发育完整的灰岩风化壳及其矿物学和地球化学特征

对于碳酸盐岩土覆土壤成因、尽管碳酸盐岩风化残积成土说被多数学者认同,但由于碳酸盐岩中酸不溶物含量极低,在风化成土过程中会伴随着巨大的体积缩小变化,原岩结构和半风化带无法保留,从而缺失了探索上覆土壤物质来源的重要中间环节,使得这种观点缺乏野外宏观证据的支持。最近,我们在贵州、湖南等地发现了数个以泥质灰岩和泥质白云岩为基岩的碳酸盐岩风化壳剖面,尚保留有较好的原岩结构,具有明显的风化壳分带和过渡现象。这些风化壳剖面的发现为深入研究碳酸盐岩风化成土过程提供了良好的研究场所。本文选取了较为典型的吉首泥灰岩风化壳剖面,从矿物学地球化学的角度来探讨碳酸盐岩风化壳的形成过程和发育特征,结果表明该风化壳既遵循非碳酸盐岩（主要是结晶岩类）风化壳的发育特征,也具有自己独特的地球化学演化规律。风化壳总体特点受碳酸盐中的酸不溶物矿物组合及化学成分的影响甚至控制,风化非碳酸盐风壳相似的发育特征。吉首泥灰岩风化壳剖面的发育特征和作者早先提出 的碳酸盐岩风化成土的两阶段模式是一致的,即以碳酸盐矿物大量淋失、酸不溶物逐渐堆积或残积为特征的早期阶段和残积物进一步风化成土的阶段,后一阶段的演化类似非碳酸盐岩类的风化过程。     

微地域搬运——碳酸盐岩红色风化壳形成过程的一种方式

由于差异溶蚀作用,由碳酸盐岩强烈风化形成的红色风化壳通常表现出独特的剖面构型:风化壳发育深厚、下伏基岩面强烈起伏波动、溶沟和石牙相间展布。以黔中岩溶台地之上发育的红色风化壳——平坝剖面为例,通过宏观地质、地球化学、粒度分析以及矿物学等方法,并以邻近的两个石灰土剖面(罗吏剖面和龙洞堡剖面)作对比,对碳酸盐岩红色风化壳的形成过程进行了讨论,论证了微地域搬运是碳酸盐岩红色风化壳尤其是厚层红色风化壳形成过程的一种方式。溶沟部位的风化壳,从风化前锋向上的一定深度范围内,为原位残积风化的产物(残积层);在此深度以上的部分,为地势较高的相邻石牙部位不同风化程度的残积物的搬运堆积(堆积层),也是导致风化指标随深度呈锯齿状波动的直接原因。后者一般组成剖面的主体。风化壳的年代地层学表现为,在残积层,从风化前锋向上,风化年龄由新到老;在堆积层,从下到上,风化年龄由老到新。风化前锋是一个重要的地球化学作用场所,在这一狭窄的界面上,伴随碳酸盐矿物的快速淋失,残余酸不溶物开始了明显分解。而风化壳的后期演化是一个缓慢而长期的过程。达到重力平衡的剖面(即风化壳表面平缓、不发生微地域搬运的剖面),在由表及里的风化作用下,从地表向下的一定深度范...     

涠洲岛和斜阳岛红色风化壳粘土矿物和化学特征及成土环境研究

选择涠洲岛和斜阳岛的两个玄武岩风化壳和一个凝灰岩风化壳,用X射线粉晶衍射法(XRD)和X射线荧光光谱法(XRF)分别测定了风化剖面各层粘土矿物和主量元素.结果表明:各风化剖面粘土矿物以7×10-10m埃洛石为主,且普遍含有针铁矿和赤铁矿,表明风化程度较高.风化剖面表层化学特征指标出现异常变化,其中一个剖面表层含有次生方解石支持了存在海岛复盐基作用对风化壳的影响.风化剖面底层的化学特征指标和粘土矿物亦表明地下水对风化壳的发育有着重要影响.热带季风气候仍然是控制该地区风化壳发育的主要因素,但海岛环境特有的复盐基作用和地下水也对风化壳的发育产生了一定影响.     

酸不溶物对碳酸盐岩风化壳发育程度的影响

通过对贵州岩溶区（包括湘西）不同地层系统碳酸盐岩发育的红色风化壳、以及结合本区和处于同一气候带的邻区不同岩类红色风化壳的对比研究,结果表明：（1）碳酸盐岩红色风化壳的发育程度明显受基岩酸不溶物成分的控制,酸不溶物的风化成熟度越高,红色风化壳的发育程度一般也越强。由于不同地层系统碳酸盐岩的酸不溶物组成不同,在此基础上发育的红色风化壳的风化强度自然存在着差异;（2）风化壳相对于母岩的进一步风化潜力或空间,随着基岩酸不溶物风化成熟度的增大而降低,从而更容易达到风化平衡;（3）在碳酸盐岩风化壳突变的岩-土界面,伴随碳酸盐的充分淋失、酸不溶物的地球化学指标发生了突变。因此,碳酸盐的溶解不但未阻滞和延缓了硅酸盐组分的分解,而且促进其快速风化。（4）在达到高岭石化甚至弱红土化阶段的酸不溶物基础上,发育的风化壳比结晶岩类风化壳具有更高的风化起点,也就表现出更高的风化强度。因此,笼统地把碳酸盐岩风化壳看作是弱于玄武岩及花岗岩等结晶岩类风化壳发育程度的弱风化类型是不妥的。     

热带地区碳酸盐岩上覆红色风化壳的成因机理及元素演化

开展热带岩溶地区红色风化壳元素地球化学演化规律研究,有助于丰富碳酸盐岩风化成土理论的认识。在越南北部选取典型的碳酸盐岩风化剖面,分析热带气候条件下碳酸盐岩上覆红色风化壳中主量元素的物质来源和演化特征。结果表明:无论Ti/Zr的元素比值分析,Hf-Zr、Nb-Ta及Sm-Nd的元素对协变分析,还是上地壳元素平均值(UCC)标准化分析,两个剖面的上覆风化壳均显示原地残积的特征,即两个剖面是碳酸盐岩的原位风化产物。碳酸盐岩风化成土过程中,CaO、MgO淋失明显,Al_2O_3和Fe_2O_3发生富集,显示两个剖面均经历较强的风化过程,但是白云岩和灰岩剖面有一定的分异特征。越南北部白云岩风化剖面从基岩到上部土层显示出稳定的Ti-Fe元素共富集特征,而灰岩剖面中Fe的增长速率明显超过Ti。白云岩上覆风化壳经历了强烈的风化作用,其脱硅作用弱于灰岩风化剖面,而富集铝的作用强于灰岩。迁移系数的演化规律说明两个剖面中长石成分(钾长石、钠长石等)或次生矿物(伊利石等)在风化成土过程中逐渐分解,同时Al、Fe、Si等稳定元素的在风化剖面中不断富集。     

湘西岩溶区风化壳的物源:石英粒度分布特征的指示

对湘西岩溶区呈镶嵌景观展布的4条风化剖面中石英粒度分布特征的进行对比研究,发现区域上碳酸盐岩风化成土作用具有极大可能性.基岩为灰岩的两条风化剖面(WC1和WC2)的频率分布曲线呈单峰窄峰态,众数值分别为4.9(φ)和4(φ);两条碎屑岩风化剖面(WC3和DBK)的频率分布曲线呈单峰宽峰态,众数值分别约为5.1(φ)和6(φ).而且各剖面基岩与上覆风化壳的石英粒度频率分布曲线呈现良好的对应关系.石英粒度的标准差、偏度、尖度等参数也显示,各剖面样品基本上分布于不同的区域.研究结果还表明:(1)母岩风化过程中,石英粒度分布特征是完全可以继承的;(2)剖面WC1和WC2为碳酸盐岩风化壳.说明在湘西岩溶区,在有利的地貌单元,碳酸盐岩是完全可以风化成土的;(3)不同风化剖面的石英粒度分布特征不同,说明在区域上,风化壳不具有共同的物源,下伏基岩是其上覆风化壳的成土母岩;(4)石英粒度分布特征是用于岩溶区风化壳物源示踪的良好指标.     

老挝南部安东花岗闪长岩砖红土型风化壳分带及微量元素地球化学特征

在热带雨林特殊生态景观中和湿热气候条件下,老挝南部阿速波省(Attapeu)安东地区(Antoum)二叠纪花岗闪长岩形成了发育完整的砖红土型风化壳,该风化壳剖面分带明显,最下部为蚀变花岗闪长岩(基岩),往上依次为半风化蚀变花岗闪长岩→高岭石残积层带→砖红土带→森林表土带.测试了采集于红土型风化壳剖面不同分带样品的20种微量元素含量,微量元素可划分出6种变化模式,其中最明显的为Cu、Mo、As、Bi、Au等在高岭土风化带上部显著富集.认为在今后土壤地球化学普查和详查中,经过加大采样深度,采用固定相态提取法或部分提取法可能是强化地球化学异常、探测深部找矿信息的有效途径.     

高海拔山地碳酸盐岩风化壳的发育特征及其地貌意义

研究区位于云南东川拱王山山顶的落雪,海拔高度在3600m左右。山顶面为一缓丘及丘间溶蚀洼地构成的第三纪残留夷平面。在夷平面上发育了碳酸盐岩的黄色风化壳。本文基于风化壳的地球化学、物理化学及矿物学等特征,重点研究了风化环境对风化壳发育特征的影响,以及风化壳与第三纪残留夷平面的关系。所研究的风化壳剖面发育于低温、降水充沛和湿润的气候条件下。分析测试结果表明,风化壳仍处于CaO、MgO淋失, SiO2富积阶段,是一种弱度风化的富SiO2风化壳。风化壳的特征表明其形成于第三纪夷平面解体之后,而不能代表第三纪夷平面的原有相关堆积。      

碳酸盐岩红色风化壳中的氧化铁矿物

氧化铁矿物是碳酸盐岩红色风化壳的主要矿物成分和重要结构单元。运用X射线衍射、透射电镜、扫描电镜、穆斯堡尔谱和电子探针等方法对碳酸盐岩红色风化壳中的氧化铁矿物进行了系统研究。碳酸盐岩红色风化壳中的氧化铁矿物主要有针铁矿、赤铁矿和磁赤铁矿。氧化铁矿物组合、含量和化学成分随成土环境和风化强度在剖面中呈明显的规律性变化,这为碳酸盐岩风化成土作用、红色风化壳成因与环境问题的深入研究提供了重要的矿物学依据。     

引起红土表层硅铝比值增大原因的可能性探讨

Si/Al或SiO2/R2O3常常作为表生化学风化作用强度的重要指标。随着化学风化作用的进行。硅铝比或硅铝铁率表现出逐渐降低的演化趋势，中国南方的红土风化壳，是强烈化学风化作用的产物，被认为处于或经历了脱硅富铝化阶段，但是在红土剖面上部常常出现该比值不降反升的现象。给运用这一指标指示化学风化强度带来了困难，通过对贵州平坝，新蒲及花溪碳酸盐岩红色风化壳化学风化程度的研究，以及对中国南方几种不同结晶母岩上发育的红土的化学风化强度指标的对比讨论。探讨了产生这种现象的可能性原因。指出Fe,Al氧化物的下渗和淋失作用及其硅质的相对富集是引起中国南方红土表层出现Si/Al和SiO2/R2O3升高的主要原因。     

白云岩之上红色粘土的磁组构特征及其成因指示意义探讨

通过与粉尘堆积,以及玄武岩和片麻杂岩风化剖面磁组构的对比,探讨了以贵州平坝白云岩之上红色粘土剖面磁组构特征及其成因指示意义。红色粘土的各向异性较弱,并且不具有明显的沉积磁组构;母岩的组构特征对红色粘土磁化率各向异性没有明显的控制“痕迹” ;红色粘土与粉尘堆积物之间磁组构特征的明显差异,表明它们在物源和形成机制方面是不同的;红色粘土磁化率及磁组构特征反映出红色粘土中磁性矿物的物质来源和成因具有一定的特殊性。      

Trace elements in ferromanganese concretions,gibbsite spots,and the surrounding terra rossa overlying dolomite: Their mobilization,redistribution and fractionation

The mobilization, redistribution and fractionation of trace elements during chemical weathering processes have been investigated on a 4.05 m thick terra rossa profile overlying dolomite on the Yunnan-Guizhou Plateau, in Southwest China. In this in situ weathering profile, the ferromanganese concretions and the gibbsite spots coexist in the terra rossa saprolite. The mass-balance evaluation reveals that titanium, Nb and Hf in the terra rossa matrix are conservative elements during chemical weathering compared to Zr. The elements of Li, Sc, V, Cr, Fe, Ga, As, Mo, Cs, Ce, Ta, Tl, Pb and Th in the terra rossa matrix include additions from external sources. Beryllium, Mn, Co, Ni, Cu, Rb, Ba and La are depleted in the shallow parts of the terra rossa profile and enriched in the deep parts. The elements of Zn, Sr, Y, Cd, Sn and U in the terra rossa profile are lost during weathering. Compared to the terra rossa matrix, the ferromanganese concretions are significantly enriched in most trace elements, especially Mn, Co, Cd, Ce, Tl and Pb. In contrast, the gibbsite spots are depleted in all trace elements, except for U. The results regarding specific inter-element relationships indicate that most trace elements have different inter-element relationships in the ferromanganese concretions, the gibbsite spots and the terra rossa matrix. This suggests that the behavior of many trace elements during mobilization and redistribution differs from their behavior during incorporation into secondary mineral phases, especially the Mn and Fe oxides and/or oxyhydroxides in the ferromanganese concretions. It is worthy to note that the fractionation between Ce and Mn occurs under intensive chemical weathering conditions. Correspondingly, beryllium exhibits a similar geochemical behavior as that of rare earth elements (except for Ce) and Y during surface weathering.     

Lanthanide tetrad effect in ferromanganese concretions and terra rossa overlying dolomite during weathering

The lanthanide tetrad effect was investigated in a 5.4 m thick terra rossa profile overlying dolomite on the Yunnan-Guizhou Plateau, China. The results demonstrate that the chondrite-normalized rare earth element pattern of dolomite bedrock displays a W-type tetrad effect. The insoluble residue from the dolomite bedrock does not exhibit any significant tetrad effect. In contrast, some ferromanganese concretions and the terra rossa show tetrad effect. It is worth noting that the conjugate M- and W-types of the tetrad effect are observed in some terra rossa samples. The tetrad effect in the ferromanganese concretions and the terra rossa possibly originates from redistribution of dissolved rare earth elements during their downwards movement in the profile and not only from water/rock interaction. Within the dolomite weathering system, the ferromanganese concretions and surrounding terra rossa present similar correlations of Eu/Eu*, Y/Ho, Sm/Nd, Ce/Ce*, with the size of the tetrad effect. The ferromanganese concretions and the terra rossa with tetrad effect are characterized by a reduced, non-chondritic Y/Ho ratio. Also the Y/Ho ratio exhibits a clear negative correlation with the size of the tetrad effect in the ferromanganese concretions and the terra rossa. In addition, the Eu/Eu* tends to increase with increasing size of the tetrad effect in the ferromanganese concretions and the terra rossa, as does the Sm/Nd ratio. The regular variation for Eu/Eu*, Y/Ho and Sm/Nd is likely a result of the fractionation of rare earth elements and yttrium with the tetrad effect. On the other hand, the correlation of the Ce/Ce* with the size of the tetrad effect in the ferromanganese concretions and the terra rossa is random. This likely indicates that the Ce behavior within weathering system is mainly controlled by redox condition, rather than tetrad effect. Comparative study indicates that the correlations of Eu/Eu*, Y/Ho, Ce/Ce*, with the size of the tetrad effect in the ferromanganese concretions and the terra rossa, are not similar to those found in a highly evolved igneous system. Nevertheless, the correlation of Sm/Nd with the size of tetrad effect in weathering system is similar to that in igneous system. In general, it appears to indicate that the tetrad effect occurrence in granitic rocks is not associated with weathering.     

Element geochemical characteristics of a soil profile developed on dolostone in central Guizhou,southern China: implications for parent materials

This study presents bulk chemical compositions of the Tongmuling soil profile, which developed on dolostone, and the overlying strata covering the bedrock in the central Guizhou province (southern China). The chemical weathering characteristics of the studied profile were investigated and the inheritance relationships between the terra rossa and overlying strata were discussed. The results show that there is no remarkable variation in the major elements and weathering indices from the rock–soil interface to the topsoil, indicating that the studied profile was not typical for in situ crustal chemical weathering. The terra rossa were mainly composed of SiO₂, Al₂O₃ and Fe₂O₃. Compared with the insoluble residues and overlying strata, the terra rossa are characterized by an enrichment of Y and Cs and depletion of Ba and Sr. The subsoil shows a notable Ce negative anomaly, characterized by heavy rare earth element enrichment (L/H = 1.55–3.74), whereas the topsoil shows a positive Ce anomaly with light rare earth element enrichment (L/H = 5.93–9.14). According to Laterite-forming capacity estimates, the terra rossa could not have only been formed from acid-insoluble residues from the bedrock; Al₂O₃ versus Fe₂O₃ and Nb plotted against Ta show significant positive correlations between the terra rossa and overlying strata. The Eu/Eu* versus Gd_N/Yb_N and ternary diagrams for Sc, Th, Zr, and Ta suggest that the overlying strata could also provide parent materials for the genesis of terra rossa.     

RED WEATHERING CRUST ON LIMESTONE AND PLANATION SURFACE OF TIBET AND ITS EASTERN DISTRICT

RED WEATHERING CRUST ON LIMESTONE AND PLANATION SURFACE OF TIBET AND ITS EASTERN DISTRICTthedevelopmentprojectofNationalKeyBasicFoundation (G19980 4 0 80 0 ) ;theprojectofTibetPlateaure searchofChineseAcademy (K2 95     

Geochemistry of the limestone of Mortas Formation and related terra rossa,Seydisehir, Konya,Turkey

The purpose of this study was to determine and evaluate the geochemical characteristics of the limestone of the Upper Cretaceous Mortas Formation and related terra rossa in a 50 km² area which is located 20 km south of the city of Seydisehir, Central Anatolia, by using data obtained from the ICP-MS analysis of randomly collected 42 samples of limestone and 18 samples of the terra rossa.The limestone of the Mortas Formation is composed of fossilliferous, gray-cream colored, medium to thick bedded, partially dolomitic carbonate rocks, and generally has dismicrite, intrapelmicrite composition. It includes the largest bauxite reservior in Turkey and has many occurences of terra rossa formation on it. According to mean distance, the Ba, Be, Hg, Mo, Nb, Sb and Th concentrations in the limestones overlying and underlying the bauxite deposits are different, but the main oxides, REE and other trace elements are same. In factor analysis, the first component reflects relative enrichment of clay against to CaO contents of the limestone, the second component corresponds to the degree of dolomitization. The PAAS-normalized REEs pattern for the Mortas Formation limestone samples illustrate similar main features as seawater.The terra rossa soils in the study area are considered to be highly weathered and weakly mature soil with respect to their generally low Al₂O₃ (21%), but high CaO (2%) contents, and their alteration indices. The element ratios in the terra rossa and limestone show that in the process of the transformation from limestone to terra rossa, Ba, Si, Ti, Al and Fe were enriched together by staying in-situ. Except Ce, all lanthanides show similar behavior, but the HREE, which were richer in limestone, were consumed fast relative to the LREE during soil formation. The association and the enrichment of Co, Cu, Cr, Ni and Pb as well as Ba, Zr, Ga, Nb and Rb in soil relative to the limestone are interpreted as being resulted from eolian transportation. Ca, Au, Hg, Sr, Se, Sb, Mo, Ag, U, Cd and Na were found to be the most mobile elements during pedogenic transformation. According to main oxide composition ratios of the limestone and terra rossa, the soils were described as representing a well washed soil completing the leaching and accumulation phase, but not totally completing the silicate weathering phase. In the processes of soil formation, 97.76% of the limestone was washed away; only 2.24% of limestone was deposited as soil. Therefore, 61 times mass reduction was realized.     

青藏高原古岩溶的存在及其与东邻地区岩溶的对比

青藏高原古岩溶属形成于土下环境,经刻蚀作用剥露地表后,以石林、岩墙等形式广泛存在于山顶夷平面的外围,并不同程度地叠置气下改造特征。根据青藏高原及东邻岩溶区覆盖型岩溶和红色风化壳的剥露情况及改造特征对比,作者认为上述地区覆盖型岩溶从东到西具有良好的一致性,是岩溶双层夷平面的组成部分,其现阶段的不同表现是不同程度刻蚀作用的结果。      

Weathering profiles in granites, Sierra Norte (Córdoba, Argentina)

Two weathering profiles evolved on peneplain-related granites in Sierra Norte, Córdoba province, were examined. Several weathering levels, of no more than 2 m thickness, were studied in these profiles. They had developed from similar parent rock, which had been exposed to hydrothermal processes of varying intensity. Fracturing is the most notable feature produced by weathering; iron oxides and silica subsequently filled these fractures, conferring a breccia-like character to the rock. The clay minerals are predominantly illitic, reflecting the mineral composition of the protolith. Smaller amounts of interstratified I/S RO type are also present, as well as scarce caolinite+chlorite that originated from the weathering of feldspar and biotite, respectively. The geochemical parameters define the weathering as incipient, in contrast to the geomorphological characteristics of Sierra Norte, which point to a long weathering history. This apparent incompatibility could be due to the probable erosion of the more weathered levels of the ancient peneplains, of which only a few relicts remain. Similar processes have been described at different sites in the Sierras Pampeanas. Reconstruction and dating of the paleosurfaces will make it possible to set time boundaries on the weathering processes studied and adjust the paleographic and paleoclimatic interpretations of this great South American region.     

Subaerial leaching process of sedimentary bauxite and the discussion on classifications of bauxite deposits

Bauxite is the ultimate fine-grained products of chemical weathering,and thus it is closely linked with the intense chemical weathering. Based on variations of parent rock and weathering processes,the weathering products can be subdivided into laterite and terra rossa,of which the former is formed by weathering of aluminosilicates and the latter is produced by the weathering of carbonates. During the intense chemical weathering,minerals in original subaerial sediments(parent rocks)would suffer a series of processes(dissolution,hydrolyzation,hydration,carbonation,and oxidation)and be destroyed or transformed,leading to formation of new minerals. In the favorable environment,continuously intense chemical weathering would cause the loss of most mobile elements(e.g., K,Na,Ca,Mg,Si)and the enrichment of Al,resulting in the formation of bauxite. Although sedimentary bauxites are closely linked with the weathering curst,they show obvious differences in formation processes. Sedimentary bauxites are composed of intense chemical weathering products that are transported from outside of the basin and re-deposited in the basin,while most weathering crusts are transformed from saprolite and/or deluvium in-situ,and they can only form low-grade bauxites. Sedimentary environments also differ in bauxite ore layers and bauxitic claystone layers. Bauxite ore layers are formed in the subaerial environment and controlled by the leaching process of groundwater in the vadose zone. Based on the analysis of bauxitization,this study proposes to use multiple parameters,such as provenance,sedimentation and mineralization,to build the new classification of Chinese bauxite deposits. In this classification,lateritic and karstic types of bauxite deposits are autochthonous or parautochthonous saprolite and/or deluvium,while sedimentary type is dominated by heterochthonous provenance.     

沉积型铝土矿的陆表淋滤成矿作用: 兼论铝土矿床的成因分类*

铝土矿是化学风化作用的细粒终极产物,与强烈的化学风化作用密切相关。根据母岩的类别及作用过程,风化作用进一步分为铝硅酸盐岩强化学风化形成的红土化作用和碳酸盐岩强化学风化形成的钙红土化作用。在强烈的化学风化过程中,地表的原始沉积物(母岩)的原生矿物发生溶蚀、水解、水化、碳酸化、氧化,破坏原始的矿物结构,形成新的细粒矿物(主要是黏土质矿物)。在适合的地质条件下,持续的强烈化学风化作用会造成大部分活动的元素(如K、Na、Ca、Mg、Si)的流失与Al的残留富集从而形成铝土矿。现在观察到的沉积型铝土矿,虽然与古风化壳具有密切联系,但沉积型铝土矿多数是由沉积过程搬运到沉积盆地中所形成的强化学风化产物的沉积层,与古风化壳的残坡积层具有显著差别,只有少数工业价值不大(品位低、品质差)的残坡积相铝土矿。铝土矿含矿岩系的沉积环境与铝土矿(尤其是高品位、高品质的铝土矿)的成矿环境不尽相同。铝土矿主要形成于暴露于大气中的陆表环境(而非水下环境),由地下水淋滤作用形成(在渗流带由活动元素流失、Al等稳定元素残留富集而成)。本研究在铝土矿成矿作用分析等基础上,提出了以铝土矿沉积物等物源和沉积、成矿作用为依据的中国铝土矿床分类方案,包括原地或准原地残坡积物成因的红土型和喀斯特型,和异地物源沉积成因的沉积型。