有关辽东五行山群“水母化石”的讨论

辽东五行山群的“水母化石”(以下简称“化石”)是刘桂芝1974年冬首先发现的。后经邢裕盛、刘桂芝(1979)以及段吉业、林蔚兴(1980)的研究、描述并发表。 澳大利亚M. F. Glaessner到化石产地进行考察后认为,五行山群的“水母化石”乃是气体逃逸或水渗漏形成的构造而非水母化石¹⁾。这引起国内地质界的广泛注意。 1981年9月,笔者实地考察了五行山群“水母化石”产地,采集了标本,进行了观察研究。并观察了沈阳地矿所和辽宁省地质局科研队的丰富标本和薄片,得到了较深刻的认识。     

2018年5月28日中国吉林松原M5.7级地震引起的液化构造*

2018年5月28日,吉林松原市宁江区毛都站镇牙木吐村发生M5.7级地震(45°16'12″N,124°42'35″E),震源深度13 km,震中位于郯庐断裂带西北侧的扶余/松原—肇东断裂带、第二松花江断裂带和扶余北断裂带交汇处。地震诱发震中距3 km范围内普遍的液化和地表裂缝,给当地居民带来严重灾害。可见液化构造以砂火山为主,其次为液化砂堆、液化砂脉和液化砂席等。液化砂火山又可分为有火山口型砂火山、无火山口型砂火山和无砂型(水)火山。地震液化伴生软沉积物变形构造有变形层理、负载构造和火焰构造、滑塌褶皱、碟状构造和包卷层理等。地震诱发液化砂火山形成过程包括液化层内超孔隙流体压力形成、上覆低渗透层破裂和水、砂喷出地表后砂涌3个阶段。液化和流化砂体在上涌过程中会注入低渗透黏土层形成各种形态的砂脉、砂席和多种类型的变形构造。垂向上地震液化结构可划分为底部松散可液化层、下部液化变形层、上部液化变形层和地表砂火山4层结构。液化层埋深2~5 m,液化层厚度2 m。松原M5.7级地震发震机制为NE-SW(35°~215°)方向挤压应力使断层活跃,推测扶余/松原—肇东断裂是主要的发震断层。松原地震液化构造研究为现代地震活动区和灾害易发区预测提供依据,为地震引发的现代软沉积物变形构造研究提供丰富的素材,兼具将今论古意义,为揭示本世纪以来郯庐断裂带北段进入了一个强断裂和地震活跃阶段提供了最新的实际资料。     

Collapsing volcanoes: the sleeping giants' threat

Dormant volcanoes are typically thought of as relatively safe environments to live around. However, under certain geological conditions, such volcanoes can be prone to collapse and may generate massive rockslide avalanches reaching tens of kilometres from the volcano.     

Forecasting volcanic events: some contemporary issues

As the regions around active volcanoes succumb to large increases in population, particularly in the developing world where most of the high-risk volcanoes are located, the threat posed by eruptions becomes increasingly serious. Improvements in eruption forecasting are critical to combat this situation, for reducing injury and loss of life, and for minimizing the detrimental effects to local economies and to the fabric of society. Better-constrained forecasts are strongly dependent on geophysical and other data gathered during a program of volcano surveillance, and we reveal how, if interpreted in terms of static rock fracturing, analysis of changes in volcanic seismicity and ground deformation may be used to forecast more accurately the onset of eruptive activity. As illustrated by recent events at several volcanoes, studies of previous activity, increased levels of monitoring, and improved training of scientists are also all crucial to improving forecasts of impending eruptions.     

Types and internal hydro-geomorphologic variability of mallines (wet-meadows) of Patagonia: Emphasis on volcanic plateaus

“Mallines” (wet-meadows) are Patagonian ecosystems that provide hydrological, biological and scenic resources. They develop in landscape locations that are favourable for water concentration. The area of each “mallín” is usually limited to a few, tens, or hundreds of hectares at most, but independently of their size, they present high variability in their internal physiographic characteristics. These are reflected on the vegetation distribution that basically responds to the space and time water distribution in the “mallín”, both at the surface as well as across the soil profile.We analyze the internal variability of a “mallín type” and present a conceptual map that illustrates the functional relationships established between four basic elements: geomorphology, hydrology, soils and vegetation, whose interrelationships allowed the differentiation of various situations, which may correspond both to different “mallines” and to subunits within the same “mallín”.     

On radon emanation as a possible indicator of crustal deformation

Radon emanation has been monitored in shallow capped holes by a Tracketch method along several active faults and in the vicinity of some volcanoes and underground nuclear explosions. The measured emanation shows large temporal variations that appear to be partly related to crustal strain changes. This paper proposes a model that may explain the observed tectonic variations in radon emanation, and explores the possibility of using radon emanation as an indicator of crustal deformation. In this model the emanation variation is assumed to be due to the perturbation of near-surface profile of radon concentration in the soil gas caused by a change in the vertical flow rate of the soil gas which, in turn, is caused by the crustal deformation. It is shown that, for a typical soil, a small change in the flow rate (3 · 10⁻⁴ cm sec⁻¹) can effect a significant change (a factor of 2) in radon emanation detected at a fixed shallow depth (0.7 m). The radon concentration profile has been monitored at several depths at a selected site to test the model. The results appear to be in satisfactory agreement.     

伊通火山群地区“白土山组”地层研究新进展

近十几年来 ,随着同位素地质年代学的发展 ,伊通火山群地区新生代地层断代问题的研究取得了突破性的进展 ,对重新厘定过去东北泛称下更新统“白土山组”地层的年代找到了突破口。通过火山岩年龄的测定、火山岩与“白土山组”接触关系及孢粉组合的研究 ,确认伊通火山岩群地区的“白土山组”的地质时代为新近纪中新世 ,与松辽平原中心的“白土山组”时代不同。     

Simulating active volcanoes

The problem with trying to understand how active volcanoes such as Mount Etna work is that we cannot see what is going on inside them. We can try to get around the difficulty by examining the exposed interiors of ancient volcanoes and by utilizing geophysical techniques that allow us to monitor subterranean magma behaviour by recording associated ground deformation, locating thermal anomalies and monitoring seismic tremors. In conjunction with this geophysical work, we can simulate the internal 'plumbing' of an active volcano using that common culinary aid, gelatine     

印度洋北部马克兰增生楔泥火山分布及主控因素探讨

为了探讨低角度俯冲背景下活动大陆边缘泥火山的分布及其主控因素,收集了大量印度洋北部马克兰增生楔地区的沉积地层、断裂构造及泥火山或泥底辟等资料。综合分析结果显示,研究区沉积地层主要由上、下两部分组成,其中,下部较细的半远洋泥质地层具有“东厚西薄”的特征,而上部较粗的马克兰砂地层具有高速沉积的特征。这种密度倒置且后期沉积速率很高的地层分布特征为该区泥底辟或泥火山的形成提供了物质基础。在马克兰增生楔,阿拉伯板块向欧亚板块汇聚的速率具有“东快西慢”的特点,而且东、西两侧走滑断层和泥火山发育。结合俯冲角度同样较低的地中海海岭板块汇聚速率与泥火山的分布特征认为,马克兰增生楔东、西两侧的泥火山主要受走滑断层的控制,而增生楔内部的泥火山主要受板块汇聚速率、逆冲断裂以及密度倒置等综合因素的控制,表现为“东多西少”的特征。     

Tectonically significant pebble types: Sheared,pocked and second-cycle examples

A history of repeated faulting, within an area, can be obtained from unconformity analysis or sediment-vector sequences (not treated in the present paper) or from studies of gravel tongues. The latter may include sheared pebbles, pocked pebbles, half-rounds, and second-cycle (or multi-cycle) pebbles. Sheared pebbles (and larger fragments) were cut by faulting after deposition, hence represent two episodes of deformation. Pocked pebbles (scarred pebbles) were ground against each other, after deposition, by a second episode. Sheared and pocked pebbles typically develop where sand matrix is not abundant; single pebbles “floating” in sandstone rarely show these features. Quartz sand schist is a fine-grained equivalent of the sheared-pebble gravel or conglomerate. Half-rounds represent transportation of sheared pebbles, after shearing; where half-rounds have been sheared, at least three episodes of deformation are indicated.A second-cycle conglomerate is one in which individual pebbles (or larger pieces) are themselves conglomerates. They likewise indicate at least two episodes of deformation.In some areas, details of displacement can be obtained best from unconformity analysis; in other areas, the special pebble types listed here may provide such details. In a few places, both types of information may be available, thus giving a fuller picture than could be obtained in other ways.The best example of a thick stratigraphic sequence containing these special pebble types (representing repeated deformation), described in the present paper, is located near Bucaramanga, Colombia. A second example from northern New Mexico is described less fully. Brief references to other occurrences, in Wyoming, Montana, Oklahoma and Alabama, are made. It is concluded that, although these pebble types may not be abundant at any one locality, they nevertheless occur at many places, and therefore can provide important information about deformational history.     

Deformation measurements using SAR interferometry: potential and limitations

Most applications of Synthetic Aperture Radar (SAR) make only use of the amplitude information in just one image. Interferometric SAR (InSAR) makes use mainly of the phase measurements in two or more SAR images of the same scene, acquired at two different moments and/or at two slightly different locations. By interference of the two images, very small slant-range changes of the same surface can be inferred. These slant-range changes can be related to topography and/or surface deformations. InSAR thus has the potential of mapping centimeter-scale ground displacements over a region many tens of kilometers in size at a resolution of a few meters making it one of the most promising space-geodetic techniques for monitoring Earth's surface deformations. The goal of this paper is to discuss some of the potential new applications of InSAR for the monitoring of deformations, and to show its major limitations. Some potential new applications of InSAR related to surface-change detection including earthquake and crustal studies, the monitoring of volcanoes and anthropogenic effects, and the monitoring of glaciers and ice sheets are presented. The discussion on the limitations of InSAR for surface-change detection focuses on atmospheric perturbations and the problem of temporal decorrelation.     

Powerful seismovibrators as a possible source of acoustic and electromagnetic disturbances

The observations of the disturbances of the acoustic, electric and magnetic fields at various distances from a vibroseismic source (5–12 Hz frequency range) are presented. Two centrifugal vibrosources (VS) with sinusoidal vibrational force onto the ground of 100 and 40 tons are used. Infrasonic signals are reliably recorded at distances up to 50 km. When the acoustic signal is large, a seismic signal with the same arrival time is also detected. Magnetic and atmospheric electric fields are detected at distances of several kilometers. These signals have practically zero lag time and precede the acoustic and seismic signals. The disturbances caused by the VS were also registered by telluric field measurements at distances up to 2 km from the source.     

The influence of grinding on the dissolution kinetics of calcite

This study of the dissolution of calcite in an acid environment demonstrates a significant dissolution anomaly for small particles. This cannot be attributed to very small, finely ground particles “stuck” to the grains, as there were too few to explain the magnitude of the observed anomaly. It is linked to the disruption resulting from the grinding. When observed in the electron microscope, the grains appear to be constructed of an aggregate of small crystals oriented in several principal directions. Their size increases progressively from the surface to the interior of the grain. An exothermic reaction is produced when the calcite is heated to 350° C. This causes a change in the microcrystalline structure leading to a nearly monocrystalline state. This recrystallisation retards the dissolution speed.     

On transient electric potential variations in a standing tree and atmospheric electricity

Transient electric potential variations have been observed in a standing poplar tree equipped with electrodes up to a height of 10.5 m. The simultaneous signals at all electrodes have the same shape and their amplitude grows linearly with height, up to values of 10 to 50 mV. This corresponds to an electric current through the tree of the order of a few μA. The frequency of appearance of the signals does not depend on the season or on the time of the day. It is suggested that the potential variations are caused by the passage of thunderstorm clouds, of little activity, whose electrically charged base could induce charges in the ground and give rise to a current flowing through the tree and discharging at its top by point discharge.     

Deep alpine valleys: examples of geophysical explorations in Austria

Results from geophysical explorations of three deep valleys, selected from different tectonic regimes in the Eastern Alps (Ötz-, Oichten-, and Drau Valley), are presented and discussed. Ongoing tectonic deformation may use tectonic structures related to these valleys. However, seismic activity is low there. During the Würm ice age, the thickness of the ice cover ranged between 300 and 1,500 m above present ground elevation. The geophysical investigations comprised reflection seismology, gravity- and resistivity surveys. The maximum depth down to the erosional base of the valleys varies from ~340 to 700 m. Distinct layer packages of the valley-infill at depths greater than 250 m were termed “old valley-fill”. Geophysical parameters and a comparison with the reflection seismic image of an intermediate layer at the recent Pasterze glacier suggest that the top of the “old valley-fill” represents the glacier bed during the decay of the Würm glaciation. Deep erosion is not related to high basal shear stress. The confluence of tributary glaciers is apparently not a significant factor for deep erosion in our examples of deep alpine valleys. We conclude that deep erosion may be related to high water pressure at the glacier bed, supported by specific processes of tectonic weakening.     

Displacement analytical prediction of shallow tunnel based on unified displacement function under slope boundary

For slope condition of ground surface, the asymmetrical deformation about the vertical center line and the horizontal center line of the tunnel cross section can be formed. A unified displacement function expressed by the Fourier series is presented to express the asymmetrical deformation of the tunnel cross section. Five basic deformation modes corresponding to the expansion order 2 are a complete deformation mode to reflect deformation behaviors of the tunnel cross section under slope boundary. Such this complete displacement mode is implemented into the complex variable solution for analytically predicting tunneling-induced ground deformation under slope boundary. All of these analytical solutions are verified by good agreements of the comparison between the analytical solutions and finite element method results. A parameter study is carried out to investigate the influence of deformation modes of the tunnel cross section, geometrical conditions of the tunnel and the slope angle, and “Buoyancy effect” on the displacement field. Finally, the proposed method is consistent with measured data of the Hejie tunnel in China qualitatively. The presented solution can provide a simplified indication for evaluating the ground deformation under slope condition of ground surface.     

Analysis of faulting in porous sandstones

Faults in porous sandstones occur in three forms: deformation bands about 1-mm thick and tens of m long and across which offsets are a few mm; zones of deformation bands constituted of many closely spaced deformation bands across which offsets are a few cm or dm; and slip surfaces, that is, distinct surfaces within zones of deformation bands across which offsets are a few m to a few tens of m. Deformation bands represent highly localized deformation; analogous localization within a field of homogeneous deformation is theoretically possible in inelastic materials with certain ranges of constitutive parameters. Crushing and consolidation of sandstone within a band cause the material there to become stiffer than the surrounding porous sandstone. A zone of deformation bands behaves mesoscopically much as a stiff inclusion in a soft matrix. According to the constitutive model assumed to investigate the formation of deformation bands, an instability can develop, and strain increments within the zone of deformation bands can become boundlessly large when the far-field stresses reach critical values. This instability is here associated with the formation of slip surfaces.     

Characterization of Iron Grains near the P/T Boundary in the Meishan Section of China

The Meishan section of China has been confirmed as the ＂Global Stratotype Section and Point＂ of the P/T boundary. In the section, the authors found several types of iron grains, including pyrite, pure iron grains and goethite. From the research of macro minerals, it is easy to find that the grains rich in iron appear from the bottom of the event layer of the section. In other words, it is probably residue of the geochemical catastrophe of that time. Therefore, it is important to trace the source of these iron grains and their relationships, which probably provides evidence for volcanic eruption or impact-volcanoes and has directive significance to the crisis during the P/T transitional period. Through the study of the characterization and relationships of these iron grains, the authors make a preliminary discussion on the P/T mass extinction.     

Geologische Problematik und Strukturanalyse Nikaraguas

The basement of northern Nicaragua is still a great problem stratigraphically. Enclosed tuffits (mainly basic, partly also intermediate to acid) appear of importance for both petrology and sedimentology. Not in the least they are guide horizons for a more accurate mapping. The vast regional distribution, commonly proved yet, suggests that the composition of the basement is considerably uniform and it seems that they do not belong to different periods and formations. Structurally the region is exceedingly complicated. The folding direction as regards plication and overthrusts is mainly to the North, but partly also to the East. Probably the “Totogalpa formation” (fanglomerates, conglomerates and sandstones, mainly reddish) which follows disconformably over the basement, already indicated, belongs to the sequence of tertiary tuffites, agglomerates, lavas etc. as they conformably form a formation of uniform composition. The relation of basement to lower Cretaceous (marine Albian; “Metapan”), which follows immediately to the south, is less clear. The lower Cretacious shows intensive and complicated folding at Siuna and it appears almost unmetamorphosed (? basement in a wider sense). The marine sediments (upper Cretacious - Miocene) of South Nicaragua are orogenetically only slightly efected (folding direction to E-N). To the North follows a thick serie of Tertiary and Quarternary volcanites (initially mainly submarinal, later on continental). Together with the NW/SE lineaments (Nicaragua depression, lines of volcanoes, coast line in the SW etc.) also NS directed ones clearly appear (coastline in the East). This direction can be found e. g. in the “granite ridge of Susucayan” and the accompanying faults in the vicinity. These latter structures may have taken an active part in the development of the flexured border of the Nicaraguan depression NW of Managua.