Petrogenesis of sediments in the absence of chemical weathering: effects of abrasion and sorting on bulk composition and mineralogy
Petrogenesis of sediments in the absence of chemical weathering: effects of abrasion and sorting on bulk composition and mineralogy
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DOI：
10.1046/j.1365-3091.1996.d01-12.x
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发表时间：
1996-04
期刊：
影响因子：
3.5
通讯作者：
H. Nesbitt;G. M. Young
中科院分区：
文献类型：
--
作者：
H. Nesbitt;G. M. Young
流入盖斯湾盆地的冰川被粉碎，随后在河流系统中进行选择性分选，对盆地沙子和泥浆的总体成分或矿物学影响很小。最引人注目的是沙子和泥浆中的长石含量以及长石-石英比率，两者都与普通基岩相似。砂和泥的长石含量范围为 48% 至 52%，而基岩平均含有 51·7% 长石。基岩中长石-石英比平均为 1·58:1，中粗砂、细砂和泥中分别为 1·54:1、1·66:1 和 1·69:1，表明细粒沉积物中长石富集程度最低。在没有明显的化学风化的情况下，水力分选后的极端磨损并没有产生成熟的沉积物，例如石英砂岩和富含粘土矿物的泥浆。然而，存在一些化学差异。镁铁质矿物在细砂和泥中的优先富集反映在整体成分中较高丰度的 MgO、FeO 和 TiO2，以及在矿物学中反映在细粒级黑云母的富集。仅关注泥浆和泥岩的整体成分研究将导致对烃源岩的镁铁质贡献的高估。这项工作表明，沉积物和沉积岩的整体成分研究应包括所有可用的粒度等级。
Comminution in the glaciers that debouch into Guys Bight Basin, followed by selective sorting in the fluvial system, has had little effect on the bulk composition, or on the mineralogy, of the basin sands and muds. Most striking are the feldspar contents, and the feldspar-quartz ratios in sands and muds, both of which remain similar to those of average bedrock. The feldspar contents of sands and muds range from 48 to 52% feldspar whereas average bedrock contains 51·7% feldspar. Feldspar-quartz ratios average 1·58:1 in bedrock and 1·54:1, 1·66:1 and 1·69:1 in the medium to coarse sands, fine sands and muds, respectively, indicating minimal feldspar enrichment in the fine-grained sediments. In the absence of appreciable chemical weathering, extreme abrasion followed by hydraulic sorting has not produced mature sediments such as quartz arenites and clay-mineral-rich muds. There is, however, some chemical differentiation. Preferential accumulation of mafic minerals in fine sands and muds is reflected in bulk compositions by higher abundances of MgO, FeO and TiO2, and in the mineralogy by enrichment of biotite in the fine grades. Bulk compositional studies focused solely on muds and mudstones will result in an overestimate of the mafic contribution from source rocks. This work shows that bulk compositional studies of sediments and sedimentary rocks should include all available granulometric grades.