Provenance and geochronology of Cenozoic sandstones of northern Borneo

The Crocker Fan of Sabah was deposited during subduction of the Proto-South China Sea between the Eocene and Early Miocene. Collision of South China microcontinental blocks with Borneo in the Early Miocene terminated deep water sedimentation and resulted in the major regional Top Crocker Unconformity (TCU). Sedimentation of fluvio-deltaic and shallow marine character resumed in the late Early Miocene. The Crocker Fan sandstones were derived from nearby sources in Borneo and nearby SE Asia, rather than distant Asian and Himalayan sources. The Crocker Fan sandstones have a mature composition, but their textures and heavy mineralogy indicate they are first-cycle sandstones, mostly derived from nearby granitic source rocks, with some input of metamorphic, sedimentary and ophiolitic material. The discrepancy between compositional maturity and textural immaturity is attributed to the effects of tropical weathering. U–Pb ages of detrital zircons are predominantly Mesozoic. In the Eocene sandstones Cretaceous zircons dominate and suggest derivation from granites of the Schwaner Mountains of southern Borneo. In Oligocene sandstones Permian–Triassic and Palaeoproterozoic zircons become more important, and are interpreted to be derived from Permian–Triassic granites and Proterozoic basement of the Malay Tin Belt. Miocene fluvio-deltaic and shallow marine sandstones above the TCU were mostly recycled from the deformed Crocker Fan in the rising central mountain range of Borneo. The provenance of the Tajau Sandstone Member of the Lower Miocene Kudat Formation in north Sabah is strikingly different from other Miocene and older sandstones. Sediment was derived mainly from granitic and high-grade metamorphic source rocks. No such rocks existed in Borneo during the Early Miocene, but potential sources are present on Palawan, to the north of Borneo. They represent continental crust from South China and subduction-related metamorphic rocks which formed an elevated region in the Early Miocene which briefly supplied sediment to north Sabah.     

Provenance of Cretaceous clastics in the Subhercynian Basin: constraints to exhumation of the Harz Mountains and timing of inversion tectonics in Central Europe

The Harz Mountains and the adjacent Subhercynian Cretaceous Basin figure as the most prominent surface representative for Late Cretaceous inversion structures in Central Europe. Facies, depositional architecture and provenance of the basin fill reflect mechanisms and timing of the exhumation of the Harz. From Hauterivian to Early Santonian there is no evidence for detrital input from the nearby Harz area. Sediments are mature quartzarenites derived from Paleozoic basement rocks and/or recycled Permian to Mesozoic sedimentary rocks. This situation changed drastically in Middle to Late Santonian when freshly exhumed and eroded Mesozoic sedimentary cover rocks of the Harz were delivered into the basin. Feldspar and lithoclasts reflect erosion of Triassic and, in places, Jurassic to Turonian strata. Apatite and garnet in heavy mineral spectra are derived from largely unweathered Lower Triassic Buntsandstein as indicated by apatite and garnet chemistry. In Early Campanian, Paleozoic lithoclasts indicate erosion cutting down into the basement of the Harz. Simultaneous strong decrease of feldspar, garnet and apatite suggest an almost complete removal of the 2–3 km thick Mesozoic cover of the Harz within only 2–4 Myr. This translates into an exhumation rate of approximately 1 mm/a consistent with apatite fission track data from granitoid rocks of the Harz Mountains.     

Provenance of Palaeozoic sandstones from the Carnic Alps (Austria): petrographic and geochemical indicators

An integrated approach of petrographic analysis, whole rock geochemistry and microprobe analysis has been applied to obtain information on the geodynamic development and the provenance for Ordovician to Permian siliciclastic successions exposed within the Carnic Alps (Austria). Sandstone detrital mode and geochemical results refine previous geodynamic interpretations. Late Ordovician samples indicate a stable craton and recycled orogenic and, possible, extensional setting. The Early Carboniferous is interpreted to represent a compressional environment, followed by a Late Carboniferous molasse-type foreland basin, and a Permian extensional geodynamic setting. Contrasting geochemical patterns of post-Variscan and Permian sequences suggest a rift setting. Electron microprobe data of detrital white mica also indicate changes in the provenance. Compositional data reflect a shift from low- to medium-grade metamorphic (Ordovician) to high-grade metamorphic (Carboniferous) to low- to medium-grade metamorphic and plutonic source rocks (Permian). Additionally, our data show that various chemical discrimination diagrams do not include all possible ranges of sandstones, and that high contents of detrital mica and ultra-stable heavy minerals may cause misclassification. Consequently, we propose the use of multi-method approach for provenance studies, including the control of geochemical data by modal analysis and heavy mineral investigations.     

Provenance of the Lower Paleozoic Balcarce Formation (Tandilia System, Buenos Aires Province, Argentina): Implications for paleogeographic reconstructions of SW Gondwana

Lower Paleozoic moderately sorted quartz–arenites from the Balcarce Formation deposited in eastern Argentina (Tandilia System) comprise mainly detrital material derived from old upper crustal material. The sources were magmatic, sedimentary, and subordinated felsic metamorphic terranes. High concentrations of tourmaline and Ti-rich heavy minerals, including zircon and nearly euhedral chromite, are common. Trace element concentrations (Nb, Cr) on rutile indicate pelitic and metabasaltic sources, respectively. Major element analyses on chromites indicate a basic volcanic protolith of mid-oceanic ridge origin, which was exposed close to the depositional basin. The delivery of chromite may be associated with convergent tectonics causing the consumption and obduction of oceanic crust during pre-Upper Ordovician times. The oblique/orthogonal collision of the Precordillera Terrane with the western border of the Rio de la Plata Craton, west of the Balcarce Basin or source further to the east from a Lower Palaeozoic extensional basin are possibilities.Geochemical and petrographic data exclude the underlying Precambrian and Cambrian sedimentary rocks as dominant sources, and favour the basement of the Río de La Plata Craton, including Cambrian rift-related granites of South Africa and the Sierras Australes (eastern Argentina), as main suppliers of detritus. Trace element geochemistry of recycled pyroclastic material, associated with the quartz–arenites, also suggests volcanic arc sources. The provenance of the pyroclastic material may either be the Puna–Famatina arc, located in north and central Argentina, or a hypothetical active margin further to the south. These ash layers are equivalent in age to volcanic zircons found in the Devonian Bokkeveld Group in western South Africa.The deposition of a glacial diamictite of Hirnantian age (Sierra del Volcán Diamictite) is interpreted as a member of the Balcarce Formation. Based on the stratigraphic re-location of the glacial diamictite and trace fossils, the Balcarce Formation is considered here to be Ordovician to Silurian in age. The Balcarce Formation can be correlated with similar rocks in South Africa, the Peninsula Formation, and the upper Table Mountain Group (Windhoek and Nardouw subgroups), including the Hirnantian glacial deposit of the Pakhuis Formation.     

Provenance of middle to late Palaeozoic sediments in the northeastern Colombian Andes: implications for Pangea reconstruction

ABSTRACT

Global-scale Palaeozoic plate tectonic reconstructions have suggested that Laurentia was obliquely approaching against the northwestern margin of Gondwana until the final agglutination of Pangea. In this contribution integrated petrographic analysis, heavy mineral analysis, and tourmaline geochemistry were done, and U–Pb detrital zircon geochronology was obtained, in late Palaeozoic sedimentary and meta-sedimentary units from the Floresta and Santander Massifs in the Eastern Colombian Andes in order to constrain their provenance and related it with the magmatic, sedimentary, and deformational record of the Gondwana–Laurentia convergence until the late Carboniferous to Permian formation of Pangea. Late Devonian to early Carboniferous sandstones from the Floresta Massif changed from sublithoarenites to lithoarenites, tracking the progressive uplift and unroofing of sedimentary and metamorphic rocks, with associated volcanic activity. The U–Pb detrital zircon geochronology from the sedimentary and metasedimentary of Floresta and Santander documents Mesoproterozoic and Palaeoproterozoic sources, and younger Ordovician to Silurian age populations, that can be related to the early to middle Palaeozoic plutonic rocks and the Amazon Craton. The limited Silurian to Early Devonian detrital ages that contrast with the more significant Middle to Late Devonian zircons that document the erosion of contemporaneous magmatic sources formed after a late Silurian to Early Devonian reduction on the magmatic activity along the proto-Andean margin. These rocks were apparently deformed and metamorphosed between the late Carboniferous and the early Permian. It is suggested that the filling and deformation record of these rocks documented the changes in plate convergence obliquity at the western margin of Gondwana associated with the migration of Laurentia until its final position in Pangea. Between the late Carboniferous and the early Permian, peri-Gondwanan continental terranes also collided with the continental margin. Over-imposed Mesozoic tectonics have contributed to the final redistribution of these terranes to their current position.

Abbreviations:LA: laser ablation inductively couple mass spectrometer; CL: cathodoluminiscence     

Provenance of the late Proterozoic to early Cambrian metaclastic sediments of the Sierra de San Luis (Eastern Sierras Pampeanas) and Cordillera Oriental, Argentina

Provenance studies have been performed utilising major and trace elements, Nd systematics, whole rock Pb–Pb isotopes and zircon U/Pb SHRIMP data on metasedimentary rocks of the Sierra de San Luis (Nogolí Metamorphic Complex, Pringles Metamorphic Complex, Conlara Metamorphic Complex and San Luis Formation) and the Puncoviscana Formation of the Cordillera Oriental. The goal was the characterisation of the different domains in the study area and to give insights to the location of the source rocks. An active continental margin setting with typical composition of the upper continental crust is depicted for all the complexes using major and trace elements. The Pringles Metamorphic Complex shows indications for crustal recycling, pointing to a bimodal provenance. Major volcanic input has to be rejected due to Th/Sc, Y/Ni and Cr/V ratios for all units. The εNd_{(540 Ma)} data is lower for the San Luis Formation and higher for the Conlara Metamorphic Complex, as compared to the other units, in which a good consistency is given. This is similar to the T_DM ages, where the metapsammitic samples of the San Luis Formation are slightly older. The spread of data is largest for the Pringles Metamorphic Complex, again implying two different sources. The whole rock ²⁰⁷Pb/²⁰⁶Pb isotopic data lies in between the South American and African sources, excluding Laurentian provenances. The whole rock Pb–Pb data is almost indistinguishable in the different investigated domains. Only the PMC shows slightly elevated ²⁰⁸Pb/²⁰⁴Pb values. Possible source rocks for the different domains could be the Quebrada Choja in the Central Arequipa–Antofalla domain, the Southern domain of the Arequipa–Antofalla basement, the Brazilian shield or southern Africa. Zircon SHRIMP data point to a connection between the Puncoviscana Formation and the Conlara Metamorphic Complex. Two maxima around 600 Ma and around 1000 Ma have been determined. The Nogolí Metamorphic Complex and the Pringles Metamorphic Complex show one peak of detrital zircons around 550 Ma, and only a few grains are older than 700 Ma. The detrital zircon ages for the San Luis Formation show age ranges between 590 and 550 Ma. A common basin can be assumed for the Conlara Metamorphic Complex and the Puncoviscana Formation, but the available data support different sources for the rest of the Complexes of the Sierra de San Luis. These share the diminished importance or the lack of the Grenvillian detrital peak, a common feature for the late Cambrian–early Ordovician basins of the Eastern Sierras Pampeanas, in contrast to the Sierras de Córdoba, the PVF and the Conlara Metamorphic Complex.     

The Early Palaeozoic high-grade metamorphism at the active continental margin of West Gondwana in the Andes (NW Argentina/N Chile)

The evolution of the Early Palaeozoic orogen of West Gondwana in the Cambrian to Ordovician basement of the Andes between ~18° and 32° S is investigated for pressure and temperature conditions and age of metamorphism. It is characterized by mid-crust temperatures commonly above the wet granite solidus (~650°C). Widespread felsic migmatite and rare granulite formed at pressures of ca 0.5?C0.7?GPa, locally 1.0?GPa. These rocks represent the deepest exhumed sections of the Early Palaeozoic crust. High pressure?Clow temperature rocks are absent. The crystallization ages, compiled from the literature in combination with new data, for near peak metamorphic conditions of these high-grade metamorphic rocks in NW Argentina and N Chile are ~530?C500?Ma and ~470?C420?Ma. Both age groups are spatially overlapping. Radiogenic isotope signatures (Sr, Nd, Pb) are used to characterize the Early Palaeozoic basement. The Pb and Sr isotope compositions of the Early Palaeozoic basement indicate mixing arrays between pre-Palaeozoic unradiogenic and radiogenic crust. Crustal residence ages (Sm?CNd T_DM) indicate a prominent event of crust formation around ~2?Ga, which is known continent-wide. This material was recycled during Midproterozoic and Early Palaeozoic orogenies without prominent additions of new crust present in the isotope record, i.e. accretion of compositional exotic material is absent.     

哈尔滨宾县砂砾石剖面沉积物组成及碎屑锆石U-Pb测年：对沉积环境和区域构造演化的指示

黑龙江宾县宁远镇中阳村剖面的砂砾石堆积过去被认为是哈尔滨地区第四纪下限的罗家窝棚组地层,对于其地层属性和沉积环境方面的研究较为薄弱。本文在野外考察的基础上,利用沉积学、矿物学、地球化学和碎屑锆石U-Pb测年对这套砂砾石堆积剖面进行研究,对其化学风化特征、源岩性质、沉积环境以及构造背景进行讨论。结果表明,这套砾石地层分选和磨圆较差,风化程度较低,无定向性排列,砾石以花岗岩（63%）、石英砂岩（22%）为主;钛铁矿（22.5%）是最主要重矿物,其次是锆石（17.4%）、赤褐铁矿（13.4%）,其它重矿物含量较少。元素地球化学揭示,沉积物中的细颗粒组分经历了中-低等的化学风化过程,大部分沉积物经历了首次循环。砾石岩性和地球化学组成共同揭示了沉积物主要来源于长英质母岩。元素地球化学的迁移与富集以及古气候判别图解指示沉积物是干热气候条件下的近距离搬运的冲洪积物。碎屑锆石U-Pb年龄分布在较窄的范围（208~129 Ma,峰值年龄~180 Ma）,与周围潜在源区锆石年龄对比,结合地貌位置,确定其物源区位于张广才岭余脉哈尔滨东南部低山丘陵带。早侏罗世源区受到古太平洋板块俯冲作用的影响,形成大陆边缘的构造背景,哈尔滨东南低山丘陵带经历了隆升和岩浆活动。与罗家窝棚组标准地层的沉积学特征对比存在明显差异,推测宁远剖面形成时间要晚于罗家窝棚组,与白土山组大致相当。这项研究对于哈尔滨地区第四纪地层的划分具有重要意义。

     

鄂尔多斯盆地晚古生代沉积岩源区构造背景及物源分析

鄂尔多斯盆地周缘物源均来自上地壳,以长英质岩石为主,主要为太古宇、元古宇的各类变火山-沉积岩组成的古老变质岩系,同时具有一定量的花岗岩和碱性玄武岩的混合,但物源成分及南北源区构造背景有所差异。在常量元素及稀土元素组成上,盆地南北物源区的沉积岩在地区及层位之间存在差异,且该变化符合大洋岛弧→大陆岛弧→活动大陆边缘→被动大陆边缘常量元素、稀土元素以及负Eu异常的变化趋势。常量元素变化分析表明盆地北部物源主要来自板块俯冲碰撞地带,与被动大陆边缘环境和活动大陆边缘环境相关,少数为与活动大陆边缘相关的岛弧构造环境有关,到晚古生代中晚期才逐渐与被动大陆边缘环境和活动大陆边缘环境相关。稀土元素对比分析表明,盆地北部物源与太古宙、元古宙的花岗片麻岩、闪长片麻岩、二长花岗岩、变余岩屑砂岩及千枚岩具有亲源性;而盆地南部早—中二叠世长期受被动大陆边缘物源影响,具有高SiO2,低Na2O的特征,这与太古宙—元古宙的太华群、秦岭群、宽坪群等岩系的高SiO2含量,K2O/Na2O>1的特征一致,到晚古生代后期,逐渐与活动大陆边缘物源相关。北秦岭晚古生代山间盆地具有快速混杂堆积的沉积特点,属于盆地外缘,并与鄂尔多斯盆地呈连续过渡的状况,物源上具有继承关系;盆地晚古生代沉积岩中Gd含量及(Gd/Yb)N比值具有随时间迁移的特征,分析表明北部物源区在太原期处于构造快速活动期,而南部物源从山西期才开始进入快速活动期,这与区域构造演化背景一致,即北部物源区抬升要早于南部。     

Field report: Sailing around the exhumed roots of the Mesozoic Patagonian paleo-accretionary wedge(Diego de Almagro Island,Chile)

We undertook a boat expedition to explore the geological framework of a very remote, lesser-known island, in the Chilean Patagonia: the Diego de Almagro Island(latitude S51°330'). This uninhabited, ca.400 km~2 Island is one of the very rare exposures of the Mesozoic accretionary subduction complex along the Chilean margin. Unstable weather, strong winds, steep topography, and very dense vegetation make an on-land mission difficult. Careful preparation based on high-resolution satellite images is advised to optimize shore access and minimize risks of injury. Despite a relatively important degree of regional reequilibration of metamorphic assemblages due to sluggish exhumation through the forearc crust, our results have shown that the island is composed of a nappe stack of ocean-floor derived slivers of metasedimentary units that exhibit very different pressure-temperature-time paths during burial by subduction under the Chilean margin and subsequent exhumation. These rocks are witness to a complex thermal evolution of the subduction zone between Jurassic and Cretaceous times from granulite facies to blueschist facies conditions as well as multiple episodes of accretion at ca. 35 -40 km in depth for almost100 Ma over the Mesozoic era.     

A Lower Palaeozoic shallow water sequence in the eastern European Variscides (SW Poland): provenance and depositional history

The Gackowa Formation of inferred Cambrian —Ordovician age is part of the metamorphosed pre-Variscan basement of the southern Kaczawa Mountains of the Sudetes region, south-west Poland. Previously variously interpreted as lavas, tuffs and sandstones, it is shown to consist of about 200 m of originally well-sorted siliclastic sedimentary rocks within a sequence of predominantly mafic volcanic rocks. Four facies have been distinguished based on relict sedimentary structures and textures and these suggest that deposition took place on a storm-dominated shelf, mostly above the wave base. The petrography, detrital zircon morphologies and geochemistry suggest affinity with, and derivation in large part from, acid volcanic rocks at a comparable stratigraphic position in a separate tectonostratigraphic unit to the south. The Gackowa Formation and its acid volcanic source rocks have a clear continental geochemical signature, in contrast with the mantle-derived basic/bimodal volcanic rocks below and above; it is suggested that the parent acid magma originated by crustal melting during the ascent of these mantle-derived magmas. A continental crust setting is inferred for the deposition of the Gackowa Formation sandstones, thus suggesting a continental setting for the associated within-plate basalts. The entire volcanic/sedimentary succession resembles elements of the Lower Palaeozoic of Germany, and all may have formed in an initial rift setting during Late Precambrian to Ordovician times.     

Unraveling multiple provenance areas using sandstone petrofacies and geochemistry: An example in the southern flank of the Golfo San Jorge Basin (Patagonia,Argentina)

The aim of this paper is to study the provenance of Late Cretaceous sandstones deposited along the south flank of the Golfo San Jorge Basin. For this purpose, detrital modes of three hundred thirty-seven sandstone samples collected in the Mina del Carmen, Bajo Barreal, and Cañadón Seco Formations were studied in ten oil fields. According to the modal composition of the sandstones, six petrofacies were defined allowing the identification of not only principal, but also secondary provenance areas. The QVM and VQM petrofacies are more than 20% metamorphic, sedimentary, and polycrystalline quartz clasts (Lm + Ls + Qpg > 20%), evidencing a secondary signal of basement supply masked by a predominant volcanic provenance. The petrofacies VP and VF are characterized by Lm + Ls + Qpg <20% and more than 20% total feldspar (Pm + Om >20%.), which indicate a supply of sediment from volcanic terrains and scarce derivation of materials from basement rocks. Based on the plagioclase/k-feldspar ratio, the VF petrofacies is interpreted to be dominated by the supply of sand grains from the Andean volcanic-arc, while VP is supposed have originated through the erosion of intermediate volcanic rock outcroppings in the Macizo del Deseado. Finally, both the VQ and QV petrofacies show Lm + Ls + Qpg <20% and Pm + Om<20%, indicating a provenance of volcanic areas coupled with minor contributions from basement rocks. During the Late Cretaceous, the Golfo San Jorge Basin underwent a sag phase that was characterized by very scarce volcanism and tectonic activity. Although these conditions did not favor defined patterns in the vertical stacking of petrofacies, the sandstones exhibit remarkable changes in their regional distribution, which were determined by the paleogeography of the basin and differences in basement composition within the source areas. Finally, a paleogeographic model for sediment circulation in the basin is proposed. This model recognizes the main fluvial dispersal trends that flowed northwest to southeast and transported large amounts of volcanic clasts (associated with petrofacies VF-VQ). To the extent that rivers flowed eastward, a secondary supply from the Precambrian basement, which were composed of low-to high-grade metamorphic rocks, was also important (petrofacies association VQM and QVM). The southwestern area of the basin is dominated by VP petrofacies that record the supply of plagioclase-rich volcanic clasts. This petrofacies likely corresponds to the erosion of Jurassic volcanic units that crop out in the Macizo del Deseado.     

Provenance and Evolution of the Guarguariiz Complex, Cordillera Frontal, Argentina

The Guarguardz Complex, basement of the Cordillera Frontal, included in the proposed Chilenia Terrane, consists of metasedimentary rocks deposited in clastic and carbonatic platforms. Turbiditic sequences point out to slope or external platform environments. According to geochemical data, the sedimentary protoliths derived through erosion of a mature cratonic continental basement. Volcanic and subvolcanic rocks with N and E-MORB signature were interbeded in the metasedimentary rocks during basin development. A compressional stage, starting with progressive deformation and metamorphism, followed this extensional stage. Continuing deformation led to the emplacement of slices of oceanic crust, conforming an accretionary prism during Late Devonian. The Guarguardz Complex and equivalent units in western Precordillera and also in the Chilean Coastal Cordillera share common evolutional stages, widely represented along the western Gondwana margin. These evidences imply that Chilenia is not an allochthonous terrane to Gondwana, but a portion of its Early Paleozoic margin. Regional configuration indicates that the Guarguardz Complex and equivalent units represent the accretionary prism of the Famatinian arc (Middle Ordovician-Late Devonian).     

Provenance of late Ashgill (Hirnantian) fine-grained sediments and pebbles in the Welsh Basin: A ND and SR isotope study

The isotope characteristics of interbedded fine-grained sedimentary rocks and pebbles from an Ashgill sequence in the Welsh Basin show that they have different provenance. Gondwana-derived continental crustal material dominates the Nd-Sr isotope signatures of the fine-grained rocks whereas the pebbles sample the Avalonian basement. Detritus from Gondwana and Avalonia accounts for the isotopic composition of most of the lower Palaeozoic sedimentary rocks of Southern Britain and this suggests that any contribution from the reworking of Lower Palaeozoic volcanic rock is minimal.     

塔里木盆地早古生代晚期构造-沉积响应

伴随相对海平面由上升转为下降的周期变化,塔里木盆地在早古生代经历了一次大规模的扩张→挤压→隆升的开合旋回,早期(震旦纪-中奥陶世)处于拉张的构造背景下,呈现西台(碳酸盐台地)东盆(满加尔-库鲁克塔格深水盆地)的古地理格局。中西部广大地区沉积了巨厚的浅水台地相碳酸盐岩,以中晚寒武世的下丘里塔格群和早中奥陶世的上丘里塔格群为标志;东部的满加尔-库鲁克塔格则以厚度不大的远洋硅-灰泥沉积为主。盆地构造性质的转换及沉积古地理的巨大改变发生于中奥陶世中晚期,以塔中、塔北的隆起和塘古孜巴斯坳陷及阿瓦提-满加尔坳陷的形成为标志,呈近南北向隆-坳相间的盆地格局。沉积记录的响应表现为碳酸盐台地的消失、陆源物质的逐渐注入和向上变粗、火山活动和火山碎屑的出现以及巨厚砂泥质浊积岩在塔东盆地内的充填等。因此,中晚奥陶世-中泥盆世是塔里木盆地海域逐渐萎缩、盆地不断隆升和相对海平面逐渐下降的一个过程。     

The southernmost record of tropical pollen grains in the mid-Cretaceous of Patagonia, Argentina

Pollen grains characteristic of tropical Northern Gondwana (Schrankipollis, Brenneripollis and Pennipollis peroreticulatus) have been recorded from the Cretaceous of Patagonia. They were recovered from the Late Albian–Cenomanian Kachaike Formation in Santa Cruz Province, southern Argentina. The palynological assemblages are dominated by gymnosperm pollen and bryophyte-pteridophyte spores, whereas angiosperms are poorly represented. The angiospermoid type Schrankipollis has not been reported previously from Argentina, and a new species S. kachaikensis is described. Two species of Brenneripollis (of uncertain affinity) and Pennipollis peroreticulatus (related to the Alismatales) are also reported. The first appearances of Pennipollis peroreticulatus are clearly diachronous from north to south, ranging from the Barremian in tropical regions to the Coniacian–Santonian in Antarctica. S. kachaikensis and P. peroreticulatus show restricted stratigraphic distributions through the Kachaike Formation and may be stratigraphically useful markers. A tetrad of Walkeripollis (related to modern Winteraceae) is also recognized. This is the oldest record of Winteraceae in the southern temperate region where the family lives today. Evidence for migration of Winteraceae from tropical Gondwana to Antarctica and Australia throughout South America, is provided by this new finding. The presence of tropical elements in the austral margin of South America gives support to previous studies on the expansion of warm temperatures towards high latitudes during the mid Cretaceous.     

鄂尔多斯盆地东南部二叠系物源分析

近几年鄂尔多斯盆地东南部上古生界陆续发现新的天然气区带,显示出巨大的勘探潜力,因此对盆地东南部二叠系物源的研究对于确定储集砂体展布规律具有重要价值。以钻测井、岩心及周边露头资料为基础,通过露头剖面古流向测定、重矿物分析、边缘相分析、相带分析的方法,确定了研究区二叠系的物源方向;研究认为鄂尔多斯盆地东南部二叠系山西组与石盒子组物源可分为北北东、北北西及南部三个方向,以延安为中心区域属于汇水区;山2段南部物源影响范围较大,影响到延安以北区域;盒8段北部物源范围较大,越过了延安,相应的南部物源范围后撤。     

Provenance of Clay Minerals in the Amami Sankaku Basin and Their Paleoclimate Implications Since Late Pleistocene

We analyzed the clay mineral assemblages, content and mineralogical characteristics of Hole U1438A sediment recovered from Amami Sankaku Basin during International Ocean Discovery Program (IODP) expedition 351. The results show that the clay minerals are mainly composed of illite (average 57%), smectite (average 26%), chlorite (average 14%) and minor kaolinite(average 3%). The crystallinity of illite in all samples are good (<0.4 Δ° 2θ), and the chemical indexes of illite in all samples are low (<0.4). Both indicate that illite in Hole U1438A formed in cold and dry climate. By comparing clay mineral assemblages of hole U1438A and the potential sediment sources, we suggest that smectite be mainly derived from the volcanic materials around Amami Sankaku Basin. Illite, chlorite and kaolinite are mainly derived from the Asian dust. The ratios of (illite+chlorite)/smectite show a phased increase over the last 350 ka, which is consistent with the cold and drying trend of the Asian continent since late Pleistocene. The high ratios of (illite+chlorite)/smectite and (illite+chlorite)/kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.     

Detrital zircon geochronology and provenance of the Chubut Group in the northeast of Patagonia,Argentina

The Chubut Group constitutes the most widespread sedimentary unit in NE Patagonia, characterized by variable-energy fluvial deposits. U–Pb analysis of detrital zircons from two sections of the Chubut Group constraint the age of the oldest sedimentary rocks in the northeast of the Somuncurá – Cañadón Asfalto Basin. In the Cañadón Williams area, at San Jorge section, 20 km NW of Telsen locality, dating of 56 detrital zircons from a medium to coarse sandstone indicated a maximum depositional age of 109 ± 1 Ma (n = 4). These sandstones were interpreted to represent shallow channels, associated with a lacustrine system. In the Telsen locality, a laser ablation analysis of 115 detrital zircons from a medium to coarse-grained sandstone, from fluvial channel facies, yielded a maximum depositional age of ca. 106 ± 1 Ma (n = 8). Both ages are consistent with volcanic events of the Barremian to Albian age in the central Patagonian Andes Region. Cathodoluminescence images of zircons from the San Jorge sample suggest an igneous origin, which is further supported by Th/U values above 0.5 in most of the grains. The distribution of the statistical modes of the main age populations of detrital zircons for the two samples [182, 185 and 189 Ma for Telsen sample (T2S) and 181 ± 1 Ma for San Jorge sample (SJS)] matches the age of the volcanic Marifil Formation. The rocks of the Marifil Formation of these ages are exposed NE to SE of the study area. The abundance of zircons of similar Jurassic ages (n = 52 for SJS and n = 105 for T2S) and the external morphology of the zircons in the sample SJS, implies a close proximity of the source area. Suggestion that the Marifil Formation was the main provenance source is also supported by northeast–southeasterly paleocurrents measured at the San Jorge and Telsen sections.     

滇西保山地块早古生代花岗岩类的年代学、地球化学及意义

位于滇西特提斯构造带保山地块的平河岩体,岩石类型主要为花岗岩、二长花岗岩,其次有少量的花岗闪长岩。4件样品的锆石U-Pb年龄变化于480～486Ma,表明这些花岗岩类侵位于早奥陶世。平河花岗岩类的K2O/Na2O值大于1,铝饱和指数(A/CNK)为1.07～1.1,属高钾钙碱性过铝质花岗岩。岩石总体上富集大离子亲石元素和Pb,亏损高场强元素。明显富集轻稀土元素[(La/Yb)N=4.33～7.05],显示明显的负Eu异常(δEu=0.25～0.48)。4件样品58个测点的锆石εHf(t)值变化范围较大(主要集中于-12.4～-3.0之间),对应的Hf同位素地壳模式年龄集中于2.2～1.7Ga。这些地球化学特征指示平河花岗岩类为S型花岗岩,主要来源于古老地壳物质(如砂屑岩)的重熔,并不同程度地混入了幔源物质。平河花岗岩类与出露于中部拉萨地体的变质酸性火山岩存在可比性,可能代表了早古生代冈瓦纳大陆原特提斯边缘岩浆弧的一部分。