Changsong Lin

Major unconformities, tectonostratigraphic frameword, and evolution of the superimposed Tarim basin, Northwest China

The Tarim basin experienced a complex tectonic evolutionary history from Sinian to Cenozoic. Eight large-scale and more than 20 subordinate unconformities defining tectonosequences of different protobasins formed in various tectonic settings have been identified within the Phanerozoic in the Tarim basin, their distribution determining the general characteristics of sequence stratigraphic framework of the basin. Tectonostratigraphic unit I (magasequence) consists mainly of the Sinian System, which formed in a rift or aulacogen setting and can been subdivided into two subordinate stratigraphic units (supersequences). Unconformity (Tg9) between Sinian and Cambrian with surface karstification is regarded as a post-rift unconformity. Tectonostratigraphic unit II comprises the Cambrian and the Ordovician and can be divided into six subordinate tectonostratigraphic units, recording the tectonogeographic evolution of the prototype basins from Cambrian to Early Ordovician passive carbonate continental margin or cratonic depression and the Late Ordovician submarine to neritic retroarc foreland and cratonic depressions. The tectonic uplift related to the formation of the unconformity Tg5-2 resulted in the remarkable change in basin tectonic setting from a passive divergent to an active convergent, with the development of the Tazhong (塔中) uplift, the Tangguzibasi (塘古孜巴斯), and the northern depression at the end of the Middle to the early Late Ordovician. The widespread angular unconformity Tg5 formed by a relatively strong compressive deformation, which caused an abrupt tectonogeographic change of the basin from abyssal to a neritic setting in response to the collision and associated tectonic deformation of the North Kunlun (昆仑) orogenesis during the Late Ordovician to the Early Silurian. Tectonostratigraphic unit III is composed of the Silurian and the Lower to Middle Devonian and characterized by the development of fluvial or deltaic and clastic littoral and neritic deposits. Large-scale terrigenous clastic depositional wedges progradated from the north to south in the southeastern slope of the basin indicate the continuously shallowing and uplifting along the northern basin margin. Tectonostratigraphic unit IV includes the Upper Devonian, Carboniferous, and Permian and can be classified into two subordinate tectonostratigraphic sequences. The angular unconformity (Tg3) at the base of the unit is the most widespread unconformity and the strong compression and uplift of the basin during this period has been suggested to be related to the collision of the Tianshan (天山) orogenesis and resulted in fundamental change in tectonic geomorphology with higher to the northeast and lower to the southwest. Tectonostratigraphic unit IV records another tectonic cycle from weak extension to compression in basin setting and is composed mainly of nearshore clastic deposits of embayment basin fills. From the Triassic, the Tarim basin evolved into a period characteristic of development of intracontinental depressions and marginal foreland basins and experienced several cycles from rapid subsidence to strong uplift and deformation, resulting in superimposition and reformation of differently orientated protobasins filled with a series of regional depositional cycles bounded by major unconformities and consisting of extremely thick alluvial and lacustrine deposits. The Kuqa foreland depression in the northwestern basin margin developed since the Triassic and deposited a clastic wedge of the Mesozoic to Cenozoic more than 100 000 m in thickness, which progradated and thin towards the southern Tabei (塔北) forebulge. The large-scale sedimentary cycles from alluvial, fluvial to lacustrine, and finally fluvial deposits are attributed to the results of foreland tectonisim from active to relatively quiet stages. The foreland tectonisim was active during the Triassic, relatively quiet during the Jurassic, and active again from the Late Jurassic to the Cretaceous. To the Eogene, the depression subsided again and the compression intermittently increased, resulting in a series of faulted and folded structural belts.

Nonlinear boundary stabilization of the wave equations with variable coefficients and time dependent delay

Abstract We study the stabilization the wave equations with variable coefficients in a bounded domain and nonlinear boundary feedback with time dependent delay. By the Riemannian geometry methods and a suitable assumption of delay, we obtain the exponential decay when the nonlinear terms are linearly bounded and a general decay when the nonlinear terms have no upper growth bound.

Detrital zircon U-Pb geochronology and its provenance implications on Silurian Tarim basin

As one of the major exploration objects of marine deposit in Tarim basin, Silurian has been paid more attention from oil/gas exploration and geologists. However, due to the widely deposit and later erosion, it is difficult to restore the original basin. The surrounding tectonic activity and provenance systems of Silurian Tarim basin have a lot of controversy. Aid of detrital zircons U-Pb dating data obtained from well drilling of Tabei (塔北) and Tazhong (塔中) areas and Sishichang (四十场) and Xiangyangcun (向阳村) outcrop profiles, integrated with other geological and geophysical data, the tectothermal evolution and provenance nature of Silurian deposit have been revealed. Zircons U-Pb dating shows Tarim basin has experienced 5–6 significant tectothermal events: 3 500–3 000 Ma Paleo-Mesoarchean, around 2 500 and 1 800 Ma Paleoproterozoic, around 1 000 and 800 Ma Neoproterozoic, and 500–400 Ma Eopaleozoic tectothermal events. These tectothermal events reflected the evolution of Tarim microplates and Tarim basin, respectively, corresponded to the forming and spilitting process of Ur supercontinent, Kenorland, Columbia and Rodinia supercontinent. Difference between the samples of Tazhong and Tabei areas indicated that North and South Tarim microplates were different in Paleo-Mesoarchean, and later evolutions were more synchronous after Paleoproterozoic. Integrated with seismic data and outcrop interpretation, the U-Pb dating results also revealed that the surrounding tectonic activities were still very active during Silurian, and indicated different regions had different source systems. At Tadong (塔东) and Manjiaer (满加尔) depressions, major source systems came from Ordovician Altyn orogenic belts. At Tabei area and northwest of Tarim basin, major source systems came from recycling orogenic zone (the activity of South Tianshan (天山) Mountain) and Precambrian stable basement (local paleo-uplifts at north of Tabei). The Ordovician uplift and orogenic zone at the south of Tarim basin and Precambrian granite basement provided lots of source systems to Tazhong area.

Stabilization of the Wave Equation with Boundary Time-Varying Delay

We study the stabilization of the wave equation with variable coefficients in a bounded domain and a time-varying delay term in the time-varying, weakly nonlinear boundary feedbacks. By the Riemannian geometry methods and a suitable assumption of nonlinearity, we obtain the uniform decay of the energy of the closed loop system.

Sedimentary facies and sequence stratigraphy of the Silurian at Tabei uplift, Tarim Basin, China

Sequence stratigraphy division and comparison of the Silurian in Tarim Basin were a hot research field in oil industry and academia. However, basic geological problems limited the exploration needed for further research. In this paper, 21 lithofacies and 5 facies associations were identified based on the grain size of sediments, sedimentary characteristics, and bioturbation conditions: (1) fluvial-dominate delta front facies association; (2) tidal flat facies association; (3) tidal channel facies association; (4) offshore-transition facies association; (5) shoreface facies association. The seismic, outcrops, and logging data were involved to divide the Silurian (including upper Ordovician Tierekeawati Fm.) at Tabei uplift into five sedimentary sequences. SQ1 (Tierekeawati Fm.) is mainly characterized by tidal flat facies association, while delta front facies association locally develops; SQ2 (the lower Kepingtage Fm.) generally consists of offshore-transition facies association; SQ3 (the upper Kepingtage Fm.) is mainly characterized by shoreface and delta front facies association. For SQ4 (Tataaiertage Fm.), the transgressive system tract (TST) is dominated by shoreface facies association, while the fluvial-dominate delta facies association widely develops in highstand system tract (HST). SQ5 (Yimugantawu Fm.) is mainly characterized by tidal flat facies association. From SQ1 to SQ2, an overall sea level transgressive process is shown, while an overall sea level regressive process is found from SQ2 to SQ5. The results are consistent with the progradation and regression trends of large regions reflected by sequence framework pattern. As to SQ3 sequence, TST and HST sandstones are the main reservoir intervals in the Silurian. Hercynian movement led to the strong uplift and extensive erosion in the Silurian at Tabei and Tazhong uplift, and is favorable to the formation of strata erosion unconformable traps.

Temporal and spatial evolution analysis: The early Paleozoic Paleo-Uplifts in the Tarim basin

Twenty unconformities, primarily superimposed types, were identified based on interpretation of a 46 000 km seismic profile combined with data from over 40 drilling wells. These respectively correspond to the main tectonic evolution stages and the boundaries between those stages. Reconstruction of the original depths of eroded strata was conducted for the Middle Caledonian, Early Hercynian, Late Hercynian, Indosinian, Early Yanshanian and Late Yanshanian unconformities using the virtual extrapolation of seismic reflection. Eroded strata thicknesses were also calculated for individual periods and intervals. Based on the reconstructed data, in combination with data from research on sedimentary facies, a paleogeomorphological profile was constructed for different tectonic evolution stages of the basin during the Early Paleozoic. The profile indicates the presence of obvious regularity in the temporal and spatial evolution of these unconformities. Based on the characteristics of paleo-uplift evolution and post-layering reconstruction, the paleo-uplifts were divided into inherited (e.g., Tazhong (塔中)), residual (e.g., North Tarim) and active (e.g., Southwest Tarim and Bachu (巴楚)) types. The huge North Tarim uplift represents a typical form of residual paleo-uplift. The Paleozoic strata in the upper layers of the uplift is in poor condition for reservoir accumulation and preservation; however, the Upper Mesozoic-Cenozoic structural layer can form a secondary reservoir that is relatively rich in oil and gas. Furthermore, the flank slope area of the uplift is always a key source for oil and gas collection and the most advantageous position for the formation of the original reservoir. The Tazhong paleo-uplift has been stable since its formation in the Late Ordovician, where petroleum accumulation has been distributed not only in the uplift, but also in the deep and slope belts of the uplift. Important breakthroughs in petroleum exploration of the slope break in the North Tazhong area dating back to the Paleozoic have further confirmed the enrichment of oil and gas in this type of uplift. The Southwest Tarim paleo-uplift is a buried type, which has given it favorable properties for hydrocarbon migration over a long time. An open question is whether the large amount of oil and gas accumulated here was transported to the current Bachu uplift.

Stratigraphic architecture and computer modelling of carbonate platform margin, late ordovician Lianglitage formation, Central Tarim Basin

According to the different geometries and reflected characteristics in the seismic sections, the carbonate platform margin of the northern slope can be summarized as three basic depositional architectures in the Late Ordovician Lianglitage (良里塔格) Formation of the Tazhong (塔中) uplift. The type one mainly located in the west of the carbonate platform margin, and it showed obvious imbricate progradation from the interior to the margin of the platform. The type two was in the middle of the carbonate platform margin, which showed retrogradational stacking pattern in the same transgressive systems tract period, and the slope strata of the platform margin showed progradational sequence in the highstand systems tract period. The type three located in the east of the carbonate platform margin, and it showed the parallel aggradational architecture. The crossing well section along the northern slope of the Tazhong carbonate platform showed that the depositional thickness became thinner from the east to the west. The thickest belt located in the east of the platform margin, and became thinner rapidly towards the basin and the platform interior. These indicated that the paleogeomorphology of the Tazhong uplift was probably high in the west and low in the east during the period of the Late Ordovician Lianglitage Formation. According to the interpretation of seismic profiles and the computer modelling result, the depositional architectures of sequence O3l-2 showed aggradation, retrogradation and progradation from the east to the west of the carbonate platform margin during the transgression period. This meant that the accommodation became smaller gradually from the east to the west along the northern carbonate platform margin of the Tazhong uplift. The difference of the accommodation was probably caused by the difference of tectonic subsidence. Also, computer-aided modelling can be used to deeply understand the importance of various control parameters on the carbonate platform depositional architectures and processes.