A BOREHOLE AT WENHASTON, NEAR HALESWORTH HOWARD MOTTRAM
In 1984 I logged some boreholes that were drilled in the Blyth River Gravel Pit at Wenhaston. One borehole (BH 5) went through the Paleogene (Lower Tertiary) strata which are relatively thin hereabouts and are poorly documented in drillers’ well logs. Although the original log of this, and other boreholes drilled at the site, have been supplied to the BGS on a few occasions, the information still doesn’t appear in Onshore Borehole Records in the BGS Information Hub. Since the time when I logged the borehole, the identification and naming of the various Paleogene strata found in the region has evolved; - Knox et al., 1990; Moorlock et al., 2000; Aldiss, 2012; 2014; 2015; King, 2016. It is therefore worthwhile not only of taking the opportunity of putting the log into the public domain but to also provide it in an updated form.
Notes
• In the table overleaf, names of Paleogene strata have been italicised for clarity.
• The pebbles in the gravels of the Westleton Beds were composed of flint. No quartzose pebbles were found in the borehole.
• The beds here attributed to the Upnor Formation are muddier and less sandy than is usual for this stratum. Here the beds are more akin to the lower part of the “Hales Clay” (HC1) which may be considered as a northerly equivalent of the Upnor Formation.
• The top 30mm of the Chalk was very strong and resembled porcellaneous limestone.
• The BGS had a borehole drilled in 1992 at TM 4178 7627. This was 850m eastsouth-east of BH 5 and the BGS borehole (“Halesworh Borehole”) encountered the tops and bases of the different Paleogene facies and the top of the Chalk at very similar levels to those in BH 5.
References
Aldiss, D. T. (2012). The stratigraphical framework for the Palaeogene successions of the London Basin, UK. British Geological Survey, Open Report OR/12/004.
Aldiss, D. T. (2014). The stratigraphical framework for the Palaeogene successions of the London Basin, UK., version 2 with minor revisions. British Geological Survey, Open Report Open Report OR/142/008.
Aldiss, D. T. (2015). Paleogene. In Lee, J.R., Woods, M.A. & Moorlock, B.S.P. (eds), British Regional Geology: East Anglia. 81-89. British Geological Survey, Keyworth. King, C. (2016). (ed. Gale, A. S. & Barry T. L.). A revised correlation of Tertiary rocks in the British Isles and adjacent areas of NW Europe. Special Report Number 27. The Geological Society of London
Knox, R. W. O’ B., Morigi, A. N., Ali, J. R., Hailwood, E. A. & Hallam, J. R. (1990). Early Paleogene stratigraphy of a cored borehole at Hales, Norfolk. Proc. Geol. Ass. 101, 145-151.
Moorlock, B. S. P., Hamblin, R. J. O., Booth, S. J. & Morigi, A. N. (2000). Geology of the country around Lowestoft and Saxmundham. Memoir of the British Geological Survey, Sheets 176 and 191 (England & Wales). British Geological Survey, Keyworth.
H. B. Mottram salhow@talktalk.net
BH 5 (National Grid Reference TM 40972 73445);-
+19.60m OD ground level
brown fine to coarse SAND & fine to medium with coarse GRAVEL.
+18.35m OD
brown – yellow gravelly fine to medium SAND.
+15.10m OD
pale yellow fine to medium SAND.
+12.40m OD
interlayered;- orange silty fine to medium SAND & pale grey silty CLAY.
some ferruginous seams, mica, carbonaceous material
+9.80m OD
orange and yellow fine to medium SAND.
some ferruginous and clay seams
+5.60m OD
orange silty fine SAND.
some mica, carbonaceous material, shell fragments, ferruginous and clay seams
+1.10m OD
red-brown silty fine to medium SAND.
some mica, carbonaceous material, clay seams
-1.40m OD
grey silty fine to medium SAND.
some shell fragments, clayey silt seams
-5.10m OD
hard grey sandy silty CLAY.
“cementstones” at -5.10 to -5.40, -7.40 to -7.70 -14.90m OD
interlayered; blue-green CLAY & silty fine SAND. -15.90m OD (transitional change)
interlayered; brown silty CLAY & fine sandy SILT. -21.40m OD (transitional change)
hard grey-brown silty CLAY. bands of fine sand and green clay
some pyrite, carbonaceous material, shell fragments
layer of flint pebbles at base
-29.40m OD
weak white CHALK. top silicified ?
-29.90m OD (base of borehole)
WESTLETON BEDS
NORWICH CRAG FORMATION
CHILLESFORD BEDS
HARWICH FORMATION
READING FORMATION
UPNOR FORMATION
ORMESBY CLAY LISTA FORMATION
WHITE CHALK GROUP