与胡修棉的讨论:水流搬运与沉积过程中掺和作用对碎屑颗粒的重要影响

胡修棉教授(2017)发表的学术论文《物源分析的一个误区:砂粒在河流搬运过程中的变化》,基于Krumbein滚筒实验结果及大量观察数据,发现现代河流的砂粒中不稳定矿物成分、磨圆度及粒径等变化与国内《沉积岩石学》教材相关结论矛盾,应用于物源分析是"以讹传讹"。受其启发,基于前人研究成果,作者进行了较深入的分析,认为滚筒实验结果对自然界河流砂的机械搬运具有一定的指示意义,即随着搬运距离的增加,颗粒逐渐变细、磨圆度变好,加之河流搬运过程中伴随的化学分解等作用,其中的不稳定成分逐渐变少。但由于掺和作用的存在,河流搬运过程中混合了搬运距离不同的颗粒,其不稳定矿物成分含量、磨圆度和粒径等均会发生变化。国内教材对上述现象均有不同程度的描述,得到广大沉积学者认可,而胡修棉教授(2017)对此论述不够。此外,胡修棉(2017)单从地理位置上划分搬运距离的长短似乎不妥。河流搬运对颗粒的磨圆度和粒径的改造作用缺乏直接的数据证明,建议利用标定法跟踪观察。     

物源分析的一个误区:砂粒在河流搬运过程中的变化*

长期以来,中国沉积学界存在一个认识误区,认为“碎屑物质在流水搬运过程中,其不稳定成分逐渐变少,粒度逐渐变小,圆度逐渐变好”,并把这一认识错误地运用到对砂岩的物源分析中。作者基于文献调研和现代河流砂研究成果,评述了关于砂粒的不稳定矿物含量、磨圆度、粒度这3个重要参数的研究进展,认为河流搬运过程中砂粒并没有向下游出现明显的不稳定矿物丢失,粒度和磨圆度也没有明显变化,这3个参数与搬运距离并无必然关系。因此,根据长石、岩屑、不稳定重矿物的多寡以及粒度大小、磨圆度好坏来推测砂岩物源区的距离远近是缺乏科学依据的。     

物源分析的一个误区:砂粒在河流搬运过程中的变化

长期以来,中国沉积学界存在一个认识误区,认为"碎屑物质在流水搬运过程中,其不稳定成分逐渐变少,粒度逐渐变小,圆度逐渐变好",并把这一认识错误地运用到对砂岩的物源分析中。作者基于文献调研和现代河流砂研究成果,评述了关于砂粒的不稳定矿物含量、磨圆度、粒度这3个重要参数的研究进展,认为河流搬运过程中砂粒并没有向下游出现明显的不稳定矿物丢失,粒度和磨圆度也没有明显变化,这3个参数与搬运距离并无必然关系。因此,根据长石、岩屑、不稳定重矿物的多寡以及粒度大小、磨圆度好坏来推测砂岩物源区的距离远近是缺乏科学依据的。     

自然重砂成因矿物学特征及找矿指示作用

自然重砂是地质体经自然风化、剥蚀、搬运、沉积等地质作用而分离出的单矿物(或矿物组合)。自然重砂矿物晶体由于仍然保留有许多矿物成因信息,包括颜色、形态、化学成分、物理性质和矿物组合等特征,因此常用于追溯源区地质体或者找矿勘查。这种方法被认为是一种经济实用的找矿方法——自然重砂测量。本文基于全国自然重砂找矿的数据资料,系统梳理了自然重砂的矿物类型、出现频率及其分布等特点,分析了自然重砂的矿物组合和成因矿物学特征,研究了自然重砂矿物的源区烙印、搬运距离及标型指示矿物组合特征,探讨了自然重砂成因矿物学研究意义及其找矿应用前景。自然重砂矿物的颜色、形态及内部结构依然保留着明确的成因矿物学信息:其颜色和晶体形态具有继承性而与其源区母体联系起来,体现源区母体的特性;其矿物组成可分出残余原生重矿物(包括造岩矿物、副矿物、矿石矿物等)和新生重砂矿物两个部分,如赤铜矿、孔雀石等反映着源区岩性体的成分或者赋存状态特征,其矿物组合也在很大程度上继承原生共生矿物而体现诸如有无矿化等意义;重砂颗粒的磨圆度、边界光滑性等表面特征反映搬运距离,有利于明确响应源区母体或者物源,而具有良好的找矿指示意义。     

莺歌海盆地东北部邻区7条主要入海河流重砂矿物特征及其地质意义

海南岛西部（琼西）是莺歌海盆地东北部的主要物质来源之一。本文对琼西7条主要河流入海口的现代河砂进行了重矿物含量、重矿物组合以及相关特征指数等分析,发现其重矿物含量、磨圆度、组合以及相关重矿物指数从北到南明显不同,反映出碎屑物质搬运距离和源区岩性也明显不同。北部珠碧江重矿物以钛铁矿、电气石、锆石、绿帘石和透闪石为主,磨圆度较差,反映物源主要为近距离的酸性至基性-超基性岩浆岩和变质岩;昌化江重矿物以钛铁矿、磁铁矿、锆石和榍石为主,磨圆比较好,物源可能主要为远距离的酸性和基性岩浆岩;中部北黎河和通天河重矿物以钛铁矿、电气石、锆石、石榴石和透闪石为主,基本没有磨圆,物源主要来自近源区,为未经远距离搬运的变质岩、酸性岩浆岩和基性火山岩;感恩河重矿物以磨圆度差的锆石、钛铁矿、榍石、电气石和褐铁矿等稳定-极稳定重矿物为主,反映源区主要为近距离搬运的岩浆岩;南部望楼河和宁远河重矿物以钛铁矿、磁铁矿、褐铁矿和绿帘石等稳定-不稳定矿物为主,反映的母岩主要为酸性岩浆岩、变质岩和中-基性岩浆岩。这些主要河流入海口的重矿物特征存在明显差异,这与其发源地、流经区域以及流经区域所发育的岩石类型相一致。通过研究琼西地区从北到南不同流域的重矿物组合体系,有助于开展莺歌海盆地源汇对比分析,建立不同区域油气储层碎屑物质来源的识别标志,对该盆地天然气储层物源识别具有重要的地质意义。     

澳门黑沙遗址沉积物的成因分析

通过孢粉分析，粒度分析，矿物成分和石英砂微观形貌分析，对史前石器发掘地黑沙遗址的沉积物成因进行了初步探讨，沉积物分选较差，矿物成熟度一般，自下而上颗粒变粗，分选性和磨圆度变好，孢粉以淡水河口成分为主，揭示黑沙遗址沉积物总体属河流搬运作用为主同时受低能潮直带波浪作用的近岸环境下的沉积，沉积物的物质来源于花岗岩，泥岩和粉砂岩，经河流中近距离搬运。     

岩浆岩砾石磨圆度地质意义的研究

定量地质学的兴起促进了地球科学的快速发展,但是国内外对砾石磨圆度与搬运距离之间定量关系的研究长期以来没有明显的进展。本次研究通过对永定河、碓臼峪、滦河和大石河四条河流进行系统的野外考察,从河流的出山口开始向下游设定考察点,详细描述各考察点砾石的磨圆度、粒度特征并进行统计分析,对岩浆岩砾石磨圆度与搬运距离的定量关系以及磨圆度的影响因素进行了研究。研究发现,岩浆岩砾石的磨圆度随着搬运距离的增大而变好,在搬运的初期变化最快,而后逐渐缓慢下来,最终磨圆度趋于稳定。岩浆岩砾石由棱角状变为次棱角状一般需要搬运3~6 km,由次棱角状变为次圆状一般要搬运12~21 km,圆状砾石大量出现至少要搬运22~31 km。砾石的磨圆度受搬运距离、母岩成分、粒度和破碎作用的影响。棱角状、次棱角状砾石容易被磨蚀,在搬运初期转化为次圆状、圆状,而圆状砾石不易磨蚀达到极圆状;岩浆岩砾石磨圆速度比石英快,比石灰岩慢;相同母岩成分的砾石,粗粒砾石比细粒砾石磨圆快;破碎作用则会降低砾石的磨圆度,使部分砾石呈现出与搬运距离不协调的磨圆特征。     

危地马拉翡翠宝石矿物学特征及其与缅甸翡翠的对比研究

危地马拉目前已成为仅次于缅甸的第二大翡翠原料供应地。这两个产地翡翠辨别的需求愈发迫切,且应用意义较大。采用显微镜观察、电子探针分析及背散射电子照相获得危地马拉蓝水料翡翠的矿物成分及结构构造特征,结合两产地翡翠产出的大地构造环境、自然地理环境、原石特征与矿物成分特征等进行对比分析。总体上,危地马拉翡翠次生原石有一定的磨圆,呈次棱角状,“皮”(风化皮)厚度较薄,较少出现翻砂现象,由“皮”向里,极少甚至几乎不存在“红雾”。相对地,缅甸翡翠次生原石发育显著的球状风化,原石通常有较好的磨圆度,棱角状不明显,“皮”厚度可达数厘米,用手压磨有显著的翻砂现象, “皮”“肉”之间偶可见“红雾”。硬玉与绿辉石成分判别图显示危地马拉翡翠中硬玉和绿辉石呈相对富Ca、贫Na的特征,而缅甸翡翠中硬玉和绿辉石整体呈相对贫Ca、富Na的特征。在Fe含量上,危地马拉翡翠中硬玉的Fe含量较缅甸翡翠中硬玉的Fe含量偏低,而危地马拉翡翠中绿辉石的Fe含量较缅甸翡翠中绿辉石的Fe含量偏高。对翡翠外观特征的充分对比和对判别图的综合分析可应用于实际中翡翠产地的区分。     

碎屑岩沉积从源到汇的“物-坡”耦合效应*

碎屑岩沉积体系的三维展布特征及其成因机制是建立沉积模式与预测其砂体分布的关键,更是沉积学研究的关键性科学问题。国内外绝大多数学者认为其平面形态和剖面充填型式均与其沉积的地形坡度、粒度粗细有密切的联系,但其定量关系并不清楚。建立不同类型沉积体中粒度和坡度之间的定量关系,对于预测沉积体中不同颗粒的运动方式及其分布至关重要。应用“源-汇”系统研究的思路,分析了供源区、搬运(输送)区及汇积区各自的地质特点,从单向水流对不同质量颗粒在静止/运动中的受力分析与沉积前总体地形斜坡设定2个角度,系统分析、推导并模拟了不同碎屑颗粒在纵向剖面上的运动轨迹,其表现为随着设定的坡型呈抛物线变化,反映出沉积物输送营力的变换及其随坡度变化的响应特征。建立了陆相碎屑岩沉积体系纵向剖面的流速与坡度的计算方程,明确指出沉积物的流速或流态决定其沉积方式,阐述了汇积区碎屑颗粒的加积型式与沉积物分布上的总体规律,由此提出碎屑岩沉积体系的“物-坡”耦合效应及其主要内涵,并从多个维度与源-汇的各区段,阐述了“物-坡”耦合效应在各种沉积体系的沉积物类型及其空间形态特征上的地质响应。     

准噶尔盆地沙湾凹陷西斜坡二叠系佳木河组物源区构造背景分析*

准噶尔盆地沙湾凹陷西斜坡二叠系佳木河组物源体系一直备受争议,导致沉积体系“众说纷纭”。利用聚类分析、多维尺度分析及主成分分析等方法,对重矿物含量、微量元素进行分析,明确了沙湾凹陷西斜坡二叠系佳木河组砂砾岩碎屑颗粒富石英(35.41%)、长石(43.2%),贫岩屑(18.71%)。稀土元素总量(ΣREE)平均值139×10^-6接近大陆上地壳(UCC)的平均值148.14×10^-6,Hf-La/Th微量元素物源判别图解和La/Sc-Co/Th值表明佳木河组属于酸性岛弧区。稀土配分模式表现为右倾分布模式,整体上具有“轻稀土元素富集、重稀土元素亏损”的特征,指示源岩以长英质火山岩为主,即“一源”。在同一物源下,又可以分为4个物源区:新光1井—中佳6井物源区,车排10井—中佳5井—中佳4井—中佳3井物源区,车排7井—车排005井体系物源区,车排5井物源区,即“四区”。构造背景判别图解揭示了佳木河组形成于大陆岛弧环境。该研究将有助于对沙湾凹陷西斜坡的沉积体系及古水系的准确恢复和远景区油气储集层的准确预测。     

THE CARBONATE FRACTION OF BEACH AND DUNE SANDS

The sand size carbonate fractions of beach and dune sands from the southeastern U.S. Atlantic coast were investigated from the standpoint of mineralogy, roundness and size distribution. The carbonate fractions of beach-dune sands used in this study range in abundance from less than 1% to over 40% and average about 10%. Calcium carbonate is least abundant in Georgia beaches and increases slightly to the north and greatly to the south. The size distribution of the carbonate fraction is similar to that of the non-carbonate fraction since both have been distributed by the same processes. The variable flat shape of calcareous fragments causes the carbonate fraction to be usually coarser and more poorly sorted than the acid insoluble residues of the samples. No regional relationship between roundness and wave energies was found in sand size materials although field observations indicate high energies strikingly round gravel sized calcareous fragments. There is some tendency for angularity to increase with decreasing grain size in the sand sizes as with quartz grains. The mineralogy of beach sand carbonate fractions is characterized by the almost total absence of high My calcite. Aragonite is the dominant mineral.     

Physical controls on sand composition and relative durability of detrital minerals during ultra‐long distance littoral and aeolian transport (Namibia and southern Angola)

Sediment in coastal Namibia to southern Angola is supplied dominantly from the Orange River with minor additional fluvial input and negligible modifications by chemical processes, which makes this a great test case for investigating physical controls on sand texture and composition. This study monitored textural, mineralogical and geochemical variability in beach and aeolian‐dune sands along a ca 1750 km stretch of the Atlantic coast of southern Africa by using an integrated set of techniques, including image analysis, laser granulometry, optical microscopy, Raman spectroscopy and bulk‐sediment geochemistry. These results contrast with previous reports that feldspars and volcanic detritus break down during transport, that sand grains are rounded rapidly in shallow‐marine environments, and that quartzose sands may be produced by physical processes. Mechanical wear is unable to modify the relative abundance of detrital components, including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly. The sole exceptions are poorly lithified or cleaved sedimentary/metasedimentary rock fragments, readily lost at the transition to the marine environment, and slow‐settling flaky micas, winnowed and deposited offshore. Coastal sediments tend to be depleted in relatively mobile amphibole, preferentially entrained offshore or re‐deposited in sheltered beaches, while less mobile garnet is retained onshore. No detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high‐energy littoral environments from the Orange mouth to south of the Namib Erg, but all minerals get rapidly rounded after passing into the dunefield. Pyroxene and opaques get rounded faster than harder quartz and garnet, but sand mineralogy remains unchanged. Excepting strong transient selective‐entrainment effects, physical processes are unable to modify sand composition significantly. Selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra‐long‐distance transport in high‐energy environments dominated by strong persistent winds and waves.     

咸化湖盆三角洲沉积模拟实验研究

为指导柴达木盆地西部地区古近系-新近系咸化湖盆油气勘探,建立咸化湖盆聚砂富砂模式,结合青海湖现代咸化湖盆沉积考察结果,开展了咸水介质条件下的三角洲沉积模拟实验研究,实验表明：咸化湖盆三角洲沉积以三角洲平原相为主,可占整个三角洲面积的80%以上,而在三角洲前缘亚相中河口坝微相最为发育;同时表明咸水介质对不同粒度沉积物的搬运距离及沉积有控制作用,较淡水介质,咸水介质中细粒沉积物在河口区快速沉降,而粗粒沉积物搬运距离更远,沉积范围也广;模拟结果也表明咸化湖盆三角洲沉积纵向上“坝上河”砂体构型发育。咸化湖盆三角洲沉积模拟实验的成功,明确了咸化湖盆储层分布特征,拓展了储层分布范围,为柴达木盆地西部地区油气勘探提供技术支持。     

神木—双山地区太原组桥头砂岩沉积特征及演化

在对砂岩的岩石学、粒度分析、地球化学、沉积构造、垂向层序、测井曲线及沉积体系展布等资料分析的基础上,研究了鄂尔多斯盆地神木-双山地区太原组桥头砂岩沉积特征,探讨了砂体沉积演化过程,建立了桥头砂岩沉积模式。桥头砂岩形成于相对海平面下降时期的辫状河-浅水三角洲沉积体系,陆源碎屑物质被河流不断向南搬运充填入盆地中,形成辫状河、浅水三角洲、障壁砂坝-潟湖-潮坪、陆表浅海在空间上共存的岩相古地理格局。     

Physical and chemical properties of sound-producing and soundless sand particles from booming sand dunes,northern China

This study here is the result of a comparative study of the geomorphic features, grain size distribution, major mineral components, and micro-textures of sound-producing and soundless sands from three geoparks in north China, and discusses the possible causes of this naturally occurring, physical phenomenon. The sound-producing sand dunes we have investigated are situated along a curvilinear belt of deserts and experience variable precipitation–evaporation rates on a yearly basis. “Singing sands” occur mainly on barchan-type dunes and adjacent to lakes or springs, whereas soundless sands are mainly located in desert areas where there is no nearby surface or groundwater sources. We have analyzed samples from nine sound-producing and two soundless sand dunes using grain size, X-ray diffraction and fluorescence, and SEM analyses. All sand types are composed largely of quartz and feldspar, but sound-producing sands also contain secondary minerals such as kaolinite (3–5%), albite (2–6%), microcline (2–5%), and calcite (5%) that are lacking in the soundless sand samples. Sound-producing sands are generally fine-grained whereas soundless sands are coarse-grained, and all sand types are generally sub-rounded to rounded indicating long transport distance from their provenance. Sphericity values of both sand types are nearly identical with predominantly oblate shapes. Surface pitting is not a unique feature of either sand types, and hence can be ruled out as a major cause of the acoustic properties of sound-producing sands. Densely distributed dissolution features such as scale-like upturned plates and silica scales on grain surfaces contribute significantly to the sound emission of singing sands. Thus, the physical–climatic conditions in deserts such as the presence of surface water and groundwater and precipitation–evaporation rates, which collectively control the formation and distribution of dissolution features on sand surfaces, have a first-order control on the production of sound-producing sands.     

姬塬油田胡154井区延长组长4+5储层特征

通过岩心观察、测井及各类分析测试资料,对姬塬油田胡1 54井区延长组长4+5油层组储层岩石学、孔隙结构和储集体物性等特征进行了研究.结果表明,研究区延长组长4+5为典型的低孔、特低孔-起低渗储层;储集砂体为成分成熟度和结构成熟度都较低的岩屑质长石砂岩和长石质岩屑砂岩;储集空间主要为粒间孔和长石溶孔;孔隙结构以小孔微喉型...     

Index test for the degradation potential of carbonate sands during hydraulic transportation

Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results.     

河流砾—砂过渡（GST）研究进展

河流从上游山区流经下游宽阔地带时,所搬运物质在磨损和分选作用下逐步变细,当沉积物减小到中粗卵砾级别时（10~20 mm）,会在相对短距离内（几倍河道宽度）快速转变为极粗砂（1~2 mm）,这种粒度突变现象被称为砾—砂过渡（gravel-sand transition,GST）。对河流砾—砂过渡进行了系统调研,介绍了其在河流中的基本特征;分析了砾—砂过渡的发生机理,包括粒度突变的外因假说、2~10 mm粒径空缺的内因解释,以及GST中加剧砾砂流动性差异的过程;也介绍了GST的空间普适性、其前后的河流转变和位置稳定性。GST的深入研究对于理解河流演化、泥沙运移、洪水风险管理、沉积物源分析具有重要意义。