Birth of Interior Drainages of the Northwestern Tibet Plateau     

ZHAO Yue  LIU Jian  LI Dunpeng  PEI unling 《《地质学报》英文版》2013,87(Z1):108-108

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Capybaras (Rodentia,Hydrochoeridae, Hydrochoerinae) and their bearing in the calibration of the late Miocene–Pliocene sequences of South America     

《Journal of South American Earth Sciences》2013

Fossil capybaras were long regarded as composed of numerous taxa, each one endemic to a particular area, a scenario completely different from the one shown by the living species. The interpretation of the record according to new criteria of ontogenetic change has demonstrated that they are useful for biocorrelation because their members have short biochrons with wide geographic distribution. The levels with capybaras of each locality would represent a short lapse within the bearing lithostratigraphic units. In turn, they would also represent short intervals within the temporal extension proposed for each Stage/Age or SALMA. All the late Miocene–Pliocene records of capybaras were analyzed and a chronological scheme was built mainly for Argentina, where records are most abundant. Numerical ages and magnetostratigraphic studies contribute to correlate this scheme with the global time scale. The Chasicoan SALMA would be correlated with part of the Tortonian Stage/Age; the Huayquerian SALMA with the late Tortonian-Messinian, and it could even extend to the earliest Zanclean. The Montehermosan SALMA would be restricted to the Zanclean. The Chapadmalalan SALMA would be correlated with the late Zanclean-early Piacenzian.  相似文献   

Pliocene basin-floor fan sedimentation in the Bay of Bengal (offshore northwest Myanmar)     

《Marine and Petroleum Geology》2014

This study addresses reservoir development and hydrocarbon occurrence of the late Pliocene basin-floor fan deposits in the northeastern Bay of Bengal. The G-series turbiditic sandstones host dry gases, biogenic in origin, of three gas fields that are juxtaposed on the western flank of the NW–SE anticline. The gas reservoirs are stacked in back-stepping fashion being sourced from northwest as part of the Bengal fan. The Shwe field (Shwe fan) has an elongate fan-shaped morphology (12 km long and 4 km wide) and occurs about 30 km off the base of slope.The Shwe field reservoirs consist of two contrasting types of turbidite deposits, lower G5.2 and upper G3.2 reservoirs. The G5.2 is characterized by stacked lobe elements in which amalgamated and layered sheet sandstones provide an excellent vertical connectivity and high net-to-gross ratio (avg. 86%). On the contrary, the G3.2 represents overbank deposits, which is characterized by thin-bedded sandstones with low net-to-gross ratio (avg. 33%) as well as low-resistivity pays.Aside from the primary depositional framework, post-depositional modifications appear to have greatly affected Shwe fan, adding complexity in establishing a geological model. A line of evidence suggests that G5.2 lobe sands were injected into overlying G3.2, mostly in the form of sills. The injected sand beds measured from G3.2 cores account for 10 m, more than half of the total net sand. The sand injection is thought to be triggered by slumping that overpressured G5.2 lobes. Post-G3.2 erosional channel complexes incised into G5.2 and G3.2, ultimately diminishing gas pool extent as well as dividing Shwe fan into multiple compartments.  相似文献   

Oligocene to Lower Pliocene deposits of the Norwegian continental shelf,Norwegian Sea,Svalbard, Denmark and their relation to the uplift of Fennoscandia: A synthesis     

《Marine and Petroleum Geology》2014

This study provides the results of the first integrated study of Oligocene–Pliocene basins around Norway.Within the study area, three main depocentres have been identified where sandy sediments accumulated throughout the Oligocene to Early Pliocene period. The depocentre in the Norwegian–Danish Basin received sediments from the southern Scandes Mountains, with a general progradation from north to south during the studied period. The depocentre in the basinal areas of the UK and Norwegian sectors of the North Sea north of 58°N received sediments from the Scotland–Shetland area. Because of the sedimentary infilling there was a gradual shallowing of the northern North Sea basin in the Oligocene and Miocene. A smaller depocentre is identified offshore northern Nordland between Ranafjorden (approximately 66°N) and Vesterålen (approximately 68°N) where the northern Scandes Mountains were the source of the Oligocene to Early Pliocene sediments. In other local depocentres along the west coast of Norway, sandy sedimentation occurred in only parts of the period. Shifts in local depocentres are indicative of changes in the paleogeography in the source areas.In the Barents Sea and south to approximately 68°N, the Oligocene to Early Pliocene section is eroded except for distal fine-grained and biogenic deposits along the western margin and on the oceanic crust. This margin was undergoing deformation in a strike-slip regime until the Eocene–Oligocene transition. The Early Oligocene sediments dated in the Vestbakken Volcanic Province and the Forlandssundet Basin represent the termination of this strike-slip regime.The change in the plate tectonic regime at the Eocene–Oligocene transition affected mainly the northern part of the study area, and was followed by a quiet tectonic period until the Middle Miocene, when large compressional dome and basin structures were formed in the Norwegian Sea. The Middle Miocene event is correlated with a relative fall in sea level in the main depocentres in the North Sea, formation of a large delta in the Viking Graben (Frigg area) and uplift of the North and South Scandes domes. In the Norwegian–Danish Basin, the Sorgenfrei-Tornquist Zone was reactivated in the Early Miocene, possibly causing a shift in the deltaic progradation towards the east. A Late Pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2.7 Ma when the Scandes Mountains were strongly eroded and became a major source of sediments for the Norwegian shelf, whilst the Frigg delta prograded farther to the northeast.  相似文献   

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

Ryo Imai  Tokiyuki Sato  Yasufumi Iryu 《Island Arc》2013,22(4):522-537

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).  相似文献   

滇西道街盆地上新世怒江埋藏砾石层、堰塞湖沉积 的发现及其磁性地层学     

赵希涛  仝亚博  吴中海  叶培盛  胡道功 《地质通报》2012,31(203):227-234

在对怒江道街—惠通桥段的考察研究中,不仅重新厘定了河谷中拔河150m以下的多级低阶地,而且在拔河180～380m的高度上发现了多级由磨圆良好、成分复杂的厚层冲积砾石层所组成的高阶地,厚近100m的堰塞湖成因的砂层及其下伏厚约100m的砾石层。冲积层的同位素年龄测定结果表明,6级低阶地形成于中更新世以来。望江楼剖面的磁性地层研究结果显示,组成相当于第九级阶地上部的湖相砂层,上部以正向极性为主,含2次短期的负极性,下部则为负极性。与标准磁性地层柱对比表明,该湖相地层形成于4.2～2.6MaBP的中—晚上新世,湖相地层之下的埋藏阶地与高阶地则应形成于上新世早期至中新世晚期。据此在进一步的区域地层对比后认为：怒江至少在中新世的中晚期已开始形成并下切,至上新世早期已下切至现今河床附近。上述研究结果为更科学地认识青藏高原东缘的强烈隆升过程提供了非常有价值的新线索。  相似文献   

滇西腾冲地区龙川江河谷上新世火山岩SHRIMP 锆石U-Pb年龄及其地球化学特征   总被引：4，自引：1，他引：3  

石玉若  吴中海  范桃园  仝亚博  杨振宇 《地质通报》2012,31(203):241-249

报道了应用SHRIMP技术测定云南腾冲地区龙川江河谷附近上新世粗面安山岩和粗面岩的年龄结果。该区粗面安山岩与粗面岩的喷发时代接近,形成时代为2.81Ma±0.11Ma,属上新世。该区火山岩具高钾钙碱性的特点,富集大离子亲石元素、稀土元素和高场强元素（如Zr、Th、Hf）的特征明显不同于典型的岛弧钙碱性火山岩,而与遭受地壳混染的软流圈源大陆玄武岩相类似,是在板内拉张环境下地幔岩浆混染了大量下地壳物质的产物。  相似文献   

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     

Ritoko Kikunaga  Ke-han Song  Shun Chiyonobu  Kazuhiko Fujita  Ryuichi Shinjo  Kyoko Okino 《Island Arc》2021,30(1):e12425

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.  相似文献   

On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk     

R.G. Dixon 《Proceedings of the Geologists' Association. Geologists' Association》2005,116(2):139-142

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昆明滇池盆地新近纪象类化石     

胡绍锦 《云南地质》2005,24(3):321-327

记述滇池盆地含煤层中首次发现的上新世剑齿象化石,包括脊棱齿象属的一个新种昆明脊棱齿象(Stegolophodon kunm ingensissp..nov.)、似元谋剑齿象(Stegodonaff.yuan-m ouensis)、玉溪剑齿象、师氏剑齿象等。这一剑齿象化石组合的发现,对研究新生代象类和滇池盆地的演化史,重新划分盆地煤系地层具有重要意义。  相似文献