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...

Micro-Area Transportation of Residues: A Style of Forming the Red Weathering Crusts of Carbonate Rocks

Owing to differential erosion, the red weathering crusts of carbonate rocks usually show special profile structures that are characteristic of thick-bedded, intensely weathered profiles and strongly undulate basement rock surface (i.e. alternate distribution of solution grooves and stone teeth). In this work a typical red weathering crust of dolomite rock (i.e. Pingba profile) is selected in a karst terrace in Guizhou Province, China. Via field geology, geochemistry, mineralogy, grain size analyses, and in comparison with two neighboring limestone soils (i.e. Luoli profile and Longdongbao profile) as well, we discussed the formation process of the red weathering crusts of carbonate rocks, and demonstrated that micro-area transportation of acid-insoluble residues of carbonate rocks is a style of forming the red weathering crusts, especially the thick-bedded those of carbonate rocks. The weathering crusts at solution grooves, at the scope of the depth upwards from weathering front, are in-situ weathering residues (i.e. residual layers); over this depth upwards, are accumulated deposits of different weathering intensity (i.e. accumulation layers) from upper adjacent stone teeth situation by micro-area transportation. This process is a direct cause leading to intense undulation of weathering indices with the depth. The latter generally compose the principal part of the profiles. At solution grooves, the chronostratigraphy of the red weathering crusts of carbonate rocks shows that, at residual layers, upwards from weathering front, the weathering age is from new to old; at accumulation layers, from bottom to top, the weathering age is from old to new. The weathering front is a main place of geochemical reaction, and at this limited-thick interface, with quick dissolution of carbonates, acid-insoluble residues begin to obviously decompose. However, ensuing evolvement of weathering crusts is very slow. When they is up to gravity balance (i.e. flat surface and no micro-area transportation), under the action of weathering from exterior to interior, at the scope of the depth from the surface downwards, the weathering profiles are gradually reconstructed and take on the developing feature of normal weathering crusts.