The Foraminiferal assemblages across three middle Turonian marl bands and a note on their genesis

P N Leary,D S Wray

doi:10.1144/jm.8.2.143

Abstract

Abstract. the changes in the Foraminiferal assemblage across three Middle Turonian marl bands show a consistent pattern, with (a) very similar gross assemblage characteristics from the white chalk below and above the marls containing an approximately 60:40% planktonic:benthonic ratio, greater than 50% non-keeled morphotypes (within the planktonic assemblage) and with infaunal and epifaunal groups well represented but (b) from within the marls the assemblage is dominated by benthonics (30:70% p:b ratio), less than 20% non-keeled morphotypes (within the planktonic assemblage) and a benthonic assemblage dominated by the infaunal groups. Although there is evidence of some dissolution within the marls, with the pitting of the thinner test walls, we propose the changes in the assemblage are not due to large scale post mortem diagenetic process. But are most likely due to environmental changes within the chalk sea, possibly caused by the ephemeral introduction into the surface waters of volcanic ash.

Highlights

INTKODUCTION Marl ban'ds are clay rich units which are found in parts of the Middle and Upper Turonian chalk of southern England
If the contact is sharp and well-defined, irregular fingers (“flasers”) of marly chalk are usually seen extending a few centimetres into the white chalk, these are believed to be a product of bioturbation (Wray, in prep.)
GIynde Marl 1 is thinner than the other two. It contains a 3 cni. seam of dark-brown, plastic, marly chalk. Both contacts with the white chalk above and below appear gradational, below the seam isolated flasers can bc seen extending to a depth of 5 cm

Summary

Introduction

INTKODUCTION Marl ban'ds are clay rich units which are found in parts of the Middle and Upper Turonian chalk of southern England. A marl seam is defined here as a thin (2-20cms), laterally extensive bed of chalk which contains a large percentage ( 1 5-35%) of non-carbonate material. The white chalk above and below the marl seam only contains between 0.5 and 3%’ non-carbonate material.

Results

Conclusion