Herenthout borehole (044E0318)
Description and interpretation
Pieter Laga
November, 2006
Part of hydro/05neb campaign
Customer and Scientific co-ordinator : SCKCEN
Master of Works : ONDRAF/NIRAS
TABLE OF CONTENTS
1. General information
2. Comments
2.1. Comment on the quality of the cores
2.2. Comment on the description
2.3. Comment on the interpretations
3. Geological description
4. Geological interpretation
4.1. Overview
4.2. Comment
4.2.1.The Pleistocene and Neogene Formations
4.2.2.The Oligocene Formations
4.2.3.The Eocene Formations
ANNEX : Photos of cores
References :
Lie S.F., Broothaers M., and Uyttendaele D. (2006) Drilling and geological report of the Essen-1 well. 1-122. Faninbel report to ONDRAF/NIRAS, Lille, Belgium.
1. General information (extract archive GSB)
Kaart nr.: 044E
PLAAT: Berlaar
Nr.: 0318 (V, d)
Type Boring: BORING
Topografische kaart: 16/6
Uitgevoerd te: HERENTHOUT
Post nr.: 2270
Adres boorplaats: Merodese Bossen, Bevelse Steenweg, 2270 Herenthout
Opdrachtgever: SCKCEN (ONDRAF/NIRAS)
Boorfirma: n.v. Smet-GWT, Dessel
Boordatum: nov.-dec.- 2005
Topografie: SCK CEN
Stalen door:
Boormethode: drilling method, straight flush and cored
Lengte & doormeters: core diameter Ø 10cm
Grondwaterstanden:
1ste maal:
Bij rust:
Tijdens pompen:
Debiet:
Waterzaak nr.:
Totale diepte: 218 m
Stalen bewaard: at the SCKCEN (Belgian Nuclear Research Centre)1
Maaiveld / ref. peil: 10.385 m a.s.l. (or m TAW); drilling table is equal to ground surface
X: 175304 m
Y: 202909 m
NIS code: 13012
2. Comments
2.1. Comment on the quality of the cores
The quality of the cores is very good in the clay and in the very clayey sand sections. The cores are usually longer than the cored length, probably due to the extension of the core sediment in the core-barrel (swelling of the clay).
In more sandy and sand section, the length of the cores is often shorter than the cored length and the cores are often disturbed (presence of open fissures, cracks and voids). In some cases, the sandy core is disturbed by fluidity of the sand (after putting down cores with a water saturated sediment in horizontal position).
2.2. Comment on the description
The description is based on the upper longitudinal section of the cores. The cores were indeed longitudinally sawed in two unequal parts, the upper one, being the thinnest part (roughly one third), was available for description, and the lower part was immediately packed under vacuum conditions.
As this material should stay available for many people, the cores couldn't be investigated destructively. For instance, slickenslide observations are mentioned only in the core numbers 86 and 106. However, in nearly all the pure heavy (wax-like) clay, this feature can be present, but a systematic search for these slickenslides should cause a destruction of the concerned cores. It is difficult to say if these features are natural or artefacts. Probably they are due to compaction and are of minor importance.
2.3. Comment on the interpretations
Preliminary remarks
Although cores should provide the best material for geological descriptions, the interpretation of a cored borehole, can not be given without any doubt.
In general, at greater depths, the characteristics of lithologic units are different than in outcrops (alteration effects near the surface and lateral facies changes at greater distances from the corresponding outcrop zone).
Despite the performance of the drilling and coring operations during the drilling of Herenthout and Essen boreholes, the recovery is not 100 %. Especially in borehole sections with sudden changes of the lithology and the presence of sandstone concretions or layers in unconsolidated sediments, core losses occurred.
In addition, full cylindrical sections of cores of 10, 18, 20 or 40 cm were cut off for laboratory research ad in the case of Essen borehole, even complete cores (of 1 m) were sent to the geomechanic laboratory and were therefore not available. Globally that means that 30 % of the cored section is not covered by a core description. Although this situation is inevitable in the given concept of research boreholes, nevertheless it means that important lithologic features can have been missed and that the reliability of the interpretation is diminished.
In many cases, the geophysical well logs can meet this loss of information. However, the actual printouts of the logs without changes in scale, do not allow to observe minor but important features of the usual log configuration in the investigated geological units.
For all these reasons, changes in the lithostratigraphic interpretation may necessarily be made once geophysical logs at a scale better adapted to the natural variability of the sediment are available and after completion of the paleontologic and the sedimentologic investigations.
3. Geological description
Description of cuttings
ref. : Lie S.F., Broothaers M., and Uyttendaele D. (2006) Drilling and geological report of the Essen-1 well. 1-122. Faninbel report to ONDRAF/NIRAS, Lille, Belgium.
Depth(m) Lithology , Colour , Grain-size (for sand only) , Glauconite content
Descrition/Remarks
Herenthout 1
Samples were described when wet.
00.00 - 01.00 S , brown , f , very low , plant material
01.00 - 02.00 S , brown , m-f , low , plant material
02.00 - 03.00 S , green brown , c-m , moderate
03.00 - 04.00 S , dark green , c-m , high , badly sorted
04.00 - 05.00 S , dark green , c-m , high , badly sorted
05.00 - 06.00 S , dark green , c , high , badly sorted
06.00 - 07.00 S , dark green , c-m , high , badly sorted
07.00 - 08.00 S , darker green , c-m , high , badly sorted
08.00 - 09.00 S , grey green , c-m , high , badly sorted
09.00 - 10.00 S , grey green , c-m , moderate , badly sorted
10.00 - 11.00 S , grey green , vc-m , moderate to high , badly sorted
11.00 - 12.00 S , grey green , vc-m , moderate to high , very badly sorted, gravel sized particles
12.00 - 13.00 S , grey green , vc-m , moderate to high , very badly sorted, less gravel sized particles
13.00 - 14.00 S , greyish dark green , m , high , moderately well sorted
14.00 - 15.00 S , greyish dark green , m , high , moderately well sorted
15.00 - 16.00 S , greyish dark green , m , high , moderately well sorted
16.00 - 17.00 S , greyish dark green , m , high , moderately well sorted
17.00 - 18.00 S , dark green , m , high , moderately well sorted
18.00 - 19.00 S , dark green , m-f , high , moderately well sorted
19.00 - 20.00 S , dark green , m , high , moderately well sorted
20.00 - 21.00 S , dark green , m , high , moderately well sorted
21.00 - 22.00 S , dark green to black , m-f , very high , moderately well sorted
22.00 - 23.00 S , dark green to black , f , very high , well sorted
23.00 - 24.00 S , dark green to black , f , very high , well sorted
24.00 - 25.00 S , dark green to black , m-f , very high , moderately well sorted
25.00 - 26.00 S , dark green to black , m-f , very high , moderately well sorted
26.00 - 27.00 S , dark green to black , m-f , very high , moderately well sorted
27.00 - 28.00 S , dark green to black , m-f , very high , moderately well sorted
28.00 - 29.00 S , dark green to black , m-f , very high , moderately well sorted
29.00 - 30.00 S , dark green to black , m-f , very high , moderately well sorted
30.00 - 31.00 S , dark green to black , f , very high , well sorted
31.00 - 32.00 S , dark green to black , f , very high , well sorted
32.00 - 33.00 S , dark green to black , f , very high , well sorted
33.00 - 34.00 S , dark green to black , f , high , moderately well sorted, shell fragments
34.00 - 35.00 S , dark green to black , f , high , moderately well sorted, shell fragments
35.00 - 36.00 S , dark green to black , f , high , moderately well sorted, shell fragments
36.00 - 37.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
37.00 - 38.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
38.00 - 39.00 S , dark green to black , m , high , well sorted
39.00 - 40.00 S , dark green to black , m , high , well sorted
40.00 - 41.00 S , dark green to black , m , high , well sorted
41.00 - 42.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
42.00 - 43.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
43.00 - 44.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
44.00 - 45.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
45.00 - 46.00 S , dark green to black , c-m , high , moderately well sorted, less shell fragments
46.00 - 47.00 S , dark green to black , c-m , high , moderately well sorted, shell fragments
47.00 - 48.00 S , dark green to black , c-m , moderate , moderately well sorted
48.00 - 49.00 S , dark green to black , c-m , moderate , moderately well sorted
49.00 - 50.00 S , grey/dark green , gr-vc , moderate , very badly sorted, coarse Q grains
50.00 - 51.00 S , grey/dark green , gr-vc , moderate , very badly sorted, coarse Q grains
51.00 - 52.00 S , dark green to black , vc-c , moderate to high , badly sorted, some coarse Q grains
52.00 - 53.00 S , dark green to black , m , moderate to high , moderately well sorted
53.00 - 54.00 S , dark green to black , c , high , moderately well sorted, shell fragments
54.00 - 55.00 S , dark green to black , c , high , badly sorted, shell fragments
55.00 - 56.00 S , dark green to black , vc-c , moderate to high , badly sorted, shell fragments
56.00 - 57.00 S , dark green to black , vc , moderate , badly sorted, shell fragments
57.00 - 58.00 S , dark green to black , vc-c , moderate , moderately well sorted, shell fragments
61.00 - 62.00 S , dark green , m , moderate , well sorted
Herenthout 2
Samples were described when wet.
20.00 - 21.00 S , dark green to black , c-m , very high , badly sorted: coarse Q grains and fine glauconite
22.00 - 23.00 S , dark green to black , c-m , very high , badly sorted: coarse Q grains and fine glauconite
23.00 - 24.00 S , dark green to black , vc-m , very high , badly sorted: very coarse Q grains (content higher than 20-21 & 22-23) and fine glauconite
25.00 - 27.00 S , dark green to black , c-m , very high , badly sorted: coarse Q grains and fine glauconite
27.00 - 30.00 S , dark green to black , c-m , very high , badly sorted: coarse Q grains and fine glauconite, small shell fragments
34.00 - 36.00 S , dark green , c-m , high , badly sorted: coarse Q grains and fine glauconite, small shell fragments
36.00 - 38.00 S , dark green , m , high , badly sorted: Q grains and fine glauconite, important amount of small and large shell fragments
38.00 - 40.00 S , dark green , c-m , high , badly sorted: coarse Q grains and fine glauconite, important amount of small and large shell fragments
40.00 - 41.00 S , dark green , m , high , moderately sorted: Q grains and fine glauconite, small amount of small and large shell fragments
41.00 - 42.00 S , dark green , m , high , moderately sorted: Q grains and fine glauconite, small amount of small and large shell fragments
42.00 - 43.00 S , dark green , c-m , high , moderately sorted: coarse Q grains and fine glauconite, very small amount of small and large shell fragments
44.00 - 45.00 S , dark green , m , high , moderately to well sorted: Q grains and fine glauconite, very small amount of small and large shell fragments
46.00 - 47.00 S , dark green , c-m , high , badly sorted: coarse Q grains and fine glauconite, small amount of small and large shell fragments
47.00 - 48.00 S , dark green , m , moderate , moderately sorted: Q grains and fine glauconite, small amount of small and large shell fragments
48.00 - 49.00 S , grey green , g-c , moderate , very badly sorted: gravel sized angular Q grains
49.00 - 50.00 S , grey green , g-c , moderate , very badly sorted: gravel sized angular Q grains, small of shell fragments
50.00 - 51.00 S , grey green , vc-c , moderate , badly sorted, shell fragments
51.00 - 52.00 S , green grey , g-c , moderate , very badly sorted, shell fragments, greener than 50-51
53.00 - 55.00 S , grey , g-f , low , very badly sorted, very coarse Q grains and green/black grains, large shell fragments, clayey
55.00 - 56.00 Cly , grey , f-vf , very low , sticky, clayey very fine sand to silt
57.00 - 58.00 S,Cly , grey , clay , very low , clayey with coarse Q grains
59.00 - 60.00 S,Cly , grey , clay , traces , clayey with coarse Q grains
60.00 - 61.00 S , greenish grey , f-vf , very low , silty,very fine sand
61.00 - 62.00 S , greenish grey , f-vf , very low , silty,very fine sand
62.00 - 63.00 S,Cly , grey , clay , traces , clayey with coarse Q grains
63.00 - 64.00 S,Cly , grey , clay , traces , clayey with coarse Q grains
64.00 - 65.00 S,Cly , grey , clay , traces , clayey and silty with coarse Q grains
65.00 - 67.00 S,Cly , grey , clay , traces , clayey with coarse Q grains
67.00 - 68.00 Cly , grey , clay , traces , clayey with coarse Q grains
68.00 - 69.00 Cly , grey , clay , traces , clayey with some coarse Q grains
69.00 - 70.00 Cly , grey , clay , traces , clayey with very small amount of coarse Q grains
70.00 - 71.00 Cly , grey , clay , traces , clayey with small amount of coarse Q grains
71.00 - 72.00 Cly , grey , clay , traces , clayey with small amount of coarse Q grains
72.00 - 74.00 Cly , grey , clay , traces , clayey with small amount of coarse Q grains
74.00 - 75.00 Cly , grey , clay , very low , clayey with very small amount of coarse Q grains
75.00 - 76.00 Cly , grey , clay , very low , clayey with very small amount of coarse Q grains, clay flakes (cut off particles)
76.00 - 77.00 Cly , grey , clay , very low , clayey with stony fragments, clay flakes (cut off particles)
77.00 - 78.00 Cly , grey , clay , traces , clayey with very small amount of coarse Q grains
78.00 - 79.00 Cly , grey , clay , traces , clayey with small amount of coarse Q grains
79.00 - 80.00 Cly , grey , clay , very low , clayey with small amount of coarse Q grains, clay flakes (cut off particles)
80.00 - 81.00 Cly , grey , clay , very low , silty material with clay flakes (cut off particles)
81.00 - 82.00 Cly , grey , clay , very low , silty material with clay flakes (cut off particles)
82.00 - 83.00 Cly , grey , clay , traces , silty material with clay flakes (cut off particles)
83.00 - 84.00 Cly , grey , clay , traces , silty material with clay flakes (cut off particles)
84.00 - 86.00 Cly , grey , clay , traces , silty material with clay flakes (cut off particles)
86.00 - 87.00 Cly , grey , clay , traces , silty material with clay flakes (cut off particles), medium to coarse Q grains
87.00 - 88.00 Cly , grey , clay , traces , silty material with clay flakes (cut off particles),medium to coarse Q grains
88.00 - 89.00 Cly , grey , clay , traces , clay flakes (cut off particles), medium to coarse Q grains
89.00 - 90.00 Cly , grey , clay , traces , clay flakes (cut off particles), medium to coarse Q grains
90.00 - 91.00 Cly , grey , clay , traces , clay flakes (cut off particles), medium to coarse Q grains, shell fragments
91.00 - 92.00 Cly , grey , clay , traces , clay flakes (cut off particles)
92.00 - 93.00 Cly , grey , clay , traces , clay flakes (cut off particles)
93.00 - 94.00 Cly , grey , clay , traces , clay flakes (cut off particles)
94.00 - 95.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), medium Q grains
95.00 - 96.00 Cly , grey , clay , traces , clay flakes (cut off particles)
96.00 - 97.00 Cly , grey , clay , traces , clay flakes (cut off particles),shell fragment
97.00 - 98.00 Cly , grey , clay , traces , clay flakes (cut off particles)
98.00 - 99.00 Cly , grey , clay , traces , clay flakes (cut off particles)
99.00 - 100.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some Q grains
100.00 - 101.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), shell fragments
101.00 - 102.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
102.00 - 103.00 Cly , grey , clay , traces
clayey material with clay flakes (cut off particles), shell fragments
103.00 - 104.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), shell fragments
104.00 - 105.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
105.00 - 106.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
106.00 - 107.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some Q grains
107.00 - 108.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), shell fragments
108.00 - 109.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some Q grains
109.00 - 110.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), coarse fragments, shell fragments
110.00 - 111.00 Cly , grey , clay , traces , less clayey material, coarse fragments, shell fragments
111.00 - 112.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), coarse fragments, shell fragments
112.00 - 113.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), coarse fragments, shell fragments
113.00 - 114.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), coarse fragments
114.00 - 116.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
116.00 - 117.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), small amount of coarse material
117.00 - 118.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
118.00 - 120.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), shell fragments
120.00 - 121.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some coarse fragments
121.00 - 122.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
122.00 - 123.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
123.00 - 125.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
125.00 - 126.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
126.00 - 127.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
127.00 - 128.00 Cly , grey , clay , traces , clayey material
128.00 - 129.00 Cly , grey , clay , traces , clayey material, some shell fragments
129.00 - 130.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
130.00 - 132.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
132.00 - 133.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some coarse fragments
133.00 - 134.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
134.00 - 135.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles)
135.00 - 136.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), shell fragment
136.00 - 138.00 Cly , grey , clay , traces , clayey material with clay flakes (cut off particles), some coarse fragments
138.00 - 139.00 Cly , grey , clay , traces , clayey material (siltier than before) with clay flakes (cut off particles), some coarse fragments
139.00 - 140.00 Cly , grey , clay , traces , clayey material (siltier than before) with clay flakes (cut off particles), some coarse fragments
140.00 - 141.00 Cly , grey , clay , traces , clayey material (siltier than before) with clay flakes (cut off particles), some coarse fragments
141.00 - 142.00 Cly , grey , clay , traces , clayey material (siltier than before) with clay flakes (cut off particles), some coarse fragments
142.00 - 143.00 S , grey , f , low , fine sand,well sorted, clay flakes
143.00 - 144.00 Cly , grey , clay , traces , clayey material (silty) with clay flakes (cut off particles), coarse fragments
144.00 - 146.00 S , grey , f , low , fine sand, well sorted, small clay flakes
146.00 - 148.00 S , grey , c-f , low , badly sorted sand,slightly clayey
148.00 - 149.00 S , grey , c-f , low , badly sorted sand,slightly clayey
149.00 - 150.00 S , grey , vc-f , low , very badly sorted sand, slightly clayey, shelly fragments
150.00 - 151.00 S , grey , c-f , low , badly sorted sand, slightly clayey
151.00 - 152.00 S , grey , vc-f , low , very badly sorted sand, slightly clayey, shelly fragments
152.00 - 153.00 S , grey , c-f , low , badly sorted sand, slightly clayey, shell fragments
153.00 - 154.00 Cly , grey , clay , traces , shell fragments
154.00 - 155.00 Cly , grey , clay , traces , sand grains
155.00 - 156.00 Cly , grey , clay , low , shell fragments, coarse fragments
156.00 - 157.00 Cly , grey , clay , low , coarse fragments, silty
157.00 - 158.00 Cly , grey , clay , low , some coarse fragments
158.00 - 159.00 Cly , grey , clay , low , sand grains
159.00 - 160.00 Cly , grey , clay , low , sand grains, coarse fragments
160.00 - 161.00 Cly , grey , clay , low , silty, coarse fragments
161.00 - 162.00 S , grey , f , low , coarse fragments
162.00 - 163.00 S , grey , m-f , low , coarse fragments, foraminifera, clayey
163.00 - 165.00 S , grey , m-f , low , coarse fragments, silty
165.00 - 166.00 S , grey , m , low clay flakes, shell fragments, coarse fragments, silty
166.00 - 167.00 S , grey , f , moderate , clayey
167.00 - 168.00 Si , grey , f , moderate , clayey
168.00 - 169.00 Si , grey , f , moderate , clayey
169.00 - 170.00 S , grey , m , low , shell fragments, foraminifera
170.00 - 171.0 S , grey , m , low , shell fragments, foraminifera
171.00 - 172.00 S , grey , vc-c , low , shell fragments, foraminifera
172.00 - 173.00 S , grey , vc-c , low , badly sorted with shell fragments, foraminifera, clayey
173.00 - 174.00 S , grey , vc-c , low , badly sorted with shell fragments, foraminifera, clayey
174.00 - 176.00 S , grey , vc-c , low , badly sorted with shell fragments, foraminifera, clayey
176.00 - 177.00 S , grey , m , traces , foraminifera
177.00 - 178.00 S , grey , m , traces , foraminifera
178.00 - 179.00 Cly , grey , clay , traces , some coarse grains
179.00 - 180.00 Cly , grey , clay , traces , a lot of coarse grains
180.00 - 181.00 , grey , vc-c , traces , badly sorted clayey sand, coarse fragments, shell fragments, clay flakes
181.00 - 182.00 , grey , vc-c , traces , badly sorted clayey sand, coarse fragments, stony fragments, clay flakes
182.00 - 183.00 , grey , vc-c , traces , badly sorted clayey sand, coarse fragments, stony fragments, clay flakes
183.00 - 184.00 , grey , vc-c , traces , badly sorted clayey sand, coarse fragments, stony fragments, clay flakes
184.00 - 185.00 , grey , vc-c , traces , stony fragments, clay flakes
185.00 - 186.00 , grey , vc-c , traces , stony fragments, clay flakes
186.00 - 187.00 grey , vc-c , traces , stony fragments, clay flakes
187.00 - 188.00 grey , vc-c , traces , stony fragments, clay flakes
188.00 - 189.00 S , grey , vc-c , traces , clayey sand, small clay flakes
189.00 - 190.00 S , grey , vc-c , traces , clayey sand, small clay flakes
190.00 - 191.00 S , grey , m , low , slightly clayey
191.00 - 192.00 S , grey , c-m , low , clayey, mm scale stone fragments
192.00 - 193.00 S , grey , m-f , low , clayey
193.00 - 194.00 S , grey , m-f , low , clayey
194.00 - 195.00 S , grey , m , low , clayey, clay flakes
195.00 - 196.00 S , grey , m , low , clayey
196.00 - 197.00 S , grey , m , low , clayey, clay flakes
197.00 - 198.00 S , grey , m , low , clayey, clay flakes
199.00 - 200.00 S , grey , m , low ,
200.00 - 201.00 S , grey , c-m , low , coarse fragments
201.00 - 202.00 S , grey , m , low ,
203.00 - 206.00 S , grey , c-m , low , some coarse fragments
206.00 - 208.00 S , light grey , c-m , traces , well sorted
Core description - P. Laga
core Nr. * drilled from to in m * (length of the recovered core)
01. 125 - 126 m (0.18 m - from 0.79 to 0.97 m)
(dried out core)
Light-brown very fine silty and clayey sand, micaceous; not calcareous; sample from the shoe of the core barrel: dark-brown mottled, clayey sand, biodisturbed
02. 126 - 127 m (0.00 m)
(sample from the shoe of the core barrel is the only sample)
Same light and dark-brown very fine sand, micaceous, silty and clayey, biodisturbed, some shell fragments; pieces of dark-brown clay intensively biodisturbed.
03. 127 - 128 m (0.72 m - from 0 to 0.72 m)
(dried out core).
Light brown very fine silty and clayey sand, micaceous; on 25 cm ; irregular contact with somewhat darker clayey sand.
Between 33.50 en 40.50 cm: a kind of "window" with a dark brown rim, angular and filled with a paler fine sand with a very fine stratification, a little bit downwards curved and with a circular track, Ø 0.5 cm, also with a dark rim from 0.40 cm: the sediment is strongly torn.
04. 128 - 129 m (0.89 m - from 0.83 - 0.72 m)
(dry sample - some open cracks in the core + a shoe sample)
Light-brown very fine sandy clay or silt, micaceous, many dark-brown small spots, some dots of shell remains on 34 and 48 cm; below (from 58 cm) larger tracks, filled up with fine loose sand; shoe sample: 6 cm, idem - with a pyrite concretion.
05. 129 - 130 m (0.00 m)
(sample from sampling shoe is the only one)
same brown-grey sandy clay to clayey sand, intensively biodisturbed.
06. 130 - 131 m (0.67 m - from 0 to 0.77 m)
(dry out core sample - core seriously disturbed from 46-67 cm)
Light brown-grey very fine grained sand, silty, clayey and micaceous traces of slightly oblique clay lenses, very much disturbed by biodisturbance; mainly not calcareous; at 42cm, some small shell remains; 46-67 cm: same sediment, but disturbed by fluidity (= disturbed core sample by liquefaction due to water saturation)
07. 131 - 132 m (0.78 m - from 0.18 to 0.96 m)
(disturbed core at the top over 5 cm and cracked from 67 to the end)
Brown fine silty sand with many more clayey spots (traces of intense biodisturbance); non calcareous, except for some shell remains at 50 cm and 81 cm; at 63-67 cm a sector of a big shell with a thin weathered wall; many small pale round spots (=tracks) and from 50 cm on also bigger tracks (Ø > 5 mm)
08. 132 - 133 m (0.83 m)
(at the top: 5 cm rubbish and seriously disturbed over an other 5 cm; disturbed by many open cracks from 38-76 cm, from 51 cm, seriously disturbed)
Same light brown-grey fine silty and clayey sand, very mottled by intense biodisturbance and traces of disturbed, more clayey sand at 30 cm: track Ø 1.5 cm, filled up with fine loose sand, small traces of shell remains at 46 cm
09. 133 - 134 m (0.84 m from -0.08 to 0.76 m - 20 cm lab. sample cut off)
(good undisturbed core from 8-33 cm, slightly disturbed core by fluidity up to 49 cm, cracked and disturbed core from 49-76 cm)
Same mottled sand till 49 cm, intensively biodisturbed; small shell remains on 2, 70 and 71 cm.
10. 134 - 135 m (0.77 m from 0.00 to 0.77 - 20 cm laboratory sample)
(disturbed core: 0 - 3 cm, 64 - 77 cm, slightly disturbed over the whole length)
Brown-grey, darker fine sand with some medium fin grains; small shell remains at 8, 13, 18, 50, 53, 56 cm - section of a bigger shell Ø > 3 cm); a few grains of glauconite; darker zone from 46-70 cm with more clayey irregular spots; a nice track from 48-50 cm, whitish at the centre with dark border
11. 135 - 136 m (0.00 m) no shoe-sample
12. 136 - 137 m (0.87 m - 20 cm laboratory sample)
(20 cm rubbish, nearly undisturbed core from 10 to 60 cm, last 17 cm disturbed, last 10 cm nearly without sedimentary details)
Slightly greenish-brown mottled fine sand, more glauconite grains, same mottled design, very biodisturbed with many tracks with darker rim; from 40-43 cm an irregular spot, filled up with more glauconitic sand; still micaceous; slightly calcareous
13. 137 - 138 m (0.85 m)
(4 cm disturbed on top and disturbed by fluidity (due to water saturation) from 63-85 cm; good core from 4-35 cm, slightly disturbed from 35-63 cm with sedimentary design and without from 63-85 cm)
Pale and darker brown mottled fine silty poorly micaceous sand with coarser medium sized grains and with some glauconite; non calcareous
14. 138 - 139 m (0.87 m from -11 to 76 cm - 20 cm laboratory sample)
(undisturbed perfect core from -4 to 27 cm; slightly disturbed, cracked with open fissures up to 55 cm; seriously cracked up to 69 cm and nearly without sedimentary design to the end)
Dark-green very fine clayey glauconite sand, many dark-green spots, fully biodisturbed, micaceous, non calcareous; a brown to rose spot at -4 to -2 cm and at 65 cm
15. 139 - 140 m (0.92 m)
(from 8-24 cm only crumbled core; from 24-28 cm broken core; from 28 cm to the bottom: nearly undisturbed core, only a few cracks)
Dark-grey clayey very fine sand or sandy clay, micaceous, few glauconite grains; from 35 cm: a pale-grey clay with green sandy lenses, intensively biodisturbed, glauconitic and micaceous; thicker clay layers at 52, 83 and 90 cm (> 2 cm thick); the clay layer at 90 cm (2 cm) is oblique (35°), no chalk; at 20 cm: remains of a tubular shell (scaphopoda?)
16. 140 - 141 m (1.07 m from -11 to 96 cm) 20 cm lab. sample: 140.21 to 140.41)
Green-grey fine to medium fine clayey glauconitic sand, some fine clay laminae disturbed by biodisturbance and very small spots and pieces of clay (broken laminae) dispersed in the sand; concentration of clay laminae at 1-3 cm, 10-12 cm, 16-19 cm; concentration of clay spots at 51-56, 63-67, 90-94 cm (rounded clay laminae); still micaceous; at 20 cm: a pyrite concretion of 4 cm x 3 cm
17. 141 - 142 m (0.87 m from -12 to 75 cm) lab. sample of 20 cm
(3 cm rubbish (fall down); good core from -9 to 75 cm, slightly disturbed from 58 cm on)
Fine green-grey slightly mottled sand intensively biodisturbed, with a few medium sized grains, micaceous, no chalk, 1 shell remain at 55 cm; from 37-63 cm: darker more clayey and glauconitic; whitish tracks at 23 cm and a 3 cm long one at 39 cm
18. 142 - 143 m (0.83 m from -12 to 71 cm - 20 cm lab. sample)
(core is disturbed by numerous open cracks, very few design visible)
Same glauconitic sand, darker more glauconitic from 40-75 cm with same pale tracks; no chalk; at 75.50 cm shell remains
19. 143 - 144 m (no core recovery)
20. 144 - 145 m (0.86 m from -10 to 76 cm - 20 cm lab. sample)
(from -10 to -4 cm: rubbish clay; from 20 cm to the end: seriously cracked by fluidity)
Dark-green glauconitic and shelly, fine grained, clayey sand; section of very thin walled shell at 32 cm (max Ø 3.5 cm) and at 56 cm; increasingly many Nummulites from 15 cm to the end
21. 145 - 146 m (0.83 m - 20 cm lab. sample)
(17 cm rubbish black clay at the top)
Dark-green fine glauconite, clayey sand with very indistinct mottles, biodisturbed, finely mottled from 40-70 cm; a few shell remains at 19, 29, 56, 63 and at 72 cm a nearly spherical pyrite concretion Ø 2.5 cm (= sand grains cemented by pyrite)
22. 146 - 147 m (0.76 m - from 21 to 97 cm)
(core segment is very thin broken up in 9 pieces; + not to much disturbed pieces are: 21-36 cm; 48-57 cm; 57-64 cm)
Grey-greenish very fine glauconitic sand; shell remains at 26-28 cm, 53-57 cm; 84, 89 and 95 cm)
21-36 cm: without sedimentary design
36-48 cm: totally fragmented core
48-57 and 57-64 cm: darker more clayey with some very indistinct strongly biodisturbed, more clayey laminae
64-97 cm: completely disturbed core by fluidity
23. 147 - 148 m (0.83 m from -6 to 77 cm - 20 cm lab. sample)
(-6 to 16 cm: rubbish, fallen down material; from 16-77 cm: very complete and undisturbed core)
Dark green grey fine clayey and glauconitic sand, from 20-58 cm: very mottled intensively biodisturbed, on top and at the bottom nearly without any sediment design, except for the few shell remains at 22, 32, 39, 41, 59, 61 and 65 cm; slightly calcareous
24. 148 - 149 m (0.55 m from 41 to 96 cm)
(very disturbed and very thin core samples, quite without any sediment design (= disturbed)
Same green-grey fine clayey glauconitic sand with some shell remains (at 48, 61, 70, 75 and 81 cm), calcareous
25. 149 - 150 m (0.70 m from 07 to 77 cm)
(disturbed and rubbish form 7 to 13 cm)
Green fine glauconitic clayey sand, with intensive biodisturbance, pale green filling up of larger tracks (Ø up to 2,5 cm); darker clayey disturbed layers and borders around the tracks; shell remains at 39 cm, 55, 58, 60, 64, and 71 cm; nearly no sediment design from 64 to 77 cm.
26. 150 - 151 m (0.85 m from -8 to 77 cm - 20 cm lab. sample at the bottom)
Same dark-green fine clayey glauconitic sand, biodisturbed and with some larger tracks (Ø up to 1,5 cm); from 48-64 cm presence of strongly biodisturbed layers of grey compact plastic clay (+ 1 cm thick), last 10 cm are slightly coloured; no chalk
27. 151 - 152 m (0.85 m from 12 to 97 cm)
(several cracks in the core)
12.00 - 35.50 grey-greenish sandy clay, intensively perforated by many small tracks and filled up with glauconitic sand; at 13 cm some shell remains; at 35-36 cm an irregular limit, (indistinct due to the biodisturbance) between a green sandy clay above and a grey less sandy clay below
35.50 - 80.00 a grey silty clay, with small black spots (sandy perforations with pyrite?) and at 70 cm a 6,5 cm long and 3,5 cm wide track filled up with a sandy silty clay with some glauconite grains
80.00 - 97.00 more plastic grey clay, still silty but less sandy
28. 152 - 153 m (0.68 m from -7 to 61 cm - 15 cm lab. sample from 81-96 cm)
(empty from 61-81 cm; core is dried out and completely broken up in pieces of approx. 5 to 10 cm )
Light grey plastic clay apparently with some very fine sand; some dark sandy joints with mica; only a small number of black spots of probably pyrite; no chalk.
29. 153 - 154 m (0.81 m from -5 to 76 cm - 20 cm lab. sample)
Pale grey plastic clay, from the top to 40 cm: decreasing number of black spots of pyritic micaceous sand (perforations?); lower part of the core with only some pale sandy spots and some black pyritic points; no chalk
30. 154 - 155 m (0.81 m from -5 to 76 cm - 20 cm lab. sample)
(dried out core)
Same pale-grey clay, plastic, only some black pyritic spots at the top (at 5 cm) also some sandy spots (fine perforations?); in the last 5 cm presence of some glauconite grains
31. 155 - 156 m (0.92 m from -8 to 84 cm - 10 cm lab. sample)
Grey-green clay with green glauconitic sand in laminae and as filling up of perforations; a grey plastic clay layer with some very small silty spots from -1 to + 2 cm; at 24 cm: a zone with very finely laminated whitish and black sand; from 45-75 cm, some black sandy spots; some micas
32. 156 - 157 m (0.82 m) from -6 to 76 cm - 20 cm lab. sample)
(completely dried out clay core with several cracks)
Green-grey very sandy glauconitic clay, intensively perforated (tracks 1-2 mm wide) filled up with glauconitic and/or pyritic sand; from 43-76 cm: dark-grey plastic clay with numerous fine pale silty spots ("vermiculations" of M. Gulinck) but perforated by larger tracks of Ø 1-2 cm), no chalk
33. 157 - 158 m (0.83 m from -7 to 76 cm)
-7.00 - 13.50 grey plastic clay with many very small silty perforations (= vermiculations) and at 11 and 13 cm, finely laminated with fine whitish sand
13.50 - 76.00 light grey sandy solid clay, some black (pyntic?) spots and pale spots, some glauconite grain at the top, increasing tot the bottom; intensively finely perforated slightly calcareous at the bottom; last few cm again grey clay without glauconite
34. 158 - 159 m (0.82 m from -9 to 73 cm - 20 cm laboratory sample)
(from -9 to +7 cm: very broken and disturbed core sample)
Light-grey slightly calcareous silty clay from -9 to 29 cm; from 29 cm to the bottom: again darker (plastic) clay with very thin silty spots (vermiculations) at the bottom; shell remains at 69 cm; obviously calcareous
35. 159 - 160 m (0.84 m from -8 to 76 cm - 20 cm lab. sample)
Light-grey silty sand or sandy silt with shell remains, very calcareous; from 20-40 cm: darker grey, still finely biodisturbed (very fine silty whitish spots); from 40-76 cm: again more compact plastic clay with "vermiculations" (silty spots)
36. 160 - 161 m (0.82 m from -6 to 76 cm - 20 cm lab. sample)
(rubbish -6 to +2 cm = dark clay)
02.00 - 08.00: dark-grey sandy clay, calcareous
08.00 - 17.00: same clay with laminae of clayey and glauconitic sand
17.00 - 76.00: dark-green to black glauconitic very clayey sand, biodisturbed with traces of shells from 33 cm, increasing to numerous calcareous spots at the bottom (a.o. weathered Nummulites)
37. 161 - 162 m (0.975 m -1.5 to 96 cm)
Dark-grey clayey sand with many Nummulites and some perforated lenses of pure dark-grey plastic clay at 13 and 20 cm; concentration of Nummulites just above the clay layer at 20 cm; at 30.5-31.50 cm an oblique very sharp limit, between an accumulation of yellowish Nummulites (from 27.50 to 31 cm) and a more green-grey fine slightly clayey sand; the grey sand changes gradually to pale-grey sand, still containing dispersed Nummulites
38. 162 - 163 m (0.75 m from 1 to 76 cm - 20 cm lab. sample)
(some open cracks in the sediment, in the last 15cm)
Fine grey nearly homogenous sand, glauconitic, clayey, only a few indistinct traces of biodisturbance, intensively homogenized by biodisturbance, very calcareous.
39. 163 - 164 m (0.75 m from 1 to 76cm - 20 cm lab. sample)
Same grey glauconitic sand, very homogeneous, some traces of shells at 12, 49, and 61 cm (thin walled Pecten shells)
40. 164 - 165 m (0.80 m from -4 to 76 cm - 20 cm lab. sample)
(-4 to 5 cm: fallen down material)
Same fine slightly clayey glauconitic homogenous sand, only a few traces of biodisturbance (pale spots)
41. 165 - 166 m (0.83 m from -7 to 76 cm - 20 cm lab. sample)
Same dark grey homogenous sand, calcareous, chalk stip at the top(core disturbed by many cracks run out and dried)
42. 166 - 167 m (0.81 m from -5 to 76 cm - 20 cm lab. sample)
(Fallen down material from -5 to +5 cm)
Dark-grey greenish strongly biodisturbed fine clayey and glauconitic sand with many indistinct traces of tracks; dispersed Nummulites are still present
43. 167 - 168 m (0.83 m from -7 to 76 cm - 20 cm lab. sample)
(-7 to 20 cm: disturbed by fluidity)
Same sand, traces of biodisturbance are more clearly visible, many slightly paler traces of tracks
44. 168 - 169 m (0.85 m from -9 to 76 cm - 20 cm lab. sample)
(strongly disturbed core from top to 23 cm, slightly disturbed from 23-40 cm)
Same grey glauconitic sand, somewhat lighter, some traces of biodisturbance (lighter spots in the lower part); very calcareous
45. 169 - 170 m (0.86 m from -10 to 76 cm - 20 cm lab. sample)
(top up to + 4 cm strongly disturbed core)
from 4-76 cm: light-grey fine glauconitic sand with several thin clay laminae around tracks and deformed by biodisturbance; shell remains at 30 cm, very calcareous
46. 170 - 171 m (0.68 m from 8 to 76 cm - 20 cm lab sample)
08.00 - 18.00: irregular contact between 15 and 20 cm; grey clay = rubbish
18.00 - 76.00: light-grey fine sand, very calcareous, with fine glauconite grains; from 22-25 cm: whitish zone with many Nummulites variolarius; on 30, 48 and 56 cm indistinct irregular figures of darker more clayey lines (biodisturbance or dissolved shells?)
47. 171 - 172 m (0.73 m from 03 to 76 cm - 20 cm lab sample)
(core is broken, but not disturbed: 6 main cracks in the core; from 14-25 cm: filled up with clay = rubbish)
Same grey fine calcareous sand with some very fine shell remains; on 26 cm same white spots; from 64-68 cm some indistinct brownish clayey lines (biodisturbance?)
48. 172 - 173 m (0.62 m from 14 to 76 cm - 20 cm lab sample)
(14-25 cm: clay = rubbish)
25.00 - 76.00: same grey fine very calcareous sand with several indistinct darker spots (= biodisturbance); only at 61 and 65 cm circular figures (= tracks)with a darker brownish more clayey rim; from 44-53 cm and from 66-74 cm also some lighter whitish spots
49. to 54. 173 - 179 m
(no recovery)
Second borehole - Herenthout 2
01. 178.39 - 178.79 m
(no recovery)
02. 209.09 - 210.00 m (0.45 m from 55 to 100 cm)
(from 209.09 to 209.30: completely disturbed core: soft clay with cuttings of calcareous glauconitic sandstone = rubbish)
55.00 - 72.50: at the top still some calcareous sandstone cuttings; brown-grey plastic clay; some small tracks filled up with fine glauconitic sand at the top; a sandy zone at 66-68 cm; lowest 2 cm: dark-grey clay with several small sandy tracks
72.50 - 75.50: dark brown-greenish clayey sand
75.50 -100.00: light-green glauconitic and micaceous fine sand and darker clayey zones, intensively biodisturbed, slightly calcareous
03. 210 - 211 m (0.85 m from 0 to 76 cm - 20 cm lab sample)
(core is much longer than the drilled section; core broken from 55-66 cm)
-9.00 - -7.00: rubbish with sandstone cuttings
-7.00 - 55.00: grey-green fine clayey sand, glauconitic and micaceous, intensively biodisturbed; no chalk
55.00 - 76.00: idem, gradually more clayey; finely at the bottom sandy clay with fine spots of dark plastic clay (biodisturbance)
04. 211 - 212 m (0.76 m from 0 to 76 cm - 20 cm core sample)
(core broken from 0-15 & from 50-76 cm; disturbed & rubbish core from 24-30 cm)
Same clayey sand and mainly sandy clay, intensively biodisturbed and broken up fine plastic clay in a more silty and sandy sediment; no chalk; at 31 cm a dark pyretic sandy spot; from 32-39 cm larger sand zone with pyretic concretions
05. 212 - 213 m (0.76 m from 0 to 76 cm - 20 cm lab sample)
(completely fragmented core, broken in numerous pieces)
Grey-green finely sandy and silty clay, micaceous; intensively biodisturbed, mixture of irregular darker clayey and lighter sand zons; no chalk
06. 213 - 214 m (0.76 m from 0 to 76 cm - 20 cm lab sample)
(from 0-27 cm core is completely broken in small pieces)
00.00 - 42.00: same silty and sandy intensively biodisturbed clay
42.00 - 76.00: grey-greenish very heavy plastic clay, nearly completely homogeneous and without any sediment design (only some very small darker irregular lines - probably pyretic)
07. 214 - 215 (0.74.5 m from 0 to 74.5 cm - 20 cm lab sample)
(core is completely broken in small pieces)
again the grey-greenish sandy and silty alternation of lighter more silty zones and darker more pure clay zones, dark from 7-30 and from 60-70 cm; the darker zones are characterized by a very fine design of pale silty spots, due to biodisturbance
08. 215 - 216 (0.76 m from 0 to 76 cm - 20 cm lab sample)
(from 0-40 cm the core is broken in numerous small pieces)
00.00 - 40.00: grey-green silty clay; a very dark (sandy) spot with pyrite (mainly amorphous)
40.00 - 76.00: grey-green very plastic heavy clay, some pyrite concretions; only a very indistinct design of darker and lighter spots as on a marble plate
09. 216 - 217 (0.76 m from 0 to 76 cm - 20 cm lab sample)
00.00 - 04.00: rubbish clayey sand
04.00 - 27.00: very heavy plastic homogeneous clay
27.00 - 42.00: slightly silty and sandy clay with very small white spots; at 34 cm a track (5 x 15 mm) filled up with pyrite concretion
42.00 - 47.00: dark grey-green heavy plastic clay
47.00 - 48.00: very finely laminated clay and fine silt/sand
48.00 - 53.00: transition from clay to sand with many small broken up clay laminae
53.00 - 76.00 olive-green very fine silty and clayey sand, traces of broken up clay laminae; from 53-65 cm some mica in the sand; no chalk
10. 217 - 218 (0.79 m from -6 to 73 cm)
-6.00 - 08.00: darker green fine clayey sand, glauconitic and micaceous
08.00 - 60.00: alternation of clay layers and sand layers; the clay layers are perforated by tracks and filled up with the green sand; clay layers: 8-14.5, 21-26, 37-41, 47-60 cm; at 25 cm a dark streak in the clay; at 55 cm a track filled up with shell remains (no Nummulites); at the bottom an oblique boundary (57 to 59.5 cm) between a brown clay layer and a green fine homogeneous glauconitic and micaceous (bigger mica pellets) sand; at the contact an accumulation of fine shell remains
60.00 - 79.00: same green glauconitic and micaceous sand
4. Geological interpretation
4.1. Overview
Top * Base * STRATIGRAPHIC UNITS
00.00 - 06.20 m Quaternary
06.20 - 28.00 m Diest Formation
28.00 - 49.20 m Berchem Formation
49.20 - 130.50 m Formation Boom
49.20 - 92.50 m Putte Member
92.50 - 112.50 m Terhagen Member
112.50 - 130.50 m Belsele-Waas Member
130.50 - 138.75 Zelzate Formation
130.50 - 138.75 m Ruisbroek Member
138.75 - 169.00 m Maldegem Formation (or St-Huibr.-Hern)
138.75 - 151.00 m Zomergem (?)& Onderdale Members
151.00 - 155.00 m Ursel Member
155.00 - 161.00 m Asse Member
161.00 - 169.00 m Wemmel Member
169.00 - 180.00 m Lede Formation
181.00 - 206.00 m Brussel Formation
206.00 - 218.00 m Tielt Formation - Egem Member
(end of the well logs)
AUTHOR: P.LAGA - Belgian Geological Survey - June 2006
4.2. Comment
4.2.1.The Pleistocene and Neogene Formations
The coring operations started in this well at a depth of 125.79 m, just above the base of the Boom Clay formation.
The interpretation of the Neogene sediments is based on the geophysical logs and on the description of boreholes in the neighbourhood, as there are: a Pidpa well (nr. 44E-180) executed in 1943 and a well at the castle of Gestel (community of Berlaar) executed in 1938 both without flush.
The boundary between the Diest and the Berchem Formations is mainly based on the thickness of the different units. The very high gamma peaks between 21.50 and 28.00 m are difficult to explain and do not correspond with the general image of the gamma curve at the boundary between these formations. Probably, the presence of mineralogical concretions caused these exceptional gamma-peaks. The presence of the Dessel Sands can 't be demonstrated.
The resistivity log marks very well the boundary between the Berchem and the Boom Formations.
4.2.2.The Oligocene Formations
The Boom Formation is represented by the Putte Member and the base of this member is marked by a very pronounced gamma peak, a nearly straight vertical resistivity curve over the whole thickness of this member, however a clear increase of the resistivity occurs at the depth of 62.50 m. This level may be the base of the W0, recognized in the Weelde borehole.
Also the gamma curve is slightly curved, with a maximum at the depth of 65 m.
The second member of the Boom Formation, the Terhagen Clay, starts at the level of 92.50 m and is characterized by a continuous downward decrease of the gamma ray.
The boundary with the underlying Belsele-Waas Member is marked by a sudden and important increase of the resistivity and an even decrease of the gamma ray. From the top the resistivity is constantly increasing downwards just to the base of the member and the formation. The first cores of this well belong to the lower part of this member. The lower boundary is marked by a darker coloured silty sand with many biodisturbance of the underlying member. The contact between the two formations is not visible on the core (disturbed core).
The underlying Zelzate Formation is represented only by the Ruisbroek Member. The resisitivity is higher and the lower gamma ray is very pronounced. The basal meter of the member is characterized by a dark green coloured glauconitic sand. On the geophysical logs however the lower boundary is very well marked and shows an important hiatus: there is a sudden and pronounced increase of the gamma ray and the SP (spontaneous potential) and an even pronounced decrease of the resistivity.
4.2.3.The Eocene Formations
The gamma ray is to low and the resistivity to high to be sure that the Zomergem Clay is present. This zone of approx. 5.00 m thickness is probably a more clayey layer within the Onderdale Sand Member, while the lowest 5 m of the member show a marked higher resistivity and lower gamma ray. The basal two meters of the member is very glauconitic.
The underlying clay layer from 151.00 m to 161.00 can be subdivided in an upper part (151 to 155 m) nearly without glauconite belonging to the Ursel Clay member and the lower part (155 to 161 m) with several glauconitic layers belonging to the Asse Clay. The top of the Ursel Clay is green coloured over 20 cm, due to perforations starting at the boundary of the upperlying Onderdale Sand Member.
The sandy glauconitic clayey sand with many Nummulites shows a higher resistivity and a lower gamma ray and corresponds to the Wemmel Member. The base is marked by an important decrease of the gamma ray and a very pronounced increase of the resitivity.
These four members belong to the Maldegem Formation (Eocene), what means that the Zelzate Formation (or equivalent lower Oligocene) is completely missing.
The Lede and the Brussel Formations have a very low gamma ray and a high resistivity.
The upper part of this package has the highest resistivity, with important high peak, due to sandstone layers and may be considered as the Lede Formation. The coring operation was stopped in the upper part of the Lede Formation because the recovery was practically nihil.
At the depth of 206 m an important and sudden increase of the gamma ray and an even remarkable decrease of the resistivity mark the boundary (with an important hiatus) with the Tielt Formation (Egem Member) of the ieper Group. The coring operations were started again in a second borehole from 209 to 218 m. The lithologic features of these cores correspond very well with the characteristics of the Egem Member.
The interpretation of the lower part of this borehole was supported by the geophysical log of the well (30W-372) of the swimming pool of the town of Herentals, situated to the north of this borehole.
ANNEX :
Photos of cores
1 Studiecentrum voor Kernenergie - Centre d'étude de l'Energie Nucléaire
Herenthout borehole - 044E0318
