Grooves and striations on the Stanthorpe Adamellite: Evidence for a possible late Middle ‐ Late Triassic age glaciation

Evidence for glacial erosion of competent intrusive igneous rock is described for sites at Quart Pot Creek, Stanthorpe, Queensland. The bedrock, comprising the Stanthorpe Adamellite, was emplaced during the Early‐Middle Triassic. It is argued that the pluton was exposed during the late Middle ‐ Late Triassic and subjected to glacial erosion at that time. This was consequent to the rapid uplift and denudation of the landscape, which accompanied the Hunter‐Bowen Orogeny. Burial of the eroded surface occurred most probably during that ice age and a subsequent period of subsidence. The ancient surface has been exhumed during more recent denudation. It is suggested that during the late Middle ‐ Late Triassic, climatic conditions remained cold enough over this part of southeastern Australia at least for valley glaciers to form and influence landscape development.     

Tertiary coal geology and stratigraphy of the Port Phillip Basin,Victoria

Results from coal‐exploration drilling in the onshore part of the Port Phillip Basin, Victoria, have established stratigraphic and age correlations of the Lower Miocene Werribee Formation brown coal deposits at Bacchus Marsh to similar brown coals at Altona. The coal deposits occur in a northwest‐southeast structural depression (the Parwan Trough) that appears to be a southeast continuation of the Ballan Graben. Recent drilling for potential coal‐bed methane in the trough has provided new data on the deeper stratigraphy not penetrated by earlier drilling, including recognition of an Upper Cretaceous to Eocene Yaloak Formation coal‐bearing interval, similar to the Anglesea area, Ballan Graben and Lal Lal Basin. Up to 200 m of coal‐bearing sediment and minor volcanics underlie the Miocene coal measures. A marine facies transition takes place between the Miocene coal swamps of the Parwan Trough, through barrier sands west of Werribee, to carbonate facies near Geelong. To the south beneath Port Phillip Bay, a similar transition probably occurs between coal swamps of the Parwan Trough and fully marine carbonate environments of the contiguous Sorrento Graben. The palaeogeographical reconstructions suggest a similar coal‐to‐carbonate facies transition as in the adjacent onshore Gippsland Basin.     

140OΜα前的后生动物实体化石?

本文首次报道了在我国豫西晚前寒武系白草坪组中发现的一种可能的蠕虫状后生动物实体化石:Ruyangia Cylindrica Hu et Meng,1989。化石产于砂岩表面浪成波痕之波谷中,圆筒状,已压扁,中空,可见长度4.5～9.5cm,直径4mm左右,虫体外壁具体环,环背间距1.5～2mm,虫体一端较大,具平行纵向边缘的纵纹,可能为头部;另一端渐尖,可能为尾部。与该实体化石伴生的有大量遗迹化石。已知白草坪组的时代超过1400Ma,因此,该实体化石的发现对研究地球上后生动物起源与早期演化等具重要意义。     

Evidence for an Hesperian-aged South Circum-Polar Lake Margin Environment on Mars

A broad pitted plain and an elongated low rise occur near the south pole of Mars between a region of major cavi (Cavi Angusti) and a regionally smooth and broad valley (Argentea Planum). Viking, Mars Global Surveyor (MGS), and Odyssey data reveal a densely pitted plain covering ∼6750 km², and containing >300 irregularly shaped, steep-walled and flat-floored depressions with a mean diameter of ∼3.5 km. At the southernmost (poleward) extent of this plain are 12 north/south trending linear valleys that are characterized by theater-shaped heads abutting a major cavi within Cavi Angusti. The pitted plain, which abuts Cavi Angusti to the southwest, is separated from the floor of Argentea Planum by a smooth, elongated low rise that extends parallel to the plain for ∼200 km. These unusual features are all found within the Hesperian-aged circumpolar Dorsa Argentea Formation, which has been interpreted by some workers to be an ice-rich glacier-related deposit. We interpret the pitted plain to represent the maximum northern extent of the Angusti lobe ice deposit. The pits are analogous in morphology and distribution to terrestrial kettle holes, which form from the melting of isolated ice-blocks surrounded and partly buried by sediment, to leave hollows. The linear valleys are consistent with sapping valleys formed from the release of an elevated groundwater table, fed by meltwater lakes. On the basis of these characteristics, relationships and analogs, we interpret the marginal facies to represent an ice-sheet/lake contact environment that existed during Hesperian time.     

Ginkgo from Lower Cretaceous Changcai Formation in Helong of Jilin, NE China

Based on gross morphological and cuticular study, two species of Ginkgo From the Lower Cretaceous Changcai Formation in Helong of Jilin. were identified from this area for the first time, including Ginkgo coriacea Florin and G. sibirica Heer. The study is significant for better understanding the paleophytogeographic, paleoecologic and stratigraphic characters of the Early Cretaceous Changcai flora.     

黄骅坳陷孔南地区孔二段湖盆结构恢复

孔南地区孔二段受到沧东断层、徐西断层等活动影响,地层结构遭受强烈的改造,原有湖盆结构发生了很大的变化。隆起区构造单元富泥质沉积,凹陷构造单元富砂质沉积,成为研究区孔二段的主要特征之一,也成为研究的难点。本文通过对研究区孔二段沉积厚度、岩相、沉积相、构造分析以及等时地层格架下的沉积体系展布规律分析等,对孔二段沉积时期湖盆结构进行了恢复,改变了以往认为孔店期为断陷产物的认识,得出孔二段沉积时期,湖盆总体为坳陷盆地,现今处于盆地中心的孔店隆起构造带为孔二期的古湖盆中心和沉降中心。这一结论对认识黄骅坳陷孔南地区盆地演化,成因机制和油气勘探具有重要的意义。     

山东东营凹陷新生代天文地层表简介

综合山东东营凹陷郝科1等6口井的天文地层研究结果提出"东营凹陷新生代天文地层表",表中列出的是"国际地层表(2004)"、"中国区域年代地层表(2000)"和0—65Ma期间天文偏心率405ka周期编号以及东营凹陷孔店组(顶部)至平原组各组的年龄以及东营凹陷新生代51Ma以来3个大的地层不整合:1)沙河街组二段下部,大约33.8—33.4Ma期间405ka周期振幅不明显、100ka周期较强,与南大西洋33.4—33.7Ma和热带太平洋33.6—33.7Ma期间沉积物中显著转折等特征可作对比;2)东营组-馆陶组界线上下,东营组三角洲顶面最后萎缩时间约为24.467Ma,推测由此至渐新世末(23.03Ma),大约近1.5Myr期间本区没有大的湖泊,而是冲积—河流相沉积,中新世初(23.03Ma)快速隆起,直到约18—16Ma开始馆下段的上部沉积,这一区域性角度不整合面形成大约持续5—7Myr;3)上新统-更新统界线上下,根据本区东辛2-4井古地磁和天文地层研究,测出布容、松山、高斯和吉尔伯特等4个极性时,求出2.546Ma—1.806Ma期间[明上(上)亚段顶]可能沉积并剥蚀过的地层厚度为129m;1.806—0.908Ma期间,因构造活动本区上升成为高山,第四系平一段底部形成了大的不整合面。     

山东济阳坳陷始新统-渐新统天文地层界线年龄分析

山东济阳坳陷沙河街组上部天文地层研究是以牛38井沙三段中亚段顶界年龄34.892Ma作为标定,分析和计算出沙二段下亚段底年龄为33.799Ma、沙段二段上亚段底为33.338Ma、沙一段底为32.940Ma和东营组底为31.829Ma。从天文地层界线年龄分析,沙三段-沙二段界线的年龄大致可对比为"国际地层表(2004)"始新统-渐新统界线年龄33.90Ma,而沙二段下亚段-上亚段界线年龄比国际始新统-渐新统界线的滞后大约600ka。在"中国区域地层表"始新统-渐新统界线年龄(32Ma)和"国际地层表"的始新统-渐新统界线年龄(33.9Ma)之差的1.9Myr,大致相当于本区计算的沙一、二段的持续时间。SP数据的小波分析表明,在沙二段-沙三上亚段界线附近,即约33.8Ma之后,约405ka周期开始变得不明显、不规则,幅度亦下降,剧烈突变发生时间在33.4Ma左右。上述界线对应偏心率周期的理论值突变的时间。因此推论始新世-渐新世转折期是偏心率多个理论周期重迭而导致的一个特殊的时期,也是本区沙二段下亚段这段地层形成不整合面的时间,大约在33.8—33.4Ma期间。     

Cretaceous–Tertiary geology of the Gangdese Arc in the Linzhou area, southern Tibet

Knowledge of the Cretaceous–Tertiary history of upper crustal shortening and magmatism in Tibet is fundamental to placing constraints on when and how the Tibetan plateau formed. In the Lhasa terrane of southern Tibet, the widely exposed angular unconformity beneath uppermost Cretaceous–lower Tertiary volcanic-bearing strata of the Linzizong Formation provides an excellent geologic and time marker to distinguish between deformation that occurred before vs. during the Indo-Asian collision. In the Linzhou area, located  30 km north of the city of Lhasa, a > 3-km-thick section of the Linzizong Formation lies unconformably on Cretaceous and older rocks that were shortened by both northward- and southward-verging structures during the Late Cretaceous. The Linzizong Formation dips northward in the footwall of a north-dipping thrust system that involves Triassic–Jurassic strata and a granite intrusion in the hanging wall. U–Pb zircon geochronologic studies show that the Linzizong Formation ranges in age from 69 Ma to at least 47 Ma and that the hanging wall granite intrusion crystallized at  52 Ma, coeval with dike emplacement into footwall Cretaceous strata. ⁴⁰Ar/³⁹Ar thermochronologic studies suggest slow cooling of the granite between 49 and 42 Ma, followed by an episode of accelerated cooling to upper crustal levels beginning at  42 Ma. The onset of rapid cooling was coeval with the cessation of voluminous arc magmatism in southern Tibet and is interpreted be a consequence of either (1) Tertiary thrusting in this region or (2) regional rock uplift and erosion following removal of overthickened Gangdese arc lower crust and upper mantle or break-off of the Neo-Tethyan oceanic slab.     

成冰纪全球冰期事件的环境效应研究进展

成冰纪全球冰期是地球历史上最极端的冰室气候事件,冰川作用波及赤道区域,全球可能都遭受了冰封,海洋广泛缺氧,生物演化进程迟滞。然而,冰期结束之后,大气氧浓度迅速升高,海洋发生逐步氧化,大型带刺疑源类和真核多细胞藻类在埃迪卡拉纪开始繁盛,出现最早的动物,地表生物圈发生了翻天覆地的变化。显然,成冰纪全球冰期事件是地球系统演化的重要转折。认识冰期的环境效应是认识埃迪卡拉纪生物演化的关键,也是打开地表宜居环境演化的钥匙。本文总结了近年来成冰纪全球冰期的气候假说、冰期沉积特征、海洋氧化还原条件及冰期后的大气与海洋环境剧变等方面的研究进展,简要分析了全球冰期研究中存在的问题,并对该领域未来研究提出了展望与建议。