Cenozoic basin development and its indication of plateau growth in the Xunhua-Guide district

The Xunhua, Guide and Tongren Basins are linked with the Laji Mountain and the northern West Qinling thrust belts in the Xunhua-Guide district. Basin depositional stratigraphy consists of the Oligocene Xining Group, the uppermost Oligocene-Pliocene Guide Group and the Lower Pleistocene. They are divided into three basin phases by unconformities. Basin phase 1 is composed of the Xining Group, and Basin phase 2 of the Zharang, Xiadongshan, Herjia and Ganjia Conglomerate Formations in the Guide Group, and Basin phase 3 of the Gonghe Formation and the Lower Pleistocene. Three basin phases all develop lacustrine deposits at their lower parts, and alluvial-braided channel plain depositional systems at upper parts, which constitute a coarsening-upward and progradational sequence. Basin deposition, paleocurrent and provenance analyses represent that large lacustrine basin across the Laji Mountain was developed and sourced from the West Qinling thrust belt during the stage of the Xining Group (Basin phase 1), and point-dispersed alluvial fan-braided channel plain deposition systems were developed beside the thrust and uplifted Laji Mountain and sourced from it, as thrusting migrated northwards during the stage of the Guide Group (Basin phase 2). Evolution of basin-mountain system in the study area significantly indicates the growth process of the distal Tibetan Plateau. The result shows that the Tibetan Plateau expanded to the northern West-Qinling at Oligocene (29–21.4 Ma) by means of northward folded-and-thrust thickening and uplifting and frontal foreland basin filling, and across the study area to North Qilian and Liupan Mountain at the Miocene-Pliocene (20.8–2.6 Ma) by means of two-sided basement-involved-thrust thickening and uplifting and broken foreland basin filling, and the distant end of Tibetan Plateau behaved as regional erosion and intermontane basin aggradational filling during the Pliocene and early Pleistocene (2.6–1.7 Ma).

     

Chronological and paleoceanographic constraints of Miocene to Pliocene ‘mud sea’ in the Ryukyu Islands (southwestern Japan) based on calcareous nannofossil assemblages

The Cenozoic sedimentary succession in Okinawa‐jima, including the upper Miocene to Pleistocene siliciclastic deposits (Shimajiri Group) and the Pleistocene reef to shelf deposits (Ryukyu Group), suggests a drastic paleoceanographic change from a ‘mud sea’ to a ‘coral sea.’ To delineate the paleoceanographic evolution of the mud sea, we quantified the stratigraphic distribution of the calcareous nannofossil assemblages from the Shimajiri Group in a 2119.49 m‐deep well (Nanjo R1 Exploratory Well) drilled in southern Okinawa‐jima (Ryukyu Islands, southwestern Japan). Four late Miocene and Pliocene datum planes were found in the studied interval: the first occurrence of Amaurolithus spp. (7.42 Ma), the last occurrence of Discoaster quinqueramus (5.59 Ma), the first occurrence of Ceratolithus rugosus (5.12 Ma), and the last occurrence of Reticulofenestra pseudoumbilicus (3.70 Ma). The calcareous nannofossil assemblages from the Tomigusuku Formation and the lower part of the Yonabaru Formation are characterized by a lower total number of coccoliths and abundant Sphenolithus abies that is associated, at times, with common Discoaster spp. Overall, these suggest the existence of oligotrophic conditions between 5.3 and >8.3 Ma. The total number of coccoliths increased and small Reticulofenestra spp. became more common in the middle part of the Yonabaru Formation, suggesting that eutrophic conditions were present between 3.5 and 5.3 Ma. The rare occurrence of calcareous nannofossils in the upper part of the Yonabaru Formation indicates a return to oligotrophic conditions at 3.5 Ma. Micropaleontological evidence suggests that these oceanographic changes were likely caused by local tectonic movement (shallowing of the sedimentary basin in which the Shimajiri Group was deposited).     

Faunal analysis of Neogene planktonic foraminifera from forearc sediments of the Japan Trench, ODP Site 1151, Leg 186

Abstract The present paper describes the general outline of Neogene paleoceanographic changes in the northwestern Pacific by means of planktonic foraminiferal assemblages. Planktonic foraminiferal fossils occur commonly in the upper Miocene to lower Pleistocene sediments of Hole 1151A, Ocean Drilling Program Leg 186 in the forearc basin off northeast Japan, with the exception of 11 barren intervals. These barren intervals are explained as a result of dissolution under organic decomposing processes. Three assemblages of planktonic foraminifers were identified by Q‐mode cluster analysis. The succession of the assemblages can be divided into four paleoceanographic stages: (i) warm‐temperate Tortonian; (ii) cold‐temperate Messinian to lower Pliocene; (iii) warm climatic optimum in the middle part of the Pliocene; and (iv) strong glacial–interglacial oscillation of the upper Pliocene to the lower Pleistocene. Three short warming events—namely, the late Miocene climatic optimum 3, the Miocene–Pliocene boundary and the middle Pliocene events—and a short cooling event of the late Miocene could be determined in the studied section of Site 1151.     

A preliminary study of NW Zhejiang foreland fold and thrust belt in Southeast China

The Upper Permian Dalong Formation (P₂d) and Changxing Formation (P₂C), and the Lower Triassic Zhengtang Formation (Tlz) are of deep-water turbidites. The sedimentary features of the NW Zhejiang are of SE-dipping passive continental margin from the Paleozoic to the early Triassic. Together with the foreland molasse basin during the late Triassic (T₃w), the tectonics of the NW Zhejiang is characterised by a tectogenesis which took place in the middle Triassic. From SE to NW, the structural style varies from multi-duplex, antiformal stack to imbricate fans, and then to Jura Mountain-type fold zone with fold-style varying gradually from large-scale tight fold to midscale chevron fold, then to cylindrical fold, reviewing a preliminary scenario of foreland fold and thrust belt. The space-distributed structures and the tectonic vergence indicate the significance of deformation in (T1-T₃). Project supported by the National Natural Science Foundation of China and Chinese Academy of Sciences.     

Tephrostratigraphy of the Pliocene to Middle Pleistocene Series in Honshu and Kyushu Islands,Japan

The Pliocene to Pleistocene Series in each sedimentary basin or area of Japan has been investigated and described; however, their stratigraphic correlation is difficult because of complex geological structures. Regional stratigraphy has therefore been established using many intercalated tephra beds, i.e. by correlating tephra beds between distant areas. A standardized stratigraphic model of the Pliocene to Middle Pleistocene Series in Japan is put forward in this paper on the basis of tephrostratigraphy, magnetostratigraphy, and biostratigraphy. This stratigraphic model is important for studies of environmental changes and explosive volcanism in this period around the Japanese island‐arc.     

The “Camporeale wedge-top Basin” (NW Sicily; Italy) in the frame of the Late Miocene Sicilian Foreland Basin System; Inferences from the Upper Tortonian–Lower Messinian Terravecchia Formation

Since the latest Oligocene–earliest Miocene the building of the Sicilian fold and thrust belt has been accompanied by development of a “peripheral” foreland basin system which migrated toward the foreland. In north-western Sicily, the sedimentary record of the foreland basin system migration is represented by a stratigraphic succession made up of several lithostratigraphic units, bounded by regional unconformity surfaces, deposited recording at least four main sedimentary phases, each characterized by the development of different types of syntectonic basins.     

Sedimentary history with biotic reaction in the Middle Permian shelly sequence of the Southern Kitakami Massif,Japan

The transition of sedimentary environments and their organism‐related responses is exemplified in the active margin setting of the Middle Permian in the Southern Kitakami Massif. The transition in the sedimentary environment began with a shallowing‐upward sequence at an upper slope to an outer shelf depositional setting that was associated with a delta system which transported abundant botanic remains in the Hoso‐o Formation. By contrast, the sediments of the overlying Kamiyasse Formation, the base of which is roughly equivalent to the lowermost Capitanian, were deposited at a lower shoreface to the outer shelf setting, which originated from complex depositional sources, including beach, near shore reef mounds and a nearby independent area of shallow and hard substratum with a considerable difference of depth. This unique depositional setting resulted in the seemingly ‘mixed’ fauna associated with this formation. The depositional environment of the overlying Kurosawa Formation is similar to that of the Hoso‐o Formation, but with far fewer monotonous biotic remains. A comparison of lithological characteristics and fossil remains with those of neighboring regions suggests that the independent mounds were generated as if the talus formed elsewhere so as to provide a large amount of skeletal elements to a deeper basin in the earliest Capitanian. Accordingly, the complex sedimentary setting observed in the Kamiyasse Formation occurs widely throughout the South Kitakami Massif, making possible the ‘mixed’ and seemingly diverse fauna from a mixture of multiple allochthonous origins.     

塔里木盆地东北缘晚新生代钻孔岩心磁性地层年代学及其构造意义

塔里木盆地的高分辨率沉积记录对于理解青藏高原隆升、亚洲内陆干旱化乃至全球气候变化至关重要.建立可靠的地层年代标尺对于研究塔里木盆地晚新生代沉积环境演化、构造运动及古气候变化具有重要意义.本文对塔里木盆地东北缘库尔勒地区的两个全取心钻孔ZK3（深500 m）、ZK5（深300 m）进行详细的磁性地层学研究,结果表明,ZK3孔中更新统底界为54.8 m,下更新统底界为167.0 m,上新统底界为432.0 m,钻孔底部年龄约为6.2 Ma,属上中新统上部;ZK5孔中更新统底界为64.7 m,下更新统底界为241.5 m,钻孔底部年龄约为3.2 Ma,属上上新统.基于上述磁性地层年代标尺,通过沉积速率分析发现ZK3孔在3.0—3.6 Ma之间沉积速率明显增大,反映了塔里木盆地北部天山在此期间的快速隆升.通过东西部多个盆地地质剖面沉积速率的对比分析发现,这期构造活动在区域上具有准同期活动特征,在时代上与晚中新世以来青藏高原快速隆升的时代一致,可能与青藏高原的隆升扩展效应有关.     

Structural evolution of the Pleistocene Cimini trachytic volcanic complex (Central Italy)

Structural, geomorphological, geophysical and volcanological data have been processed for the implementation of a dedicated GIS through which the structural evolution of the Pleistocene trachytic Cimini volcano (central Italy) has been reconstructed. The evolution of the Cimini complex includes three main close-in time phases: (1) intrusion of a shallow laccolith, rising along NW and NE trending faults and stagnating at the contact between the Mesozoic-Cenozoic and the Pliocene-Pleistocene sedimentary units constituting the bedrock of the volcano; (2) emplacement of lava domes along radial and tangential fractures formed by the swelling induced by the laccolith growth; (3) ignimbrite eruptions and final effusion of olivine-latitic lavas. Domes are both of Pelean and low lava dome type and their morphology was controlled by the location on the inclined surface of the swelled area. Some domes show to have uplifted upper Pliocene thermally metamorphosed clay sediments, suggesting a cryptodome-like growth. Comparison of the top of the Mesozoic-Cenozoic units with the top of the upper Pliocene-Pleistocene sedimentary complex, suggests that the laccolith emplaced in a graben of the Mesozoic-Cenozoic sedimentary complex filled by the Pliocene–Pleistocene sediments uplifted by the shallow intrusion. Stress patterns acting on the Cimini area have been deduced analysing the drainage network and the morphotectonic lineaments. Rose diagrams show a large dispersion of the lineaments reflecting the local presence of radial and tangential fractures. The most frequent extensional NW and NE trending lineaments have regional significance and controlled the magma uprise leading to the laccolith emplacement.     

Tectono-sedimentary evolution of the peripheral basins of the Alboran Sea in the arc of Gibraltar during the latest Messinian-Pliocene

In the peripheral basins of the Alboran Sea, five stratigraphic units (latest Messinian-Pliocene) separated by discontinuities and representing transgressive–regressive cycles have been recognized. The first unit (LM) is latest Messinian in age and precisely characterizes the Lago-Mare event at the end of the Messinian Salinity Crisis, i.e. just before the opening of the Strait of Gibraltar at the beginning of the Pliocene. The three following units (Pl-1, Pl-2 and Pl-3) are Zanclean in age, whereas the last one (Pl-4) is Piacenzian. These four Pliocene units consist of alluvial, deltaic, and littoral deposits in the marginal areas, changing to open marine deposits with planktonic components in the basinal areas, although their extension varies in each basin. Regionally, these units do not necessarily stack in a single stratigraphic succession because of tectonics that controlled their hosting basins. Thus, the LM and Pl-1 units occur only in the Malaga and Estepona-Marbella basins, revealing that the onset of the sedimentation after the Messinian evaporitic stage and the Pliocene transgression was not a single and synchronous event in the western Alboran Sea. Moreover, the Pl-3 and Pl-4 units do not appear in all basins, so that the subsequent continentalization process of these Alboran peripheral areas during the Pliocene was also diachronous.The sedimentary evolution of the peripheral basins was controlled mainly by tectonics. During the latest Messinian-early Pliocene, the sedimentation took place in a context marked by a NNW–SSE compression and ENE–WSW perpendicular tension. The onset of the sedimentation (LM and Pl-1 units) could be linked to preexisting E–W faults that mark part of the borders of the Malaga basin and the Estepona-Marbella sector. During the deposition of the Pl-2 unit, the movements of E–W, NW–SE, and NE–SW normal faults determined a continuous subsidence in several basins, resulting in the accumulation of thick clastic marine sequences (i.e. Malaga, Vélez-Málaga, and Nerja basins in Spain and Tirinesse basin in Morocco). Tectonic activity during the early Zanclean leads to a new paleogeographic configuration of the Alboran peripheral areas. The main features are: (i) continentalization of the Nerja sector in the Betics, Tetouan, and Oued Laou-Tirinesse sectors in the Rif; (ii) on the contrary, a period of intense subsidence started in the coastal sectors between Torremolinos and Manilva, allowing the development of the Pl-3 unit directly on the substratum; and (iii) the Malaga, Vélez-Málaga, and Malalyine basins maintained the marine regime, so their sedimentary infilling recorded the Pl-2–Pl-3 unconformity. Nevertheless, these last basins emerged shortly afterwards, before the end of the early Zanclean (FO of Globorotalia puncticulata), probably in relation to the beginning of the sea-level fall which characterizes the upper part of the TB 3.4 cycle by Haq et al. (1987).During the late Zanclean, sedimentation occurred only in the Betic basins, where NNE–SSW faults – conjugated with NW–SE faults – induced a major subsidence, permitting better development of the Pl-3 unit. On the contrary, NW–SE faults in the sector between Malaga and Nerja, and NE–SW faults in the Tirinesse basin, became practically inactive. Before the end of the Zanclean, the subsidence ceased also in the westernmost Betic basins, thus causing emersion, firstly in the sector between Torremolinos and Manilva and, slightly later, in the San Roque-Algeciras sector. Thus, the whole geodynamic activity conditioned the time–space evolution of the northern edge of the Alboran Sea, which was emerging throughout the Zanclean, successively from the E to the W. A similar E to W continentalization trend can be suggested for the Rifian Pliocene sectors when taking into account the Oued Laou-Tirinesse basins that emerged before the Malalyine one.Moreover, the unit boundaries do not coincide with those of the familiar Exxon coastal aggradational curve, but rather with the local or regional tectonic activity. Consequently, the correlation of the unit boundaries with those of the Pliocene deposits of the eastern Betic basins remains difficult. According to the biostratigraphical data, the Pl-1, Pl-2, and Pl-3 units correspond to the Pliocene-I by Montenat (1990), while the Pl-4 unit may be equivalent to the Pliocene-II.     

Modeling seismic reflections from thin-bed dolomite layers in diatomite formation

Abstract The origin of dolomite and its diagenesis are still not fully understood. The timing and occurrence of dolomite beds remain key problems. Many thin‐bed layers of dolomite in marine sediments were discovered at drill sites in the forearc basin west of the Japan Trench during the Ocean Drilling Program Leg 186. The thickness of the dolomite layers ranges from 0.5 to 2 m, estimated from the well log. These thin‐bed dolomite layers were able to be identified on seismic data, through quantitative analysis and comparison of the data with synthetic seismograms. Amplitude‐preserved seismic data processing with broadband high‐resolution enhancement helps to estimate the reflectivity series dominated by the large impedance contrast between the dolomite layers and the host sediments. In this report, the first geophysical evidence of large‐scale dolomitization is provided. The occurrence of thin dolomitic layers embedded in diatomaceous sediments is on a basin scale rather than being an isolated event, which constrains the type of dolomitization and the timing of layered dolomitization. It was found that thin‐bed dolomite layers occur where there is an abrupt change in sedimentation rate. Layered dolomitization starts when sedimentation rate changes (from high to low or vice versa). Two dolomite layers coincide with the Miocene–Pliocene and Pliocene–Pleistocene age boundaries. Formation of dolomite beds could be a timing signal of a dramatic change in paleoceanographic and paleoclimatic environments.     

临夏盆地新近纪郭泥沟剖面磁组构特征及其环境意义

临夏盆地在东亚新生代地层、古气候、古生物研究方面占有举足轻重的地位.本文对盆地东部的郭泥沟剖面进行了详细的岩石磁学和磁组构研究,以揭示从早中新世到早上新世临夏盆地的沉积演化过程.郭泥沟剖面沉积物中的磁性矿物有磁铁矿、磁赤铁矿、赤铁矿和针铁矿,但剩磁载体以磁铁矿和赤铁矿为主.从上庄组和东乡组的褐红色粉砂质粘土到柳树组和何王家组的褐黄色粘土,赤铁矿含量呈现降低的趋势,与沉积物颜色变化一致.郭泥沟剖面沉积物磁组构类型为正常沉积磁组构.结合岩石磁学结果和磁组构参数特征可揭示临夏盆地早中新世-早上新世沉积的演化过程：早中新世上庄组为稳定湖相沉积,古水流方向为NNW,与南北向的大夏河方向一致;中中新世气候发生较明显的干湿波动,形成了东乡组的褐红色湖相粉砂质粘土夹粉砂、砂和青灰色泥灰质粘土条带,古水流方向主要为NNW,沉积过程主要受大夏河控制;中中新世晚期,受青藏高原构造运动影响,沉积相由湖相细粒沉积物转变为虎家梁组河流相砂砾层;同时,盆地的水动力条件也发生改变,晚中新世柳树组湖相沉积过程同时受南北向大夏河和东西向洮河控制,两个方向近垂直的河流共同作用导致柳树组内沉积各向异性度较低,面理和线理均不发育,磁化率最大轴偏角分布比较分散,磁组构确定的古流向为东西向和南北向;早上新世期间,由于受青藏高原隆升影响,沉积了何王家组下部的河流相砂砾层;受构造抬升影响,大夏河重新主导何王家组上部洪泛平原相沉积过程,水动力条件较为单一稳定,古流向主要为N向,与大夏河流向一致.     

Lithostratigraphy of Permian marine sequences, Khao Pun Area, central Thailand: Paleoenvironments and tectonic history

Geologic mapping and subsurface lithostratigraphic investigations were carried out in the Khao Pun area (4 km²), central Thailand. More than 250 hand specimens, 70 rock slabs, and 70 thin sections were studied in conjunction with geochemical data in order to elucidate paleoenvironments and tectonic setting of the Permian marine sedimentary sequences. This sedimentary succession (2485 m thick) was re‐accessed and re‐grouped into three lithostratigraphic units, namely, in ascending order, the Phu Phe, Khao Sung and Khao Pun Formations. The Lower to lower Upper Permian sedimentary facies indicated the transgressive/regressive succession of shelf sea/platform environment to pelagic or abyssal environment below the carbonate compensation depth. The sedimentological and paleontological aspects, together with petrochemical and lithological points of view, reveal that the oldest unit might indicate an Early Permian sheltered shallow or lagoonal environment. Then the depositional basin became deeper, as suggested by the prolonged occurrence of bedded chert‐limestone intercalation with the local exposure of shallower carbonate build‐up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicucullus sp.) cherts. This cryptic evidence might indicate the abyssal environment during middle Middle to early Late Permian; whereas, previous studies advocated shelf‐facies environments. Following this, the depositional condition might be a major regression on the microcontinent close to Indochina, from the minor transgressive/regressive cycles that developed within a skeletal barrier, and through the lagoon with limited circulational and anaerobic conditions, on to the tidal flat to the sheltered lagoon without effective land‐derived sediments.     

Fourth‐ to third‐order cycles in the Hakobuchi Formation: Shallow‐marine Campanian final deposition of the Yezo Group,Nakagawa area,northern Hokkaido,Japan

The Yezo Group has a wide longitudinal distribution across Hokkaido, northern Japan. It represents a Cretaceous (Early Aptian–Late Maastrichtian) and Late Paleocene forearc basin‐fill along the eastern margin of the paleo‐Asian continent. In the Nakagawa area of northern Hokkaido, the uppermost part of the Yezo Group consists of the Hakobuchi Formation. Along the western margin of the Yezo basin, 24 sedimentary facies (F) represent 6 facies associations (FA), suggesting prevailing storm‐dominated inner shelf to shoreface environments, subordinately associated with shoreface sand ridges, outer shelf, estuary and fluvial environments. The stacking patterns, thickness and facies trends of these associations allow the discrimination of six depositional sequences (DS). Inoceramids Sphenoceramus schmidti and Inoceramus balticus, and the ammonite Metaplacenticeras subtilistriatum, provide late Early to Late Campanian age constraints to this approximately 370‐m thick final stage of deposition and uplift of the Yezo forearc basin. Six shallow‐marine to subordinately non‐marine sandstone‐dominated depositional sequences include four 10 to 110‐m thick upward‐coarsening regressive successions (FS1), occasionally associated with thin, less than 10‐m thick, upward‐fining transgressive successions (FS2). The lower DS1–3, middle DS4–5 and upper DS6 represent three depositional sequential sets (DSS1–3). These eastward prograding and westward retrograding recurring shallow‐marine depositional systems may reflect third‐ and fourth‐order relative sealevel changes, in terms of sequence stratigraphy.     

Comprehensive constraint on the tectono-sedimentary setting of Late Paleozoic turbidites of the Kamuste area, eastern Junggar, Xinjiang

Petrography and geochemistry, combined with sedimentation analyses allow for a thorough evaluation of the tectono-sedimentary setting of late Paleozoic turbidites of the Kamuste area, eastern Junggar. Sandstones of the Alabiye¹⁾ Formation are composed mostly of volcanic and sedimentary detritus with lesser amounts of plagioclase and quartz. They were derived from an undissected magmatic-arc provenance. The geochemistry of sandstone-mudrock suites indicates a fesic-intermediate igneous provenance, and constrains the Alabiye Formation to have derived from a differentiated oceanic-continental margin island-arc tectonic setting. Likewise, geochemistry and sandstone petrography of the Kamuste Formation reflect a mixed provenance signature dominated by magmatic arc, basement uplift, and subduction-complex sources of a differentiated continental-island arc. Sedimentation analysis indicates that the Alabiye and Kamuste formations are two sets of turbidite sequences deposited on a submarine slope and a submarine fan and basin plain respectively. In conclusion, submarine slope turbidite deposition of the Alabiye Formation records the main sedimentary response to the development of early Devonian back-arc basins of the northern Junggar tectonic belt. Submarine fan and basin plain turbidite and background hemipelagic deposition of the Kamuste Formation record the main sedimentary response to the late Early Carboniferous development of an inter-arc relict ocean basin of the eastern Junggar composite terrane.     

小江断裂带中段盆地的发育阶段及其与区域构造运动的关系

小江断裂带中段新生代发育的系列盆地，根据其发育阶段可分为始新世—渐新世、上新世—早更新世、中更新世—晚更新世和晚更新世—全新世４个阶段，并根据发育持续性可分为继承性、阶段性、复活性、新生性４种类型。由大比例尺填图所获资料及前人成果，介绍了各阶段盆地的分布特征和成因机制，讨论了盆地发育与区域构造运动、断裂活动的关系     

Sequence framework of two different kinds of margins and their response to tectonic activity during the Middle-Late Triassic,Ordos Basin

Two kinds of margin respectively occur in the Ordos Basin during the Middle-Late Triassic (Yanchang Age), one is foreland margin developed under the background of flexural subsidence by thrusting intensively in the southwest margin, and the other is intracratonic basin margin by stable subsidence in northern and central parts of the basin. The Middle-Late Triassic Yanchang Formation can be divided into four regional third-order sequences, which are separated by gentle angular unconformity or regional erosion surface, made up of lowstand system tract (LST), expanding system tract (EST) and highstand system tract (HST) from lower to upper within a sequence. But there are distinct differences of the sequence framework between the southwest margin and northern and central parts of the basin. The southwest margin develops heavy conglomerate layer and unconformity as a result of orogeny by thrusting, and the intracratonic basin margin by stable subsidence in the northern and central parts grows aggradational sandstone, conglomerate in fluvio-delta system and parallel unconformity. The depositional framework of southwest margin reflects the tectonic evolution from flexural subsidence by thrusting to rebounded uplift. The formation of sequence boundary is related to the resilient uplift and erosion. The sequence stratigraphic framework and depositional system tract configuration in the foreland basin are controlled by structural activity of the fold and thrust belt, and the sequence succession reflects episodic thrusting of the Middle-Late Triassic toward the foreland basin. The sequence evolution in northern and central parts reflects the depositional succession of fluvio-delta system under intracratonic background, composed of coarse-grained sediment in braided channel deposit at the lower, meandering channel deposit in the middle and fine-grained sediment in the flood plain at the upper, dominated by lake level fluctuation. During the deposit of the LST in the intracraton basin, accommodation space is limited, and results in abundant fluvial sediment migration laterally, erosion and transport, forming laterally sandstone composite and aggradational deposit on the alluvial plain, which constitutes specific erosion unconformity boundary.

     

Magnetic fabric of Plio-Pleistocene sediments from the Crotone fore-arc basin: Insights on the recent tectonic evolution of the Calabrian Arc (Italy)

Low-field anisotropy of magnetic susceptibility (AMS) analyses were performed on 532 samples collected in 36 (mostly lower Pliocene to lower Pleistocene) marine clay sites from the Crotone basin, a fore-arc basin located on top of the external Calabrian accretionary wedge. The Crotone basin formed since mid-late Miocene under a predominant extensional tectonic regime, but it was influenced thereafter by complex interactions with NW–SE left-lateral strike-faults bounding the basin, which also yielded post-1.2 Ma ∼30° counterclockwise block rotations. The basin is filled by continental to marine sediments yielding one of the thickest and best-exposed Neogene succession available worldwide. The deep-marine facies – represented by blue-grey marly clays gave the best results, as they both preserved a clear magnetic fabric, and provided accurate chronology based on previously published magnetostratigraphy and calcareous plankton (i.e. foraminifers and nannofossils) biostratigraphy. Magnetic susceptibility range and rock magnetic analyses both indicate that AMS reflects paramagnetic clay matrix crystal arrangement. The fabric is predominantly oblate to triaxial, the anisotropy degree low (<1.06), and the magnetic foliation mostly subparallel to bedding. Magnetic lineation is defined in 30 out of 36 sites (where the e12 angle is <35°). By also considering local structural analysis data, we find that magnetic fabric was generally acquired during the first tectonic phases occurring after sediment deposition, thus validating its use as temporally dependent strain proxy. Although most of the magnetic lineations trend NW–SE and are orthogonal to normal faults (as observed elsewhere in Calabria), few NE–SW compressive lineations show that the Neogene extensional regime of the Crotone basin was punctuated by compressive episodes. Finally, compressive lineations (prolate magnetic fabric) documented along the strike-slip fault bounding the basin to the south support the significance of Pleistocene strike-slip tectonics. Thus the Crotone basin shows a markedly different tectonics with respect to other internal and western basins of Calabria, as it yields a magnetic fabric still dominated by extensional tectonics but also revealing arc-normal shortening episodes and recent strike-slip fault activity. The tectonics documented in the Crotone basin is compatible with a continuous upper crustal structural reorganization occurring during the SE-migration of the Calabria terrane above the Ionian subduction system.     

Sequence framework of two different kinds of margins and their response to tectonic activity during the Middle-Late Triassic,Ordos Basin

Two kinds of margin respectively occur in the Ordos Basin during the Middle-Late Triassic (Yanchang Age), one is foreland margin developed under the background of flexural subsidence by thrusting intensively in the southwest margin, and the other is intracratonic basin margin by stable subsidence in northern and central parts of the basin. The Middle-Late Triassic Yanchang Formation can be divided into four regional third-order sequences, which are separated by gentle angular unconformity or regional erosion surface, made up of lowstand system tract (LST), expanding system tract (EST) and highstand system tract (HST) from lower to upper within a sequence. But there are distinct differences of the sequence framework between the southwest margin and northern and central parts of the basin. The southwest margin develops heavy conglomerate layer and unconformity as a result of orogeny by thrusting, and the intracratonic basin margin by stable subsidence in the northern and central parts grows aggradational sandstone, conglomerate in fluvio-delta system and parallel unconformity. The depositional framework of southwest margin reflects the tectonic evolution from flexural subsidence by thrusting to rebounded uplift. The formation of sequence boundary is related to the resilient uplift and erosion. The sequence stratigraphic framework and depositional system tract configuration in the foreland basin are controlled by structural activity of the fold and thrust belt, and the sequence succession reflects episodic thrusting of the Middle-Late Triassic toward the foreland basin. The sequence evolution in northern and central parts reflects the depositional succession of fluvio-delta system under intracratonic background, composed of coarse-grained sediment in braided channel deposit at the lower, meandering channel deposit in the middle and fine-grained sediment in the flood plain at the upper, dominated by lake level fluctuation. During the deposit of the LST in the intracraton basin, accommodation space is limited, and results in abundant fluvial sediment migration laterally, erosion and transport, forming laterally sandstone composite and aggradational deposit on the alluvial plain, which constitutes specific erosion unconformity boundary.     

Shimajiri Group equivalent sedimentary rocks dredged from sea knolls off Kume Island,central Ryukyus: Implications for timing and mode of rifting of the middle Okinawa Trough back-arc basin

The late Cenozoic geohistory of the Ryukyu arc is closely related to the rifting history of the Okinawa Trough. The submarine geology and stratigraphy of areas around Kume Island, which is situated near the eastern rifted margin of the middle Okinawa Trough, provide key constraints to understand the timing and mode of Okinawa Trough rifting. Here we report the lithology of sedimentary rocks dredged along slopes of ~1000-m-deep sea knolls located north and northwest off Kume Island, and their depositional ages determined by calcareous nannofossils and strontium (Sr) isotope analyses. Various types of sedimentary rocks, such as siltstone, very fine-grained sandstone, medium-grained sandstone, fossiliferous coarse-grained sandstone, and tuffaceous sandstone, were recovered at two dredge sites. These sedimentary rocks are lithologically similar to those in the Aka Formation and a part of the Maja Formation of the Shimajiri Group in nearby Kume Island. Calcareous nannofossils and Sr isotope analyses indicate their depositional ages from the early Pliocene to the early Pleistocene, which are generally consistent with those of the Aka Formation. The finding of the dredged rocks similar in lithology and ages to the Aka Formation indicates that marine deltaic area continued toward north and northwest from Kume Island during these periods. The presence of the Shimajiri Group equivalent sedimentary rocks at the dredge sites are likely related to the main rifting of the Okinawa Trough after ca. 2 Ma in the central Ryukyus.