鄂尔多斯盆地东北部马五1+2亚段岩石类型及沉积环境

受多期岩溶叠合改造影响,鄂尔多斯盆地东北部奥陶系马五₁₊₂亚段的原岩组构遭受破坏,制约了对原始沉积环境及沉积相的恢复研究。基于岩芯、薄片及阴极发光研究,通过原岩组构恢复,在区内识别出5种主要的原始碳酸盐岩类型及7种成岩作用产物岩石类型,并总结出5种岩石类型组合,分别形成于局限-蒸发台地内的颗粒滩、滩间海、丘滩复合体、台坪和局限瀉湖沉积环境。纵向上可构成局限瀉湖-颗粒滩-台坪、局限瀉湖-丘滩复合体-台坪等4种典型的向上变浅沉积序列。结果表明,颗粒岩类与含膏模孔泥（粉）晶云岩类是盆地东北部马五₁₊₂亚段最主要的原始岩类,并发育有一定规模的藻黏结岩和泥晶云岩,其中含膏模孔泥（粉）晶云岩与丘、滩向上变浅序列密切相关。这些认识将为深化区内古环境和储集岩类研究提供依据。     

雷波马湖地区地质遗迹景观资源评价

雷波马湖地区地质遗迹景观资源发育典型、分布集中,主要包括马湖湖泊景观、湿地景观、地质灾害遗迹景观、岩溶景观等类型。本文对马湖地区主要遗迹资源进行了阐述,并对其突出价值进行了定性与定量评价,得出马湖地区有建立国家级地质公园实力的结论。     

鄂尔多斯盆地中东部奥陶系马家沟组马五6亚段硬石膏产状类型与成因*

鄂尔多斯盆地中东部奥陶系马家沟组马五₆亚段硬石膏产状类型多样,基于系统的宏观与微观岩石学分析,识别并区分出星散状(A1型)、纹层状(A2型)、致密块状(A3型)、结核状或团块状(A4型)、鸡雏状或角砾状(A5型)等硬石膏产状类型。单井高频旋回和微相分析表明,马五₆亚段发育与潮坪、潟湖、鲕粒滩、砂屑滩、微生物丘等有关的5种高频向上变浅序列,硬石膏的产状类型、产出位置和分布形式等与向上变浅序列有很好的耦合关系。A1型和A2型硬石膏发育于高频向上变浅序列的下部和中部,主要与膏云质或云膏质潟湖相关,属于潟湖相原生化学沉积成因。A3型硬石膏分布于高频向上变浅序列的上部,受膏质潟湖控制,也属于原生化学沉积成因。经典的结核状硬石膏(A4-1)呈随机分布形式产于潮坪沉积序列,为成岩期交代作用或者膏化作用成因,与传统萨布哈交代成因的膏质结核相似。A4-2型硬石膏主要出现在颗粒岩和微生物岩中,主要由富含CaSO₄的下渗卤水在溶蚀孔洞中沉淀形成;A5型硬石膏发育于向上变浅序列的上部和顶部,与高频暴露有关,为准同生期以溶蚀—充填为主的岩溶改造成因。发育完整的单个高频旋回,大致经历了高频快速海侵早期、高频快速海侵晚期至缓慢海退早期、高频缓慢海退晚期和高频海退末期暴露4个演化阶段,形成了与之耦合的海相碳酸盐岩与硬石膏共生序列。这些认识将对马家沟组沉积古环境的再认识具有重要的参考意义。     

U–Pb and fission‐track dating of a submarine pyroclastic rock from southwest Japan

The Okinoshima Formation crops out on Okinoshima Island and comprises a thick sequence (> 200 m) of pyroclastic rocks and alternating beds of sandstone and mudstone. Because Okinoshima Island is located between Honshu and Tsushima Island, the Okinoshima Formation potentially provides an important record of volcanism during the opening of the Japan Sea in northwest Kyushu, as well as a record of the formation of the present Genkai Sea region. In consideration of the lack of previous geochronological work, dating (fission‐track and U–Pb) of igneous zircons extracted from the Okinoshima Formation were undertaken and studied the clay mineral alteration in the pyroclastic material in order to reveal its thermal history. These data are used to constrain the age of the Okinoshima Formation and the present Genkai Sea region. Our results show that no thermal event has reset the fission‐track age after deposition of the pyroclastic rocks, and that the Okinoshima Formation was deposited at 16.2 Ma. The present Genkai Sea region is a deep‐sea basin, and its formation at 16.2 Ma was accompanied by submarine volcanism and rapid subsidence that marked the climactic stage of Japan Sea formation. After 16 Ma, the tectonic setting of the present Genkai Sea region changed from one of extension (related to the formation of the Japan Sea) to one of compression, with uplift occurring under the influence of the clockwise rotation of southwest Japan. Consequently, after 16 Ma the present Genkai Sea region became isolated from the forming processes of the Japan Sea.     

华北克拉通北部长城系底界年龄小于1670Ma:来自北京密云花岗斑岩岩脉锆石LA-MC-ICPMS U-Pb年龄的约束

近期在北京密云沙厂北东的大龙门村附近发现一条花岗斑岩岩脉,该岩脉侵入于新太古代密云群角闪斜长片麻岩当中,其顶部则与片麻岩一起被常州沟组含砾砂岩沉积不整合覆盖.对该岩脉采用LA-MC-ICPMS进行锆石U-Pb同位素年龄测定,获得了(1 673±10)Ma的侵位年龄.这表明华北北部的常州沟组底界(也即长城系的底界)年龄小...     

Palaeogeographic reconstruction of the 1.55 Ma synchronous isolation of the Ryukyu Islands,Japan, and Taiwan and inflow of the Kuroshio warm current

In the Quaternary, the Ryukyu Islands evolved from a continental margin arc to an island arc by backarc spreading of the Okinawa Trough, accompanied by subsidence and isolation of the islands, a process that has continued to the present. Trough-parallel half grabens were filled with marine siltstone. Similar sediments filling orthogonal fault-controlled and west-draining non-tectonic valleys record island separation. New Quaternary nannofossil biostratigraphic data date the deposition of the marine siltstone at 1.552 ± 0.154 Ma. At that time, the entire 1000 km-long island chain comprising the Ryukyu Islands separated from the Asian continent by rifting extending from the Okinawa Trough to the Tsushima Strait. The Tokara, Kerama, and Yonaguni gaps, branched or transverse rifts of the Okinawa Trough, separate the island chain into subgroups of the Osumi, Amami, Okinawa, and Yaeyama islands, and Taiwan. The shallow Taiwan Strait separated Taiwan from the Chinese mainland. The Kuroshio warm current that previously ran offshore of the continental margin arc began to enter the opening backarc basin through the Yonaguni gap and to exit through the Tokara gap, flowing along the axis of the Okinawa Trough. Under influence of the warm current and because of entrapment of continentally sourced detrital sediments by the Okinawa Trough, coral reefs formed around each island. These reefs make up a unit called the Ryukyu limestone. Subsidence continued through the deposition of this limestone, resulting in further isolation of each island. Some islands did not separate from the mainland but emerged above sea level later as a result of volcanic edifice construction or forearc uplift. Following initial isolation, the Japanese islands and Taiwan may have been connected to the mainland by land bridges during some sea level low stands related to glacial periods, whereas the other islands remained isolated. Based on ages of isolation of each island, a Quaternary palaeogeographic map and ‘phylogenetic tree’ of the islands can be drawn showing the separation time of each island from the mainland and from each other. This information should be useful for phylogenetic molecular biologists studying evolution of Ryukyu endemic species and vicariant speciation and could facilitate analysis of the DNA substitution rate.     

华北克拉通南缘洛峪群-汝阳群属于中元古界长城系——河南汝州洛峪口组层凝灰岩锆石LA—MC-ICPMSU—Pb年龄的直接约束

运用LA—MC—ICPMS方法,对河南汝州阳坡村附近洛峪口组中部层凝灰岩夹层开展了锆石U-Pb同位素年代学研究,获得了1611±8Ma的高精度年龄。这一年龄第一次精确标定了该地区洛峪口组的形成时限,并显示该组顶界应接近1600Ma。由于洛峪口组位于华北克拉通南缘原划归“新元古界青白口系”洛峪群的最顶部,洛峪群又覆于“中元古界蓟县系”汝阳群之上,因此,这一新的年代学进展实际上同时也将洛峪群和汝阳群都下压到了中元古界长城系,并将洛峪群顶界限定为该地区长城系与蓟县系分界。结合区域资料,特别是熊耳群（下伏于汝阳群）火山岩近年来的年代学标定（多集中于1750～1780Ma）,可初步将该地区汝阳群一洛峪群的形成年代限定为1750～1600Ma之间,对应于国际固结纪（Statherian。1800～1600Ma）即中国长城纪中晚期。华北南缘洛峪口组形成年龄的直接约束及相关地层划分的重新厘定,为中元古代华北克拉通南北缘的准确对比及其与哥伦比亚超大陆关系、早期生命演化等重大地学命题提供了新的重要的年代学证据。     

西宁黄土堆积记录的最近13万年高原季风气候变化

青藏高原对于大气的热力和动力作用形成了高原季风气候现象.青藏高原东北部西宁盆地位于高原季风控制区,末次间冰期以来的黄土堆积记录了高原季风气候变化过程.对西宁盆地湟水阶地上的黄土堆积进行了地貌观查、地层对比和探槽及探井采样,完成了热释光和光释光测年,测量了古地磁定向样品以及磁化率、频率磁化率、CaCO3含量和粒度等古气候代用指标.结果表明,西宁黄土堆积记录的高原夏季风环流在相当于深海氧同位素阶段5e特别强,在5a和5c阶段接近于阶段3.高原夏季风和冬季风变化存在位相差以及冬季风强的时候夏季风不一定弱,夏季风弱的时候冬季风不一定强的变化模式.     

长庆气田靖边区北部奥陶系马五1储层难采储量区块综合评价

鄂尔多斯盆地长庆气田靖边区北部奥陶系马五1储层天然气藏因春开采难度较大，被称之为难采区，然其难采程度不一致，且存在较大差异，通过分析天然气难采主控因素－产能的高低及分布状况，进一步了解影响产能的沉积－成岩微相特征、储集物性、岩溶古地貌等因素，将难采程度分为最难采、难采、较难采3类，建立评价标准，并对研究区难采储量区块进行综合评价。     

五十万年来毛乌素沙漠的变迁

对沙漠-黄土边界带的古风成砂-黄土-古土壤序列的研究表明，毛乌素沙漠至少在0.5MaB.P.就已出现，但也并非从其出现之初就持续至今。沙漠-黄土边界带的风成沉积所记录的沙丘活化和固定的多次转变是第四纪时期毛乌素沙漠对气候振荡响应的结果。五十万年来，沙漠-黄土边界带的石峁剖面记录了13层古风成砂，代表了13次沙漠大规模的南侵。沙漠的南侵不仅可以发生在冰期鼎盛之时，同样也可以发生在间冰期中的寒冷气候幕出现之时。此外，鉴于沙漠-黄土边界带具有气候敏感性的特点，石峁剖面的地层记录还表明了第四纪时期不仅有冷期与暖期的多次旋回，而且冷期和暖期发生时还有次一级的气候波动。