally removed, other interactions among factors become limiting. Within each zone, species are morphologically similar, with the abundance of species being regulated by symmetric competitive interactions. Competition is often asymmetric at the boundaries of zones except when adults of small-sized forms interact with morphologically similar juveniles of larger forms. Irrespective of their extremely different morphologies, the permanent, zone-forming algal species generally combine escape from grazers or defensive adaptations with clear competitive abilities. Nevertheless, there is a clear competitive hierarchy which is expressed in vertical displacements and zonation. The lowershore habitats could potentially be occupied by any of the different types of algae. Fast growth and large size allow the kelps to occupy this zone pushing the calcareous crust dominated-zone down into shallow subtidal areas and displacing the cushions and fleshy crusts into the low and middle intertidal regions. In turn, these last forms can displace thick and thin foliose forms and filaments to upper levels on the shore. Displaced forms may exist as patches at various levels of the shore.

ZONATION OF DEEP WATER BENTHIC ALGAE IN THE GULF OF MAINE1

ABSTRACT Algal community structure is described for a deep‐water rock pinnacle in the Gulf of Maine. Three depth zones of algal dominance were apparent consisting of 1) leathery macrophytes (to 40 m), 2) foliose red algae (to 50 m) and 3) crustose algae (fleshy crusts to 55 m and coralline crusts to 63 m). Microscopic filamentous and erect calcareous algae were also present but inconspicuous. Upright macroscopic filamentous and thin sheet‐like forms were not observed on the pinnacle. Sea anemones (Metridium senile) dominated some vertical faces and abrupt prominences in the shallowest regions of the pinnacle (to 24 m) and locally appeared to set the upper vertical limits of kelp and possibly foliose reds. Laminaria sp. formed an open park‐like canopy from 24 to 30 m whereas Agarum cribrosum, the deepest kelp, grew as isolated individuals to 40 m. Peyssonnelia sp. and Leptophytum laeve were the deepest occurring fleshy (to 55 m) and calcareous crusts (to 63 m), respectively. The occurrence of these algae at record depths for the Gulf of Maine and for cold water marine environments may be the result of an absence of large herbivores and the high productivity potential of the benthos in these relatively clear waters. By compiling data on depth distribution patterns world‐wide, it is evident that the three zone structure of algal morphologies observed in the Gulf of Maine is a global phenomenon.

Upper Pleistocene and Holocene lakes in the An Nafud, Saudi Arabia

Two major lake periods were discovered in the sand sea of An Nafud and the surrounding areas. In Upper Pleistocene large lakes occurred around the dune area and in the interior of the sand sea. Their deposits were formed between 34 000 and 24 000 BP. The lakes were not conformous to the present dune relief. They had an extension of several km2 and a depth of ca. 10 m. Holocene lakes (8 400–5 400 BP) were of minor extension and restricted to the interdune depressions. Lake sediments consist of cemented sand, calcareous crusts and diatomites. Upper Pleistocene lakes were fresh water lakes, the Halocene lakes were mostly swamps depending on rising and falling aquifers in the dunes. Plant remains as pollen and macro rests show that the environmental changes didn't exceed the system of semidesert comparable to the modern plant cover. However, the Upper Pleistocene lake deposits contain some more soudanian elements as the Holocene sediments in the pollen spectra. Climatically the lake formations are interpreted as depending on a stronger influence of the mediterranean cyclones or an interaction of them with monsoonal air masses.

The application of cathodoluminescence to interpreting the diagenesis of an ancient calcrete profile

ABSTRACTA laterally extensive calcrete profile has been identified in the Late Asbian (Lower Carboniferous) shallow marine shelf limestones of the Llangollen area, North Wales. The upper surface of the profile is defined by a laterally discontinuous palaeokarstic surface and by laminated calcareous crusts which developed within the underlying limestone.The profile contains a unique series of early pore‐filling vadose cements which only occur down to 1 m below the palaeokarstic surface. Cathodoluminescence reveals that these cements pre‐date the late pore‐filling meteoric phreatic cements which occur throughout local Asbian lithologies. A spar cement stratigraphy has been established for the calcrete profile. Subaerial vadose cements comprise two generations of non‐luminescent cement, followed by a brightly luminescent generation which occasionally shows an acicular habit. This needle‐fibre calcite represents the final stage of vadose cementation. Precipitation of vadose cements was contemporary with subaerial alteration and micritization of the limestone.Textures, visible only with cathodoluminescence, provide evidence of recurrent periods of fabric dissolution. The most extensive phase of dissolution occurred immediately after the precipitation of the non‐luminescent subaerial vadose cements. Several different textures have been recorded, each reflecting the morphology of a partially dissolved substrate. Dissolution textures are generally confined to the walls of the larger pores and to early brecciation fractures. These probably acted as fluid pathways in the calcrete during early subaerial diagenesis.Much of the non‐marine micrite in the calcrete profile appears as needle‐fibre calcite under cathodoluminescence. This acicular calcite was probably formed in response to localized supersaturation of meteoric pore fluids caused by periods of near‐surface evaporation. Since needle‐fibre luminescence is strongly variable, these ambient conditions are not believed to have directly controlled the activator ion concentrations of cementing pore waters. Needle‐fibre calcite is considered to be a cement precipitate which has almost completely recrystallized to micrite, probably during the late stages of subaerial diagenesis. Two generations of subaerial micrite which define a ‘micrite stratigraphy’, have been distinguished under cathodoluminescence.Reconstructing the diagenetic history of this ancient calcrete profile has revealed that subaerial alteration was multistaged, with many diagenetic processes acting simultaneously during a single phase of emergence.

Manganese‐Rich layers in calcareous deposits along the Western shore of the Dead Sea May have a bacterial origin

Abstract Spore formers were detected in samples of calcareous crust with manganiferous laminations and in water from the Dead Sea in Israel. They were able to grow in media made with fresh water but not with synthetic Dead Sea water. Some of these spore formers were also able to oxidize Mn (II) in fresh water. No other bacteria capable of both growth and Mn(II) oxidation in hypersaline media prepared with synthetic Dead Sea water were found in the samples. However, bacteria capable of growth and Mn(II) oxidation in fresh water media were detected in water and sediment from fresh water springs at Ein Feshkha and in lake water and sediment from the beach near Wadi Kidron. Both sites are located on the western shore of the lake. These findings suggest that the manganiferous laminations in calcareous crusts and concretions in the Dead Sea along its western shore may have originated, at least in part, from manganese oxide formed by bacteria in fresh water environments on shore and washed into the lake in runof...

Calcareous duricrusts in north-western Libya

This paper describes the physiographic and chemical characteristics of calcareous crusts (calcrete) in north-western Libya. The crust in north-western Libya may be formed in two ways. The first type forms at the soil surface as a result of evaporation of shallow ephemeral lakes: the second forms within the soil profile as a result of leaching by percolating surface water saturated with CaCO 3 . The formation of the crust is a function of geological setting, climate, morphology and time.

Micromorphology of calcareous crusts from the Canadian High Arctic

Abstract The study of calcareous crusts, under the scanning electron microscope (SEM), as features of pedological development on both wet and dry Arctic sites shows that these crusts have a sequence of forms, with varied and complex grain microforms and layered internal structure. The presence of Mg is very variable and is not significantly related to the assumed development sequence. The various carbonate crusts bear witness to the development of pedological features and processes related to the intensive dissolution of carbonates by melt-water, melting ground-ice and summer rainfall, all acidulated by contact with organic matter in the soil. The reprecipitation on the undersides of stones is achieved by intense evaporation of this soil solution and a sequence of precipitated forms is described which is independent of the presence of algae, permafrost-table depth and geomorphic site or age. Grain-size and calcitan thickness are variable at all stages of development.