Effects of diagenesis on the astrochronological approach of defining stratigraphic boundaries in calcareous rhythmites: The Tortonian GSSP

Since the establishment of astrochronology, calcareous rhythmites are frequently used as the basis of high‐resolution chronostratigraphy. In particular for the Neogene, calcareous rhythmites serve as stratotypes and for absolute dating of stratigraphic boundaries (Global Stratotype Sections and Points – GSSPs). However, the exact mechanisms responsible for the formation of the rhythmic intercalation of lithologies in such successions are complex and not easily reconstructed. To a large extent this is the effect of diagenetic modifications of the original sediment. Here, two examples of Neogene calcareous rhythmites are studied; the Monte dei Corvi section and the Monte Gibliscemi section. The first is the GSSP location of the Serravallian–Tortonian boundary, whereas the second is an auxiliary stratotype for the same boundary. During the past years, astrochronological approaches were applied to these successions to considerably increase time resolution compared to the elaborated biostratigraphic database. The present study focuses on micropetrographic, trace element and clay mineralogical methods in order to gain a better understanding of the genesis of the rhythmites. In the Monte Gibliscemi section, sediment parameters that are robust against diagenetic change clearly reflect primary differences, i.e. cyclical environmental changes. In contrast, no clear primary signal is determined for the Monte dei Corvi section on a couplet scale, leaving the origin of the rhythm ambiguous. This impedes the interpretation of the latter and the comparability between the two successions, and also compromises any bed‐by‐bed correlation between the two. The unclear origin of the rhythmites of Monte dei Corvi introduces uncertainty into the applicability of astrochronology to this succession.     

Fossil pollen grains of Asteraceae from the Miocene of Patagonia: Nassauviinae affinity

Fossil pollen grains with morphological features unique in the subtribe Nassauviinae (tribe Mutisieae, Asteraceae) occur in Miocene marine deposits of eastern Patagonia, southern South America. A new morphogenus and two morphospecies are proposed to assemble fossil pollen grains characterized by having a complex bilayered exine structure with delicate columellae, separated by an internal tectum. Subprolate specimens with Trixis exine type (ectosexine thinner than endosexine, straight internal tectum) are referred to Huanilipollis cabrerae. This species is similar to pollen of recent Holocheilus, Jungia, and Proustia. Suboblate specimens with Oxyphyllum exine type (ectosexine and endosexine equally thick, zigzag internal tectum) are referred to Huanilipollis criscii. This species is similar to pollen of recent Triptilion. The spore/pollen sequences in which Nassauviinae pollen types occur suggest a wide range of vegetation types varying from forest dominated during the Early Miocene (Chenque Formation) to virtually xerophytic ones during the Late Miocene (Puerto Madryn Formation). The subtribe Nassauviinae comprises 25 genera and ca. 320 species of vines, shrubs and low trees endemic to America with a wide range of ecological preferences; the nearest living relatives of the fossil types being mostly confined to humid landscapes. The unusual occurrence of these groups during the arid characterized Late Miocene time could be attributed to the complex interplay of the mountain uplift and global circulation patterns. These forcing factors would have created a mosaic of different habitats with both patches of forest and dry-adapted species developing in relatively small regions. This is the first fossil record of Nassauviinae and confirms that this subtribe of Asteraceae was already differentiated in the Miocene.     

FIRST RECORD OF THE INDO‐PACIFIC REEF CORAL GENUS ISOPORA IN THE CARIBBEAN REGION: TWO NEW SPECIES FROM THE NEOGENE OF CURAÇAO,NETHERLANDS ANTILLES

Abstract: The coral genus Isopora, a sister group of the modern dominant Acropora until now only known from the Pliocene to Recent of the Indo‐Pacific, is recorded in the Caribbean for the first time. Two new species, Isopora ginsburgi and Isopora curacaoensis, are described from the Neogene Seroe Domi Formation of Curaçao, Netherlands Antilles. Study of large collections made systematically through the sequence indicates that Isopora first occurred in the Caribbean during the Mio–Pliocene, at approximately the same time as the origination of many modern Caribbean reef coral dominants including Acropora cervicornis. It last occurred in the region during the late Pliocene as part of a pulse of extinction, in which several genera that live today in the Indo‐Pacific became extinct in the Caribbean. Throughout its Caribbean duration, Isopora co‐occurred with the two abundant modern Caribbean species of Acropora, A. cervicornis and A. palmata. Comparisons with Neogene collections made elsewhere in the Caribbean indicate that Isopora was restricted in distribution to the southern Caribbean. Isopora species are viviparous, while Acropora are oviparous, and this difference in reproductive strategy may have played a role in the extinction of Isopora in the Caribbean. The occurrences of Isopora reported in this study are the oldest records to date of Isopora worldwide, and are important for understanding the biogeographic separation between reef coral faunas in the Caribbean and Indo‐Pacific regions.     

埕岛地区中浅层河流相砂体输导性研究——以渤海海域埕岛地区新近系为例

河流相砂体是埕岛地区中浅层主要的油气输导层和储集层,研究其输导性对油气勘探具有重要意义。研究认为,断层相连是中浅层河流相砂体输导油气的前提,构造背景影响着油气输导方向;河道沉积砂体输导性最好,堤岸沉积砂体次之,泛滥平原沉积的砂体最差。不同岩性中细砂岩输导性最好,中砂岩次之,粉砂岩第三;输导砂体物性下限随着埋深增加而减少;砂体连通性越好,输导性越好。根据砂体宏观连通基本类型,建立了厚砂体直接连通型、微断层连通型和薄砂体或物性较差砂体连通型三种输导模式,并提出中浅层河流相砂体输导性的评价思路。     

阿尔金新近纪红黏土粒度特征及古气候记录

为反演阿尔金新近纪红黏土记录的古气候、古环境信息,在已有的磁性地层学约束基础之上对剖面的粒度指标进行了系统的分析,并利用粒度端元模型(EMM)进行分解。结果表明,可分为三个粒度端元:端元1(众数粒径5.2μm)众数粒径集中分布于2～6μm,与北太平洋西风带粒度分布和中国黄土细粒组分的粒度分布相似;端元2(众数粒径20μm)呈负偏态非对称分布,众数粒径在32～16μm之间,为低空西风所搬运短距离做跃移运动的粉尘物质;端元3为双主峰分布,众数粒径57μm和2.5μm,代表着尘暴事件中风动力近源变化强度,反映混合沉积特征。其中在10.8～10.3 Ma、8～6 Ma、5.2～4.3 Ma、3.6～2.8 Ma端元1粒度含量呈减小趋势,端元2粒度百分含量呈逐渐增加趋势,中值粒径增大。13～2.6 Ma阿尔金红黏土记录显示内陆干旱化加剧事件经历了10.8～10.3 Ma、8～6 Ma、5.2～4.3 Ma、3.6～2.8 Ma四个阶段,结合前人对该剖面及邻区其他地质环境记录研究表明,亚洲内陆干旱化可能的起始时间为11 Ma左右,西风环流在本区占主导地位。全球变冷是内陆干旱化加剧的主导要素,青藏高原的阶段性隆升起着推动作用。     

Ulmus harutoriensis Oishi et Huzioka角质层特征及古环境意义

根据大量室内实验分析，对产于云南腾冲的植物化石Ulmus harutorensis Oishi et Huzioka的角质层进行了细致研究，揭示了Ulmus harutoriensis叶的表皮构造，其主要特征为：上表皮厚1．1μm，下表皮厚小于1μm，上表皮细胞大于下表皮细胞、毛基少、气孔器很小、只在下表皮发育、无规则型、散生、下陷较浅，在此基础上结合其他资料推测了古气候变化，并与现生Umlus pumila L。同时进行了气孔密度和气孔指数的统计，用生物学的方法推测了古大气CO2浓度，讨论了Berner的碳平衡模型。     

新构造运动与渤海海域上第三系大型油气田

在影响渤海海域上第三系大型油气田形成的诸多因素中,上新世—全新世的新构造运动起到了关键作用。渤海湾盆地“向心式”的演化规律（沉降、沉积中心由周围防区向海域逐渐转移）以及晚第三纪以来盆地热流值的逐渐降低,使得海域的烃源岩生、排烃晚;上新世—全新世的新构造运动形成的众多上第三系圈闭为油气聚集提供了有利场所;大量晚期断层与控凹断层、不整合面及砂体相沟通,构成了油气运移的良好通道,并调整和控制了油气的最终成藏。依据构造位置和圈闭成因可将渤海上第三系油气藏划分为３种主要类型：凸起上的背斜型油气藏、凸起—凹陷边缘断阶带的滚动背斜型和断块型油气藏、凹陷中继承性构造和反转构造型油气藏。     

塔里木盆地西南坳陷上第三系沉积相特征

塔里木盆地西南坳陷晚第三纪为北缓南陡的"箕状"坳陷,沉积体北薄南厚,沉降中心与沉积中心发生明显的错位.其内沉积了一套厚度巨大的冲积-湖泊相碎屑沉积体,可识别出曲流河相、辫状河相、冲积扇相、曲流河三角洲相、辫状河三角洲相、扇三角洲相及湖泊相等7种相类型.坳陷西南缘广泛发育辫状河三角洲相,其特征显著,明显有别于扇三角洲相及曲流河三角洲相;曲流河相及曲流河三角洲相分布在东北缘,辫状河相、冲积扇相及扇三角洲相分布在西南缘.     

The radiation of the Cape flora, southern Africa

The flora of the south-western tip of southern Africa, the Cape flora, with some 9000 species in an area of 90,000 km2 is much more speciose than can be expected from its area or latitude, and is comparable to that expected from the most diverse equatorial areas. The endemism of almost 70%, on the other hand, is comparable to that found on islands. This high endemism is accounted for by the ecological and geographical isolation of the Cape Floristic Region, but explanations for the high species richness are not so easily found. The high species richness is accentuated when its taxonomic distribution is investigated: almost half of the total species richness of the area is accounted for by 33 'Cape floral clades'. These are clades which may have initially diversified in the region, and of which at least half the species are still found in the Cape Floristic Region. Such a high contribution by a very small number of clades is typical of island floras, not of mainland floras. The start of the radiation of these clades has been dated by molecular clock techniques to between 18 million years ago (Mya) (Pelargonium) and 8 Mya (Phylica), but only six radiations have been dated to date. The fossil evidence for the dating of the radiation is shown to be largely speculative. The Cenozoic environmental history of southern Africa is reviewed in search of possible triggers for the radiations, climatic changes emerge as the most likely candidate. Due to a very poor fossil record, the climatic history has to be inferred from larger scale patterns, these suggest large-scale fluctuations between summer wet (Palaeocene, Early Miocene) and summer dry climates (Oligocene, Middle Miocene to present). The massive speciation in the Cape flora might be accounted for by the diverse limitations to gene flow (dissected landscapes, pollinator specialisation, long flowering times allowing much phenological specialisation), as well as a richly complex environment providing a diversity of selective forces (geographically variable climate, much altitude variation, different soil types, rocky terrain providing many micro-niches, and regular fires providing both intermediate disturbances, as well as different ways of surviving the fires). However, much of this is based on correlation, and there is a great need for (a) experimental testing of the proposed speciation mechanisms, (b) more molecular clock estimates of the age and pattern of the radiations, and (c) more fossil evidence bearing on the past climates.     

Eocene-Pliocene time scale and stratigraphy of the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB)

We present a general stratigraphic synthesis for the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene times. The stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years ; an index of the stratigraphically most important localitites is provided. We distinguish 14 geographical areas from the Helvetic domain in the South to the Hanau Basin in the North. For each geographical area, we give a synthesis of the biostratigraphy, lithofacies, and chronostratigraphic ranges. The relationships between this stratigraphic record and the global sea-level changes are generally disturbed by the geodynamic (e.g., subsidence) evolution of the basins. However, global sea-level changes probably affected the dynamic of transgression–regression in the URG (e.g., Middle Pechelbronn Beds and Serie Grise corresponding with sea-level rise between Ru1/Ru2 and Ru2/Ru3 sequences, respectively) as well as in the Molasse basin (regression of the UMM corresponding with the sea-level drop at the Ch1 sequence). The URGENT-project (Upper Rhine Graben evolution and neotectonics) provided an unique opportunity to carry out and present this synthesis. Discussions with scientists addressing sedimentology, tectonics, geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution. Data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors (see Berger et al. in Int J Earth Sci 2005).