Hull Geological Society
Mike Horne FGS
This is unfinished work that has not been edited or peer reviewed by the Society.
The Geochemistry of the Holderness Tills and some others
Till Geochemistry
[Mike Horne updated
1/5/2021]
Preamble and
thoughts.
There seems to be no
easy way of distinguishing the Tills of Holderness and surrounding areas other
than the colour of the matrix. This project was an attempt to investigate if the
colours are linked to geochemical markers.
The samples were
collected from cliff and beach exposures in 2007-2009, plus two archives samples
from the 1960s. They were analysed using Inductively Coupled Plasma Emission
Spectroscopy (ICP-ES). Small (whole rock) samples were prepared by manually
grinding in a mortar and pestle, picking out any gravel sized particles, and
then being extracted with aqua regia (a mixture of nitric and sulfuric acids) in
a PTFE bomb heated in a microwave [note - check this with Bob]. All samples went
through the same process.
The results for
silicon are probably not reliable because silica would not have been completely
dissolved [note – check this with Bob]. The results for sodium may not be
reliable because some samples from beach deposits will have been saturated with
sea water and other cliff deposits may have been moistened with sea water spray.
Some data from the samples are colour coded in the spreadsheet for their
probable stratigraphy.
Generalised patterns
seen so far are –
·
a few samples were high in calcium – these were overlying Chalk or the till was
derived from nearby Chalk exposures
·
The Red Band and Grey Band samples were low in calcium. Samples high in calcium
occurred near chalk exposures.
·
The Basement Till seems to have more magnesium than the Skipsea & Withernsea
Till
·
Basement Till and associated layered silts seem to be higher in phosphorus and
zirconium.
Generalised
Stratigraphy –
·
Alluvium and mere lake beds
·
Post glacial gravels
·
Withernsea Till
·
Skipsea Till
·
Smears of Rowe Chalk, Grey Band and Red Band (base to top) within the Skipsea
Till
·
Skipsea Till
·
Layered silts beneath the Skipsea Till
·
?Bridlington Crag
·
Basement Till
·
Older Tills exposed in Norfolk
Conclusions
The author and
colleagues were unable to find a geochemical signal that matches the colours of
the Tills.
Suggestions for future research.
This project used
“whole rock” for the analyses and will not be repeated by the author. This
project shows that there are possibilities for defining the Tills geochemically.
A new set of samples could be collected; more samples from the Withernsea Till
would be required. The silt and clay fractions could be separated before the
samples are analysed.
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