Hasil untuk "Stratigraphy"

P. Grootes, M. Stuiver, J. White et al.

J. Hardenbol, J. Thierry, Martin Farley et al.

Michal Šujan, Kishan Aherwar, Rastislav Vojtko et al.

The data included in this article specify the characteristics of the Upper Miocene fill of the Turiec Basin and served for reconstruction of temporal evolution of depositional systems in this intermontane basin located within the Western Carpathians (Central Europe). The borehole lithological log data were used to describe the stratigraphy of the Turiec Basin in geological sections and were gained in the Geofond archive of the State Geological Institute of Dionýz Štúr. The sedimentological data were acquired by field research applying facies analysis to nine outcrop sites. The outcrops served for grain size analyzes performed by sieving and laser diffraction, for geochemical analyzes using ICP-ES, ICP-MS and XRF, and for mineralogical analyzes of whole rock and clay fraction by XRD. Moreover, the muddy layers on outcrops served for collection of 31 samples for the authigenic 10Be/9Be dating. The geochronological data are presented by using five different initial ratios for calculation, determined within the Turiec Basin at the Late Pleistocene alluvial fan and river terrace sites as well as at two Holocene muddy floodplain sites. Another initial ratio data are gained from an Upper Miocene lacustrine succession dated independently by magnetostratigraphy in previous research. Finally, a summary of previously published strontium isotope data from the Turiec Basin is included. The interpretations of the data are provided in Šujan et al., (2023) Palaeogeography, Palaeoclimatology, Palaeoecology 628, 111746.

J. Gómez-Romeu, J. Gómez-Romeu, N. Kusznir

<p>Seismic reflection interpretation at magma-poor rifted margins shows that crustal thinning within the hyper-extended domain occurs by in-sequence oceanward extensional faulting which terminates in a sub-horizontal reflector in the topmost mantle immediately beneath tilted crustal fault blocks. This sub-horizontal reflector is interpreted to be a detachment surface that develops sequentially with oceanward in-sequence crustal faulting. We investigate the geometry and evolution of active and inactive extensional faulting due to flexural isostatic rotation during magma-poor margin hyper-extension using a recursive adaptation of the rolling-hinge model of Buck (1988) and compare modelling results with published seismic interpretation. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on published seismic reflection profiles can be generated by the flexural isostatic rotation of faults with initially high-angle geometry. Our modelling supports the hypothesis of Lymer et al. (2019) that the S reflector on the Galician margin is a sub-horizontal detachment generated by the in-sequence incremental addition of the isostatically rotated soles of block-bounding extensional faults. Flexural isostatic rotation produces shallowing of emergent fault angles, fault locking, and the development of new high-angle shortcut fault segments within the hanging wall. This results in the transfer and isostatic rotation of triangular pieces of hanging wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few kilometres in lateral extent and thickness. The initial geometry of basement extensional faults is a long-standing question. Our modelling results show that a sequence of extensional listric or planar faults with otherwise identical tectonic parameters produce very similar seabed bathymetric relief but distinct Moho and allochthon shapes. Our preferred interpretation of our modelling results and seismic observations is that faults are initially planar in geometry but are isostatically rotated and coalesce at depth to form the seismically observed sub-horizontal detachment in the topmost mantle. In-sequence extensional faulting of hyper-extended continental crust results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast, out-of-sequence faulting results in a transition to exhumed mantle with bathymetric relief.</p>

Xia Bian, Zhuyi Fan, Jiaxing Liu et al.

This paper presents a regional 3D geological modeling method based on the stacking ensemble technique to overcome the challenges of sparse borehole data in large-scale linear underground projects. The proposed method transforms the 3D geological modeling problem into a stratigraphic property classification problem within a subsurface space grid cell framework. Borehole data is pre-processed and trained using stacking method with five different machine learning algorithms. The resulting modelled regional cells are then classified, forming a regional 3D grid geological model. A case study for an area of 324 km2 along Xuzhou metro lines is presented to demonstrate the effectiveness of the proposed model. The study shows an overall prediction accuracy of 85.4%. However, the accuracy for key stratigraphy layers influencing the construction risk, such as karst carve strata, is only 4.3% due to the limited borehole data. To address this issue, an oversampling technique based on the synthetic minority oversampling technique (SMOTE) algorithm is proposed. This technique effectively increases the number of sparse stratigraphic samples and significantly improves the prediction accuracy for karst caves to 65.4%. Additionally, this study analyzes the impact of sampling distance on model accuracy. It is found that a lower sampling interval results in higher prediction accuracy, but also increases computational resources and time costs. Therefore, in this study, an optimal sampling distance of 1 m is chosen to balance prediction accuracy and computation cost. Furthermore, the number of geological strata is found to have a negative effect on prediction accuracy. To mitigate this, it is recommended to merge less significant stratigraphy layers, reducing computation time. For key strata layers, such as karst caves, which have a significant impact on construction risk, further on-site sampling or oversampling using the SMOTE technique is recommended.

A. A. Ekdale, R. Bromley, S. Pemberton

N. Ovaskainen, N. Ovaskainen, P. Skyttä et al.

<p>Using multiple scales of observation in studying the fractures of the bedrock increases the reliability and representativeness of the respective studies. This is because the discontinuities, i.e. the fractures, in the bedrock lack any characteristic length and instead occur within a large range of scales of approximately 10 orders of magnitude. Consequently, fracture models need to be constructed based on representative multi-scale datasets.</p> <p>In this paper, we combine a detailed bedrock fracture study from an extensive bedrock outcrop area with lineament interpretation using light detection and ranging (lidar) and geophysical data. Our study offers lineament data in an intermediary length range (100–500 m) missing from discrete fracture network modelling conducted at Olkiluoto, a nuclear spent-fuel facility in Finland. Our analysis provides insights into multi-scale length distributions of lineaments and fractures and into the effect of glaciations on lineament and fracture data. A common power-law model was fit to the lineament and fracture lengths with an exponent of <span class="inline-formula">−</span>1.13. However, the fractures and lineaments might follow distinct power laws or other statistical distributions rather than a common one. When categorising data by orientation, we can highlight differences in length distributions possibly related to glaciations. Our analysis further includes the topological, scale-independent fracture network characteristics. For example, we noticed a trend of decreasing apparent connectivity of fracture networks as the scale of observation increases.</p>

E. Harris

Nahideh Ghanizadeh Tabrizi, Abbas Ghaderi, Dieter Korn et al.

Abstract The Permian–Triassic sedimentary succession in the Julfa region is lithostratigraphically composed of limestones and shales of the Julfa Formation, the Zal Member shales, and the Paratirolites Limestone of the Ali-Bashi Formation, as well as shales and carbonate beds of the Elikah Formation. The Lower Julfa Beds are rich in benthic organisms such as brachiopods and corals, while the Upper Julfa Beds and Ali-Bashi Formation contain pelagic assemblages including ammonoids, fishes, and conodonts. These rocks have already been studied from different palaeontological and geochemical perspectives, but most have focused on the strata near the Permian–Triassic boundary. In the present study, ammonoids from older intervals around the Wuchiapingin–Changhsingian boundary in the four stratigraphic sections Aras Valley, Ali-Bashi 1, Ali-Bashi 4, and Zal are outlined. Fourteen genera and 22 species of ammonoids were identified and assigned to five successive biozones. The Araxocers latissimum Zone in the Lower Julfa Beds and the Vedioceras ventrosulcatum Zone in the Upper Julfa Beds document the Wuchiapingian. Following upwards, the Iranites transcaucasius-Phisonites triangulus Zone, Dzhulfites nodosus Zone and Shevyrevites shevyrevi Zone in the Zal Member confirm an early Changhsingian age. This follows the previously presented ages based on conodonts. Keywords: Permian, Julfa, Ammonoid, Wuchiapingian, Changhsingian.     Introduction The northwestern region of Iran along the Permian was a part of the Cimmerian blocks, separated from the Gondwana margin, and migrated northward parallel to the opening of the Neo-Tethys Ocean. At the Permian–Triassic boundary, this region was located near the equator, surrounded by the Neo-Tethys in the south and Paleo-Tethys in the north (Stampfli and Borel 2002; Kent and Muttoni 2020). Northwestern Iran contains valuable Lopingian successions and holds evidence of the largest extinction event in Earth's history at the end of Permian. The classical stratigraphic sections in the Caucasus and Julfa have been of interest to geologists since the 19th century. (e.g., Abich 1878; Rieben 1934; Stepanov et al. 1969; Kozur 2007; Richoz et al. 2010; Ghaderi et al. 2014a, b; Korn et al. 2016; Gliwa et al. 2020). The Permian–Triassic sequences of Julfa and Ali-Bashi mountains have been studied by Stepanov et al. (1969). They have categorized the whole succession into eight major rock units, including Genishik Beds (A), Khachik Beds (B), Lower Julfa beds (C), Upper Julfa beds (D), Permian-Triassic Transition Beds (E), Paratirolites Limestone (F), Lower Elika Formation (G) and Upper Elika Formation (H). After Stepanov et al. (1969), Teichert et al. (1973) also reviewed the Ali-Bashi Mountains region, especially the units E and F in Stepanov et al. (1969) during four parallel stratigraphic sections (sections 1 to 4). They have combined E and F units and introduced a new formation called Ali-Bashi Formation. In the following years, the rock sequences in the Ali-Bashi Mountains have been of great importance for studying molluscan fossils and conodonts. Based on conodonts, brachiopods, and ammonoids, the biostratigraphic information and chemical stratigraphy of these stratigraphic sections have been studied in various papers over the last two decades (e.g., Kozur 2007; Shen and Mei 2010; Ghaderi et al. 2014a, b; Schobben et al. 2015, 2017; Korn et al. 2016) and have greatly improved our knowledge about this lesser-known area in Central Tethys. However, there are still deficiencies in some aspects. In the present paper, ammonoid fauna of the Wuchiapingian–Changhsingian boundary in four different stratigraphic sections of Aras valley, Ali-Bashi 1 and 4, and Zal has been identified, and the biostratigraphy of the sections is presented accordingly.   Material & Methods 142 different ammonoid specimens were taken in situ from the Julfa and Zal Beds, of which 84 belong to the Aras Valley section, 11 belong to Ali-Bashi 1, 18 belong to Ali-Bashi 4, and 29 belong to the Zal. Morphological characteristics of the specimens such as conch geometry and measurements of conch diameter, whorl height and width, apertural height, umbilical width, shape of the venter, arrangement and the shape of flanks, umbilical margin and the umbilical wall, shell ornaments such as growth lines, ribs, constrictions, and suture line were investigated according to Korn (2010) method. Cross-sections and suture lines of most of the ammonoids were drawn in Corel Draw 2019 software. Systematic paleontological studies have also been performed using various references (e.g., Ruzhencev and Shevyrev 1965; Zhao et al. 1978; Bando 1979; Kotlyar et al. 1983; Korn 2003; Leonova 2011; Ghaderi et al. 2014a; Korn et al. 2016; Korn and Ghaderi 2019). The ammonoid specimens discussed in this study are stored in the museum of the Geology Department of the Ferdowsi University of Mashhad, and some in the repository of the Museum fur Naturkundeh in Berlin, Germany.   Discussion of Results & Conclusions The Lopingian ammonoid assemblages of the Julfa area have a different distribution in different parts of the sections in terms of abundance and species diversity; most of them are of late Changhsingian age in these successions (Ghaderi et al. 2014a; Korn et al. 2016). Older specimens of Lopingian have less variety and abundance. The fauna in this study includes 14 genera and 22 species of ammonoids of Julfa Beds and Ali-Bashi Formation Zal Member. Fourteen genera and 18 species have been identified in the Aras Valley section, eight genera and eight species in Ali-Bashi 1, 9 genera and 11 species in Ali-Bashi 4, and eight genera and 10 species in the Zal section. Based on the Korn and Ghaderi (2019) for the Aras Valley section and what has been obtained in the present study, the classic ammonoid biostratigraphy proposed for the Wuchiapingian–Changhsingian boundary interval in the Transcaucasia (Ruzhencev and Shevyrev 1965) revised and used for the Julfa region with some modifications. The following biozones are described here and presented in ascending order: Araxoceras latissimum Range Zone: Due to the partial outcrop of the Lower Julfa Beds in the Aras Valley section and the absence of their basal parts, the constituent interval of this biozone in the mentioned section is incomplete, and its thickness is small compared to other sections. The ammonoid assemblage accompanying this biozone in different sections includes Pseudogastrioceras relicuum, Araxoceras insolens, Prototoceras discoidale, Vescotoceras sp. and Araxoceras truncatum, which well confirms the age of early Wuchiapingin for this biozone. Vedioceras ventrosulcatum Range Zone: This biozone has extended into the Upper Julfa Beds; however, the zonal maker species Vedioceras ventrosulcatum was not observed in the studied sections in this study. Korn and Ghaderi (2019) have described other species of the genus Vedioceras, such as Vedioceras fusiforme, as a respectable alternative to the species Vedioceras ventrosulcatum and the definition of this biozone. The ammonoid fauna associated with this biozone in different sections, including Pseudogastrioceras relicuum, Pseudotoceras armenorum, Dzhulfoceras sp., and Vedioceras sp. Iranites transcaucasius - Phisonites triangulus Assemblage Zone: Korn et al. (2019) in the Aras Valley section and the authors of the present study in the other three sections, Ali-Bashi 1, 4, and Zal introduce the Iranites transcaucasius - Phisonites triangulus Assemblage Zone at the Changhsingianin base. This biozone begins with the unveiling of the Zal Member in the lowest part of the Ali-Bashi Formation. Disappearance of Dzhulfoceras and Vedioceras and the emergence of the first Iranites are the most distinctive feature of this biozone. Phisonites triangulus is also present in the platy marly limestone near the member’s base, associated with Xenodiscus dorashamensis and Pseudogastrioceras relicuum. With the onset of this biozone in the basal part of the Zal Member, there is a significant reduction in benthic versus pelagic fauna, indicating a deepening of the basin, minimization of benthos organisms such as brachiopods, and the predominance of pelagic animals like ammonoids, conodonts, and fishes. Dzhulfites nodosus Range Zone: This range zone begins with the appearance of Dzhulfites as well as the newly introduced genus Araxoceltites (Korn et al. 2019) and is located approximately in the middle of the Zal Member. The best record of this biozone in northwestern Iran is related to the Aras Valley section, where Araxoceltites sanestapanus, Dzhulfites nodosus, and Dzhulfites spinosus have been found together at -9.5 meters below the extinction horizon of the section. The ammonoids Araxoceltites laterocostatus, Araxoceltites cristatus, and Pseudogastrioceras relicuum are also present as the accompanying fauna in this biozone. Shevyrevites shevyrevi Interval Zone: This biozone with a very limited stratigraphic range at the top of the Zal Member is just located below the Paratirolites limestone and begins with the appearance of Shevyrevites shevyrevi. Arexoceltites cristatus is one of the most common species of this biozone, which is found alongside Shevyrevites and rare species belonging to Dzhulfites. The other ammonoids identified in this biozone in different sections include Araxoceltites laterocostatus, Araxoceltites sanestepanus, Dzhulfites nodosus, Dzhulfites spinosus, Pseudogastrioceras relicuum, and Shevyrevites nodosus. It should be noted that all Lopingian ammonoids found in the Julfa region, except for Pseudogastrioceras and Timorites, which are belonging to Goniatitida, are ceratitic types. The predominance of ceratitids in the studied ammonoid assemblages indicates the effect of habitat on end Guadalupian extinction. So that nectobenthic and benthopelagic taxa with less lateral compaction, living in shallower tropics, are more damaged and more severely deformed. In contrast, those with high lateral compression have the most preservation. This confirms the selective effect of extinction on the mentioned fauna, indicating in unfavorable conditions, the ceratitids migrated to deeper areas due to their ability to live in the deep-water column and even survived from the end Permian great extinction event

CHEN Qiang, LI Wenhou, SUN Jiaopeng et al.

The Caojiagou section in Qishan County, Shaanxi Province is located in the southern margin of the Ordos Basin. The well-exposed section deposited complete Ordovician strata and developed various sedimentary types, and its location has convenient transportation. In this paper, the stratigraphy and sedimentary characteristics of the Caojiagou section are introduced in detail. The lower Ordovician Yeli Formation is mainly composed of argillaceous dolomite and Mount Liangjia Formation is characterized by crystal dolomite intercalated with siliceous mass and develops stromatolites, all of which belong to tidal flat facies. The Middle Ordovician Majiagou Formation consists of medium-thin and medium-thick layers of silty-fine dolomite and limestone, belonging to open platform and platform front slope facies deposits. The Fengfeng Formation is mainly composed of medium-thin layer laminated dolomite with a great quantity of thin carbonate debris flow and turbidity current deposits, which represent the gravity flow deposit of the front slope of the platform in the deep-water environment. The Upper Ordovician Pingliang Formation mainly consists of a set of flyschoid rhythmic deposits of the continental slope facies. The Tangwangling Formation represents the debris flow environment of the continental slop and develops the ice-water deposits with typical ice-rafted dropstones.

Esperanza Fernández-Martínez, Ismael Coronado, Luna Adrados et al.

The Luna Valley complex geosite (northwestern Spain) is a region of geoheritage significance located in an area with high environmental value. Geological studies began in the mid-20th century and continue to provide scientific data of significant relevance to the knowledge regarding the Palaeozoic stratigraphy of northern Gondwana and the tectonics of the Variscan orogen. This region also has high value for geoeducation, being visited regularly by both students and the general public. Educational use of the area has promoted the creation of several publicly available materials and activities that include trails, guides, displays and brochures, as well as the development of a small museum. However, over time, weathering; the abandonment of rural life; and the intensive, uncontrolled, and careless use of this region as a geosite for scientific and educational purposes has led to significant degradation and the consequent loss of its geoheritage value. This paper describes the geology of five key geosites in the Luna Valley. This is followed by a review of the promotional initiatives carried out in the area. These data, along with our knowledge of the area, allow us to develop a heritage analysis that includes the main geological interests, conservation status and some key management issues for each of these five individual sites. Several recommendations aim to control the physical degradation of the geosites, encourage their regular monitoring and the updating of the outreach materials using virtual tools, and promote the involvement of the local population in the conservation of this unique site.

Mauricio González, José A. Álvarez-Gómez, Íñigo Aniel-Quiroga et al.

Tsunami hazard can be analyzed from both deterministic and probabilistic points of view. The deterministic approach is based on a “credible” worst case tsunami, which is often selected from historical events in the region of study. Within the probabilistic approach (PTHA, Probabilistic Tsunami Hazard Analysis), statistical analysis can be carried out in particular regions where historical records of tsunami heights and runup are available. In areas where these historical records are scarce, synthetic series of events are usually generated using Monte Carlo approaches. Commonly, the sea level variation and the currents forced by the tidal motion are either disregarded or considered and treated as aleatory uncertainties in the numerical models. However, in zones with a macro and meso tidal regime, the effect of the tides on the probability distribution of tsunami hazard can be highly important. In this work, we present a PTHA methodology based on the generation of synthetic seismic catalogs and the incorporation of the sea level variation into a Monte Carlo simulation. We applied this methodology to the Bay of Cádiz area in Spain, a zone that was greatly damaged by the 1755 earthquake and tsunami. We build a database of tsunami numerical simulations for different variables: faults, earthquake magnitudes, epicenter locations and sea levels. From this database we generate a set of scenarios from the synthetic seismic catalogs and tidal conditions based on the probabilistic distribution of the involved variables. These scenarios cover the entire range of possible tsunami events in the synthetic catalog (earthquakes and sea levels). Each tsunami scenario is propagated using the tsunami numerical model C3, from the source region to the target coast (Cádiz Bay). Finally, we map the maximum values for a given probability of the selected variables (tsunami intensity measures) producing a set of thematic hazard maps. 1000 different time series of combined tsunamigenic earthquakes and tidal levels were synthetically generated using the Monte Carlo technique. Each time series had a 10000-year duration. The tsunami characteristics were statistically analyzed to derive different thematic maps for the return periods of 500, 1000, 5000, and 10000 years, including the maximum wave elevation, the maximum current speed, the maximum Froude number, and the maximum total forces.

David J. Anastasio, Kenneth P. Kodama, Josep M. Parés et al.

Abstract High‐resolution cyclostratigraphy in growth strata are used to reconstruct unsteady folding rates at the regional‐scale Pico del Aguila anticline, southern Pyrenees, to evaluate deformation modulation. Magnetic polarity stratigraphy was used to calibrate cyclostratigraphy‐based anhysteretic remanent magnetization intensity variations to establish precessional frequencies in the growth strata record. The astronomically tuning was used to determine sedimentation rates and absolute time. Incremental tilting rates were calculated between selected horizons over ∼6 myr of fold growth. Careful treatment of uncertainties enhances confidence that the results are meaningful and results show significant variability in folding rates over time. The acceleration phase of fold growth was variable, punctuated by a prolonged period of tectonic quiescence, and correlated to sedimentation changes in the wedge‐top basin. Low dipping bedding intrinsically modulated the initial rates of folding for the first 25° of limb tilt, until ∼38.86 Ma. Then, halotectonics in the Paleogene Jaca Basin extrinsically modulated accelerating folding rates for the next 45° of limb tilting, until ∼37.42 Ma. Finally, forelimb‐steepening leading to geometric strain hardening and blunted folding rates for the last 17° of fold tightening and causing a thrust fault to cut the anticline's core. Folding ended at Pico del Aguila ∼35.10 Ma. Calculated folding rates varied between 0° ± 5.5°and 90° ± 19°/myr over 100s kyr time increments. Variations in the folding rate of the Pico del Aguila décollement anticline are attributed to both intrinsic modulation as a result of progressive bedding steepening during folding and extrinsic modulation as a result of variable deltaic sedimentation rates in the wedge‐top basin.

P. Froggatt, D. Lowe

Sara Mana, Sidney Hemming, Dennis V. Kent et al.

In the Koobi Fora region of the northeast Lake Turkana Basin (Kenya) dozens of archeological sites have been studied for decades in order to understand the behavior of Early Pleistocene hominins. Data collected from these sites have been important for demonstrating the manufacture styles of Oldowan stone-tool users, hominin dietary preferences, and processes of Early Stone Age site formation. A particularly rich locality is collection Area 130. Area 130 is noteworthy for hominin fossils KNM-ER 1805 (Homo) and 1806 (Paranthropus) as well as the FxJj 18 site complex, which represents one of the type localities for the Developed Oldowan of Koobi Fora. However, despite research beginning in the late 1960s, and several revisions to the stratigraphy and dating of the Koobi Fora Formation, few published studies provide a detailed chronostratigraphy for Area 130. The lack of a detailed chronostratigraphy has contributed to conflicting interpretations for the dates of the hominin fossils and archaeological sites. Here we present new geochronologic and paleomagnetic data to develop a chronostratigraphic framework that allows us to directly assess the age of the sediments, fossils, and artifacts from Area 130. Individual pumices from the Orange Tuff marker level and a previously unnamed tuff exposed near the FxJj 18 archaeological site complex (referred here as the FxJj 18 tuff) were analyzed for high-precision single crystal 40Ar/39Ar dating and dated at 1.763 ± 0.007 Ma and 1.520 ± 0.005 Ma respectively. Concurrently, we collected orientated paleomagnetic samples from stratigraphic levels of the KBS Member in Area 130 and used them to develop a magnetostratigraphic section. Our findings can be used to refine the sequence and chronology of the archaeological and fossils sites from Area 130 and other penecontemporaneous sites within the Lake Turkana Basin. Our data show that the first appearance of the Developed Oldowan for Koobi Fora does not correlate with any obvious evolutionary changes represented by the local hominin hypodigm nor with the arrival of a cognitively advanced hominin. Therefore we speculate that the advent of this more sophisticated type of stone tool was a response to a change in the diet of the genus Homo.

Xinhui Yang, Xinyan Ji, Yongkang Cao et al.

Abstract This paper presents a scientific examination of wall paintings at two nonmonastic sites in Gyantse, Tibet: Gazhi Lhakang, which is a family temple built in the mid-eighteenth century by local aristocrats, and the Lotso Residence, which was occupied by Nepalese merchants in the early twentieth century. Samples were analyzed with optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction. Two phases of painting—an early phase and a late phase—were identified in Gazhi Lhakang, including three distinct types of mural stratigraphy. The earlier phase features an unusual technique known as “paperhanging”, wherein the pigments were applied on a layer of Tibetan paper glued to the wall. The later phase at Gazhi Lhakang and the painting of the Lotso Residence feature a relatively simple wall treatment with fewer coating layers and no ground layer. A typical mixture of clay and sand was used for the coating layers, while the structure slightly varied from what has been described in the literature. The techniques of powder embossing, gilding, and gold outlining were adopted in both buildings. The metallic material found at Gazhi Lhakang is a gold-silver alloy, while copper was used as imitation gold at the Lotso Residence. Mineral pigments, such as azurite, malachite, orpiment, cinnabar, and iron oxide, were used for both phases of Gazhi Lhakang. Modern synthetic pigments, such as chrome yellow, emerald green, and synthetic ultramarine, were used for the Lotso Residence, indicating that it was painted after the mid-nineteenth century.

Konert Geert, A. Afifi, S. Al-Hajri et al.

The Paleozoic section became prospective during the early 1970s when the enormous gas reserves in the Permian Khuff reservoirs were delineated in the Gulf and Zagros regions, and oil was discovered in Oman. Since then, frontier exploration has targeted the Paleozoic System throughout the Middle East, driven by various economic considerations. The Paleozoic sequences were essentially deposited in continental to deep marine clastic environments at the Gondwana continental margin. Carbonates only became dominant in the Late Permian. The sediments were deposited in arid to glacial settings, reflecting the drift of the region from equatorial to high southern latitudes and back. Following late Precambrian rifting that formed salt basins in Oman and the Arabian Gulf region, the Cambrian-Devonian sequences were deposited on a peneplained continental platform. The entire region was affected by the Hercynian Orogeny, which climaxed during the Carboniferous. The orogeny manifested itself in a change in basin geometry, inversion tectonics, regional uplift and tectonism along the Zagros fault zone. This deformation caused widespread erosion of the Devonian-Carboniferous and older sections, and was probably caused by collision along the northern margin of Gondwana. The Paleozoic tectonic super cycle ended with the onset of break-up tectonics in the Permian, and the deposition of Khuff carbonates over the newly formed eastern passive margin. A major Paleozoic petroleum system embraces reservoir seal pairs spanning the Silurian to Permian sequences. Hydrocarbons occur in a variety of traps, and are sourced by the Silurian ‘hot shale’. A second petroleum system occurs in areas charged from upper Precambrian source rocks in the salt basins. Hydrocarbon expulsion estimates, taking into account secondary migration losses, suggest that some one trillion barrels of oil equivalent (BOE) may have been trapped from the Silurian ‘hot shale’ alone. However, the long and complex hydrocarbon geological evolution of the basin, combined with low acoustic contrasts between target rock units, difficult surface conditions, tight reservoirs, and deep subsurface environments, posed significant challenges to exploration and development. The critical success factor is the continuous innovative effort of earth scientists and subsurface engineers to find integrated technology solutions, that will render the Paleozoic plays economically viable.

J. McArthur

E. Chi Fru, E. Chi Fru, S. Kilias et al.

An early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Field-wide stratigraphic and biogeochemical reconstructions show two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggests the presence of a photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on a basement consisting of andesites in a ∼ 150 m wide basin in the SW margin of the basin. A banded nonfossiliferous IF (NFIF) sits on top of the Mn-rich sandstones at the transition to the renowned Mn-rich formation, capping the NFIF unit. Geochemical data relate the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions predominated by anoxia, similar to the MFIF. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average <i>δ</i>¹³C_org signature of ∼ −25‰. A similar <i>δ</i>¹³C_org signature in the MFIF could not be directly coupled to hematite by mineralogy. The NFIF, which postdates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO₂ ⋅ nH₂O) while crystalline quartz (SiO₂) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity, and abiotic Si precipitation are proposed to have collectively formed the unmetamorphosed BIF-type deposits in a shallow submarine volcanic center. Despite the differences in Precambrian ocean–atmosphere chemistry and the present geologic time, these formation mechanisms coincide with those believed to have formed Algoma-type BIFs proximal to active seafloor volcanic centers.

O. H. Walliser