Chalk is usually thought to be a homogeneous sediment with a relatively simple early diagenetic history. Here, clumped isotope analyses of samples from a core of Campanian Maastrichtian chalk are presented, indicating that material smaller than 5 µm has a different origin than the coccolith‐dominated coarser fraction. The smallest size fraction (1 to 5 µm) of chalk is dominated by calcite particles without a distinct morphology (micarbs). Clumped isotope data of the micarbs reveals formation temperatures of 14 to 18°C which is 8 to 10°C colder than those derived from coeval coccoliths. The micarbs are interpreted as the product of calcite neoformation, precipitated in the uppermost part of the sediment column (100 metres below sea floor) and linked to early dissolution of aragonitic fossils. These findings prove that early cements can be an abundant component in chalk, and thus challenge the common notion that chalk is always largely composed of calcareous nannofossils, and differs only in terms of minor constituents and degree of lithification.

中文翻译：

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对白垩纪的新认识：团簇同位素分析证实了低碳的成因

通常认为白垩是具有相对简单的早期成岩史的均质沉积物。在这里，对来自坎帕尼亚马斯特里赫特白垩岩心的样品进行了聚集同位素分析，结果表明，小于5 µm的物质的来源与以可可岩为主的较粗级分的来源不同。白垩的最小尺寸分数（1至5 µm）主要由方解石颗粒组成，没有明显的形态（低碳）。低碳的同位素数据表明，地层温度为14至18°C，比从始祖可可煤层获得的地层温度低8至10°C。碳威伯被解释为方解石新形成的产物，沉淀在沉积物柱的最上部（海床以下100米），并与石蜡化石的早期溶解有关。