Secondary Calcite Research Articles

Precipitation of secondary calcite in glacier areas; Carbon and oxygen isotopic composition of calcites from Mt. Hermon, Israel, and the European Alps

Secondary calcites from Mount Hermon, Israel can be separated into two based on their carbon and oxygen composition. The first group has the usual isotopic composition of secondary calcites which are precipitated from waters having the isotopic composition of recent groundwaters in the region. The second group is characterized by high 13 C and low 18 O values, compared with the first group. Secondary calcites from the European Alps show isotopic compositions which are similar to this second group. A model of the formation of these calcites by precipitation from snowmelt waters is presented, which explains the anomalous isotopic composition of the calcite.

Ekofisk Field, Its Geology and Petrography: ABSTRACT

The Ekofisk field is a landmark in the history of petroleum exploration. With recoverable reserves estimated at 1 billion bbl, it is the first major oil discovery in the now-burgeoning North Sea oil patch. Ekofisk is on a salt structure, and produces from approximately 700 ft of highly porous Danian limestone. Scanning electron micrographs show that this limestone is a typical chalk, formed almost entirely of coccoliths and planktonic foraminifers. Extensive fracture systems have been noted in cores. The original intergranular porosity of the rock is reduced in places by the precipitation of secondary calcite cement, possibly associated with stylolite formation. End_of_Article - Last_Page 420------------

Paläotemperaturbestimmungen an aragonitschaligen mollusken aus dem alpinen mesozoikum

16O/ 18O-determinations were applied to aragonitic mollusks from the Alpine Mesozoic. Quantitative determinations of secondary reactions are only possible for animals with aragonitic shells. The secondary calcite content was determined by means of X-rays. The samples were prepared according to the method of McCrea (1950) and their 16O/ 18O ratios were measured by means of a double-focussing mass spectrometer with a double ion collector. Only a small number of these samples were suitable for temperature determinations. The determined values were graphically extrapolated to 0% calcite. Triassic (Ladinian and Karnian) samples indicated water temperatures of 17.0°–17.9°C for benthonic organisms. Nectonic forms from the Rhaetian showed temperatures of 21.0–30.2°C. It became evident that the temperature values are dependent on the water depth at which the animals were living. ( Austroteuthis kuehni Jel. and Zapfe: juvenile 30.2°C, adult 23.7°C). The deviation of the temperature determinations is about ±1.0°C. The palaeotemperature values are referred to a salinity of 34.7‰

Magnesites and surrounding rocks in the new deposits of the Satkinsk group

The main mineral impurities of Satkinsk magnesites at the Karagaisk and Gologorsk deposits are chlorite, graphitite, secondary dolomite, talc, quartz, and pyrites. The Volch'egorsk magnesites contain appreciable quantities of secondary dolomite, calcite, chlorite, and quartz.

Flysch facies and turbidite sedimentology

The main facies of flysch in the Northern Apennines are listed, the importance of calcareous turbidites being noted. A summary is presented of Italian studies on selected sedimentologic features of the Apennines turbidites: 1. (1) Data on the occurrence of internal sedimentary structures in the turbidite rhythms, in function of thickness and grain size; the same in the flysch bands of thin or thick turbidites. 2. (2) Statistics on the occurrence and size of sole markings. 3. (3) Data on the relations between grain size and rhythm thickness. 4. (4) Types of graded bedding. 5. (5) Results of fabric studies. 6. (6) Data on the petrography of the turbidite sandstones. The sandstones are either feldspathic sandstones (up to arkoses and feldspathic litharenites) with a greywacke-like texture and secondary calcite, or very calcareous sandstones, either lithic or quartzose and fossiliferous. The micaceous matrix of the first group appears to be derived mainly from the diagenesis of clay and the fragmentation of metamorphic mica and micaceous rock fragments. The interstitial calcite of the second group is micrite and recrystallized sparry calcite; calcite as a primary cement is not common. Rock fragments are important in the classification of the sandstones. The main types are phyllite, quartzite, serpentinite, micritic limestones, dolostone and rhyolite to andesite lavas. The fact that various sandstones of the same age are different in composition and yet sandstones of different age can be grouped together, indicate the importance of separate sources repeatedly active through time. The Corsica-Sardinia Hercynian Massif was an important source, especially in the Upper Cretaceous, but in the Tertiary, internal sources in the Apennines-Western Alps geosynclinal belt became predominant. In general tectonics played an important role as a source factor in the genesis of the Apennines sandstones, but reworking appears to have been limited.

Anatomy of a Meteorite Impact Crater: West Hawk Lake, Manitoba, Canada

West Hawk Lake is a near-circular, 11,700-ft -wide, deep lake located 110 mi east of Winnipeg, Canada. The lake now completely submerges an ancient meteorite impact crater. A central drillhole passes through nearly 1080ft of slump and fallback breccia into 655 ft of rupture zone bedrock below a well-defined crater base. Petrographic analysis of core from this hole, a hole near the original crater rim, and an off-center hole reveals numerous shock features which, supplementing earlier geophysical studies, demonstrate an impact origin for this structure. These results are significant: (1) The original crater was approximately 8000 ft wide; the rim has recessed by erosion; the target rock consists of steeply dipping units of metasediments and metavolcanics. (2) Microscope criteria for shock include: abundant planar features in quartz; diagnostic parallel extension fractures; extensive isotropization of tectosilicates in quartz-mica schists (analcite is a common product of recrystallization of the isotropized phases); variable decomposition of biotite and actinolite; abundant glassy fragments and matrix-binding “melt,” now generally devitrified; shock-induced twinning and granulation in pre-impact carbonates. (3) Distribution of shock features is strongly dependent on mineral composition and particle size. Unless intensely shocked, amphibole-rich rocks are usually devoid of shock evidence, even where fragments are intermixed with shocked schistose metasediments. (4) The vertical distribution within the central hole core of intensity of shock in the breccias, as plotted on a shock log, is notably erratic. (5) Autobrecciation, cataclastic fragmentation, and injection of shocked breccia into open fractures account for observed effects in the rupture zone. (6) Zoisite and secondary calcite develop extensively within the breccia lens by solution and neo-mineralization; serpentine var. antigorite forms with the breccia matrix, and in a network of veinlets in fragments and in the rupture zone; sodium-calcium zeolites form in possibly replaced melt material at the crater base. (7) Analysis of strongly shocked rock fragments from the breccias by infrared absorption, X-ray fluorescence, electron microprobe, and argon loss methods demonstrates significant changes in the crystal structure and chemistry of constituent minerals in these materials as compared with unshocked equivalents collected off-structure. West Hawk Lake is compared with the Brent structure, the best-studied model of a simple impact crater in crystalline rocks.

Peculiar features of soil development in parna deposits in the Eastern Riverina, N.S.W

Attention is drawn to unusual features of red earth and red-brown earth soils associated with layered parna deposits in the Eastern Riverina, N.S.W., which facilitate identification and tracing of individual layers, modern soils, and paleosols in different landscapes, and subsequent elucidation of distribution, stratigraphic relations, and relative age of these and associated deposits and soils. These features include mechanical composition, subplasticity, and the occurrence of secondary calcite, magnesian calcite, barytes, dolomite, and palygorskite.

Blackening of Eolianite and Caliche Adjacent to Saline Lakes, Isla Mujeres, Quintana Roo, Mexico

ABSTRACT A partly blackened limestone and caliche rubble has been produced in situ at the edge of hypersaline lakes on the island of Mujeres off the northeast coast of the Yucatan peninsula. The angular gravel along the quiet lake shores is formed by dissolution and desiccation-fracturing of dark and lighter-colored country rock and caliche crusts. Dark-colored constituents of this rubble gravel are of two types: 1) blackened Pleistocene (?) eolianite country rock and 2) black porous laminated caliche-algal micrite crusts. Pale to dark yellowbrown constituents, which make up 50 to 75% of the rubble, are fragments of caliche and eolianite. Chemical analyses of the dark and light-colored fragments of this deposit indicate that concentrations of Fe, Mn, and S in the black rocks are equal to or less than that in the brown rocks. HCl-insoluble organic C, however, is slightly higher in the darker rocks. The blackened calcarenite is infiltrated with finely-disseminated organic matter of algal origin. The black color is attributed to preservation of the organic matter. A secondary source of the dark color may be minor amounts of iron sulfide, produced in the presence of H2S derived from bacterial reduction of sulfates within the reducing environment of an algal mat. Apparently dark-colored caliche-like crusts may be laid down in localities where caliche deposition is simultaneous with production of black algal matter. These conditions probably existed at several northeast Yucatan localities where black caliche-algal micrite fragments are found near hypersaline water. The environment necessary for the blackening of caliche or limestone is probably one in which the pH is high enough and the Eh low enough that the preservation of finely-disseminated organic material produced by algae can be accompanied by deposition of secondary calcite which includes and preserves the organic matter. In such a reducing environment associated with sulfate deposition, bacterial action may produce H2S. The black rocks of the northeast Yucatan hypersaline reas contain H2S. Blackened limestone in ancient carbonate sections may call attention to stratigraphic breaks. A few workers have recognized an association between blackened limestones and unconformities in certain Mesozoic and Paleozoic sections. The presence of layers of fragmented, dark-colored limestone may indicate subaerial exposure adjacent to hypersaline water. Black fragments in limestone strata, then, may be an aid in locating coastal areas in ancient carbonate provinces and the landward edge of evaporite deposits.

General considerations on isotopic paleotemperature determinations and analyses on Jurassic ammonites

Paleotemperature analyses have been carried out on the aragonitic outer shells and septa of three Jurassic ammonites. Postmortal alterations can be recongnized easily by the degree of conversion of original aragonite to secondary calcite. The amount of secondary calcite is used as an indication of an isotopic exchange. It often proves difficult, however, to distinguish primary from secondary calcite in calcitic fossils. Therefore, calcitic fossils should only be used for paleotemperature determinations, if they are associated with aragonitic fossils, for instance ammonites, showing a good preservation of the more unstable aragonite.

Dating Tectonism in the Indosinian–Thai–Malayan Orogen by Thermoluminescence

The thermoluminescence “ages” of a large and representative selection of limestone specimens from the Thai-Malayan geosyncline, ranging in stratigraphic age from Ordovician to Triassic, are related, not to stratigraphic age, but to tectonic and magmatic events in the Mesozoic Indosinian-Thai-Malayan orogeny. It is deduced that the revolutionary phase of the orogeny extended from early Triassic to early Cretaceous; folding of the geosynclinal sediments and accompanying recrystallization of the limestones terminated in late Jurassic, but granitic activity extended to early Cretaceous. A post-orogenic phase of granitic intrusion, accompanied by secondary calcite veining of the limestones, occurred in early Tertiary and appears to be confined to a narrow zone along the western margins of the Main Range batholith. The thermoluminescence “ages” indicate that the revolutionary phase of the orogeny extended over a period of approximately 150 million years, which is in agreement with the radiometric ages of Malayan orogenic granites.

The Petrology of Middle Devonian Limestones in South Devon, England

ABSTRACT The petrographic examination of the diagenetic and metamorphic history of these Devonian limestones, in the light of work on Recent carbonates, shows them to be a predominantly bioclastic series, ranging in composition from calcilutites to coarse biomicrites and biosparites with variable allochems and pelsparites. Six main microfacies are recognized. Despite low grade metamorphism, recognizable diagenetic events include initial cementation, subsequent solution and the introduction of secondary calcite, and the formation of authigenic minerals, quartz and felspar. The rocks are locally dolomitized, and there is evidence of limited de-dolomitization. Metamorphism has resulted primarily in the production of new fabrics, the degree of recrystallization depending upon the stress environment of the rock. In extreme examples all previous textures are destroyed. Some quartz may have been introduced concurrently with the deformation but in general there is no development of metamorphic minerals. Lack of stratigraphic correlation prevents detailed environmental reconstruction, but present evidence suggests that current interpretations of these limestones as a reef formation are erroneous. The limestones are shown to be clastic accumulations of skeletal material, probably from and within areas of prolific growth of carbonate secreting organisms. These organisms at no time formed a growth lattice having topographic expression comparable to modern reefs. Separate ecological habitats are recognized, but little explanation can be offered of the limiting factors.

Variations in the O18/O16 and C13/C12 Ratios of Diagenetically Altered Limestones in the Bermuda Islands

Marine and eolian Pleistocene sediments in the Bermuda Islands are composed largely of fragments of mollusks, Foraminifera, lithothamnoid algae, and Halimeda. The Pleistocene sediments range from unconsolidated carbonate sands to well-consolidated limestones. Recent carbonate sediments and major sediment-contributing organisms (except Halimeda) have similar and ratios which are distinctly different from the and ratios observed in the stalactites, soil bases, and secondary calcites from the limestones. Precipitation of secondary calcite in the limestones and alteration of the constituent grains cause the and ratios of the limestones to approach the values observed in stalactites and soil bases. Secondary calcites, precipitated from fresh water on the Bermuda Islands, have ratios which are controlled primarily by the average ratio of the rain water on the island. The ratios of the secondary calcites are controlled by the amount of carbon dioxide derived from the soil zone which is mixed with carbon derived from solution of the limestones through which the water has passed. Some of the limestones from the intertidal or surf-spray zone have and ratios which are distinctly different from the majority of the well-consolidated limestones. These limestones may have been lithified by cement precipitated from sea water or from fresh water which had been subjected to evaporation and to exchange of carbon with atmospheric carbon dioxide.

Paleoenvironmental Significance of Carbon Isotopic Composition of Siderite Nodules in Some Shales of Pennsylvanian Age

ABSTRACT Analysis of C13/C12 ratios of penecontemporaneous siderite nodules from shales showed complete separation of the freshwater group from the two marine groups, and a partial separation of restricted marine and marine. Some of the anomalous results can be explained by contamination by secondary calcite and possible errors of environmental classification.

Petrography of Mississippian Limestones and Cherts from the Northwestern Highland Rim, Tennessee

ABSTRACT Rocks of Mississippian age cropping out in the northwestern Highland Rim include, in ascending order, the Maury Formation, New Providence Shale, Fort Payne Chert, Warsaw Limestone, St. Louis Limestone, and Ste. Genevieve Limestone. Field and microscopic examination of the post-New Providence formations shows that each contains characteristic and lithologically distinct units reflecting variations in depositional environment. The Fort Payne is characterized by an abundance of chert which occurs either as discrete beds separated by layers of highly siliceous limestone or as very rough, irregular plates intimately associated with limestone. In both types of chert the silica is largely cryptocrystalline and probably was syngenetically concentrated from silica-rich calcareous ooze. Coarse-grained fossil-fragmental calcarenite is the dominant lithology of the Warsaw. Subordinate lithologies include fine-grained siliceous calcarenite, coquinite, and fine-grained dolomitic limestone. Clear secondary calcite is generally lacking in the Warsaw and much of the matrix in the calcarenite and coquinite appears to have developed through recrystallization. Most of the chert in the Warsaw is clearly of secondary origin. Like the Warsaw, the St. Louis consists primarily of coarse-grained fossil-fragmental calcarenite, but it differs in that much of the matrix is clear secondary calcite. Other lithologies in the St. Louis are coquinite, foraminiferal limestone, and siliecous and dolomitic limestone. Beds of shaly limestone also are present locally. The Ste. Genevieve Limestone, which is of limited extent in the northwestern part of the Highland Rim, consists of poorly sorted ooliths developed around fossil fragments in a matrix of clear crystalline calcite.

Contribuiçõa à Geologia do Maciço Alcalino de Poços de Caldas

O presente trabalho apresenta um estudo da geologia do maciço alcalino de Poços de Caldas. Pela sua área, que é da ordem de 800 quilômetros quadrados, é considerado um dos maiores complexos formados exclusivamente por rochas nefelinicas. Possui forma elíptica, com 35 km no sentido NE-SW e 30 km no sentido NW-SE e ainda um stock de foiaíto, com cêrca de 10 quilômetros quadrados. A W limita-se com a bacia sedimentar do Paraná e a E com os contrafortes da serra da Mantiqueira. O maciço está encaixado entre granito e gnaisse, que nos quadrantes SE e em menor escala no quadrante NW- foi afetado metassomàticamente pelo processo de fenitização, principalmente ao longo da direção de xistosidade. No quadrante NW o fenito é de cor cinza esverdeada e no quadrante SE sua côr é verm elha. O maciço é constituído principalmente por rochas nefelínicas, tinguaítos e foiaítos, mas possui em seu interior rochas anteriores à intrusão alcalina. São sedimentos e rochas vulcâ¬nicas formadas por tufos, brechas, aglomerados e lavas ankaratríticas. Os sedimentos acompanham o contacto com o gnaisse e afloram em maior extensão nas áreas W e S do complexo. A base do pacote sedimentar consta de camadas argilo-arenosas, com estratificação horizontal e o topo é formado por arenitos com estratificação cruzada. Acham-se perturbados e mergulham, no geral, para o interior do maciço. Sobre os sedimentos foram depositados brechas, tufos e lavas, v _ que formam uma faixa contínua no bordo N-W Nas brechas predominam fragmentos de sedimentos, gnaisse, diabásio e lavas. O cimento é rico em quartzo detrítico arredondado. Na diagênese, a ação de soluções hidrotermais é evidenciada pelo aparecimento de biotita autígena e um feltro de microcristais de aegerina e apatita. No cimento, a calcita secundária é muito comum, chegando a substituir parcial ou totalmente o quartzo. As lavas ankaratríticas, quase sempre em espéssos derrames, formam freqüentemente aglomerados. Vestígios de rochas vulcânicas são encontrados em quase todo o bordo interno, indicando que a atividade vulcânica abrangeu grande área. Após essa atividade vulcânica formaram-se fonólitos, tinguaítos e foiaítos, com freqüentes passagens de um tipo de rocha a outro. Os tinguaítos constituem a maior área do complexo e apresentam grande uniformidade. Em algumas áreas principalmente nas proximidades de Cascata afloram variedades com pseudo-leucita e analcita. Os foiaítos são intrusivos no tinguaíto, mas a “mise-en-place” provavelmente deu-se contemporáneamente, sugerida pela passagem, não raro, gradual de uma rocha a outra. Além dos vários tipos de foiaítos, equigranulares e traquitóides, afloram em pequena extensão lujaurito e chibinito. Para o mecanismo da intrusão é admitido o levantamento de blocos do embasamento cristalino que precedeu a atividade vulcânica. Durante ou após a atividade vulcânica deu-se o abatimento da parte central com formação de fendas radiais e circulares, que permitiram a subida do magma. A existência, mesmo no atual estágio de erosão, de pequenas áreas de material vulcânico perturbado pela intrusão, indica que o abatimento não foi total, tendo parte do teto servido de encaixante para a formação dos tinguaítos e diferenciação de foiaítos. Na periferia formou-se o grande dique anelar de tinguaíto, com mergulhos verticais ou quase verticais, de espessura variável, formando um anel quase completo. A dedução da forma geométrica da intrusão de tinguaítos da parte central do maciço é dificultada pela grande homogeneidade mineral e textural das rochas. O abatimento iniciou-se no centro, onde a intensidade dêste fenômeno deu-se em maior escala, sendo anterior à formação do dique anelar Evidenciando este fato, observamos no interior do dique numerosos xenólitos de rochas do interior do maciço. Finalizando os eventos magmáticos na região deu-se a intrusão dos foiaítos sob a forma de diques menores cortando o grande dique anelar A seqüência das intrusões parece ser do centro para a periferia, contrariando a observada na maioria das intrusões alcalinas. O planalto é formado de duas áreas geomorfològicamente distintas: a maior, com drenagem anelar e a menor, com relêvo entre juventude e maturidade, na qual predomina a drenagem radial. É provável que parte do sistema de drenagem obedeça às direções principais de diaclases. Após a atividade do magma alcalino ocorreram falhamentos em grande área, dos quais o principal formou o “graben*’ E-W que tangencia o bordo sul do complexo. Os recursos minerais são representados por jazidas de bauxita e de minerais zirconíferos como zircão, caldasita, baddeleyta, nos quais há teores variáveis de urânio e os depósitos de tório e terras raras. Os minerais zirconíferos e os de tório são formados a partir de fenômenos ligados a processos hidrotermais, que destruiram os minerais primários e possibilitaram a posterior precipitação em fendas

Geology of Mackinac Straits in Relation to Mackinac Bridge

The construction of Mackinac Straits bridge has provided new data on the Paleozoic and Pleistocene history of the Mackinac region. The bedrock includes carbonates, chert, shale, and gypsum of late Silurian and middle Devonian age. Leaching of salt in the Pointe Aux Chenes (Upper Silurian) formation permitted the collapse of overlying rocks and produced the Mackinac breccia, but brecciation was not so intense or of such great magnitude as suggested in earlier studies. The breccia has been reconsolidated by loading under younger sedimentary rocks, recemented by secondary calcite, and perhaps additionally compacted by loading under glacial ice. The breccia has a bearing capacity considerably in excess of the load imposed by the bridge. Glacial deposits above bedrock are till and lacustrine clays of the Valders glacial substage, although older glacial deposits occur on the northern sides of the submerged Mackinac River gorge and a tributary channel. A buried sea stack encountered in probing indicates a level ...

Some Data concerning the Mineralogy of the Karlshamn Granite

Abstract The granite, a coarse massive type, contains the following minerals: quarz, microcline, oligoclase, biotite, sphene, apatite, zircon, and magnetite with some secondary sericite, chlorite, and calcite. The minerals were isolated according to the method shown diagrammatically in Fig. 1. The relation between chemical composition and optical properties of the microcline and the biotite is elucidated. In the system of P. Niggli the granite represents a normal-granitic to yosemite-granitic magma type.

Petrography and Petrology of Scurry Reef, Scurry County, Texas

The Scurry reef of Scurry County, Texas, is a subsurface feature 23 miles long and 4-8 miles wide that is of Permian and Carboniferous age. The reef is a low mound composed chiefly of clastic organic limestone with minor amounts of black bituminous claystone. The reef limestone consists of three main textural types: calcilutite, calcarenite, and calcirudite. The calcilutite is composed mainly of particles too fine to be resolved under the petrographic microscope. Part of this fine material appears to be comminuted organic debris; the remainder may be chemically precipitated ooze. The calcarenite forms a gradational series between sorted, rounded debris in clear crystalline calcite cement and unsorted, angular debris in a matrix of lithified lime mud. The calcirudite is composed of angular, granule- to boulder-sized fragments in a matrix of lithified lime mud or lime sand. The fragments consist of organic debris and pre-existing reef limestone and claystone. The limestone contains minor amounts of secondary calcite, dolomite, and chert. Characteristic structures in the limestone are stylolites, joints, irregular fractures, and slump structures. The vast bulk of observable porosity was formed by leaching solutions. This condition may have been accomplished principally by the enlargement of primary openings through the removal of the least stable constituents. The Scurry reef was formed from the hard parts of organisms that lived, died, and were buried in essentially one locality. The two major faunal elements that could be identified in the reef are the Crinoidea and the Foraminifera, principally Fusulinidae. Corals constitute a minor element and are not numerous enough to be important here as reef-forming organisms. It is suggested that the welding of lime mud and the constant precipitation of calcite cement rigidified the accumulating material and thus acted as a substitute for the rigid organic framework that characterizes many reefs.

Authigenesis in West Virginia Sandstones

The authigenic minerals in the Oriskany, Berea, and Big Injun sandstones are quartz, calcite, dolomite, orthoclase, microcline, albite, chlorite, kaolinite, and pyrite. Most of the quartz grew in open spaces, but some replaced clastic calcite. Two stages of silicification occurred in parts of the Berea sandstone. Authigenic chlorite appears as fringes around the detrital grains or around the early quartz growths. Calcite occurs as secondary rims on clastic calcite and as a cementing material in the voids. Rhombs of dolomite occur in the interstices and as replacements of feldspar and the clayey matrix. Authigenic feldspar is present in the form of overlays around detrital grains. Secondary kaolinite occurs as an alteration product of feldspar and as a filling in many of the voids which remained after the crystallization of the other minerals. Most of the authigenic minerals formed after burial, because the secondary growths are generally free of strain and fill the cracks in fractured grains of mica and feldspar. The secondary calcite and chlorite probably formed from primary constituents in the sediments. Most of the silica was apparently derived from outside sources because little solution of quartz occurred at the points of contact between the detrita! grains.

Stratigraphy and Structure of Moose Mountain Area, Alberta

The Moose Mountain area, situated along the front range of the Canadian Rockies, 32 miles northwest of the Turner Valley oil field, Alberta, is characterized by a large domal structure that is approximately 10 miles long and 3 miles wide, and across which is exposed a series of beds that range in age from Cretaceous to Lower Carboniferous. This structural feature has been drilled at three separated locations, resulting in two very small wells and a failure. The tests were started only a few hundred feet above the Mississippian-Devonian contact. The dry hole, drilled by the McColl-Frontenac Oil Company, was carried about 2,700 feet below the top of the Cambrian; the other wells are deriving gas and oil from rocks of Devonian age. There are bituminous limestone zones in the lower part of the Devonian that are extremely porous where they crop out north and south of the Moose Mountain area; but in the McColl-Frontenac test, where these bituminous beds were encountered structurally high, the pore spaces and fractures were filled with secondary calcite.