Sedimentary characteristics and seismic geomorphology of gravity-flow channels in a rift basin: Oligocene Shahejie Formation,Qinan Slope,Huanghua Depression of Bohai Bay Basin,China     

《Marine and Petroleum Geology》2016

Deep-water gravity-flow sandstones are important hydrocarbon exploration and production targets in the Bohai Bay Basin, a Paleogene intra-continental rift basin in eastern China. In this paper, the seismic-sedimentology techniques are used to characterize, in plan view, the temporal and spatial evolution of a gravity-flow-channel complex of the Paleogene Shahejie Formation (Es) on the Qinan faulted-monoslope (Qinan Slope), Bohai Bay Basin. The results show that two or three gravity-flow channels, 9–12 km long and 0.5–2 km wide, were successively developed in later Es (Es1z–Es1s). The channels initially experienced westward migration and then shifted eastward. The corresponding wireline logs of the channel-fill sequences mainly present blocky-shaped or bell-like configurations, whereas their seismic profile features are characterized by strong amplitude reflections, such as U-shaped, plate-like, spindle-shaped and lenticular configurations.The syndepositional activity of three normal faults, i.e., the Nandagang Fault to the northwest, the Zhangbei Fault to the northeast and the Zhaobei Fault to the east led to gradient changes of the Qinan Slope, which have controlled the plan morphology (width, curvature, and bifurcation) of the gravity-flow channels. In the medium-late period of Es1z, triggered by intensive faulting on the three faults, the gradient of the Qinan Slope was steepened abruptly, resulting in an increase of flow velocity and erosion amplitude to underlying deposits. As a result, channels exhibiting narrow and straight configurations in plan view were formed. During the stage of early Es1z and Es1s, tectonic activity intensity was relatively low and the gradient of the Qinan Slope was gentle, so channels with great width and curvature were bifurcated and merged downstream.Comparison of the faulting amplitude of the three syndepositional faults suggests that the Nandagang and Zhaobei faults were inversely strengthened in the Es1z and Es1s. The Nandagang Fault to the west was found to be more active than the Zhaobei Fault to the east in the Es1z stage. This condition was reversed in Es1s. For that reason, the channels migrated to the west in the Es1z stage and then went back to the east during Es1s.Core analysis shows that the channel fills are mainly composed of sandy-debrites, slumps and turbidites. Among them, sandy debrites dominate deposition in terms of reservoir volume and hydrocarbon potential. These units primarily consist of sandstones and gravel-bearing sandstones, with bed thicknesses ranging from 10 to 40 m, an average porosity of 11% and a permeability of 25 mD. Being mostly encased in organic-rich dark mudstones, these sandy debrites are significant hydrocarbon exploration targets.The results of this study are not only useful to the hydrocarbon exploration and development planning for the Qinan Slope, but also helpful when considering other faulted-depressions in the Bohai Bay Basin and other intra-continent rifted basins around the world, particularly in terms of gravity-flow hydrocarbon exploration and research.  相似文献   

兰州盆地永登剖面晚古新世—早渐新世沉积物中粘土矿物的特征及其古气候指示意义     

邓焰平  洪汉烈  殷科  徐耀明  杜鹃  张克信 《现代地质》2010,24(4)

采用X射线衍射、扫描电镜分析方法,对兰州盆地永登剖面晚古新世—早渐新世沉积物中粘土矿物的相对含量、伊利石结晶度、显微形貌及其古气候意义进行深入研究。结果表明:晚古新世—早渐新世沉积物中粘土矿物主要为伊利石、蒙脱石、绿泥石和少量的坡缕石,其中伊利石的含量最高,而且从晚古新世到早渐新世,沉积物中伊利石的含量呈明显升高的趋势,蒙脱石则呈明显减少的趋势;在大约55 Ma处伊利石含量急剧减小,而蒙脱石含量急剧增大。此外,可见到毛发状的自生坡缕石沿蒙脱石晶片边缘交代生长,而碎屑成因的坡缕石则主要呈破碎的短棒状。粘土矿物分布特征表明,兰州盆地晚古新世—早渐新世的古气候以干旱为主导,并且经历了由相对温暖湿润到半干旱半湿润或干旱炎热的转变,这种气候转型主要受全球气候的影响,即受行星风系的控制;而在大约55 Ma处伊利石、蒙脱石的含量变化则记录了全球性的PETM事件。  相似文献   

Palaeointensity results from Ethiopian basalts: implications for the Oligocene geomagnetic field strength     

Janna Riisager  Mireille Perrin  & Pierre Rochette 《Geophysical Journal International》1999,138(2):590-596

From a large collection of Ethiopian flood basalts (~30  Myr old) sampled for magnetostratigraphy, ⁴⁰Ar/³⁹Ar geochronology and geochemical investigations, 47 samples were selected in order to test their suitability for Thellier palaeointensity experiments. Only 17 samples from eight individual flows yielded reliable palaeointensity estimates, with flow-mean virtual dipole moments ranging from 3.0 to 10.5 × 10²²  A  m² .
  A critical review of the Oligocene palaeointensity data set, including these new Ethiopian data, indicates an Oligocene mean virtual dipole moment of 5.1 ± 2.5 × 10²²  A  m² for the complete data set. After applying mild selection criteria, the reduced data set yields a mean value of only 4.6 ± 1.9 × 10²²  A  m² . This value is significantly lower than the present-day field strength but is higher than the Mesozoic dipole low mean field. This low Oligocene field might be in agreement with the high palaeosecular variation and rather high non-dipole field invoked around 30  Ma. However, the Oligocene data set is largely dependent on the palaeointensity determinations from Armenia, obtained mainly from baked contacts, which show amazingly low dispersion at both flow and between-flow levels. More data are needed to reduce the weight of these determinations on the mean value and avoid a possible bias.  相似文献   

伦坡拉盆地西部丁青湖组新发现凝灰岩锆石U- Pb年龄及其地层学意义   总被引：1，自引：0，他引：1  

曾胜强  王剑  陈文彬  付修根  孙伟  李金锋  刘君豪 《地质学报》2020,94(8):2354-2366

伦坡拉盆地丁青湖组沉积时代的确定对于研究青藏高原中部的古高度和古气候具有重要的地质意义,但由于没有精确的年龄数据,其顶部是否跨入了新近系,一直以来都存在争论。作者在伦坡拉盆地西部鄂加卒地区开展野外调查过程中,在该剖面中部和上部新发现两套凝灰岩夹层,对凝灰岩进行了LA-ICP-MS锆石U-Pb定年,获得了两件凝灰岩样品的形成年龄分别为24.05±0.24Ma(MSWD=1.07,n=24)和22.64±0.33Ma(MSWD=0.45,n=17),时代分别为晚渐新世和早中新世。根据凝灰岩锆石U-Pb年龄和前人研究成果,将鄂加卒剖面的细碎屑岩地层重新厘定为丁青湖组,并将丁青湖组的沉积时代定为渐新世-中中新世。根据丁青湖组地层厚度及沉积速率估算,该组沉积持续时间在21～23Ma之间,其顶部地层的年龄在11～13Ma左右。由此可见,伦坡拉盆地接受连续沉积一直持续到了中中新世,这比过去普遍认识的晚始新世-渐新世时期青藏高原中部的古高度和古气候变化时间更晚。前人在该地区发现的近无角犀化石、攀鲈鱼化石、棕榈科叶片化石以及孢粉化石等研究结果共同证实,青藏高原中部渐新世晚期的古海拔高度低于～2500～3000 m。因此,该区晚渐新世-早中新世温暖潮湿的气候特征很可能是受到了印度洋气流穿透的影响,而且该影响可能一直持续到了中中新世,从而造就了该时期青藏高原生物的多样性。  相似文献   

西藏伦坡拉盆地晚始新世—早渐新世黏土矿物特征及古气候意义     

路畅  夏国清  陈云  吴劲宣  包万铖  樊秋爽  石柱  郝夏炜 《沉积与特提斯地质》2023,43(3):565-579

始新世—渐新世是新生代气候从“温室”向“冰室”转变的重要节点，也是青藏高原及邻区气候格局发生重大变革的关键时期。为了重建高原中部腹地始新世—渐新世的古气候演变特征，探讨古气候变化的控制因素，利用X射线衍射分析对高原中部伦坡拉盆地382道班剖面的黏土矿物特征进行了综合研究，结果显示，伦坡拉盆地在始新世—渐新世牛堡组二段沉积的黏土矿物主要以伊利石为主，伊/蒙混层次之，高岭石与绿泥石含量极少，蒙脱石仅出现在极少样品中。黏土矿物类型及组合特征指示伦坡拉盆地在该时期整体处于寒冷干旱的气候条件，但在长周期趋势下伊利石相对含量逐渐减少，伊/蒙混层逐渐增多，显示出青藏高原中部地区的气候系统在晚始新世—早渐新世时期存在向更加湿润的气候条件转变，这种气候系统的改变可能与南亚季风在晚始新世的演化所带来的更多水汽条件和青藏高原中部中央分水岭的形成有关，但在始新世与渐新世之交，伊利石含量陡然增多，而伊/蒙混层含量则减少，且两者频繁波动，这反映了该盆地在EOT时期受到全球降温的影响。  相似文献   

阜新盆地中北部新生代辉绿岩侵入特征及其对烃源岩的影响     

吴彦佳  贾建亮  秦建义  王晓明 《地质学报》2022,96(3):1026-1040

阜新盆地中北部白垩纪沉积地层中侵入岩广泛发育.该区域侵入岩岩石学特征和空间展布规律与其形成时代,以及侵入岩带来的异常高温对烃源岩生烃演化的影响仍不明确.本文通过岩石学、地球物理测井、有机地球化学、同位素年代学等方法,探讨阜新盆地中北部新生代辉绿岩侵入特征及其油气地质意义.结果表明,研究区内侵入岩主要为辉绿岩,其主要矿物...  相似文献