Porosity and packing of Holocene river, dune, and beach sands
Porosity and packing of Holocene river, dune, and beach sands
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全新世河流、沙丘和海滩沙子的孔隙度和堆积
DOI：
10.1306/bdff87f4-1718-11d7-8645000102c1865d
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发表时间：
1991
期刊：
影响因子：
3.5
通讯作者：
E. McBride
中科院分区：
文献类型：
--
作者：
J. Atkins;E. McBride
孔隙度和填料的表层和浅埋（17米），松散的全新世砂（中至粗粒）的174个样品进行了测定点计数薄切片的环氧树脂浸渍样品在反射光的上表面。来自海滩、河口砂坝、辫状砂坝和风成沙丘的124个表层砂的平均沉积孔隙度分别为47%、48%和49%。孔隙度值范围在40%和58%之间。海滩砂的平均堆积值（CI =接触指数）为0.79，河流砂的平均CI为0.91，风成砂的平均CI为1.02。海滩砂通常含有5.5%的超大孔隙，河砂3.8%的超大孔隙，风成沙丘砂4.0%的超大孔隙。大多数过大的孔隙是沉积充填缺陷，尽管在某些海滩砂中捕获的气泡是常见的。外推我们的数据为埋藏的样品表明，沉积过大的孔隙被破坏的深度小于100米。风成涟漪层平均孔隙度为46%，颗粒下落层平均孔隙度为50%，颗粒流层平均孔隙度为51%。颗粒流与颗粒下降地层和涟漪与颗粒流地层的样品相似的粒度的包装差异是显着的。河流和海滩的单个层内的孔隙度比同一地点不同层间的孔隙度更均匀。来自特定层或相的古砂岩的孔隙度可能与采样的全新世砂岩一样均匀，除非存在具有斑片状分布的胶结物，例如碳酸盐或硬石膏。与埋藏至17 m相关的压实较小。填充更紧密，但我们测量孔隙率的技术不够灵敏，无法显示孔隙率的任何降低。埋藏至一般油气藏深度时，充填和孔隙度的变化取决于胶结作用、压实作用和次生孔隙发育的历史。然而，如果仅发生石英质河流、沙丘和海滩砂的物理压实，则孔隙度将接近26%的极限值，CI将接近5.5。
The porosity and packing of 174 samples of surficial and shallowly buried (to 17 m), unconsolidated Holocene sands (medium to coarse-grained) were determined by point counting the upper surface of thin sections of epoxy-impregnated samples in reflected light. Average depositional porosity for 124 surficial sands from beaches, river point bars and braid bars, and eolian dunes, respectively, is 47, 48, and 49%. The porosity values range between 40 and 58%. Beach sands exhibit an average packing value (CI = contact index) of 0.79, fluvial sands an average CI of 0.91, and eolian sands an average CI of 1.02. Beach sands typically contain 5.5% oversized pores, river sands 3.8% oversized pores, and eolian dune sands 4.0% oversized pores. Most oversized pores are depositional packing defects, although trapped air bubbles are common in some beach sands. Extrapolation of our data for buried samples indicates depositional oversized pores are destroyed at a depth of less than 100 m. Average porosity is 46% for eolian ripple strata, 50% for grain-fall strata, and 51% for grain-flow strata. Differences in packing are significant for grain-flow versus grain-fall strata and for ripple versus grain-flow strata for samples of similar grain size. Porosity is more uniform within individual beds from a river and a beach than among different beds at the same localities. Porosity of ancient sandstones from a particular bed or facies may be as uniform as sampled Holocene sands, unless cements having patchy distribution, such as carbonate or anhydrite, are present. Compaction associated with burial to 17 m is minor. Packing is tighter, but our technique of measuring porosity is not sensitive enough to show any decrease in porosity. Changes in packing and porosity upon burial to common hydrocarbon reservoir depths will depend on individual histories of cementation, compaction, and secondary porosity development. However, if only physical compaction of quartzose river, dune, and beach sands takes place, porosity would approach a limiting value of 26% and CI would approach 5.5.