scholarly journals Basin evolution in response to flat subduction in the Altiplano

2021 ◽  
pp. jgs2021-003
Author(s):  
Brook Runyon ◽  
Joel E. Saylor ◽  
Brian K. Horton ◽  
James H. Reynolds ◽  
Brian Hampton
Keyword(s):  
Foreland Basin ◽  
Flat Slab ◽  
Content Type ◽  
Link Type ◽  
Early Oligocene ◽  
Provenance Data ◽  
Thrust Belts ◽  
Fold And Thrust Belts ◽  
Basin Formation ◽  
Supplementary Material

This contribution assesses models for basin formation in the Altiplano. New magnetostratigraphy, palynology, and 40Ar/39Ar and U-Pb geochronology from the central Corque Syncline demonstrate that the 7.4 km-thick section was deposited between 36.7 and 18.7 Ma. The base of the section post-dates exhumation in both the Western and Eastern cordilleras, precluding deposition in a classic retroarc foreland basin setting. Rotated paleomagnetic vectors indicate counterclockwise rotation of 0.8°/Myr since the early Oligocene. Detrital zircon provenance data confirm previous interpretations of Eocene–early Oligocene derivation from the Western Cordillera and a subsequent switch to an Eastern Cordilleran source. Flexural modeling indicates that loads consistent with paleoelevation estimates cannot account for all subsidence. Rather, the timing and magnitude of subsidence is consistent with Eocene emplacement and Oligocene–early Miocene resteepening of a flat slab. Integration of the magmatic, basin, and deformation history provides a coherent model of the effects of flat subduction on the overriding plate. In this model flat subduction controlled basin formation in the upper plate, with subsidence enhanced in front of the zone of flat subduction but reduced over the crest of the flat slab. We conclude that the Altiplano was conditioned for plateau formation by Eocene–Oligocene flat subduction.Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-beltsSupplementary material:https://doi.org/10.6084/m9.figshare.c.5664345

Accommodation of India–Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold–thrust belt, northern margin of the Tibetan Plateau

2021 ◽  
pp. jgs2020-207
Author(s):  
Feng Cheng ◽  
Andrew V. Zuza ◽  
Peter J. Haproff ◽  
Chen Wu ◽  
Christina Neudorf ◽  
...  
Keyword(s):  
Strike Slip ◽  
Luminescence Dating ◽  
Thrust Belt ◽  
Block Rotation ◽  
Content Type ◽  
Link Type ◽  
Northeastern Tibet ◽  
Thrust Belts ◽  
Fold And Thrust Belts ◽  
Supplementary Material

Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a−1, which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent.Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MNThematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts

scholarly journals Environmental variability in response to abrupt climatic change during the Last Glacial–Interglacial Transition (16–8 cal ka BP): evidence from Mainland, Orkney

2019 ◽  
Vol 56 (1) ◽  
pp. 30-46 ◽  
Author(s):  
Ashley M. Abrook ◽  
Ian P. Matthews ◽  
Alice M. Milner ◽  
Ian Candy ◽  
Adrian P. Palmer ◽  
...  
Keyword(s):  
Early Career ◽  
Early Holocene ◽  
Content Type ◽  
Last Glacial ◽  
Principal Curve ◽  
Link Type ◽  
Supplementary Material ◽  
Career Research ◽  
The Last Glacial ◽  
Millennial Scale

The Last Glacial–Interglacial Transition (LGIT) is a period of climatic complexity where millennial-scale climatic reorganization led to changes in ecosystems. Alongside millennial-scale changes, centennial-scale climatic events have been observed within records from Greenland and continental Europe. The effects of these abrupt events on landscapes and environments are difficult to discern at present. This, in part, relates to low temporal resolutions attained by many studies and the sensitivity of palaeoenvironmental proxies to abrupt change. We present a high-resolution palynological and charcoal study of Quoyloo Meadow, Orkney and use the Principal Curve statistical method to assist in revealing biostratigraphic change. The LGIT vegetation succession on Orkney is presented as open grassland and Empetrum heath during the Windermere Interstadial and early Holocene, and open grassland with Artemisia during the Loch Lomond Stadial. However, a further three phases of ecological change, characterized by expansions of open ground flora, are dated to 14.05–13.63, 10.94–10.8 and 10.2 cal ka BP. The timing of these changes is constrained by cryptotephra of known age. The paper concludes by comparing Quoyloo Meadow with Crudale Meadow, Orkney, and suggests that both Windermere Interstadial records are incomplete and that fire is an important landscape control during the early Holocene.Supplementary material: All raw data associated with this publication: raw pollen counts, charcoal data, Principal Curve and Rate of Change outputs and the age-model output are available at https://doi.org/10.6084/m9.figshare.c.4725269Thematic collection: This article is part of the ‘Early Career Research’ available at: https://www.lyellcollection.org/cc/SJG-early-career-research

scholarly journals The naming of the Permian System

2021 ◽  
pp. jgs2021-037
Author(s):  
Michael J. Benton ◽  
Andrey G. Sennikov
Keyword(s):  
System Level ◽  
Naming Time ◽  
Content Type ◽  
Red Sandstone ◽  
Link Type ◽  
Permian System ◽  
Urgent Task ◽  
Great Leader ◽  
Supplementary Material ◽  
Access To Documents

The naming of the Permian by Roderick Murchison in 1841 is well known. This is partly because he ‘completed’ the stratigraphic column at system level, but also because of the exotic aspects of his extended fieldwork in remote parts of Russia and Murchison's reputed character. Here, we explore several debated and controversial aspects of this act, benefiting from access to documents and reports notably from Russian sources. Murchison or Sedgwick could have provided a name for the unnamed lower New Red Sandstone in 1835 based on British successions or those in Germany, so perhaps the Imperial aim of naming time from British geology was not the urgent task some have assumed. Murchison has been painted as arrogant and Imperialistic, which was doubtless true, but at the time many saw him as a great leader, even an attractive individual. Others suggest he succeeded because he stood on the shoulders of local geologists; however, his abilities at brilliant and rapid geological synthesis are undoubted. Two unexpected consequences of his work are that this arch conservative is revered in Russia as a hero of geological endeavours, and, for all his bombast, his ‘Permian’ was not widely accepted until 100 years after its naming.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5412079

scholarly journals Dating protracted fault activities: microstructures, microchemistry and geochronology of the Vaikrita Thrust, Main Central Thrust zone, Garhwal Himalaya, NW India

2018 ◽  
Vol 481 (1) ◽  
pp. 127-146 ◽  
Author(s):  
Chiara Montemagni ◽  
Chiara Montomoli ◽  
Salvatore Iaccarino ◽  
Rodolfo Carosi ◽  
Arvind K. Jain ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Garhwal Himalaya ◽  
Main Central Thrust ◽  
Content Type ◽  
Mylonitic Foliation ◽  
Link Type ◽  
Thrust Zone ◽  
Supplementary Material ◽  
Structural Boundary

AbstractThe timing of shearing along the Vaikrita Thrust, the upper structural boundary of the Main Central Thrust Zone in the Garhwal Himalaya, was constrained by combined microstructural, microchemical and geochronological investigations. Three different biotite–muscovite growth and recrystallization episodes were observed: a relict mica-1; mica-2 along the main mylonitic foliation; and mica-3 in coronitic structures around garnet during its breakdown. Electron microprobe analyses of biotite showed chloritization and a bimodal composition of biotite-2 in one sample. Muscovite-2 and muscovite-3 differed in composition from each other. Biotite and muscovite 39Ar–40Ar age spectra from all samples showed both inter- and intra-sample discrepancies. Biotite step-ages ranged between 8.6 and 16 Ma and muscovite step-ages between 3.6 and 7.8 Ma. These ages cannot be interpreted as ‘cooling ages’ because samples from the same outcrop cooled simultaneously. Instead, the Ar systematics reflect sample-specific recrystallization markers. Intergrown impurities were diagnosed by the Ca/K ratios. The age data of biotite were interpreted as a mixture of true biotite-2 (9.00 ± 0.10 Ma) and two alteration products. The negative Cl/K–age correlation identified a Cl-poor muscovite-2 (>7 Ma) and a Cl-rich, post-deformational, coronitic muscovite-3 grown at ≤5.88 ± 0.03 Ma. The Vaikrita Thrust was active at least from 9 to 6 Ma at c. 600°C; its movement had ended by 6 Ma.Supplementary material: Thermometric and 39Ar–40Ar data are available at https://doi.org/10.6084/m9.figshare.c.4069076

Contractional salt tectonics and role of pre-existing diapiric structures in the Southern Pyrenean foreland fold–thrust belt (Montsec and Serres Marginals)

2021 ◽  
pp. jgs2020-085 ◽  
Author(s):  
Laura Burrel ◽  
Antonio Teixell
Keyword(s):  
Cross Sections ◽  
Foreland Basin ◽  
Salt Tectonics ◽  
Structural Development ◽  
Field Observations ◽  
Content Type ◽  
Growth Strata ◽  
Structural Style ◽  
Supplementary Material

Triassic Keuper evaporites have long been recognized as the main detachment level for thrusting in the Pyrenean fold–thrust belts. The deformed Late Cretaceous–Eocene foreland basin of the Southern Pyrenees has structures and stratal geometries that can be interpreted as related to salt tectonics (e.g. unconformities, rapid thickness variations, long-lived growth fans and overturned flaps), although they have been overprinted by shortening and thrusting. Based on field observations and published maps, we build new structural cross-sections reinterpreting two classic transects of the Southern Pyrenees (Noguera Ribagorçana and Noguera Pallaresa river transects). The sequential restoration of the sections explores the variations in structural style, addressing the role of halokinesis in the tectonic and sedimentary development. In the Serres Marginals area, we propose that salt pillows and diapirs started developing locally during the Mesozoic pre-orogenic episode, evolving into a system of salt ridges and intervening synclines filled with early synorogenic sediments. Rapid amplification of folds recorded by widespread latest Cretaceous–Paleocene growth strata is taken as marking the onset of contractional folding in the area. During Pyrenean compression, folding mechanisms transitioned from dominantly halokinetic to a combination of buckling and differential sedimentary loading. Squeezing of salt diapirs and thrust welding occurred as salt ridges were unroofed. We provide new field observations that lead to a reinterpretation of the regional structural development and contribute to the debate about the role of salt tectonics in the Pyrenees.Supplementary material: Table S1, giving the thickness of the main stratigraphic units, is available at https://doi.org/10.6084/m9.figshare.c.5287737

Palaeolatitudinal distribution of the Ediacaran macrobiota

2021 ◽  
pp. jgs2021-030
Author(s):  
Catherine E. Boddy ◽  
Emily G. Mitchell ◽  
Andrew Merdith ◽  
Alexander G. Liu
Keyword(s):  
Taxonomic Composition ◽  
Supplementary Information ◽  
Cambrian Explosion ◽  
Content Type ◽  
Link Type ◽  
Environmental Perturbations ◽  
Significant Difference ◽  
Evolutionary Trajectories ◽  
Cambrian Radiation ◽  
Supplementary Material

Macrofossils of the late Ediacaran Period (c. 579–539 Ma) document diverse, complex multicellular eukaryotes, including early animals, prior to the Cambrian radiation of metazoan phyla. To investigate the relationships between environmental perturbations, biotic responses and early metazoan evolutionary trajectories, it is vital to distinguish between evolutionary and ecological controls on the global distribution of Ediacaran macrofossils. The contributions of temporal, palaeoenvironmental and lithological factors in shaping the observed variations in assemblage taxonomic composition between Ediacaran macrofossil sites are widely discussed, but the role of palaeogeography remains ambiguous. Here we investigate the influence of palaeolatitude on the spatial distribution of Ediacaran macrobiota through the late Ediacaran Period using two leading palaeogeographical reconstructions. We find that overall generic diversity was distributed across all palaeolatitudes. Among specific groups, the distributions of candidate ‘Bilateral’ and Frondomorph taxa exhibit weakly statistically significant and statistically significant differences between low and high palaeolatitudes within our favoured palaeogeographical reconstruction, respectively, whereas Algal, Tubular, Soft-bodied and Biomineralizing taxa show no significant difference. The recognition of statistically significant palaeolatitudinal differences in the distribution of certain morphogroups highlights the importance of considering palaeolatitudinal influences when interrogating trends in Ediacaran taxon distributions.Supplementary material: Supplementary information, data and code are available at https://doi.org/10.6084/m9.figshare.c.5488945Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosion

Diamondiferous lamproites of Ingashi field, Siberian craton

2021 ◽  
pp. SP513-2020-274
Author(s):  
S. I. Kostrovitsky ◽  
D. A. Yakovlev ◽  
I. S. Sharygin ◽  
D. P. Gladkochub ◽  
T. V. Donskaya ◽  
...  
Keyword(s):  
Trace Element ◽  
Siberian Craton ◽  
Major Elements ◽  
Primary Sources ◽  
Content Type ◽  
Link Type ◽  
Ultramafic Lamprophyre ◽  
Dating Methods ◽  
Supplementary Material

AbstractIngashi lamproite dykes are the only known primary sources of diamond in the Irkutsk district (Russia) and the only non-kimberlitic one in the Siberian craton. Ingashi lamproite field placed in Urik-Iya graben within Prisayan uplift of Siberian craton. Phlogopite-olivine lamproites contain olivine, talc, phlogopite, serpentine, chlorite, olivine, garnet, chromite, orthopyroxene, clinopyroxene as well as Sr-F-apatite, monazite, zircon, armolcolite, priderite, potassium Mg-arfvedsonite, Mn-ilmenite, Nb-rutile, and diamond. The only one ultramafic lamprophyre dyke is composed mainly of serpentinized olivine and phlogopite in the talc-carbonate groundmass and similar (to Ingashi lamproites) accessory assemblage with the same major elements compositions. Trace element and Sr-Nd isotopic relationships of the Ingashi lamproites are similar to classic lamproites. Different dating methods have provided the ages of lamproites: 1481 Ma (Ar-Ar phlogopite), 1268 Ma (Rb-Sr whole rock) and 300 Ma (U-Pb zircon). Ingashi lamproite ages are controversial and require additional study. Calculated pressure of 3.5 GPamax for clinopyroxenes indicating that lamproite magma originated deeper than 100 km. Cr-in-garnet barometer (Grutter et al., 2006) shows a 3.7-4.3 GPamin and derivation of Ingashi lamproites deeper than 120 km depth. Based on the range of typical cratonic geotherms and presence of diamonds, the Ingashi lamproite magma originated at a depth greater than 155 km.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5493128

Lead, zinc and arsenic contamination of pit lake waters in the Zeida abandoned mine (High Moulouya, Morocco)

2021 ◽  
pp. geochem2021-009
Author(s):  
Lamiae EL ALAOUI ◽  
Abdelilah Dekayir ◽  
Mohammed Rouai ◽  
EL Mehdi Benyassine
Keyword(s):  
Organic Matter ◽  
Iron Oxides ◽  
Environmental Issues ◽  
Abandoned Mine ◽  
Equal Proportion ◽  
Pit Lake ◽  
Content Type ◽  
Link Type ◽  
Supplementary Material ◽  
Lake Waters

In the Zeida abandoned mine, pit lake waters exhibit alkaline pH and high conductivity. The concentrations of the total dissolved lead and zinc are very low due to their adsorption on clay minerals and iron oxyhydroxides. Conversely, arsenic concentrations in two lakes (ZL1 and ZA) exceeded WHO water quality guidelines. The As content is relatively high in ZL1 lake and exists mainly as As(V). In ZA lake, As(III) occurs in low concentration compared to the total dissolved arsenic, while dimethylarsenic acid [H2AsO2(CH3)2, DMA) prevails. This means that arsenic was methylated by organic matter produced by microorganisms such as chlorella. The sequential extraction of floor sediments in two lakes shows that the bioavailable arsenic contents change between the two lakes. In ZA lake, the sediments show high concentrations of lead and arsenic compared to ZL1 sediment since it is surrounded by mining waste tailings, which are rich in such chemical elements. An arsenic leaching test of ZA sediment shows that bioavailable arsenic is distributed in equal proportion between clay/carbonates, sulfide-organic matter, and iron oxides (HFO) phases, while in ZL1, most of the arsenic is linked to hydrous iron oxides (HFO).Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issuesSupplementary material:https://doi.org/10.6084/m9.figshare.c.5545316

scholarly journals The nature and origins of decametre-scale porosity in Ordovician carbonate rocks, Halahatang oilfield, Tarim Basin, China

2020 ◽  
Vol 177 (5) ◽  
pp. 1074-1091
Author(s):  
Estibalitz Ukar ◽  
Vinyet Baqués ◽  
Stephen E. Laubach ◽  
Randall Marrett
Keyword(s):  
Tarim Basin ◽  
Velocity Gradient ◽  
Fractured Reservoirs ◽  
Gradient Tensor ◽  
Fault Rocks ◽  
Content Type ◽  
Velocity Gradient Tensor ◽  
Link Type ◽  
Isotopic Analyses ◽  
Supplementary Material

At >7 km depths in the Tarim Basin, hydrocarbon reservoirs in Ordovician rocks of the Yijianfang Formation contain large cavities (c. 10 m or more), vugs, fractures and porous fault rocks. Although some Yijianfang Formation outcrops contain shallow (formed near surface) palaeokarst features, cores from the Halahatang oilfield lack penetrative palaeokarst evidence. Outcrop palaeokarst cavities and opening-mode fractures are mostly mineral filled but some show evidence of secondary dissolution and fault rocks are locally highly (c. 30%) porous. Cores contain textural evidence of repeated formation of dissolution cavities and subsequent filling by cement. Calcite isotopic analyses indicate depths between c. 220 and 2000 m. Correlation of core and image logs shows abundant cement-filled vugs associated with decametre-scale fractured zones with open cavities that host hydrocarbons. A Sm–Nd isochron age of 400 ± 37 Ma for fracture-filling fluorite indicates that cavities in core formed and were partially cemented prior to the Carboniferous, predating Permian oil emplacement. Repeated creation and filling of vugs, timing constraints and the association of vugs with large cavities suggest dissolution related to fractures and faults. In the current high-strain-rate regime, corroborated by velocity gradient tensor analysis of global positioning system (GPS) data, rapid horizontal extension could promote connection of porous and/or solution-enlarged fault rock, fractures and cavities.Supplementary material: Stable isotopic analyses and the velocity gradient tensor and principal direction and magnitude calculation are available at https://doi.org/10.6084/m9.figshare.c.4946046Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

scholarly journals Discussion on ‘Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa’ by Shi et al. 2021 (JGS, jgs2021-060)

2021 ◽  
pp. jgs2021-111
Author(s):  
Martin R. Smith ◽  
Alavya Dhungana
Keyword(s):  
Bayesian Approach ◽  
Early Cambrian ◽  
Content Type ◽  
Animal Body ◽  
Link Type ◽  
Stem Group ◽  
Cambrian Radiation ◽  
Supplementary Material ◽  
Chengjiang Biota

Exceptionally preserved fossils are key to reconstructing the origin of the modern animal body plans in the Cambrian radiation. The Panarthropod phyla Euarthropoda, Onychophora and Tardigrada have roots in a ‘lobopodian’ grade typified by broadly cylindrical organisms with sclerotized dorsal plates and paired ventral projections. A similar anatomical configuration has been taken to link certain palaeoscolecid worms with the earliest ecdysozoans. Shi et al. (2021) contend that these similarities evolved convergently, and that palaeoscolecids are priapulan relatives with little bearing on the panarthropod evolution.Here we show that this conclusion holds only under a particular treatment of inapplicable character states with known shortcomings. When inapplicable tokens are handled more rigorously, palaeoscolecids are most parsimoniously reconstructed as stem-group panarthropods with homologous dorsal plates and ventral projections – highlighting the degree to which the treatment of inapplicable data can influence fundamental evolutionary conclusions. As the position of palaeoscolecids depends so strongly on the underlying methodology, and is highly uncertain under a Bayesian approach, we consider it premature to exclude the possibility that panarthropods evolved from a grade of palaeoscolecids with dorsal plates and ventral projections.Supplementary material:https://doi.org/10.6084/m9.figshare.16419522

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