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Facies effects on the behaviour of Nd and Sr isotope systems in turbidite mudrocks during diagenesis
Author(s) -
EVANS JANE A.,
ZALASIEWICZ JAN A.,
CHOPEYJONES ANNE
Publication year - 2009
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.2008.01001.x
Subject(s) - diagenesis , geology , sedimentary rock , turbidite , geochemistry , facies , sedimentary depositional environment , mineralogy , paleontology , structural basin
A detailed Sm/Nd, epsilon Nd and Rb/Sr profile through a 30‐cm thick section of Silurian (Llandovery) interbedded turbiditic and hemipelagic mudrocks from the central Wales Basin shows well‐marked chemical and isotopic trends. The variations reflect an interplay of depositional mode and diagenetic fractionation. Sm and Nd values are substantially higher and Sm/Nd ratios tend to be lower in the organic‐rich hemipelagite layers due to diagenetic concentration in the hemipelagites. There is a corresponding depletion in the turbidite mudstones. Epsilon Nd values range from −0·8 to −7·1 and this is attributed to diagenetic modification of Sm/Nd ratios causing scatter in back‐calculated epsilon values. Rubidium–strontium ratios in this succession fall within a narrow range, due to homogenization during diagenesis. By contrast, data from a hemipelagite‐dominated (condensed) succession near the northern margin of the Welsh Basin show a lower range of epsilon Nd values and a higher scatter of Rb/Sr values, consistent with less fluid throughput during burial compaction and hence less diagenetic redistribution in these rocks. These patterns demonstrate the sensitivity of mudrock trace element and isotope compositions to both small‐scale sedimentary structure and large‐scale basin architecture.