Calcareous Sandstone Research Articles

Maastrichtian to Paleocene depositional environment of the Dakhla Formation, Western Desert, Egypt: sedimentology, mineralogy, and integrated micro- and macrofossil biostratigraphies

Integrated sedimentology, mineralogy, geochemistry, and microfossil and macrofossil biostratigraphies of the Maastrichtian–early Paleocene Dakhla Formation of the Western Desert, Egypt, provide improved age resolution, information on the cyclic nature of sediment deposition, and the reconstruction of depositional environments. Age control based on integrated biostratigraphies of planktic foraminifera, calcareous nannofossils and macrofossils yields the following ages for stratigraphic and lithologic sequences. The contact between the Duwi and Dakhla formations marks the Campanian/Maastrichtian boundary (zone CF8a/b boundary) and is dated at about 71Ma. The age of the Dakhla Formation is estimated to span from 71Ma at the base to about 63Ma at the top (zones CF8a–Plc). The Cretaceous/Tertiary (K/T) boundary is within the upper unit of the Kharga Shale Member and marked by a hiatus that spans from 64.5Ma in the lower Paleocene (base Plc) to at least 65.5Ma (base CF2, base M. prinsii zones) in the upper Maastrichtian at Gebel Gifata, the type locality of the Dakhla Formation. As a result, the Bir Abu Minqar horizon, deposited between about 64.2 and 64.5Ma (Plc(l) zone), directly overlies the K/T boundary hiatus. Major hiatuses also span the late Maastrichtian–early Paleocene in sections to the northwest (c.61.2–65.5Ma at North El Qasr, c.61.2–69Ma at Bir Abu Minqar and c.61.2–65.5Ma at Farafra), and reflect increased tectonic activity.During the Maastrichtian–early Paleocene a shallow sea covered the Western Desert of Egypt and the clastic sediment source was derived primarily from tectonic activity of the Gilf El Kebir spur to the southwest of Dakhla and the Bahariya arch. Uplift in the region resulted in major hiatuses in the late Maastrichtian–early Paleocene with increased erosion to the southwest. The area was located near the palaeoequator and experienced warm, wet, tropical to subtropical conditions characterized by low seasonality contrasts and predominantly chemical weathering (high kaolinite and smectite). A change towards perennially more humid conditions with enhanced runoff (increased kaolinite) occurred towards the end of the Maastrichtian and in the early Paleocene with shallow seas fringed by Nypa palm mangroves. Sediment deposition was predominantly cyclic, consisting of alternating sandstone/shale cycles with unfossiliferous shales deposited during sea-level highstands in inner neritic to lagoonal environments characterized by euryhaline, dysaerobic or low oxygen conditions. Fossiliferous calcareous sandstone layers were deposited in well-oxygenated shallow waters during sea-level lowstand periods.

Chronostratigraphy of aeolianites from the Sharon Coastal Plain of Israel

The Sharon Coastal Plain in Israel is composed mainly of sand dune fields and aeolianite ridges. Three major sand accumulation periods are documented in the terrestrial record along the cliffs of the Sharon Coastal Plain, between 65 to 50 ka, from 7 to 5 ka and from 5 to 0.2 ka. These seem to correlate with the periods of sapropel formation in the Mediterranean Sea and so with periods of strongly increased African monsoon activity. The accumulation of the stratigraphically oldest aeolianite (Kurkar, Unit 5) appears to correlate with sapropel S2, formed about 55 ka BP. The uppermost aeolianite (calcareous sandstone, Unit 2) seems to correlate with sapropel S1, formed at about 7.8±4.0 ka BP. Major soil formations occurred between 35 and 25 ka resulting in a Rhodoxeralf soil/Grumusolic Dark Brown soil, and between 15 and 12 ka resulting in a Rhodoxeralf (hamra) soil. At least seven weak weathering horizons (regosol-type soils) are intercalated in the aeolianite of Unit V and two regosols are present in the Holocene aeolian sand of Unit I.

Impact of urbanization on hydrochemical evolution of groundwater and on unsaturated-zone gas composition in the coastal city of Tel Aviv, Israel

The coastal city of Tel Aviv was founded at the beginning of the 20th century. The number of its inhabitants and its water consumption increased rapidly. This study analyses a 15-year record (1934–1948) of pre-industrial development of groundwater chemistry in the urban area. Archive data on concentrations of major ions, dissolved gases (CO 2 and O 2), organic matter, and pH were available for each half-year during the period of 1934–1948. The major factors causing changes in the chemistry of groundwater flowing in three sandy sub-aquifers have been seawater encroachment due to overpumping, and infiltration of effluents from pit-latrine collectors. Influence of these factors decreases with depth. Landward-penetrating seawater passed through clayey coastal sediments, interbedded among sands and calcareous sandstones, and spread into the Kurkar Group aquifer. This has led to exchange of sodium (dominant in seawater) with calcium adsorbed on clay particles, enriching groundwater with calcium. Intensity of cation exchange decreases inland and with depth. Infiltration of pit-latrine effluents has introduced large amounts of ammonium into the unsaturated zone. Its rapid oxidation in unsaturated sediments has caused massive nitrate production, accompanied by pore-water acidification. This process induces dissolution of vadose carbonate, resulting in enrichment of groundwater recharge in calcium. Anthropogenically induced dissolution of calcite in the unsaturated zone has been the major factor for the increase of Ca 2+ concentration in groundwater, accounting for about 80% of this increase. In the interface zone, an additional 20% of calcium has been supplied by cation exchange. Owing to pH increase caused by denitrification in the aquifer, Ca 2+-rich waters supersaturated with calcite could be formed, especially in the capillary fringe of the uppermost sub-aquifer, which could induce calcite precipitation and ultimately lead to the cementation of sandy aquifers. Urban development has caused drastic changes in the gas content in the unsaturated zone and in groundwater. Carbon dioxide was intensively generated by nitrification–denitrification processes, by hydration of urea, to a lesser degree by oxidation of organic matter, and probably by anoxic biodegradation of organics. Between 1934 and 1948, concentrations of CO 2 in unsaturated sediment air rose from 3.2% to 7.6%. In the unsaturated zone, oxygen consumption for oxidation of ammonium and organic matter lowered O 2 concentrations in sediment air to unusually low values of 3.9–12.9%. Nitrification in the urban unsaturated zone could thus serve as a pump, sucking in atmospheric oxygen at a rate of about 0.3–0.5 g m −2 day −1. The extreme concentrations of CO 2 and O 2 in unsaturated sediments have been preserved due to production and consumption of gas under conditions of diminishing areas open to the atmosphere, uncovered by buildings and by roads.

Thermo-Hygrometric Evaluations in the Recovery of Rocky Buildings of the “Sassi of Matera”(Italy)

The Sassi of Matera are a very interesting example of a rocky settlement. The limestone walls often present high moisture content which negatively influences the room microclimate. In the first part of this paper, rooms without evident problems of moisture were analyzed for the purpose of carrying out a statistical analysis, to be repeated in analogous situations and to identify the distribution of what we can define as background moisture of the rocky installation. The knowledge of moisture, however, greatly influences the evaluation of heat loss since thermal conductivity of a material increases with an increase in the percentage of water that is contained within it. Consequently, the second part of the paper deals with thermal conductivity and other thermal physical properties related to the moisture of the calcareous sandstone present in the installation of the “Sassi,” continuing the analysis initiated in a previous work.

Sedimentary rock-hosted gold mineralization at Zalaa Uul, Khentii Range, northeastern Mongolia

The recently discovered Zalaa Uul occurrence exhibits gold concentrations averaging about 1 ppm in silicified breccias as wide as 100 m. Most mineralization is hosted in brecciated siltstone, shale, and calcareous sandstone of the Permian Ulz Formation that exhibits multiple stages of silicification. Rock geochemistry indicates: (1) gold is strongly associated with arsenic and silver; (2) antimony, tellurium and thallium are locally anomalous but poorly correlated with gold; (3) mercury is spatially correlated with copper; and (4) Ag:Au ratios are low (≤3). A low-level Cu–(Hg + Sb, ±Au + As) anomaly occurs over an hypothesized feeder breccia. The feeder breccia occupies a major northwest-dipping reverse fault zone between dominantly greenschist-facies phyllite and schist of the Upper Proterozoic Toshint Formation and unmetamorphosed marine clastic rocks of the permian Ulz Formation. Ground magnetometer surveys identified a magnetic body, thought to represent part of an intrusive complex at depth, within the reverse fault zone, down-plunge from the ∼70° northwest-dipping feeder breccia. Altered rhyolite dikes crop out in the vicinity of the feeder breccia. The potentially economic gold grades are 2 to 3 km outboard of the feeder breccia and may represent the distal Au + As zone of an intrusion-related mineralizing system. Alteration, regional structural and geophysical setting, host rocks and trace element geochemistry, and finely disseminated nature of gold particles are similar to Carlin-type gold systems in the Great Basin of the western USA, but local geology, magnetically mapped intrusive bodies, and trace element zonation suggest affinity with some intrusion-related gold systems.

Access to the coast and erosion control: use of wastes on local engineering works in the coast of Gaza City

Investment in the coastal resources of Gaza City is vital to various developmental issues and projects. Access to the coast and coastal erosion represent two major geo-environmental problems to the city. This paper describes local engineering works developed by the municipality and local people to overcome such problems. A cliff of calcareous sandstone – Kurkar as it is locally known – (up to 18 m high), is located at a distance of 20–50 m from the water–land contact. People who need to reach the beach must cross this Kurkar cliff. The engineering works used to facilitate access to the beach are: old automobile tires, white waste skeletons (refrigerators) and construction waste, where long stairs were designed using these materials. Meanwhile the engineering works which were used as erosion control measures include: rock gabions, concrete wastes, construction waste, concrete walls and shallow excavations. Such practices are commonly used in third world countries and are characterized by inexpensive transportation and implementation costs. The performance of these methods was evaluated from an economic, environmental and safety point of view. Suggestions were made to improve the performance of these practices in the future.

Cu-Au Skarn Mineralization, Minas de Oro District, Honduras, Central America

The Minas de Oro Cu-Au skarn and replacement deposits are located in the highlands of central Honduras, 90 km north-northwest of the capital of Tegucigalpa. The deposits formed in Cretaceous volcano-sedimentary rocks following the emplacement of an early Paleocene granodiorite to dacite intrusive complex. Three types of skarn (Type IA, IB, and IC) and a low-temperature replacement mineralization (Type II) are recognized. Type IA skarn consists of massive brown-green andradite and lesser magnetite and pyroxene. Type IB skarn has magnetite + hematite as the main constituent and garnet 50% pyrrhotite + chalcopyrite with interstitial garnet or pyroxene. Au and Cu occur in potentially economic concentrations in all skarn types while other metals such as Ag, Pb, Zn, and Mo are locally present in significant quantities. The highly variable distribution and nature of the skarn deposits is controlled by: (1) intrusive activity, (2) composition of host rocks, (3) faulting and fracturing, and (4) attitude of host carbonates. Type II Au-Cu-As mineralization occurs in calcareous sandstone and conglomerate 2 km distal from skarns and comprises clots of Cu sulfides hosted within a zone of brecciation and quartz flooding. Garnet and/or magnetite skarn is not present and the mineralizing event appears to have been a low-temperature replacement type. The similarity of coeval Au-Cu-Fe skarns in central Guerrero, southern Mexico to Minas de Oro skarns, and the similar local stratigraphy is consistent with the generally accepted theory that the Chortis block originated from southern Mexico and during the Tertiary moved southeast to its present position.

The roots of glazing techniques : copper metallurgy ?

This paper reports on finds of greenish, partially bluish and red glazed furnace fragments from 3rd millennium ВС copper smelting sites at Feinan and at Timna, Wadi Arabah which, due to their geographic location, could have been of significance for the production of glazes in Egypt (" Egyptian faience" '). The weathered glazes consist of Ca-Al- siliceous glass originally high in alkalis, the latter extracted by leaching over the millennia. The presently observed green color is due to minor concentrations of divalent copper; the color is considered to have been blue originally, with changes to green due to weathering processes. Glaze formation is the result of furnace-constructions using locally available calcareous sandstone, which during smelting reacted with potassium and additional calcium from charcoal ash and with copper from the ore. Comparable glazes have not yet been observed elsewhere at prehistoric smelting sites, probably due to inadequate composed raw materials. Experimental work was carried out to replicate the formation of glazes during copper smelting in order to prove technological relationships to glaze-manufacturing processes. The experimental results confirmed the archaeological evidence. Decisive points in common between glaze formation in copper smelting furnaces and " Egyptian faience" are a quartz-rich matrix and its chemical reaction with copper and alkali-salts at high temperatures. Major differences are high potassium concentrations in our samples while sodium was found to be a major constituent in "Egyptian faience ". Chronological problems are not yet sufficiently solved, since the earliest glazed beads predate the archaeometallurgical evidence discussed in this paper.

Recognition and distinction of normal and forced regression in cyclothemic strata: a Plio-Pleistocene case study from eastern North Island, New Zealand

Abstract The Tangoio block of eastern North Island, New Zealand contains an exceptionally well exposed, 550 m thick sequence of Plio-Pleistocene cyclothemic sedimentary rocks, the Petane Group, that were deposited along the western margin of a shallow (<200 m) pericontinental seaway. The cyclicity that characterizes the Petane Group in this area was generated through recurring 40 ka (sixth-order) sea-level changes of c. 75–150 m. Data from more than 100 sections indicates that the strata consist of five distinct cyclothems, each consisting of a lower formation of mudstone deposited in midshelf environments (highstand system tract, HST), and an upper formation dominated by coarse-grained facies deposited in shallow marine and occasionally non-marine environments. Western exposures of HST mudstones in the lower portion of the Petane Group shoal up into shallow marine siliciclastic sandstones, fluvial gravels and siltstones. The transition is gradational and is consistent with progradation of a siliciclastic shoreline during late sea-level highstand. The shoaling upward siliciclastic sandstone interval represents a regressive system tract (RST) whereas the fluvial beds represent a lowstand system tract (LST). LST gravel beds are sharply overlain by a transgressive surface of erosion and fining-upward siliciclastic sandstone facies of a transgressive systems tract (TST). Carbonate sediments replaced siliciclastic sandstones as the dominant coarse-grained lithology in the upper Petane Group, probably due to bypass of siliciclastic sediment during sea-level fall. Transitions from HST mudstone into carbonate sand and bioclastic limestone (coquina) are generally sharp everywhere except the downdip eastern portions of the Tangoio block. The contacts represent regressive surfaces of erosion produced during falling stages of sea-level and/or ravinement surfaces formed during rising phases of sealevel (transgressive surfaces of erosion). Carbonate facies atop these erosional surfaces are generally interpreted as TST deposits, except for the uppermost limestones in the Petane Group that occur below a sequence boundary and therefore represent a forced regression systems tract (FRST). Stratal position is the only distinguishing characteristic of FRST limestones in the Petane Group, otherwise they are identical to TST deposits. In eastern portions of the Tangoio block, HST mudstones pass gradationally into RST calcareous sandstones and LST limestones. Systems tracts here are bounded by correlative conformities rather than erosive surfaces indicating continuous sedimentation during sea-level fall and lowstand. Differences in sedimentation and subsidence rates between carbonate and siliciclastic sedimentary systems, are responsible for the different stratal architecture of systems tracts in the Petane Group.

First find of the Early Permian Lower Gondwana plant remains and palynomorphs from the Chhongtash Formation (Upper Shyok valley), eastern Karakoram, India

A sedimentary sequence mainly consists of black shale, siltstone, calcareous sandstone and dark argillaceous limestone overlying pillow lava and thinly bedded limestone of the Chhongtash Formation near Chhongtash locality (Upper Shyok valley, eastern Karakoram, India) contains abundant, but poorly preserved plant fossils and palynomorphs probably referable to the Early Permian or Late Asselian (~275 Ma) interval. The plant fossils and associated palynological assemblages of eastern Karakoram show a marked similarity to the marine Lower Gondwana assemblages of the Salt Range and Talchir-Karharbari assemblages of Central India. Based on the present discovery it is suggested that, before the accretion of Cimmerian microplates to the Eurasian continent, the Karakoram microplate in its incipient state was not far from the Salt Range and located along the northern margin of the Indian subcontinent as Peri-Gondwanan microplate.

Nature of sedimentary deposits in the western Makgadikgadi basin, Botswana

Quaternary sedimentation in the western Makgadikgadi basin of north central Botswana is evaluated on the basis of new evidence from satellite imagery and sedimentological analyses. Thematic Mapper imagery interpretation, combined with field evidence, has led to the identification of geomorphological features which are mainly composed of light grey calcareous sandstones (formerly calcretes) overlain by dark grey sands. The literature suggests that palaeolake Makgadikgadi I formed and developed intermittently after initial downwarping in the early–mid Pleistocene. The calcareous sandstones were formed when calcium carbonate precipitation took place in pre-existing Kalahari sands along the western shoreline of Makgadikgadi I. Field evidence, supported by X-ray diffraction and SEM analyses, indicates that CaCO3precipitated mainly in marshy conditions around plant roots and stems and in association with bacteria in embayments along the lakeshore. The sandstones thickened and became partially indurated as a result of increasing palaeolake levels. Deposition was terminated by renewed tectonism which uplifted the shoreline zone relative to the lake basin, leading to falling palaeolake levels. Post-uplift reworking led to case hardening and pedogenic calcrete formation in the upper sections of the calcareous sandstones. Sedimentary conditions altered during the late Pleistocene. Extensive distributaries from the proto-Okavango system incised the shoreline ridge contributing to the filling of Makgadikgadi II. Satellite data suggest that the proto-Okavango rivers formed a series of fan deltas at this time along the western Makgadikgadi basin. Widespread dispersal of fluvial grey sands took place as a result of basin tilting which led to anastomosing channels flowing southward possibly around 18,000 B.P. These results, although preliminary in nature, augment previous geomorphological analyses by adding some detail in terms of depositional environments and by providing a tentative age and origin for the ubiquitous grey sands.

Thelocarpella gordensis gen. et sp. nov. (Ascomycetes lichenisati, Acarosporaceae)

Thelocarpella gordensis Nav.-Ros. et Cl. Roux gen. et sp. nov., a crustose lichen with endolithic thallus, is only known from the type locality, in Provence (south-east of France), on calcareous sandstone. This species is characterized by entirely immersed perithecioid ascomata, a hamathecium consisting of a typical paraphysoid network, multispored asci (more than 1000 spores in optical section), and colourless small oblong spores. The genus Thelocarpella differs from Thelocarpon by having bitunicate asci with a distinctly thicker wall. Heterogeneity of the genus Thelocarpon and the systematic position of Thelocarpella and Thelocarpon are discussed. The genus Trimmatothelopsis Zschacke is considered a synonym of Acarospora A. Massal. and Thelocarpon robustum Eitner identical with Acarospora smaragdula var. murina (Sandst.) H. Magn.Key words: lichens, Thelocarpella, Thelocarpon, taxonomy.

Habitat correlates of European rabbit (Oryctolagus cuniculus) distribution after the spread of RVHD in Cadiz Province, Spain

AbstractEuropean rabbit Oryctolagus cuniculus abundance was evaluated relative to habitat variables within two zones in Cadiz Province (south‐east Spain), 2 years after the spread of rabbit viral haemorrhagic disease (RVHD). The study areas were low‐lying regions of mixed pasture/agriculture, Mediterranean forest and matorral, west (Zone A) and east (Zone B) of the Sierra de Cadiz mountain chain. A total of 111 sites was selected to sample all existing habitat types. Relative rabbit density in each site was estimated using a pellet count method in one 50×2 m transect. Mean pellet densities were 21.05 pellet m−2 in Zone B and significantly lower, 5.85 pellets m−2 in Zone A. Physical variables, such as vegetation characteristics (density, height and patchiness of cover‐layer vegetation, etc.), topographical characteristics and human influences, cover‐layer vegetation species (woody stemmed shrub species or trees forming dense stands), and ground‐layer vegetation species (herbaceous species forming a low‐lying layer) were determined within transects. In addition to these variables, soil types, rock type and land form, as well as the presence of aquifers, irrigation, and the proximity of rivers, were determined for each site. Significantly higher pellet densities were found in mixed grassland/matorral and cork oak/matorral than in all other habitats. Pellet density was negatively correlated with density of ground‐layer vegetation, while high pellet densities were associated with medium‐height ground‐layer vegetation (50–100 cm). The presence of Entisols was negatively associated with pellet density. The cover‐layer species Pistacia lentiscus, Quercus coccifera, Quercus suber, Opuntia ficus‐indica and the ground‐layer grasses all showed positive associations with pellet density, while the ground‐layer species Echium gaditana and Scorpiurus vermiculatus were negatively associated with pellet density. Multivariate analyses identified the mixed grassland/matorral and cork oak forest/matorral habitats as explaining most of the variation in pellet density. The height of cover‐layer vegetation was negatively associated, while Opuntia and table‐and/calcareous sandstone were positively associated, with mixed grassland/matorral. Distance from habitation and human impact were negatively associated and Quercus suber was positively associated with cork oak forest/matorral. Comparison with previous studies suggest that the low pellet counts in this study represent very low rabbit densities and the population as a whole appears depleted and fragmented.

Quaternary Stratigraphy and Paleogeography of the Galilee Coastal Plain, Israel

The Quaternary deposits in the Galilee coastal plain comprise alternating calcareous sandstone, red loam, dark clay, and uncemented sand. The calcareous sandstone in the lower part of the sequence represents a Pliocene to early Pleistocene marine transgression, and is covered unconformably by the late Quaternary sequence. The base of this sequence has an estimated age of ∼500,000 yr. It is covered unconformably by marine calcareous sandstone in the west, which represents the global high sea-level stand of isotope stage 7.1, and is known as one of the “Tyrrhenian” events in the Mediterranean area. The overlying members represent the low sea-level stand of stage 6, the first a red paleosol indicating a relatively wet phase and the second an eolianite unit representing a drier phase. The eolianite forms longitudinal, subparallel ridges that formed contemporaneously. The overlying marine sandstone, which contains one of the diagnostic fossils of the “Tyrrhenian” events, the gastropodStrombus buboniusLMK, accumulated during the global high stand of stage 5.5. The last glacial period left no sedimentary record. The Holocene is represented by a marine clay unit that is covered by sand. The present study establishes a complete and detailed chronostratigraphic sequence for an eastern Mediterranean beach, which contains the gastropodS. buboniusLMK.S. buboniuson the Galilee coast is attributed to stage 5.5 and, therefore, establishes an east–west Mediterranean correlation, which can be used for linking Mediterranean events to paleo-sea levels and global climate changes.

Stone anchors near Black Fort, Galle, Sri Lanka

Stone anchors have been recovered along the Indian coast as a part of the maritime archaeological studies at the National Institute of Oceanography (NIO), Goa. Study of stone anchors provides clues to understand the ancient maritime trade contacts of India with other countries. These anchors resemble those found in the Mediterranean Sea, Persian Gulf and Red Sea Coast. Underwater explorations at Bet Dwarka, Dwarka, Goa, Visawada and Somnath have yielded stone anchors of widely varying shapes, sizes and weights ranging between 16 and 410 kg. Sixteen (10 Indo-Arabian, 4 Ringstone and 2 Single hole type) of the total of 269 stone anchors have been studied to determine provenance of rock through petrographic analysis using thin section studies, X-ray Fluorescence (XRF), and Scanning Electron Microscope – Energy Dispersive Spectrometer (SEM-EDS).Our results suggest that these anchors were made from various rock types, such as granodiorite, dolerite, varieties of basalt, schist, calcareous sandstone, limestone and sandstone. The coastal tract of western India has exposures of all these rock types of igneous and sedimentary rock suites while ultramafic rocks occur inland along the Gujarat and Rajasthan border. It is inferred that these stone anchors have been sourced from rock formations from Gujarat, Goa, Karnataka and Maharashtra regions for use in maritime trading activities of the ancient and medieval periods.

Colour changes of Notos calcareous sandstone as related to its colonisation by microorganisms

Studies were carried out in order to correlate changes in colour of rock surfaces, with bioreceptivity of calcarenite stone used to built the Baroque town of Noto (Syracuse, Sicily) and the microflora associated with surface colouring defined as ‘orange and/or grey patinas’. Our results showed a different contribution of microorganisms to the orange and grey colouring of rock surfaces. Algae and bacteria are mainly related to the orange colour, while black pigmented microorganisms are strongly related to the greying of rock surfaces. Water availability and sun exposure control this different distribution of microorganisms. Noto calcareous sandstones possess a high bioreceptivity.

Stratigraphy of the Late Aptian Lower Greensand around Nutfield, Surrey

A detailed study of Lower Greensand deposits exposed in the fuller's earth workings of Nutfield. Surrey, has yielded new information on their lithofacies and stratigraphy. Two informal lithostratigraphic units, representing contrasting depositional regimes, are proposed for the Sandgate Formation of the Nutfield area. These units are of member status but, pending a comprehensive review of Upper Aptian lithostratigraphic nomenclature, they are provisionally assigned the informal terms Nutfield Beds and Redhill Sands. The Nutfield Beds are characterized by muddy, bioturbated, calcareous sandstones, deposited in quiet-water environments; they include economically important beds of fuller's earth, deposited as reworked volcanic ash. The overlying Redhill Sands consist of poorly consolidated, glauconitic sandstones, characterized by large-scale foresets of tidal bar origin. The Nutfield Beds form a geographically restricted lens, up to 15 m thick, lying within a syndepositional basin referred to as the ‘Nutfield Basin’ in this study. The underlying cherty sandstones ( c . 1–2 m), which constitute the top of the Hythe Formation, show a similarly restricted distribution. The Redhill Sands are also thickest ( c . 15 m) in the middle of the basin, but extend beyond the limits of the Nutfield Beds to the west. Relatively rapid subsidence within the Nutfield Basin combined with high sea-level stand during deposition of the Nutfield Beds produced conditions favourable for the accumulation and subsequent preservation of volcanic ash (now fuller's earth) deposits. Five candidate sequence boundaries have been identified in this study. SB1 is placed at a level within the uppermost Hythe. SB la is placed at the base of a thin glauconitic, pebbly sandstone bed that underlies the top-Hythe cherty sandstones. The cherty sandstones and the Nutfield Beds are interpreted as transgressive and highstand deposits within the same sequence. SB2 is drawn at the base of the Redhill Sands, and SB2a at the base of a unit of pebbly, clay-rich sandstone within the upper part of the Redhill Sands. SB3 is taken at the base of the Folkestone Sands, and is marked by an erosional surface with a relief of up to 4.5 m. Biostratigraphic control is not sufficiently precise to allow correlation of the sequences with those identified in the coastal sections of Folkestone.

PREDICTION OF CARBONATE RESERVOIRS AND TRAPS BY APPLYING SEQUENCE STRATIGRAPHY IN THE EASTERN WARBURTON BASIN, SOUTH AUSTRALIA

The Early Palaeozoic eastern Warburton Basin unconformably underlies the Cooper and Eromanga Basins. Four seismic sequence sets (I−IV) are interpreted. Among them, sequence set II is subdivided into four Cambro-Ordovician depositional sequences. Sequence 1, the oldest, is a shallow shelf deposit that occurs only in the Gidgealpa area. Sequences 2 and 3 were deposited in a wider area; from west to east, environments varyied from deep siliciclastic ramp, carbonate inner-shelf, peritidal, shelf edge, and slope-to-basin. Their seismic reflection configurations are high-amplitude, regionally parallel-continuous, layered patterns, locally mounded geometry, as well as divergent-fill patterns. Sequence 4, the youngest, was deposited in a mixed siliciclastic and carbonate, storm-dominate shelf. Its seismic reflection configurations are moderate amplitude, parallel-layered patterns, decreasing in amplitude upwards.Boundaries between the four sequences generated good secondary porosity in the carbonates. Karst development is interpreted to have generated much of this porosity in shelf and peritidal carbonates, and carbonate build-ups. Shoal-water sandy limestone and calcareous sandstone of Sequence 4 may be other potential reservoir rocks. Potential source rocks comprise mudstone and shale of slope and basin lithofacies. There are two kinds of stratigraphic trap. One is in Sequences 2 and 3, associated with high-relief carbonate build-ups encased in lagoonal mudstone and shelf edge sealed by transgressive siltstone and shale. The other is a transgressive marine shale enclosing porous dolostone of the karstified Sequence 1. In addition, petroleum may have migrated from Permian source rocks of the Cooper Basin to karstified carbonate reservoirs of the Warburton Basin at unconformities.

Geomorphology and palaeoclimatology of some Upper Cretaceous palaeosols in central India

The Late Cretaceous (Maastrichtian) Lameta Formation exposed around Jabalpur in central India comprises a pedogenically modified fluvial succession. Accumulation of early diagenetic calcite cement during penecontemporaneous pedogenesis has transformed the fluvial sandstones into calcareous sandstones. The microscopic features of the palaeosol material include floating grain fabric, root traces, laminated micrite-microspar, micrite envelopes and corona structures, illuvial clay envelopes, poikilotopic spars and minor amounts of siliceous grain and void cutans. The palaeosol profiles of the Lameta Formation can be classified into eleven different types, nine of which are comparable to present-day mature aridisols and two to inceptisols. Nine to thirteen palaeosol profiles are present in the individual sections of the Lameta Formation within the study area. Each profile comprises two to four distinct pedohorizons arranged in vertical succession. There are six types of pedohorizons present in the area of study, namely, partly altered hosts, light-coloured and poorly cemented horizons, horizons with root traces and root-related alterations, horizons of subspherical glaebules, horizons of platy-fused glaebules and subhorizontal root traces and horizons with solution features. They show many characteristics similar to the present-day soil horizons, for example those termed C, Bk, K, A and E by pedologists. The palaeosol characteristics show correspondence to the nature of fluvial channel migration and the depth of the groundwater table (controlled by the geomorphic setting). A shallow groundwater table favoured the development of rootmat-bearing and gleyed horizons. Horizons with vertical root traces and glaebules occur where the groundwater table was low. Mature and thin palaeosols developed in those parts of the Lameta fluvial tract that were characterized by stable channels and wide floodplains. In contrast, thin and comparatively immature soils occurred in the parts where laterally migrating channels were operative. The characteristics of the Lameta palaeosols suggest that a hot and semiarid climate prevailed for most of the time represented by the Lameta Formation, but short-term wet spells occurred during the initial and the terminal phases of the Lameta accumulation. The low latitudinal palaeoposition of India and the absence of the palaeo-monsoon circulation might have produced the hot and semiarid climatic setting during this time.

Evaluation of Corrosion Inhibitor for Low-pH Ammonium Nitrate-Methanol Completion Fluid

Summary A specially formulated completion fluid, low-pH ammonium nitrate-methanol-water mixture (ANM), compatible with argillaceous and calcareous Adriatic Sea sandstone formations, appears to be very corrosive for steel wellbore equipment. More than 12 commercially available, as well as some originally formulated, chemical additives were laboratory tested at room temperature using weight-loss and electrochemical methods to find an effective corrosion inhibitor for ANM. Two inhibitors, a commercially available, organic, amine base (OA) and an originally formulated, inorganic, ammonium dihydrogen phosphate base (IB), showed effective protection of carbon steel in contact with ANM fluid (corrosion rate was less than 5 mil/yr). Both selected corrosion inhibitors did not exhibit any additional rock permeability impairment during fluid-rock compatibility flow tests if ANM fluid was filtered before injection into the core samples. For inorganic inhibitor IB, additional filtration of inhibited fluid is not required.