Isotopic composition of a calcite-cemented layer in the Lower Jurassic Birdport Sands, southern England; implications for formation of laterally extensive calcite-cemented layers
Isotopic composition of a calcite-cemented layer in the Lower Jurassic Birdport Sands, southern England; implications for formation of laterally extensive calcite-cemented layers
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DOI：
10.1306/d4267bb3-2b26-11d7-8648000102c1865d
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发表时间：
1993-07
影响因子：
2
通讯作者：
P. A. Bjørkum;O. Walderhaug
中科院分区：
文献类型：
--
作者：
P. A. Bjørkum;O. Walderhaug
摘要在英格兰南部多塞特郡下侏罗纪浅海Bridport砂的海岸暴露区，对横向延伸（> 3 km）且厚度为0.5 m的连续方解石胶结层中的107个方解石胶结物样品进行了18 OPDB和13 CPDB值的测量。样品取自二维网格，样品之间的水平和垂直间距为10 cm，并沿沿着横跨方解石胶结层的单独垂直线。18 OPDB值在-4.8和-9.2之间变化，并从方解石胶结层中间横向间距为0.5-1 m的点径向向外减小。因此，18 OPDB值表明方解石胶结层是由结核合并形成的。测得的所有13个CPDB值都在-2.2到-0.5的狭窄范围内，这表明该层中方解石胶结物的主要来源是生物碳酸盐。
ABSTRACT 18OPDB and 13CPDB values have been measured on 107 calcite cement samples from a laterally extensive (> 3 km) and continuous calcite-cemented layer 0.5 m thick in the coastal exposures of the Lower Jurassic shallow-marine Bridport Sands in Dorset, southern England. The samples were taken from a two-dimensional grid with 10-cm horizontal and vertical spacing between samples and along individual vertical lines across the calcite-cemented layer. 18OPDB values vary between -4.8 and -9.2 and decrease radially outwards from points with lateral spacings on the order of 0.5-1 m in the middle of the calcite-cemented layer. The 18OPDB values therefore indicate that the calcite-cemented layer was formed by merging of concretions. All 13CPDB values measured are in the narrow range -2.2 to -0.5, which suggests that the dominant source of calcite cement in the layer was biogenic carbonate.