国内外岩溶塌陷监测方法综述

岩溶塌陷是全球广泛分布的地质灾害问题,严重影响和制约了岩溶地区社会、经济发展,因此,开展岩溶塌陷监测工作,对塌陷预测预报具有及其重要的作用。岩溶塌陷的监测技术与塌陷形成的机理关系密切。该文分析了岩溶塌陷的分布规律和形成的条件,系统总结了国内外岩溶塌陷的监测内容、技术方法、各自优缺点,如BOTDR监测、TDR监测、地质雷达监测、水动力条件监测及地-沉降等方法,为系统性地开展岩溶塌陷监测工作提供技术和方法参考,展望了未来的岩溶塌陷监测工作,认为岩溶塌陷监测需结合塌陷的形成机理、塌陷地区覆盖层特征及水动力条件,综合利用多种监测手段联合进行,并形成完善的监测网络。     

松辽盆地南部深层致密砂岩气储层形成机制及成藏主控因素

为了加快松辽盆地南部(简称松南)深层致密砂岩气勘探开发进程,开展致密砂岩储层形成机制及成藏主控因素研究。通过对松南深层致密砂岩的分析,根据致密砂岩岩性组合特征将已发现的深层致密气类型划分为稳定厚层砂型、砂泥互层型、泥包砂型3种类型,储层物性普遍差,孔隙度多小于6%,渗透率主体<0.10×10^-3μm²,属于特低孔、特低渗储层。通过对松南典型致密储层矿物成分与微观特征的分析发现,致密砂岩有效储层形成主要受3个方面因素控制：一是早成岩期发育绿泥石包壳,有效抑制成岩中后期粒间钙质胶结、硅质胶结的发生,保护原生残余粒间孔隙;二是富火山岩岩屑溶蚀形成次生孔隙;三是生烃增压产生大量微裂缝,改善储层渗流特征。在此基础上总结出松南致密砂岩气成藏控制因素,即充足气源提供物质基础、斜坡古沟谷与断裂控砂、次生溶蚀与微裂缝控储、断裂活动与稳定盖层控富。     

三江平原中东部沼泽湿地形成及其演化趋势的探讨

三江平原中东部是沼泽湿地集中连片分布地区。研究区有阶地沼泽和河漫滩沼泽两大类型沼泽分布,进一步可划分为4个沼泽体,即小叶章（Calamagrostis angustifolia）—毛苔草（Carex lasiocarpa）沼泽;毛苔草沼泽;睡菜（Menyanthes trifoliata）—水木贼（Equisetum limosum）沼泽;漂筏苔草（Carex pseudocuraica）—毛苔草沼泽。研究区沼泽湿地形成的主要自然因素为：①新构造运动的大面积沉降;②地势低平,坡降平缓、河道变迁,复杂的微地貌,易于积水,促使沼泽湿地的大面积形成;③厚3～17m的第四纪粘土层沉积地表,使地表渗透性差;④气候因素,研究区处于温带大陆性湿润季风气候区,雨量集中于夏季,且多秋雨,冬季积雪深度大,封冻期长,季节性冻土层厚;⑤水文因素,河流比降小,糙率大,流速缓,多为沼泽性河流,春汛与夏汛之间只出现平水不出现枯水,洪水期间,洼地和河流受松花江、黑龙江等大河、大江的洪水顶托,研究区的承泄条件差,内水不能外排,长期积蓄地表。目前研究区沼泽有变干的趋向。     

Self-regulated gravitational accretion in protostellar discs

We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular non-axisymmetric density perturbations. The amplitude of these density perturbations decreases with time, though this process is moderated by swing amplification aided by the existence of the disc's sharp outer edge. Our global modelling of the protostellar disc reveals that there is typically a residual non-zero gravitational torque from these density perturbations, i.e. their effects do not exactly cancel out in each region. In particular, the net gravitational torque in the inner disc tends to be negative during first several million years of the evolution, while the outer disc has a net positive gravitational torque. Our global model of a self-consistently formed disc shows that it is also self-regulated in the late phase, so that it is near the Toomre stability limit, with a near-uniform Toomre parameter Q ≈ 1.5–2.0. Since the disc also has near-Keplerian rotation, and comparatively weak temperature variation, it maintains a near-power-law surface density profile proportional to r ^−3/2.     

南图尔盖盆地Aryskum坳陷钾盐的测井响应特征及其分布

钾盐作为战略资源,在农业、工业等领域具有重要的使用价值。世界大多数固态钾资源发现于大规模的石油勘探过程中,充分利用各种油气地质、地球物理资料开展钾盐勘探对于国家发展尤为重要。位于哈萨克斯坦的南图尔盖盆地地质构造简单、资源勘探潜力较大。文中以南图尔盖盆地Aryskum坳陷为研究区块,基于其沉积地质特点,结合多口井的常规测井资料及前人研究成果,综合分析自然伽马、自然电位、三孔隙度等测井曲线的响应特征,含钾层段具体表现为自然伽马异常高值,并通过无铀伽马曲线等排除铀、钍元素影响,扩径使得中子值偏高,自然电位异常幅度由砂岩层的负异常变化为正异常,电阻率值偏高,密度值介于2.25~2.45 g/cm³,声波时差在270~350 μs/m范围内。基于含钾层测井曲线特点,利用测井曲线综合识别法、重叠法、交会图法进行研究区钾盐识别。在研究区30余口井中发现有可溶性钾盐层分布,分布在M-Ⅱ-3、M-Ⅱ-2小层底部,其中M-Ⅱ-3层底部为主要钾盐层段,并对各井含钾层段累计厚度进行统计分析。最后,借助地层对比分析含钾层段在横向和纵向上的展布情况,通过等厚图的绘制开展了找钾有利区分析,拓展了测井资料在南图尔盖盆地钾盐勘查中的应用,进而为今后研究区钾盐找矿提供重点方向。     

The origin of the initial mass function and its dependence on the mean Jeans mass in molecular clouds

We investigate the dependence of stellar properties on the mean thermal Jeans mass in molecular clouds. We compare the results from the two largest hydrodynamical simulations of star formation to resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell & Bromm. The initial conditions of the two calculations are identical except for the radii of the clouds, which are chosen so that the mean densities and mean thermal Jeans masses of the clouds differ by factors of 9 and 3, respectively.
We find that the denser cloud, with the lower mean thermal Jeans mass, produces a higher proportion of brown dwarfs and has a lower characteristic (median) mass of the stars and brown dwarfs. This dependence of the initial mass function (IMF) on the density of the cloud may explain the observation that the Taurus star-forming region appears to be deficient in brown dwarfs when compared with the Orion Trapezium cluster. The new calculation also produces wide binaries (separations >20 au), one of which is a wide binary brown dwarf system.
Based on the hydrodynamical calculations, we develop a simple accretion/ejection model for the origin of the IMF. In the model, all stars and brown dwarfs begin with the same mass (set by the opacity limit for fragmentation) and grow in mass until their accretion is terminated stochastically by their ejection from the cloud through dynamically interactions. The model predicts that the main variation of the IMF in different star-forming environments should be in the location of the peak (due to variations in the mean thermal Jeans mass of the cloud) and in the substellar regime. However, the slope of the IMF at high masses may depend on the dispersion in the accretion rates of protostars.     

基于机器学习的锆石成因分类研究

锆石是在自然界中多种温压条件下能够稳定保存,并记录原岩年龄信息的副矿物。锆石微量元素能完整记录地质演化过程信息。通过微量元素分析锆石成因的研究已久,通常利用Th-U图解和La_N-(Sm/La)_N图解等二元图解对锆石进行分类研究。然而,随着锆石研究的深入,以及二元图解无法呈现数据高维度信息的局限性,传统图解已经不能满足对锆石类型进行准确判别,且对已知类型的锆石出现判定偏差。因此,本文将地质大数据与机器学习相结合,训练出高维度锆石成因分类器。文中收集了3 498条不同成因类型的锆石微量元素数据,并通过测试和运用随机森林、支持向量机、人工神经网络和k近邻等4种机器学习算法,最终得出准确率为86.8%的线性支持向量机锆石成因分类器,用于锆石类型的判定与预测。这项工作为锆石分类研究提供了更高维度的判别手段,极大提高了微量元素分析成因结果的精度。将锆石微量元素数据与机器学习方法相结合,是大数据分析与机器学习技术在地球化学研究中的积极探索。     

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

Impact megadomes and the origin of the martian crustal dichotomy

We show that a sufficiently energetic impact can generate a melt volume which, after isostatic adjustment and differentiation, forms a spherical cap of crust with underlying depleted mantle. Depending on impact energy and initial crustal thickness, a basin may be retained or impact induced crust may be topographically elevated. Retention of a martian lowland scale impact basin at impact energies ∼3 × 10²⁸-3 × 10²⁹ J requires an initial crustal thickness greater than 10 km. Formation of impact induced crust with size comparable to the martian highlands requires a larger impact energy, ∼1-3 × 10³⁰ J, and initial crustal thickness <20 km. Furthermore, we show that the boundary of impact induced crust can be elliptical due to a spatially asymmetric impact melt volume caused by an oblique impact. We suggest the term “impact megadome” for topographically elevated, impact induced crust and propose that processes involved in megadome formation may play an important role in the origin of the martian crustal dichotomy.