Jurassic Research Articles

Bee, and; Honey

“Bees” Bees is about the bees becoming extinct and being forgotten when you die. Bees Boys Jurassic “Honey” Honey is about putting honey into coffee and thinking about dying while there is a sandstorm.

The Maliac Ocean: the origin of the Tethyan Hellenic ophiolites

The Hellenides, part of the Alpine orogeny in Greece, are rich in ophiolitic units. These ophiolites and associated units emplaced during Jurassic obduction, testify for the existence of one, or several, Tethyan oceanic realms. The paleogeography of these oceanic areas has not been precisely described. However, all the authors now agree on the presence of a main Triassic–Jurassic ocean on the eastern side of the Pelagonian zone (Vardar Domain). We consider that this Maliac Ocean is the most important ocean in Greece and Albania. Here, we limit the detailed description of the Maliac Ocean to the pre-convergence period of approximately 70 Ma between the Middle Triassic rifting to the Middle Jurassic convergence period. A quick overview on the destiny of the different parts of the Maliac Ocean during the convergence period is also proposed. The studied exposures allow to reconstruct: (1) the Middle to Late Triassic Maliac oceanic lithosphere, corresponding to the early spreading activity at a Mid-Oceanic Ridge; (2) the Western Maliac Margin, widely exposed in the Othris and Argolis areas; (3) the Eastern-Maliac Margin in the eastern Vardar domain (Peonias and Paikon zones). We established the following main characteristics of the Maliac Ocean: (1) the Middle Triassic rifting marked by a rapid subsidence and volcanism seems to be short-lived (few My); (2) the Maliac Lithosphere is only represented by Middle to Late Triassic units, especially the Fourka unit, composed of WPB-OIB and MORB pillow-lavas, locally covered by a pelagic Middle Triassic to Middle Jurassic sedimentary cover; (3) the Western Margin is the most complete and our data allow to distinguish a proximal and a deeper distal margin; (4) the evolution of the Eastern Margin (Peonias and Paikon series) is similar to that of the W-Margin, except for its Jurassic terrigenous sediments, while the proximal W-Margin was dominated by calcarenites; (5) we show that the W- and E-margins are not Volcanic Passive Margins; and (6) during the Middle Jurassic convergence period, the Eastern Margin became an active margin and both margins were affected by obduction processes.

Palynotaphofacies analysis applied to Jurassic marine deposits, Neuquén Basin, Argentina

Fil: Martinez, Marcelo Adrian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto Geologico del Sur. Universidad Nacional del Sur. Departamento de Geologia. Instituto Geologico del Sur; Argentina

On the Evolutionary History of Uleiella chilensis, a Smut Fungus Parasite of Araucaria araucana in South America: Uleiellales ord. nov. in Ustilaginomycetes.

The evolutionary history, divergence times and phylogenetic relationships of Uleiella chilensis (Ustilaginomycotina, smut fungi) associated with Araucaria araucana were analysed. DNA sequences from multiple gene regions and morphology were analysed and compared to other members of the Basidiomycota to determine the phylogenetic placement of smut fungi on gymnosperms. Divergence time estimates indicate that the majority of smut fungal orders diversified during the Triassic–Jurassic period. However, the origin and relationships of several orders remain uncertain. The most recent common ancestor between Uleiella chilensis and Violaceomyces palustris has been dated to the Lower Cretaceous. Comparisons of divergence time estimates between smut fungi and host plants lead to the hypothesis that the early Ustilaginomycotina had a saprobic lifestyle. As there are only two extant species of Araucaria in South America, each hosting a unique Uleiella species, we suggest that either coevolution or a host shift followed by allopatric speciation are the most likely explanations for the current geographic restriction of Uleiella and its low diversity. Phylogenetic and age estimation analyses, ecology, the unusual life-cycle and the peculiar combination of septal and haustorial characteristics support Uleiella chilensis as a distinct lineage among the Ustilaginomycotina. Here, we describe a new ustilaginomycetous order, the Uleiellales to accommodate Uleiella. Within the Ustilaginomycetes, Uleiellales are sister taxon to the Violaceomycetales.

Calcareous nannofossils at the Triassic/Jurassic boundary : stratigraphic and paleoceanographic characterization

In this work, calcareous nannofossils are identified for the first time in the uppermost Triassic sequence of the Lombardy Basin (Southern Calcareous Alps, Italy). Two zones are recognized, namely the NT2b (latest Triassic) and the NJT1 (earliest Jurassic). Two species resulted to be good markers to constrain the TJB interval: Prinsiosphaera triassica and Schizosphaerella punctulata . Nannofossil data are calibrated with C isotopic chemostratigraphy obtained for carbonate and organic matter. Size reduction of P. triassica and a decline in the abundance of Triassic nannofossils are detected soon after the “precursor Carbon Isotope Excursion (CIE) and culminated during the “initial negative CIE” characterized by lowest nannofossil abundances and small-sized P. triassica . The extinction of Triassic nannofossils occurred in distinctive steps within the “initial negative CIE”, while the Jurassic S. punctulata is first observed at the base of the “main negative CIE”. The latest Triassic nannofossil decline in abundance, size reduction and extinctions, represent a progressive deterioration associated to the Central Atlantic Magmatic Province (CAMP) volcanism. Our findings are consistent with nannofossil changes at supraregional scale and indicate that the massive CAMP flood basalts were preceded by initial volcanic pulses. We speculate that a combination of climate change, fertilization and ocean acidification started to influence the calcification process prior to the “initial negative CIE”. Nannoplankton extinctions were not simultaneous and might imply limited capacity for adaptation in the early stages of evolutionary history. However, originations of new taxa soon after the disappearance of Triassic forms suggest the ability to rapidly overcame extreme stressing conditions.

Deep-sea mass-flow sediments and their exotic blocks from the Ropianka Formation (Campanian-Paleocene) in the Skole Nappe : a case from the Wola Rafałowska section (SE Poland)

Flysch deposits of the Ropianka Formation (Wiar and Leszczyny members; Skole Nappe) at Wola Rafalowska include two different sediments that contain exotic pebbles, cobbles and boulders. The first one is a graded conglomerate that contains mostly cobbles of sandstones, gneisses, Stramberk-type limestones, volcanic rocks, pegmatites and ferruginous siltstones. The second one is a pebbly mudstone that contains clasts of sandstones, stone coal, grey mudstones, volcanic rocks, schists, limestones, marls, black mudstones, conglomerates, volcaniclastic rocks and quartz gravels that are floating within a muddy matrix. Genesis of the conglomerate is unclear because it shows features typical of debris flows (poorly sorted, matrix- to clast-supported, large amount of cobble to boulder fraction) as well as high density turbiditic currents (indistinct normal gradation, small amount of cohesive material, crushed clasts that suggest interaction between grains during transportation and at least partly turbulence during flow). The pebbly mudstone represents typical debris flow deposits (large amount of cohesive material, matrix-supported, poorly sorted, lack of grain gradation and traction structures that suggest laminar flow). Limestones occurring in both exotic-bearing sediments show different Upper Jurassic–lowest Cretaceous facies of a carbonate platform, which was involved in the source area of the Skole Basin, along with its basement. They can be interpreted as deposits of: 1) platform-margin reefs and a platform slope: a) partly silicified coral boundstone, b) microbial-coral boundstone, c) silicified sponge-microbial boundstone grading into peloidal-ooidal grainstone with bioclasts, and d) strongly silicified limestone with intraclasts and bioclasts; 2) deeper, platform slope to toe-of-slope area – bioclastic wackstone; 3) inner platform, including: a) partly silicified wackstone with peloids, small intraclasts and bioclasts, and b) microbial bindstone. Moreover, some exotic clasts are built of Albian–Cenomanian wackstone with abundant sponge spicules and planktonic foraminifers, which are interpreted as deeper shelf sediments. Taking into account the geometry of thrust sheets from the site of the exotic-bearing sediments to the edge of the Skole Nappe, along the most probable transportation path, including tectonic/erosional reduction and different variants of slope inclination, the distance of the mass flows attained at least 25–97 km from the shelf edge.

Black shales and other sediments with high organic matter contents in Phanerozoic climatic cycles: Communication 2. Black shales during the Pangea existence

According to recent concepts, the Earth surface was permanently transformed during its geological history. Some stages of its evolution were marked by the convergence of separate continental blocks to result in the formation of supercontinents, which resisted successfully centrifugal processes. Other stages were characterized by the opposite tendency: after their long existence, the supercontinents became disintegrated into several large and small blacks, the motion of which was accompanied by opening of new sea basins and closure of former basins with the oceanic crust. The second half of the Paleozoic was marked by amalgamation of large continental blocks. In the Devonian, collision between Laurentia and Baltica culminated in the formation of the Euroamerica continent. After the closure of the Ural paleocean in the terminal Carboniferous–initial Permian, it was united with the Siberian and Kazakhstan continental blocks. These events provided the prerequisites for the formation of a new supercontinent (Pangea), which acquired its final configuration at the end of the Permian. One of its segments located mainly south of the equator included Gondwana. Another segment located northward included Euroamerica, Kazakhstan, Siberian, and two China continental blocks. During its geological history, Pangea suffered many dramatic events including several extinctions of organisms. The most significant event took place in the terminal Permian–initial Triassic and at the transition between the Triassic and Jurassic periods.

Sedimentary Petrology Characteristics and Their Implications for Provenance of Flowerpot Basin Jurassic System in Yanqing County, Beijing

The characteristics of sedimentary petrology are significant in determining geological provenance. By using field outcrop observation and indoor identification of thin sections, the characteristics of Jurassic system Tuchengzi Formation clastic rocks exposed in the Beijing Yanqing “flowerpot” basin, which include rock types, clastic composition and cement type, etc. have been analyzed systematically to identify the provenance direction and tectonic setting and nature of the provenance. Research shows that the sedimentary rocks in this area belong to analluvial fan and braided river sedimentary rock system and include mainly conglomerates, lithic sandstone, and feldspathic lithic sandstone. The main compositions of the conglomerate are dolomite and limestone. Nearly 50% to 70% of the sandstones are mainly polycrystalline quartz; 10% to 15% are feldspar; and 40% to 55% are composed of debris from mainly magmatic and metamorphic rocks. A Dickinson triangular diagram indicates that the provenance type in this area is recycled orogny evolving from clastic recycled orogeny such as a collisional orogenic belt to a transitional recycled orogeny. On the basis of the geographic position and tectonic setting, three types of provenance can be identified in the Jurassic system Tuchengzi Formation. The far source provenances are Archean erathem basement metamorphic rocks in the northern basin and granite or adamellite that intruded rocks of the Late Jurassic epoch of the Yanshanian period in the northeast. The nearby provenance is the Mesoproterozoic erathem Changchengian system and Jixianianian system dolomite in both the east and west.

“印度板块”研究回顾及思维再完善—换个方式审视地球暨庆祝中国地质博物馆建馆100周年(1916-2016)

依据当今非洲大裂谷的发育过程可以推断出，2亿多年前由于受到裂谷系的作用，致使冈瓦纳古陆全面解体，出现了南美洲板块、非洲板块、澳大利亚板块、南极洲板块、印度-印支板块；之后裂谷系又逐渐发展成大西洋海岭、印度洋海岭、太平洋海岭。古生物学又证实，“印度板块”与“印支板块”都生存有三叠纪恐龙动物，这表明“印支板块”曾经是冈瓦纳大陆的一部分，与“印度板块”曾经也是一个相互连接的整体，即“印度-印支板块”。从冈瓦纳大陆分离出来，“印度-印支板块”于晚三叠世后期至早侏罗世初期，在赤道附近同“华南大陆板块”发生撞击，自此并入欧亚板块，并将冈瓦纳大陆的海生爬行动物鱼龙、棘皮类海百合及陆生恐龙等生物先后带入亚洲南部的贵州、云南、四川等地区。随着印度-印支板块与欧亚板块向北移动，印度-印支板块又受到来自“东经九十度海岭”的切割，新的裂谷系将其由南至北分成西部的印度板块和东部的印支板块。被分割的印度板块在“东经九十度海岭”和马尔代夫海岭合力推动下，向北移动，至喜马拉雅地区，再次与欧亚板块发生撞击，形成当今的地貌景观。两次撞击都与裂谷系相关联，因此对裂谷系的认识，有助重塑印度板块的运动轨迹，有助重新解释中生代以来众多的地质现象。 At about 200 ma ago, Gondwanaland was split by a rift system, according to the development process of present East African Rift system, into South America Plate, Africa Plate, Australia Plate, Antarctic Plate and India-Indochina Plate. The rift system itself developed to the present Mid-Atlantic Ridge, Indian Ridges, and Pacific Ridges gradually. Triassic dinosaurs, found at both Indian and Indo-China plates, showed that Indo-China Plate was also a part of Gondwanaland and that Indian Plate and Indo-China Plate were located together as Indian-Indo-China Plate. When separated from Gondwanaland, and collided with South-China Plate, it was merged in Eurasian Plate at the Equator in Late Triassic-Early Jurassic period. The collision had brought Gondwana fauna like sea reptiles Ichthyosaurus, crinoids, and terrestrial dinosaurs to South China (Guizhou, Yunnan, Sichuan, etc.). In its further movement northward, Indian-Indo-China Plate was split by the Ninety East Ridge into two parts from south to north: Indo-China Plate at its east and Indian Plate at its west. Indian Plate, driven jointly by the Ninety East Ridge and Maldive Ridge, moved northward and collided with Eurasian Plate again, at the region of present Himalaya, forming present Himalaya topography. The two collisions were caused by the forming of rift systems. So understanding the formation of the rift systems is the key to reconstruct the route of Indian Plate movement which in turns helps to interpret many geological phenomena happened since Mesozoic.

Evidence of macrophagous teleosaurid crocodylomorphs in the Corallian Group (Oxfordian, Late Jurassic) of the UK.

Teleosaurids were a group of semi-aquatic crocodylomorphs with a fossil record that spanned the Jurassic Period. In the UK, abundant specimens are known from the Oxford Clay Formation (OCF, Callovian to lower Oxfordian), but are very rare in the Kimmeridge Clay Formation (KCF, Kimmeridgian to lower Tithonian), despite their abundance in some contemporaneous deposits in continental Europe. Unfortunately, due to the paucity of material from the intermediate ‘Corallian Gap’ (middle to upper Oxfordian), we lack an understanding of how and why teleosaurid taxic abundance and diversity declined from the OCF to the KCF. The recognition of an incomplete teleosaurid lower jaw from the Corallian of Weymouth (Dorset, UK) begins to rectify this. The vertically oriented dentition, blunt tooth apices, intense enamel ornamentation that shifts to an anastomosed pattern apically, and deep reception pits on the dentary unambiguously demonstrates the affinity of this specimen with an unnamed sub-clade of macrophagous/durophagous teleosaurids (‘Steneosaurus’ obtusidens + Machimosaurus). The high symphyseal tooth count allows us to exclude the specimen from M. hugii and M. mosae, but in absence of more diagnostic material we cannot unambiguously assign DORCM G.3939 to a more specific level. Nevertheless, this specimen represents the first mandibular material referable to Teleosauridae from the poorly sampled middle-upper Oxfordian time-span in the UK.

Early Bajocian Marine Gastropods from the Neuquén Basin, Argentina

Fil: Ferrari, Silvia Mariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Centro Nacional Patagonico; Argentina

Enigmatic Red Beds Exposed at Point of Rocks, Cimarron National Grassland, Morton County, Kansas

Point of Rocks, a high-relief bluff overlooking the Cimarron River valley in Morton County, Kansas, is capped by distinct white beds of Neogene Ogallala Formation calcrete that overlie red beds of shale, siltstone, and sandstone. These unfossiliferous red beds are currently assigned to the Jurassic System; however, their age has long been debated due to a lack of marker beds, index fossils, and nearby correlative outcrops. As a result, geologists over the years have assigned the rocks to systems ranging from the Permian to the Cretaceous. In this study, four stratigraphic sections were measured in the red beds and three bulk samples were collected to determine the uranium-lead age distributions of detrital zircon (DZ) populations. Red-bed strata composed of fissile shale and sandstone are interpreted as alluvial overbank deposits, while dominantly trough cross-bedded and planar-laminated sandstones are interpreted as tidally influenced fluvial deposits. Detrital zircon age peaks can be grouped into at least seven subpopulations with a youngest single zircon age of 263.8 ± 12.1 Ma, a more conservative age of 293.0 ± 6.95 Ma based on the youngest grouping of three grain ages overlapping at 2σ, and a complete absence of Mesozoic age zircons. In addition, copper oxides along partings and fractures suggest that the red beds once hosted copper sulfides, a common constituent of regional Permian-Triassic red beds. The DZ data--in conjunction with the identification of the Permian Day Creek Dolomite marker bed in logs of nearby drilling tests--strongly suggest that the enigmatic red beds cropping out at the base of Point of Rocks should be assigned to the Guadalupian Big Basin Formation, the uppermost Permian unit in Kansas.

Where are the remnants of a Jurassic ocean in the eastern Mediterranean region?

The subduction polarity of Tethyan oceanic lithosphere during Jurassic is a controversial topic in relation to the geodynamic evolution of the Alpine–Himalayan system. We present new geological, geochemical and zircon U–Pb data from four different regions of the Eastern Pontides Orogenic Belt, a key area of the Alpine–Himalayan system. We discuss the origin of the magmatism and also the existence of an ocean in the eastern Mediterranean region during the Jurassic period. Jurassic intrusions, predominantly gabbro, tonalite and minor diorite, are well exposed in the southern and axial zones of the orogenic belt. Thermobarometry indicates that high-pressure (6–10kb) crystallization of these intrusions occurred at temperatures of 1183–1250°C. Zircon U–Pb dating from 10 samples show ages between 195 and 165Ma, indicating that magmatism occurred between Sinemurian and Callovian time. We characterize the intrusions from electron microprobe, zircon geochronology, and whole rock and Sr, Nd, and Pb isotopes. Our data show that the studied intrusions are broadly tholeiitic, except for two calc-alkaline bodies, and formed in an arc-related setting with minimal involvement of older crust or sediment.The most widely accepted model proposes that the ultramafic–mafic rocks exposed between the Pontide arc and the Tauride belt are remnants of a Jurassic Penrose-type and/or suprasubduction zone ophiolite. However, new zircon U–Pb age data from mafic lithologies cutting the Kop ultramafic massif do not support this model and clearly indicate that the ultramafic lithologies are Paleozoic or older in age and are not remnants of a Jurassic ocean that known as ‘’Northern Branch of Neotehtys”.

Мезозой ДДЗ: перспективи, методи дослідження та оцінки нафтогазоносності

Oil and gas perspective Mesozoic complex in Dnieper-Donets depression includes Triassic, Jurassic and Lower part of Cretaceous systems. Its common thickness can reach one kilometer and much more. The deposit complex widely spread in Preaxial and Northern near-edge zones of Depression. Geologic and log data about potential Triassic and Jurassic rocks hydrocarbons bearing on several of tens local structures, not including here already known Mesozoic fields, there exist missed productive layers and even stratigraphic complexes, point on exclusive interesting character of this exploration direction. The fact is strange and hardly explainable, but since 1960s years systematic study of Mesozoic rocks in Eastern Ukraine has not been executed. Meanwhile, there are no theoretic foundations which contradict to possibility of Mesozoic commercial hydrocarbon pools forming on most part of Eastern Ukrainian oil and gas bearing basin territory, on the contrary, most of its uplifts have favourable genetic, migrational and accumulative terms of Triassic, Jurassic, and probably Cretaceous hydrocarbon pools existence. Triassic and Jurassic systems deposits of DDD characterized by small and middle bedding depth, freandly thermic, pressure and hydrogeochemical environment. Perspective folds and uplifts mostly sityated in areas with convenient search and development infrastructure. Rational searching complex of works, directed on Mesozoic pools discovery and commercial exploitation proposed.

The rise of birds: 225 million years of evolution

Dinosaurs have become so popular that their flying relatives are often neglected, even though they are still among us. Birds, the living are successful vertebrates which have evolved, adapted and survived over a period of 225 million years. This text is a detailed, illustrated review of the fossil record of birds in a modern context. Palaeontologist, Chatterjee, provides a chronology documenting the long odyssey of birds since Protoavis - which may have taken to the air some 75 million years before the widely known first bird, Archaeopterix. Throughout the text, the author offers details from the history of birds past and present, including: some intelligent theropods such as dromaeosaurs were arboreal and could climb trees with their swivel wrist joint and stiff tail, and glide from tree to ground; the discovery of downy theropod dinosaurs from China indicates that upper jaw mobility, not feathers, is the most distinctive characteristic of birds; and most birds were wiped out 65 million years ago, along with dinosaurs, by large meteoritic impacts. However, a few lineages of birds rebounded from this catastrophe and underwent an explosive evolution. The volume also discussed the significance of the many recently discovered bird and possible bird fossils, from Europe to China to Latin America. Chatterjee outlines varying theories of how animal flight developed and explains, in terms of comparative anatomy, what makes a bird a bird. The book covers some of the greatest events in avian development: their emergence in the Triassic pangean world; their flight refinement and global diversification during the continental breakup of the Jurassic and Cretaceous periods; their sudden decline at the end-Cretaceous extinction; their rebound and explosive radiation during the Cenozoic era; and finally their destiny with us.

U-Th-Pb “multi-phase” approach to the study of crystalline basement: application to the northernmost sector of the Ivrea-Verbano Zone (Alps)

In situ U-Pb geochronology was carried out on amphibolites and siliciclastic metasediments of the Kinzigite Formation exposed in the northernmost sector of the Ivrea-Verbano Zone (Finero area). The aim is to shed light on the tectono-metamorphic evolution of this intermediate-lower crustal section and its bearing with the evolution of the southern and better known sectors of the IVZ. Based on field observation and petrography a metamorphic gradient gently increasing from amphibolite to upper amphibolite facies (from SE to NW) characterizes the whole metamorphic sequence. Metapelites consist mainly of biotite, quartz, plagioclase, garnet, and sillimanite; muscovite progressively disappears as K-feldspar appears and becomes abundant. Amphibolites are made of green-brown hornblende and plagioclase and may contain clinopyroxene defining thin layers together with plagioclase and titanite. Both metapelites and amphibolites show mylonitic deformation which is more intense towards NW, i.e. towards the lower structural levels. The mylonitic deformation strongly affected the lower crustal metabasic rocks of External Gabbro unit (Finero Mafic Complex). Zircon, monazite and titanite U-Pb geochronology was carried out with laser ablation (LA)-ICP-MS on amphibolites, migmatitic paragneiss and mafic granulites occurring as slivers of the Kinzigite Formation in the External Gabbro unit of the Finero Mafic Complex. The multi-chronological approach allowed recognizing three discrete tectono-metamorphic events, at Permian, Triassic and Jurassic. Zircon and monazite yielded Permian ages suggesting (re)crystallization during an high temperature event characterized by both metamorphism and magmatism. Titanite dating provided Triassic and Jurassic ages that were interpreted as U-Pb resetting ages. A Triassic perturbation of the U-Pb system was also recorded by zircon and monazite as rare domains. The tectono-metamorphic reconstruction of the evolution of the northernmost IVZ, as revealed by the new geochronological data, is only partially in agreement with the temperature-time evolutions depicted for the southern sectors of the IVZ. Permian ages indicating magmatism and high temperature metamorphism are common throughout the IVZ, as well as the Jurassic ages related to local thermal pulses and tectonic activity. Conversely, the occurrence of well-constrained Triassic ages is in fact peculiar of the Finero area. Two possible explanations may account for this Triassic event: Triassic ages are possibly related to the thermal effect and fluid circulation during the emplacement of the External Gabbro unit; or alternatively, they are the response to the ductile deformation largely recognized in the whole area. This study is a further evidence of the necessity of approaching crystalline basement with multiple geochronometers in order to unravel the complete tectono-metamorphic evolution.

A new macroflora from the Middle Jurassic (Bathonian) of NW Jordan and its palaeoenvironmental significance

A new macroflora from the Middle Jurassic (Bathonian) of NW Jordan and its palaeoenvironmental significance

Discovery and reservoir-forming geological characteristics of the Shenmu Gas Field in the Ordos Basin

By the end of 2014, the giant Shenmu Gas Field had been found in the Ordos Basin with an explored gas-bearing area of 4069 km2 and the proved geological gas reserves of 333.4 billion m3. This paper aims to review the exploration history of this field and discusses its reservoir-forming mechanism and geological characteristics, which may guide the further discovery and exploration of such similar gas fields in this basin and other basins. The following research findings were concluded. (1) There are typical tight sand gas reservoirs in this field primarily with the pay zones of the Upper Paleozoic Taiyuan Fm, and secondly with those of the Shanxi and Shihezi Fms. (2) Gas types are dominated by coal gas with an average methane content of 88% and no H2S content. (3) The gas reservoirs were buried 1700–2800 m deep underneath with multiple pressure systems and an average pressure coefficient of 0.87. (4) The reservoir strata are composed of fluvial delta facies sandstones with an average porosity of 7.8% and permeability of 0.63 mD, having high pressure sensibility and a strong water-locking effect because the pore throat radius are mostly less than 1 μm. (5) There are different dynamics at various stages in the gas reservoir-forming process. The abnormal well-developed strata pressure was the main reservoir-forming force at the Early Cretaceous setting stage while the fluid expansibility became the main gas-migrating force at the uplift and denudation stage after the Early Cretaceous period. (6) Gas reservoirs with ultra-low water saturation are mainly controlled by many factors such as changes of high temperature and high pressure fields in the Late Jurassic and Early Cretaceous periods, the charging of dry gas at the highly-mature stage, and the gas escape and dissipation at the post-reservoir-forming periods. (7) Natural gas migrated and accumulated vertically in a shortcutting path to form gas reservoirs. At such areas near the source rocks, large-scale gas reservoirs were easily found with plenty of gas sources and high gas saturation; but at those far from the source rocks, relatively small-scale and mostly secondary gas reservoirs were discovered.

Assessing the influence of escalation during the Mesozoic Marine Revolution: Shell breakage and adaptation against enemies in Mesozoic ammonites

Escalation is evolution driven by interactions between individuals and their enemies. We examined escalation in ammonites using repair scars, which are indicative of sub-lethal predation. Because ornamentation is considered an antipredatory adaptation, we tested several hypotheses concerning the relationship between ornamentation and repair scars. We also investigated the possibility of complex sutures as a defensive trait. Ornamentation, suture complexity, and repair scar frequency (RF) data were collected from 26 Jurassic and Cretaceous ammonite genera from North America and Europe. Ornamentation was gauged as a ratio of rib thickness to shell diameter. RF was measured as percent individuals with scars and as average number of scars per individual. Suture complexity factor (CF) was calculated as a weighted count of suture features. Data on 1180 specimens revealed a significant inverse correlation between RF and shell ornament, contrary to our hypothesis that more highly ornamented shells will exhibit more repairs due to increased survivorship of attacks. Taxa exhibiting ornate ornamentation had fewer repair scars than expected, and taxa with ribs and nodes but no keel had more repair scars than expected. Repair frequencies of shells with different ornament types were found to differ between North American and European shells. No other geographic variation was found. Taxa with tightly spaced ribs were found to exhibit more repair scars. Rib size had no significant correlation with longitudinal scar size, disconfirming our hypothesis that scars on taxa with larger ribs were less able to propagate. Scars were concentrated on the first 90° of the shell, suggesting attacks at the aperture, and no right-left-medial selectivity of predatory attacks was found. Although some workers have suggested an antipredatory role for complex sutures, no relationship was found between CF and RF. Body size had a significant effect on repair scar occurrence in all but one of the taxa tested. Repair scar frequency and degree of ornamentation increased through the Jurassic and Cretaceous Periods. The data presented here support the traditionally held hypothesis that repair scars on ammonite shells represent interactions between ammonites and their enemies.

Mesozoic vein-type Pb–Zn mineralization in the Pyrenees: Lead isotopic and fluid inclusion evidence from the Les Argentières and Lacore deposits

The Axial Zone of the Pyrenees contains numerous sedimentary-exhalative Pb–Zn deposits formed during the Early Palaeozoic, which have been the subject of several studies. In addition to these, base-metal vein-type mineralizations are also exposed within the Axial Zone metasediments. These deposits, however, have not been investigated in depth and the timing and geodynamic context of their formation has not been specifically addressed. The vein-type Pb–Zn deposits of Les Argentières and Lacore are located in Devonian terranes of the eastern Pyrenees, south of the Mesozoic Aulus basin. They are interpreted as having been emplaced under an extensional setting. They are characterized by silver-rich tetrahedrite that occurs with Pb–Zn sulphides deposited by low-temperature NaCl–CaCl2 brines. Lead isotopic 208Pb/204Pb and 206Pb/204Pb ratios acquired on galena show more radiogenic values compared to those from the Palaeozoic sedimentary-exhalative mineralization, thus indicating younger ages. According to the model ages, the formation of the two deposits may be narrowed down to middle Late Triassic and Late Jurassic periods, respectively, which allows us to argue in favour of the role of pre-Alpine rifting phases in hydrothermal fluids circulation and mineralization deposition in a vein system bounding the Mesozoic Aulus basin.