Primary fabric ellipsoids in sandstones: implications for depositional processes and strain analysis
Primary fabric ellipsoids in sandstones: implications for depositional processes and strain analysis
复制标题
砂岩中的原生组构椭球体：对沉积过程和应变分析的影响
DOI：
10.1016/0191-8141(94)90094-9
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发表时间：
1994
影响因子：
3.1
通讯作者：
Hao Yu
中科院分区：
文献类型：
--
作者：
S. Paterson;Hao Yu
当测量变形碎屑岩的应变时，地质学家通常假设以下一种或多种情况：（1）物体最初是圆形的;（2）物体最初是非圆形的，但具有统一的方向;（3）物体群最初有一个组构，但这个组构与层理有对称的关系;或者（4）即使在应变之后，初始组构也是可识别的。为了评估这些假设，我们测量了来自四个沉积环境的43个非应变、分选不良砂岩中的组构椭球体：（俄勒冈州海岸外的扇和深海平原沉积）;加州的白垩纪大峡谷层序（弧前沉积）：白垩纪鸽子角组，加州（增生和滑塌浊积岩）和产自加州和澳大利亚陆内盆地的交错层砂岩。结果表明：（1）在二维剖面中，单个颗粒的轴比变化较大，但通常较小（<3/1），轴比较大的颗粒更多地（但不总是）与层理成小角度;（2）三维颗粒群的平均比率和取向限定了非球形组构椭球体，这些组构椭球体的形状变化很大，XY面的方位变化很大，不平行于层理或交错层理。这些结果表明，在变形砂岩中测量的组构椭球体必须进行校正的存在下，初级组构时，试图计算应变。然而，由于原生组构椭球体的方向和形状可变，且与层理缺乏关系，应变最多只能通过将应变样本中测量的最终椭球体乘以具有各种方向和形状的倒数原生组构椭球体来计算。这些数据和颗粒和基质胶结物中的微观结构也反对在这些碎屑支撑的富含砂的单元，而不是建议，主要的织物主要反映在沉积过程中的颗粒包装过程中，和/或在鸽子点样品的情况下，坍塌和包装。
When measuring strains in deformed clastic rocks, geologists usually assume one or more of the following: (1) objects were initially circular; (2) objects were initially non-circular but had uniform orientations; (3) object populations initially had a fabric, but that this fabric had a symmetrical relationship to bedding; or that (4) initial fabrics are recognizable even after straining. To evaluate these assumptions, we measured 43 fabric ellipsoids in non-strained, poorly sorted sandstones from four depositional settings: DSDP core 174 (fan and abyssal plain deposits off the coast of Oregon); the Cretaceous Great Valley sequence, California (fore-arc deposits): the Cretaceous Pigeon Point Formation, California (accreted and slumped turbidites); and crossbedded sandstones from intracontinental basins in California and Australia. Our results indicate the following: (1) in two-dimensional cuts, individual grains have variable but usually small axial ratios (<3/1) and grains with larger axial ratios are more often, but not always, oriented at small angles to bedding; (2) averaged ratios and orientations of populations of grains in three dimensions define non-spherical fabric ellipsoids, but with small axial ratios (average principal ratios = 1.31:1.14:1); (3) these fabric ellipsoids show a wide range of shapes; and (4) orientations of fabric ellipsoidXYplanes have highly variable orientations and are not parallel to bedding or cross-bedding. These results indicate that fabric ellipsoids measured in deformed sandstones must be corrected for the presence of primary fabrics when attempting to calculate strains. However, because of the variable orientations and shapes of the primary fabric ellipsoids and lack of relationship to bedding, strains can, at best, only be bracketed by multiplying final ellipsoids measured in strained samples by reciprocal primary fabric ellipsoids having a variety of orientations and shapes.These data and microstructures in grains and matrix cements also argue against significant compaction during burial in these clast-supported, sand-rich units and instead suggest that the primary fabrics largely reflect grain packing processes during deposition, and/or slumping and packing in the case of the Pigeon Point samples.