Calcarenite Research Articles

The "Tears of the Virgin" at Lakes Entrance, southeast Australia were made by the intertidal barnacle Chthamalus antennatus (Cirripedia: Thoracica) and cyanobacteria.

Curious eroded depressions, most resembling an eye shedding an elongate tear, are found in gently sloping, intertidal, carbonate-rich arenite outcropping on the sea coast near Lakes Entrance, Victoria, southeast Australia. The depressions, known locally as "Tears of the Virgin," are evidently formed by multiple generations of a barnacle, Chthamalus antennatus Darwin, 1854 in association with cyanobacteria. While the round part of a depression offers the barnacle a modicum of protection from impacts during high tides, it is also partially inhabited by cyanobacteria, which extend into and tend to fill the elongate tear. As such, this appears to be the first case of mutualism between a higher invertebrate and cyanobacteria, with the cyanobacteria reducing the barnacle's risk of desiccation while receiving metabolic wastes from it during low tides. It is also the first record of a balanomorph barnacle eroding calcareous arenite beneath its shell, the net effect of which would be expected to reduce its adhesion to the substrate. However, the siliceous residue, resulting from the barnacle's dissolution of the more than 80% of the calcite-rich sedimentary rock, is sequestered in delicate folds on the inside of the shell wall as it grows. A brief review of cirripedes capable of excavation includes the first photographic documentation of excavation of a mollusc shell by a verrucomorph.

FIRST RECORD OF DUGONGIDAE (MAMMALIA: SIRENIA) FROM THE FLORESTA CALCARENITES FORMATION (LATE BURDIGALIAN – EARLY LANGHIAN, REGGIO CALABRIA, SOUTHERN ITALY)

A sirenian rib has been recovered at Motta San Giovanni (Reggio Calabria) in the “Floresta Calcarenites”, a Formation cropping out in Sicily and Calabria and dated late Burdigalian-Langhian. Although the rib is not a diagnostic bone for taxonomy, its presence in southern Calabria extends the knowledge about the paleobiogeography of the Family Dugongidae in the Mediterranean basin. The find is hitherto the only record of sirenians in the Floresta calcarenites. Moreover, the specimen extends back to the Early-Middle Miocene (late Burdigalian-Langhian) the occurrence of sirenians in Calabria, previously determined thanks to substantial material from the Late Miocene (Tortonian) of the Monte Poro area (Vibo Valentia). The paleoenvironment of the Floresta calcarenites was a warm and shallow sea, consistent with the paleoecology of Dugongidae.

Petrography, mineralogy, chemical and technical properties of the building stone of ostuni cathedral (Italy): Inferences on diagnostics and conservation

Ostuni Cathedral represents an outstanding example of the monumental sacred architecture spread in Apulia (southern Italy) during the Middle Ages. The church dates back to the 15 th century and combines the local Romanesque tradition with Gothic stylistic features and elements of Dalmatian, Venetian and Arabic architecture. Between 2006 and 2007, a conservative restoration was carried out on the Cathedral. The operations mainly concerned the masonry, which is built of a local stone material known as “Pietra gentile”, a soft and porous calcarenite with an excellent workability and carvability. This research aims at characterizing the stone used in the monument and its state of conservation. For this goal, on-site macroscopic observations were integrated with sample analyses by means of optical microscopy, X-ray powder diffraction and scanning electron microscopy equipped with microanalysis. In this way, the petrographic classification of the used lithotype and the chemico-mineralogical characterization of its alteration products were carried out. Finally, structural diagnostics of the masonry was performed, through on-site non-destructive ultrasonic and sclerometric tests. The results presented allow evaluating, only few years after the latest restorations, the weathering kinetics and durability of the monumental stone, with a particular highlight on its short-term modifications. The main alterations detected, i.e. black crusts, salt crusts, oxalate patinas and discolorations, are produced by cyclic weathering or previous conservative treatments; moreover, several patterns of physical decay are observable, alveolization and differential erosion principally, which highly affect the technical performance of the stone. These data supply further information about a material that has been studied only recently in archaeometry, although very significant in Apulia from a cultural point of view.

The Old Fort Point Formation: Redefinition and formal subdivision of a distinctive stratigraphic marker in the Neoproterozoic Windermere Supergroup, southern Canadian Cordillera

Abstract The southern Canadian Cordillera strata of the Neoproterozoic Windermere Supergroup form an areally extensive outcrop belt of deep-marine sedimentary rocks. Within this generally monotonous pile of siliciclastic and minor carbonate rocks, the Old Fort Point Formation forms a lithologically and geochemically distinctive unit that serves as a key regional stratigraphic marker. New sedimentologic and stratigraphic work demonstrates that it is lithologically distinctive, mappable and correlatable on a regional scale and deserves formal recognition. The Old Fort Point Formation comprises three lithostratigraphic members that have a consistent stratigraphic relationship across the basin and can easily be distinguished from lithofacies in the enveloping strata of the Windermere Supergroup. The basal Temple Lake Member is composed primarily of siltstone to mudstone that grades upward into rhythmically interstratified limestone-siltstone. The middle Geikie Siding Member is a thin, organic-rich mudstone-pelite. The Whitehorn Mountain Member is the uppermost unit and varies locally and regionally in thickness and lithology, including diamictite, breccia to conglomerate, mudstone to siltstone, subarkose, quartzarenite, calcareous arenite, arenaceous limestone, and limestone. This unique lithostratigraphic unit is here formally named the Old Fort Point Formation and other site-specific names should be discontinued. The use of the name Old Fort Point Formation is an attempt to simplify part of a complicated and informally defined stratigraphic nomenclature currently in use for rocks in the Neoproterozoic Windermere Supergroup, southern Canadian Cordillera.

Effects of thermal-heating cycle treatment on thermal expansion behavior of different building stones

Several types of natural stone show dimensional instability causing damage if used outdoors. The extent of damage basically depends on the orientation of the crystal texture in the stone slabs, the so-called preferred orientation. In order to examine the characteristics of natural stone, the measurement was done with a quadruple-dilatometer. The dilatometer is a testing device for measuring the linear thermal expansion of materials as a function of temperature. Enabling the analysis, a quadruple-dilatometer was built which allows testing of four samples simultaneously under same conditions. Several types of marble (Wachauer marble), limestone (Mannersdorfer limestone, Mocca Creme, Schwarzenseer limestone and Veselje Unito), calcareous arenite (St. Margarethener calcareous arenite), quartz arenite (Sun Imperial) and granite (Neuhauser granite and Chinese granite G603) have been analyzed, to create an assemblage of the thermal expansion properties of several stone types.

Risananeiza crassaparies n. sp. from the upper Chattian of Porto Badisco (southern Apulia, Italy).

A new species of Rotaliidae, Risananeiza crassaparies n. sp., is described from the upper Chattian of the Porto Badisco Calcarenites (Salento Peninsula, Southern Italy). The studied specimens are assigned to the foraminiferal genus Risananeiza based on the presence of vertical canals in both the ventral and dorsal side of the test, and an intraseptal canal system that evolves into marginal sutural canals. The new species differs from the type species of the genus, R. pustulosa, in having a lower chamber lumen, and smaller dimension.

The Baroque architecture of Scicli (south-eastern Sicily): characterization of degradation materials and testing of protective products

Scicli and the other baroque cities of the “Val di Noto” (Catania, Militello, Caltagirone, Palazzolo, Siracusa, Noto, Ragusa e Modica), were recently included in the World Heritage List. These cities were completely destroyed following the earthquake of 1693 and then were involved in an intense period of rebuilding and artistic flowering. In particular, Scicli was reconstructed with the almost exclusive use of a local calcarenite, which belongs to the Ragusa Formation. Due to its nature, this carbonate rock is subject to many alteration and degradation forms (chromatic alteration, alveolization, differential disaggregation, efflorescence, decohesion, exfoliation and detachment). Therefore, different products (beeswax, vegetable oils, natural and synthetic resins) were used in the past often with the aim to preserve the monuments from decay. In this study, through a diagnostic analysis, the degradation materials occurring in the churches of St. Matteo, St. Michele and Carmine in the city of Scicli, as well as residues of treatments carried out in the past, have been identified. In addition, three different types of protective products were tested in laboratory, with the aim of assessing their protective effectiveness in terms of hydrorepellence and response to accelerated aging and salt crystallization tests. Laboratory tests showed that, among the tested products, the Polisiloxane can be regarded as the most suitable for this type of substrate.

MIDDLE AND LATE HETTANGIAN RADIOLARIANS FROM THE MT. CAMICIA SUCCESSION (GRAN SASSO, CENTRAL APENNINES - ITALY)

Well-preserved middle and late Hettangian radiolarians have been discovered S-E of Mt. Camicia (Central Apennines) in limestone beds that contain also Hettangian ammonites. These beds are part of an Upper Triassic to Lower Jurassic carbonate succession, which crops out in the eastern part of the Gran Sasso range. This succession includes euxinic deposits (bituminous dolostone) and other pelagic sediments (mudstone and calcarenites) which developed in a basin rimmed by a carbonate platform. In the same time interval, the well-known formations of Dolomia Principale and Calcare Massiccio were forming on this platform. In this paper we examine the radiolarian assemblages collected in three levels of the ammonite bearing beds, and we define two new genera ( Squinabolia and Turritus ) and eight new radiolarian species ( Anaticapitula parvireticulata , Anaticapitula triangularis, Farcus aquilensis, Farcus leonseveroi , Parahsuum vraddense , Squinabolia multispinata, Turritus venturii, Zhamoidellum sphaericus ), and we define twenty four other species, for a total of thirty eight identified species. The ammonites in the lowest level indicate a middle Hettangian age, those from the two upper levels a late Hettangian. In the Western Tethys successions bearing Hettangian radiolarians are rare and have been found together with ammonites only in the Mt. Camicia section described in this paper. This section permits to correlate the radiolarian assemblages with the ammonite zonation.

A NEW STROMATOLITE OCCURRENCE IN THE NSUZE GROUP, PONGOLA SUPERGROUP OF NORTHERN KWAZULU-NATAL, SOUTH AFRICA

A new site containing stromatolite-bearing silicified carbonates horizons is described in the Nsuze Group within the Nkandla Basin of the Pongola Supergroup. The stromatolite-bearing carbonate units are interbedded with calcareous arenite and represent stratiform biostromes exhibiting both smooth and wrinkled laminations. Microbially-accentuated current ripples are regularly preserved upon stratiform stromatolitic substrates. The recognition of these stromatolite-bearing units in a previously undifferentiated Nsuze Group succession not only increases the area in which these accretionary, organo-sedimentary structures have been identified, but more importantly can provide the basis for regional lithostratigraphic correlation between the relatively well-defined stratigraphy of the main Pongola Basin and the more deformed and much less well-defined sequences in the structurally complex Nkandla Basin. The improved understanding of the regional stratigraphy generated by the recognition of this stromatolite-bearing marker horizon will provide a fundamental factor in deciphering the relationships of Pongola Supergroup inliers and the tectonic development of the region during the Mesoarchaean.

On the formation of dissolution pipes in Quaternary coastal calcareous arenites in Mediterranean settings

AbstractA large number of uniform cone‐shaped dissolution pipes has been observed and studied in Quaternary coastal calcareous arenites in Apulia and Sardinia (Italy) and Tunisia. These cylindrical tubes have a mean diameter of 52·8 cm and are up to 970 cm deep (mean depth for sediment‐free pipes is 1·38 m). They generally have smooth walls along their length, are perfectly vertical and taper out towards their bottoms. Their development is not influenced by bedding nor fractures. Sometimes their walls are coated by a calcrete crust. Their morphology has been studied in detail and their relationships with the surrounding rocks and with the environment have been analysed. The perfectly vertical development is a clear evidence of their genesis controlled by gravity. The depth of the dissolution pipes can be described by an exponential distribution law (the Milanovic distribution), strongly suggesting they developed by a diffusion mechanism from the surface vertically downward. We believe dissolution pipes preferentially form in a covered karst setting. Local patches of soil and vegetation cause infiltration water to be enriched in carbon dioxide enhancing dissolution of carbonate cement and local small‐scale subsidence. This process causes the formation of a depression cone that guides infiltrating waters towards these spots giving rise to the downward growth of gravity‐controlled dissolution pipes. A change of climate from wetter phases to drier and hotter ones causes the formation of a calcrete lining, fossilizing the pipes. When the pipes become exposed to surface agents by erosion of the sediment cover or are laterally breached the loose quartz sand filling them may be transported elsewhere. Copyright © 2010 John Wiley & Sons, Ltd.

THE MID- JURASSIC MARINE TRANSGRESSION IN EAST AFRICA: NEW DATA ON THE DEPOSITIONAL ENVIRONMENT AND AGE OF THE LOWER KAMBE FORMATION (AALENIAN TO BAJOCIAN) IN THE MOMBASA AREA (S.E. KENYA)

The Lower Kambe Formation crops out from Mombasa towards the northeast, along the coastal area of Kenya; it was deposited during the first phases of the Middle Jurassic marine transgression. The lithology of the Lower Kambe Fm. varies passing from the southern areas towards the north: near Mombasa, this formation consists of an alternance of calcareous and marly intervals; the marly levels become thinner and tend to disappear towards the north, where the succession becomes entirely calcareous and shows features of a carbonate platform. According to field observations, in the Mwachi River area near Mombasa, four lithological units crop out, that we consider as informal members, namely from bottom : (a) Calcarenitic member (Cam), well bedded calcarenites and some conglomerates; (b) Lower Shaly member (LSm), marly shales with marly limestone beds; (c) Conglomeratic member (Cgm), alternance of calcarenitic beds and levels of conglomerates; (d) Upper Shaly member (USm), marly shales and siltstones with thin beds of calcilutites and quartz sandstones. The sedimentological features of the Cam point to a shoreline environment, possibly shoreface; those of the LSm to a mid/outer ramp; the onset of tectonically active slopes is evidenced by the occurrence of gravity flow structures in the fine-grained sediments. At the top of LSm a marked shallowing of the deposition environment occurred. The Cgm was deposited on a inner ramp, where polymictic coarse deposits (arenaceous, shaly and carbonate clasts) indicating a strong erosion of the coastal areas, were intercalated to the wave-winnowed calcarenites; also the calcarenitic upper portion of the Cgm was deposited on an high energy inner ramp depositional environment. Upwards, a deepening occurred, as the fine sediments of the USm point to a mid/outer ramp. The age of the Lower Kambe Formation has been determined by several Authors on the basis of ammonites; in this work calcareous nannofossils stratigraphy is provided. The age given by ammonites is Bajocian; the calcareous nannofossil assemblage, found in various localities along the Mwachi River, indicates an Aalenian - Bajocian p.p. age. The discrepancy is possibly due to a complex geological situation (faults ?) in the localities with ammonites.

3 - SOUTHERN TUSCANY - B - COLLINE METALLIFERE

In the last decades the geology of Southern Tuscany (Giannini et al., 1971; Boccaletti et al., 1982, cum bibl.) has been greatly improved by lithostratigraphic, biostratigraphic and geophysic studies, and by deep geothermal drillings (with a depth down to 3000 m b.g.l.) (Bertini et al., 1991; 1994; Elter and Pandeli, 1996, cum bibl.). The geological setting of this area is composed, from top to bottom, of the following tectono-stratigraphic units (Figs. 1 and 2): a. Neo-autochthon (post-orogenic). It is formed by the sediments filling the extensional basins, generally oriented along to the Apenninic chain. They unconformably lie on the stack of Ligurian and Tuscan Units, and are represented by lacustrine-marine (late Tortonian-Messinian), marine (Pliocene) and lacustrine-fluvial (early Villafranchian-Quaternary) sediments. b. Ligurian, sub-Ligurian and epi-Ligurian Units. They are composed of five tectonic units: 1- Upper Ophiolitic Unit (Late Jurassic-Early Cretaceous: Vara Supergroup), largely represented by Palombini Shales with some ophiolitic outcrops. 2- Lower Ophiolitic Unit, (Jurassic-Early Cretaceous: Vara Supergroup), including thick ophiolitic successions. This unit is stratigraphically capped by: 3- The syn-orogenic Upper Paleocene- Middle Eocene epi-Ligurian Lanciaia Fm. (ophiolitic breccias and sandstones, grading upward to a mainly carbonate-siliciclastic flysch). 4- Monteverdi Marittimo Unit (Southern Tuscany Elminthoid Flysch Group): consisting of a calcareousmarly- arenaceous flysch of Late Cretaceous- Early Paleocene age. 5- Canetolo Unit (Paleocene- Middle/Late Eocene), made up of shales with limestone, calcarenite and graywacke intercalations. This unit belongs to the sub-Ligurian paleogeographic Domain (close to the Adria margin). c. Tuscan Nappe. It is composed, from top to bottom, of the following non-metamorphic formations: Macigno (Late Oligocene-Early Miocene), “Scisti Policromi” (Early Cretaceous- Oligocene), Tuscan Cherts (Malm), Posidonia Marlstones (Dogger), “Rosso Ammonitico” and Limano Cherty Limestones (Middle-Late Liassic), “Calcare Massiccio” (Late Triassic?-Early Liassic), Spezia Fm. (Rhaetian), Burano Anhydrites (Norian-Rhaetian). In this succession lateralvertical facies changes and sedimentary unconformities are present, mainly in Middle-Late Jurassic times. Furthermore, the Tuscan Nappe is often tectonically laminated or locally lacks (“Serie Toscana Ridotta” = Reduced Tuscan Series Auctt.) by low-angle extensional faulting with flat-ramp-flat geometry (Fig. 3). The Tuscan Nappe lies on the Tuscan Metamorphic succession (Monticiano-Roccastrada Unit) which is quoted below. d. Monticiano-Roccastrada Unit. The upper part of this unit is a complex pile of tectonic slices made up of epimetamorphic Lower to Upper Paleozoic formations, Triassic “Verrucano”, Tocchi Fm. and non-metamorphic Upper Triassic anhydrite-carbonate successions. The lower part is made up of ?Upper Cambrian-?Lower Ordovician siliciclastics and metabasites (Phyllitic-quartzitic Complex), which include relics of Hercynian schistosity. In the subsurface of Larderello geothermal area, the Phyllitic-quartzitic Complex overlies ?Lower Paleozoic/?pre-Paleozoic Micaschist Complex (see Stop 5). The Colline Metallifere area is characterised by high heat flow (>650 mWm-2 in the Larderello geothermal field), by lithosphere thinning (Moho at a depth of about 22 km in the Grosseto area), by the uplift of the metasomatised and partially melted mantle, and by anatectic crustal magmatism (Boccaletti et al., 1985; Mongelli et al., 1991).

JURASSIC PALAEOGEOGRAPHY OF THE TRANSDANUBIAN CENTRAL RANGE (HUNGARY)

The Transdanubian Central Range (TCR) is a flattened range of hills in northern Transdanubia (Hungary), formed mainly by Mesozoic carbonate rocks showing strong facies similarities with the Southern Alps and the Austroalpine domain. The Jurassic system is divided into several formations of predominantly pelagic limestones. Ammonoids are frequent and were collected bed-by-bed in numerous sections, providing an excellent biostratigraphic resolution. The thickness of the Jurassic system is usually small but changes along the strike of the TCR. It reaches a maximum thickness of 500 m in the western part; is very variable (10-400 m) in the central segment (Bakony Mts.) and rather low (less than 100 m) in the east (Gerecse). In the Bakony segment, the thickness variation reflects the strongly dissected topography of the Jurassic sea-floor. Synsedimentary tectonics is dominated by normal faults; tilted blocks and listric faults may be inferred only in the east. Five main steps were identified in the palaeogeographic evolution: 1) Late Hettangian: carbonate oolitic shoals prevail, except for a few sites where non-deposition or neritic sediments occur. 2) Sinemurian and Pliensbachian: tectonic disintegration resulted in an intricate pattern of submarine horsts and intervening basins, with condensed sedimentation or non-deposition on the horsts and thicker, continuous sedimentary sequences in the basins. The submarine topographic highs are surrounded by aprons of redeposited material (scarp breccias, brachiopod coquinas, crinoidal calcarenites, spiculitic cherty limestones), while pure or argillaceous limestones (Rosso Ammonitico) prevail in the distal areas. 3) Early Toarcian: the Tethys-wide anoxic event is superimposed on the previous submarine bottom topography; the resulting black shales and sedimentary Mn-ores are concentrated on the western sides of some horsts. 4) Dogger to Early Malm: radiolarites with heterochronous lower and upper boundaries (Aalenian to Kimmeridgian) prevail, except for the top of some submarine topographic highs. The absence of uppermost Bathonian to Lower Oxfordian carbonates suggests that the whole TCR sunk below the CCD in those times. 5) Latest Jurassic: the uniform deposition of Rosso Ammonitico and Biancone in the Late Kimmeridgian and Tithonian is interrupted only in the Early Tithonian by local intercalations of scarp breccias and coarse biodetrital limestones. This is interpreted as the last manifestation of synsedimentary tectonic movements along the faults bordering the submarine horsts. Based on palaeogeographic similarities and analogies in Jurassic times, the TCR is visualized as the northern foreground of the Trento platform/plateau (lying north of the later Insubric lineament), where the block-tectonic disintegration and differential subsidence started earlier and resulted in a bottom morphology more dissected than in the South Alpine part of this west Tethyan passive margin.

ANATOMY OF A SEMIARID COASTAL SYSTEM: THE UPPER CARNIAN OF LOMBARDY (ITALY)

The mixed terrigenous-carbonate-evaporitic S.Giovanni Bianco Formation and dolomitic Campolungo Tongue (upper part of the Breno Formation), generally 2OO to 3OO m thick, are assigned to the Late Carnian. They respectively overlie lagoonal limestones (Gorno Fm.) and peritidal carbonates (Annunciata Member of the Breno Fm.), and underlie intraformational breccias and recrystallized limestones (Castro Fm.). Recognition of an unconformity, ascribed to a relative fall of sea-level (sequence boundary), allowed us to subdivide the Upper Carnian succession into two parts. ln the lower part (SGBL), six lithosomes were recognized. Red to green alluvial clastics in the south-east and south-west pass northward to mixed terrigenous-carbonate coastal sediments and finally to dolostones deposited in carbonate tidal flats. In the proximal sections of the Brescia Prealps, renewed north-westward progradation of alluvial redbeds with intercalated calclithite conglomerates points to a stage of teconic uplift. A distinct increase in quartz, representing a regional petrographic marker followed all across Lombardy, indicates deepening of erosion into the metamorphic wallrocks of the volcanic belt. A major hiatus at the top of the SGB1 is best documented in the northern Presolana area by a silcrete crust directly overlying the Julian Annunciata Member of the Breno Formation. In the Brembana Valley area, the discontinuity occurs within a greenish siliciclastic coastal plain succession, and may be traced at the top of a marker interval of interbedded reddish siltstones and sandstones. The upper part (SGB2) consists of four lithosomes. Greenish sandstones and siltstones, accumulating in coastal plains in the south-west, passed northward to mudrocks and dolostones. In the southernmost Camonica Valley area, mudrocks are locally interbedded with calcarenites containing bored or pedogenized lithoclasts ripped from the underlying sequence and varied bioclasts, restifiying to relatively open shallow-marine conditions during transgression. Next, thick gypsum accumulated in coasral salinas barred by locally oolitic platform carbonates to the north. Rare sandstone lenses occurring in the Brembana Valley at the top of the unit conrain exclusive rhyolitic detritus, indicating either a terminal phase of explosive volcanism or erosion of older felsic volcanic products.

Undrained and partially drained behaviour of end bearing piles and bells founded in untreated calcarenite. Application brief : Murff, J D Int J Num Anal Meth GeomechV13, N3, May–June 1989, P327–330

Undrained and partially drained behaviour of end bearing piles and bells founded in untreated calcarenite. Application brief : Murff, J D Int J Num Anal Meth GeomechV13, N3, May–June 1989, P327–330

Development of an augen gneiss terrain

Augen gneisses and related migmatites commonly form extensive areas in deep crystalline terrains and are interlayered with horizons of undoubted metasedimentary rocks. Augen gneiss, migmatite, and hornblende gneiss near McMurdo Sound, Antarctica, is interlayered with calcareous metasedimentary rocks on all scales and passes gradationally into quartzo-feldspathic gneiss. Numerous discontinuous lenses and layers of metasedimentary rocks in augen gneiss have been disrupted by transposition of layering and form tectonic inclusions. Calc-silicate layers have reacted with the surrounding rocks and become partially amphibolitized. Field evidence suggests that augen gneiss formed from quartzo-feldspathic gneiss by local metasomatism that accompanied strong deformation and smoothed out original metasedimentary differences. Locally partial melting took place. The final result is a sequence of augen gneiss, hornblende gneiss, and migmatite with thin amphibolite lenses and layers. The metasedimentary rocks are correlated with lower grade limestones and calcareous arenites including graywackes 125 km to the south. The quartzo-feldspathic gneiss would thus represent highly metamorphosed graywacke and sandstone. Augen gneiss and quartzo-feldspathic gneiss have similar chemical compositions, but augen gneiss seems to be somewhat more mafic. The composition of augen gneiss is more mafic than average continental shield surface rock and less mafic than the average crustal rock. Evidence indicates that augen gneiss and related rocks formed by homogenization of rocks that were originally sedimentary and its composition may reflect the bulk composition of material supplied to the crust earlier in the earth's history.

Petrology, Palaeontology, Carson Creek North Reef Complex, Alberta

ABSTRACT The Carson Creek North reef complex occurs in the subsurface of west-central Alberta, with an area of about 24 sq mi and a maximum thickness of about 350 ft. The reef complex and the underlying reef platform form the Swan Hills Formation of the Beaverhill Lake Group of probable late Middle and early Upper Devonian age. Structure maps, isopach maps, and cross-sections illustrate the atoll-like reef geometry and paleotopography. Stromatoporoids and algae were by far the most important reef organisms. Brachiopods, corals, and other fossils are common, but were not as important in governing reefal development. Many of the organisms, especially the stromatoporoids, appear to have been environmentally controlled, allowing the reef complex to be subdivided into 7 biotopes each having distinctive biosomes. Integrated data allow the reef complex to be divided into 5 facies, 11 microfacies, and 32 rock types. Geomorphic localities envisaged for the rock types vary from deep quiet water to shallow turbulent water to subaerial. The most important diagenetic features which have affected the reef-complex limestones are, biological diagenesis, cementation, lithification, neomorphism, solution and fracturing, compaction and development of authigenic accessory minerals. In general, however, post-depositional diagenesis has not greatly altered the original sedimentary features. The geological history of the reef complex has been portrayed in 6 major stages of development: (1) Reef Platform Development -- mild transgression and deposition of a biostromal-type carbonate unit; (2) Biohermal Development -- more extensive transgression resulting in biohermal reef growth; (3) Green Shale Development -- major regression with subaerial erosion, solution of reefal carbonate and consequent accumulation of argillaceous insolubles; (4) Bank Development -- stability or mild transgression resulting in a calcarenite bank unit; (5) Reef Death -- regression and erosion of the reef resulting in termination of reef growth; (6) Waterways Development -- transgression and deepening of the water resulting in argillaceous non-reef sedimentation.