Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination

The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (?9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc.     

Basement structural architecture and hydrocarbon conduit potential of polygonal faults in the Cooper‐Eromanga Basin,Australia

A thorough and complete understanding of the structural geology and evolution of the Cooper‐Eromanga Basin has been hampered by low‐resolution seismic data that becomes particularly difficult to interpret below the thick Permian coal measures. As a result, researchers are tentative to interpret the basement fault architecture within the basin, which is largely undefined. To provide a better understanding of the basement fault geometry, all available two‐dimensional seismic lines together with 12 three‐dimensional seismic surveys were structurally interpreted with assistance from seismic attribute analysis. The Upper Cretaceous Cadna‐owie Formation and top Permian reflectors were analysed using a common seismic attribute technique (incoherency) that was used to infer the presence of faults that may have otherwise been overlooked. Detailed basement fault maps for each seismic survey were constructed and used in conjunction with two‐dimensional seismic data interpretation to produce a regional basement fault map. Large north‐northeast–south‐southwest‐striking sinistral strike–slip faults were identified within the Patchawarra Trough appearing to splay from the main northeast–southwest‐striking ridge. These sinistral north‐northeast–south‐southwest‐striking faults, together with field‐scale southeast–northwest‐striking dextral strike–slip faults, are optimally oriented to have potentially developed as a conjugated fault set under a south‐southeast–north‐northwest‐oriented strike–slip stress regime. Geomechanical modelling for a regionally extensive system of Cretaceous polygonal faults was performed to calculate the Leakage Factor and Dilation Tendency of individual faults. Faults that extend into Lower Cretaceous oil‐rich reservoirs with strikes of between 060°N and 140°N and a high to near‐vertical dip angle were identified to most likely be acting as conduits for the tertiary migration of hydrocarbons from known Lower Cretaceous hydrocarbon reservoirs into shallow Cretaceous sediments. This research provides valuable information on the regional basement fault architecture and a more detailed exploration target for the Cooper‐Eromanga Basin, which were previously not available in literature.     

祁连山西段玉门断裂晚第四纪活动特征及相关问题的讨论

新的证据显示,位于祁连山西段酒西盆地南部的玉门断裂的最新活动时代为晚更新世末,并兼有一定的走滑分量.这一结果表明,酒西盆地块体周边断裂的活动具有同时性的特点,酒西盆地块体可能发生过顺时针旋转.     

青藏高原东南缘构造旋转的古地磁学证据

本文在总结青藏高原东南缘近年来地质研究进展的基础上,从古地磁学的角度讨论其新生代以来的构造运动特征.结果表明:相对稳定的欧亚大陆,新生代以来山泰地块发生了约20°～80°顺时针旋转,局部地区旋转量甚至高达135°,且中部地区的旋转量明显高于南北地区;印支地块经历了～30°的顺时针旋转;川滇地块的顺时针旋转量沿102°E...     

Paleomagnetic evidence for a pre-early Eocene (∼ 50 Ma) bending of the Patagonian orocline (Tierra del Fuego,Argentina): Paleogeographic and tectonic implications

The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ～ 700 km long orogenic re-entrant with an interlimb angle of ～ 90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ～ 50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous–earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32 ± 2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E–W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N–S compression and northward displacing fold–thrust sheets during Eocene–early Miocene times (50–20 Ma), an unexpected kinematics considering coeval South America–Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E–W left-lateral Magallanes–Fagnano strike–slip fault system (MFFS), running a few kilometres south of our sampling sites. We thus speculate that strike–slip fault offset in the Fuegian Andes may range in the lower bound values (～ 20 km) among those proposed so far. In any case our data exclude any influence of strike–slip tectonics on the genesis of the great orogenic bend called Patagonian orocline.     

Late Quaternary Activity of the Chuxiong-Nanhua Fault and the 1680 Chuxiong M_S6(3/4) Earthquake

In this paper,according to the results of the satellite imagery interpretation and field investigation,we study the active features and the latest active times of the ChuxiongNanhua fault,the Quaternary basins formation mechanism,and the relationship between the fault and the 1680 Chuxiong M_S6 3/4earthquake. Several Quaternary profiles at Lvhe,Nanhua reveal that the fault has offset the late Pleistocene deposits of the T2 and T3 terraces of Longchuan river, indicating that the fault was obviously active in late Quaternary. The Chuxiong-Nanhua fault has been dominated by dextral strike slip motion in the late Quaternary,with an average rate of 1. 6-2. 0 mm/a. Several pull apart Quaternary basins of Chuxiong,Nanhua,and Ziwu etc. have developed along the fault.The 1680 Chuxiong M_S6 3/4earthquake and several moderate earthquakes have occurred near the fault. The Chuxiong-Nanhua fault are the seismogenic structure of those earthquakes,the latest fault movement was in the late-Pleistocene,and even the Holocene.In large area,the Chuxiong-Nanhua fault and the eastern Qujiang fault and the Shiping fault composed a set of NW-trending oblique orientation active faults,and the motion characteristics are all mainly dextral strike slip. The motion characteristics,like the red river fault of the Sichuan-Yunnan Rhombic Block southwestern boundary,are concerned with the escaping movement of the Sichuan-Yunnan Rhombic Block.     

向错-位错组合模型模拟渭河盆地地壳水平变形特征

基于向错-位错组合模型模拟渭河盆地内主要断层的滑动与转动运动变形,通过数值计算获得断层滑动及转动变形引起的地表水平位移,并与盆地内实测GPS水平位移进行了对比。结果表明:采用向错-位错组合模型能够完整地描述断层实际的滑动与转动运动变形状态,组合模型模拟断层滑动与转动引起的地表水平位移与实测GPS水平位移,无论在量级或是运动趋势上均具有较好的一致性特征。     

Paleomagnetism of the Upper Paleozoic of the Novaya Zemlya Archipelago

The rock magnetic and paleomagnetic results from the Upper Paleozoic sedimentary sequences composing the isles of the Novaya Zemlya Archipelago are presented. The recorded temperature dependences of the magnetic susceptibility, the magnetic hysteresis parameters, and the results of the first-order reversal curve (FORC) measurements suggest the presence of single-domain or pseudo-single-domain magnetite and hematite grains in the rocks. The Upper Paleozoic deposits overall are promising for unraveling the tectonic evolution of the Barents–Kara region. Together with the rock magnetic data, the positive fold and reversal tests testify to the primary origin of the indentified magnetization components. However, the interpretation of the paleomagnetic data should take into account the probable inclination shallowing. New substantiation is offered for the paleomagnetic poles for Early Devonian and Late Permian. For the first time, paleomagnetic constraints are obtained for the Late Carboniferous boundary. It is shown that the Early Cimmerian deformation stage within the Paikhoi–Novaya Zemlya region is associated with the sinistral strike slip displacement along the Baidaratskii suture during which the internal structure of the Southern Novaya Zemlya segment could undergo shear in addition to the nappe-thrust transformations. The Northern Novaya Zemlya segment, which is shifted northwest with respect to the Southern segment, was deformed in the thrusting mode with an overall clockwise rotation of this segment relative to the East European Craton.     

喜马拉雅东构造结周边地区主要断裂现今运动特征与数值模拟研究

本研究通过对东构造结及其周边地区主要断裂进行野外考察,通过GPS观测数据和地质、地球物理资料的综合分析,建立三维有限元模型;运用数值模拟方法对东构造结周边地区主要断裂现今运动特征进行模拟研究,取得一些初步的认识:(1)东构造结北侧和东侧地块总体上围绕构造结发生顺时针旋转,右旋走滑的东南边界断裂不是嘉黎断裂,可能是阿帕龙...     

Late Quaternary Activity of the Chuxiong-Nanhua Fault and the 1680 Chuxiong MS6 ¾ Earthquake

In this paper, according to the results of the satellite imagery interpretation and field investigation, we study the active features and the latest active times of the Chuxiong-Nanhua fault, the Quaternary basins formation mechanism, and the relationship between the fault and the 1680 Chuxiong M_S6 ¾ earthquake. Several Quaternary profiles at Lvhe, Nanhua reveal that the fault has offset the late Pleistocene deposits of the T2 and T3 terraces of Longchuan river, indicating that the fault was obviously active in late Quaternary. The Chuxiong-Nanhua fault has been dominated by dextral strike slip motion in the late Quaternary, with an average rate of 1.6-2.0mm/a. Several pull apart Quaternary basins of Chuxiong, Nanhua, and Ziwu etc. have developed along the fault. The 1680 Chuxiong M_S6 ¾ earthquake and several moderate earthquakes have occurred near the fault. The Chuxiong-Nanhua fault are the seismogenic structure of those earthquakes, the latest fault movement was in the late-Pleistocene, and even the Holocene. In large area, the Chuxiong-Nanhua fault and the eastern Qujiang fault and the Shiping fault composed a set of NW-trending oblique orientation active faults, and the motion characteristics are all mainly dextral strike slip. The motion characteristics, like the red river fault of the Sichuan-Yunnan Rhombic Block southwestern boundary, are concerned with the escaping movement of the Sichuan-Yunnan Rhombic Block.     

Review and new interpretation for the propagation characteristics associated with the 1999 Chi‐Chi earthquake faulting event

The Chi‐Chi earthquake (M_W = 7.6) took place in central western Taiwan in 1999. The earthquake caused reactivation of the Chelungpu Fault and resulted in 100‐km‐long surface ruptures. The fault strikes mostly north–south to NNE–SSW; however, the northern tip of the southern segment of the surface ruptures rotates clockwise to define an east–west trend, then jumps to a shorter NNW‐trending rupture. The largest vertical displacement is recorded in the Shihkang area of the Shihkang–Shangchi Fault Zone, where vertical slips are up to 8–10 m. The Shihkang–Shangchi Fault Zone displays a complex fault pattern as a linkage damage zone between two fault segments with the greatest concentration of faults and fractures. Our new interpretation, based on recent published geometric, kinematic, and geophysical studies on the Chi‐Chi earthquake fault, suggests that the Shihkang–Shangchi Fault Zone is not a simple termination zone, but may be an ‘overstep zone’ or a ‘transfer zone’. Slip analysis along the surface ruptures indicates that they are composed of three fault segments and the amount of slip partly depends on the intersection angle between slip direction and fault strike. Our numerical modeling for the area indicates that Coulomb stress changes are mainly concentrated on tips and bends of the surface ruptures. Slip patterns indicate that the fault propagates toward the northeast. Therefore, this study suggests high potential for future earthquake activity along the unruptured Shangchi segment. Hence, future geohazard studies should focus on the Shangchi segment to evaluate potential earthquakes, determine recurrence intervals, and reduce future earthquake hazards.     

Quaternary tectonic rotation in central Japan: Paleomagnetism of the Eboshidake volcanic rocks

Abstract   Neotectonic crustal deformation in central Japan near a triple-junction of plates is investigated on the basis of paleomagnetic data. The progressive thermal demagnetization test isolated characteristic remanent magnetization from 18 sites of the early Quaternary Eboshidake volcanic rocks erupted around the termination of active strike-slip faults. The site-mean directions show considerably large scatter in declinations, and easterly deflection in average (D_m = −161.7°). On the basis of inclination statistics, measured inclinations (I_m = −48.9°, δI = 6.6°) are concordant with an expected value from latitude of the study area. Because the sampling was planned to cover a wide stratigraphic range and eliminate the effect of geomagnetic secular variation, an easterly deflection is attributed to clockwise rotation around vertical axis. Together with previous paleomagnetic data, the present study indicates that clockwise-rotated areas in central Japan are aligned on a northeast–southwest recent shear zone delineated through geodetic survey. Deflection and scatter of paleomagnetic declinations of the Eboshidake volcanic rocks are much greater than those extrapolated from a recent strain rate, and might be explained by complicated motion anticipated at fault terminations and/or enhanced crustal rotation under elevated temperatures around a Quaternary volcanic province.     

Large N-S convergence at the northern edge of the Tibetan plateau? New Early Cretaceous paleomagnetic data from Hexi Corridor, NW China

Nine Early Cretaceous paleomagnetic sites have been collected in the Yumen area of the Hexi Corridor (NW China). Magnetic directions isolated at lower temperatures fail the fold test, and lie close to the geocentric axial dipole field direction before tilt correction. High temperature components are carried by magnetite and/or hematite, all with normal polarity, and pass the fold test. The average paleomagnetic pole from the nine sites is at λ=75.5°N, φ=169.9°E (A₉₅=7.7°). These results are consistent with those from other areas of the North China block (NCB), but significantly different from those from the Qaidam Basin on the southern side of the Qilian Mountains. They suggest that: (1) the Yumen region behaved as a rigid part of the NCB since at least the Early Cretaceous; (2) 740±500 km of north-south directed convergence has taken place between the NCB and Qaidam, within the Qilian Mountains and (3) extrusion of Qaidam was accompanied by a 23±5° relative rotation with respect to North China. This is larger than implied by the maximum left lateral slip on the Altyn Tagh fault system. The same data imply some 1000±800 km of Cenozoic motion between the Tarim and NCB blocks, which were so far believed to have formed a rigid entity since at least the Jurassic. One interpretation could be that all Tarim and Qaidam Cretaceous paleomagnetic samples from red beds, but not those from Yumen and the NCB, suffered significant inclination shallowing, as observed in Cenozoic red beds from Central Asia. So far, we do not find support for this possibility. Possible tectonic interpretations include: (1) the existence of a large, as yet uncharted, tectonic discontinuity between Tarim and the NCB in the vicinity of the desert corridor near 95-100°E longitude; (2) the occurrence of significant deformation within southwestern Tarim, to the north of Yingjisha where paleomagnetic sites were obtained, or (3) persistent clockwise rotation of Tarim with respect to the NCB, for at least 20 Ma, at the rate found for current block kinematics.     

断层附近地面地震动空间分布

运用震源位错模型, 分析矩形垂直断层及倾斜断层走向滑动和倾向滑动的近场地震动场，以地表地震动的傅立叶振幅谱比为参量考察断层附近地震动空间分布的特点. 结果表明, 断层附近的地震动强度主要受近旁子断层的控制，高强度的地震动分布在紧靠断层两侧有限的带状区域内，长周期分量受断层破裂传播方向性的影响. 走向滑动的方向性影响主要表现在垂直于断层走向的分量，倾向滑动则表现在平行于断层走向的分量，且深震在地面上引起的地震动强度分布比浅震要平缓，影响范围宽. 倾斜断层产生的地震动有明显的上盘效应，空间分布不对称，与观测结果相符. 最后给出了断层附近近场地震动强度分布拟合函数的表达式，并与美国的1997统一建筑规范规定的近场因子作了比较.      

Fault tectonic analysis of Kii peninsula,Southwest Japan: Preliminary approach to Neogene paleostress sequence near the Nankai subduction zone

The southern part of the Outer Zone of Southwest Japan including the Kii peninsula belongs to the tectonic ‘shadow zone’, where fewer conspicuous active faults and less Quaternary sediments develop than in the Nankai subduction zone and Inner Zone of Southwest Japan. In order to study the paleostress sequence of the Kii peninsula, we analyzed fault‐slip data and tension gashes at pilot sites of Early–Middle Miocene forearc sediments and Late Cretaceous accretionary complex. According to the results, six faulting events are reconstructed in sequence: (i) east–west extension (normal faulting); (ii) east–west compression and north–south extension (strike‐slip faulting); (iii) NNW–SSE compression and ENE–WSW extension (strike‐slip faulting); (iv) northeast–southwest compression and northwest–southeast extension (strike‐slip faulting); (v) WNW–ESE compression (strike‐slip or reverse faulting); and (vi) NNE–SSW extension. The north–south to NNW–SSE trending dyke swarm of Middle Miocene age in the Kii peninsula is thought to be related to Event 3, implying that Event 3 was active at least during the Middle Miocene. Because Event 6 is recognized solely at a site, the overall latest faulting event seems to be Event 5. Assuming that the compression results from the motion of the crust or plate, the compression direction of Event 5 is in good accordance with the present‐day WNW crustal velocity vectors of the Kii peninsula. The stress trajectory map of Southeast Korea and Southwest Japan reveals that the current compression directions of the Kii peninsula correspond to the combinatory stress fields of the Himalayan and Philippine Sea tectonic domains.     

合肥市地壳浅部三维速度结构及城市沉积环境初探

合肥市位于合肥盆地东南缘,东侧紧邻郯庐断裂带,多条大型隐伏断裂穿过市区.为进一步认识合肥城市下方隐伏断裂的空间展布、性质,以及城市复杂的沉积环境,本文利用布设在合肥市区的58套三分量短周期地震仪组成的台阵,获得了37天的三分量连续波形数据,通过基于射线追踪的面波走时直接成像方法反演得到了合肥市地壳浅部0.6~3.6 km的三维剪切波速度结构,速度结构图像展现了地壳浅部的横向不均匀性和纵向成层性,揭示出NNE、NWW和近EW三组不同走向的隐伏断裂在城市地下浅部的构造特征.取得以下认识：（1）合肥市南、北方向在浅地表（2 km以内）存在显著速度差异,速度分界线位置与已知的近EW向的蜀山断裂一致,断裂南侧呈现低速凹陷,北侧则为高速隆起.低速中心深度达2~3 km,速度异常与该断裂在合肥盆地东部演化过程中的构造反转沉积了不同地层有关;（2）合肥市区存在明显的高速异常带,其走向、位置与穿过该区域的郯庐断裂带西支主干断裂相符,其中五河—合肥断裂在市区北部以东呈现低速凹陷特征,低速区范围与肥东凹陷晚白垩纪以来的沉积构造边界一致,认为肥东凹陷的最大沉积厚度可达2 km以上;（3）合肥市中心跨郯庐断裂带西支主干断裂之间呈现明显的凹、隆相间的复杂构造,推测其是在多组断裂的共同拉伸作用下形成的小型沉积盆地,沉积中心位于郯庐断裂带内部,最大厚度可达3~4 km.由于其展布方向在不同深度与该区域断裂的走向具有明显的相关性,推测不同深度的沉积形态与郯庐断裂带在不同时期的构造演化过程有关.     

2016年4月16日熊本地震滑动分布反演与分析

综合利用强震数据、GPS数据和InSAR数据基于双断层模型反演熊本地震滑动分布,通过选择合理的介质模型和平滑因子,分别对数据进行单独反演和联合反演。从结果分析可以看出:三种数据联合反演的结果最优,最终滑动模型为:断层1走向为236°,倾角65°,滑动角-150.6°,最大滑动量为6m;断层2走向为206°,倾角72°,滑动角-155°,最大滑动量为4m。基于K-net和Kik-net获取永久位移快速反演得到的滑动分布结果与基于GPS数据,Sentinel-1A InSAR数据反演甚至联合反演得到滑动分布结果比较一致,表明大震后利用高密度强震动台网后快速获取滑动分布用于震后应急响应和灾害评估是切实可行的,同时认为此次地震发震断层为右旋走滑的断层系统。     

Active tectonics around the junction of Southwest Japan and Ryukyu arcs: Control by subducting plate geometry and pre‐Quaternary geologic structure

The origin of active faults in the Inner zone of the western part of Southwest Japan was explained by a decrease of the minimum principal stress and reactivation of ancient geologic structures. Although the E–W maximum principal stress in Southwest Japan due to the collision of the Southwest and Northeast Japan arcs along the Itoigawa–Shizuoka Tectonic Line is assumed to decrease westward, the density of active strike‐slip faults increases in the western margin of the Southwest Japan Arc (western Chugoku and northern Kyushu) where the subducting Philippine Sea Plate dips steeply. The E–W maximum compressional stress is predominant throughout Southwest Japan, while the N–S minimum principal stress that is presumably caused by coupling between Southwest Japan arc and Philippine Sea Plate decreases due to the weak plate coupling as the plate inclination increases under the western margin of Southwest Japan. The increase of the fault density in the western margin of the arc is attributed to a decrease of the minimum principal stress and consequent increase of shear stress. Low slip rates of the active faults in this region support the view that the westward increase of fault density is not a response to increasing maximum stress. These faults of onshore and offshore lie in three distinct domains defined on the basis of fault strike. They are defined domains I, II, and III which are composed of active faults striking ENE–WSW, NW–SE, and NE–SW, respectively. Faulting in domains I, II, and III is related to Miocene rift basins, Eocene normal faults, and Mesozoic strike‐slip faults, respectively. Although these active faults are strike‐slip faults due to E–W maximum stress, it is unclear whether their fault planes are the same as those of pre‐Quaternary dip‐slip faults.     

Paleoposition of Southwest Japan at 16 Ma: Implication from paleomagnetism of the Miocene Ichishi Group

New paleomagnetic data from shallow-marine sediments of the Ichishi Group suggest a clockwise tectonic rotation of Southwest Japan in the Middle Miocene. Samples have been collected from mud or tuff layers at 17 sites. Stability of remanent magnetization has been examined by using alternating field and thermal demagnetization. The polarity sequence, composed of four normal and seven reversed polarity sites, is correlated to Polarity Epoch 16 (15.2–17.6 Ma), based on micropaleontological assignment of the upper Ichishi Group to Blow's Zone N8. The mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast. This result suggests that Southwest Japan was subjected to a clockwise rotation through 45° since 16 Ma. The clockwise rotation can be explained by the drift of Southwest Japan associated with the spreading of the Japan Sea during the Middle Miocene.     

Paleomagnetism of the Yuanmou Basin near the southeastern margin of the Tibetan Plateau and its constraints on late Neogene sedimentation and tectonic rotation

New paleomagnetic investigation was carried out on the late Neogene fluviolacustrine sequence of the Yuanmou Basin, located near the southeastern margin of the Tibetan Plateau. Magnetostratigraphic results indicate nine reverse magnetozones (R1 to R9) and eight normal magnetozones (N1 to N8) in the sedimentary profile, which can be correlated to the geomagnetic polarity timescale from C3n.3r to C1r.1r. The age of the sedimentary sequence of the Yuanmou Basin can thus be paleomagnetically constrained to an interval from early Pliocene to Pleistocene, with sedimentation rates varying from 12.5 to 55 cm/kyr. In addition to its highly resolved magnetostratigraphic sequence, the Yuanmou Basin provides a record of Plio-Pleistocene tectono- and climato-sedimentary processes. The mean declinations of the seventeen polarity units (excluding samples with transitional directions) can be grouped into three distinct directional intervals, Group I (2.58–1.37 Ma), Group II (4.29–2.58 Ma) and Group III (4.91–4.29 Ma). These directions indicate that the Yuanmou Basin has probably experienced vertical-axis clockwise rotation of about 12° from 1.4 Ma to 4.9 Ma, which may be related to slip activity of the Red River fault to the southwest and the Xianshuihe–Xiaojiang fault to the east.