Geological Journal
0072-1050
1099-1034
Anh Quốc
Cơ quản chủ quản: WILEY , John Wiley and Sons Ltd
Lĩnh vực:
Geology
Các bài báo tiêu biểu
Tectonic setting of Triassic magmatic and metallogenic event in the Duobaoshan mineralization area of Heilongjiang Province, NE China
Tập 52 Số 1 - Trang 67-91 - 2017
Petrographical, mineralogical, and geochemical characteristics of the Palaeocene lateritic bauxite deposits of Kachchh Basin, Western India Petrographical, mineralogical, and geochemical characteristics of a blanket‐type lateritic bauxite deposit, bordering the Deccan basalt in Kachchh, are investigated to interpret the parent rock, lateritization processes, and palaeogeographical position of the basin. The presence of partly weathered vesicular basalt at the base of the succession along with partly preserved plagioclase, augite, and hornblende in petrographical observations suggests the in situ nature of these bauxites. X‐ray diffraction analysis reveals gibbsite as the major bauxitic mineral associated with kaolinite, goethite, titanium‐rich anatase, calcite, haematite, and quartz as subconstituents. The presence of gibbsite, kaolinite, and goethite in the majority suggests that warm and humid climatic conditions prevailed during the lateritic bauxite formation. SEM‐EDS analysis shows that most of the gibbsites are mesocrystalline with particle sizes 50–200 μm that coexists with microcrystalline goethite, kaolinite, rutile, and haematite. These deposits are classified as bauxite, ferruginous bauxite, and laterite, based on chemical composition. The high CIA values (86.6–98.1%) suggest their formation under high run‐off and water‐logged conditions similar to that which prevails in the equatorial region. The Zr–Cr–Ga ternary plot testifies to the mafic composition of the parent rock. The major oxides and chondrite‐normalized trace and REEs behaviours, (La/Sm)N ratio (~5.77), and Eu anomaly of these lateritic bauxites suggest that they (bauxites) were formed in situ by the intensive leaching and alteration of the basaltic parent rock, and the process of bauxitization followed the path of deferruginization and destruction of kaolinite. The development of a lateritic regolith over the Deccan basalt was possible during Palaeocene time when the Indian Plate was in complete isolation and the Kachchh region was positioned near the equator in the Southern Hemisphere.
Tập 54 Số 4 - Trang 2588-2607 - 2019
The eogenetic karst of the Cambrian Longwangmiao Formation in the Yangtze Platform: Implications for the eustatic and stratigraphic correlations of Toyonian (Cambrian) To make a better understanding of the stratigraphic correlation and ocean processes during the transition from Series 2 to Series 3 in the Cambrian, this study investigated the characteristics and origin of the palaeokarst in the uppermost part of the Longwangmiao Formation (Toyonian) and established the carbon isotopic curves of the shallow‐water succession. Macroscopically, the palaeokarst features have been identified, including the exposed surface, karstic trough, discolouration, and breccia in the upper part of the Longwangmiao Formation. The exposed surface is divided into the bedrock, weakly weathering zone, intensely weathering zone, dissolved‐collapsed zone, and weathering clay layer at the Dingzhai section. The reddish aluminous oxide and the stratiform‐dissolved pore are recognized in the Gaodongmiao section. The clast‐support breccia and matrix‐support breccia develop in the palaeokarst zone. Microscopically, three dissolution‐filling zones in grainstone (the matrix zone, half‐dissociated zone, and mixed‐filling zone) dissolved fibrous cement in the early diagenetic stage, microspar cement in a bright homogeneous luminescence, and medium‐crystal calcite showing a zonation luminescence are identified indicating the facies‐controlled attributes. The δ13 C values are characterized by a lower range (4.4‰ to −2.1‰) in the karst zone. The REE pattern shows enriched middle REE, negative Eu anomalies, and low Y/Ho ratio, which is different from the nature of seawater. It is proposed that the palaeokarst in the upper part of the Longwangmiao Formation is the eogenetic karst controlled by high‐frequency sea‐level fluctuations. Two negative δ13 C excursions (values −4.4‰ in D2 and −3.6‰ in D1) are respectively recognized, the top boundary and middle part of the Longwangmiao Formation. Based on the regional and global correlations, the excursion of D2 is the diagenetic signal in the shallow‐water setting, which correlated to ROECE event (Redlichiid‐Olenellid Extinction Carbon isotope Excursion) that occurred around the boundary between Series 2 and Series 3 in the Cambrian. The local signal of D2 is attributed to the sea‐level falling.
Tập 54 Số 6 - Trang 3720-3736 - 2019
Identification of facies‐controlled eogenetic karstification in the Upper Cretaceous of the Halfaya oilfield and its impact on reservoir capacity Penecontemporaneous dissolution has been considered as the dominant origin of reservoir formation, whereas epigenetic dissolution has also played certain roles in the improvement of reservoir capacity in the Upper Cretaceous Mishrif Formation in the Middle East. Here, we report a possible new reservoir origin based on a case study in the Halfaya oilfield of Iraq, that is, facies‐controlled eogenetic karstification. The most representative evidence is that early selective dissolution is not only present in relative high‐energy categories of rocks but also in low‐energy ones in the cored intervals. Meanwhile, the occurrence frequency of karstification varies among different environments and associated lithologies. In grainstones and packstones, spongy‐like dissolution pores and irregular karst channels are widely developed, with fillings and massive plastic breccias. In contrast, in wackestones, lots of high‐angle karst channels are developed based on biological burrows, and the karst is more frequently observed in the shoal environment than in the low‐energy environments. These characteristics are indication of eogenetic karstification. The model of this karstification can be attributed to a multiple superimposition of short‐term exposure during the penecontemporaneous stage and the medium‐term exposure after the shallow burial stage. The karst has impact on reservoir capacity, according to which 3 areas are divided in the increasing order, namely, the tight bedrock area, spongy‐like dissolution pores area, and karst channels and vugs‐filled area, among which the karst channels and vugs‐filled area is the most favourable for oil accumulation. This understanding might be general to the Mishrif reservoirs in the entire Middle East.
Tập 54 Số 1 - Trang 450-465 - 2019
Incompleteness of the Permian–Triassic fossil record: a consequence of productivity decline? Abstract Analysis of published data shows that, for most animal groups, the fossil record in the immediate aftermath of the end‐Permian biotic crisis is less complete than during the Late Permian or Middle Triassic. Completeness is measured by the Simple Completeness Metric. The interval of poor quality fossil record spans the entire Lower Triassic and may have serious consequences for our perception of the magnitude of the end‐Permian event. A model is presented which seeks to explain this phenomenon. There is abundant evidence that levels of primary productivity were severely reduced in the very latest Permian. In response to this, animal biomass must also have been reduced. The biomass of a particular taxon is the product of the size of individual organisms multiplied by the number of individuals. Those taxa that reduced population size, but maintained original body size, would tend not to be preserved (apparent extinction) and would also be more prone to ‘real’ extinction. Those taxa that retained large population sizes, but reduced body size, would resist extinction and would also maintain their presence in the fossil record. One testable prediction is that taxa present in the fossil record in the immediate aftermath of the end‐Permian crisis will have smaller body size than their pre‐event relatives, regardless of their initial size. Anecdotal evidence supports this prediction. Such a biomass reduction model may also be applicable to other mass extinction events. Copyright © 2001 John Wiley & Sons, Ltd.
Tập 36 Số 3-4 - Trang 341-353 - 2001
Early Triassic carbon isotope excursions from South China: proxies for devastation and restoration of marine ecosystems following the end‐Permian mass extinction Abstract Early Triassic carbon isotopes are measured based on 1422 carbonate bulk samples from 10 Lower Triassic sections in different palaeogeographic settings in South China. Early Triassic fluctuation ofδ 13 C is used as a proxy for environmental change to discuss the devastation and restoration of marine ecosystems following the biggest Phanerozoic mass extinction at the end of the Permian. Early Triassicδ 13 C profiles derived from various depositional settings in South China yield comparable excursion patterns. A dramatic negative shift ofδ 13 C across the Permian/Triassic boundary is followed by a moderate increase inδ 13 C values throughout the Induan. A positiveδ 13 C anomaly occurs near the Induan/Olenekian boundary, followed by a Smithian interval of lowerδ 13 C values. A distinct positive shift inδ 13 C coincides with the Smithian/Spathian boundary, and is followed by a high Spathian plateau ofδ 13 C values. Thus the distinctδ 13 C anomalies coincide well with key stratigraphic boundaries. Early Triassic intervals of lowδ 13 C values correspond to a decline in benthic generic diversity in South China and intervals of highδ 13 C values are coupled with an increase in biodiversity. The Early Triassic fluctuations ofδ 13 C profiles are good proxies for perturbations of ecologic environments, indicating multiple phases of devastation–restoration of marine ecosystems punctuated by several unexpected extraneous events such as volcanic activity. The initial restoration of marine ecosystems may have occurred earlier in the Induan and the ecosystems were subsequently destroyed during the Smithian. Biotic and environmental recoveries occurred at the Spathian, while the ecosystems eventually returned to normal levels in the early Middle Triassic. Copyright © 2007 John Wiley & Sons, Ltd.
Tập 42 Số 3-4 - Trang 371-389 - 2007
Depositional facies controls on the diagenesis and reservoir quality of the Messinian Qawasim and Abu Madi formations, onshore Nile Delta, Egypt The Messinian Qawasim and Abu Madi formations are the main hydrocarbon exploration targets in the onshore Nile Delta. Qawasim Formation constitutes prograditional deltaic system from prodelta and distal delta‐front (distal deltaic facies) to proximal delta‐front and delta‐plain (proximal deltaic facies). Abu Madi sediments on the other hand change upward from continental subaerial gravity‐flow and fluvial facies to marginal‐marine estuarine facies. The seismic attribute (RMS amplitude) and petrophysical analyses revealed that solely the Qawasim proximal deltaic and Abu Madi fluvial facies define the potential reservoir targets. The reservoir quality of the Qawasim distal deltaic and the Abu Madi estuarine facies was completely deteriorated during eodiagenesis by calcite and glauconite cementation (mean > 7.3% and 4.5%, respectively). Conversely, the depositional setting of the Qawasim proximal deltaic and Abu Madi fluvial facies favoured a precipitation of scattered eodiagenetic calcite (mean < 2.5%), which supported the facies framework against mechanical compaction and preserved the intergranular volume (IGV). Chemical compaction, smectite infiltration, quartz cementation, and clay minerals authigenesis were more pronounced in the relatively deeper Abu Madi fluvial facies. These burial attributes caused a large‐scale reservoir heterogeneity. Therefore, the relatively shallower Qawasim proximal deltaic facies presents the best reservoir target in the Messinian sequence of the Nile Delta. This study reveals that in analogous systems, the depositional environment largely controls the diagenetic pathways and, hence, the reservoir quality.
Tập 54 Số 3 - Trang 1797-1813 - 2019
Late Pan‐African magmatism and crustal development in northeastern Egypt Abstract The voluminous Pan‐African calc‐alkaline granitic suite of the Ras Gharib crustal segment in northeastern Eygpt provides a typical example of orogenic magmatism. The 552 ± 7 Ma‐old granodiorite–adamellite and leucogranite suite is compositionally broad (58 to 77 wt.% SiO2 ) and exhibits calc‐alkaline geochemical trends and trace‐element characteristics typical of the volcanic‐arc granites. The rocks contain oligoclase, albite, K‐feldspar, calcic amphibole, biotite, titanite, zircon, and magnetite. The suite exhibits typical features characteristic of I‐type granites. We contend that the magma was formed by partial melting of a modified oceanic crust at an active continental margin during the late stage of the Pan‐African orogeny. The process may have involved assimilation of Early Pan‐African dioritic country rocks. The more felsic units were produced by progressive fractionation of that magma. The petrological–geochemical evidence suggest that the Pan‐African crust in northeastern Egypt did not develop in an extensional tectonic regime, as proposed recently.
Tập 22 Số 4 - Trang 281-301 - 1987
Continental margin basins in East Asia: tectonic implications of the Meso‐Cenozoic East China Sea pull‐apart basins The East China Sea basins, located in the West Pacific Continental Margin (WPCM) since the late Mesozoic, mainly include the East China Sea Shelf Basin (ECSSB) and the Okinawa Trough (OT). The WPCM and its adjacent seas can be tectonically divided into five units from west to east, including the Min‐Zhe Uplift, ECSSB, the Taiwan–Sinzi Belt, OT, and the Ryukyu Island Arc, which record regional tectonic evolution and geodynamics. Among those tectonic units, the ECSSB and the OT are important composite sedimentary pull‐apart basins, which experienced two stages of strike‐slip pull‐apart processes. In seismic profiles, the ECSSB and the OT show a double‐layer architecture with an upper half‐graben overlapping on a lower graben. In planar view, the ECSSB and the OT are characterized by faulted blocks from south to north in the early Cenozoic and by a zonation from west to east in the late Cenozoic. The faulted blocks with planar zonation and two‐layer vertical architecture entirely jumped eastward from the Min‐Zhe Uplift to the OT during the late Cenozoic. In addition, the whole palaeogeomorphology of the ECSSB changed notably, from pre‐Cenozoic highland or mountain into a Late Eocene continental margin with east‐tilting topography caused by the eastward tectonic jumping. The OT opened to develop into a back‐arc basin until the Miocene. Synthetic surface geological studies in the China mainland reveal that the Mesozoic tectonic setting of the WPCM is an Andean‐type continental margin developing many sinistral strike‐slip faults and pull‐apart basins and the Cenozoic tectonic setting of the WPCM is a Japanese‐type continental margin developing dextral strike‐slip faults and pull‐apart basins. Thus, the WPCM underwent a transition from Andean‐type to Japanese‐type continental margins at about 80 Ma (Late Cretaceous) and a transition in topography from a Mesozoic highland to a Cenozoic lowland, and then to below sea‐level basins. Copyright © 2013 John Wiley & Sons, Ltd.
Tập 50 Số 2 - Trang 139-156 - 2015
Crustal evolution in the South Tianshan Terrane: Constraints from detrital zircon geochronology and implications for continental growth in the Central Asian Orogenic Belt The South Tianshan Terrane (STT) is located in the boundary between the south‐western Central Asian Orogenic Belt (CAOB) and the Tarim Craton and is a key area for understanding the geologic and tectonic history of the craton and the orogenic belt. In this paper, we report detrital zircon ages from the Late Palaeozoic and Mesozoic clastic sedimentary rocks from the southern part of STT. In combination with the U–Pb ages for felsic igneous and meta‐igneous rocks exposed in the STT and adjacent tectonic units, we identify several distinct age populations. Provenance analysis suggests that the detrital zircon grains were predominately derived from the felsic magmatic rocks in the Tarim Craton and South Tianshan Terrane. The pre‐Neoproterozoic age populations may be associated with the early history of the Tarim Craton. Several pulses of Neoproterozoic magmatism are revealed by our dataset, presumably related to the assembly and break‐up of the supercontinent Rodinia. The 995 to 901 Ma detrital zircon grains were likely sourced from magmatic rocks associated with the assembly of Neoproterozoic Tarim to Australia. Among the age population of 886 to 752 Ma, the older group might be related to the subduction‐related magmatism after the assembly of Rodinia, and the younger one records a protracted magmatic event in a continental rift‐related setting associated with the break‐up of Rodinia. Two younger Neoproterozoic age populations (736 to 694 Ma and 665 to 610 Ma), showing narrow spreads with weak peaks, represent the waning stages of igneous activities related to the break‐up of Rodinia. Regarding the Palaeozoic evolution, together with other evidence, our data indicate a two‐stage subduction model for the SW Palaeo‐Asian Ocean. The 490 to 384 Ma age population corroborates the existence of Early Palaeozoic continental arc magmatism at the northern margin of Palaeozoic Tarim generated by the bidirectional subduction of the South Tianshan Ocean. After a ~30 My period of tectonomagmatic quiescence, the second stage is marked by the northward subduction of the South Tianshan Terrane during Late Devonian to Early Carboniferous. The final collision of Tarim and the south‐western CAOB likely occurred during the Late Carboniferous, followed by syn‐ and post‐collisional magmatism, as represented by the 320 to 265 Ma age population. Based on the detrital zircon ages in conjunction with the Hf isotopic features of zircons from Palaeozoic igneous rocks, our study does not support the model of large‐scale Phanerozoic net continental growth in the South Tianshan Terrane.
Tập 54 Số 3 - Trang 1379-1400 - 2019