Mineral Clasts Research Articles

THE TRANSFORMATION OF CARBONIC SANDSTONE POROSITY OF THE DONBAS

Fuel and power complex of the country is in need for alternative energy sources, where methane being found in coal deposits can be considered as one in the range. The Donets Basin is a perspective area for extracting coalbed methane in the terms of energy resources concomitant. In order to evaluate the possibility of developing the Donbass as a coal gas deposit with complex exploitation it is needed extra research of reservoir rock properties. Previously established regularities of transforming open porosity and volume density of sandstones are of great practical importance, and are the basis for further studies of reservoir rock properties. In this paper, particular attention was paid to the study of transformations of sandstones closed porosity. To observe the transformation process of rocks closed porosity caused by changing conditions was used microscopic method is one of the applied ones giving the possibility to observe gas inclusions in clastic mineral grains at high magnification (from 100 to 1200 power with the use of immersion liquid). Presumably, these gas inclusions are a part of closed porosity so it is suggested to divide the closed porosity into the cement-closed porosity and mineralogical closed porosity. Mineralogical closed porosity can serve as an indicator of rocks transformation grade and the study of gas inclusion transformation taken place in sandstone quartz grains provides the partial answer to the issue of changing gas component in the rocks pore space with increasing rocks catagenesis stage.

Petrogenesis of Mantle Polymict Breccias: Insights into Mantle Processes Coeval with Kimberlite Magmatism

Mantle polymict breccias sampled by kimberlite magmas are complex mixtures of mantle minerals and rock clasts, cemented together by olivine, phlogopite, orthopyroxene, ilmenite, rutile and sulphides. Because of the kimberlite-like texture (i.e. mineral clasts of diverse origin and composition set in a magmatic matrix) and the large geochemical heterogeneity preserved in polymict breccias, these rocks are believed to derive from primitive or precursor kimberlite magmas. Therefore, the study of such xenoliths can provide constraints on the processes occurring in the mantle during the early stages of kimberlite ascent, and possibly on the composition of kimberlite melts. To constrain the petrogenesis of these unusual rocks, we have studied two samples of polymict breccia from the Bultfontein kimberlite (Kimberley, South Africa) and compared our results with published data for other polymict breccias. The most abundant phase in the matrix of the studied samples is olivine with a narrow range in Mg# (∼88–89), but variable Ni–Mn–Ca contents. Similar compositions are characteristic of magmatic olivine in the Bultfontein and nearby De Beers kimberlites. Orthopyroxene is the dominant phase in the matrix of polymict breccias surrounding clinopyroxene clasts, which, like the other silicate mineral clasts, are highly resorbed. The matrix orthopyroxene exhibits variable compositions, with significant enrichment in Ca, Na, Cr, Sr, Ba and light rare earth elements in the grains adjacent to clinopyroxene. The other main matrix phases (phlogopite, ilmenite and rutile) also display variable compositions. Matrix olivine hosts primary carbonate-rich inclusions similar to those observed in polymict breccia ilmenite. These inclusions were previously interpreted as an alkali-carbonate melt trapped during ilmenite growth. This alkali-carbonate melt may represent the parental melt to the matrix minerals of the polymict breccias. The variable composition of the matrix minerals is attributed to rapid, small-scale (centimetre to millimetre) variations in the melt composition owing to clast dissolution, possibly coupled with wall-rock assimilation, closely followed by fast cooling. Partial digestion of silicate porphyroclasts increased the Si content of the matrix melt, thus allowing crystallization of orthopyroxene. Further arguments in favour of a genetic relationship between polymict breccias and kimberlite magmas are provided by (1) similar Hf isotope compositions of polymict breccia ilmenite and South African kimberlites, (2) overlapping olivine compositions in polymict breccias and the host Bultfontein kimberlite, and (3) the occurrence of alkali-carbonate inclusions in polymict breccia and kimberlite minerals. Polymict breccias are interpreted as failed kimberlite intrusions, which metasomatized the magmatic conduit through which subsequent pulses of kimberlite magmas ascended. These wall-rock interactions would limit reactions between later pulses of kimberlite melt and mantle wall-rocks, thus enhancing the ability of kimberlite magmas to reach the surface.

Petrography and geochemistry of impactites and volcanic bedrock in the ICDP drill core D1c from Lake El'gygytgyn, NE Russia

AbstractThe 3.6 Ma old and 18 km diameter El'gygytgyn impact structure in NE Siberia was drilled in 2008/09 by ICDP (International Continental Scientific Drilling Program). A 517 m long core hole (D1c) was drilled into the outer flank of the central uplift structure, with an overall core recovery of approximately 63%. Thereby, approximately 315 m lake sediments and approximately 202 m impactites were recovered. Here, we present a detailed petrographic and geochemical assessment of the impact breccia and bedrock sections in this core. The 97 m long lower bedrock unit (517–420 m below lake floor [blf]) consists of an ignimbrite. In the overlying upper bedrock unit (420–390 mblf), the core recovered a sequence of similar ignimbrite and several decimeters of mafic rocks. We interpret these units as rocks that are located close to their former, preimpact position, but have been somewhat rotated due to collapse of the central uplift (i.e., it represents parautochthonous basement). From about 390 to 328 mblf occurs a suevite package with an impact melt poor, clast‐dominated matrix, and lithic and mineral clasts that cover the entire range of volcanic target rocks known from the El'gygytgyn region. All stages of shock metamorphism (unshocked to melted) were observed in clasts, and in microclasts of the matrix, of suevite from different depths. Immediately below this package, at the contact to the underlying bedrock, occurs a 1 m wide sheared zone within vitrophyric ignimbrite, which we consider the actual crater floor. The uppermost approximately 12 m, from 328–316 mblf depth, seem to comprise reworked suevite, consisting of a mixture of sediments and suevite with more and, on average, stronger shocked minerals than found in the main suevite unit. This includes a small component of glassy spherules and impact melt fragments. Toward the top of this unit, lake sediments progressively become the dominant material in this section. We assume that this unit contains a fallback component from the ejecta plume that was mixed with the first sediments of the postimpact crater lake, and possibly some rocks that slumped off the inner crater wall—similar to a thin layer at the base of the sediment section of borehole LB‐5A recovered in Lake Bosumtwi (Ghana).

Petrography and petrogenesis of some Indian basaltic achondrites derived from the HED parent body: Insights from electron microprobe analyses

Three Indian achondrites, viz., Bholghati howardite, Lohawat howardite and Pipliya Kalan eucrite and two other achondrites, viz., Bereba eucrite and Johnstown diogenite are studied for their petrography and mineral chemistry. All these achondrites are derived from the HED parent body. Both Bholghati and Lohawat howardites are polymict breccias and contain pieces of eucrites and diaogenites (lithic clasts), pyroxene and minor olivine as mineral clasts, and small proportion of ilmenite and pure iron metal. Eucrite clasts are noncumulate basaltic in nature, whereas diogenite clasts are mostly composed of orthopyroxene with minor clinopyroxene and anorthite. Both howardite samples contain orthopyroxene, pigeonite and augite. Notable characteristics observed in Lohawat howardite include crystallization of orthoenstatite first at a high-temperature followed by ferrosilite, pigeonite olivine and augite from a basaltic melt. Piplia Kalan eucrite is noncumulate, unbrecciated and basaltic in nature and display ophitic/sub-ophitic or hypidiomorphic textures. It contains ~60% pyroxenes (clinoenstatite and pigeonite) and ~40% plagioclase feldspars (bytownite to anorthite). The observed mineralogy in the Piplia Kalan eucrite suggests its crystallization from a high-temperature basaltic melt crystallized at low pressure. Two other achondrite samples, viz., Bereba eucrite and Johnstown diogenite are also studied. The Bereba eucrite shows cumulate nature which is probably formed by small-degree melts of ilmenite-bearing gabbro, whereas the Johnstown diogenite crystallized from a slow cooling of a Ca-poor basaltic melt derived from cumulates formed from the magma ocean, similar to the origin of the noncumulate eucrites.

Molluscan mulching at the margins: investigating the development of a South Island Māori variation on Polynesian hard mulch agronomy

AbstractHard mineral clast sediments applied to dry archaeological fields in the distant apical islands of the Polynesian triangle are frequently associated with sweet potato / kūmara (Ipomoea batatas (L) Lam.) cultivation. In a novel variation on this practice, north‐western South Island Māori deposited tuangi (Austrovenus stutchburyi (Wood, 1828)) mollusc beach valves to cap 10–20 cm deep planting holes or pits by or around the sixteenth century AD at Triangle Flat, Golden Bay. Discrete tuangi beach valve sediment had been extended over much of the larger field surface in association with shallow (<10 cm deep) planting depressions. Surface shell deposits would have suppressed weed growth, redirected radiant energy onto young kūmara plants, and conserved planting pit soil and moisture against disruptive and desiccating winds, respectively. The temporal extension of Triangle Flat shell sediment could be related to socio‐economic and political pressures to improve kūmara production from a fixed land unit. However, since climate change beginning in the sixteenth century brought cooler temperatures and eventually, stronger westerly winds to this region, it seems more likely that shell mulch was extended to maintain shallow planting soils and production in a colder, windier period. This local, kūmara‐focused development may have been encouraged by the opportunity to apply ritually safe and perhaps spiritually potent, uncooked tuangi beach shell to tapu cultivation surfaces.

Geologic and economic potentials of minerals and industrial rocks in Jordan

This work discusses status of the geologic and economic potentials of minerals and industrial rocks in Jordan. The major mineral resources are presented in details and the paper is designed to cover the lack of published data in this field. Geologically, the structural framework of Jordan is controlled largely by Arabian Nubian Shield in the south, block—faulted areas in the east, upwarping in north and east, and Wadi Araba-Dead Sea Transform Fault in the western part. The geologic environments include Precambrian crystalline basement (Late Proterozoic) of Arabian Nubian Shield (ANS) that is composed of igneous and metamorphic rocks at south-western part. Paleozoic rocks at southern and southeastern part consist of clastic minerals which are dominated by sandstone, whereas Mesozoic sedimentary rocks are widespread throughout southwestern, northern to southeastern parts of the country. They mainly consist of major industrial rocks and minerals such as phosphate, oil shale, limestone, dolomite, chalk, marble, gypsum, diatomite and tripoli. Cenozoic Era is composed of sedimentary and volcanic rocks in different parts of Jordan. There are more than twenty nonmetallic minerals and four main metallic deposits within the various geologic environments. This paper summarizes their distribution, chemical and mineralogical characteristics, in addition to their production statistics.

Sedimentology and origin of Meyghan lake/playa deposits in Sanandaj–Sirjan zone, Iran

The inland lake/playa of Meyghan is a closed basin in the Sanandaj–Sirjan tectonic zone of Iran, containing largest mineable sodium sulfate deposit of the Middle East. The Late Pleistocene–Holocene sediments of this lake/playa were studied for sedimentological and mineralogical characteristics, brine evolution path and the record of climatic variations in the area. Minerals of this lake/playa are mainly evaporites along with some fine-grained clastic components. Evaporite minerals include calcite, gypsum, halite, glauberite, thernadite, polyhalite, natron along with minor volumes of bassanite and sylvite. Gypsum and halite abundances show increasing trend from margin to the center forming a Bull’s-eye pattern. Main clastic components are fine-grained quartz, muscovite, clay minerals, calcite and organic matters. Clay minerals are the most dominant clastic minerals in these sediments. In the surface sediments of Meyghan lake/playa, illite and chlorite abundances reduce from the margin to the center which is contrary to the general patterns of clay distribution in other playas. Inflowing water with low percentage of ions and Na–(Ca)–(Mg)–SO4–Cl–(CO3) type evolve into a brine with high ions concentration during the geochemical evolution and mineral deposition. Finally, geochemical evolution resulted in a Na–SO4–Cl type brine. While clastic components (calcite, quartz and so on) show increasing trend with depth, evaporites abundances show opposite trends. Furthermore, the average grain size of sediments increases with depth indicating higher energy in the past. Typical sedimentary structures of lake/playa environment that are present include efflorescent salt crusts composed of halite, tepees, polygonal structures as the most common sedimentological features of this basin as well as Puffy Grounds. In conclusion, sedimentary records of this lake/playa represent important climatic changes in the area from relatively more humid cold climate in the Late Pleistocene to semi-arid warm climate in the Holocene, with higher evaporation rate.

Interpreting U–Pb data from primary and secondary features in lunar zircon

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U–Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th–U–Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal–plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U–Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal–plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U–Pb isotopic systems.

국내 석회동굴(고씨동굴, 백룡동굴, 성류동굴)에 분포하는 박쥐 구아노의 광물학적 특성

동굴 속에서 박쥐 배설물에 의하여 형성된 구아노에는 쇄설성 광물과 더불어 배설물 내의 성분과 주변 암석과의 반응 등을 통하여 생성된 다양한 황산염 및 인산염 광물들이 존재한다. 따라서 이러한 광물들의 연구는 광물형성에 영향을 미치는 동굴 내 지구화학적 환경에 대한 기본적인 정보를 제공한다. 본 연구는 국내의 대표적인 세 석회동굴에서 구아노의 시료를 채취하여 이들에 대한 광물학적 특성과 화학 성분 비교를 통하여 동굴 내 구아노를 구성하는 기본적인 광물 성분을 밝히고 이들의 특성에 영향을 미치는 인자를 도출하고자 실시되었다. 연구 결과 고씨동굴의 경우 채취된 시료에서 운모, 석영, 장석과 같은 쇄설성 광물과 더불어 많은 양의 석고가 함께 산출되었다. 석고의 양은 하부로 갈수록 증가하며 이것은 백룡동굴과 석류동굴과는 다른 특징이다. 백룡동굴의 시료는 쇄설성 광물로 카올리나이트를 추가적으로 포함하며 상대적으로 매우 적은 양의 석고를 포함한다. 성류동굴 시료의 경우 쇄설성 광물의 성분은 고씨동굴과 같으나 석고 대신 바사나이트가 미량으로 관찰된다. 이러한 광물의 분포는 구아노 시료의 화학분석 결과와 일치한다. 이러한 결과를 종합하여 볼 때 고씨동굴에서는 많은 양의 박쥐 배설물로부터 상대적으로 습도가 높거나 홍수가 자주 일어나는 환경에서 이차광물이 형성되었음을 의미한다. 또한 성류동굴의 경우는 비교적 건조한 환경에서 생성되는 바사나이트의 존재로 미루어 볼 때 다른 동굴에 비하여 상대적으로 건조한 환경에서 생성되었음을 지시한다. The guano formed from the bat excrement in a cave contains various sulfate and phosphate minerals formed from the reaction of bat excrement with surrounding rocks and clastic minerals. Therefore, the mineral compositions in the guano provide basic informations on the geochemical environments affecting mineral formation in a cave. This study was conducted to study the mineral compositions of guano and the factors affecting those compositions by comparing mineralogical and chemical compositions in three different limestone caves in Korea. The guano samples in Gossi Cave contain detrital minerals such as illite, quartz and feldspar and relatively large amount of gypsum. The contents of gypsum increase with increasing depth, which is different from the samples collected in other caves. The samples collected from Baekryong Cave have the similar mineral compositions to those in Gossi Cave, but they also contain additional kaolinite and very small amount of gypsum. The samples in Sungryu Cave have similar mineralogical compositions to those in Gossi Cave, but contian bassanite instead of gypsum. The mineralogical compositions are well correlated with the chemical compositions of guano. The mineral compositions indicate that, in Gossi Cave, the minerals were formed by the reaction of large amount of bat excrement with surrounding rocks in high humidity condition or in the condition of frequent floods. In the case of Sungryu Cave, bassanite which can be formed in a dry condition indicates that minerals were formed in a relatively low humidity condition.

Coal petrography, mineralogy and geochemistry of lignite samples from the Ogwashi–Asaba Formation, Nigeria

Organic sediments picked up randomly from seven small outcrops within the Ogwashi–Asaba Formation, southern Nigeria, are examined and evaluated by means of coal petrology and chemical and mineralogical analyses in order to determine the palaeoenvironmental conditions and the factors controlling their formation. Six samples proved to be low-rank coals C to B (lignite), one carbonaceous shale. The lignite samples display low ash yield, low telohuminite and high detrohuminite and liptinite contents; they contain small amounts of clastic minerals, mainly quartz and clays, which point to the topogenous character of the depositional palaeoenvironment. The palaeomires formed in a continental basin crossed by the mid-Tertiary palaeo-Niger River; the latter, as well as the tropical rainfall supplied the mires with water. The dense vegetation cover on the mire surface and the surroundings and/or the low relief energy of the broad area restricted the inorganic influx resulting in high-grade coal formation. As the outcrops are distributed over a distance of 60km, the expected reserves of good quality lignite constitute a very promising exploration target.

A provenance study of mineral matter in coal from Appalachian Basin coal mining regions and implications regarding the respirable health of underground coal workers: A geochemical and Nd isotope investigation

Abstract This study presents geochemical data produced from the analysis of coal and adjacent rock samples retrieved from coal mining regions in the U.S. to examine mineral matter provenance. Study sites included the Northern Appalachian Basin, where the units of interest were the Lower Kittanning Coal bed, the overlying Columbiana Shale, and the underlying paleosol (Allegheny Formation). Additional study sites were located in the Central Appalachian Basin, where sampling was conducted on strata associated with multiple coal beds of Middle and Lower Pennsylvanian age. The Central Appalachian Basin rock and coal samples were much lower in overall mineral matter and contained very little carbonate (calcite and siderite) or pyrite mineralogy, which was common at the Northern Appalachian Basin sites. Elemental analysis of rock samples indicated a trend of enrichment in Ca, Mg, Mn, Na, and K cations in the immediate overburden compared to the underlying rock in the Central Appalachian Basin. A similar trend was observed in coal related strata from the Northern Appalachian Basin which was attributed to epigenetic marine incursions. Rare earth element (REE) concentrations were determined in the samples, and showed Eu and Ce anomalies when normalized by chondritic values. The total REE content of the overburden is generally less than that of the underlying rock units. Neodymium isotopic analysis of the Lower Kittanning coal, overburden, and paleosol from the Northern Basin indicate partial resetting of the Sm–Nd system close to the time of deposition. The data indicate a common Appalachian source for the clastic mineral matter in the overburden, underclay, and coal mineral matter. The geochemical findings of this study may provide a viable method for distinguishing respirable dust sources in both Appalachian Basins. There are potential applications for this research to aid in the respiratory health of underground coal miners.

Structure and sedimentary formations of the northern Yana-Kolyma Fold System, Yakutia

The structure, geodynamics, and sedimentary formations of the northern Yana-Kolyma Fold System and the adjacent part of the Verkhoyansk Fold System are considered on the basis of the published sheets of the State Geological Map on a Scale of 1: 200000, field observations of the authors, and literature sources. The important structure-forming role of the frontal uplift of the Kolyma-Omolon Superterrane that was thrust over in the northwestern direction is shown. The at-least-twofold shortening, thrust faulting, and large-scale offsets of the large blocks of the distal part of the Verkhoyansk continental margin and the Nagondzha paleotrough are related to this effect. An attempt is made to settle some debatable questions concerning the tectonic position of the Kular Uplift, the cause of the inconsistent structural patterns of the Jurassic and Triassic sequences at the southwestern margin of the Polousnyi Synclinorium, the counter vergence of folds in its northern and southern zones, the regional tectonic evolution in the Late Jurassic, and the eastward change in the composition of the heavy clastic mineral assemblages contained in the Upper Triassic and Jurassic rocks.

Sedimentary geochemical response to human impact on Lake Nõmmejärv, Estonia

INTRODUCTION A number of palaeoecological investigations have proved that the geochemical composition of lake sediments serves as a valuable archive of information for the reconstruction of natural as well as human-induced processes that shape the present character of a lake's ecosystem (Engstrom & Wright, 1984; Birks & Birks, 2006; Battarbee et al., 2007). The use of chemical proxies is particularly important for analysis of sediments that accumulated during the last centuries when intensified human activities began to alter natural biogeochemical pathways, causing disturbance of natural systems at an elemental level (Boyle, 2001; Tylmann, 2005; Punning et al., 2007). Previous investigations show that during the last century the natural ecosystem of Lake Nommejarv in NE Estonia became affected by human activities that resulted in significant alterations in its sediment and water composition as well as in its ecological status (Vesiloo, 1987; Sagris, 1989; Varvas, 1994; Punning et al., 1997). As a result of the implementation of environmental protection measures and the political transition at the beginning of the 1990s, the industrial impact in the area connected with oil shale mining and power plants has become less pronounced. A complex palaeoecological study, which was carried out at the beginning of the 1990s, showed that this factor seems to positively contribute to a decrease of pollution connected with atmospheric fallout as well as to the overall tendency of the lake ecosystem to return to pre-disturbance conditions (Punning et al., 1997). Based on geochemical and stable isotope proxies, this study aims to describe the changes in the geochemical composition of the sediment as a response to the presumed reduction in the human impact on the lake during the last 20 years. It also attempts to detect what anthropogenic factors continue to control the present state of the lake. To document and understand the ways in which human impact on the ecosystems interacts with natural processes is one of the essential prerequisites for establishing sustainable and efficient land management (Oldfield & Dearing, 2003). STUDY AREA Lake Nommejarv is located in NE Estonia (58[degrees]03' N and 26[degrees]30' E) in the western part of the Kurtna lake district (Fig. 1). The lake is 15 ha in area and its maximum depth is 7 m (Varvas & Punning, 1993). Its catchment has a forested area in its western and eastern parts, peatland to the north, and arable land in the south (Fig. 1a). Human influence began to intensify at the end of the 19th century when drainage of the surrounding bogs and pastures started. During the 1920s, the natural flow of the Raudi Stream (Fig. 1a) was directed to the lake, changing it from a closed to an open system. Local human impact on the lake continued to increase with the construction of a military camp on the shore at the beginning of the 1930s, which was used then for military and later, including today, for tourist activities (Punning et al., 1997). At the beginning of the 1950s, oil shale mining began in the vicinity of the Kurtna lake district. Expansion of oil shale mining and related industries such as oil-shale-based power engineering became a strong industrial factor in the region (Erg, 2003). Local kukersite oil shale forms horizontal sequences in the limestone from which it has been extracted in underground mines. To facilitate the discharge of groundwater from mines, several Kurtna lakes have been utilized and interconnected with channels. In 1970 the Raudi Stream was completely transformed into an artificial channel and mine water started to flow through Lake Nommejarv. Variation in the discharge has been largely governed by seasonal fluctuations and the volume of mining waters (from 25 000 to 54 000 [m.sup.3] [h.sup.-1]) (Sagris, 1989). Water is also carrying mine clastic mineral debris, which consists of carbonate matter, siliciclastic (silica-bearing sedimentary rock) particles, and oil shale remains and is high in sulphate ions and calcium (Bauert & Kattai, 1997; Erg, 2003). …

A POSSIBLE MESOARCHAEAN IMPACT STRUCTURE AT SETLAGOLE, NORTH WEST PROVINCE, SOUTH AFRICA: AEROMAGNETIC AND FIELD EVIDENCE

A 25 to 30 km wide magnetic anomaly within the >2.79 Ga granite-greenstone rocks of the northwestern Kaapvaal Craton is spatially associated with megabreccia outcrops near the village of Setlagole in the North West Province, South Africa. The breccia comprises angular to rounded clasts of TTG gneisses, granites and granodiorites, with lesser amounts of amphibolite, calc-silicate rock and banded iron-formation as well as unusual dark grey to black, irregular, centimetre- to decimetre-sized clasts that show evidence of fluidal behaviour and plastic deformation during incorporation into the breccia. The largest clasts reach up to several metres in size. Evidence of fluvial transport is found in rare thin sandy to gritty layers that show crude bedding and upward-fining with layers dipping gently to the northeast. The breccia matrix is highly variable but is dominated by angular mineral clasts (mainly quartz and feldspar, with subsidiary biotite, amphibole and epidote) with interstitial chlorite. The clasts show variable amounts of alteration (saussuritization, sericitization, chloritization of biotite and amphibole). The dark clasts contain angular quartz and feldspar and small biotite fragments in a cryptocrystalline chlorite-dominant matrix. Textures indicate a lower greenschist facies metamorphic overprint. The absence of lava, dolomite or quartzite clasts suggests that the breccia formed prior to the deposition of the Neoarchaean Ventersdorp and Eoproterozoic Transvaal Supergroups, whereas the metamorphic grade indicates that it postdates the ca. 2.79 Ga amphibolite-facies metamorphic peak in the region. This suggests a late Mesoarchaean or early Neoarchaean (ca. 2.79 to 2.71 Ga) age for the breccia. A similar age is inferred for the magnetic anomaly based on postulated cross-cutting dyke ages. Despite a comprehensive search, unequivocal shock-diagnostic microdeformation features have not yet been found in either the breccia or the highly-weathered granitic gneiss outcrops in the central parts of the anomaly. The unusual plastically-deformed dark clasts may represent chloritized mud clasts or impact melt clasts. Geochemical data on these clasts and other components of the megabreccia provide no conclusive support for a meteoritic origin, but the unparalleled composition of the clasts and their high trace element abundances of Ni, Cr, V, Zn and Co relative to rocks of the Kraaipan granite-greenstone basement, suggests an unusual origin for this matrix material. Given the distinctive nature of the breccia and its proximity to a large circular magnetic anomaly, it is postulated that the megabreccia could represent a mass or debris flow in a marine setting triggered by an impact tsunami or resurge. Subsequent faulting may have led to the preferential preservation of these deposits. This interpretation of the Setlagole megabreccia and geophysical anomaly is evaluated in terms of other possible modes of origin and it is concluded that a meteoritic source best fits the available data.

Microstratigraphic and multi-analytical evidence for advanced Neanderthal pyrotechnology at Abric Romani (Capellades, Spain)

The complexity of social behaviour by Neanderthal communities is consolidated by illustrating the sophistication of fire-linked activities in their home-based contexts. This was achieved by relating the microfacies analysis of cultural deposits to combustion structures at the Abric Romani (Capellades, Spain). The geometry and nature of cultural microfacies from a selection of hearths and their surrounding empty areas were characterized in thin sections. The related bulk fraction from the distinctive individual microstrata was extracted, water-sieved and examined under the binocular microscope. The selective micro-sampling was performed from the collection of undisturbed blocks in combustion structures of layer J (1995 excavation). The procedure was applied to combustion structures from the lower layer O (2009 excavation). The integrated micromorphological observation and binocular sorting allowed identification of a similar assemblage of components that are closely linked to distinctive anthropic microfacies. Individual grains were characterized by ESEM-EDAX, X-ray diffraction, and Raman spectrometry. X-ray fluorescence analysis was performed on the host matrix. The specific association of remarkable components/cultural microfacies is identical for the combustion structures of layers O and J. The four groups components identified comprise carbonaceous polymorphs, allochthonous mineral clasts, organo-phosphatic compounds, and native metals. The phase association of organic and mineral phases allowed recognition of a common natural precursor rich in hydrocarbon species and metallic compounds that were probably extracted from a Miocene source. Microscale analysis in thin sections linked the combustion microfacies to the transformation contexts of the metal-rich carbonaceous precursors. Heat-resistant polymers and graphitic components associated with wood ash are suggested to trace pyrolitic residues from flaming combustion. The intimate mixing of the metal-rich carbonaceous polymorphs to finely crushed heated bones allowed identification of pyrogenic transformations of the fossil fuel with fresh biomass. Analysis at microscale in thin sections linked the processed by-products to finely prepared and meticulously consolidated surfaces showing distinctive colours: yellow, brown, blue, green, red, white, and black. The repeated surface preparation and their exceptional preservation at microscales illustrate the great concern of Neanderthal occupants for maintaining the long term memory of their carefully designed home space. The recognition of advanced pyrotechnology by using fossil fuels for lighting, firing, spatial design, colouring in the combustion structures of Abric Romani incites speculation on the exceptional social status of this home-based camp site. Further development of the microfacies/multi-analytical analysis should more deeply penetrate the social sophistication of Neanderthal communities.

Influence of hydrodynamic regime on the mineral composition of deep-sea sediments

The composition of sand-silt and pelite fractions of deep-sea sediments deposited under different hydrodynamic conditions was studied. Assemblages of clastic, clayey, biogenic, and authigenic minerals formed under the influence of surface and bottom currents were traced. It is shown that biogenic opal, fine-dispersed celestobarite, and authigenic protosyngenetic ferromanganese micronodules, which are composed of only manganese phases, represent indicators of cyclonic gyres characterized by enhanced bioproductivity. Collophane (bone detritus), phillipsite, palagonite, and large celestobarite crystals prevail in mineral assemblages below the anticyclonic gyres, whereas ore micronodules are depleted in manganese. Surface and bottom currents control the distribution of clastic (terrigenous edaphogenic, terrestrial-volcanogenic) and clay minerals, as well as biogenic opal in the form of Ethmodiscus frustules in sediments. Edaphogenic mineral assemblages represent the reliable indicators of bottom currents.

Lithology, mineral assemblages and microbial fingerprints of the evaporite-carbonate sediments of the coastal sabkha of Abu Dhabi and their extraterrestrial implications

AbstractDeep-core and surface samples collected from the coastal sabkha of Abu Dhabi were subjected to a multi-proxy study, including petrographic, geochemical and spectroscopic analyses. The sediments studied are composed of biochemical carbonate-evaporite mineral suites, such as calcite, dolomite, aragonite and gypsum, as well as clastic minerals, such as quartz, feldspar and serpentine. These sediments were also strongly influenced by microbial activities as reflected by the presence of cyanobacterial mats, boring, gas bubble structures, pustular and other macro and micro textures. A combination of marine, fluvial, aeolian, and groundwater processes shaped the geomorphology of the area and led to the formation of such mineral suites, as well as their microbial contents. Data collected from Mars indicate that its surface regolith contains sandstone composed of siliciclastic basaltic debris, as well as carbonate (e.g. magnesite) and evaporite (e.g. jarosite and relics of gypsum) mineral assemblages. Additional data suggest the presence of geomorphic features, characteristic of an arid climate, such as sand dunes and desert varnish. The hydrological model for the Late Noachian-Hesperian period of the plant proposed the existence of a surficial layer containing endolithic and stromatolitic cyanobacterial lamina. The combination of the coastal sabkha of Abu Dhabi with its carbonate-evaporite mineral suites, the neighbouring sand dune fields of the Empty Quarter Desert and the basaltic sediments resulted from weathering the ophiolitic Northern Oman Mountains to form a candidate terrestrial geologic province that may explain the mineral association of Mars and its potential biosignatures. The lithological features and the mineral association of the sabkha can be recognized by the present day detection equipment used on Mars, and even if their biosignatures are degraded, their existence may be inferred from these features.

Matrix and whole-rock fractionations in the Acfer 094 type 3.0 ungrouped carbonaceous chondrite

Abstract– We used the electron microprobe to study matrix in the ungrouped type 3.0 carbonaceous chondrite Acfer 094 using 7 × 7-point, focused-beam arrays; data points attributable to mineral clasts were discarded. The grid areas show resolvable differences in composition, but differences are less pronounced than we observed in studies of CR2 LaPaz Icefield (LAP) 02342 (Wasson and Rubin [2009]) and CO3.0 Allan Hills A77307 (Brearley [1993]). A key question is why Acfer shows an anomalously uniform composition of matrix compared with these other carbonaceous chondrites. Both whole-rock and matrix samples of Acfer 094 show enhancements of Ca and K; it appears that these reflect contamination during hot desert weathering. By contrast, the whole-rock abundance of Na is low. Although weathering effects are responsible for some fractionations, it appears that nebular effects are also resolvable in matrix compositions in Acfer 094. As with LAP 02342, we infer that the observed differences among different areas were inherited from the solar nebula and may have been carried by porous chondrules that experienced low (about 20%) degrees of melting. Acfer 094 has been comminuted by one or more impact events that may also have caused volatile loss. Thus, despite preserving evidence (e.g., an exceptionally high content of presolar SiC) implying a high degree of pristinity, Acfer 094 is far from pristine in other respects. This evidence of comminution and an O-isotopic composition similar to values measured in metamorphosed CM chondrites suggest that Acfer was hydrated before being outgassed by the inferred impact event. Convection within the plume associated with the impact event probably also contributed to the homogenization of the Acfer 094 matrix.

The comparative behavior of apatite‐zircon U‐Pb systems in Apollo 14 breccias: Implications for the thermal history of the Fra Mauro Formation

Abstract— We report secondary ion mass spectrometry (SIMS) U‐Pb analyses of zircon and apatite from four breccia samples from the Apollo 14 landing site. The zircon and apatite grains occur as cogenetic minerals in lithic clasts in two of the breccias and as unrelated mineral clasts in the matrices of the other two. SIMS U‐Pb analyses show that the ages of zircon grains range from 4023 ± 24 Ma to 4342 ± 5 Ma, whereas all apatite grains define an isochron corresponding to an age of 3926 ± 3 Ma. The disparity in the ages of cogenetic apatite and zircon demonstrates that the apatite U‐Pb systems have been completely reset at 3926 ± 3 Ma, whereas the U‐Pb system of zircon has not been noticeably disturbed at this time. The apatite U‐Pb age is slightly older than the ages determined by other methods on Apollo 14 materials highlighting need to reconcile decay constants used for the U‐Pb, Ar‐Ar and Rb‐Sr systems. We interpret the apatite age as a time of formation of the Fra Mauro Formation. If the interpretation of this Formation as an Imbrium ejecta is correct, apatite also determines the timing of Imbrium impact. The contrast in the Pb loss behavior of apatite and zircon places constraints on the temperature history of the Apollo 14 breccias and we estimate, from the experimentally determined Pb diffusion constants and an approximation of the original depth of the excavated samples in the Fra Mauro Formation, that the breccias experienced an initial temperature of about 1300–1100 °C, but cooled within the first five to ten years.

Playas of the Thar Desert: Mineralogical and Geochemical Archives of Late Holocene Climate*

This study presents a synthesis of the published data and summarizes new data on mineralogy and geochemistry of the late Holocene playa sediments from the Thar Desert, located in the down stream of southwest monsoon. The eastern margin of the Desert is semi-arid (>400 mm a -1 ), whereas the western region is arid (200-300 mm a -1 ). The negative water budget (higher evapo-transpiration/precipitation) has led to the presence of a number of playas in the region. The assemblage of clastic minerals is similar and constitutes quartz, plagioclase, K-feldspar, amphibole, mica and chlorite. The non-clastic mineral assemblage is variable and comprises of both evaporite minerals and carbonates. The geochemical proxies enabled differentiation of the shallow depth profiles at five different playas into horizons of varying chemical weathering, aeolian input and evaporation. Between ca.1.3-3.1 ka, the dominance of proto-dolomite, [Ca >1 (Fe,Mg) (CO 3 ) 2 ] in the eastern playas and presence of gypsum (CaSO 4 .2H 2 O) in the western playas suggest that the present day climatic gradient might be exiting during the late Holocene.