scholarly journals The Mandalovoo–Gurvansayhan terranes in the southern Gobi of Mongolia: new insights from the Bayankhoshuu Ruins section

2021 ◽  
Author(s):  
A. Munkhjargal ◽  
P. Königshof ◽  
J. A. Waters ◽  
S. K. Carmichael ◽  
S. Gonchigdorj ◽  
...  
Keyword(s):  
Middle Devonian ◽  
Facies Analysis ◽  
Volcanic Rocks ◽  
Late Devonian ◽  
Basaltic Lava ◽  
Sedimentary Sequence ◽  
Early Devonian ◽  
Subaerial Exposure ◽  
Arc Setting ◽  
Devonian Age

AbstractThe Bayankhoshuu Ruins section in southern Mongolia is characterized by strongly thrusted and folded sequences. Overall, three sections ranging from Ordovician to Carboniferous rocks were studied. Facies analysis combined with stratigraphic data provide improved lithostratigraphic descriptions of Palaeozoic successions in the Mushgai region. The overall marine sedimentary sequence is punctuated by volcanic rocks–basaltic lava of Silurian and Middle Devonian age and volcaniclastic bentonite and tuff in the Middle to Late Devonian and Mississippian suggesting an island arc setting. The Minjin Member of the Botuulkhudag Formation (Middle Devonian to Late Devonian) is primarily composed of thick basaltic and subaerial volcanic rocks with minor silicified siltstone and chert inclusions. Thicker successions of limestone occur in the Ordovician/Silurian, Early Devonian, and the Mississippian. The macrofauna is scarce, except distinct limestone horizons where different fossil groups were recognized. Microfossils, such as radiolarians and conodonts, are scarce and generally poorly preserved. However, based on the re-study of collections from earlier publications and new conodont data, a more detailed biostratigraphic record of the Khoyormod, Botuulkhudag, and Arynshand formations of the Bayankhoshuu Ruins section can be developed. For instance, the Arynshand Formation likely ranges from the late Bispathodus ultimus conodont biozone to the Scaliognathus anchoralis–Doliognathus latus conodont biozone. A tectonic breccia occurs in the early Mississippian and is overlain by a red shale of remarkable thickness at the top of this formation which points to subaerial exposure in the early Mississippian (near the Tournaisian/Visean transition). Due to strong tectonic overprint and/or facies, some unconformities/hiatuses occur. Most strata are intensively folded and faulted, ranging from centimeter to meter scale. Overall, deposition likely occurred on either the Mandalovoo or Gurvansayhan Terrane.

New insights into the origins and radiation of the mid-Palaeozoic Gondwanan stem tetrapods

2018 ◽  
Vol 109 (1-2) ◽  
pp. 139-155 ◽  
Author(s):  
John A. LONG ◽  
Alice M. CLEMENT ◽  
Brian CHOO
Keyword(s):  
Middle Devonian ◽  
Late Devonian ◽  
Early Devonian ◽  
Biogeographic History ◽  
History Of ◽  
Scan Data ◽  
Devonian Age ◽  
High Degree ◽  
Phylogenetic Models

ABSTRACTThe earliest tetrapodomorph fishes appear in Chinese deposits of Early Devonian age, and by the Middle Devonian they were widespread globally. Evidence for the earliest digitated tetrapods comes from largely uncontested Middle Devonian trackways and Late Devonian body fossils. The East Gondwana Provence (Australasia, Antarctica) fills vital gaps in the phylogenetic and biogeographic history of the tetrapods, with the Gondwanan clade Canowindididae exhibiting a high degree of endemism within the early part of the stem tetrapod radiation. New anatomical details of Koharalepis, from the Middle Devonian Aztec Siltstone of Antarctica, are elucidated from synchrotron scan data. These include the position of the orbit, the condition of the hyomandibular, the shape of the palate and arrangement of the vomerine fangs. Biogeographical and phylogenetic models of stem tetrapod origins and radiations are discussed.

New chonostrophiid brachiopods from the Famennian (Late Devonian) of the Santanghu Basin, Xinjiang, northwest China

2002 ◽  
Vol 76 (2) ◽  
pp. 229-238
Author(s):  
Zhong-Qiang Chen ◽  
Neil W. Archbold
Keyword(s):  
Middle Devonian ◽  
New Genus ◽  
Early Carboniferous ◽  
Northwest China ◽  
Late Devonian ◽  
New Genera ◽  
New Genus And Species ◽  
Early Devonian ◽  
Median Septum ◽  
Devonian Age

Two new genera of the Chonostrophiidae are proposed herein to accommodate the resupinate shells from the Famennian sediments of the Late Devonian in the Santanghu Basin of the Balikun area, Xinjiang Province, northwestern China. Santanghuia santanghuensis new genus and species is distinguishable from other chonostrophiids by the possession of a pair of long dorsal anderidia and absence of a dorsal median septum. Balikunochonetes liaoi new genus and species is distinct because of the presence of a pair of anderidia with secondary anderidia, and a dorsal median septum. Santanghuia new genus is considered to be phylogenetically related to Chonostrophia of late Early to Middle Devonian age, while Balikunochonetes has possibly given rise to Chonostrophiella of Early Devonian age and is a likely ancestor of Tulcumbella of Early Carboniferous age.

scholarly journals Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

2021 ◽  
Vol 100 ◽  
Author(s):  
Alexander J.P. Houben ◽  
Geert-Jan Vis
Keyword(s):  
The Netherlands ◽  
Core Material ◽  
Late Devonian ◽  
Time Interval ◽  
The South ◽  
Early Devonian ◽  
The North ◽  
Depositional Settings ◽  
Palynological Study ◽  
Devonian Age

Abstract Knowledge of the stratigraphic development of pre-Carboniferous strata in the subsurface of the Netherlands is very limited, leaving the lithostratigraphic nomenclature for this time interval informal. In two wells from the southwestern Netherlands, Silurian strata have repeatedly been reported, suggesting that these are the oldest ever recovered in the Netherlands. The hypothesised presence of Silurian-aged strata has not been tested by biostratigraphic analysis. A similar lack of biostratigraphic control applies to the overlying Devonian succession. We present the results of a palynological study of core material from wells KTG-01 and S05-01. Relatively low-diversity and poorly preserved miospore associations were recorded. These, nonetheless, provide new insights into the regional stratigraphic development of the pre-Carboniferous of the SW Netherlands. The lower two cores from well KTG-01 are of a late Silurian (Ludlow–Pridoli Epoch) to earliest Devonian (Lochkovian) age, confirming that these are the oldest sedimentary strata ever recovered in the Netherlands. The results from the upper cored section from the pre-Carboniferous succession in well KTG-01 and the cored sections from the pre-Carboniferous succession in well S05-01 are more ambiguous. This inferred Devonian succession is, in the current informal lithostratigraphy of the Netherlands, assigned to the Banjaard group and its subordinate Bollen Claystone formation, of presumed Frasnian (i.e. early Late Devonian) age. Age-indicative Middle to Late Devonian palynomorphs were, however, not recorded, and the overall character of the poorly preserved palynological associations in wells KTG-01 and S05-01 may also suggest an Early Devonian age. In terms of lithofacies, however, the cores in well S05-01 can be correlated to the upper Frasnian – lower Famennian Falisolle Formation in the Campine Basin in Belgium. Hence, it remains plausible that an unconformity separates Silurian to Lower Devonian strata from Upper Devonian (Frasnian–Famennian) strata in the SW Netherlands. In general, the abundance of miospore associations points to the presence of a vegetated hinterland and a relatively proximal yet relatively deep marine setting during late Silurian and Early Devonian times. This differs markedly from the open marine depositional settings reported from the Brabant Massif area to the south in present-day Belgium, suggesting a sediment source to the north. The episodic presence of reworked (marine) acritarchs of Ordovician age suggests the influx of sedimentary material from uplifted elements on the present-day Brabant Massif to the south, possibly in relation to the activation of a Brabant Arch system.

Pre-Acadian copper mineralization in the English Lake District

1999 ◽  
Vol 136 (2) ◽  
pp. 159-176 ◽  
Author(s):  
D. MILLWARD ◽  
B. BEDDOE-STEPHENS ◽  
B. YOUNG
Keyword(s):  
Quartz Crystal ◽  
Volcanic Rocks ◽  
Wall Rock ◽  
Lake District ◽  
Early Devonian ◽  
Rock Fragments ◽  
Copper Mineralization ◽  
English Lake District ◽  
Fibre Strain ◽  
Devonian Age

The Ordovician sedimentary and igneous rocks of the English Lake District host a widespread suite of epigenetic metalliferous veins dominated by copper sulphides with abundant arsenopyrite, pyrite and accessory galena and sphalerite. New field and microstructural evidence from examples of this suite at Coniston, Wasdale, Honister, Newlands and Borrowdale shows that the veins were strongly cleaved during the Early Devonian (Emsian) Acadian orogenic event. The principal evidence includes the continuity of wall-rock cleavage fabrics with pressure solution seams in the veins and consistently orientated cleavage through enclosed, rotated wall-rock fragments and chloritic mats. There is also widespread complex intracrystalline deformation in quartz, cataclasis of arsenopyrite and pyrite, fracturing and/or buckling of bladed hematite, and growth of quartz or mica-fibre strain fringes. Chalcopyrite was partially or totally remobilized, enabling it to migrate along quartz crystal boundaries, and invade brecciated pyrite. Previous K–Ar Early Devonian age determinations for the mineralization are considered to have been reset. The pre-Acadian age of this mineralization, its style and relationship to the volcanic rocks permits a genetic link with the final phases of Caradoc magmatism.

New arthrodires (placoderm fishes) from the Aztec Siltstone (late Middle Devonian) of southern Victoria Land, Antarctica

2014 ◽  
Vol 62 (1) ◽  
pp. 44 ◽  
Author(s):  
Gavin C. Young ◽  
John A. Long
Keyword(s):  
South Africa ◽  
New Taxa ◽  
Middle Devonian ◽  
Late Devonian ◽  
Dorsal Plate ◽  
Victoria Land ◽  
Small Collection ◽  
Vertebrate Assemblage ◽  
Devonian Age

A small collection of arthrodire remains is described from the Devonian Aztec Siltstone of southern Victoria Land, Antarctica. Barwickosteus antarcticus, gen. et sp. nov., is a small phlyctaeniid arthrodire probably closely related to Barrydalaspis from the Bokkeveld Group of South Africa. Grifftaylor antarcticus, gen. et sp. nov., is a generalised phlyctaeniid resembling Phlyctaenius and Neophlyctaenius. New specimens of Boomeraspis show that it had a high-spired trunk-armour with a median dorsal plate of similar proportions to Tiaraspis, Mithakaspis, Turrisaspis or Africanaspis. Other fragmentary median dorsal plates are provisionally referred to Turrisaspis and Mulgaspis. With these new taxa the vertebrate assemblage from the Aztec Siltstone comprises at least 37 genera and 50 species, making it one of the most diverse of Middle–Late Devonian age.

Implications of spore evidence for Late Devonian age of the Piskahegan Group, southwestern New Brunswick

1988 ◽  
Vol 25 (9) ◽  
pp. 1349-1364 ◽  
Author(s):  
D. C. McGregor ◽  
S. R. McCutcheon
Keyword(s):  
New Brunswick ◽  
Eastern Europe ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Surface Expression ◽  
Alluvial Fan ◽  
Late Devonian ◽  
Red Sandstone ◽  
Stratigraphic Position ◽  
Devonian Age

The predominantly volcanic Piskahegan Group has commonly been considered Early Carboniferous, based on its stratigraphic position. However, spores recently discovered in the Carrow Formation, an alluvial fan deposit in the exocaldera facies, indicate that most, if not all, of the group is of Late Devonian (late Famennian) age. The spore assemblage includes several species reported previously from Ireland, Belgium, and eastern Europe, some of them apparently restricted to the southern parts of the Old Red Sandstone Continent in Late Devonian time. Comparison of records of earliest occurrences suggests that the incoming of some species was diachronous. Volcanic rocks of the Piskahegan Group are coeval with post-Acadian, tin–tungsten-bearing granites elsewhere in New Brunswick and are considered the surface expression of plutonism that resulted from Acadian continental collison.

The Middle to Late Devonian Høybakken detachment, central Norway: 40Ar–39Ar evidence for prolonged late/post-Scandian extension and uplift

2004 ◽  
Vol 141 (3) ◽  
pp. 329-344 ◽  
Author(s):  
M. A. KENDRICK ◽  
E. A. EIDE ◽  
D. ROBERTS ◽  
P. T. OSMUNDSEN
Keyword(s):  
Middle Devonian ◽  
Early Carboniferous ◽  
White Mica ◽  
Late Devonian ◽  
Brittle Deformation ◽  
Southwestern Part ◽  
Early Devonian ◽  
Southern Margin

The regionally significant 0.5–2 km thick Høybakken detachment in central Norway bounds the southern margin of the Central Norway Basement Window and exhibits a well-developed top-to-the-WSW fabric characteristic of late Scandian, Devonian ductile extension. 40Ar–39Ar data obtained from hornblende, mica and K-feldspar mineral separates of rocks collected in a transect through the Høybakken detachment yield well-defined plateau and isochron mineral ages. Early Devonian exhumation and cooling of the Høybakken detachment footwall is recorded by hornblende ages of ∼ 400 Ma and mica ages of ∼ 390 Ma. The mylonitic fabric overlying the footwall records younger Middle Devonian mica crystallization ages of 384–381 Ma that are among the youngest extensional ductile fabrics dated in the Caledonides and suggest prolonged extensional activity on the Høybakken detachment. After inferred cessation of ductile extension at 381 Ma, the rate of uplift and cooling was reduced, and the footwall records Late Devonian to Early Carboniferous K-feldspar ages of 371–356 Ma. Prolonged extensional activity at Høybakken is compatible with recent U–Pb ages of deformed titanite crystals and established Rb–Sr ages of white mica in shear-related pegmatites, both from the southwestern part of the Fosen Peninsula, and 40Ar–39Ar ages of syn-tectonic mica overgrowth from the adjacent Hitra–Snåsa Fault. Together, these ages suggest the onset of ductile extension soon after ∼ 401 Ma, and with the Middle Devonian crystallization ages determined here, suggest that ductile extension on the Høybakken detachment had a duration of 11–20 Ma. The youngest age of 320 Ma was obtained from a K-feldspar in a cataclastic granite of the Høybakken detachment's hangingwall and is considered to date a phase of post-Scandian brittle deformation that overprinted the mylonitic shear fabric.

Silurian and Devonian base maps

1985 ◽  
Vol 309 (1138) ◽  
pp. 57-77 ◽  
Keyword(s):  
Great Britain ◽  
North America ◽  
Middle Devonian ◽  
Northern Europe ◽  
Late Devonian ◽  
The South ◽  
Early Devonian ◽  
Red Sandstone ◽  
Palaeomagnetic Data

During the Silurian and Devonian, the sequence of continental collisions that were ultimately to result in the formation of the supercontinent of Pangaea had begun. By the Early to Middle Devonian North America (Laurentia), Acadia, Great Britain, and Northern Europe (Baltica) had collided to form the ‘Old Red Sandstone’ continent (Laurussia). Palaeomagnetic data, however, indicate that the configuration of the continents that made up Laurussia did not resemble the pre-breakup, Mesozoic reassembly. Rather, Britain, Baltica, and Acadia were displaced 10—20° to the south with respect to Laurentia. New palaeomagnetic data for Laurentia and Gondwana, suggests that the ocean separating the northern and southern continents was relatively narrow during the early Devonian, and may have been nearly closed by the late Devonian.

scholarly journals Early Devonian Arc-Related Volcanic Rocks in the Haerdaban, North Margin of the Yili Block: Constraint on the Southward Subduction of the Junggar Ocean

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1248
Author(s):  
Youxin Chen ◽  
Shengqiang Zhu ◽  
Xianzhi Pei ◽  
Lei He ◽  
Jun Zhao ◽  
...  
Keyword(s):  
Middle Devonian ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Age Dating ◽  
Magma Source ◽  
Heat Accumulation ◽  
Early Devonian ◽  
Northern Margin ◽  
T Values

The origin and tectonic implication of Early–Middle Devonian magmatism in the northern margin of YB (Yili Block) remain enigmatic and are important for understanding Late Paleozoic evolution of the Junggar Ocean and southern Kazakhstan Orocline. Here, we present the systematic study of whole-rock geochemical and Sr–Nd isotope features as well as U–Pb–Hf isotope characteristics of zircon crystals for newly identified Early Devonian volcanic rocks from the northern margin of YB. The volcanic rocks are composed of rhyolite, rhyolite porphyry, and rhyolitic tuff. Zircon U-Pb age dating indicates they were formed at ca. 407~418 Ma. They have high SiO2 (70.16–77.52 wt.%) and alkali (5.10–9.56 wt.%) contents, and high Zr + Nb + Ce + Y content (~456 ppm), indicative of A-type magma. Their relative depletion of Nb, Ta, and Ti, and enrichment of LILEs show arc affinity. Their low initial 87Sr/86Sr ratios (0.699708–0.709822) and negative εNd(t) values (−1.8 to −4.0) indicate a mainly continental magma source and their positive εHf(t)values (+6.13 to +14.81) are possibly due to the garnet effect. All these above reveal that volcanic rocks were generated by re-melting of lower crust under a high temperature condition, which was induced by long-lived heat accumulation with no or minimal basalt flux. Combined with active continental margin inference evidenced by contemporaneous sedimentary rocks, we attribute the generation of the volcanic rocks to a continental arc setting related to the southward subduction of Junggar oceanic crust. Thus, we infer the Early–Middle Devonian arc-related magmatic rocks in the northern margin of YB are eastward counterparts of the southern limb of the Devonian Volcanic Belt, which resulted from a relatively steady-state southward subduction.

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