Journal of Earth Science

Conodont Biostratigraphy across the Permian-Triassic Boundary at the Xinmin Section, Guizhou, South China

Ning Zhang, Haishui Jiang, Wenli Zhong, Haohao Huang, Wenchen Xia

2014, 25(5): 779-786. doi: 10.1007/s12583-014-0472-0

[Abstract](880) [FullText HTML] (107) [PDF 1005KB](238)

Abstract:
A continuous sedimentation at the Xinmin Section, Anshun, Guihzou Province, with the Upper Permian Talung Formation dominated by bedded siliceous rocks, and the Lower Triassic Luolou Formation consisting mudstones and marls as well as siliceous mudstones at its basal part indicates that it represents a deeper-water basinal facies across the Permian-Triassic boundary. Based on a systematic conodont biostratigraphic work, nine conodont species belong to two genera have been identified in this study. It enable us to establish five conodont zones at this section, in ascending order, they are: Clarkina changxingensis Zone (beds 1-3-4-2), Clarkina yini Zone (beds 4-3-5-1-1), Clarkina meishanensis Zone (beds 5-1-2-5-2), Hindeodus changxingensis Zone (beds 5-3-1-5-3-2) and Hindeodus parvus Zone (beds 5-3-3-5-3-4), respectively. According to the first occurrence of Hindeodus parvus in bed 5-3-3, the Permian-Triassic boundary is placed at the base of bed 5-3-3. This conodont zonation of the Xinmin Section provides precise biostratigraphic framework for further investigations on the geological events across the Permian-Triassic boundary at this section. In addition, the new conodont data also reveals that several siliceous beds occurred at the basal Triassic. It provides an exception of Early Triassic Chert Gap.

Aptian-Albian Transition in Central Tunisia: Tectonosedimentary and Paleogeographic Records

Imen Marco, Ferid Dhahri, Taoufik Haji, Noureddine Boukadi

2014, 25(5): 787-798. doi: 10.1007/s12583-014-0478-7

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Abstract:
The Aptian-Albian series are characterized, in Tunisia, by several variations in subsidence rates and records discrete unconformity between Albian and Aptian in central and southern Tunisia. In central Tunisia Upper Aptian regressions were sustained until the beginning of Albian with a low sea level stand. In this paper, wells data gathered from central Tunisia exposes well expressed Aptian-Albian hiatus associated to several partial sedimentary gaps, erosion surface and unconformities and correlated with the "Aptian Crisis" highlighted at the Tethyan scale. This latter is coeval with an extensional regime in concurrence with the African rifting responsible for halokinesis movements and magmatism and leaded to the establishment of paleoreliefs as much as tilted blocks and half grabens in central Tunisia. Deposition shows regional hiatus and lateral transition from platform facies to south to, open marine facies to the north. The structural configuration of this domain within normal faulting, horsts and grabens leaded to the establishment of several distinct basins with different subsidence rates. Discordances occur specially around and upward uplifted blocks and emerged land and are especially associated with Aptian reef, karsts and shallow marine facies. They are unconformably overlaid by the transgressive open marine facies of Albian-Cenomanian series acknowledged as source rock in Central Tunisia. In addition, the reefal Aptian facies is considered a potential reservoir rocks in central Tunisia and it is frequently associated to mineralization and Hydrocarbure reservoirs.

Geochemical characteristics and new eruption ages of ruby-related basalts from southeast Kenya

Tawatchai CHUALAOWANICH, Chakkaphan SUTTHIRAT, Visut PISUTTHA-ARNOND, Christoph HAUZENBERGER, Chinghua LO, Tongyi LEE, Punya CHARUSIRI

2014, 25(5): 799-821. doi: 10.1007/s12583-014-0482-y

[Abstract](777) [FullText HTML] (120) [PDF 2158KB](160)

Abstract:
Two ruby-related basaltic fields were recently discovered in the southeast region of Kenya, exposed in the Nguu and Ngulai Hills vicinities. These fields host abundant deep-seated xenoliths, including corundum-bearing granulites. The basalts are alkaline affinity having compositions from foidrite to basanite. The Ngulai basalts have a wider range of SiO₂ (38.2 wt.%–44.8 wt.%) covering those of the Nguu basalts (38.7 wt.%–42.3 wt.%). This overlapping behavior also holds for other major oxides and trace elements, e.g., Al₂O₃, Na₂O, K₂O, Cr, Ni, Rb and Ga. The overall OIB-like incompatible patterns with strong K depletion and slight spike of Ti enrichment signatures imply low degrees of partial melting of the upper mantle region source induced under a mantle plume-related process. The K-depletion signature indicates a residual K-bearing phase still retained in the source domain. Chondrite-normalized REE patterns exhibiting strong LREE enrichment without Eu anomalies suggest that plagioclase fractionation is insignificant. New ⁴⁰Ar/³⁹Ar ages indicate eruption events occurred during the Pleistocene times, which are around 2 Ma for the Ngulai basalts and 0.9 to 1.6 Ma for the Nguu basalts. Clinopyroxene-basalt thermobarometric calculations yield the equilibrium P-T ranges of ~8-29 kbar and 1 200–1 450 ℃.

A Review of Mg Isotope Analytical Methods by MC-ICP-MS

Yajun An, Fang Huang

2014, 25(5): 822-840. doi: 10.1007/s12583-014-0477-8

[Abstract](721) [FullText HTML] (216) [PDF 884KB](372)

Abstract:
Application of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has led to big breakthrough of analytical methods for metal stable isotopes, resulting in rapid progresses in non-traditional stable isotope geochemistry. As a new geological tracer, Mg isotopes have been widely applied in studies of almost all important disciplines of geochemistry. High precision Mg isotope data measured by MC-ICP-MS are now available with precision about 0.05‰ amu⁻¹ (2SD) or better. Because mass bias caused by chemical procedure and instrument can easily cause significant analytical error, it is still a challenge to obtain accurate Mg isotope data for natural samples. In this paper, we systematically review the development of analytical technique of Mg isotopes, with a detailed description of a series of important techniques used in the measurement process, including calibration of instrumental mass-bias, chemical purification process, matrix effect, and pitfalls for high precision isotope analyses. We compare standard data from different labs and establish a guideline for Mg isotope analysis procedure. Additionally, we briefly discuss the behaviors of Mg isotopes during geological processes including equilibrium and kinetic Mg isotope fractionations, such as magma differentiation, chemical and thermal diffusion, and continental weathering. Finally, we propose some future prospects for Mg isotope geochemistry in both high and low temperature geological processes.

Geochronology and Geochemistry of Middle–Late Ordovician Granites and Gabbros in the Erguna Region, NE China: Implications for the Tectonic Evolution of the Erguna Massif

Shuo Zhao, Wenliang Xu, Wei Wang, Jie Tang, Yihan Zhang

2014, 25(5): 841-853. doi: 10.1007/s12583-014-0476-9

[Abstract](909) [FullText HTML] (256) [PDF 810KB](226)

Abstract:
Zircon U-Pb ages,Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif,NE China were presented in this paper. The petrogenesis of these rocks and the Early Paleozoic tectonic evolution of the massif were discussed. Zircons from the granites and gabbros are of magmatic origin based on their cathodoluminescence (CL) images. The ²⁰⁶Pb/²³⁸U ages obtained from 20 spots on zircons from the granites range from 446±9 to 464±10 Ma,yielding a weighted mean age of 455±10 Ma; and 16 spots on zircons from the gabbros range from 465±10 to 466±7 Ma,yielding a weighted mean age of 465±2 Ma. Chemically,the Late Ordovician granites in the Erguna Massif are weakly peraluminous and similar to A-type granites. The granites and gabbros are all enriched in light rare earth elements and large ion lithophile elements (e.g.,Rb,K),and depleted in heavy rare earth elements and high field strength elements (e.g.,Nb,Ta,and Ti); they all exhibit marked negative Eu anomalies. Their zircon ɛ_Hf(t) values range mainly from +1.86 to +6.21 (for the granites) and +1.39 to +3.89 (for the gabbros),except for one spot with a value of −0.27 (for a gabbro). The T_DM1 ages for the gabbros and T_DM2 ages for the granites vary from 928 to 1 091 Ma and from 1 287 to 1 675 Ma,respectively. It is concluded that the primary magma of the granites could have been derived by partial melting of Mesoproterozoic newly accreted crustal material,whereas the primary magma of the gabbros originated by partial melting of a depleted mantle wedge that had been metasomatized by fluids derived from a subducted slab. These Middle-Late Ordovician granites and gabbros constitute a typical bimodal igneous rock association,implying an extensional environment that was probably related to the post-collisional development of the Erguna and Xing'an massifs in the early Early Paleozoic.

Geochronology and Geochemistry of Middle–Late Ordovician Granites and Gabbros in the Erguna Region, NE China: Implications for the Tectonic Evolution of the Erguna Massif

Shuo Zhao, Wenliang Xu*, Wei Wang, Jie Tang, Yihan Zhang

2014, 25(5): 841-853. doi: 10.1007/s12583-014-0476-9

[Abstract](680) [PDF 541KB](172)

Abstract:
Zircon U-Pb ages, Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif, NE China were presented in this paper. The petrogenesis of these rocks and the Early Paleozoic tectonic evolution of the massif were discussed. Zircons from the granites and gabbros are of magmatic origin based on their cathodoluminescence (CL) images. The 206Pb/238U ages obtained from 20 spots on zircons from the granites range from 446±9 to 464±10 Ma, yielding a weighted mean age of 455±10 Ma; and 16 spots on zircons from the gabbros range from 465±10 to 466±7 Ma, yielding a weighted mean age of 465±2 Ma. Chemically, the Late Ordovician granites in the Erguna Massif are weakly peraluminous and similar to A-type granites. The granites and gabbros are all enriched in light rare earth elements and large ion lithophile elements (e.g., Rb, K), and depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, and Ti); they all exhibit marked negative Eu anomalies. Their zircon εHf(t) values range mainly from +1.86 to +6.21 (for the granites) and +1.39 to +3.89 (for the gabbros), except for one spot with a value of -0.27 (for a gabbro). The TDM1 ages for the gabbros and TDM2 ages for the granites vary from 928 to 1 091 Ma and from 1 287 to 1 675 Ma, respectively. It is concluded that the primary magma of the granites could have been derived by partial melting of Mesoproterozoic newly accreted crustal material, whereas the primary magma of the gabbros originated by partial melting of a depleted mantle wedge that had been metasomatized by fluids derived from a subducted slab. These Middle–Late Ordovician granites and gabbros constitute a typical bimodal igneous rock association, implying an extensional environment that was probably related to the post-collisional development of the Erguna and Xing’an massifs in the early Early Paleozoic.

Deformation Styles of the Uthai Thani-Nakhon Sawan Ridge within the Chainat Duplex, Thailand

Pattarapong Prasongtham, Pitsanupong Kanjanapayont

2014, 25(5): 854-860. doi: 10.1007/s12583-014-0483-x

[Abstract](616) [FullText HTML] (149) [PDF 1990KB](291)

Abstract:
Uthai Thani-Nakhon Sawan structural ridge is the 35 km mountain length lying in N-S direction within the Chainat duplex at the Central Thailand. The ridge, which is clearly seen from satellite image in the flat areas of the Central Plain, is composed of Triassic mylonitic granite and Silurian-Devonian metamorphosed sedimentary rocks. Satellite image interpretation, geological mapping, field data and microstructure analysis have been integrated for the understanding of structural style of Uthai Thani-Nakhon Sawan ridge. The rocks within the ridge had been deformed under sinistral ductile shear which was shown by foliations, stretching lineations, S-C fabrics, sigmoid clasts, mineral fish and S-folded both in outcrops and under microscope. The major N-S, minor NNW-SSE striking ridges and foliation planes indicate the paleostress of σ₁ in the NW-SE direction. The major sinistral motion of this region probably ended at ~30 Ma. All structural elements and deformation style of Uthai Thani-Nakhon Sawan ridge relate to the Chainat duplex geometry and Mae Ping fault zone activity during Tertiary.

The Stress State of the Beichuan-Jiangyou Segment of the Longmenshan Fault before and after the Wenchuan M_S 8.0 Earthquake

Chengjun Feng, Qunce Chen, Chengxuan Tan, Xianghui Qin, Peng Zhang, Wen Meng

2014, 25(5): 861-870. doi: 10.1007/s12583-014-0473-z

[Abstract](920) [FullText HTML] (148) [PDF 881KB](165)

Abstract:
After the Wenchuan M_S 8.0 Earthquake, which occurred on May 12, 2008, in Sichuan Province, China, we conducted a series of hydraulic fracturing stress measurements in three 200 m deep boreholes (ZK01, ZK02, and ZK03) drilled in Beichuan and Jiangyou regions near the northeastern segment of Longmenshan fault belt in 2009. These measurements revealed the near-surface stress field in the fault region one year after the Wenchuan M_S 8.0 Earthquake. However, the lack of the stress measurements before the earthquake in the same region makes it difficult to understand variations of the in situ stress field (near-surface) by comparative analysis. In order to determine the unknown horizontal principal stresses before the earthquake in Beichuan and Jiangyou regions, the following research method was tentatively applied. Firstly, we calculate the static co-seismic stress field by linear elastic finite element numerical simulation with ANSYS, based on the co-seismic static displacement generated by the Wenchuan M_S 8.0 Earthquake along the central Longmenshan fault plane in Beichuan and Jiangyou. Secondly, combining hydraulic fracturing measurements (after the earthquake) with the co-seismic stress (simulation), the magnitudes and orientations of horizontal principal stresses before the earthquake were calculated. Finally, the variation of the in situ stress (near-surface) in Beichuan and Jinagyou, both before and after the Wenchuan M_S 8.0 Earthquake, were obtained by comparative analysis. To do this the magnitude of S_Hmax was decreased on average by 13.01 and 6.54 MPa after the earthquake in ZK02 and ZK03, respectively and the magnitude of S_Hmin was decreased by 2.54 and 5.29 MPa in ZK02 and ZK03, respectively. Following the earthquake, the average direction of S_Hmax rotated anticlockwise by 42.5°.

Sequence Stratigraphy and Sedimentary Facies of Lower Oligocene Yacheng Formation in Deepwater Area of Qiongdongnan Basin, Northern South China Sea: Implications for Coal-Bearing Source Rocks

Jinfeng Ren, Hua Wang, Ming Sun, Huajun Gan, Guangzeng Song, Zhipeng Sun

2014, 25(5): 871-883. doi: 10.1007/s12583-014-0479-6

[Abstract](1817) [FullText HTML] (156) [PDF 2089KB](252)

Abstract:
For unveiling coal-bearing source rocks in terrestrial-marine transitional sequences, the sequence stratigraphic framework and sedimentary facies of Lower Oligocene Yacheng Formation of Qiongdongnan Basin were investigated using seismic profiles, complemented by well bores and cores. Three third-order sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center, namely SQYC3, SQYC2 and SQYC1 from bottom to top. Coal measure in Yacheng Formation of Qiongdongnan Basin were deposited within a range of facies associations from delta plain/tidal zone to neritic sea, and three types of favourable sedimentary facies associations for coal measure were established within the sequence stratigraphic framework, including braided delta plain and alluvial fan, lagoon and tidal flat, and fan delta and coastal plain facies associations. Results shown that, in the third-order sequences, coal accumulation in landward areas (such as delta plain) of the study area predominantly correlates with the early transgressive systems tract (TST) to middle highstand systems tract (HST), while in seaward areas (such as tidal flat-lagoon) it correlates with the early TST and middle HST. The most potential coal-bearing source rocks formed where the accommodation creation rate (Ra) and the peat-accumulation rate (Rp) could reach a state of balance, which varied among different sedimentary settings. Furthermore, intense tectonic subsidence and frequent alternative marine-continental changes of Yacheng Formation during the middle rift stage were the main reasons why the coal beds shown the characteristics of multi-beds, thin single-bed, and rapidly lateral changes. The proposed sedimentary facies associations may aid in predicting distribution of coal-bearing source rocks. This study also demonstrates that controlling factors analysis using sequence stratigraphy and sedimentology may serve as an effective approach for coal-bearing characteristics in the lower exploration deepwater area of South China Sea.

Diagenetic Aspects of the Lower Paleocene Sachun Formation Carbonates, Zagros Basin, Southwestern Iran

Solmaz Arzaghi, Massih Afghah

2014, 25(5): 884-894. doi: 10.1007/s12583-014-0480-0

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Abstract:
The Sachun Formation in the Zagros Mountains Ranges was sampled on the basis of changes in lithology and 150 vertically oriented thin-sections were prepared and subjected to detailed petrographic study. Evaporite, carbonate and shale/marl facies are identified here. These facies which have been laid in 4 facies belts of supratidal, intertidal, lagoon and barrier, deposited on a ramp platform. Petrographic studies showed that the Sachun Formation has had a complex diagenetic history. The following diagenetic events occurred in the carbonate microfacies: micritization, dissolution, silicification, dolomitization, hematitization, compaction, fracturing and stylolitization. The diagenetic features observed petrographically in the carbonate microfacies represent changes which took place under three diagenetic environments (eogenic, mesogenic, and telogenic) with three different marine, burial, and meteoric diagenetic conditions. The diagenetic sequence of events that affected the Sachun Formation includes micritization and micrite envelope features which have been reported from an eogenic/marine environment.

The Use of Ground Penetrating Radar for Mapping Rock Stratigraphy and Tectonics: Implications for Geotechnical Engineering

Awni T Batayneh, Taisser Zumlot, Habes Ghrefat, Mahmud M El-Waheidi, Yousef Nazzal

2014, 25(5): 895-900. doi: 10.1007/s12583-014-0475-x

[Abstract](609) [FullText HTML] (104) [PDF 397KB](214)

Abstract:
This paper presents results from ground penetrating radar surveys using the SIR-10B GPR instrument (manufactured by Geophysical Survey System Inc., USA), with 400 MHz monostatic antenna (model 5 103). Survey was made over 3 excavation levels along the highway section at the Ras en Naqab escarpment area, Southwest Jordan. A total of 217 m along 4 profiles were covered in the winter of 2012. The objectives of the study are (i) to evaluate the resolution of the GPR technique in the field for detecting and locating anomalies caused by subsurface structures like cavities, fractures and faults, and (ii) to describe stratigraphic nomenclature of the subsurface rocks of the area. 2D interpretation of the obtained data and the geological information demonstrate a strong correlation between the GPR anomalies and the subsurface geology. Based upon the lateral and vertical velocity changes with depth, the thickness and orientation of the subsurface layers are outlined. Analysis of the exposed section shows good agreement between the estimated thicknesses of lithostratigraphic units and the quantitative assessment of the radar waves velocity inferred from GPR data.

New Conceptual Fold-Fracture Model Including Prefolding Fractures, Based on Fuyang-Lin'an Anticline, Zhejiang Province

Youpu Dong, Ancheng Xiao, Lei Wu, Xuying Li

2014, 25(5): 901-911. doi: 10.1007/s12583-014-0481-z

[Abstract](895) [FullText HTML] (95) [PDF 1849KB](234)

Abstract:
Field observations of the crossing relationships of fractures have been used to explain the sequence of fractures. Based on field observations from Fuyang-Lin'an anticline, located near Hangzhou, Zhejiang Province, this paper proposes that the formation of synfolding fractures was influenced dominantly by one fracture set, which developed prior to folding and the orientation was nearly parallel to the bedding. The length of the prefolding fractures is longer than the synfolding fractures. These prefolding fractures cut thicker strata into small pieces and form a dense network of fractures in thicker strata. Most synfolding fractures, which are oblique to the bedding, are truncated by prefolding fractures in thicker strata. The synfolding fractures, which result from local stress, are inferred to form during folding. Here, the mechanism of truncation was analyzed using finite-element models. The approach was based on the idea that natural fractures can be interpreted or inferred from stress distribution. The presence or absence of prefolding fractures is shown to strongly control the distribution of stress, and this control has an important implication for interpreting the fracture truncation mechanism from geomechanical models.

Distribution Characteristics of Geohazards Induced by the Lushan Earthquake and Their Comparisons with the Wenchuan Earthquake

Zhiqiang Yin, Wuji Zhao, Xiaoguang Qin

2014, 25(5): 912-923. doi: 10.1007/s12583-014-0471-1

[Abstract](801) [FullText HTML] (108) [PDF 1760KB](225)

Abstract:
The Lushan Earthquake induced a large number of geohazards. They are widely distributed and caused serious damages. The basic characteristics, formation mechanisms and typical cases of geohazards induced by Lushan Earthquake are described, and compares to the relationships of Lushan and Wenchuan earthquakes between geohazards and earthquake magnitude, geomorphology, slope angle, elevation and seismic intensity in the most affected areas in the article. (1) The numbers and volumes of landslides and rockslides differ significantly between the two earthquakes due to their differing magnitudes. The Lushan Earthquake is associated with fewer and smaller-magnitude geohazards, within the immediate area, which mainly consist of small-and medium-sized shallow landslides and rockslides, and occur on steep slopes and mountain valleys. The largest landslide induced by Lushan Earthquake is the Gangoutou Landslide debris flow with a residual volume of about 2.48×10⁶ m³. The most dangerous debris flow is at Lengmugou gulley in Baoxing County, which has similar geomorphological features and disaster modes as a previous disaster in Zhouqu County, Gansu Province. (2) Geohazards induced by the Lushan Earthquake show four mechanisms: cracking-rockslides-collision-scraping and then debris flows, cracking-rockslides, vibration-rainfall-rockslides-landslide and then debris flow, vibration-throwing or scrolling. (3) There are significant similarities and differences between the geohazards induced by these two earthquakes. The types of geohazards are the same but the volume, quantity and other factors differ: geohazards are concentrated on slope angles of 10°–40° in the Lushan Earthquake area, especially within 10°–20°, and at absolute elevation of 500–2 000 m above sea level (a.s.l.). Geohazards within the Wenchuan Earthquake area are concentrated on steeper slope angles of 30°–40° at higher absolute elevations of 1 500–2 000 m.s.l..

Zircon U-Pb SHRIMP Ages from the Late Paleozoic Turpan-Hami Basin, NW China

Xiang Mao, Jianghai Li, Huatian Zhang

2014, 25(5): 924-931. doi: 10.1007/s12583-014-0484-9

[Abstract](1169) [FullText HTML] (107) [PDF 682KB](237)

Abstract:
Permian volcanic rocks are widely distributed in the Turpan-Hami Basin, which is part of the Central Asian orogenic belt. Here we present SHRIMP zircon data for the rhyolite in Well Baocan 1, one of the deepest wells in the basin. The 283.9±2.7 Ma reported in our study provides the best precise age determination for the Yierxitu Formation, the oldest Permian layer of Hami Depression, one of the three substructural units of the Turpan-Hami Basin, and a potential hydrocarbon reservoir in this basin. Our data refines earlier imprecise ³⁹Ar-⁴⁰Ar ages and shows that the volcanic rocks both inside the Turpan-Hami Basin and along its margin are almost coeval. We delineate a collisional orogenesis, and the new age of 283.9±2.7 Ma may limit the latest time of the collision orogenesis.

Tectonic Setting of the Barm Firuz Lake, Zagros Mountains, Iran: Inferred from Structural and Karstic Evidence

Babak Samani

2014, 25(5): 932-938. doi: 10.1007/s12583-014-0474-y

[Abstract](637) [FullText HTML] (120) [PDF 1189KB](238)

Abstract:
This paper presents the role of tectonic and karstic processes in the formation and evolution of Barm Firuz Lake within the Zagros Mountains of Iran. This lake with elevation of 3 340 m from sea level is located in the crest of the Barm Firuz anticline. Results show that the structural evolution of the Barme Firuz Lake is related to both tectonic and karst processes. Therefore the term of tectonokarstic has been used for structural evolution of the lake. Structural studies especially on the stylolite structures revealed the occurrence of an important component of simple shear deformation in the study area. Based on structural and karstic evidence around the lake, the fault-dissolution sink model with oblique pure shear component is suggested as kinematic model of the Barm Firuz Lake evolution in the Zagros Mountains of Iran.

2014 Vol. 25, No. 5

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