Publication Laka-library:
Seismische opdeling van de Boomse Klei in omgeving van Mol (Vol 1)
| Author | Jooris Els |
| Date | 1997 |
| Classification | 2.03.4.10/05 (BELGIUM - WASTE) |
| Front | 
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From the publication:
Abstract: The Boom Clay lithocolumn has been resampled for a detailed study of the foraminifera. The vertical changes of the microfaunal assemblages, mainly those of the benthic foraminifera, strongly coincide with previously observed lithological/facies changes, such as rich assemblages coinciding with high CaCO3 concentrations (i.e. abundant calcitic microfossils, molluscs and other tests) or poor assemblages with high organic matter content in the silty to heavy clays. An interval, rich in organic matter occurs in the middle to upper part of the Boom Clay (roughly coinciding with the outcropping part of the Putte Clay Member), and yields strongly impoverished foraminifera associations, only comprising some rare agglutinated taxa. This facies-bound foraminiferal zone can be correlated with the "Rupel-3" zone (and upper part of the R-2 zone) of the Septaria Clay Formation of northern Germany, with its similar organic-rich facies. It is thought that this episode coincides with a humid and warm temperate climatic phase, and the rich supply of terrestrial organic matter (more than 50% terrestrial, as mainly derived from the adjacent land), caused acidic conditions at the sediment-water interface and in surficial sediments, leading to dissolution of most of the calcitic tests. The underlying calcareous-rich Terhagen member, similar to the R-2 zone in Germany, contains less organic matter and is not decalcified. On the other hand it appears that some thin marly layers (i e. calcareous-rich horizons, generally bearing septaria concretions), coincide with rich and diversified microfaunas, which appear to be enriched both in planktonic and benthonic microfossils. It is thought that specific (probably HCO3- anion rich, i.e. CaCO3- saturated, or only weakly undersaturated) watermasses, as e.g. occurring during warm arid periods, may have triggered (as far as sufficient appropriate nutrients were available) these relatively brief periods (of some thousands of years) of "high productivity" of carbonate secreting organisms, thus favouring the primary deposition of these CaCO3-rich intercalations, which later formed these septaria- bearing horizons.
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