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首页> 外文期刊>Sedimentology: Journal of the International Association of Sedimentologists >Microfacies and diagenesis of older Pleistocene (pre-last glacial maximum) reef deposits, Great Barrier Reef, Australia (IODP Expedition 325): A quantitative approach
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Microfacies and diagenesis of older Pleistocene (pre-last glacial maximum) reef deposits, Great Barrier Reef, Australia (IODP Expedition 325): A quantitative approach

机译：澳大利亚大堡礁（IODP Expedition 325）的较晚更新世（最后冰川期之前）礁沉积物的微相和成岩作用：定量方法

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摘要

During Integrated Ocean Drilling Program Expedition 325, 34 holes were drilled along five transects in front of the Great Barrier Reef of Australia, penetrating some 700 m of late Pleistocene reef deposits (post-glacial; largely 20 to 10 kyr BP) in water depths of 42 to 127 m. In seven holes, drilled in water depths of 42 to 92 m on three transects, older Pleistocene (older than last glacial maximum, >20 kyr BP) reef deposits were recovered from lower core sections. In this study, facies, diagenetic features, mineralogy and stable isotope geochemistry of 100 samples from six of the latter holes were investigated and quantified. Lithologies are dominated by grain-supported textures, and were to a large part deposited in high-energy, reef or reef slope environments. Quantitative analyses allow 11 microfacies to be defined, including mixed skeletal packstone and grainstone, mudstone-wackestone, coral packstone, coral grainstone, coralline algal grainstone, coral-algal packstone, coralline algal packstone, Halimeda grainstone, microbialite and caliche. Microbialites, that are common in cavities of younger, post-glacial deposits, are rare in prelast glacial maximum core sections, possibly due to a lack of open framework suitable for colonization by microbes. In pre-last glacial maximum deposits of holes M0032A and M0033A (>20 kyr BP), marine diagenetic features are dominant; samples consist largely of aragonite and high-magnesium calcite. Holes M0042A and M0057A, which contain the oldest rocks (>169 kyr BP), are characterized by meteoric diagenesis and samples mostly consist of low-magnesium calcite. Holes M0042A, M0055A and M0056A (>30 kyr BP), and a horizon in the upper part of hole M0057A, contain both marine and meteoric diagenetic features. However, only one change from marine to meteoric pore water is recorded in contrast with the changes in diagenetic environment that might be inferred from the sea-level history. Values of stable isotopes of oxygen and carbon are consistent with these findings. Samples from holes M0032A and M0033A reflect largely positive values (δ~(18)O: -1 to +1‰ and δ~(13)C: +1 to +4‰), whereas those from holes M0042A and M0057A are negative (δ~(18)O: -4 to +2v and d13C: -8 to +2‰). Holes M0055A and M0056A provide intermediate values, with slightly positive d13C, and negative δ18O values. The type and intensity of meteroric diagenesis appears to have been controlled both by age and depth, i.e. the time available for diagenetic alteration, and reflects the relation between reef deposition and sea-level change.
机译：在325号综合海洋钻探计划探险期间，沿着澳大利亚大堡礁前的五个样带钻了34个孔，穿透了约700m的晚更新世珊瑚礁沉积物（冰川后;主要是BP 20至10年）。 42至127 m。在三个样带上钻出的七个深度为42至92 m的水深的孔中，从下部岩心段回收了较老的更新世（比上一次冰期最大值晚，> 20 kyr BP）礁石沉积物。在这项研究中，对后六个孔中的100个样品的相，成岩特征，矿物学和稳定同位素地球化学进行了研究和量化。岩性主要由谷粒支撑的纹理构成，大部分沉积在高能，礁石或礁石斜坡环境中。定量分析允许定义11个微相，包括混合的骨骼泥石和花岗石，泥岩-瓦克石，珊瑚泥石，珊瑚花岗石，珊瑚线藻类花岗石，珊瑚-藻类泥石，珊瑚线藻类泥石，哈利米达花岗石，微双辉石和Caliche。在年轻的冰川后沉积物的腔体中常见的微辉石，在前冰期前冰期最大的核心部分很少见，这可能是由于缺乏适合微生物定植的开放框架所致。在孔M0032A和M0033A（> 20 kyr BP）的前冰期最大沉积物中，海洋成岩作用占主导地位。样品主要由文石和高镁方解石组成。孔M0042A和M0057A包含最古老的岩石（> 169 kyr BP），具有成岩成岩作用，样品主要由低镁方解石组成。孔M0042A，M0055A和M0056A（> 30 kyr BP）以及孔M0057A上部的水平线包含海洋和陨石成岩特征。然而，与从海平面历史推断出的成岩环境的变化相比，从海洋到陨石孔隙水只有一种变化被记录下来。氧和碳的稳定同位素的值与这些发现一致。来自孔M0032A和M0033A的样品反映出较大的正值（δ〜（18）O：-1至+ 1‰和δ〜（13）C：+1至+ 4‰），而来自孔M0042A和M0057A的样品为负值（ δ〜（18）O：-4至+ 2v和d13C：-8至+ 2‰）。孔M0055A和M0056A提供的中间值是d13C稍为正，而δ18O值为负。高温成岩作用的类型和强度似乎已受到年龄和深度的控制，即成岩作用改变的时间，并反映了礁石沉积和海平面变化之间的关系。

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