Showing papers in "Carbonates and Evaporites in 2001"
TL;DR: Two types of sinkholes are observed along the Dead Sea shore, Israel as mentioned in this paper, which are associated with vadose dissolution in Mount Sedom salt diapir, and with dissolution under the watertable along the retreating Dead Sea.
Abstract: Two types of sinkholes are observed along the Dead Sea shore, Israel. The first is associated with vadose dissolution in Mount Sedom salt diapir. The second is associated with dissolution under the watertable along the retreating Dead Sea shore. The Dead Sea level is falling dramatically, mainly because of human activity. Simultaneously, the lake shores suffer tremendous impact since the late 1980s: The ground is collapsing and subsiding in hundreds of points along the lake, with people, roads and property being swallowed in the more catastrophic events. The collapse is believed to result from dissolution of salt by aggressive groundwater, following the retreat of Dead Sea level and the groundwater halocline. Geological evidence suggests that a previous major lake level fall occurrednaturally∼2000 BCE. This may provide a new explanation for a curious historical-geological phrase in the book of Genesis, suggested to record formation of collapse sinkholes which occurred in response to the historic falling lake level, associated with climatic desiccation.
55 citations
TL;DR: The evaporite formations (in outcrop and at shallow depth) cover an extensive area of the Spanish territory and record a wide time span from the Triassic up to the present day as discussed by the authors.
Abstract: The evaporite formations (in outcrop and at shallow depth) cover an extensive area of the Spanish territory. These soluble sediments are found in diverse geological domains and record a wide time span from the Triassic up to the present day. Broadly, the Mesozoic and Paleogene formations (Alpine cycle) are affected by compressional structures, whereas the Neogene (post-orogenic) sediments remain undeformed.
41 citations
TL;DR: In addition to the prominent calcite, aragonite, and gypsum, eleven other minerals were identified by means of X-ray diffraction, scanning electron microscopy, and the electron microprobe.
Abstract: Speleothem samples from ten caves located in the northeastern and southwestern corners of San Salvador Island (Bahamas) were analyzed by means of X-ray diffraction, scanning electron microscopy, and the electron microprobe. In addition to the prominent calcite, aragonite, and gypsum, already known to occur in San Salvador caves, eleven other minerals were identified. The minerals are celestite, SrSO4; cesanite, Na3Ca2(SO4)3OH; ardealite, Ca2(HPO4)(SO4)·4H2O; brushite, CaHPO4·2H2O; hydroxylapatite, Ca5(PO4)3OH; fluorapatite, Ca5(PO4)3F; chlorapatite, Ca5(PO4)3Cl; collinsite, Ca2(Mg,Fe)(PO4)2·2H2O; witlockite, β-Ca3(PO4)2; niter, KNO3, and nitratine, NaNO3. Cesanite has not been previously reported from a cave. This is the second reported occurrence of collinsite. San Salvador Island, on the eastern edge of the Bahamian Platform, is the location of a large number of relatively small flank margin caves. In adition TO the more obvious speleothems — stalactites, stalagmites, and flowstone — the San Salvador caves contain a variety of crusts and soils of unknown mineralogy. This paper is an account of an investigation of samples collected from ten of these caves. Prior to the result reported here, only calcite, aragonite, and gypsum had been identified in the various speleothems from caves on San Salvador Island (Vogelet al. 1990; Schwabeet al. 1993).
25 citations
TL;DR: Speleothems from Oregon Caves National Monument, a dissolutional cave system located in the Klamath Mountains of southwest Oregon, are composed mainly of columnar calcite crystals Columnar calcites form through syndepositional lateral coalescence of crystallites and precipitate under stable hydrodynamic conditions in humid, temperate climates Numerous discontinuities from short-lived events (<100 years) punctuate the calcites as mentioned in this paper.
Abstract: Speleothems from Oregon Caves National Monument, a dissolutional cave system located in the Klamath Mountains of southwest Oregon, are composed mainly (>90%) of columnar calcite crystals Columnar calcites form through syndepositional lateral coalescence of crystallites and precipitate under stable hydrodynamic conditions in humid, temperate climates Numerous discontinuities from short-lived events (<100 years) punctuate the calcites Minor fabrics, such as transitional- and randomly-oriented elongate calcites are seeded on these discontinuities and detrital layers Columnar calcites eventually overrun sub-horizontally oriented crystals as a result of competitive growth Large (≈750 μm) crystal terminations indicate growth under increased water film resulting from greater flow and/or ponding 14 Useries dates provide mean growth rates of 56 to 279 mm/ka during interglacial periods (marine isotope stages 11 through 9, substage 5e, and late stage 2 through stage 1), and indicate short growth intervals during early-to mid-interglacial periods Several outcrop-scale discontinuities represent periods of prolonged growth stoppage Growth cessation occurred during the colder phases of stages 8–9 and 6–7, which translate into hiatuses of 775 and 99 ka respectively Given the sensitivity of alpine regions to climate change and the lack of evidence for continental or alpine glaciation, the hiatuses are presumed to be caused by groundwater freezing during extended periglacial conditions, triggered by the lowering of periglacial thresholds by as much as 1800 m during glacial periods
22 citations
TL;DR: In this article, the authors show that the Las Tienditas carbonates of the La Laja Fm. show a gradual decrease from the base (+3.4 ‰PDB) to the top with a minimum of −1.6‰ observed at ∼15m from the top.
Abstract: Upper Precambrian-Lower Cambrian sequences in the Tucuman, Salta and Jujuy provinces, NW Argentina, comprise sandstone, slate, conglomerate and black limestone (Las Tienditas/Volcan Fms.) with abundant Vendian/Tommotian trace fossils in the clastic facies rocks. The Precordillera basin, San Juan province, represents a continuous carbonate sequence belonging to the Lower to Middle Cambrian La Laja Fm. The Pie-de-Palo Range, Pampean Range, characterized by carbonates intercalated with greenschist/amphibolite facies metaclastic rocks, forms a part of the Precordillera basement. The δ13C values in carbonates of the Las Tienditas Fm. show a gradual decrease from the base (+3.4 ‰PDB) to the top with a minimum of −1.6‰ observed at ∼15m from the top, the latter having a higher clay content. Carbonates in a 700m thick section within La Laja Fm. is marked by a slightly positive δ13C values at the base (marly) with a negative anomaly (−2.0‰) at ∼20 m above, followed by a small positive anomaly (+0.5‰) ∼100 m from the base. All the values above this point are around −0.5‰ with a negative anomaly (−2.0‰) recorded at ∼240m above the base. Seawater87Sr/86Sr values define a non-monotonic increase (0.70870–0.71082) through the carbonates in Las Tienditas Fm. while the La Laja Fm carbonates vary from 0.70926 to 0.71030, with higher values at the base. C and Sr isotopes, thus suggest that the Las Tienditas carbonates record the Precambrian-Cambrian transition (∼15m from the top of studied section). The same is also evident at ∼30 m from the base of the La Laja Fm. The narrow range of δ13C variation (−1.4 to +1.3‰) and87Sr/86Sr in the 0.709–0.710 range for the Caucete Group carbonates of the Pie-de-Palo Range, although unequivocally, appear to be in consonance with a Vendian to Tommotian age, reinforced by the presence of the trace fossils Didymaulichnus and Gordia.
19 citations
TL;DR: Celestite-bearing evaporite mineralization is common in the Tertiary evaporitic units of the Ulas-Sivas basin, East-Central Turkey as discussed by the authors, where it is known that the mineralization can be traced back to the 3rd millennium.
Abstract: Celestite-bearing evaporite mineralization is common in the Tertiary evaporitic units of Ulas-Sivas basin, East-Central Turkey.
14 citations
TL;DR: The Lower Cretaceous Chachao Formation in the Malargue anticline area consists of wackestone, packstone, and minor grainstone and mudstone rich in benthic fauna which were deposited in a shallow carbonate ramp as discussed by the authors.
Abstract: The Lower Cretaceous Chachao Formation in the Malargue anticline area consists of wackestone, packstone, and minor grainstone and mudstone rich in benthic fauna which were deposited in a shallow carbonate ramp. These shell beds are composed of a lowdiversity molluscan fauna mostly dominated by oysters, other benthic pelecypods (Eryphila sp.,Ptychomya sp.,Pecten sp.,Pinna sp.,Trigonia sp.,Cucullaea sp.), serpulids (Sarcinella sp.,Parsimonia sp.), and occasional ammonites (Olcosthepanus curacoensis).
14 citations
TL;DR: A reef monitoring program off Roatan, Bay islands, Honduras has produced base line data for platform bathymetry, major macrofauna distribution, and sediment attributes as discussed by the authors, and measurements of total suspended solids and sedimentation rate were made.
Abstract: A reef monitoring program off Roatan, Bay islands, Honduras has produced base line data for platform bathymetry, major macrofauna distribution, and sediment attributes. Because erosion accompanying accelerated island development will be increasing in the near future, measurements of total suspended solids and sedimentation rate were made. Results show TSS range from 8 to 70 mg/l in the summer and 30 to 222mg/l in the winter. Sedimentation rates in the fore reef, where finer-grained terrigenous material would potentially accumulate, are 0.14mg/cm2/day to 7.07mg/cm2/day in the summer and 41 to 71mg/cm2/day in the winter. The summer values are well within the ranges of published results from other Caribbean carbonate platforms, however winter values are up to ten times that of other localities.
14 citations
TL;DR: The Hirsizdere magnesite deposit is found in the upper Miocene-Pliocene lacustrine sediments of the cameli formation in the western Aegean depression zone, which was uplifted to form a broad anticline and in which consecutive faults and fractures developed due to the neotectonic activities as mentioned in this paper.
Abstract: The Hirsizdere magnesite deposit is found in the upper Miocene-Pliocene lacustrine sediments of the cameli formation in the western Aegean depression zone, which was uplifted to form a broad anticline and in which consecutive faults and fractures developed due to the neotectonic activities. Thick alternation of carbonate cemented and weakly cemented conglomerate, sandstone, mudstone intercalated with a few thin dolomite and magnesite layers is exposed at the lower part of the sequence. These units are overlain by magnesite and dolomite in association with thin claystone and sandstone layers and lenses. Green and claret red-brown smectite is observed in detrital materials as well as in sandy carbonate units, and is accompanied by serpentine, amphibole, illite, feldspar and quartz, whereas sepiolite is developed in the form of 3–5 cm thick, yellow and greenish brown colored veins, or as thin films liming parallel to the vein axis within the magnesite unit. SEM studies show that sepiolite fibers are grown in the form of meshworks and bridges between relict carbonate mineral grains. The presence of plant stem imprints, and the abundance of gastropod and ostracode shells in carbonate units indicate shallow and alkaline lake conditions. Field observations and detailed mineralogical, chemical and micromorphological determinations indicate that sepiolite is formed by diagenetical transformation of magnesite during the movement of silica-rich meteoric water through the fractures of carbonate units under near-surface alkaline conditions.
10 citations
TL;DR: The micro-caves exhibit a range of features dominated by speleothemic calcite, microborings, algal filaments, hyphae, and calcite spherulites, which support the role of micro-organisms in bioerosion and subsequent cementation of carbonate rocks in the terrestrial environment as discussed by the authors.
Abstract: Subaerial Quaternary limestones exposed on raised beach terraces on the Atlantic coastline north of Casablanca, Morocco, are undergoing rapid denudation by fungal and cyanobacterial destructive processes. Erosion is accomplished by penetration of the substrate by mycelia, including dissolution of carbonate substrate which subsequently becomes trapped in the biofilms in the photic zone along the terraces. The cyanobacteria cause biophysical disintegration, redistribution and biosynthesis of mineral components. Invasion of the pore space created by cyanobacteria is followed by microbially mediated carbonate cementation, beginning with the precipitation of several generations of crystallographically diverse carbonate cements. The micro-caves exhibit a range of features dominated by speleothemic calcite, microborings, algal filaments, hyphae, and calcite spherulites, which support the role of micro-organisms in the bioerosion and subsequent cementation of carbonate rocks in the terrestrial environment.
8 citations
TL;DR: Ooids occurring in the middle Jurassic-lower Cretaceous carbonate sediments of Akseki, Antalya (Turkey) are of two distinct kinds as mentioned in this paper : type 1 ooids are small and of irregular shape.
Abstract: Ooids occurring in the middle Jurassic-lower Cretaceous carbonate sediments of Akseki, Antalya (Turkey) are of two distinct kinds. Type 1 ooids are small and of irregular shape. They have 1 to 4 cortical laminae with a fine radial structure and patchy micritization. The nucleus of this type is composed of micrite and in places is not visible. In the radial part of this kind of ooid, microporosity and/or microopenings seem to be micro-borings. Type 2 ooids are large and well rounded with vaguely visible nuclei. They display fine concentric micritic laminae which coincide with endolithic microorganisms and microborings of fossils.
TL;DR: Capillary pressure curves are the basis for delineating a petrophysical facies as discussed by the authors, which is a mappable rock unit of similar Petrophysical characteristics, imparted by the depositional and diagenetic environment.
Abstract: A petrophysical facies is a mappable rock unit of similar petrophysical characteristics, imparted by the depositional and diagenetic environment. Capillary-pressure curves are the basis for delineating a petrophysical facies.
TL;DR: In this article, the nature and genesis of silt-size carbonate fractions in the Northern Red Sea was investigated via detailed SEM, XRD and ICP analyses of the sediments.
Abstract: The nature and genesis of silt-size carbonate fractions in the Northern Red Sea is investigated via detailed SEM, XRD and ICP analyses of the sediments. Results show that inorganic aragonite represents only 25% of the fine silt and clay fractions, but up to 60% of the total coarse silt. In general there is a compositional trend of increasing proportion of Mg-calcite with decreasing grain size of the sediments. Petrographic examination demonstrates that the coaree silt size carbonates are mainly composed of comminuted pieces of unaltered carbonate or micritized marine skeletal debris. On the other hand, the fine and very fine silt fractions are mainly composed of authigenic carbonate, formedin situ, and replacing the comminuted pieces of carbonate debris. The argument for the inorganic origin of the fine carbonate fractions is based on the detectable increase in the Sr content of aragonite, and the increasing proportion of Mg-calcite with decreasing grain size of the sediments. It is concluded that the Mg-calcite component provides a more important clue to the origin of the silt fraction. Micritization of skeletal grains is an important source of carbonate mud. Thus Mg-calcite from the Red Sea reefal sediments, either as skeletal or cryptocrystalline lumps, is the principal source of this component in the carbonate mud, especially in the clay size fractions. The Carbonate mud in the study area is mineralogically similar to the Belize carbonate mud, and differs from the Bahamss and Arabian gulf carbonate sediments.
TL;DR: In this article, combined field studies, thin-section examination and scanning electron microscopy were utilized to study the diagenesis of the Quaternary carbonates in twelve stratigraphic sections along the coastline of Qatar.
Abstract: Combined field studies, thin-section examination and scanning electron microscopy were utilized to study the diagenesis of the Quaternary carbonates in twelve stratigraphic sections along the coastline of Qatar. The sequence is dominated by calcarenites. It comprises three lithostratigraphic units representing two transgressive phases of the Pleistocene sea separated by a regressive phase. Diagenesis has modified the original textural and compositional characteristics of the Quaternary rocks considerably. Dissolution and cementation played major roles, whereas neomorphism and compaction were much less effective. Dissolution resulted in the development of fabric-and nonfabric-selective types of porosity. Cementation was mainly by calcite and, rarely, aragonite, gypsum and silica. Calcite crystals are nonferroan, mainly low-magnesian and have wide ranges of size, habit and distribution patterns. Aragonite cements are commonly crystals are nonferroan, mainly low-magnesian and have wide ranges of size, habit and distribution patterns. Aragonite cements are commonly isopachous and consist of fibrous and needle-like crystals. Massive and fibrous gypsum and cryptocrystalline and microcrystalline silica fill intergranular pores and microchannels. Aggrading and degrading neomorphism were selective. Compaction effects were more profound in calcarenites which were not subjected to early cementation. The diagenesis of the Quaternary carbonates occurred in a wide spectrum of settings which prevailed during the eogenetic, mesogenetic and telogenetic phases. The marine phreatic environment witnessed the commence of cementation with aragonite and high-magnesian calcite and the formation of micritic envelopes of fossil shells. The early phases of dissolution, micritization of other allochems and aggrading neomorphism occurred under mixed phreatic conditions. Most of the recorded diagenetic effects were developed in the meteoric vadose and phreatic environments. These include the completion of the dissolution events, the cementation with sparitic low-magnesian calcite, silica and gypsum, and the conversion of aragonite into low-magnesian calcite. There are remarkable variations in the nature and intensity of freshwater cementation throughout the sequence which indicate marked fluctuations in the groundwater levels.
TL;DR: In this paper, the dolomite reveals rather monotonous aphanocrystalline to very finely crystalline crystals (2-20 μm) composed of idiotopic or planar dolOMite fabric.
Abstract: Surface and near-surface sediments in southeastern part of the United Arab Emirates show extensive development of dolomite that is characterized by whitish, dense rocks, partially dissected by veinlets of gypsum and well-developed coarse calcite crystals. The dolomite reveals rather monotonous aphanocrystalline to very finely crystalline crystals (2–20 μm) composed of idiotopic or planar dolomite fabric. Densely packed dolomite aggregates of clotted texture are observed. Moreover, several horizons of peloidal textures are recognized. The fossil content includes freshwater molluscs, foraminifera and gastropods embedded in very fine dolomite crystals., whereas dolomite forming the skeletal grains is considerably coarser (about 40 μm). The most common carbonate porosity type is fossil moldic followed by vug and channel porosity. Interparticle and intraparticle porosity, that may suggest possible dissolution by later diagenetic fluids, are only locally significant. Vari-sized blocky sparry calcite crystals are frequently observed as pore-filling cement.
TL;DR: The Ingonish area of northern Nova Scotia offers the most extensive exposure of the Macumber Formation, the basal carbonate unit of the Lower Carboniferous (Middle Visean) Windsor Group of Nova Scotia and New Brunswick.
Abstract: The Ingonish area of northern Nova Scotia offers the most extensive exposure of the Macumber Formation, the basal carbonate unit of the Lower Carboniferous (Middle Visean) Windsor Group of Nova Scotia and New Brunswick. The area also shows tectonic-free sedimentary characteristics of this unit. The formation consists of two principal lithologic units, a basal, black, earthy, carbonaceous limestone normally about 0.5 m thick and a thinly stratified, peloidal dolomudstone up to 17.5 m thick. At Burke Head, the dolomudstone is cut by at least 25 massive tufa mounds, elongated in cross-section and intersecting their surrounding strata by rising northeastward at angles of 15 to 25 degrees. At east Ingonish Island the basal unit is anomalous in being both dolomitized and thicker (5 m); there, both units are cut by at least 20 smaller massive tufa mounds. The mounds at both localities formed over deep-water hydrothermal vents, i.e., marine hot springs; the fossils of abundant chemosynthetic tubeworms surround the lower mounds on east Ingonish Island. The Macumber Formation overlies Horton Group braided-stream facies sandstones, and presumably underlies nearby, thick gypsum deposits of the Windsor Group.
TL;DR: Wang et al. as discussed by the authors discussed the relationship between crustal movement and the distribution of hermatypic corals and found that Tabulata distribution is related to paleolatitude.
Abstract: Comprehensive study of hermatypic corals throughout geological time indicates that they commonly occurred in the northern hemisphere during the Paleozoic and that they migrated regularly and gradually southward. The distribution of Tabulata, in particular, is related to paleolatitude (Wang Baoyu 1994). This paper discusses the relationship between crustal movement and the distribution of hermatypic corals.