Limestone Sequence Research Articles

Ordovician and Devonian microfacies of Sierra Agua Verde, central Sonora, Mexico: A new locality of the Nuia Province from western Laurentia

The Lower Ordovician carbonate rocks exposed in the Tuntunudé hill north of the Sierra Agua Verde, northeast of the town of Mátape, in central Sonora, consists of intraformational breccia, conglomeratic limestone, sandy limestone and limestone, which are overlain by a mixed succession of quartz sandstone and dolomitic sandstone. This succession is in turn unconformably overlain by an Upper Devonian sequence of dolomitic limestone, marl, conglomeratic limestone and sandy dolomite. The Lower Ordovician rocks contain abundant bioclasts of gastropods, brachiopods, trilobites, echinoderms, and sponges. Their microfacies show a marine medium to low energy environment, with sedimentation dominated by distal tempestites in laminar stages and intraclast debris formation during deposition. The depositional paleoenvironment corresponds to a marine middle-to-outer ramp. These strata are characterized by conodonts belonging to the Oepikodus communis and Reutterodus andinus biozones, as well as cyanobacteria incertae sedis Nuia sibirica. Devonian rocks overlying the Ordovician strata contain bioturbation and abundant bioclasts of echinoderms, brachiopods, bryozoans, gastropods, chaetetiform sponges, stromatoporoids; and also, colonial corals like Hexagonaria attenuata, Phillipsastrea hennahii and Phillipsastrea jachowiczi, monothalamous foraminifera like Vicinosphaera sp., monoserials such as Tikhinella measpis and planispiral such as Nanicella gallowayi. The microfacies show a high-energy environment in marine tropical shallow open-sea lagoonal waters, with ooids and reef building organisms.

An inception framework hypothesis for karst development in the Burren, Ireland

The Inception Horizon Hypothesis (IHH) postulates that certain stratigraphic horizons in a limestone sequence, combined with structural surfaces such as joints, provide a framework for cave development. Although subsurface and surface karst landforms are fundamentally linked, the IHH has not yet been extended to surface karstification. We tested this extension of the IHH in the world-renowned Burren karst due to its stratigraphic and structural simplicity. We used very high-resolution remote sensing datasets and detailed fieldwork to develop an updated map of the Burren's surface karst features, combined with a 3D geological model containing over 60 km of mapped cave passages.Our analysis shows that karstic connectivity between the surface and subsurface is primarily provided by a suite of vertically-persistent calcite and silica-rich veins, which form a non-stratabound fracture system across the Burren. The flow pathways provided by these veins then intersect the following inception horizons: (i) boundaries between distinct lithological units in the limestone sequence; (ii) crinoidal cycle tops, and more sporadically chert lenses, within one of those units (the Slievenaglasha Formation); (iii) thin horizons of non‑carbonates (‘clay wayboards’) within another unit (the Aillwee member). At the surface, the same horizons have been preferentially exploited by glacial processes, creating surfaces from which meteoric waters now recharge the subsurface and form new surface karst depressions and other karst landforms. Our new inception framework for karstification thus provides a new basis for understanding surface and subsurface connectivity in the karst critical zone in the Burren landscape, and it provides new geological insight into the functioning of carbonate critical zones more generally.

Facies distribution, paleoenvironment and hydrocarbon potential of Kanawa Member of Pindiga Formation, Gongola Basin, Northern Benue Trough, Nigeria

The Gongola sub-basin is a frontier inland sedimentary basin consisting of Cretaceous to Tertiary sediments, believed to have been deposited in continental to coastal shallow marine complex. The Kanawa Member of Pindiga Formation is a sequence of limestone and shale. Sedimentology, facies analysis, biostratigraphy, thermal maturity assessment and kerogen typing were conducted on these strata to determine the facies, facies associations, facies successions, paleoenvironment, age, and hydrocarbon generation potential. The studied sequences are of Turonian–Santonian age, deposited due to a major transgression of the basal part of the Pindiga Formation. The shale-limestone series of the Kanawa Member is interpreted as lagoon-to-shallow marine deposits of a carbonate ramp depositional system. The sediments consist of mainly wackestone and packstone facies and shallow marine foraminiferal, suggesting that the Kanawa Member was deposited under low-energy condition. The presence of Ammobaculites subcretacea, Haplophragmoides bauchensis, Haplophragmoides pindigensis, Haplophragmoides excavata, Ammobaulites pindigensis, Ammobaculites bauchensis, Ammobaculites gombensis, Ammobaculites benuensis Ammoastuta nigeriana, Reophax guineana and Miliammina pindigensis foraminiferal assemblages, indicating Late Cretaceous age. Hydrocarbon potential is interpreted to be gas prone although, minor oil could be expected. These correspond to temperature range (TAI values) of 60 to 75 indicating thermally matured for both oil and gas generation.

Petrophysical Evaluation of Arkoses Reservoirs Based on Well Logs and Plug Samples: A Case Study From Alagamar Formation, Southeastern Portion of Onshore Potiguar Basin, Brazil

The Potiguar Basin is a sedimentary basin located in northeastern Brazil. It covers about 48,000 km² and extends from onshore to offshore. The onshore basin is thought to have formed during the Late Cretaceous, as a result of the opening of the Equatorial South Atlantic Ocean, filled with a thick sequence of sedimentary rocks, including sandstones, shales, and limestones, which were deposited in a variety of processes, including marine, deltaic, and fluvial. The study area is in the southern portion of the basin and the reservoir is composed of arkose sandstones deposited by alluvial fan and fluvial systems of the Upanema Member of the Alagamar Formation, which belongs to the post-rift phase of the Potiguar Basin. Recently, new drilling campaigns revealed a reservoir heterogeneity in these deposits, which requested a new petrophysical approach. Using conventional well logs and petrophysical laboratory analysis of plug samples, this study evaluated the best way to calculate the effective porosity, and shale volume and to understand the stratigraphic controls in the distribution of these properties. Three reservoir zones were mapped: the basal one, Zone 3, has disconnected sand bodies, low porosity, and high shale content; Zone 2 has better petrophysical properties, lateral distribution, and connectivity between the fans and Zone 1 is the better reservoir zone with larger sand bodies, higher porosity values, and well-connected fans.

Rhuddanian to Aeronian (Llandovery, early Silurian) carbon isotope stratigraphy throughout carbonate sequences in the upper Yangtze region, South China block

AbstractThe Xiangshuyuan Formation (middle Rhuddanian to middle Aeronian stages of the Llandovery Series, lower Silurian) records a shelly fauna representing recovery after the end‐Ordovician mass extinction in a well‐oxygenated shallow carbonate platform of the Upper Yangtze region, South China Block. Carbon isotope stratigraphy is documented from limestone sequences of the formation at the Qiankou section, northeast Guizhou. The early Aeronian carbon isotope excursion (EACIE, with an amplitude of about 2 ‰ and peak value of 2.44 ‰) is identified in the middle and upper parts of the formation (Ozarkodina obesa conodont Biozone). The EACIE recorded herein correlates well with those in Baltica, Canada, and the United States; together with its records from organic material (δ13Corg) the data verify that the EACIE is a global event. The beginning of the EACIE can be used as a chemostratigraphic marker defining the Rhuddanian/Aeronian boundary in strata that lack high‐resolution biostratigraphic constraints.

The Early Jurassic sequence of Lyme Regis, Dorset, England and its place in the history of geology and palaeontology

Abstract The cliffs and foreshore at Lyme Regis on the Dorset coast expose a sequence of Early Jurassic marine limestones and mudstones of the Blue Lias Formation and the overlying Charmouth Mudstone Formation, the lowest units of the Hettangian–Aalenian Lias Group. Known for its fossils since at least the mid-seventeenth century, this coastal section became famous in the early nineteenth century for the bones of ‘fossil crocodiles’. Many of the most significant discoveries were made by a family of fossil dealers whose best-known member was Mary Anning (1799–1847). Anning and her family recovered the first scientifically described ichthyosaurs, the first complete plesiosaur and the first British pterosaur to be identified. Anning's finds from Lyme Regis formed the basis of the pioneering palaeoenvironmental reconstruction Duria antiquior . Her geologist friends, some with close personal associations to the town, did much to publicize her discoveries and contribute to both her fame and that of the locality. This famous coastal section, with its important historical associations with a key period in the development of geology and the source of so many significant discoveries in the early nineteenth century, now lies within the Jurassic Coast UNESCO World Heritage Site.

Geoconservation of Groundwater in the Getourism Area of Olele Village for the Development of the Tomini Bay Geopark

Geoconservation is an important effort in preserving geological diversity. Geoparks act as a link to encourage geoconservation. This research aims to evaluate the geology, geosite potential and groundwater availability in Olele Village, Gorontalo. This research aims to determine geological conditions, geosite potential, groundwater availability and groundwater conservation measures. The methods of literature survey, field survey, field data collection and ArcGis 10.8 data analysis were used. Stratigraphy shows the sequence of Reef Limestone (Ql), Pinogu Volcanic Rock (TQpv), Bone Diorite (Tmb), and Bilungala Volcanic Rock (Tmbv). Geomorphology includes reef terrace plains, alluvial plains, pyroclastic flow hills, and lava flows. Lithological contacts between reef limestone and pyroclastic breccia mark the Olele Geosite. Water quality is influenced by the level of rock passability and rainfall. Olele Village has good groundwater potential with a groundwater table depth of 1-8 meters. Groundwater conservation measures involve monitoring, public education, water use management, sustainable agriculture, wetland rehabilitation, development of alternative infrastructure, and mitigation of tourism impacts. Thus, this research emphasizes the need for sustainable strategies for the conservation of geological and groundwater resources in this area.

Age assignment of dolomite in palaeo-reservoirsof the Qiangtang Basin: New evidence from palaeontology and carbonate in situ U-Pb dating

The dolostone in the south Qiangtang depression has been proven to be a favourable reservoir rock of the famous Longeni-Angdaerco palaeo-reservoir, being of great significance for oil and gas exploration in the Qiangtang basin. However, its geochronology and diagenetic process are still controversial. In particular, the previous interpretation that oil-bearing dolostone belongs to the Middle Jurassic Buqu Formation is challenged by recent works. Based on previous macro-palaeontological studies, we carried out the latest micro-palaeontological identification and carbonate in-situ U–Pb isotope dating analysis to re-assign the depositional age of the dolomite in the palaeo-reservoirs. We also establish a high-resolution diagenetic time framework of dolomite combined with microscopic identification, scanning electron microscope, and rare earth elements analysis. In this study, age-diagnostic foraminifers, which include Lituolipora termieri, Siphovalvulina colomi, Siphovalvulina variabilis, Siphovalvulina gibraltarensis, Duotaxis metula, and Variostoma sp., were recovered from the overlying and underlying limestone sequences of the studied Xiaogaxiaona palaeo-reservoir section. These foraminiferal assemblages suggest a Late Triassic to Early Jurassic age of the carbonate sequences. Nine U–Pb ages of different carbonate components were obtained. Contrary to previous dolomitization models, U–Pb dating suggests a Late Triassic metasomatic dolomitization event (216.2 ± 6.1 Ma to 210.1 ± 9.4 Ma), which was likely driven by seawater fluids. This event was probably followed by calcite vein cementation (U–Pb ages of 203 ± 13 Ma). Another Early Jurassic dolomitization event (185.5 ± 3.8 Ma to 182.7 ± 5.8 Ma) perhaps involved the mixed-zone model. Finally, saddle dolomite cement yielded Early and Middle Jurassic ages of 181 ± 18 Ma and 161 ± 23 Ma and crystallized in pre-existing vugs, representing two hydrothermal fluid events. This study suggests that the palaeo-reservoir carbonate successions were probably deposited in the Late Triassic rather than the previous suggestion of the Middle Jurassic. The high-resolution time framework of the dolostone in the palaeo-reservoir reveals a possible link between dolomitization and hydrocarbon accumulation in basin-scale fluid-flow events in the Qiangtang Basin.

Late Cretaceous arc magmatism in the Western Pontides (Turkey) – temporal and chemical changes

ABSTRACT During the Late Cretaceous, a magmatic arc extended from the Lesser Caucasus through the northern margin of the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans for a distance of 2700 km. We studied the arc volcanic rocks in three regions in the Western Pontides and reviewed the geological data on the Lesser Caucasus-Pontide-ABTS magmatic arc, which shows several common features. Prior to the start of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data show that magmatism in the Lesser Caucasus-Pontide-ABTS arc started in the Turonian (ca. 93 Ma) peaked in the middle Campanian (80–78 Ma) and became rare and sporadic after the late Campanian (ca. 75 Ma). Magmatism was dominantly calc-alkaline to high-K calc-alkaline and shows typical subduction geochemical signatures. Late Cretaceous volcanism took place in a submarine and extensional environment. In the Lesser Caucasus-Pontide-ABTS belt, the arc volcanic rocks are overlain by Maastrichtian to Palaeocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Kefken region in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The Maastrichtian volcanic rocks show a more varied geochemistry than the older arc volcanic rocks, and include alkaline basalts, calc-alkaline basalts, and adakites. The coeval start of arc magmatism in the 2700-km-long Lesser Caucasus-Pontide-ABTS belt is related to the inception of the Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of sub-ophiolite metamorphic rocks in Anatolia. The end of magmatism is linked to a marked decrease in the convergence rate during the Campanian, which was also partitioned between the northern and southern Tethyan subduction zones.

Dolomitization mechanism of Pila Spi formation (middle- late eocene) in the high folded zone, Northern Iraq

Petrographic analysis and geochemistry of the Pila Spi Formation (Middle-late Eocene) were investigated from two outcrop sections (Gali-Zakho and Shaqlawa), within the High Folded Zone, northern Iraq. This formation consists of fine to coarsely crystalline dolomites and limestone sequences. Despite the fact that these strata have been buried and impacted by several episodes of dolomitization and dissolution, some intervals in the Pila Spi Formation have acquired porosity. Dolomicrite, dolomicrosparite, dolosparite, vein, and saddle dolomite are the five primary kinds of dolomite textures recognized based on fabric, grain size, and elemental analysis. Dolomicrite produced the sabkha model in a low-energy hypersaline sedimentary environment, since these rocks had unusually high Sr and Na values, lower Fe and Mn values. The dolomicrosparite and dolosparite developed in a shallow burial environment using the seepage-reflux model, and these rocks had a higher formation temperature, low Sr and Na levels, and a broad range of Fe and Mn values, indicating that they were impacted by meteoric water. The vein and saddle dolomite evolved as a result of the burial model at increased temperature since these rocks had the lowest Sr and Na contents, the greatest MgO and CaO contents, and the highest Fe and Mn values. In selective dissolution processes, the early sabkha, the seepage-reflux model of dolomitization, and the synchronous cycle of meteoric freshwater, many porous intervals were formed.

Accretion of an early Paleozoic Alaska-type arc onto northern North China: Implications for continental growth of the Central Asian orogenic belt

The accretionary orogenesis of the Central Asian orogenic belt is essential for understanding the reconstruction and growth of the Asian continent. The origin and accretion of the Bainaimiao arc along the northern margin of North China remain controversial. Here, a comprehensive study of field geology, geochemistry, and geochronology was performed on plutons and an ophiolite-bearing accretionary complex in the Ganqimaodu region, Inner Mongolia. Geochemical data indicate that ca. 445−431 Ma plutons were generated in an intra-oceanic arc and represent the western extent of the Bainaimiao arc. Field mapping and zircon U-Pb dating revealed that the ophiolitic mélange contains ca. 470−435 Ma tectonic blocks of ultramafic rocks, gabbros, plagiogranites, and metavolcanic and siliceous rocks in a matrix of intensely foliated quartz schist. The pillow basalt−limestone sequence might have originated from a seamount and then been incorporated into the accretionary complex. Northward subduction of the South Bainaimiao Ocean was responsible for the early Paleozoic tectonic evolution of the Bainaimiao arc, based on the spatial-temporal configuration of arc magmatism and accretionary complexes. Integration of new data with previous studies indicates that the Bainaimiao arc was an Alaska-type arc with various components of intra-oceanic and continental arcs. We suggest that a scissor-like arc-continent collision led to the accretion of the Bainaimiao arc onto the northern margin of North China, which played a fundamental role in the continental growth of the southern Central Asian orogenic belt.

Numerical studies and analysis on reaction characteristics of limestone and dolomite in carbonate matrix acidizing

Carbonate reservoirs with abundant oil and gas resources are mainly composed of limestone and dolomite. As the acid-rock reaction progresses, limestone is gradually consumed and more acid gradually reacts with the slower dolomite. However, the existing acid rock-reaction models do not consider the competition between limestone and dolomite with acid, and cannot objectively describe the degree of contribution of limestone and dolomite to wormholes at each stage of acidizing. Here, an acidizing model was developed to study and analyze the effect of the reaction characteristics of limestone and dolomite on the carbonate acidizing. In this study, the probability of limestone and dolomite contact with acid is assumed to be related to the content of limestone and dolomite, and a new acid-rock reaction model is proposed by considering the reaction rate and reaction sequence of limestone and dolomite. The acid-rock reaction model is coupled with the porous medium heat transfer model and the two-scale continuum model, and a comprehensive carbonate acidizing model is established. The model can respond to the competition between limestone and dolomite in each stage of acidizing at different temperatures and quantitatively characterize the dynamic change of different mineral contents. Based on the model, this work studies and analyzes the effects of the temperature, dolomite characteristics (uniform, blocky, and columnar) and distribution orientation on wormholes propagation and acidizing efficiency. The simulation results show that the comprehensive carbonate acidizing model can accurately reveal the higher contribution of limestone to the wormhole when the temperature is less than 338 K. As the temperature increases, the difference of reaction rate between limestone and dolomite gradually decreases, and the contribution of dolomite to the wormholes increases. When the temperature is 418 K, the dissolution of limestone and dolomite in the wormholes and the area around the wormholes is almost the same. Moreover, when the temperature is 298 K, the smaller size and density of blocky and columnar dolomite can make the wormholes tortuous and complicated, thus reducing the acidification efficiency. When the size and density are larger, the presence of dolomite can hinder the generation of branching wormholes and guide the propagation of wormholes, enhancing the acidizing efficiency. In addition, the orientation of dolomite does not change the propagation distance of wormholes, but it changes the propagation orientation of wormholes. This study privates a guide for the acidizing treatment of carbonate reservoirs with the different mineral compositions of limestone and dolomite.

The Flims rock avalanche: structure and consequences

The Flims rock avalanche has a gliding surface that cuts down section in a limestone sequence and does not follow a weak horizon. The gliding surface is parallel to bedding and/or to the penetrative Alpine foliation in the limestone that is characterized by a shape-preferred orientation of calcite grains. Predisposition was governed by structural weaknesses in form of sub-vertical fault zones within solid limestone. Faults controlled the orientation of lateral scarps of the rock avalanche. The main body of the rock avalanche behaved as semi-coherent mass, which preserved the original overall structure. The internal deformation occurred by dynamic fragmentation, which was distributed rather heterogeneously. Fragmentation starts by the formation of veins consisting of comminuted limestone. In a later stage crosscutting veins coalesce to form a texture with entirely comminuted limestone (“rock flour”) containing angular shattered fragments of limestone of variable sizes. The involvment of the post-glacial water-saturated substrate contributed to the long-runout of the Flims rock avalanche. The substrate was plowed bulldozer-wise at the front of the rock avalanche and escaped upward through the moving rock avalanche as clastic dikes and blow-out pipes. Bulldozing raised the valley floor in front of the rock avalanche by more than 100 m and, on the margins, entrained pieces of the valley flank and the neighboring, older Tamins rock avalanche deposit. The liquefied substrate breached the Tamins rock avalanche at Reichenau and entrained fragments thereof down the valley. The fragments now form the famous tumas of Domat/Ems, Felsberg and Chur. Lake Ilanz, dammed the by Flims rock avalanche, experienced a first major outburst shortly after its formation.

Изотопно-геохимические характеристики минерального заполнения палеополостей в верхнедевонских-нижнекаменноугольных известняках на восточном склоне Среднего Урала (окрестности с. Першино)

Lithology and geochemistry of carbonate filling in ancient karst cavities in the Famennian-Tournaisian limestone sequence of the Rezh subzone at the eastern slope of the Middle Urals are considered. Mineral filling of paleocavities differs from typical modern subaerial speleothems. Caves are mainly filled with white massive coarse-grained calcite (cave spar), red-colored argillaceous-carbonate microgranular deposits (carbonates with an admixture of terra rossa, cave laminites) and collapse breccias, composed of host limestones fragments. The rare earth elements (REE) patterns and the isotopic composition of carbon indicate a very weak effect (or its absence) of soil or meteoric waters on the carbonate system: the speleothem calcite inherited these characteristics from the host limestones. At the same time, the isotopic composition of oxygen indicates the primary meteoric genesis of solutions and/or relatively high temperatures of calcite crystallization. Most likely, the studied speleothems were formed from solutions of surface origin circulating in the sedimentary strata for a long time (hypogene sediments).

Microfacies and Sequence Stratigraphy of the Saadi Formation within the sequences of the (Torunian - Santonian) cycle in Balad and Tikrit / Salah al-Din Governorate / Iraq

The current study included a study of the microfacies and sequence stratigraphy of Saadi Formation in two subsurface sections within the Balad and Tikrit oilfields, the first represented (Ba-5) with a thickness of (120) m, and the second section (TK-6) the thickness of this formation (270))m. The formation under study consisted of chalk limestone sequences with the layers of marley limestone, the study showed that the lower bounder is compatible with the of Tanuma Formation in both sections, while the upper bounder is conformable with the Mashura Formation within well (Ba-5) and is unconformable with the Hartha Formation in a well (TK-6).Petrographic study showed the presence of many microfacies at divided into five main microfacies and six submicrofacies Lime mudstone microfacies, Lime wackstone microfacies divided to (Calcispheres lime wackestone and Rotalid lime wackestone submicrofacies), Lime packestone microfacies divided to (keeled planktonic foraminiferal lime packstone, Hedbergella lime packstone, Calcispheres lime packstone and Rotalid lime packstone submicrofacies), lime grainstone microfacies and crystalline microfacies. Depending on microfacise the paleoenvironment of formation extended from slope, open marina, deep shelf and deep sea.The sequence stratigraphy defined of study divide to the sequences into sets, and each sets represents a sedimentary cycle that event a rise and fall in sea level during a certain period of time, the formation in well (Ba-5) compound one sequence and well (TK-6) consist three sequence, the sequence begins with the sequence boundary of (Type-2) and after the transgression system tract (TST) it deposit by Retrogadation and the upper surface of this tract represented by the Maximum Flood Surface (MFS), followed high stand system tract (HST) deposited in progradation pattern, which is characterized by a gradual decrease in sea level and a shallowing sedimentary environment. The presence of three sequence cycles through the Tk-6 well is due to the fact that the Tikrit field is shallower than the Balad field of sedimentation and is located at the edges of the deeper part of the sedimentary basin and the beginning of the shallowing, which is affected more The processes of marine Transgression, where the final report of the well (Tk-6) showed that the succession of shallow sedimentary facies with deep facies as shown, indicating the instability of the substratum and its significant impact on tectonic movements.

Paleoceanographic evolution in the South Atlantic Ocean (Kwanza Basin, Angola) during its post-salt foundering

Calcareous nannofossil distribution, environmental magnetism, and geochemical data provide stratigraphic evidence concerning the paleoceanographic changes across the lower/middle Albian and the Oceanic Anoxic Event 1b (OAE1b, Kilian Level) at South Atlantic Ocean. In this study, we analyzed samples from the sedimentary records at Deep Sea Drilling Project (DSDP) Site 364, Kwanza Basin, Angola. This section is associated with the initial phases of evolution of the South Atlantic Ocean, characterized by the deposition of extensive evaporite layers under restricted marine conditions, which were preserved in many sedimentary basins of the Brazilian and African continental margins. The open marine conditions that followed this period are recorded in the sequences of limestones interbedded with organic matter-rich black shales. In the Kwanza Basin, Site 364 contains a well-preserved sedimentary record of these post-salt sequences. In this study, we address the Lower Cretaceous sedimentary records at Site 364 from a paleoceanographic perspective, investigating the influence of OAE1b and local paleoenvironmental conditions. Our data analysis indicates a progressive reduction in hypersaline conditions during the lower/middle Albian. In these conditions, five paleoceanographic intervals (PIs) were described, which show different evidence of dysoxia/anoxia and salinity fluctuations, euxinic intervals, surface-water temperature changes, and hydrothermal activity signals, as well as possible ocean acidification episodes. These paleoceanographic conditions at Site 364 are associated with a stratified thermocline composed of warm surface-water from the North Atlantic (Western Tethys) and cool deep-water incursions from the Austral Atlantic, which strongly affected the composition of the calcareous nannofossil assemblages. We propose that the lower/middle Albian paleogeographic and paleoceanographic conditions observed in the Kwanza Basin were likely related not only to local events linked to the early development of the South Atlantic, but also to the OAE1b - Kilian Level recognized in several basins from around the world.

Recently Discovered Thick Bentonite Bed Hosted by the Lithothamnium Limestones (Badenian) in the Polish Part of the Carpathian Foredeep: The Evidence for Volcanic Origin

In this paper, we discuss the hypothesis on the volcanic origin of the precursor sediments for a thick (0.6 m) clay bed, hosted by the sequence of lithothamnium limestones of the Pińczów Formation. Combined X-ray powder diffraction, imaging methods (optical and electron microscopy), and chemical analysis were used to document the volcanic markers, which were preserved in the rock studied. The results obtained show that the clay bed discussed is bentonite in origin. This bentonite, which can be called Drugnia Rządowa bentonite, is composed almost entirely of montmorillonite with little admixtures of quartz and biotite. A small amount of calcite is present, but only in the top of the bed. Despite that, the bentonite contains nothing but clay material—it is a model example of entirely altered pyroclastic rock, which retains texture originally developed in volcanic glass fragments and reveals the preserved original features of the precursor fallout pyroclastic deposits (rhyolitic in character). The thick bentonite beds, discovered for the first time within the Badenian lithothamnium limestones of the Pińczów Formation, can be considered as a record of a violent, explosive volcanic event related to the closure of the Outer Carpathian basin and the development of the Carpathian Foredeep.

Geology, geochemistry and depositional history of the Port Campbell Limestone on the eastern flank of the Otway Basin, southeastern Australia

A fully cored sequence of Hesse Clay, Port Campbell Limestone and uppermost Gellibrand Marl in the onshore Otway Basin, southeastern Australia, offers new insight into the evolution of the middle Miocene Port Campbell Limestone. The Port Campbell Limestone comprises grey unconsolidated to semi-consolidated and rarely lithified bioclastic muddy carbonate sands in a stack of thin repetitive cycles within cycles of predominantly shoaling-upward character. A glauconitic band with a distinctive mollusc–echinoderm–bryozoan fauna provides a distinctive marker interval in the sequence. In mineralogy, the Port Campbell Limestone is predominantly calcite with traces of remnant aragonite in muddier low-permeability sands, and with dolomitic zones in permeable intervals. The small non-carbonate component of the Port Campbell Limestone is between 3 and 15 wt% and comprises quartz silt with minor clay, feldspar and mica. Dissolution overprints are prominent throughout the carbonate sequence. Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources. Foraminifera are common and generally well preserved. Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma. Shallowing after 14 Ma indicates variable paleodepths of <70 m during and following the end of the Middle Miocene Climatic Transition (MMCT) at ca 13.2 Ma when the sequence was emergent for a brief but undetermined period, corresponding with sharp changes in geochemical ratios. Observed cyclicity in these mid-shelfal, cold-water carbonates is strongly correlated with orbital forcings—eccentricity and obliquity. Sedimentation rates determined from cyclostratigraphic analysis indicate 4–6 cm/kyr at the end of the MMCO, diminishing to 1.5–3 cm/kyr during the MMCT and the subsequent accumulation of the Port Campbell Limestone. KEY POINTS The Port Campbell Limestone is a stack of thin repetitive depositional cycles within cycles. The cyclicity is strongly correlated with orbital forcings—eccentricity and obliquity—and this is reflected in the geochemistry. Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma. The sequence was emergent for a brief but undetermined period at ca 13.2 Ma, corresponding with sharp changes in geochemical ratios. Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources.

Études du Paléolithique du Japon à partir des téphras

Many studies and discussions have been made on the problem of when the earliest human beings appeared in Japan. In general, hominid fossils in the latest Pleistocene are not preserved except for coralline limestone sequence in Ryukyu islands, but earlier Paleolithic tools were excavated from volcanic ash soil with a 14C age of about 30,000–35,000 yr. BP or younger at several archeological sites in almost all Japan. Recent studies, however, show a need for revision and refinement of these ages because calibration techniques have progressed from conventional to calendar ages and high-resolution oxygen isotope chronology has given a global standard sequence. Aïra-Tn tephra (AT), the most important time-marker of the Paleolithic age in Japan, was formerly dated at 21,000–22,000 yr 14C BP by conventional radiocarbon methods but was dated again at ca. 24,500 yr 14C BP by accelerated mass spectrometry radiocarbon methods. However, it has been further calibrated to a high-resolution calendar age of 30,000cal yr. by varve chronology of lake sediments of Suigetsu of central Japan, well matched with combined date between oxygen isotope dates based and calibration from AMS radiocarbon dates. As the earliest Paleolithic tools in south Kanto are found in volcanic ash soil significantly below AT ash and above Sambe-Ikeda ash (SI, ca.46 ka), just above the oxygen isotopic stage 3.3, they are estimated to be dated slightly older than 40ka. Palaeo-environment at that time is estimated mild to cool climate and relatively low sea level after the oxygen isotope stage 3.3. Sill land bridges between Japan islands and continents have not been formed at major straits. We have not yet obtained useful data for calibration older than ca. 45ka. Also, correlation of oxygen isotopic fluctuation with the terrestrial sequences is incomplete in Stage 3.

Quantitative analysis of Cenozoic faults and fractures and their impact on groundwater flow in the bedrock aquifers of Ireland

Faults and fractures are a critical store and pathway for groundwater in Ireland’s limestone bedrock aquifers either directly as conductive structures or indirectly as the locus for the development of karst conduits. From the quantitative analysis of post-Devonian faults and fractures in a range of lithological sequences, this report describes the principal characteristics of Cenozoic strike-slip faults and joints, the youngest and the most intrinsically conductive fractures within Irish bedrock. Analysis of these structures in more than 120 outcrop, quarry, mine and cave locations in a range of bedrock types, provides a basis for: (1) definition of quantitative models for their depth dependency, lithological control, scaling systematics and links to preexisting structure, (2) conceptualisation of their impact on groundwater behaviour, and (3) estimation of groundwater flow parameters. The quantitative models provide constraints on fracture-controlled flow connectivity. Commonly observed decreases in sustainable flows and water strike interceptions with depth are attributed to increasing confinement and decreasing fracture connectivity and dissolution. Faults and joints have quite different end member geometries, with faults having strongly heterogeneous scale-independent properties and joints more often showing scale-dependent stratabound properties. The highest and most sustainable groundwater flows are usually associated with the complexity of structure of Cenozoic faults and of preexisting Carboniferous structures (on which conductive fracturing localises), enhanced by karstification and strongly jointed limestone bedrock particularly in the near-surface. Increased groundwater flow is promoted within bedded, rather than massive (i.e. unbedded), limestone sequences, characterised by bedding-parallel fractures and karst connecting otherwise subvertical fractures and subvertical wells.