Composition and provenance of the Upper Cretaceous to Eocene sandstones in Central Palawan, Philippines: Constraints on the tectonic development of Palawan

Abstract Sandstones from the Upper Cretaceous to Eocene succession of Central Palawan are rich in quartz grains and acidic volcanic rock fragments. Potassium feldspar grains and granitic rock fragments are commonly observed. The moderate to high SiO₂ and low FeO plus MgO contents of the sandstones support the proposal that clasts were derived from a continental source region. Southern China (Kwangtung and Fukien regions) is inferred to be the source area of the sandstones. The sedimentary facies of the Upper Cretaceous to Eocene succession consist of turbidite and sandstones, suggesting that they were deposited in the deep sea portions of submarine-fans and basin plains situated along a continental margin. These features indicate that the Upper Cretaceous to Eocene succession of the Central Palawan were derived and drifted from the southern margin of China. The tectonic history related to the formation of Palawan Island is also discussed.     

TECTONIC EVOLUTION OF THE EOCENE DROSH-VOLCANO-SEDIMENTARY BASIN IN NW-KOHISTAN ISLAND ARC TERRANE, HINDUKUSH, N. PAKISTAN

In NW Himalayas, the suture zone between the collided Indian and the Karakoram plates is occupied by crust of the Cretaceous Kohistan Island\|Arc Terrane [1] . Late Cretaceous (about 90Ma) accretion with the southern margin of the Karakoram Plate at the site of the Shyok Suture Zone turned Kohistan to become an Andean\|type margin. The Neotethys was completely subducted at the southern margin of Kohistan by Early Tertiary, leading to collision between Kohistan and continental crust of the Indian plate at the site of the Main mantle thrust.More than 80% of the Kohistan terrane comprises plutonic rocks of (1) ultramafic to gabbroic composition forming the basal crust of the intra\|oceanic stage of the island arc, and (2) tonalite\|granodiorite\|granite composition belong to the Kohistan Batholith occupying much of the intermediate to shallow crust of the terrane mostly intruded in the Andean\|type margin stage [2] . Both these stages of subduction\|related magmatism were associated with volcanic and sedimentary rocks formed in Late Cretaceous and Early Tertiary basins. This study addresses tectonic configuration of Early Tertiary Drosh basin exposed in NW parts of the Kohistan terrane, immediately to the south of the Shyok Suture Zone.     

pH的量传体系及其观测仪器的计量标准

本文主要介绍了有关ｐＨ标度、国家ｐＨ基准和ｐＨ工作标准的建立方法、标准缓冲溶液的配置与保存方法以及ｐＨ的量值传递体系。由于海洋现场ｐＨ观测仪器在测量原理和计量标准等方面与常规实验室ｐＨ计室完全相同,因而只要采用国家ｐＨ计量标准和合理的计量检定方法对仪器进行校准检定,便可以使观测量值溯源到国家基准,从而海洋调查资料达到准确一致的目的。另外,本文作者还阐述了实验室ｐＨ主的计量检定方法,提出了对现场观测     

Higher plant biomarker signatures of Early Eocene sediments of North Eastern India

The biomarkers, molecular fossils of paleobiota, have been studied in detail from a coal-bearing sequence of Early Eocene Lakadong sandstone member of Sylhet Formation of Upper Assam Basin, NE India, using gas chromatography–mass spectrometry. Corresponding hydrocarbon source potential of the same unit has been studied using Rock-Eval pyrolysis. The Rock-Eval data suggest dominant terrestrial land plant contribution, i.e., Type III kerogen and the sediments of the section had entered the early stage of catagenesis. The alkane and isoprenoid distributions are characterized by odd over even preference (OEP) (1.1–1.2) of n-alkanes and high pristane/phytane ratio (2.9–7.6) which corroborate the Rock-Eval data. The distribution of aliphatic biomarkers is characterized by dominance of C₂₄ tetracyclics over C₂₃ tricyclics, high concentration of des-E hopane, moderate to high C₂₉/C₃₀ hopane ratio, extremely low oleanane index and low C₃₅ homohopane index. The extremely low oleanane index is correlated with a high degree of aromatization of oleanane skeleton, favoured by acidic swampy depositional environment. The presence of diterpanes at the base of the Early Eocene section indicates contribution from gymnosperms (Coniferales order of land plants) whereas angiospermous biomarkers with oleanoid skeleton are also preserved. This pattern subsequently evolved to angiosperm dominated towards the top of the section with no gymnosperm signature indicating possible climatic variation during the Early Eocene. Towards the top of the section presence of bicadinanes indicates contribution of Dipterocarpaceae family of trees and advent of the evergreen tropical rain forest element in eastern India in Early Eocene, similar to the pattern found in western India, e.g., Cambay and Kutch basins.     

Slab partial melts from the metasomatizing agent to adakite,Tafresh Eocene volcanic rocks,Iran

Geochemical and mineralogical characteristics of the Eocene volcanic succession in Tafresh area of the Urumieh–Dokhtar Magmatic Assemblage (UDMA) are unique in the 2000‐km‐length assemblage. Demonstrating rather steep rare earth element (REE) patterns and the widespread presence of amphibole (+biotite) phenocrysts are two distinct characters that dominate the Eocene volcanic succession of mainly andesitic composition. Coincidence of the geochemical and mineralogical characteristics of the whole volcanic succession with adakites, rather amphibole‐ (+biotite) rich dacitic (with 61–64 wt% SiO₂) stocks and dykes, is considered as the key in unraveling the role of ‘slab‐derived melt contribution’ in petrogenesis of the volcanic succession. Slab‐derived melting has been an ongoing process that metasomatized some parts of the mantle wedge from which hybrid rocks (andesites) are derived. Basalts with distinct signatures of slab melt metasomatism are yet another support for the occurrence of slab melting. Interlayering of normal, island‐arc‐type calc‐alkaline volcanic rocks with the slab‐melt metasomatized basalts and hybrid andesites suggests that the slab melting has been motivated by the subduction. Formation of the Tafresh Caldera, the likely consequence of an explosive eruption, is compatible with the volatile‐bearing nature of the adakitic volcanism in the study area. It is indicated by the ubiquitous presence of the hydrous minerals. Beneath the Tafresh area, in Eocene time, the subducting slab seems to have reached a critical high depth that is enough for the development of amphibolite–eclogite. The slab deformation, motivated by the geometry of subduction and/or the underlying mantle's steeper geotherms, is suggested to have resulted in the slab melting that helped develop a rock assemblage unique to the UDMA.     

Paleogene carbon isotope excursions in the Bunkers Hill borehole: Hampshire Basin, UK

This study demonstrates that the Bunkers Hill borehole, which is located within the Hampshire Basin, contains a carbon isotope excursion (CIE) in the Upnor Formation followed by a positive recovery from another CIE within the overlying Reading Formation. This study has also shown that the CIE in the Upnor Formation predates the Paleocene/Eocene Thermal Maximum (PETM), while the carbon isotope recovery at the base of the Reading Formation is most likely related to it. The positive carbon isotope trend, before a return to more negative values, seen throughout the majority of the Reading Formation can also be seen in coeval deposits in the Jubilee 404T borehole in the London Basin and in the Tienen Formation in the Doel and Kallo boreholes from the Belgium Basin. This indicates that this post-PETM carbon isotope signal may, therefore, be regional if not global in nature.     

Shark and ray faunas in the Middle and Late Eocene of the Fayum Area, Egypt

The Eocene rocks exposed in the Fayum Area, Egypt, are well known for their fossil vertebrates but in recent times the sharks and rays have been largely neglected. Extensive surface collecting, supplemented with bulk samples, has produced large collections from the Midawara, Gehannam, Birket Qarun and Qasr el-Sagha formations, spanning the Bartonian and Priabonian stages and from palaeoenvironments varying from open muddy shelf to very shallow estuarine systems. In total about 90 species of sharks and rays are recorded, many of them previously unrecognised, resulting in some of the most diverse fossil chondrichthyan assemblages known from the Tertiary. Teeth of these species suggest that they occupied a wide range of ecological niches from top predator to tiny benthic invertebrate feeder to planktivore. Many of the species are limited in their stratigraphical range and show potential to be used, at least locally, as biostratigraphical indicators for stratigraphically poorly constrained vertebrate sites elsewhere in North Africa. Distinctly different faunas from different sedimentary environments indicate a strong environmental control on the distribution of many species.     

湖北江陵凹陷深层高温富钾卤水特征及其成因探讨

江汉盆地江陵凹陷深处赋存高温富钾卤水,含卤地层主要是古新统沙市组。富钾卤水的分布受持续的继承性沉降中心(洼陷)、沙市组含盐系、石盐-硫酸盐沉积相的控制,聚集在砂岩、玄武岩、辉绿岩和白云岩等孔隙-裂隙内,裂隙的发育又与局部构造(背斜、盐构造等)枢纽部共轭裂隙带有关。古新世,盐湖已经蒸发浓缩到钙芒硝-石盐阶段,可能短暂达到硫酸镁盐和硫酸钾镁盐阶段。以后,原生的晶间卤水在成岩后期受到玄武岩侵入和高温流体影响,发生变质作用、去镁和去硫酸根作用,同时带入丰富的钾、铷、铯等元素,最后形成了高温富钾卤水。这种成矿过程可称为地下热事件激发成矿机制,值得进一步探讨。     

云南丽江古近纪风成沉积的发现及其气候意义

云南丽江地区宝相寺组（E2b）下部（原美乐组）一直被认为是水成沉积,本文认为其属于风成沉积。宝相寺组下部巨厚砂岩的主体岩性为紫红色中细粒石英砂岩,不含泥质和云母等悬移质,大型高角度平板状交错层理发育,厚度巨大,风成沙丘前积层特征明显。石英砂的磨圆度高,在电子显微镜下普遍可见风成砂所特有的碟形撞击坑、新月型撞击坑及毛玻璃化表面等特征,可能为沙漠风成沙丘沉积。研究区古近纪以来的沉积特征表明,青藏高原东部的气候经历了一个由干旱到潮湿的重大转变。推测这种气候转变可能是始新世、渐新世之交全球变冷变干事件（EOGM）在青藏高原东部的沉积响应,也可能与青藏高原初次快速隆升及东亚古季风的开始形成有关。     

昌潍坳陷潍北凹陷孔二段优质烃源岩成因与分布

昌潍坳陷潍北凹陷烃源岩分布在孔二段(即始新统孔店组二段),包括暗色泥岩、灰质泥岩和油页岩3种类型,前人对灰质泥岩和油页岩的生烃贡献未进行深入研究。利用有机地球化学方法结合热模拟实验对潍北凹陷各种类型烃源岩品质进行分析,研究表明油页岩和灰质泥岩有机质丰度较高、干酪根类型主要为Ⅰ型和Ⅱ1型,为优质烃源岩;暗色泥岩有机质类型和丰度较差,基本为无效烃源岩。优质烃源岩集中分布在孔二上亚段下部和孔二中亚段上部的油页岩和灰质泥岩中,平面上分布在瓦城断阶带东部和灶户鼻状构造带,与已发现油气藏具有良好的对应性。古生物学标志、古盐度及古氧相分析表明孔二段烃源岩形成于内陆咸化湖泊沉积环境。郯庐断裂带左—右旋转换期构造活动强度较弱和晚古新世到早始新世期间发生的大陆分离事件造成的温暖湿润气候促成了优质烃源岩的发育。