Upper Unit Research Articles

Application of Resistivity and Seismic Refraction Tomography for Landslide Stability Assessment in Vallcebre, Spanish Pyrenees

Geophysical surveys are a noninvasive reliable tool to improve geological models without requiring extensive in situ borehole campaigns. The usage of seismic refraction tomography (SRT), electrical resistivity tomography (ERT) and borehole data for calibrating is very appropriate to define landslide body geometries; however, it is still only used occasionally. We present here the case of a Spanish Pyrenees slow-moving landslide, where ERT, SRT and lithological log data were integrated to obtain a geological three-dimensional model. The high contrasts of P-wave velocity and electrical resistivity values of the upper materials (colluvial debris and clayey siltstone) provided accurate information on the geometry of the materials involved in the landslide body, as well as the sliding surface. Geophysical prospecting allowed us to identify the critical sliding surface over a large area and at a reduced cost and, therefore, gives the geophysical method an advantage over borehole data. The three-dimensional model was used to carry out stability analyses of a landslide in 2D and 3D, which, coherently with previous studies, reveal that the lower part is more unstable than the upper units.

The soft-sediment deformation structures and the siliceous concretion presence as indicators of the depositional processes during Middle Paleocene to Middle Eocene in the Apulian Platform Margins in Kefalonia Island, Greece

Kefalonia Island is situated in western Greece and geologically corresponds to the Apulian Platform Margins (APM), with the Apulian Platform lying to the west and the Ionian Basin to the east. The studied deposits, with a thickness up to 164.5, extend along the 650 m long Agia Efimia bay, ranging from the Middle Paleocene (Selandian) to the uppermost Eocene (Priabonian), during the latest part of the rift stage. Fieldwork measurements of soft-sediment deformation structures (SSDS), paleocurrent directions, the size and abundance of siliceous concretions (SC) and siliceous beds (SB), and shale horizons were correlated with the age of selected samples, and thus, the relation of the tectonic regime with the depositional conditions was presented. As SSDS could represent an indicator of tectonic activity and instability of the basin floor instability, the size and the abundance of the SSDS whereas used to identify the parameters that produced the basin floor instability like the intensity of tectonic activity. The studied section, with a general NE-SW orientation, was subdivided into five (5) different units. The changes of these units in paleocurrent directions, the size, the abundance, and the thickness of SSDS, SC, and SB and the presence of shale horizons in the upper unit, characterize a gradual change of the depositional conditions in the APM, from the Upper Paleocene (Selandian) to the Upper Eocene (Priabonian). The factor that influenced the abovementioned changes was related with the presence and the activity of normal faults that produced instability of the basin floor. Therefore, a reduction in tectonic activity from the Paleocene to the Eocene is suggested.

Sedimentology and sequence stratigraphy of lacustrine deep-water fine-grained sedimentary rocks: The Lower Jurassic Dongyuemiao Formation in the Sichuan Basin, Western China

Despite the sedimentology of deep-water fine-grained sedimentary rocks from marine environments having received highlighted attention in recent years, their counterparts from the lacustrine environments are rarely reported. Based on a complete sedimentological, petrographic, and geochemical analysis of three continuous cored wells of the Lower Jurrasic Dongyuemiao Formation, Sichuan Basin, West China, this study illustrates the range of lithofacies, cyclicities, and transportation and deposition mechanisms of this lacustrine deep-water succession. The aim of this research is to establish a synthesis depositional model for lacustrine deep-water fine-grained sedimentary systems in the Sichuan Basin. The results indicate that seven lithofacies were developed in the Dongyuemiao Formation and they were stacked in a repeated pattern to constitute ca 10–20 m thick composite cycle sets. A typical composite cycle set comprises an upper and lower unit. Specifically, the lower unit is characterized by basal relatively coarse-grained detrital-rich lithofacies interpreted to record gravity flows that grade upward into relatively fine-grained detrital-lean lithofacies interpreted as suspension deposits from the water column. The upper unit is stacked in a reverse pattern and characterized by basal relatively fine-grained detrital-lean lithofacies that grade upward into relatively coarse-grained detrital-rich lithofacies. Such cyclicities in the Dongyuemiao Formation are associated with third-order lake level variations. Specifically, the relatively coarse-grained detrital-rich lithofacies is interpreted to be deposited from low-density turbidity currents, likely hyperpycnal turbidity flows, during maximum lake level regression when terrigenous fluvial and delta systems developed in the basin margin. The relatively fine-grained detrital-lean lithofacies is interpreted to be deposited from suspension fallout during maximum lake level transgression. This cyclicity pattern and frequent occurrence of sediment gravity flow deposits in the Dongyuemiao Formation suggests a dynamic hydrographic condition in the deep-water lacustrine environment of the Sichuan Basin.

Fold formation in Kurdish Zagros (N Iraq)

Analysis of seismic sections and wells near the frontal folds of Iraqi Kurdistan (Low- and Highly folded zone) document the interplay of folds, faults and possible mechanisms of their generation.Serial sections from 3D seismic volume in the Low folded zone are interpreted based on calibration wells. Sections display fold evolution from low amplitude kinked monocline to high amplitude ramp folding. The fold continues towards the exposed Safeen anticline with a subvertical limb. These lowland sections can also be considered as the lateral growth segment of Safeen anticline.Three geoseismic sections through frontal folds were constructed with variable quality seismic and dips, formation tops from surface and from mountains wells. These sections show tight anticlines with thrust faults cutting to near surface on both limbs; remnant normal faults; a subvertical southern limb crossed by flat thrusts; and a Triassic ductile core.Sections suggest that this part of Zagros is built of two ‘rigid’ units: an upper, Mesozoic-Neogene and a lower, Paleozoic one, separated by a ductile detachment along the lower Triassic. The upper unit is prone to folding and faulting, the lower one to faulting. The detachment in-between comprises the Kurrachine C, lower Triassic Beduh and Mirga Mir formations, and potentially the top members of Permian Chia Zairi formation. Detachment is possibly dominated by evaporites. Our detachment is thicker than only Beduh-Mirga Mir detachment proposed by recent reconstructions of others.Folds are initiated as detachment folds above thickened parts of the Lower Triassic, then evolve into ramp folds. Ramp is formed by the merger of flat thrusts with pre-existing steep earlier normal faults that affect the Mesozoic section. Shear and drag beneath these ramps lead to steepening of the southern limb and to fault propagation. A basal flat thrust is the final element of this fault propagation stage. Underlying rigid Paleozoic can form imbricates that push the Triassic detachment upwards, creating passive folds. These Paleozoic imbricates dip to the south and not to the north, as suggested by reconstructions of others. Finally, strike slip shear documented at outcrops also contributes to the final fold form.Own and others' surface geological observations, indications from seismic and radiometric data suggest that fold generation started in Late Cretaceous, continued in the Paleogene in internal Highly folded zone. In our study area only Late Neogene fold growth can be documented, which is in harmony with 5–8 Ma uplift dates of others. Others’ geomorphologic work suggests fold lateral growth is a quick process. We propose that regional folds, such as Safeen anticline grow in distinct short periods separated by longer quiet intervals.

Origin and palaeodepositional environment of evaporites in the Bala sub-basin, Central Anatolia, Türkiye

ABSTRACT Bala is located in Central Anatolia and is a sub-basin of the Tuzgölü basin, which consists of many basins formed in response to the closure of the Neotethys ocean. The evaporites in Bala sub-basin formed under the influence of regional uplifting during the Middle Eocene period with gradual shallowing in response to the structural compressional regime. The Bala sub-basin comprises four units from bottom to top: the Lower Unit (BU1) consisting of mudstone, claystone with limestone layers; the Evaporites (BU2) containing dominant gypsum with anhydrite; mixed siliciclastic-carbonate-evaporitic deposits (BU3); and the Upper Unit (BU4) containing conglomerate-sandstone-claystone and siltstones. The evaporitic unit, which are the main subject of study consists of primary selenitic gypsum, anhydrite, locally celestite crystals and secondary gypsum formed due to the anhydritization of primary gypsum and then hydration of these anhydrites. The results obtained from mineralogical-petrographic, geochemical and isotopic (δ18O and δ34S) investigations indicate that these evaporites were deposited in shallow marine to sabkha environments dominated by arid conditions. The presence of primary selenite crystals, the anhydrite with nodular, chicken-wire, and mosaic structures support precipitation occurred in a partially saline shallow water. The excessive thickness of the evaporitic accumulation, chaotic masses including gypsum breccia, salt diapirs and dome structures are attributed to tectonic processes acting during the formation of the Central Anatolian basins.

Characterization of the inverted metamorphic gradient of the Passos Nappe (SE-Brazil) based on multiple geothermobarometers

Inverted metamorphic gradients are recognized in several Proterozoic to Phanerozoic orogens. However, the mechanisms that are responsible for the formation of these gradients are still a matter of discussion. In the southern Brasília Orogen, an inverted metamorphic gradient is recorded in the Passos Nappe, that comprises a sequence of metasedimentary rocks with minor intercalations of tholeiitic metamafic rocks, metamorphosed under greenschist facies (biotite zone) at the bottom and high-pressure granulite facies at the top. This paper presents a detailed investigation of pressure and temperature conditions along the Passos Nappe by integrating conventional geothermobarometry in metamafic rock and single-trace elements geothermometry (Zr-in-rutile and Ti-in-quartz) in quartzite. Nine lithostratigraphic units are identified in the Passos Nappe, which are informally named A to I, from the bottom to top, adding up to a minimum thickness of 4.56 km. In mafic rocks, the increase of metamorphic conditions is indicated by: (1) chemical variation of amphiboles, from actinolite/edenitic hornblende in Unit C, to pargasitic hornblende in Units E and G, and Fe-pargasite in Units H and I; (2) plagioclase composition varying from An1-13 in Unit C, An15-27 in Unit D to andesine at upper units; and (3) occurrence of clinopyroxene from the top of Unit E upwards. Additional petrographic features in quartzite also corroborate these insights, such as: the increase of grain size of both quartz and rutile, from bottom to top; the morphology of rutile crystals; the mechanism of quartz recrystallization (subgrain rotation dominates in lower units while grain boundary migration dominates in upper units) and the occurrence of rutile needles in quartz in the upper units, which suggest a continuous gradient. Combined application of Zr-in-rutile and Ti-in-quartz geothermometers in quartzite provided the following average temperature and pressure values for each unit: 673 °C and 11.7 kbar for Unit E, 690 °C and 9.5 kbar for Unit G, 747 °C and 11.6 kbar for Unit H and 758 °C and 11.3 kbar for Unit I. Our data indicate that the Zr-in-rutile and Ti-in-quartz systems do not re-equilibrate in metamorphic conditions lower than 600 °C. The extrapolation of these results to the low-grade units indicate: 496 °C and 4.8 kbar at Unit A, 504 °C and 4.8 kbar at Unit B, 502 °C and 4.4 kbar at Unit C. The results obtained with the geothermometer hornblende-plagioclase and the geobarometer garnet-rutile-ilmenite-plagioclase-quartz in metamafic rocks yielded the following average values for each unit: 486 °C and 5.0 kbar at Unit C, 568 °C and 6.0 kbar at Unit D, 622 °C and 8.1 kbar at Unit E, 650 °C and 8.4 kbar at Unit G, 743 °C and 9.4 kbar at Unit H and 723 °C and 11.2 kbar at Unit I. Since the two geothermobarometric approaches are based on independent chemical systems, the results obtained represent robust estimates for the temperature and pressure conditions for the inverted metamorphic gradient of the Passos Nappe. Comparing the inverted metamorphic gradient at the Passos Nappe with classical occurrences at the Himalaya Orogen, it is possible to assume that both origins were similar, which probably involved isotherm inversion due to subduction, channel flow process associated with shear heating and transport of higher pressure rocks over low-pressure rocks by reverse ductile shearing.

A bird assemblage across the MIS 9/8 boundary: The Middle Pleistocene of Galería (Atapuerca)

Quaternary faunal remains are key for the understanding of the effect of climatic changes on both animal and human populations. Here we show for the first time in Atapuerca the analysis of an avian assemblage through the MIS9/8 boundary, a moment of climatic deterioration that coincides with the spread of Neanderthals and the adoption of Levallois technology. A total of 603 bird remains belonging to 17 taxa have been identified in the Middle Pleistocene units GIII and GIV (Galería site, Atapuerca, Spain). The assemblage is dominated by the extinct raven Corvus corax antecorax, followed by other cave-dwelling taxa. The palaeoenvironmental reconstruction points to the presence of open landscapes and water bodies in the lower units. Both the number of remains and the taxa diversity decreases dramatically towards the upper unit. This general decreasing concurs with the beginning of the MIS8 stage, and it is observed in other faunal groups in Atapuerca, pointing to a MIS8 glacial stage in the Iberian Peninsula stronger than previously described.

Marine mammals fossil remains and synthesis of the sedimentary and paleontological record of the Furninha Cave Pleistocene (Peniche, Portugal)

The Gruta da Furninha is a cave-site in Lower Jurassic limestones, of mainly marine genesis located at ~850 m SE of the Carvoeiro Cape, on the southern coast of the Peniche peninsula (central western mainland Portugal). The entrance gallery, situated in the middle of the cliff, is at ~15 m of altitude. This cave contained a rich and diverse fossiliferous set of Late Pleistocene vertebrates, distributed in several stratigraphic levels, currently housed at the Geological Museum of LNEG (Lisbon). The cave had a record of primitive human occupations documented by 106 Middle to Late Paleolithic artefacts, found in the lower lithostratigraphic unit (Pleistocene). It had also another human occupation in an upper unit (Neolithic, Holocene), where were found human skeleton elements and artefacts. This study focuses on two teeth previously identified as crocodile, housed in collections of the Geological Museum in the assemblages of the Furninha Cave and on a set of five bones, housed at Centro Português de Geo-História e Pré-História (CPGP) collected in a marine terrace in the Furninha cliff. The occurrence of crocodile remains in the Upper Pleistocene of Portugal is not consistent with the fossil record of this period or with the environmental conditions associated with the fully marine paleoenvironments around Furninha Cave. A more detailed analysis of these teeth and their stratigraphic location, now supports that they are cetacean teeth with ~80 ka, which is consistent with the fossil association, depositional environments and climate conditions of the Late Pleistocene in mainland Portugal. To add to these two teeth, in 2017 in sedimentary field work in the marine terraces on the cliffs of the Gruta da Furninha, at the level of 4 to 7 m, found five bones remains, which could be carpal bones of marine mammals.

Diagenesis and reservoir quality of Oligocene Barail Group of Upper Assam Shelf, Assam and Assam Arakan basin, India

The Oligocene Barail deltaic sandstones are the main oil reservoirs in Upper Assam Basin. Nonetheless, the diagenetic alterations and their impact on reservoir quality on Barail sandstones are virtually unknown. The present study aims to know the ways diagenesis plays the role for the invariable hydrocarbon production from these clastic reservoirs within the Barail Group. Samples representing the lower unit of Barail Group known as Barail Main Sand (BMS) and the upper unit known as Barail Coal Shale (BCS) were studied using a combination of petrographic, scanning electron microscopy (SEM), X-ray diffraction (XRD) of clay and wireline log techniques. The average framework composition of BMS is Q49.42F4.18R14.75 while the BCS are composed of Q51.33 F3.89 R14.04. The BMS are moderately hard, fine to medium grained, sub angular to sub rounded, moderately well sorted, dominantly of lithic arenite type and porosity value ranges from 10 to 22.01%. The sandstones of BCS Unit are moderately hard, light grey, fine to very fine grained and usually have low porosity except the channel sands. Both the BMS and BCS have undergone various diagenetic alterations which are observed as mechanical compaction, authigenesis of cements and clays, dissolution and alteration of unstable clastic grains. The identified clay minerals are kaolinite, illite and chlorite. Smectite is occasionally observed as mixed layered smectite-illite clay. The diagenetic alterations along with the clay minerals occupying as pore-filling and lining cements have critically influenced the reservoir quality of both BMS and BCS units of Barail Group. Proper treatment of these clay minerals could aid in the prevention of formation damage to a large extent.

Nitrogen isotope evidence for oxygenated upper ocean during the Cryogenian interglacial period

The Cryogenian interglacial period have witnessed dramatic changes in climate, oceanic environment and biological evolution. The nitrogen isotopic composition, as an important biogeochemical proxy, has the potential to track both the nutrient cycling and redox conditions in the past. However, nitrogen isotopic data during this interglacial time is rather limited. Here, we present integrated data for nitrogen isotopes (δ15N), as well as organic carbon isotopes (δ13Corg), iron (Fe) speciation, pyrite morphology and trace elements from the Cryogenian interglacial Datangpo Formation derived from a drill core from South China to figure out the nitrogen cycling and coeval redox states. The results reveal a gradual oxygenation bottom waters along with deepening O2-H2S chemocline from euxinic black shale in the lower unit (LU), to oxic siltstone in the upper unit (UU), which is consistent with the redox variation inferred in previous studies. Sedimentary δ15N values constantly remain positive (mean value> + 4‰) throughout the Datangpo Formation and display an increase from the LU to the UU. We interpreted the positive δ15N values in the LU as a result of denitrification related to the development of euxinic conditions. The further increase towards the UU associated with limited nutrient supply may indicate the existence of a stable nitrate reservoir in the upper water column, which was consistent with an increased oxygenation during the interglacial time. The elevated O2 levels and bioavailable nitrogen in seawater may have further contributed to the appearance of the earliest metazoan. In addition, our data lay good foundation for further global δ15N correlations among other interglacial successions.

Rock Type and Pore Throat Radius of Zubair Formation in the W Oil Field: Analysis Utilizing Core and Log Data

The Zubair Formation is a prolific oil reservoir in several southeastern Iraq oil fields. The formation comprises thick sandstones with interbedded shales and siltstones of Lower Cretaceous age (Hauterivian to lower Aptian). The environment of the Zubair Formation consists of fluviodeltaic, deltaic, and marine sandstones. In southern Iraq, the area is subdivided into informal members (oldest to youngest). The Lower Shale, lower sand, middle shale, main pay upper sand, and the upper shale. At the W oilfield, the main pay member is an oil producer. The thickness is of the main reservoir about 100 meters thick. A recent study focused on the Main Pay upper sand, which is divided into three informal units. The upper unit H and lower unit L reservoir units are connected by shale intervals (K unit) that extend throughout the field area laterally. There exist four depositional lithofacies of Zubair Formation fluvial, channel, mouth bar, and prodelta depositional lithofacies. Four Facies were defined according to gamma-ray sandstone, shaly sand, sandy shale, and shale Facies. The Zubair formation has four types of rocks (RRT1, RRT2, RRT3, and RRT4) due to heterogeneity. The RRT1 is characterized by 10%-25% porosities and 10-1000 mD permeability. The RRT2 has a similar porosity range to RRT1, 15%–25%, but an order ofmagnitude lower permeability range from 10-100 mD. RRT3 is considered to have high porosity and low permeability is thought to have great storage but poor flow potential. RRT 3 is characterized by 6%-15% porosities and <10 mD permeability. Meanwhile, RRT4 is considered to have low porosity and low permeability. Various rock types showed in the H unit due to heterogeneity, which composed this unit. The K unit unveiled RRT4 due to shale Facies. The rocks types common of unit L are RRT1 and RRT2 where the L unit mostly ranged from sandstone to shaly sand Facies.

Evaluation of Petrophysical Characteristics of Mishrif and Yamama Reservoirs, in Garraf Oil Field, Southern Iraq, Based on Well-Logging Interpretation

The Mishrif and Yamama Formation are the main reservoirs in the Garraf oilfield, Nasiriyah city, of the Euphrates Subzone, Mesopotamian Basin, Southern Iraq. The Garraf oilfield structural pattern corresponds with the similar anticline forming the oilfields of Rafidain and Dujaila and is parallel to the main trend of Zagros, indicating simple coaxial deformation. The petrophysical properties are evaluated using the Interactive Petrophysics V3.5 software. This comprises determining the lithology, mineralogy, and matrix for the investigated reservoirs, as estimating clay volume, total, effective, and secondary porosity, water saturation, permeability, and determining the net pay and gross thickness. The findings of this investigation indicated that the Mishrif formation is divided into two main units separated by a marl layer, with the upper unit having poor reservoir qualities and the lower unit having favorable ones. As a result, there are nine reservoir units in the lower main unit (M1, M1.2, M2, L1, L1.2, L2, L2.2, L2.3, and L2.4). The best and largest reservoir unit capacity is Unit L1.2, with exceptional petrophysical characteristics. Lower units L2.2, L2.3, and L2.4 are nearly saturated in reservoir water, with a little oil in some wells. YA, YB1, and YB2 are the three reservoir units that make up the Yamama formation. Unit YA is the best reservoir unit because of its petro physical properties.

Electro-Facies and Petrophysical Properties of the Hartha Formation in Selected Wells of East Baghdad Oil Field

The Hartha Formation is a major carbonate succession deposited during the Late Campanian period. The current study depends on four selected wells (EB 1, 2, 4 and 30) within the East Baghdad oil field to study electrofacies and petrophysical properties related to the reservoir characterization. The Hartha Formation is divided into three electro-facies units using GR and SP logs in Petrel software. The upper unit of the Hartha Formation is composed mainly of limestone. The middle unit is composing of thick layers of shale. The lower unit is composed mainly of limestone with few shale layers. The three units are divided into three types of rocks in relation to the total porosity: 1. High-moderate active porosity rocks (type I). 2. Moderate active porosity rocks (type II). 3. Low-non pores rocks (type III). The lower unit represents the shale–dominated part of the Hartha Formation, with low to non-pores rocks (type III). This zone is revealed in all studied wells. These are limit presences for the high to moderate active porosity type (I) within the shale bands lithofacies appear in the studied wells. The middle unit is divided into two subzones. The upper part of this zone is characterized by high to moderate active porosity (type I), while the lower one shows moderate active porosity (type II) and low to non-pores rocks (type III) due to the high ratio content of shale. Upper rock-unit is expressed by high-moderate active porosity rocks (type I), which shale content is very low. This porosity type is identified through the upper unit at the East Baghdad oil field. These characteristic features are highly consistent with the low to moderate shale value rock unit.

Field Description and Lithostratigraphic Study of Sargelu Formation in Rania and Sargelu sections, Northern Iraq

The Sargule Formation was deposited during the Middle Jurassic, representing one of the most important source rocks in Iraq and surrounding areas.
 Jurassic successions are commonly exposed as an isolated patch at some eroded anticline’s cores and limbs in the High Folded Zone, Imbricate Zone, and Thrust Zones of northern Iraq. The Sargelu section is located in Sargelu village at Surdash anticline, while the Rania section is located in Rania city near Hanjira village at Shaweri anticline. Fieldwork in Rania and Sargelu Sections allow to divide Sargelu Formation lithostratigraphically into many subdivisions as follow:
 The Sargelu Formation in the Rania section is about 40 m and can be divided into two lithologic units; the upper thin to medium bituminous limestone beds alternated with thin chert beds, and the lower thin to medium bituminous limestone beds alternated with fissile gray shale beds.
 the The Sargelu section comprises 180m and is divided into three units; the upper unit consists of dark gray limestone beds and thin brownish-black of laminated shale. The middle unit includes dark chert alternated with dark gray bituminous limestone and brownish-black laminated shale. At the same time, the lower unit consists of dark gray bituminous limestone beds alternated with medium brownish-black laminated shale beds.

Properties and stratigraphy of polar ice patches in the Canadian High Arctic reveal their current resilience to warm summers

Ice patches are ubiquitous in polar regions and are a key element for landscape evolution. We present new insights into polar desert ice patch formation based on snow and ice properties at Ward Hunt Island (Canadian High Arctic, 83°N). Our results demonstrate that ice patches are composed of two distinct units. The upper unit is characterized by very fine granular and bubbly ice with a clear oblique layering. By contrast, the lower unit is strikingly different with coarse crystals, lower porosity, and a high frequency of fractures. For both units, superimposed ice formation at the base of the deep snowpack stands out as the primary ice aggradation process. The distinct properties of the lower unit likely result from a long period of kinetic ice crystal growth indicating a minimum age of several hundred years. A radiocarbon date of 3 487 ± 20 cal BP suggests that ice patches could potentially date back to the late Holocene. This old ice was recently truncated during warmer summers between 2008 and 2012, but the ice patch quickly recovered its volume during cooler summers. The old age of the ice patches and their rapid regeneration after melt events suggest their resilience to current warmer summers.

Dolomite–magnesite formation and polymetallic mineralization in a rift-sag basin on the western margin of the Red Sea: Paleoenvironmental, hydrothermal, and tectonic implications

ABSTRACTThe present study gives new insight on the formation conditions of dolomite and magnesite in an early–middle Miocene succession related to a half-graben rift-sag basin on the western margin of the Red Sea. The studied Miocene succession comprises two units of siliciclastic–carbonate rocks separated by a magnesite bed. The succession is enriched with epigenetic–supergenetic polymetallic minerals, dominated by zinc-bearing ferromanganese oxides. These represent oxidized Mississippi Valley-type deposits (MVT) formed during uplifting in late Miocene–Pliocene time. Multistage dolomitization (four dolomite types: D1–D4) and magnesite authigenesis, enhanced by tectonic uplifting and faulting related to the Red Sea rifting, have been recorded. The first dolomite phase (D1) is pervasive early diagenetic dolomicrite (replacement type), which is dominant in the lower unit. Magnesite occurs as microcrystalline aggregates exclusive to the lower unit, where its authigenesis was after D1 and before D2. Occurrence of magnesite was mostly related to a restricted environment in a sag fault-bounded basin with shallow evaporative hypersaline conditions in coastal areas. D2 dolomite occurs in the lower and upper units as replacement and/or cement type of medium- to coarse-crystalline dolomite crystals. The three magnesium-rich carbonates (D1, magnesite and D2) are related to successive events of sea-level fall and rise in mesohaline and hypersaline conditions. Enrichment of magnesite and D2 dolomite with Na (up to 2.16 wt.%) and Sr (up to 1483 ppm) supports their formation under more saline evaporative conditions if compared with D1 dolomite which was formed in near-normal sea water or mesohaline fluids. The third and fourth dolomite phases (D3 and D4) are late diagenetic pore-filling coarsely crystalline and zoned, and restricted mainly to faulted areas associated with the polymetallic ore deposits. Elemental analyses of the four dolomite phases show different chemistries, i.e., non-ferroan dolomites (D1 and D2), alternation of manganiferous and non-ferroan zones (D3) and/or ferroan-type dolomite (D4). Stable- isotope values of the four dolomite types (δ18OVPDB of –7.82‰ to –5.88‰) and geochemistry suggest involvement of shallow evaporative conditions in coastal areas, enhanced either by dry and hot climate or by hydrothermal process in their formation. Nonetheless, the localized occurrence of D3 and D4 types along the faults, their concomitant occurrence with the epigenetic–supergenetic polymetallic ore deposits, and the preservation of unaltered feldspar grains ruled out the meteoric-water interaction and reinforce the fault-controlled and deep-seated hot fluid evolution for these two dolomite types. The underlying ultramafic and serpentinite rocks along with the intercalated magnesium-rich clays and/or the modified seawater most probably played a critical role in the diagenesis and/or precipitation of dolomite and magnesite. The proposed model can contribute to better understanding the genetic mechanisms of magnesite and dolomite hosted by mixed siliciclastic–carbonate deposits and their relations with MVT mineralization conditions in rift basins.

A 600 years sediment record of heavy metal pollution history in the Danube Delta

Heavy metal pollution in the Danube Delta (in sediments, water and living organisms) has recently received increasing attention due to its impact on ecosystems health and water quality. However, long term records of heavy metal contamination are not available to date. In this study radiometric dating and geochemical analyses for major elements (Al, Fe, Ca and S) and metals (Cu, Zn, Pb, Ni, Cr and Cd) were performed on the top 4 m of a 9-m sediment core retrieved from the alluvial plain of Sulina distributary channel aiming to reconstruct the heavy metal geological background and contamination history and discuss the possible origins (natural vs. anthropogenic) of metals and the main factors driving their temporal variation. Chronological analysis revealed that the top 4 m of the core span the last ~600 years. Three distinct sediment units (U1: 400–200, U2: 200–140, U3: 140–15) were identified based on the downcore element concentration variation. The lower unit (400–200 cm, ~1450–1700 CE) shows an upward increase of Cu, Zn, Pb, Ni, Cr and Cd metal contents, which are strongly correlated with Al. Enrichment factor (EF) analysis indicates that metals detected in this unit are derived primarily from natural sources. In contrast, metals show elevated EF values within the middle (200–140 cm, ~1700–1770 CE) and upper unit (140–15 cm, ~1770 CE to present). The highest degrees of enrichment of Cu, Zn and Cd occur in the peat layer of the middle unit (U2) which displays higher organic carbon and sulfur contents, indicating that diagenetic enrichment of detected metals occurs under reducing condition. Overall, sediment contamination is moderate while the level increases with time. This study provides new insights into the metal contamination history of deltaic environments and yields baseline values for heavy metal contents in pristine sediments deposited prior to the onset of anthropogenic impact.

Sedimentary environment and tectonic setting of the clastic formation of the Tanjianshan Group in the Tuomoerrite area, North Qaidam

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物，也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究，而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中，对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段，其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合；上岩性段包含海底扇内扇、中扇和外扇沉积，且以中扇环境的沉积为主。垂向上，它们呈现出粒度向上逐渐变细特征；空间上，具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩，其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩；长石主要为斜长石；石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主，并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育，呈现出典型的浊流沉积特征；同时在局部露头见有滑塌构造和波痕。区域上，这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧；古水流分析显示，它们的碎屑物质主要来自于其北东方向。这些结果表明，柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。;Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

Stratigraphic reconstruction of the lower–middle Miocene Goto Group, Nagasaki Prefecture, Japan

AbstractThe Goto Islands are located at the westernmost tip of the Japan archipelago, and preserve a lower–middle Miocene sedimentary sequence deposited during rifting of the continental margin and opening of the Sea of Japan. The stratigraphy of the Goto Group and new K–Ar, fission‐track, and U–Pb age data were used to determine the initial conditions of rifting in southwest Japan. The thickness of the Goto Group is 2000–3000 m. The lower unit (ca. 22–17.6 Ma) consists of thick, greenish, volcaniclastic rocks with basaltic volcanic material, representing the initial stages of continental rifting. The middle unit (ca. −17.6 Ma) consists of alternating sandstones and shales deposited in lacustrine and meandering fluvial environments in a syn‐rift sedimentary basin during a period of volcanic activity. The upper unit (ca. 17.6–16.8 Ma) consists of thick sandstones of fluvial–deltaic facies that were deposited during rapid subsidence at the continental margin. This unit was deposited by a large fluvial system that flowed into the Sea of Japan. These sequences contain relatively cooler to warmer flora (Daijima‐type) and record the warm period of the Miocene Climatic Optimum. The Goto felsic volcanic rocks (16.8 ~ 15.4 Ma) unconformably overlie the Goto Group, and granitic magmatism (ca. 16–14.5 Ma) occurred after sedimentation of the Goto Group. The widespread lacustrine, meandering–braided fluvial, and vast deltaic systems of the Goto Group, and felsic volcanism, were formed due to rapid subsidence that produced a horst‐and‐graben basin during the early stages of rifting of a volcanic arc along the eastern margin of Eurasia. These events occurred from 22.0 to 16.8 Ma before and during the formation of the Sea of Japan.

The Messinian evaporites of the Mesaoria basin (North Cyprus): A discrepancy with the current chronostratigraphic understanding

Large volume of evaporites were deposited during the Messinian Salinity Crisis (MSC) across the Mediterranean. These evaporites are currently outcropping on land and are interpreted by seismic profiles beneath the Mediterranean floor. Biostratigraphic, magnetostratigraphic and astrochronologic data recovered from sediments below and above outcropping evaporites, together with gypsum facies associations and stratigraphic cyclicity, are the cornerstone of what is known as the MSC ‘three-stage’ model: Primary Lower Gypsum (PLG) – MSC stage 1, Resedimented Lower Gypsum (RLG) - MSC stage 2, and Upper Gypsum (UG) – MSC stage 3. Although this litho- and chronostratigraphic model is mainly based on the gypsum succession in Sicily, it is being currently applied by many investigators across the Mediterranean. The Mesaoria basin, in North Cyprus, hosts well exposed MSC gypsum deposits of the Kalavasos Fm. Two informal units are distinguished in the gypsum succession. The lower unit, largely consisting of clastic gypsum deposits, is conformably overlaid by the upper unit, mostly consisting of ‘in situ’ vertically-oriented selenite deposits. Based on the lithostratigraphic gypsum succession, the lower unit could be tentatively assigned to RLG - MSC stage 2, while the upper unit could correspond to UG - MSC stage 3. However, our lithologic and geochemical (δ 34 S sulfate δ 18 O sulfate , 87 Sr/ 86 Sr) data in gypsum points that the upper unit fits with those of the PLG – MSC stage 1. For the first time, thick vertically-oriented selenite beds with lithofacies and geochemical signatures diagnostic of PLG deposits lay conformably over clastic gypsum successions diagnostic of RLG deposits in the currently accepted ‘three-stage’ model. In North Cyprus, ‘in situ’ selenite platforms and ‘clastic’ gravity-flow gypsum deposits are coeval involving erosion and redeposition during the same evolutive stage. The complete gypsum succession in North Cyprus must be considered as MSC Lower Evaporites in the ‘two-step’ model (Lower Evaporites and Upper Evaporites) classically proposed prior to the ‘three-stage’ model. We show how nearby Messinian evaporite basins in the same island (North and South Cyprus) can produce different sedimentary records. Our data cast doubts on the systematic application of the ‘three-stage’ litho- and chronostratigraphic model to North Cyprus and other MSC Mediterranean evaporite successions. This work highlights the importance of local processes in the sedimentation and distribution of MSC evaporites in active tectonic settings, and alerts against extrabasinal MSC correlations based on gypsum facies distribution. • North Cyprus hosts important Messinian Salinity Crisis (MSC) evaporite deposits • MSC gypsum successions in North and South Cyprus are different • Geochemical data assigns North Cyprus evaporites to the MSC Lower Evaporites • The MSC gypsum succession in North Cyprus differs from the three-stage model • Extension of the Sicily based three-stage model to other basins is questionable