Late Triassic-Early Jurassic Research Articles

Jurassic tectonostratigraphic evolution of the Junggar basin, NW China: A record of Mesozoic intraplate deformation in Central Asia

Mesozoic basins in northwest China provide important records for investigating relationships between intraplate deformation in Central Asia and tectonic processes at Asian boundaries. The present study, using well, seismic, outcrop, and thermochronology data in the Junggar Basin and neighboring areas, describes the main features of Jurassic strata in the basin, analyzes the Jurassic evolution of the basin and neighboring mountain belts, and discusses possible mechanisms of Jurassic intraplate deformation in Central Asia. During the Early-Middle Jurassic, episodic uplift of surrounding mountain belts kept the Junggar Basin a contractional closed basin, and alluvial fan, fluvial, delta, and lacustrine depositional environments successively developed from surrounding ranges to the central basin. During the Late Jurassic, the western and central parts of the basin were folded and uplifted, and deposition migrated mainly to the eastern basin. During the latest Jurassic-earliest Cretaceous, pre-Cretaceous strata in the eastern and northeastern Junggar Basin were folded and uplifted, and coarse-grained sediments were transported from surrounding uplifts to the central basin. We suggest that Jurassic episodic deformation events in the Junggar Basin and other areas of Central Asia are related to the Qiangtang collision during the Late Triassic-Early Jurassic, the closure of the western Mongol-Okhotsk Ocean at the Early/Middle Jurassic boundary, a collision of a microcontinent in the Pamir with the southern Asian margin during the late Middle Jurassic-early Late Jurassic, the collision of the Kolyma-Omolon Block with Siberia at the end of the Jurassic, and the subsequent closure of the eastern Mongol-Okhotsk Ocean during the latest Jurassic-earliest Cretaceous.

Analysis of structural deformation in the North Dabashan thrust belt, South Qinling, central China

The North Dabashan thrust belt, which is located in South Qinling, is bounded by the Ankang fault on the north and the Chengkou–Fangxian fault on the south. The North Dabashan thrust belt experienced multiple stages of structural deformation that were controlled by three palaeostress fields. The first structural event (Middle Triassic) involved NNW–SSE shortening and resulted in the formation of numerous dextral strike-slip structures along the entire Chengkou–Fangxian fault zone and within the North Dabashan thrust belt, which suggests that the South China Block moved to the NW and was obliquely subducted under the North China Block. The second structural event (Late Triassic–Early Jurassic) involved NE–SW shortening that formed NW–SE-trending structures in the North Dabashan thrust belt. The third structural event (Late Jurassic–Early Cretaceous) involved ENE–WSW or nearly E–W shortening and resulted in additional thrusting of the North Dabashan thrust belt to the WSW and formation of the WSW-convex Chengkou–Fangxian fault zone, which has an oroclinal shape. Owing to the pinning of the Hannan massif and Shennongjia massif culminations, numerous sinistral strike-slip structures developed along the eastern Chengkou–Fangxian fault zone and were superimposed over the early dextral strike-slip structures.

Geochronology and geochemistry of the Sangri Group Volcanic Rocks, Southern Lhasa Terrane: Implications for the early subduction history of the Neo-Tethys and Gangdese Magmatic Arc

The Sangri Group volcanic rocks are distributed along the southern margin of the Lhasa Terrane on the northern side of the Indus-Yarlung Zangbo suture zone. This Group consists of the Mamuxia and Bima formations and has long been considered to be Late Jurassic to Early Cretaceous in age. In this paper, we report for the first time zircon LA-ICPMS U-Pb ages, whole-rock major and trace element geochemistry, as well as Sr-Nd isotope data of the Bima Formation volcanic rocks in the Sangri County, Tibet. Two samples collected from the Bima Formation volcanic rocks yield zircon U-Pb ages of 195 ± 3 Ma and 189 ± 3 Ma, respectively. These data suggest that the Bima Formation volcanic rocks formed during the Early Jurassic rather than the Late Jurassic-Early Cretaceous as previously reported. The volcanic rocks of the Bima Formation are dominantly composed of basalt and andesite that are enriched in LILEs and LREEs, but depleted in HFSEs, showing typical characteristics of arc volcanic rocks. They also show positive εNd (t) (+ 4.09 to + 7.02) values and low initial 87Sr/86Sr (0.7032 to 0.7050) ratios, similar to the MORB of the Indus-Yarlung Zangbo ophiolites, indicating that the Bima Formation volcanic rocks were derived from a depleted mantle wedge. The magmas subsequently experienced juvenile crust contamination and fractional crystallization during ascent. Geochemical features of magmas of the Bima Formation volcanic rocks are interpreted to be generated by the northward subduction of Neo-Tethys beneath the southern Lhasa Terrane as early as ~ 195 Ma. Coeval with a large volume of Late Triassic-Early Jurassic felsic intrusions within the Gangdese arc, the Gangdese magmatic arc is interpreted to be initiated at a juvenile continental margin during the Late Triassic-Early Jurassic, although a possible intra-oceanic arc setting cannot be excluded.

Age of the Khangai batholith and challenge of polychronic batholith formation in Central Asia

The Central Asian fold belt (CAFB) exhibits many manifestations of granitoid magmatism. The granite formation is largely determined by the convergence of the Siberian continent with structures of the Paleo� Asian ocean, which was practically continuous from the Late Riphean until the Early Mesozoic. This pro� cess was responsible for development of differentage folded domains (Early and Late Baikalian, Cale� donian, Hercynian, and IndoSinian) and conjugate subductionrelated magmatic (including granitoid) belts. An important role in granite formation also belonged to mantle plumes in addition to conver� gence. Their influence on the lithosphere resulted in the formation of giant batholiths represented by accu� mulations of closely spaced large granite plutons (1). Such batholiths were formed in the Late Cambrian- Early Ordovician (Altai-Sayany), Early Permian (Angara-Vitim), Late Permian-Early Triassic (Khan� gai), and Late Triassic-Early Jurassic (Khentei). The individual batholiths are >120 000-150 000 km 2 in size. The geological position of batholiths is independent from basement structures, and they usually comprise several terranes differing in their geological, including magmatic, history. Therefore, batholiths frequently include granitoids independent of them with respect to their formation time and formation conditions. Nevertheless, such a cooccurrence of differentage granites within a single region provides grounds for assumption of the polychronic nature of batholiths and their very long development history (2). This problem is of principal significance for interpreting the geodynamic evolution of the Central Asian fold belt and understanding the nature of granitoid magma� tism. One of the possible approaches to its solution consists in defining differences in the distribution of igneous rocks of different age groups and different geodynamic origin. For example, igneous rocks of the convergence zone are usually characterized by a distri� bution along belts, while products of plume magma� tism are localized above their sources. Precisely such an approach was used for consider� ing the problem of polychronic granite formation in the Khangai batholith. Recent geochronological investigations have revealed the relatively significant scatter of granitoid ages ranging from 300 to 220 Ma with dates of 269-242 Ma being prevalent (3-5) (Fig. 1). At the same time, these data are insufficient for solving the abovementioned problem, since no geochrono� logical dates are available for several key massifs in the southern, central, and southwestern parts of the batholith. Therefore, geochronological investigations of granitoids were conducted in the Tatsin Gol, Erdene Tsogt, Eginaba, Buyant Gol, and Yarugin Gol massifs located in these areas of the batholith. The Tatsin Gol massif is the largest one in the south� eastern part of the Khangai batholith. It is a typical representative of the granodiorite-granite formation, or the Khangai intrusive complex. The massif is com� posed of hornblende-biotite and biotite granodior� ites, monzogranites, and granites. They were formed during two intrusion phases. The first phase is largely represented by granodiorites accompanied by quartz diorites and tonalities. The rocks of the second phase include mediumto coarsegrained monzogranites and granites usually with a distinct porphyroid texture. For geochronological investigations, a sample of light gray porphyroid biotite-hornblende granites (Sample KHAN�09/46) was taken from the central part of the

Transgression-regression event element geochemistry records of southwestern Fujian in Late Triassic-Middle Jurassic

Southwest Fujian area has experienced a large-scale transgression-regression cycle in Late Triassic-Middle Jurassic and the maximum transgression has taken place in Early Jurassic. The migration and enrichment of geochemical element in the continuous fine-grained sediments in the basin recorded the paleosalinity and the paleodepth. The changes of paleosalinity and paleodepth indicate the sea (lake) level relative change in every period of Late Triassic-Middle Jurassic in southwestern Fujian. The relative change curve of sea (lake) level in southwestern Fujian is established based on the m value (m=100×w(MgO)/w(Al2O3)) and the ratios of w(B)/w(Ga), w(Sr)/w(Ba) and w(Ca)/w(Mg). The curve indicates that level I sea-level relative change in southwestern Fujian is composed of the transgression in Late Triassic-Early Jurassic and the regression in the late period of Early Jurassic-Middle Jurassic. The level III sea-level relative change is frequent, which is composed by the lake level descent-lake level rise-lake level descent of Wenbin Shan formation in Late Triassic, the regression-transgression-regression of Lishan formation in Early Jurassic and the lake-level rise-lake level descent-lake level rise-lake level descent of Zhangping formation in Middle Jurassic. The transgression-regression cycle in southwestern Fujian is significantly controlled by the sea-level change in the north of South China Sea. The relative change curve trends of the level I sea-level in the north of South China Sea and the one in southwestern Fujian are the same. The maximum transgressions both occur in Early Jurassic. The level III sea-level curve reflects the fluctuation of a transgression and two regressions in the early period of Early Jurassic.

Geochronological and geochemical constraints on the Erguna massif basement, NE China – subduction history of the Mongol–Okhotsk oceanic crust

We present new geochronological and geochemical data for granites and volcanic rocks of the Erguna massif, NE China. These data are integrated with previous findings to better constrain the nature of the massif basement and to provide new insights into the subduction history of Mongol–Okhotsk oceanic crust and its closure. U–Pb dating of zircons from 12 granites previously mapped as Palaeoproterozoic and from three granites reported as Neoproterozoic yield exclusively Phanerozoic ages. These new ages, together with recently reported isotopic dates for the metamorphic and igneous basement rocks, as well as Nd–Hf crustal-residence ages, suggest that it is unlikely that pre-Mesoproterozoic basement exists in the Erguna massif. The geochronological and geochemical results are consistent with a three-stage subduction history of Mongol–Okhotsk oceanic crust beneath the Erguna massif, as follows. (1) The Erguna massif records a transition from Late Devonian A-type magmatism to Carboniferous adakitic magmatism. This indicates that southward subduction of the Mongol–Okhotsk oceanic crust along the northern margin of the Erguna massif began in the Carboniferous. (2) Late Permian–Middle Triassic granitoids in the Erguna massif are distributed along the Mongol–Okhotsk suture zone and coeval magmatic rocks in the Xing’an terrane are scarce, suggesting that they are unlikely to have formed in association with the collision between the North China Craton and the Jiamusi–Mongolia block along the Solonker–Xra Moron–Changchun–Yanji suture zone. Instead, the apparent subduction-related signature of the granites and their proximity to the Mongol–Okhotsk suture zone suggest that they are related to southward subduction of Mongol–Okhotsk oceanic crust. (3) A conspicuous lack of magmatic activity during the Middle Jurassic marks an abrupt shift in magmatic style from Late Triassic–Early Jurassic normal and adakite-like calc-alkaline magmatism (pre-quiescent episode) to Late Jurassic–Early Cretaceous A-type felsic magmatism (post-quiescent episode). Evidently a significant change in geodynamic processes took place during the Middle Jurassic. Late Triassic–Early Jurassic subduction-related signatures and adakitic affinities confirm the existence of subduction during this time. Late Jurassic–Early Cretaceous post-collision magmatism constrains the timing of the final closure of the Mongol–Okhotsk Ocean involving collision between the Jiamusi–Mongolia block and the Siberian Craton to the Middle Jurassic.

LA‐ICP‐MS Zircon U‐Pb Dating of Intermediate‐Acidic Intrusive Rocks and Molybdenite Re‐Os Dating from the Bangpu Mo (Cu) Deposit, Tibet and its Geological Implication

AbstractThe multi‐stage intrusions of intermediate‐acid magma occur in the Bangpu mining district, the petrogenic ages of which have been identified. The times and sequences of their emplacement have been collated and stipulated in detail in this paper by using the laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating method. The ages of biotite monzogranite that were formed before mineralization in the southwest of this mining district are 70±1 Ma (mean square of weighted deviates (MSWD) = 9.5, n= 8) and 60.60±0.31 Ma (MSWD=3.8, n= 16), which belong to the late Cretaceous–early Paleocene in age. That means, they are products of an early tectonic‐magmatic event of the collision between the Indian and Asian continentals. The ages of ore‐bearing monzogranite porphyry and ore‐bearing diorite porphyrite are 16.23±0.19 Ma (MSWD= 2.0, n= 26) and 15.16±0.09 Ma (MSWD=3.9, n= 5) separately, which belong to the middle Miocene in age; namely, they are products of the Gangdese post‐collision extensional stage when crust‐mantle materials melted and mixed as well as magmatic intrusion simultaneously occurred. Some zircons with ages of 203.6±2.2 Ma (MSWD=1.18, n= 7) were captured in the ore‐bearing diorite porphyrite, which shows that there had been tectono‐magmatic events in the late Triassic–early Jurassic. Molybdenum (copper) ore‐bodies produced in the monzogranite porphyry and copper (molybdenum) ore‐bodies produced in the diorite porphyrite are the main ore types in this ore deposit. The model ages of Re‐Os isotopic dating for the 11 molybdenite are 13.97–15.84 Ma, while isochron ages are 14.09±0.49 Ma (MSWD=26). The isochron ages of seven molybdenite from molybdenum (copper) ore with monzogranite porphyry type are 14.11±0.31 Ma (MSWD=5.2). There is great error in the isochron ages of four molybdenite from copper (molybdenum) ore with diorite porphyrite type, and their weighted average model ages of 14.6±1.2 Ma (MSWD=41), which generally represent the mineralization age. The results about the Re‐Os isotopic dating of molybdenite in the ore of different types have limited exactly that, the minerlazation age of this ore deposits is about 14.09 Ma, which belongs to the middle Miocene mineralization. The Bangpu deposit has a uniform metallogenic dynamics background with the porphyry type and skarn‐type deposits such as Jiama, Qulong and others.

Tectonic history of the Zhangguangcailing Group in eastern Heilongjiang Province, NE China: Constraints from U–Pb geochronology of detrital and magmatic zircons

In this paper we present U–Pb age data of detrital and magmatic zircons from sedimentary and volcanic rocks in the Zhangguangcailing Group (ZG), NE China, to constrain the tectonic evolution of the region as a whole. The ZG consists of slightly metamorphosed volcanic and sedimentary rocks, and from bottom to top is divided into the Zhenggou, Hongguang, and Xinxing suites. Zircons from three schists in the Zhenggou suite give 12 main groups of age populations (from 226 to 861Ma), whereas zircons from a basaltic andesite give a Late Triassic age (211±2Ma). In the Hongguang suite, zircons from two schists and a greywacke give 6 main groups, 5 main groups, and 3 main groups of age populations (from 262 to 916Ma), respectively, whereas zircons from a gabbro–diorite and two volcanic rocks give ages of 259, 219, and 317Ma, respectively. Zircons from a schist in the Xinxing suite give 12 main groups of age populations (from 284 to 1837Ma). These results, together with the field relationships of the rocks, indicate (1) that the sedimentary and volcanic rocks of the ZG have diverse ages (from Early Paleozoic to Early Mesozoic), (2) that the rocks do not lie in a logical stratigraphic sequence, and (3) that the rocks represent a tectonic mélange. Based on the youngest age (211Ma) for volcanic rocks within the ZG, and the age of deformation (174–184Ma) of the Heilongjiang Complex, we propose that the tectonic mélange formed during the Late Triassic–Early Jurassic. Furthermore, the occurrence of detrital zircons with ages of 0.8–0.9, 1.8, and 2.4–2.5Ga implies the existence of Neoproterozoic magmatism and the remnants of a Precambrian basement in the Songnen–Zhangguangcai Range Massif, NE China.

Late Triassic, Early and Middle Jurassic Radiolaria from ferromanganese-chert ‘nodules’ (Angelokastron, Argolis, Greece): evidence for prolonged radiolarite sedimentation in the Maliac-Vardar Ocean

In the Argolis, the Basal Sequence, constituting the eastern Pelagonian margin which bordered the Maliac-Vardar oceanic domain, includes shallow-water carbonates of Late Triassic-Early Jurassic, condensed pelagic limestones of Early-Middle Jurassic, radiolarian cherts of late Middle-Late Jurassic age and siliceous mudstones and sandstones rich in ophiolite fragments. Up-section, coarse breccias, including clasts of boninites derived from the ophiolite obducted onto the Pelagonian margin in Late Jurassic times crop out. Near Angelokastron a small quarry exposes pervasively sheared dark reddish-brown, radiolarian-bearing cherty shales with disrupted fragments of chert and chert nodules impregnated by ferro-manganese oxides. These shales occur in the footwall of a thrust bringing them into contact with the Pantokrator Limestone of the Basal Sequence. We collected more than 30 samples of the chert fragments and the shaly matrix. Thirteen nodules and one matrix sample yielded determinable radiolarians. Low to non-detectable concentrations of trace metals such as Co, Cr, Cu, Ni, Zn, and Pb indicate a hydrothermal origin of the ferro-manganese mineralization. The radiolarian taxa found indicate four age groups for the nodules that are embedded in the siliceous shale matrix that yielded a Middle Jurassic age (middle Bathonian). The first group includes a nodule of Late Triassic age (late Norian to Rhaetian); the second group nodules of Early Jurassic age (late early to late Pliensbachian and probably middle-late Toarcian); the third group nodules of early Middle Jurassic age (Aalenian–Bajocian); the last group finally includes nodules of late Middle Jurassic age (Bajocian–Bathonian). The presence of Upper Triassic to Middle Jurassic Mn-impregnated chert nodules in a Middle Jurassic matrix indicates a deep oceanic environment of deposition outside the Pelagonian realm (easternmost Adria Plate), which at that time was a shallow-water carbonate platform with a thin pelagic limestone cover. The chert nodules are with all certainty derived from the oceanic Maliac-Vardar domain and were, together with their host formation, tectonically emplaced onto the Pelagonian margin. We speculate that these nodules, more lithified than their matrix, were exhumed on the slope of an intra-oceanic accretionary wedge and were redeposited in the Middle Jurassic siliceous mudstones on the floor of the subducting Maliac-Vardar Ocean.

Crustal thickening along the West Antarctic Gondwana margin during mid-Cretaceous deformation of the Triassic intra-oceanic Dyer Arc

Subduction-related Mesozoic mafic dykes in eastern Palmer Land, Antarctic Peninsula, record the development of an intra-oceanic arc terrane, the Dyer Arc, probably of late Permian–Triassic age, represented by a tholeiitic dyke group. Arc rocks were deformed in late Triassic–early Jurassic and mid-Cretaceous times on the Gondwana margin. Eruption of syn- to post-mid-Cretaceous orogenesis magmatism is represented by a calc–alkaline group of dykes. The tholeiitic dykes intruded immature granitic crust of the Eastern Zone sub-terrane of the Central Domain, one of the magmatic terranes of the Pacific margin of Gondwana. The calc–alkaline dykes straddle the major tectonic boundary between the Central Domain and the continental margin Eastern Domain. 132 dykes were studied, 82 of which are calc–alkaline, 48 tholeiitic and two shoshonitic, across an area of approximately 4000km2. Tholeiitic dykes strike broadly NNW–SSE, transposed into parallelism with the strike of the tectonic boundary during Cretaceous orogenesis whereas calc–alkaline dykes strike tightly ESE–WNW at a high angle to the boundary. The tholeiites pre-date late Triassic deformation and metamorphism, and are interpreted as dominantly Triassic in age, whereas Ar–Ar dated calc–alkaline dykes are younger (~100Ma and ~97Ma) and field relations indicate that they overlap with the waning phase of the mid-Cretaceous Palmer Land Event. The tholeiites have trace element abundances similar to, but more depleted than, those of modern intra-oceanic arcs, as recorded by Zr/Hf ratios. Nb/Yb versus TiO2*/Yb and Sm/Yb versus La/Sm plots are used to model depths of partial melting. The tholeiites were mostly generated at shallow depths corresponding to 2.5 and certainly less than 3.0GPa in largely garnet-free mantle. The calc–alkaline magmas were generated at pressures greater than 3.0 to possibly >3.5GPa, in the garnet zone. The deepening of the mantle source, and onset of calc–alkaline magmatism are interpreted to have been caused by deformation of the intra-oceanic arc terrane on the Gondwana margin, and lithospheric thickening during the Palmer Land Event.

Controlling factors of underpressure reservoirs in the Sulige gas field, Ordos Basin

Based on the study of low-pressure distribution characteristics, the main factors that control the formation of low-pressure reservoirs in the Sulige gas field are analyzed from several aspects, such as structural evolution, sedimentary characteristics and formation fluid features. It is suggested that the gas pool pressure is low and affected greatly by buried depth. Its roof and floor developed several layers of uncompacted mudstone, indicative of good property and pressure sealing conditions. The formation water also indicates favorable preservation conditions. The reservoir pressure of the Sulige gas field experienced 4 major evolutionary stages: the normal pressure stage of the Late Triassic-early Jurassic, the pressure rising stage of the Middle Jurassic-Late Jurassic, the sustainable pressure increasing stage of the Early Cretaceous, and the pressure decreasing stage of the late Early Cretaceous. The pore rebound and temperature decrease caused by intense tectonic uplift after the late period of Early Cretaceous, caused the reservoir pressure of the Sulige gas field to reduce by 0.673 MPa and 23.08% of the original strata pressure, respectively. The low pressure of the Sulige gas field is related to sedimentary assemblage, tectonic evolution and hydrocarbon accumulation.

Syn-rift volcanism of the Neuquen Basin, Argentina: relationships with the Late Triassic-Early Jurassic evolution of the Andean margin.

The Neuquen Basin constitutes one of the most conspicuous features of the Andean margin of Gondwana during Mesozoic times. The initial syn-rift infill (Late Triassic-Early Jurassic) of this ensialic extensional basin involved a profuse magmatic activity (Precuyano Cycle). Outcrops of the southern depocentres of the basin (Chachil, Catan Lil, Chacaico, Sanico y Piedra del aguila) were studied in order to analyze the characteristics of this magmatic cycle. Shallow intrusive, lava flow and pyroclastic accumulation units of the syn-rift sequence conform up to 70% of the total infill. The syn-rift sequence shows a particular spatial-temporal evolution from mainly intermediate volcanic rocks at the base to mainly acidic pyroclastic rocks to the top. Volcanic feeding-systems were characterized by shallow and multiple-injection magmatic chambers. Eight main alteration facies related to syn- and post-volcanic stages were determined. Trace element data show that the lava and pyroclastic products share a co-magmatic trend, dominated by intermediate to acid products. Rocks belong to the sub-alkaline series, mostly calc-alkaline and transitional, and in a lesser extent tholeiitic, with orogenic signature. Nevertheless, the stratigraphical and compositional features (>50% of acid volcanic products) suggest some differences with typical arc-series. Recent models to explain the magmatic systems in complex convergent margins were discussed (i.e., intra-crustal and extra-crustal models), being chosen an extra-crustal model to justify the compositional and stratigraphical features of the Precuyano Cycle. According to this model the partial melting of an underplating ‘silicic cold plume’ (metasediment-oceanic crust melanges derived from subducted slab) would explain the wide distribution transversal to the margin of the Precuyano volcanism, whereas the degree of partial melting of the ‘plume’ would explain the prevailing composition of the cycle: andesitic and daciticrhyodacitic compositions. The onset of extension made possible the rising of the initial andesitic volcanism, whereas during either the rifting climax or along the sites with major crustal extension, the high viscosity acid magmas would have been preferentially risen. Finally, an Andean segmentation at 40°S would explain the development of an extensional segment towards the north, where the Neuquen basin was developed, and the magmatic arc towards the south, represented by the Subcordilleran Batholith.

Characteristics of Yichun Late Triassic - Early Jurassic Monzogranite

As building material, Granite has been extensively used. It is important to clear the geochemical characteristics of granites. The paper introduce the Late Triassic-Early Jurassic monzogranite, it mainly located in the south of Yichun area, which were intruded by medium grain monzogranite and syenogranite in Late Triassic-Early Jurassic. According to previous information, this granite distributed in Tangwanghe is widely in the south of study region. Rock type is coarse-medium grain porphyritic biotite monzogranite amphibole-bearing, the edge of the granite (Yishan Forest western) with a flow structure (once believed as gneissic structure), which was classified as Late Carboniferous coarse grained porphyritic gneissic monzogranite in 1:25 million regional geological survey. According to the SHRIMP dating from monzogranite gain the age is 201.5±2.9Ma, showing that the granite was formed in Late Triassic-Early Jurassic.

The first Haramiyid (Mammalia, Allotheria) from the Jurassic of Russia

103 The order Haramiyida is one of the most ancient mammal groups. The first known haramiyids come from the Upper Norian (Upper Triassic, about 212 Ma) of Europe. In the Late Triassic–Early Juras sic, haramiyids were common in European mammal faunas and rare in North America [1, 2]. Previously, Middle Jurassic haramiyids have only been found in England [3, 4]. Late Jurassic haramiyids occur in Tanzania [5, 6] and China [7, 8]. The latest haramiy ids are probably recorded in the Upper Cretaceous (Maastrichtian) of India [9]. Apart from the unique find of a partial skeleton of Haramiyavia in the Upper Triassic of Greenland [10], haramiyids are only rep resented by isolated teeth. In the present study, a new haramiyid species from the Middle Jurassic of Siberia is described; it is represented by isolated upper and lower teeth. The material comes from the Itat For mation of the Berezovsk quarry locality in the south ern Krasnoyarsk Territory, which has previously yielded remains of various docodonts, an eutricon odont, dryolestid, amphitheriid, and a more advanced mammal from the stem group of Zatheria (for review, see [11]). The nomenclature of tooth cusps of haramiyids follows Butler ([1], see also [2]). The collection examined is stored in the Borissiak Paleontological Institute of the Russian Academy of Sciences, Moscow (PIN). Class Mammalia Linnaeus, 1758

Atmospheric oxygen remodels cardiac outflow tract in the American alligator

The in-series circulatory systems of mammals and birds evolved from an ancestral system capable of shunting blood between the systemic and pulmonary circuits, as seen in extant amphibians and non-avian reptiles. To test whether atmospheric oxygen level can affect cardiac outflow tract morphology, we exposed hatchlings of the American alligator to chronic hypoxia (12%O2), normoxia (21%O2) and hyperoxia (30%O2). After three months, we quantified the perimeter of the left aorta (LAo), right aorta and pulmonary artery from histologic sections, and calculated their maximum (circular) cross-sectional area (CSA). Relative to the total outflow CSA, LAo fraction was 0.17 in hypoxia, 0.24 in normoxia and 0.26 in hyperoxia, suggesting the outflow tract remodels in response to blood flow distribution. In vivo recordings from juvenile alligators confirmed that shunt magnitude via LAo decreases with acute exposure to hypoxia and increases in hyperoxia. We posit that a pulmonary bypass shunt in tetrapods was maintained by global hyperoxia of the Late Carboniferous-Early Permian, but reduced by hypoxia of the Late Triassic-Early Jurassic. The latter period coincides with the appearance of mammals and theropod dinosaurs (avian ancestors). Once the shunt was lost, the mammalian and theropod cardiovascular systems would have been committed to the obligatory in-series circulation. Funded by NSF IOS 922756.

Age and origin of the South Caspian Basin

The South Caspian Basin (SCB) is a relic of the back-arc basin in the margin of the Tethys paleoocean. The SCB has an oceanic-type crust and is filled with a thick (15–28 km) sedimentary series. In the modern structure, it is a part of the South Caspian microplate, which also comprises the Lower Kura and West Turkmenian depressions, parts of the Kopet Dagh and Alborz ranges. The geological and seismological data evidence an underthrust (or, probably, subduction) of the South Caspian Basin’s lithosphere beneath the Apsheron threshold and the simultaneous westward displacement of the South Caspian Microplate (SCM). Different authors refer the South Caspian Basin’s formation to the Early Mesozoic, Late Jurassic, and Paleocene. In this paper, on the basis of geologic information, a two-phase model of the South Caspian Basin’s opening is considered. The first phase is referred to the Late Triassic-Early Jurassic, when the sinking of the Kopet Dagh Basin and the opening of the Great Caucasus rift began as well. Jointly, these three structures formed a prolonged basin related to the development of the Early Mesozoic subduction zone. The age of the oceanic crust in the central part of the South Caspian Basin calculated by the thermal flux is 200 Ma. The second phase of the South Caspian Basin opening referred to the Eocene is related to the extension in the back-arc part of the Elbrus volcanic arc. The formation of the oceanic crust in the southwestern part of the South Caspian Basin and in the Lower-Kura depression is associated with this phase, which is proved by the high values of the thermal flux.

A new sauropodomorph dinosaur from the Early Jurassic of Patagonia and the origin and evolution of the sauropod-type sacrum.

BackgroundThe origin of sauropod dinosaurs is one of the major landmarks of dinosaur evolution but is still poorly understood. This drastic transformation involved major skeletal modifications, including a shift from the small and gracile condition of primitive sauropodomorphs to the gigantic and quadrupedal condition of sauropods. Recent findings in the Late Triassic–Early Jurassic of Gondwana provide critical evidence to understand the origin and early evolution of sauropods.Methodology/Principal FindingsA new sauropodomorph dinosaur, Leonerasaurus taquetrensis gen. et sp. nov., is described from the Las Leoneras Formation of Central Patagonia (Argentina). The new taxon is diagnosed by the presence of anterior unserrated teeth with a low spoon-shaped crown, amphicoelous and acamerate vertebral centra, four sacral vertebrae, and humeral deltopectoral crest low and medially deflected along its distal half. The phylogenetic analysis depicts Leonerasaurus as one of the closest outgroups of Sauropoda, being the sister taxon of a clade of large bodied taxa composed of Melanorosaurus and Sauropoda.Conclusions/SignificanceThe dental and postcranial anatomy of Leonerasaurus supports its close affinities with basal sauropods. Despite the small size and plesiomorphic skeletal anatomy of Leonerasaurus, the four vertebrae that compose its sacrum resemble that of the large-bodied primitive sauropods. This shows that the appearance of the sauropod-type of sacrum predated the marked increase in body size that characterizes the origins of sauropods, rejecting a causal explanation and evolutionary linkage between this sacral configuration and body size. Alternative phylogenetic placements of Leonerasaurus as a basal anchisaurian imply a convergent acquisition of the sauropod-type sacrum in the new small-bodied taxon, also rejecting an evolutionary dependence of sacral configuration and body size in sauropodomorphs. This and other recent discoveries are showing that the characteristic sauropod body plan evolved gradually, with a step-wise pattern of character appearance.

Triassic high-strain shear zones in Hainan Island (South China) and their implications on the amalgamation of the Indochina and South China Blocks: Kinematic and 40Ar/ 39Ar geochronological constraints

A kinematic and geochronological study has been carried out on the Triassic high-strain shear zones in Hainan Island, the southern South China Block. There are WNW- and NE-trending high-strain shear zones with greenschist- to amphibolite-facies metamorphism in this island. Kinematic indicators suggest a dextral top-to-the-NNE thrust shearing for the WNW-trending high-strain shear zones and a sinistral top-to-the-SE thrust shearing for the NE-trending shear zones. The quartz c-axis orientations of mylonitic rocks exhibit the domination of basal slip and some activation of a rhombohedra gliding system. The timing of shearing for these shear zones has been constrained by the 40Ar/ 39Ar dating analyses of synkinematic minerals. Middle Triassic (242–250 Ma) and late Triassic–early Jurassic (190–230 Ma) have been identified for the WNW- and NE-trending shear zones, respectively. A synthesis of these kinematic and thermogeochronological data points to a two-stage tectonic model for Hainan Island, that is, top-to-the-NNE oblique thrusting at 240–250 Ma followed by top-to-the-SE oblique thrusting at 190–230 Ma. In combination with the available data from the southern South China and Indochina Blocks, it is inferred that South Hainan and North Hainan have affinity to the Indochina and South China Blocks, respectively. The tectonic boundary between South Hainan and North Hainan lies roughly along the WNW-trending Changjiang–Qionghai tectonic zone probably linking to the Song Ma and Ailaoshan zones. The middle Triassic structural pattern of Hainan Island is spatially and temporally compatible with those of the South China and Indochina Blocks, and thus might be a derivation from the amalgamation of the Indochina with South China Blocks in response to the closure of the Paleotethys Ocean and subsequent subduction/collision.

Transitional fossil earwigs - a missing link in Dermaptera evolution

BackgroundThe Dermaptera belongs to a group of winged insects of uncertain relationship within Polyneoptera, which has expanded anal region and adds numerous anal veins in the hind wing. Evolutional history and origin of Dermaptera have been in contention.ResultsIn this paper, we report two new fossil earwigs in a new family of Bellodermatidae fam. nov. The fossils were collected from the Jiulongshan Formation (Middle Jurassic) in Inner Mongolia, northeast China. This new family, characterized by an unexpected combination of primitive and derived characters, is bridging the missing link between suborders of Archidermaptera and Eodermaptera. Phylogenetic analyses support the new family to be a new clade at the base of previously defined Eodermaptera and to be a stem group of (Eodermaptera+Neodermaptera).ConclusionEvolutional history and origin of Dermaptera have been in contention, with dramatically different viewpoints by contemporary authors. It is suggested that the oldest Dermaptera might possibly be traced back to the Late Triassic-Early Jurassic and they had divided into Archidermaptera and (Eodermaptera+Neodermaptera) in the Middle Jurassic.

Bentho-planktonic evidence from the Austrian Alps for a decline in sea-surface carbonate production at the end of the Triassic

A high-resolution micropalaeontological study, combined with geochemical and sedimentological analyses was performed on the Tiefengraben, Schlossgraben and Eiberg sections (Austrian Alps) in order to characterize sea-surface carbonate production during the end-Triassic crisis. At the end-Rhaetian, the dominant calcareous nannofossil Prinsiosphaera triassica shows a decrease in abundance and size and this is correlated with a increase in δ18O and a gradual decline in δ13Ccarb values. Simultaneously, benthic foraminiferal assemblages show a decrease in diversity and abundance of calcareous taxa and a dominance of infaunal agglutinated taxa. The smaller size of calcareous nannofossils disturbed the vertical export balance of the biological carbon pump towards the sea-bottom, resulting in changes in feeding strategies within the benthic foraminiferal assemblages from deposit feeders to detritus feeders and bacterial scavengers. These micropalaeontological data combined with geochemical proxies suggest that changes in seawater chemistry and/or cooling episodes might have occurred in the latest Triassic, leading to a marked decrease of carbonate production. This in turn culminated in the quasi-absence of calcareous nannofossils and benthic foraminifers in the latest Triassic. The aftermath (latest Triassic earliest Jurassic) was characterised by abundance peaks of “disaster” epifaunal agglutinated foraminifera Trochammina on the sea-floor. Central Atlantic Magmatic Province (CAMP) paroxysmal activity, superimposed on a major worldwide regressive phase, is assumed to be responsible for a deterioration in marine palaeoenvironments. CAMP sulfuric emissions might have been the trigger for cooling episodes and seawater acidification leading to disturbance of the surface carbonate production at the very end-Triassic.