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61.
62.
Here we report the first 2obaichthyid gar from the Lower Cretaceous (Aptian) Codó Formation of the Parnaíba Basin, Northeastern Brazil. It shows the following obaichthyid characters: numerous odontods firmly attached to the outer surface of the dermal bones, free and mobile maxilla, presence of interopercle, lack of contact between the metapterygoid and ectopterygoid, absence of lacrimomaxillary bones, and a prominent spine at the posterior margin of the scales. Due to the presence of scales bearing a prominent ventral posterior spine and a number of additional posterior marginal spines, the fish from the Codó Formation is noticeably the same species found in the Albian Santana Formation of the Araripe Basin, Dentilepisosteus laevis. Although probably restricted to fresh or brackish water, the new discovery adds one more taxon to the assemblages found in the Parnaíba and the Araripe basins. The new record extends the temporal range of this species down into the Aptian (about ∼10 myr older than the previous occurrence). 相似文献
63.
Here we describe a new record of a sauropod dinosaur from the Lower Cretaceous (Hauterivian–Barremian) Rio Piranhas Formation, Sousa Basin, NE Brazil. Dinosaur fossil bones from this deposit were unknown until now. Thus, the discovery of a sauropod fibula from this locality is highly significant. Our discovery represents an indeterminate titanosaur and the earliest stratigraphic occurrence of this group in central Gondwana. When compared to chronocorrelate titanosaur trackmakers of this geological unit, this fossil specimen appears substantially smaller. Histological analysis of the fibula suggests that this is a relatively young individual (approximately 40–50% adult body size) that had passed its most rapid phase of early juvenile growth, but had not yet attained somatic maturity. Thus, the fibula recovered is from a young individual rather than from a small-bodied adult titanosaur. 相似文献
64.
Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages that extend far beyond the size of the orebody. Understanding the mineral assemblages and spatial extent of these hydrothermal footprints is crucial for successful exploration, but is commonly hindered by the impact of regolith processes on the Earth's surface. Hyperspectral drill core (HyLogger?-3) data were used to characterise alteration mineralogy at the Mt Olympus gold deposit located 35 km southeast of Paraburdoo along the Nanjilgardy Fault within the northern margin of the Ashburton Basin in Western Australia. Mineralogy interpreted from hyperspectral data over the visible to shortwave (400–2500 nm) and thermal (6000–14500 nm) infrared wavelength ranges was validated with X-ray diffraction and geochemical analyses. Spaceborne multispectral (ASTER) and airborne geophysical (airborne electromagnetic, AEM) data were evaluated for mapping mineral footprints at the surface and sub-surface. At the deposit scale, mineral alteration patterns were identified by comparing the most abundant mineral groups detected in the HyLogger data against lithology logging and gold assays. Potential hydrothermal alteration phases included Na/K-alunite, kaolin phases (kaolinite, dickite), pyrophyllite, white mica, chlorite and quartz, representing low-T alteration of earlier greenschist metamorphosed sediments. The respective zoned mineral footprints varied depending on the type of sedimentary host rock. Siltstones were mainly characterised by widespread white-mica alteration with proximal kaolinite alteration or quartz veining. Sandstones showed (1) distal white mica, intermediate dickite, and proximal alunite + kaolinite or (2) widespread white-mica alteration with associated intervals of kaolinite. In both, sandstones and siltstones, chlorite was distal to gold mineralisation. Conglomerates showed distal kaolinite/dickite and proximal white-mica/dickite alteration. Three-dimensional visualisation of the gold distribution and spatially associated alteration patterns around Mt Olympus revealed three distinct categories: (1) several irregular, poddy, SE-plunging zones of >0.5 ppm gold intersected by the Zoe Fault; (2) sulfate alteration proximal to mineralisation, particularly on the northern side of the Mt Olympus open pit; and (3) varying AlIVAlVISiIV–1(Mg,Fe)VI–1 composition of white micas with proximity to gold mineralisation. Chlorite that developed during regional metamorphic or later hydrothermal alteration occurs distal to gold mineralisation. ASTER mineral mapping products, such as the MgOH Group Content used to map chlorite (±white mica) assemblages, showed evidence of correlation to mapped, local structural features and unknown structural or lithological contacts as indicated by inversion modelling of AEM data. 相似文献
65.
X.-M. Yang 《Australian Journal of Earth Sciences》2016,63(6):755-770
The Gorgon Platform is located on the southeastern edge of the Exmouth Plateau in the North Carnarvon Basin, North West Shelf, Australia. A structural analysis using three-dimensional (3D) seismic data has revealed four major sets of extensional faults, namely, (1) the Exmouth Plateau extensional fault system, (2) the basin bounding fault system (Exmouth Plateau–Gorgon Platform Boundary Fault), (3) an intra-rift fault system in the graben between the Exmouth Plateau and the Gorgon Platform and (4) an intra-rift fault system within the graben between the Exmouth Plateau and the Exmouth Sub-basin. Fault throw-length analyses imply that the initial fault segments, which formed the Exmouth Plateau–Gorgon Platform Boundary Fault (EG Boundary Fault), were subsequently connected vertically and laterally by both soft- and hard-linked structures. These major extensional fault systems were controlled by three different extensional events during the Early and Middle Jurassic, Late Jurassic and Early Cretaceous, and illustrate the strong role of structural inheritance in determining fault orientation and linkage. The Lower and Middle Jurassic and Upper Jurassic to Lower Cretaceous syn-kinematic sequences are separated by unconformities. 相似文献
66.
Radiometric and palynological data of the Upper Oligocene–Lower Miocene Soma Formation from the Kalk?m-Gönen Basin yield new results related to age and palynological contents. In this study, Upper Oligocene strata from the Dani?ment and Linfa areas and Lower Miocene strata from the Bengiler area were sampled palynologically and for radiometric dating. The Dani?ment assemblage, which is older than the Linfa assemblages, mainly contains coniferous and evergreen to deciduous mixed mesophytic forest elements. Relatively high quantities of the altitudinal plants Picea and Abies, indicate a cooler palaeoclimate. The Linfa associations mainly include coniferous and riparian elements. Pollen of the riparian plant Alnus and Taxodiaceae indicative for the swamp forest community was predominant, probably as a result of a high lake level. There is a hiatus during the Oligocene–Miocene transition, probably showing a non-depositional phase and sea-level fall indicating the Mi-1 glaciation event. Higher in the sequence, the Aquitanian Bengiler sediments include high amounts of coniferous forest elements as well as components indicative for the evergreen and deciduous mesophytic forest and also riparian forest and swamp forest. Due to presence of thermophilous taxa Reveesia, Mastixiaceae and Arecaceae, a warm and humid palaeoclimate is inferred according to quantitative analyses using the Coexistence Approach. 相似文献
67.
Much attention have been recently paid to the upper Ordovician Wufeng shale (O3w) and lower Silurian Longmaxi shale (S1l) in the Jiaoshiba area of Sichuan Basin, which is now the largest producing shale gas field in China. Field emission scanning electron microscopy (FE-SEM), low pressure gas (N2 and CO2) adsorption, helium pycnometry, X-ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in O3w-S1l shale formation in the Jiaoshiba area. FE-SEM images show that organic matter (OM) pores are dominant in the organic-rich samples and these pores are often irregular, bubble-like, elliptical and faveolate in shape, while in organic-poor samples, limited and isolated interparticle (interP), intraparticle (intraP) and OM pores are observed. Reversed S-shaped isotherms obtained from nitrogen adsorption are type Ⅱ, and hysteresis loops indicate that the shape of micropore in the samples is slit-or plate-like. BET surface areas and total pore volume vary from 12.2 to 27.1 m2/g and from 1.8 × 10−2 to 2.9 × 10−2 cm3/g, with an average of 19.5 m2/g and 2.3 × 10−2 cm3/g, respectively. Adsorption volume from both N2 and CO2 adsorption increases with respect to TOC contents. Porosities obtained from helium porosimetry are comparable with these from gas (CO2 and N2) adsorption in O3w-S1l shale. However, porosity determined by quantitative FE-SEM analysis is much smaller, which is mainly related to limited resolution and the small areas of investigation.Based on the Frenkel-Halsey-Hill (FHH) model of low-pressure N2 adsorption, fractal dimensions of the pores varied from 2.737 to 2.823. Relationships between pore structure parameters and TOC content, mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores. Samples with higher TOC content, higher quartz content and lower clay content tend to contain more heterogeneous micropores, resulting in higher fractal dimensions and more complicated pore structure in shales. Therefore, fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in O3w-S1l shale. 相似文献
68.
SHAN Xin YU Xinghe Peter ?CLIFT LI Yalong JIN Lin SU Dongxu DU Yonghui ZHOU Jinsong HAN Xiaoqin 《《地质学报》英文版》2018,92(1):268-285
69.
A new tree fern stem,Tempskya zhangii sp. nov. (Tempskyaceae) from the Cretaceous of Northeast China
A new Cretaceous tree fern species from the family Tempskyaceae, Tempskya zhangii sp. nov., from Keshan County, Heilongjiang Province, Northeast China, is described based on silicified fragments. The species is characterized by dichotomizing stems embedded in a matrix of adventitious roots, together forming a solid and compact false trunk. The dorsiventral stems are composed of solenosteles, and their internodes are short with 2–3 (rarely 4) leaf traces. A three-layered cortex includes a sclerenchymatous outer zone, parenchymatous middle zone, and an inner zone composed of sclerenchyma band and parenchyma cells. The pith consists of a parenchymatous outer zone and sclerenchymatous inner zone. The petiole has a single C- or U-shaped vascular strand. The adventitious root has diarch xylem surrounded by an inner sclerenchymatous and an outer parenchymatous cortex. In possessing these characters, T. zhangii is more similar to T. wyomingensis from the Cretaceous of North America than to other species of Tempskya. However, the Chinese species distinctly differs from T. wyomingensis in having a sclerenchymatous outer cortex, parenchymatous middle cortex, and sparse parenchyma in the xylem. It is the first record of Tempskya from China and the fourth from Asia. This species, together with Cyatheaceae, Osmundaceae, Cycadeoidaceae, and conifers found in the same region constituted the plant community at the time. 相似文献
70.
Land subsidence in densely urbanized areas is a global problem that is primarily caused by excessive groundwater withdrawal. The Kathmandu Basin is one such area where subsidence due to groundwater depletion has been a major problem in recent years. Moreover, on 25 April 2015, this basin experienced large crustal movements caused by the Gorkha earthquake (Mw 7.8). Consequently, the effects of earthquake-induced deformation could affect the temporal and spatial nature of anthropogenic subsidence in the basin. However, this effect has not yet been fully studied. In this paper, we applied the SBAS-DInSAR technique to estimate the spatiotemporal displacement of land subsidence in the Kathmandu Basin before and after the Gorkha earthquake, using 16 ALOS-1 Phased Array L-band Synthetic Aperture Radar (PALSAR) images during the pre-seismic period and 26 Sentinel-1 A/B SAR images during the pre- and post-seismic periods. The results showed that the mean subsidence rate in the central part of the basin was about ?8.2 cm/year before the earthquake. The spatial extents of the subsiding areas were well-correlated with the spatial distributions of the compressible clay layers in the basin. We infer from time-series InSAR analysis that subsidence in the Kathmandu basin could be associated with fluvio-lacustrine (clay) deposits and local hydrogeological conditions. However, after the mainshock, the subsidence rate significantly increased to ?15 and ?12 cm/year during early post-seismic (108 days) and post-seismic (2015–2016) period, respectively. Based on a spatial analysis of the subsidence rate map, the entire basin uplifted during the co-seismic period has started to subside and become stable during the early-post-seismic period. This is because of the elastic rebound of co-seismic deformation. However, interestingly, the localized areas show increased subsidence rates during both the early-post- and post-seismic periods. Therefore, we believe that the large co-seismic deformation experienced in this basin might induce the local subsidence to increase in rate, caused by oscillations of the water table level in the clay layer. 相似文献