Quaternary seismic facies of the atlantic continental rise

High-resolution seismic profiles collected by Parasound and SES-2000 deep profilers during Cruise 26 of the R/V Akademik Sergei Vavilov (2009) along the continental slope base of South America, NW Africa, and West Europe are correlated with the deep-sea drilling boreholes. Lithofacies interpretation of the Quaternary deep-water seismic facies of hemipelagites, bottom current deposits (contourites), and gravitites (turbidites, mud flow deposits) is presented. The data obtained reveal the domination of contourites in the accumulation of continental rise apron under conditions of relatively scarce terrigenous material supply. It is shown that acoustically stratified seismic facies under these conditions commonly reflect interbedding of the terrigenous clay and biogenic calcareous ooze related to the Pleistocene glacial/interglacial cycles.     

Contribution of mineralogical and geochemical data to the study of northeast atlantic deep quaternary sediments: trace-elements as bottom-current indicators

Geochemical and mineralogical study of sixty cores from the northeast Atlantic Ocean used various analyses by X-ray diffraction and fluorescence spectrometry. Thus, we know the clay mineral, carbonate, quartz, feldspar, and trace-element content of the Quaternary sediments from the last interglacial period. These data have been treated in two ways: (1) analysis of the geographical distribution of the components calculated on a carbonate free basis; and (2) statistical analysis establishing the correlation coefficient that exists between the lithological supports and chemical elements.Thus, genetic groups are defined and are correlated to their original sources. For example, smectite-FeTi group is associated with Iceland; feldspar-NiCu with the Faeroe Islands; Illite-Chlorite-RbPb to acidic continental provinces; and SrCaCO₃ to plankton (pàrtially).The lithological supports (smectite, feldspar, carbonate, etc.) are scattered by currents, since chemical elements are associated with them, having a high degree of correlation, it should be possible to utilize these elements as paleohydrologic tracers.     

基于地震相分析的孔隙度预测

这里主要讨论在地震相分析下的孔隙度预测。其基本原理是：首先对研究区块进行前期常规解释（合成记录、层位追踪、构造及断层解释）,在此基础上利用地震相分析技术,并结合测井及岩芯资料对研究区进行沉积相带划分,将地震信息转化为地质信息;然后根据相带划分结果,对单一相带中的密度、声波速度与孔隙度井资料进行统计,拟合获得相关最好的波阻抗与孔隙度关系公式,这样多个相带就有不同的孔隙度计算公式;最后通过反演得到的波阻抗计算获得孔隙度。由于在横向上加入了地质解释,所以通过这种方法能够有效结合地质规律,提高三维孔隙度预测精度,还能更好地进行孔隙流体预测及储层评价。     

地震相分析技术在煤田地震勘探中的应用

地震相分析技术日渐成为煤田岩性地震勘探的一门新技术。阐述了基于波形分类的地震相分析方法,通过人工神经网络地震相检测技术对不同的波形进行分类,达到区分不同目标体的目的。以圈定火成岩发育范围、预测煤层冲刷变薄带和识别断层、陷落柱等地质异常体为例,讨论了地震相分析技术在煤田岩性地震勘探方面的效果。     

A wavelet-based multifractal analysis of seismic data for facies identification. Application on the pilot KTB borehole

The main goal of this paper is to identify reflection from seismic data using the multifractal formalism. Firstly, the wavelet transform modulus maxima lines method is applied with a sliding window of 128 samples at the seismic seismogram data. After that, we estimate the generalized fractal dimension. Application at the noisy synthetic seismic seismogram of the pilot Kontinentales Tiefbohrprogramm de Bundesreplik Deutschland borehole shows that the three fractal dimensions related to the three first moments are a good tool that can separate between reflection dues to the change of facies and random noise.     

Crustal structure of Japan as derived from explosion seismic data

Crustal structures of Japan were investigated under the Upper Mantle Project in three profiles, Kurayosi-Hanabusa, western Japan; Atumi-Noto, central Japan; Kesennuma-Oga, northeastern Japan. These investigations have revealed that the crust of Japan is of continental type. The variation of the crustal structure reflects the topography, especially the water depth; so the thinning of the crust occurs near the shore where the water depth increases rapidly. The velocity below the Mohorovi?i? discontinuity is smaller than 8.0 km/sec, but it is possible that a deeper layer with a velocity of over 8.0 km/sec may exist. The basaltic layer in central Japan, if existing at all, must be thin.     

A three-dimensional crustal model of southwest Germany derived from seismic refraction data

From densely covered seismic refraction data obtained in 1978 (Urach experiment) and 1984 (“Schwarzer Zollern-Wald” experiment) and from seismic reflection data and results from previous refraction investigations, a three-dimensional crustal model of southwest Germany was derived. Travel-time and amplitude information of seismic refraction data were interpreted with two-dimensional forward modeling (ray tracing) to calculate two crustal cross sections in southwest Germany. These results fill a gap in the existing data and enabled the construction of a detailed three-dimensional crustal model.While seismically the upper crust is laterally homogeneous (5.9–6.0 km/s) throughout the area, the middle and lower crust show pronounced lateral variations in thickness, velocity, and reflectivity. The Moho is a flat surface at a relatively shallow depth (25–26 km). We classify the middle and lower crust of southwest Germany into two characteristic crustal types. Type I consists of a mid-crustal low-velocity zone (5.4–5.8 km/s) overlying a thick (> 10 km), high-velocity (6.6–6.8 km/s) lower crust. Type II has no prominent mid-crustal low-velocity zone, and a thin (< 10 km), low-velocity (6.3–6.4 km/s) lower crust. The crustal types correlate with the major geologic units exposed in the area: Type I is present beneath the Black Forest, forming the eastern flank of the Rhinegraben and beneath the Swabian Jura, while Type II is present beneath the intervening Triassic sediments. Beneath the South German Molasse Basin, a low-velocity zone is also present in the upper middle-crust. Seismic reflection investigations have shown that the lower crust in southwest Germany comprises a stack of layers of alternating high- and low-velocities. The lateral variation of the reflectivity of this laminated lower crust has been recognized even on refraction data. We found that high-reflectivity of the lower crust correlates to high average velocity (6.7–6.8 km/s) in the lower crust (Type I). Thus, the average velocity of the lower crust in southwest Germany seems to be an indicator of the intensity of its lamination. The uppermost mantle has a velocity of 8.3 km/s in the area and a strong, positive velocity gradient.     

地震相分析技术在滨里海盆地AS油田沉积相分析中的应用

针对滨里海AS地区的勘探开发目标层系,运用人工神经网络和主组分分析等技术和方法,对研究区的地震反射波形变化特征及其反映的地质特征进行识别和分类,得到地震相图,应用主要地震相单元中单井相分析成果建立地震相与沉积相的对应关系,将地震相转化为沉积相.该方法弥补了单纯用钻井资料进行沉积相划分的缺陷,提高了沉积相划分精度.     

New finds of older quaternary mollusks in sediments of the Black Sea

Doklady Earth Sciences -     

Mollusks from the lower quaternary Chauda sediments of the Black Sea

The analysis of paleontological remains in many samples from the Lower Quaternary Chauda sediments drilled and cored on the Bulgarian shelf of the Black Sea revealed widespread mollusks of the genera Didacna and Dreissena (Didacna tschaudae guriana, D. tschaudae, D. pleistopleura, D. crassa guriensis, Dreissena rostriformis tschaudae, D. rostriformis abchasica) accompanied by reworked Neogene representatives of the genus Digressodacna. In numerous places of a continental slope and an adjacent deep-sea depressions near Crimea and Caucasus the similar mollusc assemblage is described in the redeposited state for the first time. The composition of palynological spectra and diatom assemblages in shelf sediments indicates climate changes during the Chaudan period. The Chaudan mollusk fauna from the Black Sea sediments, which is lacking Caspian Bakuan species characteristic of the Chauda stratotype, is compositionally close to the mollusk assemblage from basal layers of the Chauda Horizon in the Guriya area of Georgia (“Gurian” Chauda). These data imply repeated changes in the level of the Chaudan basin between present-day isobaths of −30...−50 to −140 m.     

南黄海盆地北部坳陷白垩系地震相分析

在数千公里地震剖面解释基础上,选用频率、振幅、连续性及内部反射结构等4个地震参数,采用“构形 结构 振幅 频率 连续性”的地震相复合命名原则,总结出南黄海盆地北部坳陷白垩系近10种地震相单元,5种沉积相类型。沉积特征分析表明,在没有钻井揭示的白垩系中、下部,其油气潜力有可能比泰州组更加可观,是很好的烃源岩。钻井资料也表明白垩系具有生、聚油过程,这进一步说明白垩系中、下部的生烃潜力。中、新生界的数套物性较好的储、盖层和众多与油气大规模运移时间匹配良好的构造圈闭,使白垩系成为南黄海盆地找油的首要对象。     

Paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic

We first re-examined the apparent polar wander curves for stable Eurasia and Africa since the Triassic. These curves were then combined together with curves of North and South America according to the kinematics of the Atlantic ocean and a synthetic polar wander curve was given. Then, most of the paleomagnetic results from the Tethys mobile belt, from the Atlantic to the Pamirs, were analysed.Several groups of plates, microplates and blocks can be seen. First, relatively stable regions like Maghreb and Sicily, which have not moved much. Then we have a group formed by Iberia, Sardinia, Italy and, to a lesser extent, Corsica and the Western and Central Alps. For these blocks, movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of Africa, but they are sometimes stronger.To the east, a major change takes place. The north of the Aegean Sea and the Ionian zone are clockwise rotated and these rotations are recent: Oligocene-Miocene for the first part, Pliocene to the present for the second part.A major problem arises in Turkey, Caucasus and Iran. Paleomagnetic results indicate a position far to the south of Eurasia, and, at the same time, geological evidence is in favour of a position close to Eurasia. We discuss these discrepancies.     

Reconnaissance of quaternary sediments from Khasi Hills,Meghalaya

Khasi Hills area of Meghalaya, one of the highest rainfall zones of the world has been explored to understand the spatial and temporal extent of Quaternary sediments. In general such deposits are restricted to shallow depths in most of the sites except in one site where it is 600 cm thick. AMS C-14 dates of these deposits suggest that sediments deposited are mostly of Holocene or in rare cases belong to later part of Pleistocene. Early Quaternary deposit is either missing or yet to be explored from this region. Natural hazards combined with human activity effecting degradation of vegetation and sediment cover are probably the main cause for poor Quaternary exposure at the region.     

New results on palaeoenvironmental conditions in equatorial Africa derived from alluvial sediments of Cameroonian rivers

The ReSaKo project undertook extended fieldwork across southern Cameroon to explore the palaeoenvironmental information recorded in the alluvial sediments of equatorial African rivers. 160 hand-corings reaching maximum depths of 550 cm were carried out on alluvial ridges and floodplains of major Cameroonian fluvial systems. These multilayered, sandy to clayey alluvia contain sedimentary form-units and palaeosurfaces, which provide excellent additional proxy data archives for the reconstruction of palaeoenvironmental conditions in western equatorial Africa. Coring transects and sedimentary profiles document grain-size shifts and distinguishable sedimentary units in the stratigraphic record, which evidence (fluvial-)morphological adjustments of the fluvial systems in response to external forcing and (river-) intrinsic variability. 76 ¹⁴C-(AMS)-dated samples from organic sediment and macro-rests (fossil organic remains like wood, leafs, etc.) embedded in these sedimentary units indicate Late Pleistocene to recent ages (uncalibrated ¹⁴C-ages: 48–0.2 ka BP). The tentative interpretation of the alluvial record yields excellent additional information on the complex feedbacks between climate, ocean, fluvial as well as ecological systems and human activity in a little-studied region with high sensitive tropical ecosystems. δ¹³C-values (?35.5 to ?18.0‰) of the dated samples indicate the persistence of C₃-dominated gallery forests across the rivers (‘fluvial rain forest refuges’) despite several climatic fluctuations (aridifications, e.g. Last Glacial Maximum around 20 ka BP, Younger Dryas 13–11 ka BP). This research complements earlier results from additional terrestrial and marine proxy data archives on the Late Quaternary history of monsoonal western equatorial Africa.     

吐鲁番-哈密盆地胜北(SB)地区中上侏罗统地震相与沉积相分析

选用频率、振幅、连续性及内部反射结构 4个地震参数 ,对吐鲁番—哈密盆地SB(胜北 )地区中上侏罗统主要层系进行了地震相分析 ,作出了地震相平面分布图。经过综合解释 ,把地震相转换成了沉积相。该区中晚侏罗世主要发育冲积扇、泛滥平原、扇三角洲、辫状河三角洲及湖泊沉积。     

地震沉积学在川东北YB地区沉积相分析中的应用

将地震沉积学理论应用于川东北YB地区陆相须家河组二段沉积相分析。以低频层序界面为约束条件,采用三维地震相位展开技术建立高频层序地层格架;利用三维Wheeler变换技术自动拉平高分辨层序地层格架的地震同相轴,建立等时年代地层格架,将地震数据体转换为年代地层数据体;在此基础上,提取具有等时意义的年代地层切片进行沉积相分析。结果表明:该方法能直观地反映沉积体的几何形态、展布规律、纵向演化和平面变迁等特征,对后续的勘探开发具有指导意义。     

Upper quaternary laminated sapropelic sediments from the continental slope of Baja California

Core MD02-2508 retrieved from the plateau of the continental slope off Baja California recovered a 40-m-thick section of sapropel (up to 15% C_org), calcareous clay, and diatom ooze with the age of 120 ka at the core bottom. The section is subdivided into three units: Unit I (Holocene) consists of the laminated sapropel; Unit II comprising oxygen isotope stages (MIS) 2, 3, and 4 is represented by homogeneous calcareous clay with interbeds of slightly siliceous sapropelic mud; and Unit III (MIS-5) is composed of laminated sapropelic diatom ooze. Laminated intervals are characterized by the intercalation of two lamina types: (1) dark-colored organic-rich laminae containing multi-species “oceanic” diatom assemblages, as well as radiolarians, coccoliths, planktonic and benthic foraminifera; (2) lighter-colored laminae consisting of diatom ooze with the neritic colonial diatom assemblages commonly composed of one to three species of a single genera. The dark laminae are assumed to be generated within a high productivity zone over the slope, whereas light ones likely represent diatom mats produced by short-term boisterous phytoplankton blooms, possibly in the coastal upwelling.     

New data on the most ancient early quaternary glaciation in Gornyi Altai

The data presented in this work introduce substantial corrections into the Upper Cenozoic stratigraphy and geological history of Gornyi Altai. They provide evidence for the most ancient Early Pleistocene glaciation in this region. This follows from finds of faceted boulders buried in the Bashkaus Formation. Pale-omagnetic investigations revealed in the latter a wide zone of negative polarity corresponding to the Matuyama Chron in the magnetostratigraphic scale and made it possible to correlate the formation with the Lower Pleistocene in the standard stratigraphic scale. It is shown that global cooling at the beginning of the Quaternary Period stimulated development of glaciation on the southern slope of the Kuraiskii Range exceeding in size its present-day scale.     

Wavefield analysis of crosswell seismic data

Despite the numerous advantages of crosswell seismic data over surface seismic data, crosswell seismic geophysics is still underutilized and underdeveloped. The factors limiting the full utilization of crosswell data include the lack of standardized methods for processing and imaging the data. This is because crosswell data is not completely understood. To improve the understanding of crosswell data, we performed acoustic and elastic modeling of a west Texas carbonate oilfield data using finite difference methods and crosswell geometry. To account for the different wave modes in the field data, we decomposed the full data into its constituent wave modes. Results of the forward modeling show that elastic synthetic data is a better representation of crosswell field data than the popular acoustic synthetic data. Wavefield decomposition gave insight into the time-space kinematics behavior of the different wave modes that constitute the full data. Overall, the study improved our understanding of crosswell field data. The learning from this study has been utilized to perform data-driven reflection enhancement processing where the discerned characteristic of different seismic arrival is utilize to suppress unwanted and enhanced the desired wave modes. The processing reduced the complex data to only up-going P-P reflections that can be imaged to reveal the subtle geological structures of the oilfield.