High-precision geochronology of the Early Cretaceous Yingcheng Formation and its stratigraphic implications for Songliao Basin,China

The Songliao Basin in Northeast Asia is the largest and longest-lived rift basin and preserves a near-continuous continental succession of the most of the Cretaceous period, providing great material to investigate the adaption of the terrestrial systems to the Cretaceous greenhouse climate and tectonic events. However, the paucity of precise and accurate radioisotopic ages from the Early Cretaceous strata of the Songliao Basin has greatly held back the temporal and causal correlation of the continental records to the global Early Cretaceous records. Three tuff layers intercalated in the Yingcheng Formation have been intercepted by the SK-2 borehole, which offer excellent materials for radioisotopic dating and calibration of the chronostratigraphy of the Lower Cretaceous sequence of Songliao Basin. Moreover, the Yingcheng Formation recorded the largest and the last of the two major volcanic events in Songliao Basin, which also represents a turning point in the basin evolution history of Songliao from syn-rift stage to post-rift stage. Here we report high-precision U–Pb zircon geochronology by the CA-ID-TIMS technique on three tuff samples from the Yingcheng Formation of the SK-2 borehole in the Songliao Basin to construct a greatly improved, absolute age framework for the Yingcheng Formation and provide crucial age constraints for the Songliao Lower Cretaceous Strata. The new CA-ID-TIMS geochronology constrained the Yingcheng Formation at 102.571 + 0.320/?2.346 Ma to ca. 113 Ma, correlating to the Albian Stage. Combined with the previous published Songliao geochronology, the Quantou Formation is constrained to between 96.442 + 0.475/?0.086 Ma and 91.923 + 0.475/?0.086 Ma; the Denglouku Formation is constrained to between 102.571 + 0.320/?2.346 Ma and 96.442 + 0.475/?0.086 Ma; the age of the Shahezi Formation is estimated at ca. 113 Ma to ca. 118 Ma, which could extend to ca. 125 Ma in some locations in Songliao Basin. The major unconformity between the Yingcheng Formation and the Denglouku Formation, which represents the transition of the basin from syn-rift to post-rift is thus confined to between 102.571 + 0.320/?2.346 Ma and 96.442 + 0.475/?0.086 Ma. This is roughly contemporaneous with the change in the direction of the paleo-Pacific plate motion from west-southwest to north or northwest in mid-Cretaceous, suggesting their possible connections.     

Sea level changes in the upper Aptian-lower/middle(?) Turonian sequence of Cauvery Basin,India – An ichnological perspective

Cauvery Basin, a pericratonic rift basin along the Eastern Continental Margin of India, evolved during the breakup of the Eastern Gondwanaland. It exposes both syn-rift and later post-rift passive margin deposits ranging from Barremian to Miocene. The Karai Formation, upper Aptian-lower/middle (?) Turonian represents the oldest passive margin in the Cauvery Basin. It is bounded at both contacts by major sequence boundaries viz. the break-up unconformity and the Turonian tilt event. The present communication deals with the ichnology of the Karai Formation and its integration with sedimentary facies and biostratigraphy to interpret the sea level changes during deposition. A traverse between the villages Karai and Kulakkalnattam was studied in detail for this purpose. Based on the lithological position, characters and internal grain size trends, the Karai Formation is sub-divided into four informal lithologic units; the lower three units, constitute a lithostratigraphic unit known in literature as the Gypsiferous Clay Member, while the uppermost, corresponds to the Sandy Clay Member. At the base, clays of the Karai Formation unconformably onlap onto the Precambrian basement or the fluvial syn-rift deposits across the break-up unconformity. Upper Aptian to middle Cenomanian, units I and II showing the distal Cruziana ichnofacies, deepening of the basin and a retrogradational stacking pattern represent a transgressive system tract (TST). This long phase of transgression is attributed to continuous accommodation created by the post-breakup thermal subsidence. The upper part of unit II (middle Cenomanian) shows condensation, with its top representing the maximum flooding surface (MFS). Upper Cenomanian to lower/middle (?) Turonian, units III and IV characterised by a shift from the distal Cruziana to the Skolithos ichnofacies, an initial aggradational and later deltaic, progradational stacking pattern resulting from a fall in the relative sea level and filling up of accommodation space represent the highstand system tract (HST). A further fall in the relative sea level led to the exposure, incision and erosion of the Karai Formation over which the younger transgressive sequence of the Trichinopoly Group was deposited with an angular unconformity.     

南海南沙海域沉积盆地构造演化与油气成藏规律

据钻井、地震剖面、区域地质及磁异常条带分析解释,南沙海域及其邻区的主要沉积盆地的形成演化受裂谷起始不整合面和破裂不整合面分隔,可分为前裂谷期、裂谷期和后裂谷期3个构造阶段。大中型油气藏相关数据的统计表明,南沙海域及邻区大中型油气藏的成藏要素和油气田发育受构造阶段控制。(1)烃源岩发育具有分期、分区特征,礼乐盆地发育前裂谷期、裂谷1幕烃源岩;万安、曾母、西北巴拉望盆地发育裂谷2幕烃源岩,文莱-沙巴盆地发育后裂谷期烃源岩。(2)储层发育具有分期、分带特征,表现为外带老(裂谷2幕)、内带新(后裂谷期)。(3)圈闭类型包括构造、岩性地层圈闭及构造-岩性地层等因素形成的复合圈闭,大致具有内带以地层圈闭为主,外带以构造圈闭为主的特征。(4)大中型油气田分布具有外带砂岩富油气、内带碳酸盐岩富气特点。(5)南沙海域及邻区发育两个后裂谷期主含油气区,即东部巴兰三角洲砂岩背斜油气区和西部卢卡尼亚碳酸盐台地气区。其中,大中型气田的成藏要素组合为裂谷2幕烃源岩、后裂谷期碳酸盐岩储层和地层圈闭;大中型油气田则为后裂谷期烃源岩、砂岩储层和背斜圈闭。     

Structure of the Lithosphere and Mesozoic Sedimentary Basins in Western Liaoning,Northern Liaoning,and Songliao,Northeast China

The western Liaoning, northern Liaoning, and Songliao areas represent three different tectonic units with different lithospheric thermal-mechanical properties in terms of composition, thickness of the thermal lithosphere, effective elastic thickness, depth of the detachment surface, and strength of the lithosphere. Western Liaoning is characterized by a thick lithosphere with high rigidity and strength, whereas Songliao and northern Liaoning are characterized by relatively thin lithosphere with low rigidity and strength. These differences controlled the development of distinct types of basins under an extensional regime during the Early Cretaceous. The basins in western Liaoning are controlled by faulting rather than by thermal subsidence. The Songliao basin is controlled both by faulting and by thermal subsidence, and thus both syn- and post-rift sequences developed with the same thickness in the center of the basin. In contrast, in northern Liaoning, the basins are mainly controlled by faulting, and to a lesser extent by subsequent thermal subsidence. As a part of east China, where more than 93% of the proven oil reserves of China are distributed, the western Liaoning-northern Liaoning-Songliao area also has attracted considerable attention for its hydrocarbon potential. The Songliao basin is proven to be the largest non-marine petroliferous basin and one of the most important oil- and gas-producing basins in China. In addition, the Tieling-Changtu basin and the Zhezhong depression in northern Liaoning show some petroleum potential. In contrast, basins in western Liaoning represent a limited prospect for oil and gas.     

Stages in the Magura Basin: a case study of the Polish sector (Western Carpathians)

The Magura Basin domain developed in its initial stage as a Jurassic-Early Cretaceous rifted passive margin that faced the eastern parts of the oceanic Alpine Tethys. In the pre- and syn-orogenic evolution of the Magura Basin the following prominent periods can be distinguished: Middle Jurassic-Early Cretaceous syn-rift opening of basins (1) followed by Early Cretaceous post-rift thermal subsidence (2), latest Cretaceous–Paleocene syn-collisional inversion (3), Late Paleocene to Middle Eocene flexural subsidence (4) and Late Eocene - Early Miocene synorogenic closing of the basin (5). The driving forces of tectonic subsidence of the basin were syn-rift and thermal post-rift processes, as well as tectonic loads related to the emplacement of accretionary wedge. This process was initiated at the end of the Paleocene at the Pieniny Klippen Belt (PKB)/Magura Basin boundary and was completed during Late Oligocene in the northern part of the Magura Basin. During Early Miocene the Magura Basin was finally folded, thrusted and uplifted as the Magura Nappe.     

Stages and conditions of metamorphism of mafic granulites in the Early Precambrian complex of the Angara–Kan terrane (southwestern Siberian Craton)

We present results of study of mineral assemblages and PT-conditions of metamorphism of mafic garnet–two-pyroxene and two-pyroxene granulites in the Early Precambrian metamorphic complex of the Angara–Kan terrane as well as the U–Pb age and trace-element and Lu–Hf isotope compositions of zircon from these rocks and the zircon/garnet REE distribution coefficients. The temperatures of metamorphism of two-pyroxene granulites are estimated as 800–870 to ~ 900 °C. Mafic garnet–two-pyroxene granulites contain garnet coronas formed at 750–860 °C and 8–9.5 kbar. The formation of the garnet coronas proceeded probably at the retrograde stage during cooling and was controlled by the rock composition. The age (1.92–1.94 Ga) of zircon cores, which retain the REE pattern typical of magmatic zircon, can be taken as the minimum age of protolith for the mafic granulites. The metamorphic zircon generation in the mafic granulites is represented by multifaceted or soccerball crystals and rims depleted in Y, MREE, and HREE compared to the cores. The age of metamorphic zircon in the garnet–two-pyroxene (~ 1.77 Ga) and two-pyroxene granulites (~ 1.85 and 1.78 Ga) indicates two episodes of high-temperature metamorphism. The presence of one generation (1.77 Ga) of metamorphic zircon in the garnet–two-pyroxene granulites and, on the contrary, the predominance of 1.85 Ga zircon in the two-pyroxene granulites with single garnet grains suggest that the formation of the garnet coronas proceeded at the second stage of metamorphism. The agreement between the zircon/garnet HREE distribution coefficients and the experimentally determined values at 800 °C suggests the simultaneous formation of ~ 1.77 Ga metamorphic zircon and garnet. Zircon formation by dissolution/reprecipitation or recrystallization in a closed system without exchange with the rock matrix is confirmed by the close ranges of ¹⁷⁶Hf/¹⁷⁷Hf values for the core and rims. The positive ε_Hf values (up to + 6.2) for the zircon cores suggest that the protolith of mafic granulites are derived from depleted-mantle source. The first stage of metamorphism of the mafic granulites and paragneisses of the Kan complex (1.85–1.89 Ga) ended with the formation of collisional granitoids (1.84 Ga). The second stage (~ 1.77 Ga) corresponds to the intrusion of the second phase of subalkalic leucogranites of the Taraka pluton and charnockites (1.73–1.75 Ga).     

Early Cretaceous subsidence of the Naturaliste Plateau defined by a new record of volcaniclastic-rich sequence at IODP Site U1513

The Naturaliste Plateau is a submarine continental ribbon rifted from the southwest Australian margin during the Early Cretaceous breakup of East Gondwana. It occupied a key position near the juncture of Greater India and the boundary between Australia and Antarctica. However, details of the Early Cretaceous evolution of the plateau are not well known because of limited data. Drilling at Site U1513 during IODP Expedition 369 recovered the first complete Lower Cretaceous succession on the eastern Naturaliste Plateau. The succession includes syn-rift volcanic rocks, Hauterivian to early Aptian volcaniclastic-rich sedimentary rocks, and Albian claystone strata. The 235-m thick volcaniclastic-rich sequence represents the missing post-breakup record in the southwest Australian rifted margin. It spans the transition from syn- to post-rift phase during the final stages of breakup between Greater India and Australia-Antarctica. We report the lithological, petrophysical, geochemical, paleontological, and paleomagnetic characteristics of the sequence, and then synthesize the results to define the Early Cretaceous depositional environment and subsidence history of the Naturaliste Plateau. From the early Hauterivian, weathered volcanic products were eroded and re-deposited locally as a volcaniclastic-rich sequence, with a major contribution from the southern Naturaliste Plateau. The depositional environment evolved from a shelf to upper bathyal condition during the Hauterivian through early Barremian with a decreasing sedimentation rate. This period is defined as a late syn-rift subsidence phase by NW-SE trending extension. After the final breakup with Greater India, the plateau remained at upper bathyal depths with little deposition until the early Aptian. Mid–lower bathyal depths inferred from the Albian claystone strata suggest that the post-rift thermal subsidence commenced during the late Aptian. This two-phase post-rift subsidence reflects the proximity or high temperature of mantle plume, possibly the Kerguelen plume, and its westward migration relative to the southwest Australian rifted margin.     

松辽盆地南部白垩纪裂后期异常沉降分离

为了研究松辽盆地白垩纪裂后期沉降的动力机制,以松辽盆地南部长岭、十屋凹陷为例,用回剥法和应变速率反演方法对研究区钻井和地层剖面资料进行了研究。结果表明：观测得到的裂后沉降和模拟预测的理论裂后沉降结果存在较大差异,异常沉降量达160~800 m;并且异常沉降经历了两次沉降高峰期,分别出现在裂后期的泉头组及嫩江组沉积时期,平均沉降速率最大值出现在泉头组沉积时期,达16 m/Ma,同期地壳应变速率也达到裂后期最大值,约为6 Ga^-1。该异常沉降除受到裂后期基底断裂和盆地小型正断层活动的小部分影响外,可能主要受控于中生代晚期Izanagi俯冲板片在松辽盆地深部的下拽作用及其诱发的深部地幔流动,属动力沉降。     

The Ediacaran–Early Cambrian detrital zircon record of NW Iberia: possible sources and paleogeographic constraints

Ediacaran and Early Cambrian sedimentary rocks from NW Iberia have been investigated for detrital zircon U–Pb ages. A total of 1,161 concordant U–Pb ages were obtained in zircons separated from four Ediacaran samples (3 from the Cantabrian Zone and one from the Central Iberian zone) and two Lower Cambrian samples (one from the Cantabrian Zone and one from the Central Iberian Zone). Major and trace elements including REE and Sm–Nd isotopes were also analyzed on the same set of samples. The stratigraphically older Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 600 Ma based on detrital zircon content and is intruded by ca. 590–580 Ma granitoids constraining the deposition of this part of the sequence between ca. 600 and 580 Ma. The stratigraphically younger Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 553 Ma. The Ediacaran sample from the Central Iberian Zone has an identical within error maximum sedimentation age of ca. 555 Ma. The detrital zircon U–Pb age patterns are very similar in all the Ediacaran samples from both zones including the main age groups ca. 0.55–0.75 Ga, ca. 0.85–1.15 Ga and minor Paleoproterozoic (ca. 1.9–2.1 Ga) and Archean (ca. 2.4–2.6 Ga) populations. Kolmogorov–Smirnov statistical tests performed on this set of samples indicate that they all were derived from the same parent population (i.e., same source area). The same can be said on the basis of Nd isotopes, REE patterns and trace element concentrations. The two Cambrian samples, however, show contrasting signatures: The sample from the Cantabrian Zone lacks the ca. 0.85–1.15 Ga population and has a high proportion of Paleoproterozoic and Archean zircons (>60 %) and a more negative ε _Nd and higher T _DM values than the Ediacaran samples. The Early Cambrian sample from the Central Iberian Zone has the same U–Pb detrital zircon age distribution (based on KS tests) as all the Ediacaran samples but has a significantly more negative ε _Nd value. These data suggest apparently continuous sedimentation in the NW Iberian realm of northern Gondwana between ca. 600 and 550 Ma and changes in the detrital influx around the Ediacaran–Cambrian boundary. The nature and origin of these changes cannot be determined with available data, but they must involve tectonic activity on the margin as evidenced by the angular unconformity separating the Ediacaran and Lower Cambrian strata in the Cantabrian Zone. The absence of this unconformity and the apparent continuity of detrital zircon age distribution between Ediacaran and Cambrian rocks in the Central Iberian Zone suggest that the margin became segmented with significant transport and sedimentation flux changes in relatively short distances. As to the paleoposition of NW Iberia in Ediacaran–Early Cambrian times, comparison of the data presented herein with a wealth of relevant data from the literature both on the European peri-Gondwanan terranes and on the terranes of northern Africa suggests that NW Iberia may have lain closer to the present-day Egypt–Israel–Jordan area and that the potential source of the hitherto enigmatic Tonian–Stenian zircons could be traced to exposed segments of arc terranes such as that described in the Sinai Peninsula (Be’eri-Shlevin et al. in Geology 40:403–406, 2012).     

Sedimentology,stratigraphy and palynological occurrences of the late Cretaceous Erlian Formation,Erlian Basin,Inner Mongolia,People's Republic of China

The Erlian Basin is one of the non-marine Cretaceous basins of north-east China that developed during the late Mesozoic continental extension in eastern Asia. This basin experienced two major tectonic events: (i) a syn-rift stage that was dominated by a fluvial–lacustrine depositional environment and (ii) a post-rift stage that was dominated by a fluvial environment. A new sedimentological study performed on Erlian Formation drill cores has led to the determination of an architectural model and to the subsequent characterisation of the stratigraphic evolution of this sedimentary unit during the late Cretaceous. The palynological occurrences that were identified in samples provided a possible stratigraphical age for the Erlian Formation.Sediments of the Erlian Formation occur at the top of the Cretaceous stratigraphic column of the Erlian Basin and were deposited during the post-rift stage. Facies architecture and the ideal succession of facies that were identified for this formation exhibit two different members, both dominated by a fluvial depositional environment: (i) the lower member, which is dominated by channels of a braided river system and (ii) the upper member, which is dominated by overbank deposits. The lower member expresses a tectonically induced uplift as indicated by channels clustering under negative accommodation, whereas a period of stratigraphic base-level rise that is associated with an increase of accommodation is identified in the upper member. Therefore the Erlian Formation highlights an alternation of short uplifts that were dominated by braided fluvial channel deposits with periods of stratigraphic base-level rise that were dominated by overbank deposits. This sedimentological architecture has significant metallogenic implications for the origin of confined permeable sandstone layers, which represent adequate host-rocks for roll front-type uranium deposits.The palynological assemblage Exesipollenites, Ulmipollenites/Ulmoideipites, Buttinia and Momipites that were recognised in two samples of the Erlian Formation has revealed a post-late Campanian age therefore more likely indicating a late Cretaceous age of deposition for the sediments of the Erlian Formation.     

Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent: Insights from the shoshonitic high Ba–Sr Montezuma granitoids

New,integrated petrographic,mineral chemistry,whole rock geochemical,zircon and titanite UPb geochronology,and zircon Hf isotopic data from the Montezuma granitoids,as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex,provides new insights into the late-to post-collisional evolution of the northeastern Sao Francisco paleocontinent.U-Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca.2.2 Ga to 1.8 Ga and comprise distinct groups.Group I have crystallization ages between ca.2.15 Ga and 2.05 Ga and are interpreted as inherited grains.Group II zircon dates vary from 2.04 Ga to1.9 Ga and corresponds to the crystallization of the Montezuma granitoids,which were constrained at ca.2.03 Ga by the titanite U-Pb age.Inverse age zoning is common within the ca.1.8 Ga Group III zircon ages,being related to fluid isotopic re-setting during the Espinhaco rifiting event.Zircon ε_(Hf)(t) analysis show dominantly positive values for both Group I(-4 to+9) and Ⅱ(-3 to+8) zircons and T_(DM2) model ages of 2.7-2.1 Ga and 2.5-1.95 Ga,respectively.Geochemically,the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids,enriched in LILES and LREE,with high to moderate Mg#and depleted in some of the HFSE.Their lithochemical signature,added to the juvenile signature of both inherited and crystallized zircons,allowed its classification as a shoshonitic high Ba-Sr granitoid related to a late-to post-collisional lithosphere delamination followed by asthenospheric upwelling.In this scenario,the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc,being these hybrid magma interpreted as the source of the Montezuma granitoids.The Corrego Tingui Complex host rocks are akin to a syn-to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks.The results presented in this study have revealed the occurrence of juvenile rocks,probably related to an island arc environment,that are exotic in relation to the Paleo-to Neoarchean crust from the Sao Francisco paleocontinent's core.     

Upper Carboniferous to Lower Permian transgressive–regressive sequences of central Spitsbergen,Arctic Norway

Investigation of the Upper Carboniferous to Lower Permian sedimentary strata of central Spitsbergen shows that this highly cyclic rock succession is composed of four long-term transgressive–regressive cycles. These long-term cycles are themselves composed of stacked higher order cycles. Transgressive phases are characterized by increasing accommodation space, and include a basal transgressive part of marked retrogradation of facies belts and thickening-upward component cycles. Regressive phases are characterized by decreasing accommodation space, displayed by progradation of facies belts, overall shallowing and increased restriction of the depositional environment, influx of coarse terrigenous sediments and increasing evidence of exposure and/or non-deposition. The oldest transgressive–regressive sequence identified, Sequence 1, is of Serpukhovian to Bashkirian age and represents a syn-rift sequence. Also composed of syn-rift sediments is the transgressive–regressive Moscovian to mid-Gzhelian-aged Sequence 2. The late Gzhelian to late Asselian Sequence 3 is mainly a post-rift sequence. The youngest sequence, Sequence 4, is of Sakmarian to possible Artinskian age, and is also composed of post-rift sediments. The individual transgressive–regressive cycles are defined as second-order cycles, based on lithological signatures, lateral extent of bounding unconformities, and the actual time period the cycles span. Local tectonic activity is believed to control to some extent the development of short-term cycles in the syn-rift succession. However, cyclicity within the long-term cycles is mainly controlled by eustatic sea-level fluctuations, and therefore enables them to be correlated to other Circum-Arctic regions. Copyright © 1999 John Wiley & Sons, Ltd.     

The North Tyrrhenian–Northern Apennines post-collisional system: constraints for a geodynamic model

The North Tyrrhenian–Northern Apennines post-collisional system (NTAS) has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up-to-date geotectonic and evolutive framework consistent with structural data. The continental rifting began to affect the most internal (western) side of the system in the middle (?)-upper Miocene, while the most external (eastern) zones were touched by rifting only in Pleistocene times. The birth and development of extensive, asymmetric basins took place with a progressive speeding up of rifting towards the external sectors. A diachronous, regionally extended and eastward rejuvenating unconformity, recognizable within the Neogene–Quaternary basins, marks the passage from the syn-rift to the post-rift tectonic regime. While the first is everywhere dominated by extension, the second one produces vertical movements. Reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component. Three zones that experienced different post-rift vertical movements are thus recognized in the NTAS: subsidence in the North Tyrrhenian deep water region; tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western Tuscany, strong uplift in eastern Tuscany. The updated structural data demonstrate that the NTAS upper crust is crosscut by both Tyrrhenian-dipping and Apennine-dipping low-angle detachment planes, above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions: to the west and to the east, respectively. The coexistence of opposite-dipping crustal surfaces bears two fundamental implications for the NTAS geodynamics. First it stresses the importance of the anti-Apennine transfer faults, since they separate crustal blocks of opposite extension polarity. Secondly, it testifies that the extension tectonics not only re-utilized former crustal thrust planes, but also gave origin to new significant E- and NE-dipping detachment planes. Plan and crossview geometries of faults, together with considerations on the role of the metamorphic core complexes, point to an interpretation of the NTAS structure that is more consistent with the ‘anastomosing shear’ model rather than the 'simple shear' or the ‘delamination’ ones.     

松辽盆地北部裂后反转期层序地层格架及其形成机制

应用高精度层序地层学分析的原理和方法, 通过对研究区新处理的区域性地震反射剖面、测井和岩心等资料的综合分析, 建立了松辽盆地北部裂后反转期层序地层格架.通过盆地的充填记录、湖平面变化和区域演化等信息, 论证了松辽盆地裂后反转期各级界面的地质属性, 分析了其形成机制, 建立了盆地的沉积演化过程模型.研究表明, 盆地裂后反转期发育的一级界面SB02和二级界面SB03、SB11均是区域构造挤压事件的响应界面; 而湖平面的变化和物源供给导致了三级层序体系域构成样式的多样化; 嫩江组二、三段识别出的7个四级层序则是在三级湖平面旋回的高位稳定期盆地物源充足、沉降速率较低的条件下形成的.本研究为松辽盆地中浅层隐蔽油气勘探提供了重要的等时地层对比格架.      

From foredeep to orogenic wedge-top: The Cretaceous Songliao retroforeland basin,China

Songliao Basin, the largest Mesozoic intracontinental nonmarine basin in eastern China, initiated during the latest Jurassic as a backarc extensional basin; rifting failed and thermal cooling controlled subsidence through the early Late Cretaceous. Integrating 2-D and 3D reflection seismic and borehole data with regional geological studies, we interpret sedimentary sequence and structural patterns of the Coniacian-Maastrichtian fill of Songliao Basin as defining a retroforeland basin system developed after 88 Ma (marked by the T11 unconformity in the basin), including (1) significant increase in the thickness of the Nenjiang Formation eastward towards orogenic highlands of the Zhangguangcai Range and the convergent continental margin; (2) a shift of detrital provenance in the basin from north to southeast; and (3) propagation of E-W shortened structures, increasing eastward in amplitude, frequency, and degree of inversion toward the orogen. During latest Cretaceous, foreland basin fill progressively deformed, as the foredeep evolved to a wedge-top tectonic setting, marked by the basin-wide T04 unconformity within the upper Nenjiang Formation at 81.6 Ma. Much of the basin was brought into the orogenic wedge and eroded by the end of the Cretaceous. Late Jurassic/Early Cretaceous backarc rifting of uncratonized basement comprised of accreted terranes likely facilitated and localized the foreland. Synrift normal faults reactivated and extensively inverted as thrust faults are prominent in the eastern 1/3 of the basin, whereas folds developed above detachments in shaley early post-rift strata dominate the western 2/3 of the basin. Songliao foreland development likely was driven by changing plate dynamics and collision along the Pacific margin after 88 Ma.     

Sedimentary dynamics and extensional structuring related to early Cretaceous rifting of Neocomian and Barremian deposits of the interior basin of Gabon

Recent field and subsurface data about the early Neocomian N’dombo series and the Neocomian to mid-Barremian Schistes series of the interior basin of Gabon further our understanding of the initial stages of early Cretaceous N40–60°E extensional rifting. The syn-rift series comprise fluvial–lacustrine claystones–sandstones, rare conglomerates, and carbonates. The syn-rift fill begins with braided-stream feldspathic sandstones. These are overlain first by fluvial–lacustrine deposits and then by predominantly lacustrine–palustrine claystones, which are potential petroleum source rocks. The claystones are eroded in part and are capped by the pre-Aptian angular unconformity marking the end of Cretaceous rifting in the interior basin. This change in syn-rift facies and depositional environments reflects a rise in base level in response to accelerated subsidence after the initial stage of rifting. The syn-rift deposits form two fining-upward sequences several 100–1000 m thick.     

Stratigraphy and evolution of the Galve sub-basin (Spain) in the middle Tithonian–early Barremian: Implications for the setting and age of some dinosaur fossil sites

A review of the stratigraphy of the Galve sub-basin (western Maestrazgo Basin, eastern Spain) around the Jurassic–Cretaceous transition is presented here, based on new data acquired after extensive geological mapping and logging complemented with facies analysis, new biostratigraphic data and a revision of the published information available. The results obtained are relevant for a more detailed understanding of the tecto-sedimentary evolution of the studied basin during the transition between two stages of rift evolution (i.e., syn-rift sequences 1 and 2). In addition, new information on the age and setting of numerous dinosaur fossil- and track-sites found across the Galve sub-basin and in the northern part of the nearby Penyagolosa sub-basin is provided here. Two new lithostratigraphic units are defined and characterized, the Aguilar del Alfambra and the Galve formations. The previous stratigraphic framework considered only two lithostratigraphic units (the Villar del Arzobispo and El Castellar formations) bounded by a single regional unconformity, and this resulted in significant misinterpretations. The whitish limestones, red lutites and cross-bedded sandstones of the Aguilar del Alfambra Formation were deposited in transitional environments, ranging from coastal lutitic plains to restricted lagoons. Of particular interest are the laminated micritic-peloidal limestones with abundant fenestral porosity (supratidal ponds to intertidal flats), which preserve common dinosaur footprints. This unit is bounded by widespread unconformities and is of very variable thickness (0–450 m), controlled by extensional tectonics operating at the climax of syn-rift sequence 1 during the latest Tithonian–middle Berriasian. The overlying Galve Formation is of variable thickness (from 0 to 100 m) and is also bounded by regional unconformities described in detail here. It consists of red lutites with cross-bedded and tabular-burrowed sandstones representing channel and overflow deposits in an alluvial floodplain. The sauropod dinosaur Aragosaurus ischiaticus found in this unit has a controversial age assignment. The age of the Galve Formation is poorly constrained from late Berriasian to Hauterivian, but new biostratigraphic data presented here, combined with the correlation with the nearby Penyagolosa and Salzedella sub-basins, suggest a possible equivalence to the upper Berriasian–lower Valanginian sequence deposited during the initial stage of syn-rift sequence 2.     

U-Pb and Lu-Hf isotope record of detrital zircon grains from the Limpopo Belt - Evidence for crustal recycling at the Hadean to early-Archean transition

Detrital zircon grains from Beit Bridge Group quartzite from the Central Zone of the Limpopo Belt near Musina yield mostly ages of 3.35-3.15 Ga, minor 3.15-2.51 Ga components, and numerous older grains grouped at approximately 3.4, 3.5 and 3.6 Ga. Two grains yielded concordant Late Hadean U-Pb ages of 3881 ± 11 Ma and 3909 ± 26 Ma, which are the oldest zircon grains so far found in Africa. The combined U-Pb and Lu-Hf datasets and field relationships provide evidence that the sedimentary protolith of the Beit Bridge Group quartzite was deposited after the emplacement of the Sand River Gneisses (3.35-3.15 Ga), but prior to the Neoarchean magmatic-metamorphic events at 2.65-2.60 Ga. The finding of abundant magmatic zircon detritus with concordant U-Pb ages of 3.35-3.15 Ga, and ¹⁷⁶Hf/¹⁷⁷Hf of 0.28066 ± 0.00004 indicate that the Sand River Gneiss-type rocks were a predominant source. In contrast, detrital zircon grains older than approximately 3.35 Ga were derived from the hinterland of the Limpopo Belt; either from a so far unknown crustal source in southern Africa, possibly from the Zimbabwe Craton and/or a source, which was similar but not necessarily identical to the one that supplied the Hadean zircons to Jack Hills, Western Australia. The Beit Bridge Group zircon population at >3.35 Ga shows a general εHf_t increase with decreasing age from εHf_3.9Ga = −6.3 to εHf_3.3-3.1Ga = −0.2, indicating that Hadean crust older than 4.0 Ga (T_DM = 4.45-4.36 Ga) was rejuvenated during magmatic events between >3.9 and 3.1 Ga, due to a successive mixing of crustal rocks with mantle derived magmas. The existence of a depleted mantle reservoir in the Limpopo’s hinterland is reflected by the ∼3.6 Ga zircon population, which shows εHf_3.6Ga between −4.6 and +3.2. In a global context, our data suggest that a long-lived, mafic Hadean protocrust with some tonalite-trondhjemite-granodiorite constituents was destroyed and partly recycled at the Hadean/Archean transition, perhaps due to the onset of modern-style plate tectonics.     

U–Pb SHRIMP and Sm–Nd geochronology of granite–gneiss complexes and implications for the evolution of the Central Brazil Archean Terrain

The paper is a first attempt to unravel the Archean multi-stage metaplutonic assemblage of the Meso/Neoarchean terrane of the State of Goiás, Central Brazil, by means of the U–Pb SHRIMP zircon and Sm–Nd techniques. Two stages of granitic plutonism, spanning ca. 140 m.y., were precisely established for the accretion of the gneiss protoliths. The earliest stage embraces tonalitic to granodioritic and minor granitic orthogneisses with Nd juvenile signature, emplaced from ca. 2845 to ca. 2785 Ma, interpreted as the roots of an early arc. Inherited zircon xenocrysts and Nd isotopic data indicate that the juvenile magmas underwent contamination from a sialic crust as old as 3.3 Ga, from which there are, so far, no recognizable exposures. The second stage comprises granodioritic to granitic gneisses and lasted from ca. 2711 to 2707 Ma. Based on their Nd isotopic signatures and on inherited zircon crystals, their protoliths are interpreted as dominantly crustal-derived. The SHRIMP data from zircon crystals did not depict a Paleoproterozoic overprinting on the Archean gneisses, which is due to geological processes with prevailing temperatures below the isotopic stability of the U/Pb/Th system in the mineral. These processes comprise crustal extension and intrusion of a mafic dike swarm at ca. 2.3 Ga, followed by low grade events mostly related to shear zones between ca. 2.15 and 2.0 Ga. The study also revealed the extent of the Pan- African tectono-thermal overprinting on the Archean orthogneisses. Most of the zircon populations show morphological evidence of metamorphic peripheral recrystallization dated between ca. 750 and 550 Ma. One of the banded gneisses with a crystallization age of ca. 2700 Ma (2σ) has a more complex zircon population including magmatic new grains, which yielded a precise 206Pb/238U crystallization age of 590 ± 10 Ma (2σ). These new grains are interpreted to have grown in anatectic veins injected within strongly sheared gneiss.The data characterize a widespread Pan-African-aged metamorphic overprinting, culminating with localized anatexis of the Archean orthogneisses.     

The first record of Eocene tuff in a Paleogene rift basin near Nantou,Western Foothills,central Taiwan

Microfossils and a U–Pb age dating on zircon grains in the tuff beds exposed in the axial part of the Tsukeng anticline along the Pinglin River in the Western Foothills near Nantou, central Taiwan, show an occurrence of the Eocene volcanics unconformably beneath the uppermost part of the Latest Oligocene Wuchihshan Formation. This is the first discovery of the Eocene tuff exposed in the Western Foothills.The proposed Miocene “Tsukeng Formation” and “Takeng Formation” of Ho et al. (1956) named for sequences exposed in the Nantou area, Western Foothills, have to be abandoned and the standard Oligocene–Miocene lithostratigraphy used commonly in the Western Foothills of northern Taiwan is properly applicable in central Taiwan. The thick pink–brown–green colored volcanics unconformably beneath the uppermost Wuchihshan Formation is named for the first time as the Pinglin Tuff which contains Late Middle Eocene calcareous nannofossils (Zone NP16) consistent with a U–Pb age dating (38.8 ± 1 Ma) on zircon grains in the tuff. The Pinglin Tuff is overlying the Middle Eocene Chungliao Formation which contains indigenous larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannofossils of Zones NP14–15. The Middle Eocene Pinglin Tuff and Chungliao Formation represent the Paleogene syn-rift sequence unconformably overlain by the Latest Oligocene–Miocene post-rift sequence. This is the first document with conclusive paleontological data and age dating showing an occurrence of Paleogene marine rift basin exposed in the Western Foothills. This study also confirms similar Tertiary basin architecture between the Taiwan Strait–Pearl River Mouth Basin in the NE South China Sea and the Western Foothills onland central Taiwan.