K‐feldspar alteration to gel material and crystallization of glauconitic peloids with berthierine in Cretaceous marine sediments—sedimentary implications (Prebetic Zone, Betic Cordillera, SE Spain)
K‐feldspar alteration to gel material and crystallization of glauconitic peloids with berthierine in Cretaceous marine sediments—sedimentary implications (Prebetic Zone, Betic Cordillera, SE Spain)
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DOI：
10.1002/gj.1093
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发表时间：
2008-01
影响因子：
1.8
通讯作者：
J. Jiménez-Millán;J. M. Castro
中科院分区：
文献类型：
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作者：
J. Jiménez-Millán;J. M. Castro
利用X射线衍射仪、光学显微镜、扫描电子显微镜、高分辨透射电子显微镜和分析电子显微镜等方法，研究了内前陆半远洋单元(东部贝特克迪勒拉)豪特里亚凝聚层中的绿泥石球体。形成凝聚层的沉积物以丰富的球状至卵形绿色绿泥石球体为特征，呈放射状裂隙。石英、长石和白云母也很丰富，而磷酸钙很少检测到。对球团的X射线衍射分析表明，球体中含有海绿石和少量的石榴石。扫描电子显微镜和高分辨电子显微镜数据显示了长石的溶解特征，富硅铝凝胶状物质填充了钾长石微孔，结晶良好的海绿石和硫化石包夹在一起。海绿石化过程的最后阶段导致近晶前驱体的转化。沉积和矿物学特征表明，海绿石是原地成因的。沉积环境为南伊比利亚大陆古边缘带上的远洋半深海斜坡。在一般海侵背景下，低沉积速率导致沉积物凝结。边缘受到伸展构造的影响，形成倾斜的块体，导致侧向相变化。钾长石的溶解可能发生在它们在海洋环境中沉积之后，但早于海绿石化作用。因此，需要大气水的流入，这很可能与邻近涌出区(倾斜地块的较高部分)的地下通量有关。版权所有©2007 John Wiley&Sons，Ltd.
Glauconitic peloids from a Hauterivian condensed level in a hemipelagic unit of the Internal Prebetic (Los Villares Formation, eastern Betic Cordillera) have been studied by X‐ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). The sediments forming the condensed level are characterized by abundant spherical to ovoid green glauconite peloids with radial cracks. Quartz, feldspar and muscovite are also abundant, whereas calcium phosphate is rarely detected. XRD analysis of the peloids reveals glauconite and small amounts of berthierine. SEM and HRTEM data show feldspar dissolution features, a Si–Al‐rich gel‐like substance filling K‐feldspar micropores and interlayering of well‐crystallized glauconite and berthierine packets. The last stage of the glauconitization process resulted in conversion of the smectitic precursor. Sedimentary and mineralogical features indicate an autochthonous origin for the glauconite. The depositional environment was a distal, hemipelagic ramp on the Southern Iberian Continental Palaeomargin. Low sedimentation rates lead to sediment condensation in a general transgressive context. The margin was affected by extensional tectonics, creating tilted blocks, resulting in lateral facies changes. The dissolution of K‐feldspars probably occurred after their deposition in the marine environment but predating the glauconitization. An influx of meteoric water is therefore required, probably related to subsurface fluxes from adjacent emergent areas (the higher parts of tilted blocks). Copyright © 2007 John Wiley & Sons, Ltd.