TY - JOUR

T1 - Towards a new understanding of the genesis of chalk

T2 - Diagenetic origin of micarbs confirmed by clumped isotope analysis

AU - Tagliavento, Mattia

AU - John, Cédric M.

AU - Anderskouv, Kresten

AU - Stemmerik, Lars

PY - 2021/2

Y1 - 2021/2

N2 - 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.

AB - 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.

KW - Chalk

KW - clumped isotopes

KW - early diagenesis

KW - micarbs

U2 - 10.1111/sed.12802

DO - 10.1111/sed.12802

M3 - Journal article

AN - SCOPUS:85096989381

VL - 68

SP - 513

EP - 530

JO - Sedimentology

JF - Sedimentology

SN - 0037-0746

IS - 2

ER -