Jhs. Macquaker, PALEOENVIRONMENTAL SIGNIFICANCE OF BONE-BEDS IN ORGANIC-RICH MUDSTONESUCCESSIONS - AN EXAMPLE FROM THE UPPER TRIASSIC OF SOUTH-WEST BRITAIN, Zoological journal of the Linnean Society, 112(1-2), 1994, pp. 285-308
A combined field-based/petrographic study to investigate the formation
of Rhaetian 'bone-beds' from the Westbury Formation, Upper Triassic o
f south-west Britain, has been undertaken. 'Bone-beds' in the Westbury
Formation have been found at the top of coarsening upward successions
, on flooding surfaces which underlie organic-rich mudstones. These 'b
one-beds' are frequently found either overlying or amalgamated with 's
hell-beds', and often contain large (up to cobble-sized) intraclasts.
This work indicates that they formed during a period of relative sea-l
evel rise, when the sediment was being reworked (forming a transgressi
ve lag) and a condensed section had developed. Phosphate authigenesis
is thought to have occurred at the oxic/Fe-reduction interface, where
the pore waters were dysoxic, enriched with dissolved phosphate and re
latively acidic. 'Bone-bed' formation was terminated when siliciclasti
c mud prograded over the condensed section and 'normal' anoxic/suifidi
c pore water conditions were established in the sediment.