scholarly journals Palaeo-earthquake events during the late Early Palaeozoic in the central Tarim Basin (NW China): evidence from deep drilling cores

Geologos ◽  
2014 ◽  
Vol 20 (2) ◽  
pp. 105-123 ◽  
Author(s):  
Bizhu He ◽  
Xiufu Qiao ◽  
Cunli Jiao ◽  
Zhiqin Xu ◽  
Zhihui Cai ◽  
...  
Keyword(s):  
Tarim Basin ◽  
Spatial Association ◽  
Late Ordovician ◽  
Tectonic Activity ◽  
Earthquake Activity ◽  
Seismogenic Fault ◽  
Upper Ordovician ◽  
Deep Drilling ◽  
Stress Regime ◽  
Nw China

Abstract Various millimetre-, centimetre- and metre-scale soft-sediment deformation structures (SSDS) have been identified in the Upper Ordovician and Lower-Middle Silurian from deep drilling cores in the Tarim Basin (NW China). These structures include liquefied-sand veins, liquefaction-induced breccias, boudinage-like structures, load and diapir- or flame-like structures, dish and mixed-layer structures, hydroplastic convolutions and seismic unconformities. The deformed layers are intercalated by undeformed layers of varying thicknesses that are petrologically and sedimentologically similar to the deformed layers. The SSDS developed in a shelf environment during the early Late Ordovician and formed initially under shear tensile stress conditions, as indicated by boudinage-like structures; during the latest Ordovician, SSDS formed under a com-pressional regime. The SSDS in the Lower-Middle Silurian consist mainly of mixed layers and sand veins; they formed in shoreline and tidal-flat settings with liquefaction features indicating an origin under a compressional stress regime. By Silurian times, the centre of tectonic activity had shifted to the south-eastern part of the basin. The SSDS occur at different depths in wells that are close to the syn-sedimentary Tazhong 1 Fault (TZ1F) and associated reversed-thrust secondary faults. Based on their characteristics, the inferred formation mechanism and the spatial association with faults, the SSDS are interpreted as seismites. The Tazhong 1 fault was a seismogenic fault during the later Ordovician, whereas the reversed-direction secondary faults became active in the Early-Middle Silurian. Multiple palaeo-earthquake records reflect pulses and cyclicity, which supports secondary tectonic activity within the main tectonic movement. The range of SSDS structures reflects different developments of tectonic activity with time for the various tectonic units of the centralbasin. The effects of the strong palaeo-earthquake activity coincide with uplift, fault activity and syn-tectonic sedimentation in the study area during the Late Ordovician to Middle Silurian.

scholarly journals Multifractal Analysis of Pore Structure and Evaluation of Deep-Buried Cambrian Dolomite Reservoir with Image Processing: A Case from Tarim Basin, NW China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Xiaojun Zhang ◽  
Haodong Han ◽  
Jun Peng ◽  
Yingchun Gou
Keyword(s):  
Pore Structure ◽  
Thin Section ◽  
Tarim Basin ◽  
Clustering Analysis ◽  
Multifractal Analysis ◽  
Pore Space ◽  
Tectonic Activity ◽  
Petrophysical Properties ◽  
Nw China ◽  
Crystalline Dolomite

Reservoir pore space assessment is of great significance for petroleum exploration and production. However, it is difficult to describe the pore characteristics of deep-buried dolomite reservoirs with the traditional linear method because these rocks have undergone strong modification by tectonic activity and diagenesis and show significant pore space heterogeneity. In this study, 38 dolostone samples from 4 Cambrian formations of Tarim Basin in NW China were collected and 135 thin section images were analyzed. Multifractal theory was used for evaluation of pore space heterogeneity in deep-buried dolostone based on thin section image analysis. The physical parameters, pore structure parameters, and multifractal characteristic parameters were obtained from the digital images. Then, the relationships between lithology and these parameters were discussed. In addition, the pore structure was classified into four categories using K-means clustering analysis based on multifractal parameters. The results show that the multifractal phenomenon generally exists in the pore space of deep-buried dolomite and that multifractal analysis can be used to characterize the heterogeneity of pore space in deep-buried dolomite. For these samples, multifractal parameters, such as αmin, αmax, ΔαL, ΔαR, Δf, and AI, correlate strongly with porosity but only slightly with permeability. However, the parameter Δα, which is usually used to reveal heterogeneity, does not show an obvious link with petrophysical properties. Of dolomites with different fabrics, fine crystalline dolomite and medium crystalline dolomite show the best petrophysical properties and show significant differences in multifractal parameters compared to other dolomites. More accurate porosity estimations were obtained with the multifractal generalized fractal dimension, which provides a new method for porosity prediction. The various categories derived from the K-means clustering analysis of multifractal parameters show distinct differences in petrophysical properties. This proves that reservoir evaluation and pore structure classification can be accurately performed with the K-means clustering analysis method based on multifractal parameters of pore space in deep-buried dolomite reservoirs.

Acritarch assemblages from the Middle–Upper Ordovician in the Aksu area, northwestern margin of the Tarim Basin, Xinjiang, China

2020 ◽  
Vol 295 (2) ◽  
pp. 169-183 ◽  
Author(s):  
Kui Yan ◽  
Thomas Servais ◽  
Longlong Shan ◽  
Jun Li
Keyword(s):  
Tarim Basin ◽  
Late Ordovician ◽  
Northwestern Part ◽  
Upper Ordovician ◽  
The World ◽  
Northwestern Margin ◽  
Stratotype Section ◽  
Compositional Changes

Upper Darriwilian to middle Katian (Ordovician) outcrops are well exposed in the Kalpin (Aksu) area, in the northwestern margin of the Tarim Basin, Xinjiang, China. The Dawanxigou and Sishichang sections in the Kalpin area, near the Dawangou Auxiliary Stratotype Section and Point (ASSP), were palynologically investigated. Both sections provide well-preserved acritarch assemblages dominated by acanthomorph, sphaeromorph and netromorph morphotypes, attributed to 36 species and 20 genera. A comparison of the acritarch assemblages with coeval microfloras from other parts of the world confirms a wide cosmopolitism distribution, indicative of a breakdown of acritarch provincialism during the Late Ordovician. Several acritarchs from the Tarim Basin are restricted to the Late Ordovician, and as they are distributed worldwide, they present a potential for global bio-stratigraphical correlations. The acritarch assemblages from the different sections of the northwestern part of the Tarim Basin show slightly variable compositions, probably caused by different palaeo-ecological settings. The diversity and compositional changes of the acritarch assemblages, combined with the sedimentological evidence, suggest a transgressive sequence from the Sargan Formation to the Qilang Formation.

Upper Ordovician marine red limestones, Tarim Basin, NW China: A product of an oxygenated deep ocean and changing climate?

2019 ◽  
Vol 183 ◽  
pp. 103032 ◽  
Author(s):  
Mu Liu ◽  
Daizhao Chen ◽  
Xiqiang Zhou ◽  
Dongjie Tang ◽  
Theodore R. Them ◽  
...  
Keyword(s):  
Tarim Basin ◽  
Deep Ocean ◽  
Upper Ordovician ◽  
Nw China ◽  
Changing Climate

scholarly journals Multiphase Calcite Cementation and Fluids Evolution of a Deeply Buried Carbonate Reservoir in the Upper Ordovician Lianglitag Formation, Tahe Oilfield, Tarim Basin, NW China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Jiaqing Liu ◽  
Zhong Li ◽  
Lijuan Cheng ◽  
Jiawei Li
Keyword(s):  
Fluid Inclusion ◽  
Tarim Basin ◽  
Meteoric Water ◽  
Oil And Gas ◽  
Isotope Analysis ◽  
Carbonate Reservoir ◽  
Upper Ordovician ◽  
Nw China ◽  
Tahe Oilfield ◽  
Homogenization Temperatures

Oil and gas have been found in the Upper Ordovician Lianglitag Formation carbonates in the Tahe Oilfield, Tarim Basin, NW China. This study documents the origin of diagenetic fluids by using a combination of petrology, SIMS, fluid inclusion, and radiogenic isotope analysis. Six stages of calcite cements were revealed. C1-C2 formed in marine to early burial environments. C3 has relatively low δ18OVPDB values (−8.45‰ to −6.50‰) and likely has a meteoric origin. Meteoric water probably fluxed into aquifers during the Early Paleozoic and Late Paleozoic uplift. C4 has δ18OVPDB values typically 3‰ higher than those of C3, and probably formed during shallow burial. C5 displays relatively negative δ18OVPDB values (−8.26‰ to −5.12‰), and the moderate-to-high fluid-inclusion temperatures imply that it precipitated in burial environments. C6 shows homogenization temperatures (up to 200°C) higher than the maximum burial and much lower salinities (<10.61 wt% NaCl), which may suggest that the fluid was deeply recycled meteoric water. The average 87Sr/86Sr ratios of fracture- and vug-filling calcite cements are much higher, indicative of incorporation of radiogenic Sr. Caves and fractures constitute the dominant reservoir spaces. A corresponding diagenesis-related reservoir evolution model was established that favors exploration and prediction.

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