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Sr isotope evolution of Maastrichtian seawater, determined from the chalk of Hemmoor, NW Germany
Author(s) -
McLaughlin Ó.M.,
McArthur J.M.,
Thirlwall M.F.,
Howarth R.,
Burnett J.,
Gale A.S.,
Kennedy W.J.
Publication year - 1995
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.1995.tb00550.x
Subject(s) - geology , marl , diagenesis , paleontology , baltica , isotopes of strontium , geochemistry , plateau (mathematics) , isotope , structural basin , ordovician , mathematical analysis , physics , mathematics , quantum mechanics
In 140 metres of Maastrichtian White Chalk (nannofossil chalk) exposed near Hemmoor, NW Germany, values of 87 Sr/ 86 Sr increase from 0.707760 in the Belemnella sumensis Zone (Lower Maastrichtian) at the base of the section (‐54.5 m; referred to 0 m at a prominent marl, M900) to 0.707821 in the Belemnella baltica/danica Zone (Upper Maastrichtian) at the top of the section (+84.5 m). A plateau in 87 Sr/ 86 Sr occurs between ‐5m and +50m in the section, probably as a result of a very high rate of sedimentation in this interval. A belemnite and associated nannofossil chalk have similar 87 Sr/ 86 Sr values, suggesting that there has been little diagenetic alteration of the 87 Sr/ 86 Sr ratios in the chalk, which therefore preserves its original 87 Sr/ 86 Sr. Comparison of 87 Sr/ 86 Sr and nannofossil zonations for sequences at Bidart, France, and DSDP Sites reveals discordance and so possible diachronism of the basal boundaries of nannofossil Zones CC25B and CC25C.