Devonian Carboniferous Strata Research Articles

Tectono-stratigraphic framework and evolution of East Junggar Basin, Central Asia

The late Paleozoic development of the East Junggar Basin and adjoining mountain belts was critical to the construction of the larger Central Asian Orogenic System, yet the structural framework of basement rocks and overlying strata of the basin and their spatio-temporal relationship with adjacent thrust-bounded ranges remain poorly constrained. In this study, we conducted reflection seismology and compiled existing geologic observations of the East Junggar Basin and adjacent Bogda Shan to the south and Kelameili Shan to the north to construct cross sections depicting the tectono-stratigraphic framework and evolution of the region. Our work shows that Carboniferous–Permian strata overlying basement rocks in the East Junggar Basin occur in structural uplifts and depressions and feature at least five major unconformities. The structure of the East Junggar Basin is characterized by: (1) horsts and grabens involving basement rocks and overlying Carboniferous–Jurassic strata; (2) series of stratigraphic depressions marked by Jurassic–Cretaceous strata; and (3) a south-dipping monocline in uppermost Neogene–Quaternary strata. Mesozoic–Cenozoic strata are absent along the northern margin of the East Junggar Basin at the Kelameili Shan. Strata are generally older from the Kelameili Shan to the northern East Junggar Basin where Devonian–Carboniferous strata are thrust southward over younger strata. In contrast, thicker sequences of Cretaceous–Quaternary strata are present in the southern portion of the East Junggar Basin. Strata of the East Junggar Basin were deposited in a foreland depression formed in the footwall of a leading, north-directed thrust of the Bogda Shan. The overall tectono-stratigraphic framework of the East Junggar Basin is a product of tectonic activity varying in time and space along the northern and southern basin-mountain interfaces since the late Paleozoic.

Detrital zircon U–Pb ages and geochemistry of Devonian–Carboniferous sandstones and volcanic rocks of the Hida Gaien belt, Southwest Japan: Provenance reveals a Gondwanan lineage for the early Paleozoic tectonic evolution of proto-Japan

Devonian–Carboniferous strata in the Hida Gaien belt, Southwest Japan, are characterized by a change in the dominant lithology from clastic rocks and limestones to volcanic rocks. The sandstone compositions and detrital zircon U–Pb ages indicate that the Devonian sedimentary rocks were derived from various basement rocks, including granite and basalt, that were uplifted, exposed, and eroded during the Early–Middle Devonian (398–383 Ma). The source of sediment to these strata changed to basalts and rhyolites in the early Carboniferous (∼346 Ma). Early Carboniferous bimodal volcanic rocks are present in the Hida Gaien and South Kitakami belts, the southeastern margin of the South China block (Hainan), and the Jilin area (NE China) of the eastern Central Asian Orogenic Belt (CAOB). The Cambrian–Silurian zircon grains (540–480 Ma and 460–420 Ma) in the Hida Gaien belt were derived from arc basement of a similar age to the South Kitakami and Kurosegawa belts, the Jiamusi–Khanka–Bureya (NE China and the Russian Far East) and Songliao–Xilinhot (Inner Mongolia) blocks in the eastern CAOB, and the eastern South China and Indochina blocks. The Devonian strata also contain Precambrian zircon grains derived from Mesoarchean basement (∼3000 Ma) and the Grenvillian tectonothermal event (∼1000 Ma), suggesting sediment supply from NE Gondwana (the Thomson and Lachlan orogens of eastern Australia) or related continental remnants. Detrital zircon U–Pb age spectra similar to those of the Devonian strata of the Hida Gaien belt are also observed in Silurian–Devonian metasedimentary rocks in the Jilin area. During the early Paleozoic, the Hida Gaien belt, the eastern margin of the South China block, and the magmatic arcs and microcontinents in the eastern CAOB were located close to NE Gondwana along the western margin of the Paleo-Pacific Ocean.

Late Carboniferous thin-skinned deformation in the Lublin Basin, SE Poland: Results of combined seismic data interpretation, structural restoration and subsidence analysis

The aim of this study was to investigate the factors, which controlled the lateral change of structural style in the southeastern part of the Lublin Basin (Poland). Five selected seismic reflection profiles were interpreted with a focus on structural interpretation. Along the representative seismic reflection profile, a geological cross-section was constructed and restored. The structural model was supplemented/refined with core analysis to characterize the deformation mode affecting Silurian strata at a sub-seismic scale (i.e. below the seismic vertical resolution). Published palaeothickness maps were used to estimate the pre-deformation thickness of partly eroded Carboniferous rocks. The results of cross-section restoration were then compared to the subsidence modelling carried out for one deep well. The study revealed that during Late Carboniferous shortening, a thick layer of Silurian shales played the role of detachment level, above which brittle Devonian–Carboniferous strata were folded and thrust. The lateral extent of thin-skinned deformation was controlled by the presence of a step in the basement and the pinching out of the Silurian strata. In the northwestern part of the Lublin Basin, the Kock Fault Zone acted as a region of strain concentration, where Silurian shales were tectonically thickened, and shows a ductile style of deformation resembling the mushwad structures of the Appalachian fold-and-thrust belt.

Palaeozoic multiphase magmatism at Barleik Mountain, southern West Junggar, Northwest China: implications for tectonic evolution of the West Junggar

The West Junggar lies in the southwest part of the Central Asian Orogenic Belt (CAOB) and consists of Palaeozoic ophiolitic mélanges, island arcs, and accretionary complexes. The Barleik ophiolitic mélange comprises several serpentinite-matrix strips along a NE-striking fault at Barleik Mountain in the southern West Junggar. Several small late Cambrian (509–503 Ma) diorite-trondhjemite plutons cross-cut the ophiolitic mélange. These igneous bodies are deformed and display island arc calc-alkaline affinities. Both the mélange and island arc plutons are uncomfortably covered by Devonian shallow-marine and terrestrial volcano-sedimentary rocks and Carboniferous volcano-sedimentary rocks. Detrital zircons (n = 104) from the Devonian sandstone yield a single age population of 452–517 million years, with a peak age of 474 million years. The Devonian–Carboniferous strata are invaded by an early Carboniferous (327 Ma) granodiorite, late Carboniferous (315–311 Ma) granodiorites, and an early Permian (277 Ma) K-feldspar granite. The early Carboniferous pluton is coeval with subduction-related volcano-sedimentary strata in the central West Junggar, whereas the late Carboniferous–early Permian intrusives are contemporary with widespread post-collisional magmatism in the West Junggar and adjacent regions. They are typically undeformed or only slightly deformed. Our data reveal that island arc calc-alkaline magmatism occurred at least from middle Cambrian to Late Ordovician time as constrained by igneous and detrital zircon ages. After accretion to another tectonic unit to the south, the ophiolitic mélange and island arc were exposed, eroded, and uncomfortably overlain by the Devonian shallow-marine and terrestrial volcano-sedimentary strata. The early Carboniferous arc-related magmatism might reflect subduction of the Junggar Ocean in the central Junggar. Before the late Carboniferous, the oceanic basins apparently closed in this area. These different tectonic units were stitched together by widespread post-collisional plutons in the West Junggar during the late Carboniferous–Permian. Our data from the southern West Junggar and those from the central and northern West Junggar and surroundings consistently indicate that the southwest part of the CAOB was finally amalgamated before the Permian.

Palaeoenvironmental and palaeoceanographic controls on black, laminated mudrock deposition: example from Devonian–Carboniferous strata, Alberta, Canada

Abstract Sedimentological, palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling, in tandem with an expanded and intensified oxygen minimum zone, promoted deposition of upper Famennian to lower Tournaisian laminated, organic-rich mud rocks of the Exshaw Formation on the Alberta cratonic platform. Exshaw mud rocks represent the culmination of an upper Devonian transgression that commenced with deposition of open marine carbonates of the Big Valley Formation. The transgression was abruptly halted at the Devonian–Carboniferous boundary by a rapid eustatic sea-level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the Exshaw Formation. The siltstones grade into laminated, organic-lean mud rocks to the north in more distal offshore shelf settings. These mudrocks reflect a period of low primary production but continued anoxia of bottom waters. Continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward-located physical barrier. Following this event was a relative sea-level rise that led to deposition of black, laminated mudrocks of the Banff Formation.