Rb–Sr dating of the Bokan Mountain granite complex and its country rocks

1985 ◽  
Vol 22 (8) ◽  
pp. 1233-1236 ◽  
Author(s):  
Richard Lee Armstrong
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Country Rock ◽  
Rock Samples ◽  
Minimum Age ◽  
Granite Complex ◽  
Rock Suite ◽  
Peralkaline Rock

Seven out of 11 whole-rock samples of the Bokan granitic complex give a Rb–Sr isochron date of 151 ± 5 Ma (Late Jurassic) as a minimum age for the complex. This result is discordant with published Early to Middle Jurassic K–Ar and U–Pb dates for the same unique peralkaline rock suite. A Late Jurassic age is tenable if excess radiogenic Ar and a trace of xenocrystic zircon are postulated to explain the previously reported results and the U–Pb data are reinterpreted to give an age between 156 ± 6 and [Formula: see text]. Granitic country rock for the complex is dated by Rb–Sr at 432 ± 19 Ma (Early Silurian), in agreement with published K–Ar dates.

Radiolarian assemblages of Middle and Late Jurassic to early Late Cretaceous (Cenomanian) ages from an olistolith record pelagic deposition within the Bornova Flysch Zone in western Turkey

2012 ◽  
Vol 183 (4) ◽  
pp. 307-318 ◽  
Author(s):  
Ugur Kagan Tekin ◽  
M. Cemal Göncüoglu ◽  
Seda Uzuncimen
Keyword(s):  
Late Cretaceous ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Western Turkey ◽  
Oceanic Basin ◽  
Platform Margin ◽  
Lowermost Part ◽  
Early Late ◽  
Radiolarian Assemblages

Abstract The Bornova Flysch Zone (BFZ) in NW Anatolia comprises several olistoliths or tectonic slivers, representing various parts of the Izmir-Ankara ocean. Radiolarian assemblages extracted from one of the olistoliths of the BFZ, cropping out along the Sögütlü section, to the NE Manisa city, were studied in detail. The lowermost part of the section contains latest Bajocian – early Callovian radiolarian taxa, followed by radiolarian assemblages indicating Late Jurassic to early Late Cretaceous (Cenomanian) ages. Previous studies reveal that the Izmir-Ankara oceanic basin was initially opened during late Ladinian – early Carnian. The new radiolarian data obtained from this olistolith reveals that relatively condensed, and possibly more or less continuous, pelagic sedimentation took place during the late Middle Jurassic to early Late Cretaceous in a non-volcanic oceanic basin closer to the Tauride-Anatolide platform margin.

scholarly journals A review of the fossil record of non-baenid turtles of the clade Paracryptodira

2019 ◽  
Author(s):  
Walter G. Joyce ◽  
Jérémy Anquetin
Keyword(s):  
North America ◽  
Middle Jurassic ◽  
Fossil Record ◽  
Late Jurassic ◽  
Feeding Strategies ◽  
Aquatic Environments ◽  
Taxonomic Review ◽  
Nomina Invalida ◽  
Nomina Dubia

The fossil record of non-baenid paracryptodires ranges from the Late Jurassic (Kimmeridgian) tothe Paleocene of North America and Europe only. Earlier remains may be present as early as the Middle Jurassic (Bathonian). Only a single dispersal event is documented between the two continents following their breakup during the Cretaceous in the form of the appearance of the Compsemys lineage in the Paleocene of France. Non-baenid paracryptodires were restricted to freshwater aquatic environments, but display adaptations to diverse feeding strategies consistent with generalist, gape-and-suction, and hypercarnivorous feeding. Current phylogenies recognize two species rich subclades within Paracryptodira, Baenidae and Pleurosternidae, which jointly form the clade Baenoidea. A taxonomic review of non-baenid paracryptodires concludes that of 34 named taxa, 11 are nomina valida, 15 nomina invalida, and 8 nomina dubia.

First records of Somalinautilus (Cephalopoda: Nautiloidea) from the Jurassic of Southern Germany – inferences for trans-provincial migrations

2020 ◽  
Vol 298 (2) ◽  
pp. 137-146
Author(s):  
Günter Schweigert
Keyword(s):  
Sea Level ◽  
Geographic Distribution ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Southern Germany ◽  
First Time ◽  
Lower Kimmeridgian ◽  
Lower Bathonian

The Late Jurassic nautiloid Somalinautilus antiquus (Dacqué, 1910), previously only known by the holotype from Lower Kimmeridgian strata of Ethiopia, is reported from the Lower Kimmeridgian (Platynota Zone) of Southern Germany. This unexpected record largely expands the known geographic distribution of this species. Another species of Somalinautilus, S. clavifer Tintant , 1994, is recorded for the first time from the Middle Jurassic (Lower Bathonian, Zigzag Zone) of Southern Germany. A short stratigraphic and palaeogeographic review of Somalinautilus occurrences is provided. Faunal migrations of nautiloids over large distances were probably triggered by sea- level highstands and/or palaeocurrents.

scholarly journals Ore Formation During Jurassic Subduction of the Tethys Along the Eurasian Margin: Constraints from the Kapan District, Lesser Caucasus, Southern Armenia

2019 ◽  
Vol 114 (7) ◽  
pp. 1251-1284 ◽  
Author(s):  
Johannes Mederer ◽  
Robert Moritz ◽  
Massimo Chiaradia ◽  
Richard Spikings ◽  
Jorge E. Spangenberg ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Ore Deposits ◽  
Sulfide Deposit ◽  
Short Time Interval ◽  
Ore Formation ◽  
Magmatic Arc ◽  
Argillic Alteration ◽  
Lesser Caucasus ◽  
Host Rocks

Abstract The Kapan mining district in the southernmost Lesser Caucasus is one of the few locations along the central Tethyan metallogenic belt where ore-forming processes were associated with magmatic arc growth during Jurassic Tethys subduction along the Eurasian margin. Three ore deposits of the Kapan district were investigated in this study: Centralni West, Centralni East, and Shahumyan. The ore deposits are hosted by Middle Jurassic andesitic to dacitic volcanic and volcaniclastic rocks of tholeiitic to transitional affinities below a late Oxfordian unconformity, which is covered by calc-alkaline to transitional Late Jurassic-Early Cretaceous volcanic rocks interlayered with sedimentary rocks. The mineralization consists of veins, subsidiary stockwork, and partial matrix replacement of breccia host rocks, with chalcopyrite, pyrite, tennantite-tetrahedrite, sphalerite, and galena as the main ore minerals. Centralni West is a dominantly Cu deposit, and its host rocks are altered to chlorite, carbonate, epidote, and sericite. At Centralni East, Au is associated with Cu, and the Shahumyan deposit is enriched in Pb and Zn as well as precious metals. Both deposits contain high-sulfidation mineral assemblages with enargite and luzonite. Dickite, sericite, and diaspore prevail in altered host rocks in the Centralni East deposit. At the Shahumyan deposit, phyllic to argillic alteration with sericite, quartz, pyrite, and dickite is dominant with polymetallic veins, and advanced argillic alteration with quartz-alunite ± kaolinite and dickite is locally developed. The lead isotope composition of sulfides and alunite (206Pb/204Pb = 18.17–18.32, 207Pb/204Pb = 15.57–15.61, 208Pb/204Pb = 38.17–38.41) indicates a common metal source for the three deposits and suggests that metals were derived from magmatic fluids that were exsolved upon crystallization of Middle Jurassic intrusive rocks or leached from Middle Jurassic country rocks. The δ18O values of hydrothermal quartz (8.3–16.4‰) and the δ34S values of sulfides (2.0–6.5‰) reveal a dominantly magmatic source at all three deposits. Combined oxygen, carbon, and strontium isotope compositions of hydrothermal calcite (δ18O = 7.7–15.4‰, δ13C = −3.4−+0.7‰, 87Sr/86Sr = 0.70537–0.70586) support mixing of magmatic-derived fluids with seawater during the last stages of ore formation at Shahumyan and Centralni West. 40Ar/39Ar dating of hydrothermal muscovite at Centralni West and of magmatic-hydrothermal alunite at Shahumyan yield, respectively, a robust plateau age of 161.78 ± 0.79 Ma and a disturbed plateau age of 156.14 ± 0.79 Ma. Re-Os dating of pyrite from the Centralni East deposit yields an isochron age of 144.7 ± 4.2 Ma and a weighted average age of the model dates of 146.2 ± 3.4 Ma, which are younger than the age of the immediate host rocks. Two different models are offered, depending on the reliability attributed to the disturbed 40Ar/39Ar alunite age and the young Re-Os age. The preferred interpretation is that the Centralni West Cu deposit is a volcanogenic massive sulfide deposit and the Shahumyan and Centralni East deposits are parts of porphyryepithermal systems, with the three deposits being broadly coeval or formed within a short time interval in a nascent magmatic arc setting, before the late Oxfordian. Alternatively, but less likely, the three deposits could represent different mineralization styles successively emplaced during evolution and growth of a magmatic arc during a longer time frame between the Middle and Late Jurassic.

New winter crane flies (Insecta: Diptera: Trichoceridae) from the Jurassic Daohugou Formation (Inner Mongolia, China) and their associated biota

2006 ◽  
Vol 43 (1) ◽  
pp. 9-22 ◽  
Author(s):  
Junfeng Zhang
Keyword(s):  
New Species ◽  
Middle Jurassic ◽  
Inner Mongolia ◽  
Late Jurassic ◽  
Sedimentary Rocks ◽  
New Genera ◽  
Crane Flies ◽  
Geological Age ◽  
Wide Range ◽  
Biostratigraphic Correlation

Four extinct new species referable, respectively, to three extinct new genera within Trichoceridae have been recovered from the Jurassic Daohugou Formation in Ningcheng, Chifeng, Inner Mongolia, China: Archaeotrichocera ephemera gen. et sp. nov., Tanyochoreta integera gen. et sp. nov., Tanyochoreta chifengica sp. nov., and Sinotrichocera parva gen. et sp. nov. The specimen described earlier as trichocerids from China, Mesotrichocera laiyangensis Hong and Wang 1990, does not belong to this family. The Daohugou biota comprises a wide range of vertebrate and invertebrate organisms that inhabited, a small lake, luxurious everglade, streams, and forest with volcanoes nearby. The Daohugou Formation can be compared to the Karabastau and Haifanggou formations based on biostratigraphic correlation. The geological age for trichocerid-bearing nonmarine volcano-sedimentary rocks may be latest Middle Jurassic (Callovian) or earliest Late Jurassic (Oxfordian) rather than early–middle Middle Jurassic or Early Cretaceous.

The Middle-Late Jurassic Yanliao entomofauna

2018 ◽  
Vol 1 (1) ◽  
pp. 3 ◽  
Author(s):  
DIYING HUANG ◽  
CHENYANG CAI ◽  
YANZHE FU ◽  
YITONG SU
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Volcanic Eruptions ◽  
Northern China ◽  
Fossil Insects ◽  
Age Difference ◽  
Jehol Biota ◽  
Burmese Amber ◽  
In The Beginning ◽  
Insect Assemblage

The Yanliao entomofauna, first established by Hong in 1983, refers to a Middle Jurassic insect assemblage widely distributed in northern China. The fossil insects are primarily preserved in the Haifanggou Formation and its correlated strata. In the beginning of this century, the Yanliao entomofauna was revived thanks to the discovery of abundant exceptionally preserved fossils, especially a huge number of insects, in the Daohugou area. Then, the Yanliao biota became well-known, and subsequently enlarged with more fossils collected from the interbeds of the overlying Tiaojishan Formation. Recently, the Yanliao biota has been divided into an early assemblage, represented by the Daohugou beds (Middle Jurassic to earliest Late Jurassic), and a late assemblage, represented by the Linglongta beds (early to middle Late Jurassic). The early insect assemblage, i.e. fossil insects from Daohugou, contains at least 24 insect orders, representing one of the most diverse entomofaunas in geological history. The age difference between core fossil layers of the Daohugou assemblage and the Linglongta assemblage is less than 5 Ma, but no same animal species from both have been discovered to date, because of violent tectonic movements and fierce volcanic eruptions. The representative insect from the early assemblage is Yanliaocorixa chinensis, which is distinctly different from the dominated corixids from the late assemblage. Insects of Yanliao entomofauna generally resemble those from the Shar Teg biota from Mongolia and the Karatau biota from Kazakhstan. The Yanliao biota rapidly declined in middle of the Late Jurassic (ca. 155 Ma) with the advent of arid climate, whereas some of the relict groups migrated southwards. Until the mid-Cretaceous, represented by the Burmese amber, a number of endemic insect groups of Daohugou are still recorded, but they have never been found in the Jehol biota, representing relicts of the Yanliao entomofauna. 

First record ofOphthalmosaurus(Reptilia: Ichthyosauria) from the Tithonian (Upper Jurassic) of Mexico

2010 ◽  
Vol 84 (1) ◽  
pp. 149-155 ◽  
Author(s):  
Marie-Céline Buchy
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Field Work ◽  
First Record ◽  
Upper Jurassic ◽  
Marine Transgression ◽  
North East ◽  
The Pacific ◽  
Invertebrate Assemblages ◽  
Marine Reptile

From the Middle Jurassic on, the Tethys basin opened westward; the existence of a Carribean corridor linking the European and Pacific realms now appears well supported by comparison of marine reptile assemblages (e.g., Gasparini and Fernández, 1997, 2005; Gasparini et al., 2000; Fernández and Iturralde-Vinent, 2000; Gasparini and Iturralde-Vinent, 2001, 2006; Gasparini et al., 2002). Marine transgression in Mexico began during the Callovian, as evidenced by the evaporites of the Minas Viejas Fm. However, microfossils and invertebrate assemblages indicate that the Mexican Gulf remained isolated from both the European Archipelago and the Pacific, at least temporarily, until the middle Berriasian; the Florida uplift and southward movement of Yucatan were proposed as possibly forming a barrier (Salvador et al., 1993; Adatte et al., 1994, 1996; Goldhammer, 1999; Goldhammer and Johnston, 2001; Gasparini and Iturralde-Vinent, 2006). After almost a decade of field work and examination of collections, the Late Jurassic marine reptile assemblage of north-east Mexico confirms the conclusions drawn from microfossils and invertebrates. Poorly diagnostic ichthyosaur remains, with various thalattosuchians, numerically dominate the assemblage. Sauropterygians are rare, mainly represented by large pliosaurids of unclear affinities, a few vertebrae attributed to elasmosaurids, and a unique cryptoclidid. Turtles are yet to be reported (Frey et al., 2002; Buchy et al., 2003, 2005b, 2006a–d; Buchy, 2007, 2008a, b; material currently under study).

Late Jurassic - Early Cretaceous paleoenvironmental evolution of the Transbaikal basins (SE Siberia): implications for the Mongol-Okhotsk orogeny

2017 ◽  
Vol 188 (1-2) ◽  
pp. 9 ◽  
Author(s):  
Marc Jolivet ◽  
Anastasia Arzhannikova ◽  
Andrei Frolov ◽  
Sergei Arzhannikov ◽  
Natalia Kulagina ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Tectonic Setting ◽  
Alluvial Fan ◽  
Crustal Thickening ◽  
Compressive Deformation ◽  
Transbaikal Region ◽  
Meandering River ◽  
The North

The Late Jurassic - Early Cretaceous tectonic evolution of SE Siberia was marked by the closure of the Mongol-Okhotsk ocean. While this geodynamic event led to compressive deformation and denudation in a wide area encompassing the North-Altay, Sayan and Baikal Patom ranges, it was contemporaneous to widespread extension from the Transbaikal region situated immediately north of the suture zone to the Pacific plate, affecting eastern Mongolia and northeastern China. In this study we review the paleontological and sedimentological data available in the Russian literature and provide new macro-floral and palynological data from the Mesozoic sediments of three Transbaikal basins. These data are used to describe the paleoenvironmental and paleoclimatic evolution of the Transbaikal area in order to assess the topographic evolution of the region in relation with the closure of the Mongol-Okhotsk ocean. We establish that the Transbaikal basins evolved in a continuously extensional tectonic setting from at least the Early-Middle Jurassic to the Early Cretaceous. The associated sedimentary environments are characterized by retrogradation from alluvial fan–braided river dominated systems prevailing during the Early to Middle Jurassic initial opening of the basins to meandering river– lacustrine systems that developed during the Late Jurassic - Early Cretaceous interval. No evidence of high relief topography was found and we conclude that, while compression and denudation occurred in the North Altai, Sayan and Patom ranges, in the Transbaikal region, the docking of the Mongolia-North China continent to Siberia was a “soft collision” event, possibly involving a major strike-slip displacement that did not lead to an orogenic event implying strong compressive deformation, crustal thickening and topography building.

scholarly journals A new stem turtle from the Middle Jurassic of Scotland: new insights into the evolution and palaeoecology of basal turtles

2008 ◽  
Vol 276 (1658) ◽  
pp. 879-886 ◽  
Author(s):  
Jérémy Anquetin ◽  
Paul M Barrett ◽  
Marc E.H Jones ◽  
Scott Moore-Fay ◽  
Susan E Evans
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Evolutionary History ◽  
Sister Group ◽  
Late Triassic ◽  
Sister Group Relationship ◽  
New Taxon ◽  
Crown Group ◽  
History Of ◽  
Isle Of Skye

The discovery of a new stem turtle from the Middle Jurassic (Bathonian) deposits of the Isle of Skye, Scotland, sheds new light on the early evolutionary history of Testudinata. Eileanchelys waldmani gen. et sp. nov. is known from cranial and postcranial material of several individuals and represents the most complete Middle Jurassic turtle described to date, bridging the morphological gap between basal turtles from the Late Triassic–Early Jurassic and crown-group turtles that diversify during the Late Jurassic. A phylogenetic analysis places the new taxon within the stem group of Testudines (crown-group turtles) and suggests a sister-group relationship between E. waldmani and Heckerochelys romani from the Middle Jurassic of Russia. Moreover, E. waldmani also demonstrates that stem turtles were ecologically diverse, as it may represent the earliest known aquatic turtle.

scholarly journals A turiasaurian sauropod dinosaur from the Early Cretaceous Wealden Supergroup of the United Kingdom

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e6348
Author(s):  
Philip D. Mannion
Keyword(s):  
Early Cretaceous ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Western Europe ◽  
Phylogenetic Analyses ◽  
Neural Spine ◽  
Faunal Turnover ◽  
The United Kingdom ◽  
The Usa ◽  
The Uk

The Jurassic/Cretaceous (J/K) boundary, 145 million years ago, has long been recognised as an extinction event or faunal turnover for sauropod dinosaurs, with many ‘basal’ lineages disappearing. However, recently, a number of ‘extinct’ groups have been recognised in the Early Cretaceous, including diplodocids in Gondwana, and non-titanosauriform macronarians in Laurasia. Turiasauria, a clade of non-neosauropod eusauropods, was originally thought to have been restricted to the Late Jurassic of western Europe. However, its distribution has recently been extended to the Late Jurassic of Tanzania (Tendaguria tanzaniensis), as well as to the Early Cretaceous of the USA (Mierasaurus bobyoungi and Moabosaurus utahensis), demonstrating the survival of another ‘basal’ clade across the J/K boundary. Teeth from the Middle Jurassic–Early Cretaceous of western Europe and North Africa have also tentatively been attributed to turiasaurs, whilst recent phylogenetic analyses recovered Late Jurassic taxa from Argentina and China as further members of Turiasauria. Here, an anterior dorsal centrum and neural arch (both NHMUK 1871) from the Early Cretaceous Wealden Supergroup of the UK are described for the first time. NHMUK 1871 shares several synapomorphies with Turiasauria, especially the turiasaurs Moabosaurus and Tendaguria, including: (1) a strongly dorsoventrally compressed centrum; (2) the retention of prominent epipophyses; and (3) an extremely low, non-bifid neural spine. NHMUK 1871 therefore represents the first postcranial evidence for Turiasauria from European deposits of Early Cretaceous age. Although turiasaurs show clear heterodont dentition, only broad, characteristically ‘heart’-shaped teeth can currently be attributed to Turiasauria with confidence. As such, several putative turiasaur occurrences based on isolated teeth from Europe, as well as the Middle Jurassic and Early Cretaceous of Africa, cannot be confidently referred to Turiasauria. Unequivocal evidence for turiasaurs is therefore restricted to the late Middle Jurassic–Early Cretaceous of western Europe, the Late Jurassic of Tanzania, and the late Early Cretaceous of the USA, although remains from elsewhere might ultimately demonstrate that the group had a near-global distribution.

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