An Update of the Lithostratigraphy of the Ieper Group

1 Proposal Lithostratigraphy Ieper Group 06/2016

3 An update of the lithostratigraphy of the Ieper

4 Group. 5

6 Etienne Steurbaut, Marleen De Ceukelaire, Tim Lanckacker, Johan Matthijs, 7 Peter Stassen, Hervé Van Baelen, Noël Vandenberghe

9 To refer to the present document in publications use the following reference :

10 Steurbaut, E. , De Ceukelaire,M., Lanckacker T., Matthijs, J., Stassen, P., Van Baelen H., 11 Vandenberghe, N., 2016. Lithostratigraphy Ieper Group. 12 http://ncs.naturalsciences.be/Paleogene‐Neogene/proposals‐and‐discussions.

15 Table of Contents 16

17 An update of the lithostratigraphy of the Ieper Group...... 1 18 Introduction ...... 7 19 Context of the review...... 8 20 The use of geophysical well logs and a compendium of reference logs...... 9 21 Relationship between lithostratigraphy and bio‐chronostratigraphy...... 10 22 IEPER GROUP ...... 11 23 Authors: ...... 11 24 Description: ...... 12 25 Age: ...... 12 26 Regional distribution: ...... 12 27 Stratotype ...... 13 28 Subdivisions ...... 13 29 Kortrijk Formation ...... 15

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30 Authors ...... 15 31 Description ...... 15 32 Stratotype ...... 15 33 Area ...... 16 34 Thickness ...... 16 35 Members ...... 16 36 Age ...... 16 37 Remarks ...... 16 38 Het Zoute Member ...... 16 39 Authors ...... 16 40 Description ...... 16 41 Regional occurrence and previous name: ...... 17 42 The volcanic ash: ...... 17 43 Stratotype ...... 17 44 Mont‐Héribu Member ...... 17 45 Authors ...... 17 46 Description ...... 17 47 Regional occurrence and previous names: ...... 18 48 Stratotype ...... 19 49 Orchies Member ...... 19 50 Authors ...... 19 51 Description ...... 19 52 Regional occurrence and previous names: ...... 20 53 Stratotype ...... 21 54 Geophysical borehole references and Subdivisions of the Orchies Member ...... 21 55 Roubaix Member ...... 23 56 Authors ...... 23 57 Description ...... 23 58 Regional occurrence and previous names: ...... 24 59 Stratotype ...... 24 60 Geophysical borehole references ...... 25 61 Aalbeke Member ...... 25

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62 Authors ...... 25 63 Description ...... 25 64 Regional occurrence and previous names ...... 26 65 Stratotype ...... 26 66 Geophysical borehole references ...... 27 67 ‘pink silt’ bed ...... 27 68 Mons‐en‐Pévèle Formation ...... 27 69 Authors ...... 27 70 On the Formation status: ...... 27 71 Description : ...... 28 72 Regional occurrence and previous names: ...... 28 73 Lithological trends and paleogeography: ...... 29 74 Stratotype ...... 30 75 Geophysical borehole references ...... 31 76 Tielt Formation ...... 31 77 On the position of the Egem Member ...... 31 78 Tielt Formation ...... 31 79 Authors ...... 31 80 Description ...... 31 81 Stratotype ...... 32 82 Area ...... 32 83 Thickness ...... 32 84 Members ...... 32 85 Age ...... 32 86 Remarks ...... 32 87 Kortemark Member ...... 33 88 Authors ...... 33 89 Description ...... 33 90 Regional occurrence and previous names ...... 34 91 Stratotype ...... 34 92 Geophysical borehole references ...... 35 93 Egemkapel Member ...... 35

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94 Authors ...... 35 95 Description ...... 35 96 Regional occurrence and previous names ...... 36 97 Stratotype ...... 36 98 Geophysical borehole references ...... 37 99 Hyon Formation ...... 37 100 Authors ...... 37 101 Description ...... 38 102 Regional occurrence and previous names ...... 38 103 Stratotype ...... 39 104 Biostratigraphy ...... 39 105 Egem Member ...... 39 106 Authors ...... 39 107 Description ...... 39 108 Regional occurrence and previous names ...... 40 109 Stratotype ...... 40 110 Geophysical borehole references ...... 40 111 Mont‐Panisel Member and the Bois‐la‐Haut Member ...... 41 112 Authors ...... 41 113 Name ...... 41 114 Description ...... 41 115 Regional occurrence and previous names ...... 41 116 Stratotype ...... 44 117 Geophysical borehole references ...... 44 118 Differentiation between the Mont‐Panisel and the Egem Members: ...... 45 119 Gentbrugge Formation ...... 45 120 Author ...... 45 121 Description ...... 46 122 Stratotype ...... 46 123 Area ...... 46 124 Thickness ...... 46 125 Members ...... 46

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126 Age ...... 47 127 Kwatrecht Member ...... 47 128 Authors ...... 47 129 Description ...... 48 130 Regional occurrence and stratigraphic position ...... 48 131 Stratotype ...... 48 132 Geophysical borehole references ...... 49 133 Merelbeke Member ...... 49 134 Authors ...... 49 135 Description ...... 49 136 Regional occurrence and previous names ...... 49 137 Stratotype: ...... 50 138 Geophysical borehole references ...... 50 139 Pittem Member ...... 51 140 Authors ...... 51 141 Description ...... 51 142 Regional occurrence and previous names ...... 52 143 Stratotype ...... 52 144 Geophysical borehole references ...... 52 145 Hooglede Sandstone Bed ...... 52 146 Authors ...... 52 147 Description ...... 53 148 Regional occurrence and previous names: ...... 53 149 Stratotype ...... 53 150 Vlierzele Member ...... 53 151 Comment on the stratigraphic ranking ...... 53 152 Authors ...... 54 153 Description ...... 54 154 Regional occurrence and previous names ...... 55 155 Stratotype ...... 56 156 Geophysical borehole references ...... 56 157 Aalterbrugge Bed ...... 56

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158 Authors ...... 56 159 Description ...... 56 160 Boundaries...... 57 161 Regional Occurrence ...... 58 162 Stratotype ...... 58 163 Remark ...... 58 164 COMPENDIUM OF REFERENCE LOGS WITH COMMENTS ...... 59 165 Brugge (023W0454) ...... 61 166 Gent (055W1020) ...... 61 167 Hijfte (040E0373) ...... 61 168 ON‐Kallo 1 (014E0355) ...... 62 169 Kerksken (086E0340) ...... 63 170 Kester (101W0079) ...... 63 171 Knokke (011E0138) ...... 63 172 Kruishoutem (084E1412) ...... 65 173 Merchtem (072E0229) ...... 65 174 Merksplas (017W0280) ...... 66 175 Mol SCK 15 (031W0237) ...... 66 176 Oosterzele (070E0237) ...... 67 177 Pittem (053W0073) ...... 67 178 Rijkevorsel (007E0200) ...... 67 179 Tielt (053E0061) ...... 67 180 Wieze (072W0159) ...... 68 181 Wortegem (084W1475) ...... 68 182 Zemst‐Hofstade (073E0397) ...... 68 183 Zemst‐Weerde (073E0359) ...... 69 184 Referenties: ...... 70 185

186

187

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188 Preface

189

190 The working group was installed by the Paleogene‐Neogene subcommission meeting in 191 2014 (S.Louwye chair, K.De Nil, secretar). Working Group Members are Marleen De 192 Ceukelaire, Tim Lanckacker, Johan Matthijs, Peter Stassen, Etienne Steurbaut, Hervé Van 193 Baelen, Noël Vandenberghe (coordination by N.Vandenberghe and M. De Ceukelaire). A 194 first meeting was held 20th December 2014 and a discussion text was drafted 20th February 195 2015. Comments received were discussed by the Paleogene‐Neogene subcommission on 196 13th July 2015. A revised draft was discussed by a working group meeting on 14th August 197 2015. This new version 7 is based on these discussions and has been complemented by a 198 series of geophysical well logs interpreted in terms of the lithostratigraphic subdivisions 199 proposed and discussed in the text. The document is forwarded to the Working Group in 200 October 2015 for approval to submit it to the Subcommission for posting as discussion text 201 on the NCS website. The discussion period on the website ended March 2016. The present 202 text results from a final discussion meeting by the working group in April 2016. The text is 203 submitted in May 2016 for approval to the Subcommission Paleogene‐Neogene.

204 Acknowledgements

205 Michiel Dusar, Katrien De Nil , Rik Houthuys, Thierry Smith and Laurent Wouters and are 206 sincerely thanked for their valuable contributions to the discussions.

207

208

209 Introduction 210 The present Ieper Group lithostratigraphy as officialised by NCS presents the 211 outcome of a synthesis work by the Ieper Group working group. The data 212 present the understanding of the lithostratigraphy in mid 2016, based on 213 published data and the evaluation by the working group members.

214 The use of the electronic stratigraphic compendium, as practised by NCS 215 since several years, is replacing the traditional periodic edition of a printed 216 book version. This approach offers the possibility to continuously adapt the 217 lithostratigraphy with new finding , respecting the procedure of NCS 218 (National Committee of Stratigraphy), and hence keeping the 219 lithostratigraphic nomenclature always up to date. This electronic version 220 will therefore in the future be modified as research progresses and all

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221 modifications will always be properly authored so that an appropriate 222 reference can be made to the new contributions.

223 To refer to the present document in publications use the following reference 224 Steurbaut, E. , De Ceukelaire,M., Lanckacker T., Matthijs, J., Stassen, P., Van Baelen H., 225 Vandenberghe, N., 2016. Lithostratigraphy Ieper Group. 226 http://ncs.naturalsciences.be/Paleogene‐Neogene/proposals‐and‐discussions.

227 Briefly discussed are the context of the review, the reason for the emphasis 228 on geophysical wells, and the role of biostratigraphic data in the 229 lithostratigraphic interpretation.

230 Context of the review. 231 The objective of the present revision is to complement the lithostratigraphy 232 of the Ieper Group published in 2001 (Laga et al., 2001). This last publication 233 reflected the activities in the Tertiary Subcommission at that time. The review 234 published in 2001 framed in an initiative of the National Stratigraphic 235 Commission and was limited to the lithostratigraphy at formation level. The 236 Laga et al (2001) reference document has been the basis for the NCS website 237 until now.

238 The Ieper Group is characterised by clay‐dominated sediments overlying, in 239 most situations, the Landen Group strata and, if not outcropping, underlying 240 the sand‐dominated Zenne Group sediments. According to Laga et al. (2001) 241 in their reference document for Paleogene and Neogene lithostratigraphy, 242 the Ieper Group consists of the Kortrijk, Tielt and Gentbrugge Formations and 243 members in these Formations are only listed. These subdivisions are also 244 used on the 1:50 000 geological maps of Flanders, edited in the last decades 245 of the 20th century.

246 Especially the additional description of the members, and where possible, 247 horizons, identified in the Formations, made the present review necessary 248 and also modifications at the formation level itself arisen since 2001 needed 249 to be integrated in a new synthesis.

250 The present update is based on the earlier description of members in 251 Maréchal & Laga (1988), Geets et al. (2000) and Steurbaut (1998) as far as 252 appropriate. All modifications, discussions and additions are supported by 253 the relevant literature references.

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254

255 The use of geophysical well logs and a compendium of reference logs. 256

257 In the present update the use of geophysical borehole logs in the 258 characterisation and definition of lithostratigraphical units is formally 259 introduced. This is a logical evolution as substantial amounts of data on the 260 Ieper Group are derived from subsurface reconnaissance studies.

261 In comparison to common field observations in outcrops and clay pits, 262 geophysical logs in boreholes offer the advantage of characterising the 263 vertical succession of several stratigraphic units and commonly offer a 264 continuous characterisation of the transition and boundaries between 265 lithostratigraphic units.

266 Natural‐gamma‐ray (GR) logs and resistivity (RES) logs are the commonly 267 available geophysical data, but also other logs can serve as proxies for 268 lithology.

269 Continuously recorded data in geophysical borehole logs offer a consistent 270 way to subdivide the stratigraphic column in ‘lithological intervals’ with 271 similar properties. Such intervals can be based upon upward coarsening or 272 fining up trends, levels of changing trends, or any particular log signature. 273 Trends and levels can be correlated between boreholes. Although a purely 274 geophysical stratigraphic subdivision can be made irrespective of already 275 known lithostratigraphic units, in this review it is chosen for the logical 276 approach to accommodate the traditional field and core borehole‐based 277 lithostratigraphy into the newly discussed geophysical log subdivisions. It is 278 also realised that at this stage a one to one relationship between a 279 geophysical log‐defined limit and a field defined boundary between units will 280 not always be possible; in such cases the specific choices made are explained 281 in the text.

282

283 The geophysical‐well‐log‐based lithostratigraphic subdivision and 284 interpretation of the Ieper group interval has benefited from several previous 285 attempts. An early attempt correlated logs irrespective of existing

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286 lithostratigraphic nomenclature: based on trends and events 9 correlation 287 levels were identified in 8 large plates (Vandenberghe et al., 1991). 288 Subdivisions and correlations have been published by Steurbaut (1998) and 289 Vandenberghe et al. (1998). A subdivision of the Kortrijk Formation using 290 resistivity logs was proposed by De Ceukelaire & Jacobs (1998). Van Marcke 291 et al. (2005), Welkenhuysen & De Ceukelaire (2009) and Walstra et al. (2014) 292 applied pattern recognition and correlation in numerous examples across 293 North Belgium.

294 To illustrate the subdivisions discussed in the text a set of 19 well log 295 interpretations is added as a reference compendium. The borehole localities 296 are chosen to cover the whole area of occurrence of the Ieper Group.

297 Brugge 023W0454, Gent 055W1020, Hijfte 040E0373, Kallo 014E0355, Kester 298 101W0079, Kerksken 086E0340, Knokke 011E138, Kruishoutem 084E1412, 299 Merchtem 072E0229, Merksplas 017W0280, Mol 031W0237, Oosterzele 300 070E0237, Pittem 053W0073, Rijkevorsel 007E0200, Tielt 053E0061, Torhout 301 052E0195, Wieze 072W0159, Wortegem 084W1475, Zemst‐Hofstade 302 073E0397, Zemst‐Weerde 073E0359.

303 In an exemplary way on these logs, most, but not always all, units are 304 identified, depending on the quality of the logs.

305 Subdividing logs requires particular attention to boundary levels between 306 units, straightforward in case marked jumps in properties are observed. In 307 the Ieper Group, lithological properties such as grain size are often evolving 308 within units and not constant as the definition of a lithostratigraphic unit 309 intuitively might suggest. In such cases the precise definition of the upper and 310 lower limiting surfaces can be more subject to debate. The guideline in the 311 choice should be the picking of those boundary surfaces that have the best 312 chance of being recognised in other logs, in the field and in borehole 313 descriptions.

314

315 Relationship between lithostratigraphy and bio‐chronostratigraphy. 316

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317 The subdivisions aimed at in this review are exclusively lithostratigraphic. For 318 many current purposes a coherent and consistent lithostratigraphic 319 nomenclature in a region, such as proposed in this review, is a prerequisite. 320 Obviously a deeper stratigraphic understanding of strata needs 321 lithostratigraphic data to be complemented by biostratigraphic data. This is 322 not the aim of this review.

323 On the other hand, in the case of lithologically similar packages, as is the case 324 in the Ieper Group, biostratigraphy can be required to differentiate such 325 packages and eventually confirm suspected hiati or lateral lithofacies 326 changes. Geophysical well log correlation is also helped by paleontological 327 support.

328 Biostratigraphy is also the key methodology to correlate between regions and 329 basins and to situate the deposits in the international chronostratigraphic 330 chart. The Ieper Group strata are all Ypresian or Lower Eocene. Details of the 331 bio‐ and chronostratigraphy are to be discussed separately on the website. 332 Basic biostratigraphic data are given in Steurbaut (1987, 1991, 1998, 2006, 333 2011) for calcareous nannoplankton zonations, in De Coninck (1975, 1991, 334 1996) for dinoflagellate data and in Kaaschieter (1961) and Willems (1982) for 335 foraminifera data. Summary descriptions are available in Steurbaut et al. 336 (2003). Magnetostratigraphy is another means for interregional and inter‐ 337 basin correlations. In the Ieper Group, clay‐pit sections have been 338 investigated for magnetostratigraphy by Ali et al. (1993). A methodology for 339 integrating all stratigraphic data, and including in particular the obvious 340 cyclicity in the Ieper Group strata, is the sequence stratigraphy approach, also 341 relying heavily on geophysical well logs. Such an approach however is already 342 interpretative and strongly depends on biostratigraphic calibration; therefore 343 it will be dealt with in the chronostratigraphy section of the website.

344 IEPER GROUP 345 Authors: 346 The term Ieper Group was introduced by Maréchal (1993, p 224), and 347 described by Steurbaut (1998, p 109) and in Geets et al. (2000). The Ieper 348 Group includes all strata previously grouped in the Ieper and Vlierzele 349 formations by Steurbaut & Nolf (1986). The present revision of the

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350 stratigraphic hierarchy between the different formations and members 351 within the newly defined group is based on their suitability for mapping and 352 their lithological and faunal distinctive properties.

353 The Ieper Group is named after the town of Ieper, Ypres in French, in West 354 Flanders; Ypres is also the reference name for the Ypresian global stage.

355 Description: 356 The Ieper Group contains marine sediments which consist dominantly of clay 357 in the lower part of the Group and become silty towards the top of the 358 middle part and evolve to fine sandy sediments in the upper part of the 359 Group.

360 Age: 361 The Ieper Group almost coincides with the Ypresian or early Eocene age. Only 362 the Tienen Formation of the Landen Group, below the Ieper Group, 363 represents the very earliest Ypresian and the basal part of the Zenne Group 364 above represents the very late Ypresian. Therefore the age of the Ieper Group 365 can be estimated between about 55 and 49 Ma (see Vandenberghe et al. 366 2012 in GTS 2012).

367 Regional distribution: 368 The Ieper Group occurs in the western, central and northern part of Belgium. 369 The Group outcrops are located especially in northern Hainaut, south and 370 central West and East Flanders, west and southwest of Brabant; the Group 371 occurs in the subsurface of the Antwerp and Limburg Campine. Outliers occur 372 in the Mons basin south of the Sambre river. Towards the east in the Brabant, 373 Limburg and Antwerp provinces, the Ieper Group thins and disappears. Maps 374 of the different Formations in the Ieper Group, recognised at different 375 moments in the development of the Ieper Group stratigraphic research and 376 practice, can be found in Maréchal (1993), (Walstra et al., 2014) and can be 377 consulted at the D.O.V. website:

378 https://dov.vlaanderen.be/dovweb/html/3isohypsen.html#waar. 379 https://dov.vlaanderen.be/dovweb/html/services.html#NPisohypsen or 380 https://dov.vlaanderen.be/dovweb/html/3G3Ddata.html.

381 The Ieper Group overlies the Landen Group or locally Paleozoic rocks. In the 382 Gent area and in the northwest the Ieper group is covered by the Aalter

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383 Formation of the Zenne Group. To the north and the east the Group is 384 overlain by the Brussels or Lede Formations of the Zenne Group. In the 385 exceptional case of the absence of these formations the Ieper group can be 386 covered by the Maldegem Formation or the Sint‐Huibrechts‐Hern Formation 387 in the southeast. In the coastal plain, the alluvial plains of the Leie and the 388 Upper‐Scheldt, the Ieper Group is overlain by thick late Quaternary 389 sediments.

390 The maximal thickness is about 200m and thinning occurs towards the south 391 and the east.

392 Stratotype:

393 The lower boundary stratotype is defined in Steurbaut (1998) at 288m depth 394 in the Knokke borehole (011E0138) at the contact between the Tienen 395 Formation (Oosthoek Member) and the Kortrijk Formation (Zoute Member), 396 topographic map sheet 5/6 Westkapelle with coordinates X = 78.776, Y = 397 226.370, Z = +4,91 m.

398 The upper boundary stratotype is defined in Steurbaut (1998) in the profile of 399 the Mont‐des‐Récollets (Cassel, France) at the contact of the Vlierzele 400 Member and the Aalter Formation of the Zenne Group described in Nolf & 401 Steurbaut, 1990, mapsheet XXIII‐3,Cassel, France with coordinates X = 62.000, 402 Y = 344.500, Z = +143 m.

403

404 Subdivisions:

405 The lithostratigraphic subdivisions recognised have been ranked and 406 represented in a schematic table below ; the two columns in the table 407 emphasize that the units represented in the right column occur in an area 408 lateral of the units listed in the left column; their precise lateral 409 correspondence is not entirely known. The table is schematic and a regional 410 distribution of the units is represented in more detail in the figure 411 “doorsnede” in bijlage.

412 The units are further discussed in the text in their approximate stratigraphic 413 order , from old to young.

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414

415 LITHOSTRATIGRAPHIC TABLE IEPER GROUP

416

417 Zenne Group Aalter Formation 418 419 Ieper Group Gentbrugge Formation 420 Aalterbrugge Member 421 Vlierzele Member 422 Pittem Member 423 Hooglede Bed 424 Merelbeke Member 425 Kwatrecht Member 426 427 ______428 ___ 429 Hyon Formation

430 Mont‐Panisel Member

431 Egem Member Bois‐la‐Haut Member 432 ______433 434 Tielt Formation 435 Egemkapel Member 436 Kortemark Member 437 ______438 Kortrijk Formation

439 Aalbeke Member

440 441 ______

442 Roubaix Member Mons‐en‐Pévèle Frm 443 444 ______445 Orchies Member Orchies Member 446 (Upper,Middle, Lower ) Mont‐Héribu Member 447 Het Zoute Member /

448 Landen Group Tienen Formation 449 ......

450

451

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452 Kortrijk Formation.

453 Authors: Geets (1988), Steurbaut (1998).

454 Description: the formation is an essentially marine deposit, consisting mainly 455 of clayey sediments.

456 A standard sequence contains from bottom to top:

457 ‐ an alternation of horizontally laminated, glauconiferous clayey sands or 458 sandy clay, and compact, silty clay or clayey silt, locally bioturbated. The base 459 consists of oxidized and indurated clayey sand, with lenses of pure sand 460 (Mont Héribu).

461 ‐ a homogeneous deposit of very fine silty clay, with some thin intercalations 462 of coarse silty clay or clayey, very fine silt (Orchies Mbr);

463 ‐ a less homogeneous deposit of clayey, coarse or medium silt, with some 464 sand containing layers; fossil rich layers occur; the whole deposit becomes 465 more sandy to the east and the south (Roubaix Mbr);

466 ‐ a very fine and compact clay and in addition also silty clay parts (Aalbeke 467 Mbr).

468 To the east, in the Brabant and the Campine, and towards the Mons basin, 469 the deposits become more sandy.

470 Stratotype:

471 The formation is defined by boundary stratotypes in Steurbaut (1998). The 472 lower boundary stratotype is placed at 288 m depth in the Knokke borehole 473 (011E0138) at the base of the Het Zoute Mbr. Sheet 5/6 (Westkapelle). Co‐ 474 ordinates: x = 78.776, y = 226.370, z = +4.91 m. The upper boundary has been 475 placed in the Tielt borehole (068E0169) at the top of the Aalbeke Mbr. This 476 upper boundary is located at 48.5 m in the compendium (Tielt 053E0061); in 477 earlier versions (Geets, 2000), the Aalbeke top was mislocated at 71 m. 478 Steurbaut (1998, p117) correlated the in‐the‐present‐text defined top of 479 Aalbeke Member (see also further details under Aalbeke Mbr) with the top of

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480 his unit D of the Kortemark silt member (sensu Steurbaut (1998)) in the Tielt 481 borehole located at 46.7 m. Sheet 21/6 (Wakken). Co‐ordinates: x =76439, y = 482 187576, z = +48 m.

483 Area: the formation is found in the western and central part of Belgium. It 484 outcrops in the north of Hainaut, the southern and central part of West‐ 485 Flanders, the south of East‐Flanders Flanders and the southwest of Brabant. 486 Outliers occur in the Mons Basin and south of the river Sambre.

487 The regional distribution map of the occurrence of the Kortrijk Formation in 488 Belgium is figured in Maréchal (1993, p 221) and Walstra et al. (2014) and can 489 be consulted at the D.O.V. website (dov.vlaanderen.be).

490 Thickness: 125 m in the northern part of West‐Flanders, but the thickness 491 decreases in eastern and southern direction.

492 Members: the formation is subdivided into the Het Zoute Mbr, Mont Héribu 493 Mbr, Orchies Mbr (Lower, Middle, Upper), Roubaix Mbr and the Aalbeke Mbr.

494 Age: early and middle Ypresian.

495 Remarks: the formation is also discussed by Cornet (1874), De Ceukelaire & 496 Jacobs (1998), De Coninck (1975), De Coninck et al. (1983), de Heinzelin & 497 Glibert (1957), De Moor & Geets (1975), Geets (1990), Gosselet (1874), 498 Gulinck (1965, 1967), Gulinck & Hacquaert (1954), King (1990), Laga & 499 Vandenberghe (1980), Maréchal (1993), Ortlieb & Chelloneix (1870), 500 Steurbaut (1988), Steurbaut & Nolf (1986), Vandenberghe et al. (1991) and 501 Wouters & Vandenberghe (1994).

502

503 Het Zoute Member 504 Authors : based on King (1990), Steurbaut (1998),Geets et al. (2000)

505 Description :

506 Silty to sandy clay, bioturbated and with irregular pockets and lenses of very 507 fine silty sand. Fine grained mica, woody debris and glauconite are present in 508 sieve residues throughout the unit (King, 1990). Coarse grained angular to

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509 subangular grains are identified as degraded volcanic ash. Pebbles occur in 510 the base of the overlying clay.

511 Regional occurrence and previous name: 512 The Zoute Member is a thin unit of almost 5 m thickness found at the base of 513 the Ieper Group section in the Knokke borehole (011E0138) at the Zoute 514 hamlet and first described in detail by King (1990,p70) and at that time 515 named Member X by this author. The name Het Zoute Member was proposed 516 by Steurbaut (1998, p110). It was erroneously interpreted as Mont‐ Héribu 517 Member by Geets & De Geyter (1990, p25).

518 This unit has no equivalent in other sections of the Ieper Group in Belgium 519 where it corresponds to a hiatus between the Landen and Ieper Groups; this 520 is confirmed in Steurbaut (2006, p77).

521 The volcanic ash: 522 The indication of volcanic activity is a particular property of this unit. The 523 other indication of volcanic grains in the basal sediments of the Ieper Group 524 clays are the heavy mineral types in the basal clays, identified as Mont‐Héribu 525 as reported by Geets (1993).

526 This volcanic activity is related to the ash series at base of the Eocene in the 527 North Sea Basin and correlates to the A1 Division of the London Clay 528 Formation (King, 1990, p 80).

529 Stratotype 530 Knokke borehole 011E0138, interval 288 to 284,1 m depth. Geological Map 531 5/6 (Westkapelle)

532 Coordinates: X = 78.776, Y = 226.370, Z = + 4,91 m.

533

534 Mont‐Héribu Member 535 Authors : De Coninck et al. (1983, p 98), Steurbaut and Nolf (1986,p 123), 536 Steurbaut (1998), Geets et al. (2000),

537 Description :

538 Alternating horizontal laminae of glauconite bearing clayey sand or sandy

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539 clays with compact silty clays or clayey silts. Locally burrows are present. The 540 base of the unit consists of cemented clayey sand and lenses of just sand. The 541 unit occurs at the very base of the Ieper Group, except where the Zoute Mbr 542 is present. 543 The definition of the Mont‐Héribu is limited to the sandy base of the Ieper 544 Group. This sandy base is 6 m in the Mons Basin, maximal 10 m southwest of 545 Brussels but in most boreholes it is limited to 1 to 2m and rarely noticed in 546 most boreholes (see for example sections in Gulinck, 1967). Therefore the 547 interpretation of the extension of the Mont‐Héribu Member in the 1:50 000 548 mapping of Flanders is exaggerated and comprises for a large part the 549 overlying Orchies Member. The definition refers to a grain‐size distribution 550 with only a limited clay fraction and a coarser fraction that gradually evolves 551 upward over a short distance to the larger clay content of the Orchies 552 Member. This short pattern of rapidly fining upwards is the typical signature 553 on GR and RES logs (see borehole logs ON‐Kallo‐1 014E0355, Rijkevorsel 554 007E0200).

555 On geophysical well logs

556 In some logs of the compendium, the very short change‐over interval from 557 sandy to clay deposit as observed on RES, GR logs could be considered as 558 Mont Héribu Member although generally it is considered too short to be 559 individually marked. In the ON‐Kallo well, core control allows to identify 560 1.30m of silty clay interpreted as Mont‐Héribu Member at the base of the 561 Ieper Group overlying the Tienen Formation at 401.35m (core) depth 562 (Mohammad, 2009).

563

564 Regional occurrence and previous names: 565 The unit was first reported as ‘Argile de l’ Eribus’ (Cornet, 1874, p 567) at the 566 locality Eribus (‘Mont de l’Heribu’, south of Mons) which geology was studied 567 by Ortlieb & Chelloneix (1870, p 168). In the Mons Basin the unit can reach up 568 to 6m and; its maximum thickness is reported from Bierghes (southwest of 569 Brussels) where it reaches 10m (Geets, 1991, including grain‐size data). In 570 many borehole descriptions this unit is not formally recognised as an 571 individual unit, or supposed to be reduced to just a few cm thickness; King

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572 (1991) interprets the occurrence of the Mont‐Héribu Member in central West 573 Flanders and not in the Knokke well 011E0138.

574 What is mapped as Yb on the Geological maps 1:40 000 logically corresponds 575 to the Mont‐Héribu Member. In the Stratigraphic Register by the Conseil 576 Géologique (1929) and translated by the Aardkundige Raad (1932), it is 577 included in the Lower Ypresian Y1a.

578 Stratotype :

579 Sand pit at the Mont de l’Héribu south of Mons between +57.5 en +51.4 m 580 topographic height on the geological map 151 Mons‐Givry (topographic map 581 45/7).

582 Coordinates: X = 119.750, Y = 124.510, Z = + 57,5 m.

583

584 Orchies Member 585 Authors : Gosselet (1874, p 611), Steurbaut (1998), Geets et al. (2000)

586 Description:

587 Compact and heavy stiff bluish‐grey clay occurring at the base of the Ieper 588 Group only separated from the base itself by the underlying sandy Mont‐ 589 Héribu Member where this latter is present. The Orchies Member is overlain 590 by more sandy or silty clay deposits of the Roubaix Member or Mons‐en‐ 591 Pévèle Formation. The thickness can be up to 40 m. A pebble layer has been 592 reported occasionally at its base (Ya on the 1:40 000 geological maps).

593 Whereas in the visual description of macroscopic samples, even from cores, it 594 is very hard to see any further lithological subdivision of the Orchies Member, 595 the geophysical log signatures (see reference boreholes in compendium) do 596 show a systematic variability interpreted as grain‐size and mineralogical 597 variations.

598 The top of the very high gamma‐ray section at the base of the Orchies 599 Member, about 10 to 15 m thick, is a correlatable surface (see also further 600 Geophysical logs and Subdivisions). It corresponds to the top of the mistakenly 601 named Mont‐Héribu Member (KoMh) unit in the correlation figures in

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602 Welkenhuysen and De Ceukelaire (2009 figs 12,14,16,18, 20, 22, 24) and 603 approximately to the level 1 in the plates in Vandenberghe et al. 1991).

604 The top of the Orchies clay Member/ base Roubaix Member or base Mons‐ 605 en‐Pévèle Formation, is defined by the top of the very clay‐enriched 606 sediment. This level could be identified with confidence in descriptions of a 607 series of destructive boreholes by G. De Geyter (1990, Archives Belgian 608 Geological Survey) as the transition from silty clay above to heavy clay below. 609 (courtesy Marleen De Ceukelaire).

610

611 Regional occurrence and previous names: 612 The Orchies Member consistently occurs where the Ieper Group occurs in 613 Belgium. In the Hainaut area thickness is between 10‐16m whilst in central 614 Flanders and north Belgium thickness can be over 40 m. Towards the east in 615 Brabant its thickness is reduced to a few meters.

616 Originally the name was introduced by Gosselet (1874, p 611) to indicate the 617 compact and stiff clays at the base of what is now known as the Ieper Group 618 sediments; later, as a refinement of the lithostratigraphy, the sandy and silty 619 Mont‐Héribu Member at its base was individualised as a separate unit and 620 the name Orchies Member was reserved for the compact heavy clays above 621 the Mont‐Héribu Member (Steurbaut, 1998). The later introduced name 622 Saint‐Maur Member (Belgian stratotype area, Geets, 1988; Maréchal, 1993), 623 used in the legend of the 1:50 000 mapping in Flanders is a synonym of the 624 Orchies Member although it (Saint‐Maur unit) was generally used in a more 625 restrictive way, because the lower part of the Orchies Member was 626 erroneously assigned to the Mont Héribu Member; it is preferred to maintain 627 the original name Orchies, a small locality to the southeast of Roubaix in 628 Northern France.

629 On maps 1:25 000 of the Brabant Wallon (Nivelles‐Genappe, Braine‐le‐Comte 630 ‐Féluy) the ‘Formation de Carnières’ is used for a unit ‘close to Orchies’.

631 On the legend of the geological maps 1:40 000 the Orchies Member was 632 included in the Yc clayey deposits and in the stratigraphic register (1929, 633 1932) in the Y1a.

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634 The ‘argilite de Morlanwelz’ is a lateral equivalent of the Orchies Member 635 (Steurbaut, 1991).

636 The Wardrecques and Bailleul members are reported in King (1991). The 637 lower part of the Wardrecques member belongs to the Orchies Member 638 whilst the upper part and the Bailleul member corresponds to the Roubaix 639 Member (King, 1991). This subdivision is not commonly used in the literature 640 but the position of Wardrecques and Bailleul members is well documented in 641 boreholes of the Moeskroen‐Kortrijk‐Marke‐Ooigem area by King (1991, fig. 642 11). In this area at least 5 glauconiferous beds occur, each less than 15 cm 643 thick (King, 1991).

644

645 Stratotype:

646 The Wahagnies clay pit (“Briquetterie de Libercourt”) in northern France, map 647 sheet XXV‐5 (Carvin). Ortlieb & Chelloneix (1870, p25) had already used the 648 name ‘Argile de Wahagnies’ to indicate the Orchies Member compact clays 649 (Steurbaut, 1998). In the clay pit, the base is defined by the basal pebble bed 650 below about 8 m of stiff clays. Coordinates: X = 649.250, Y = 310.600, Z = +50 651 m.

652 The upper boundary, marking the limit with the overlying Roubaix Member, 653 is proposed in the Kallo well 027E0148 (Gulinck, 1969) at 341m depth 654 (Steurbaut, 1998, p 112) (see also below).

655 Geophysical borehole references and Subdivisions of the Orchies Member 656 Several horizons in the Orchies clay Member can be defined and correlated 657 with reasonable confidence across the whole area of occurrence of the 658 Orchies Member.

659 The base of the Orchies is defined by the appearance of very clay enriched 660 sediments and a corresponding rapid installation of a high GR level.

661 The top of the Orchies clay Member/ base Roubaix Member or base Mons‐ 662 en‐Pévèle Formation, is defined by the top of the very clay‐enriched 663 sediment. This level could be identified with confidence in descriptions of a 664 series of destructive boreholes by G. De Geyter (1990, Archives Belgian

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665 Geological Survey) as the transition from silty clay above to heavy clay below. 666 (courtesy Marleen De Ceukelaire). On the geophysical logs, this level can 667 most easily and reproducibly be picked below the base of the first marked 668 sandy excursion on RES logs (labeled 6 in the compendium) and the 669 corresponding sharp drop in GR.

670 This defined top of the Orchies Member occurs at a short distance above the 671 Orchies/Roubaix boundary defined by Steurbaut (1988) and labeled OR ES88 672 on the logs in the compendium where appropriate; this OR ES88 boundary 673 was put at 331,5m in the BGD‐Kallo borehole. However, this last level is a thin 674 sandy layer systematically occurring close to the now defined top of the 675 Orchies Clay Member, with a corresponding small log signature identifiable in 676 GR and RES. This thin sand layer and corresponding geophysical log 677 signature, can also be traced in the cored Mol SCK15/1974 borehole 678 described by Gulinck & Laga (1975) just below the Mons‐en‐Pévèle 679 Formation. This observation leads to the conclusion that the base of the 680 Roubaix Member and the Mons‐en‐Pévèle Formation develop at about the 681 same moment in that part of the basin.

682 In 1998 Steurbaut (1998) picked another boundary between the Orchies and 683 Roubaix Members in the BGD‐Kallo well 027E0148 at 341m instead of at 684 331,5m as before in Steurbaut (1988). The log signature associated with this 685 1998 definition, labeled OR ES98, can easily be recognised as it is plotted by 686 Steurbaut (1998, Fig.10) on a series of logs including the Rijkevorsel well 687 007E0200 also included in the compendium; it occurs at a marked GR low , 688 slightly more than about 10m below the top of the Orchies Member.

689 Therfore it is agreed to keep this level as a formal subdivision of the Orchies 690 Member, defining the Upper Orchies Member between this level and the top 691 of the Member.

692

693 The lower part of the Member with stable very high GR readings can also be 694 reliably delineated by the top of this high GR reading, where the signal 695 recedes to lower readings. This level defines the boundary between the 696 Lower Orchies Mmeber below and the Middle Orchies Member above it. The

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697 OR ES98 level , defines the boundary between the Middle and Upper Orchies 698 Member.

699 Still other horizons have a reliable correlation potential as illustrated in 700 Steurbaut (1998, Fig 10 ), Vandenberghe et al. (1991), Van Marcke et al. 701 (2005) and others. For example a change in GR gradient recognized in the 702 ON‐Kallo well 014E0355in the compendium at 375m (Mohammad, 2009) can 703 be correlated with the 416,5m level in the ON‐Doel well, in which it is named 704 the Orchies/Roubaix boundary (Van Marcke et al., 2005). However such 705 horizons are not used to further officially subdivide the Orchies Member.

706

707

708

709 Roubaix Member 710 Authors: Gosselet (1874), Steurbaut & Nolf (1986, p 123), Steurbaut (1998), 711 Geets et al. (2000).

712 Description:

713 In contrast with the underlying (Orchies Member) and overlying (Aalbeke 714 Member) compact heavy clays, the Roubaix Member consists of more silty to 715 fine sandy calcareous clays. The thickness varies from about 40m in south 716 Belgium to 60m in North Belgium. Calcareous fossils like nummulites and 717 molluscs are present. Glauconite‐rich horizons occur. The more 718 heterogeneous composition of the sediment is shown by layering (see e.g. 719 Marke quarry in Steurbaut, 2006 fig. 7), also well visible in the geophysical 720 well logs.

721 Several of these specific layers, labeled 1 to 6 in the log examples in the 722 compendium, can be recognised and correlated between well logs with a 723 reasonable degree of confidence. Based on the correlation of these levels, 724 Welkenhuysen and De Ceukelaire (2009) have selected a specific level as the 725 boundary level between the Orchies and the Roubaix Member which 726 corresponds approximately to the position of the Steurbaut (1988) definition.

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727 On the geophysical logs in the compendium, this level can most easily and 728 reproducibly be picked below the base of the first marked sandy excursion 729 on RES logs (labeled 6 in the compendium) and the corresponding sharp drop 730 in GR.

731

732 Regional occurrence and previous names: 733 The Roubaix Member occurs over northwest France, north Hainaut, east and 734 west Flanders. Towards the south the occurrence of sandy layers becomes 735 more pronounced whilst to the northwest the Member becomes more clayey 736 and hardly distinguishable from the underlying Orchies Member (Geets et al., 737 2000). Towards the southeast and the east the Roubaix Member evolves into 738 a fine sandy unit, the Formation of Mons‐en‐Pévèle (see further).

739 The later introduced Moen Member (Belgian stratotype area, Geets, 1988; 740 Maréchal, 1993) used in the legend of the 1:50 000 mapping of Flanders, is 741 synonymous with the Roubaix Member. Roubaix is a town in North France 742 and was the original reference for this clay type as described by Gosselet 743 (1874) and therefore the name Roubaix Member is retained.

744 In the 1:40 000 mapping the Roubaix Member was mapped in the Yc unit, 745 however in the Kortrijk area it was erroneously mapped as Yd (Steurbaut & 746 Nolf, 1986; Geets et al., 2000). In the Stratigraphic Register of the Conseil 747 Géologique (1929) and the Aardkundige Raad (1932), the Roubaix Member is 748 included in the Y1a unit.

749 Stratotype:

750 The Roubaix Member was previously exposed along the Bossuit Canal at 751 Moen (near Kortrijk) (Steurbaut & Nolf, 1986) and in the Marke and Heestert 752 clay pits near Kortrijk. As these outcrops are no longer accessible a reference 753 section for the lower boundary is choosen in the Kallo well (Gulinck, 1969) at 754 341m depth (see further) whilst an upper boundary with the overlying stiff 755 clays has been visible in the former Kobbe clay pit (DOV kb29d97e‐B989) at 756 Aalbeke (x= 68.450, y= 164.300, z= 49 m) Steurbaut (1998).

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757 Geophysical borehole references 758 The base of the Roubaix Mbr has been defined in the literature in 2 different 759 ways by Steurbaut (1988, 1998). In the Kallo log (014E0355) (Steurbaut,1988) 760 the boundary between the Orchies and Roubaix Members is put at the top of 761 heavy clay at 331,5m whilst in the 1998 definition the boundary is put 10m 762 lower at 341m. The correlation between the Kallo well 027E0148 (without 763 geophysical logs) and the ON‐Kallo‐1 014E0355 with geophysical logs 764 (courtesy Peter Stassen) allows to identify the log signatures associated with 765 the two definitions. The 1998 definition is also plotted on a series of logs by 766 Steurbaut (1998, Fig.10) located in West‐Flanders but also on the Rijkevorsel 767 well – 007E0200. Therefore the two boundaries can systematically be 768 indicated as OR ES 88 and OR ES 98 on ON‐Kallo‐1 – 014E0355 and Rijkevorsel 769 – 007E0200 and on many other borehole logs in the compendium (see also 770 Mons‐en‐Pévèle Fm).

771 The boundary level between the Orchies and Roubaix Members as defined 772 above (see Description)corresponds to the level selected by Welkenhuysen 773 and De Ceukelaire (2009, e.g. in the Merchtem and the Gent boreholes).

774 Aalbeke Member 775 Authors: De Moor & Geets (1975), Steurbaut & Nolf (1986), King (1991), 776 Steurbaut (1998)

777 Description:

778 A very compact heavy clay without sand fraction of some 10 m thickness 779 sharply contrasting with more silty to fine sandy overlying (Tielt or Hyon 780 Formations) and underlying units (Roubaix Member or Mons‐en‐Pévèle 781 Formation). The Aalbeke Member is mostly non calcareous. Small pale brown 782 to yellow phosphate nodules are common in the Aalbeke Member.

783 It can be pointed out that this pure clay unit is relatively thin and therefore 784 can be mistaken for other even thinner clay units above, namely the 785 Egemkapel and the Merelbeke units. To unequivocally identify these different 786 clay‐rich layers, a complete vertical succession is often required or support by 787 micropaleontological characterisation.

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788 In most geophysical log responses the lower boundary of the Aalbeke 789 Member is sharply marked; at present there is no field outcrop of the contact 790 between the Roubaix and Aalbeke Members.

791 It is strongly suspected that the top of the Aalbeke Member is an erosive 792 contactas it is overlain by different lithological units in different areas: in clay 793 pits in Aalbeke, it is overlain by the Mont‐Panisel Member of the Hyon 794 Formation, in central Flanders by the Kortemark Member, and in SE Flanders 795 and Brabant by the Hyon Formation. Also, at the base of the overlying 796 Kortemark Member in the De Simpel clay‐pit erosion can be observed 797 (Steurbaut, 1998; Vandenbergh et al., 1998). The upper boundary can be 798 sharp (e.g. Kerksen borehole 086E0340 in compendium, data Geological 799 Service Company; Brugge ‐ 023W0454) or more generally the upper part of 800 the clay unit shows a gradual coarsening upward. In the latter case, the upper 801 boundary of the Aalbeke Member in contact with the Kortemark Member is 802 put at the top of this coarsening upwards section.

803

804 Regional occurrence and previous names:

805 The Aalbeke Member is exposed in the hills around Kortrijk, where also the 806 type locality Aalbeke is located, and in the adjacent border area of north 807 France where it corresponds to the ‘argile de Roncq’ (see De Coninck, 1991 808 fig.9). It occurs in the subsurface of the whole Flanders and has an average 809 thickness of about 10 m varying between 5 and 15 m.

810 On the geological maps 1:40 000 the Aalbeke Member was part of the Yc unit 811 and in the Stratigraphic Register of the Conseil Géologique (1929) and 812 Aarkundige Raad (1932) it is part of Y1a. In the Kortrijk area, on the 1:40000 813 sheets it was mapped erroneously as the ‘P1m’ unit (Merelbeke Member of 814 the Gentbrugge Formation).

815 Stratotype:

816 Several clay pits exist in Aalbeke and the De Witte clay pit, the extension of 817 the now filled‐up Kobbe clay pit – DOV kb29d97e‐B989 (X = 68.450, Y = 818 164.300, Z = + 49 m), designated as stratotype by Steurbaut (1998) (map

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819 sheet 29/5‐6 (Mouscron ‐ Zwevegem), is the logical new unit stratotype 820 locality.

821

822 Geophysical borehole references 823 Exemplary log signatures with the identification of a base and a top of the 824 Aalbeke Member are the boreholes logs of Gent 055W1020, Kallo 014E0355, 825 Merchtem 072E0229, Pittem 053W0073, Rijkevorsel 007E0200, Torhout 826 052E0195, Wieze 072W0159.

827

828 ‘pink silt’ bed 829 Within the Aalbeke Member outcrops in the Kortrijk area a pronounced 830 pinkish silty layer of some dm thickness occurs. It might serve as a 831 stratigraphic marker bed. However the bed is not given an official bed status 832 as it is not yet established that only one such layer occurs in a complete 833 Aalbeke Member section.

834

835

836 Mons‐en‐Pévèle Formation 837

838 Authors :

839 King (1991), Steurbaut & Nolf (1986), Steurbaut & King (1994, p180), 840 Steurbaut (1998)

841 On the Formation status: 842 Although the Formation status is given to the Mons‐en‐Pévèle sand unit , 843 arguments could be forwarded to consider it as a Member of the Kortrijk 844 Formation. A member status could logically reflect the lateral transition zone 845 with vertically alternating sandy layers and clay layers (such as e.g. in the 846 Mouscron borehole in fig.10 as an undifferentiated Kortrijk Formation in King 847 (1991)). The Mons‐en‐Pévèle unit is not included in the Kortrijk Formation 848 because of the sandy nature of the former in contrast with the dominantly

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849 clay nature of the latter. Also the Mons‐en Pévèle sand unit can be properly 850 mapped with considerable thickness in Hainaut where it links up with the 851 Cuise Sand of the Paris Basin; such a map unit usually gets the formation 852 status. Also, the 1:25 000 mapping in Wallonia uses the status ‘Formation de 853 Mons‐en‐ Pévèle’. Therefore in the present review it has been chosen to rank 854 the Mons‐en‐Pévèle sandy unit as a Formation.

855 Description : 856 Succession of one or a few m thick laminated packages of pure very fine sand 857 (60‐80µm), often cross stratified, and strongly bioturbated clayey sand; the 858 latter are more important closer to the base. The sand is micaceous with 859 commonly very fine glauconite. Several coarser beds are packed with 860 Nummulites, appearing for the first time in the basin in the Mons‐en‐Pévèle 861 Formation. Locally cemented layers occur, a.o. nummulitic limestone beds.

862

863 Regional occurrence and previous names: 864 The Mons‐en Pévèle Formation is occurring southeast of a line through Lille 865 (North France) (see map in King, 1991), from Mons‐en‐ Pévèle (North France) 866 to Tournai and Ronse and further eastwards. Mons‐en‐Pévèle is a locality 867 south of Lille in North France and the name ‘Sables de Mons‐en‐Pévèle‘ was 868 introduced by Ortlieb & Chellonneix (1870, p 27).

869 Towards the east in Brabant, the Ieper Group thins and a typical clayey basal 870 part is distinguished from an upper fine sandy unit. The basal clay 871 corresponds to the Orchies Member of the Kortrijk Formation whilst the sand 872 has been given a lithostratigraphic name, the Vorst/Forest sand. It was shown 873 by King (1991) that these fine sands are equivalent to the Mons‐en‐Pévèle 874 Member. Logically therefore the Bierbeek sand above the Orchies Member in 875 the Leuven area (geological map 1:50 000 sheet 32 Leuven, Vandenberghe & 876 Gullentops, 2001) can be considered as a decalcified sand of the Mons‐en‐ 877 Pévèle Member, in a similar way as the sands above a thin clay unit in north 878 Brabant (Rillaar) and Limburg (e.g. Veldhoven, Beringen) as figured by Gulinck 879 (1967) and discussed by Fobe (1989a).

880 From a nomenclature point of view, in the transition zone of laterally 881 interfingering units such as the Roubaix and Mons‐en Pévèle units, the ICS

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882 Stratigraphic Guide recommends that a somewhat arbitrary boundary should 883 be chosen in mapping and borehole description, obviously accompanied by 884 an appropriate explanation in the legend or description. In the case of the 885 Roubaix/Mons‐en‐Pévèle limit the present review suggest that if the unit 886 consists of over 50 to 60% sand layers, the unit should be named Mons‐en‐ 887 Pévèle Fm and otherwise the unit should be classified as Roubaix Member of 888 the Kortrijk Formation. For example the 368‐407 m section in the Mol SCK 889 borehole 031W0237 is mainly described as fine sand with minor clay layers 890 (Gulinck & Laga, 1975) and is therefore to be named Mons‐en‐Pévèle Fm. 891 Localities with Mons‐en‐Pévèle sand are listed in Steurbaut & Nolf (1991, 892 Fig.3) and appear systematically between Ronse and Brussels. According to 893 the lithological description (sand/clay proportion) the log signature in the 894 borehole Merchtem 072E0229 should be classified as the Roubaix Mbr and in 895 the Kester borehole 101W0079 as Mons‐en‐Pévèle Fm. However an 896 inspection of shape of the RES and GR logs allows to consider the boreholes 897 Merchtem (compendium) , Meise (see profile Gent‐Zemst and Meise‐ 898 Rotselaar),.as transitional signatures between Roubaix and Mons‐en‐Pévèle.

899 The criterion will need further refinement and the study of more wells. Also it 900 has to be recognised that the descriptions of the boreholes, especially if 901 destructive, are often not accurate enough to reliably decide on the number 902 of sand layers. Also if grain‐size data are available, it will be needed to define 903 how exactly to apply the criterion; e.g. at first glance the amount of >62µm 904 fraction in the borehole Kattem (087W0479) south of Aalst (Geological 905 Service Company, 2003) is high enough to describe the unit below the 906 Aalbeke Member as the Mons‐en‐Pévèle Member. The same holds for the 907 application of the GR/RES log values in determining how much sand layers 908 occur in the interval. Maybe the 50‐60% sand layer boundary will need to be 909 changed or maybe it will appear practical to introduce a new transitional 910 lithological unit.

911

912 Lithological trends and paleogeography: 913 Paleogeographically, from central Flanders towards the east and the south, 914 several clay enriched facies of the Kortrijk Formation are replaced by more 915 sandy deposits (maps in Steurbaut, 2006). The lateral transitions are well

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916 documented and figured in King (1991). The Roubaix Member laterally 917 interfingers with the Mons‐en‐Pévèle Fm. More southwards to the Paris basin 918 the closer to the base of the Ieper Group starts the occurrence of the sand 919 unit (profiles in King, 1991). The sands are known as the Mons‐en‐ Pévèle 920 Member and grade into the ‘Cuisian‘ sands in the Paris Basin. The Aalbeke 921 Clay extends over the Mons‐en‐Pévèle Sand into the Paris basin where it 922 corresponds to the Laon clay (King, 1991). Where the ‘argilite de Morlanwelz’ 923 is a lateral equivalent of the Orchies Member (Steurbaut, 1991) more sandy 924 facies in southern direction in the Hainaut province with specific names such 925 as the Godarville sand and the Peissant sand (Steurbaut & Nolf, 1986) are 926 included, without a specific stratigraphic status in the Mons‐en‐Pévèle 927 Member. The Morlanwelz Sand, with a Formation status, is figured in 928 Steurbaut (1998 p 145; Steurbaut et al., 2003 p 11) as a lateral equivalent of 929 the Roubaix Member but as a separate unit underlying the Mons‐en‐Pévèle 930 Sand Formation (see also Steurbaut, 1998 p 110); however this subdivision is 931 not retained in the present review due to a lack of precise data.

932

933 It should be noticed that the reverse lithological trend logically is also present 934 in the north direction leading King (1991, p 361, 370) to introduce the name 935 Flanders member for the homogeneous Ieper Group clays beneath the Egem 936 Member in the Knokke well. In this review this suggestion is not followed as 937 these very clay rich sections can still be subdivided using existing 938 nomenclature such as ‘the Tielt and Kortrijk Formations ‘ (see Welkenhuysen 939 and De Ceukelaire, 2009 fig. 16) (see also Knokke well in the compendium) 940 and as the geophysical well log divisions of these clay‐rich sections can even 941 be recognised further north in the Netherlands (de Lugt, 2007).

942 Stratotype:

943 No formal stratotype has been designated. Logically the Mons‐en‐Pévèle hill 944 south of Lille and north of Douai in North France is the preferred reference 945 area (see Steurbaut, 1998 p 116); also the Waaienberge (Wayenberghe) 946 railway section near Ronse ( described in King 1988 (1990) p 359 and figured 947 in Steurbaut & Nolf 1988 (1990) p 328) is a potential stratotype section.

948

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949 Geophysical borehole references 950 The following borehole logs in the reference compendium have a Mons‐en‐ 951 Pévèle signature Zemst‐Hofstade – 073E0397, and are confirmed by analysis 952 in the Mol – 031W0237, Kester‐ 101W0079 wells.

953 Typical Roubaix Mbr log response confirmed by clay dominated lithology can 954 be observed in Kallo ‐ 014E0355, Knokke ‐ 011E0138.

955 The signature in the Merchtem–072E0229 borehole is somewhat 956 intermediate but according to the borehole description sand‐layers represent 957 only 24 % of the interval and therefore the interval is classified as Roubaix 958 Mbr base on the 50‐60% sand layer criterion (see above).

959

960 Tielt Formation 961 On the position of the Egem Member 962 The Egem Member, traditionally ranked into the Tielt Formation (see a.o. also 963 1:50 000 map legend), has in this review been ranked in the Hyon Formation. 964 The Hyon Formation has been introduced in the literature by Steurbaut 965 (1998, p 115) and described in the review by Geets et al. (2000) but was not 966 retained in the official NCS stratigraphy by Laga et al., (2001). The grouping of 967 the Egem Member in the Hyon Formation has been suggested by Steurbaut 968 (2011) applying the logic to group the sandy deposits, like the Egem Member, 969 in the Hyon Formation and the clayey deposits like the Kortemark and 970 Egemkapel Members in the Tielt Formation. This definition is also practical 971 when no distinction can be made between the sand members (Egem and 972 Mont‐Panisel) of the Hyon Fm, as is the case in the subsurface occurrence in 973 northeast Belgium

974 Tielt Formation 975 Authors: Geets (1988b), Steurbaut (1998). 976 977 Description: this marine unit consists in general of a very fine sandy, coarse 978 silt and clay. 979

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980 Stratotype: at its base the formation is defined by the top of the Aalbeke 981 Member (see Aalbeke Member). In the compendium this boundary is placed 982 at 48.5m in the Tielt 053E0061 borehole (see also Aalbeke Member). 983 Steurbaut (1998) defined a boundary in the Tielt 068E0169 borehole in which 984 the Aalbeke top was located at 71 m (see also Geets, 2000) which is different 985 from the present definition (see Aalbeke Member). Steurbaut (1998) 986 correlated the in‐the‐present‐text defined top of the Aalbeke Member with 987 the top of his unit D in the Kortemark silt Member (sensu Steurbaut 1998) of 988 the Tielt 068E0169 borehole located at 46.7 m ( Sheet 21/6 (Wakken). Co‐ 989 ordinates: x =76439, y = 187576, z = +48 m).

990 The upper boundary is placed at the base of the Egem Mbr in the "Ampe" 991 quarry ‐ 053W0060 (see Steurbaut, 1998 Figs 5,11). Sheet 21/1 (Wingene). 992 Co‐ordinates: x = 70.150, y = 190.150, z = +44 m. 993 994 Area: the western and northern part of Belgium. The formation outcrops in 995 the north of Hainaut, the south and the centre of East‐ and West‐Flanders 996 and the western and southwestern part of Brabant. Outliers occur in the 997 Mons Basin and south of the river Sambre. The regional distribution map of 998 the Tielt Formation is figured in Maréchal, R. (1993, p 222), Walstra et al. 999 (2014) and in https://dov.vlaanderen.be 1000 1001 Thickness: maximum 25 m in the centre of the outcrop area. It decreases to 1002 the south and the east, and probably to the north. 1003 1004 Members: the formation is subdivided into the Kortemark Mbr and the 1005 Egemkapel Mbr. 1006 1007 Age: Middle to Late Ypresian. 1008 1009 Remarks: the formation is also discussed by De Coninck (1973), De Moor & 1010 Geets (1973), Geets (1979), Laga et al. (1980), Maréchal (1993), Steurbaut 1011 (1988), Steurbaut & Nolf (1986). 1012

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1013 Kortemark Member 1014 Authors: Steurbaut & Nolf (1986), Steurbaut (1998), Geets (1988), Geets et al. 1015 (2000).

1016 Description:

1017 A grey silty clay unit with sandy layers of several dm thickness have been 1018 observed near the base. The presence of silt and sand is distributed in layers 1019 of cm to dm. Several subunits can be distinguished as proposed by Jacobs et 1020 al. (1996a, b) and Steurbaut (1998). The Kortemark Member occurs between 1021 heavy clay units: the Aalbeke Member below and the Egemkapel Member 1022 above. The maximal thickness is about 25 m (Geets et al., 2000).

1023

1024 In the top of the underlying Aalbeke Member a gradual coarsening upwards 1025 occurs, ended by a sharp coarsening that marks the start of coarser sediments 1026 in the Kortemark Member (see analyses from Geets (1991) and interpreted in 1027 Steurbaut (1998)). In geophysical log patterns the start of the coarsening 1028 upwards interval in the Aalbeke Mbr above its very clay‐rich main part, as 1029 well as the sharp coarse shift at the top of the coarsening upwards part of the 1030 Aalbeke Mbr which marks the position of a fine sand layer, can be observed 1031 fairly consistently (e.g. Torhout 052E0195, Tielt 053E0061, Gent 55W1020, 1032 On‐Kallo 1 014E0355). The formal boundary between the Aalbeke and 1033 Kortemark Members is drawn at the position of the major grain‐size shift and 1034 the income of the first fine‐sand layer (correlation profiles in Welkenhuysen 1035 and De Ceukelaire, 2009). This boundary definition at the base of the lowest 1036 fine‐sand layer has the advantage to correspond to an observable horizon 1037 with water outflow in the upper part of the Desimpel clay pit in Kortemark 1038 (Steurbaut,1998, Fig.5).

1039

1040 Detailed lithological analyses of the Kortemark Member sections in the Tielt 1041 borehole 068E0169 and the Kortemark and Egem extraction pits, are figured 1042 in Geets (1991) and Steurbaut (1998, p 117). Details in the geophysical well 1043 log signature in the Kortemark Member can be correlated between wells,

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1044 especially the significant higher values of the resistivity, standing for more 1045 sandy layers, can be correlated between the different logs.

1046

1047 Regional occurrence and previous names:

1048 The Kortemark Member occurs north of Kortrijk and in particular in the west 1049 of Flanders where it can reach 25 m thickness. It is also known towards the 1050 east and northeast of Flanders (Antwerp Province) where it becomes thinner.

1051 In the southeast of East Flanders and the neighbouring eastern Brabant 1052 provinces, the Mont‐Panisel Member overlies the Aalbeke clay Member in 1053 Kerksken (086E0340) and Kattem (087W0479) (Geological Service Company, 1054 2003), implying the disappearance towards the east of the Kortemark 1055 Member and the Egemkapel Member (see also Mont‐Panisel Member). Also 1056 on the map sheet 23 Mechelen, Buffel et al. (2009) note that the Kortemark 1057 Member disappears to the east and is only present in the western part of the 1058 map.

1059

1060 In the 1:40 000 geological map legend the Kortemark Member is included in 1061 the Yc unit and in the Stratigraphic Register of the Conseil Géologique(1929) 1062 and the Aardkundige Raad (1932) in the Y1a division.

1063 In the Bolle & Jacobs (1993) nomenclature the unit Yd1c unit is tentatively 1064 correlated to the Kortemark Member. In the present review the Yd2 unit of 1065 these authors, a 5 m densily packed fine glauconitic sand underlying the 1066 Egemkapel clay Member, is also included in the Kortemark Member, 1067 notwithstanding its resemblance to the Egem Sand above. (see also 1068 Egemkapel Member)

1069

1070 Stratotype:

1071 Steurbaut (1998) has proposed the level of about 71m below surface in the 1072 Tielt borehole (068E0169); map sheet 21/6 x=76.439; y=187.576; z=48) for the 1073 lower boundary with the underlying Aalbeke Member. However, in‐the‐

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1074 present‐text the base of Kortemark has been replaced at a level in the 1075 Kortemark Desimpel quarry corresponding to the level at 48 m depth in the 1076 Tielt borehole according to the log interpretation Tielt 053E0061 in the 1077 compendium. Indeed because the top of the Aalbeke Member gradually 1078 becomes siltier upwards (see analyses in Steurbaut, 1998 fig. 5) it has been 1079 argued in‐the‐present‐synthesis that the first marked sandy layer in the 1080 Desimpel clay pit in Kortemark (marked as ‘ sharp junction waterflow’ at the 1081 base of subunit C in Steurbaut 1998 p 117) (map sheet 20/3‐4 Kortemark‐ 1082 Torhout, x= 57.050,y= 190.400, z= +16m) is a more easily recognisable 1083 lithostratigraphical horizon to mark the base of the Kortemark Member. In 1084 the present review this level is chosen as the formal boundary between the 1085 Aalbeke and Kortemark Members (see discussion in Description above).

1086

1087 The top of the Kortemark Member has during many years (80’s and 90’s) 1088 been exposed in the classical Egem extraction pit – 053W0060 (map sheet 1089 21/1, x= 70.150, y= 190.150) as an erosive contact with the overlying 1090 Egemkapel (see Steurbaut, 1998, p 117).

1091 Geophysical borehole references 1092 Reference boreholes with geophysical log pattern of the Kortemark Mbr 1093 between the Aalbeke and Egemkapel clay Mbrs are in the outcrop area of the 1094 unit : Tielt ‐ 053E0061, Kruishoutem – 084E1412, Gent – 055W1020, Torhout 1095 052E0195, Pittem ‐053W0073 and also Knokke – 011E0138, Rijkevorsel – 1096 007E0200, Kallo – 014E0355.

1097

1098

1099 Egemkapel Member

1100 1101 Authors: Steurbaut (1998), Geets et al. (2000).

1102 Description:

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1103 A thin heavy clay unit of about 6m thick, contrasting with underlying silty to 1104 sandy clays of the Kortemark Member and the sandy overlying deposits of 1105 the Egem Member. The unit is thinner than the Aalbeke Member. In the Egem 1106 Quarry the unit has an erosive basis with a characteristic lag deposit of fossils, 1107 mainly fish remains but also snake vertebrae and bird bones and even a rare 1108 mammal tooth (Steurbaut, 1998; Smith & Smith, 2003,2013); also, a thin 1109 transgressive sandy layer, less than 1m thick, occurs just overlying the erosive 1110 basis and well expressed on some borehole logs. This thin basal lag sand is 1111 different from and should not be confused with the underlying sandy top of 1112 the Kortemark Member (the Yd2 unit, Jacobs et al., 1996a,b). Also the upper 1113 boundary with the Egem Member is erosive. The Egemkapel Member is a 1114 clay‐rich unit, contrasting sharply with the more silty and sandy unit below 1115 (Kortemark Member) and above (Egem Member) as shown in core 1116 descriptions (see e.g. unit Yd3 in Jacobs et al., 1996a fig. 9), grain‐size analysis 1117 (see Steurbaut, 1998 fig. 5;) and in the geophysical well pattern (see 1118 compendium).

1119

1120 Regional occurrence and previous names:

1121 In the legend of the 1:40 000 maps it was included in the top of the Yc unit.

1122 Steurbaut & Nolf (1986) included the Egemkapel clay in the top of the 1123 Kortemark silt unit and Jacobs et al. (1996 a, b) in the Egem Member.

1124 As a thin unit, the Egemkapel was only individualised as a separate Member 1125 when its consistent occurrence over the whole central Flanders north of the 1126 Mons area became obvious (see e.g. Walstra et al., 2014). The unit disappears 1127 towards the east of the East Flanders and Brabant but is still recognised in the 1128 Kallo wells 027E0148 & 014E0355 north of Antwerp and in the Rijkevorsel 1129 well – 007E0200.

1130

1131 Stratotype:

1132 The name Egemkapel refers to the hamlet where the Ampe – 053W0060 or 1133 Egem extraction pit is located (map sheet 21/1, x= 70.150, y= 190.150). The

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1134 clay unit has been exposed in this pit during a long time in the 80’s and 90’s, 1135 occurring between two erosive horizons: at its base with the underlying 1136 Kortemark Member and at its top with the strongly erosive base of the Egem 1137 Member of the Hyon Formation.

1138 A detailed description of the Ampe extraction pit anno 1994‐1995, comprising 1139 the Egemkapel, Egem and Pittem Members can be found in Willems (1995) 1140 and Steurbaut, 2015).

1141 Geophysical borehole references 1142 To define the Egemkapel Member on the geophysical logs the reference must 1143 be the Egem quarry section correlated by Steurbaut (1998,Fig.5) to the close‐ 1144 by Tielt borehole using grain size and log signature: the thickness is 4,5m 1145 with sharp boundaries and a very clay‐rich core of 2‐3 m; sharp boundaries 1146 are confirmed in geotechnical logs (Bolle & Jacobs, 1993;Jacobs et al., 1147 1996a,b) an by grain size data in the BGD‐ Kallo borehole (Geets, 1990).

1148 This logic was followed to identify the pattern in the reference boreholes, a 1149 thin marked GR and RES excursion, exemplary expressed in boreholes : Tielt ‐ 1150 053E0061, Kruishoutem – 084E1412, Gent – 055W1020, Rijkevorsel – 1151 007E0200, Brugge – 023W0454, Torhout 052E0195, Pittem‐ 053W0073.

1152 Mohammad (2009) and Van Marcke et al. (2005) included additional clay 1153 layers from the underlying Kortemark Member in their identified Egemkapel 1154 Member.

1155

1156

1157

1158

1159 Hyon Formation 1160

1161 Authors: Steurbaut and King (1994), Steurbaut (1998, p 115), Geets et al. 1162 (2000)

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1163 The Hyon Formation has been introduced in the literature by Steurbaut and 1164 King (1994) at the occasion of the study of the Mont‐Panisel research 1165 borehole (Dupuis et al., 1988) and formalised by Steurbaut (1998, p 115). The 1166 Hyon Formation was reported in the review by Geets et al. (2000) but not 1167 retained in the official NCS stratigraphy by Laga et al. (2001). In addition to 1168 the original descriptions in the literature, also the Egem sand unit has been 1169 included now as a Member in the Hyon Formation to make a lithological 1170 distinction more practical between a sandy Hyon Formation and a clayey Tielt 1171 Formation in which the Egem Member was traditionally included.

1172

1173 Description 1174 Fine sand, with dispersed clay or layers of clay, rich in galuconite and 1175 including sandstone layers and concretions.

1176 Members

1177 Egem Member, Mont‐Panisel Member , Bois‐la‐Haut Member

1178 Regional occurrence and previous names:

1179 The Egem Member of the Hyon Formation occurs over most of the provinces 1180 West and East Flanders and part of the Antwerp Campine whilst the Mont‐ 1181 Panisel Member of the Hyon Formation occurs in the Brabant and Hainaut 1182 area where its thickness reaches maximum 25m (Steurbaut, 2006); further 1183 northwards the Mont‐Panisel Member is only locally preserved from erosion 1184 (Steurbaut, 2006). The lateral geometrical relationship between the two 1185 sandy Members had already been noticed in the classical lithostratigraphic 1186 paper by Steurbaut & Nolf (1986), in which the Mont‐Panisel Member was 1187 indicated as ‘Panisel Sand’. The relationship between the sand members has 1188 been interpreted in sequence stratigraphic reconstructions (Vandenberghe et 1189 al., 1998, 2004; Steurbaut, 2011).

1190 The introduction of the Hyon Formation arranges the position of the strata in 1191 the hills of Bois‐la‐Haut and Mont‐Panisel, located in the village of Hyon 1192 southeast of Mons (map figure 1 in Steurbaut & King, 1994), and which are at 1193 the origin of the former classic but now obsolete ‘Paniselian’ stage 1194 (Steurbaut, 2006). The problematic geometric position of the ‘Panisel sand’ in

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1195 Brabant and in outliers in the Hainaut area, as it was demonstrated in 1196 Steurbaut& Nolf (1986), has been solved by the introduction of the Hyon 1197 Formation.

1198

1199 Stratotype:

1200 The section between 0 and 21,85m depth in the Mont‐Panisel borehole 1201 (151E0340) on the topographic sheet 45/7‐8 (Mons‐Givry) (x=122.300, y= 1202 125.375, z= +102m). This location is an outlier and at this location the Egem 1203 Member does not occur.

1204 Biostratigraphy : upper part of nannoplankton NP12 (Steurbaut,2006).

1205

1206 Egem Member 1207 Authors: Laga et al. (1980); Steurbaut & Nolf (1986); Steurbaut (1988, 1998) ; 1208 Geets (1979).

1209 Description:

1210 The sediment is a finely laminated, well sorted, mica and glauconite 1211 containing and generally fossiliferous fine sand. Lamination is mainly 1212 horizontal with in addition cross lamination, hummocky stratification and 1213 infilling of broad shallow gullies. Heavy clay layers occur of cm and dm scale 1214 often cut by erosive sand‐filled channels. The base of the Egem Member is a 1215 strongly erosive level with active channelling above the Egemkapel Member. 1216 A marked paleoseismite horizon occurs in the middle of the Egem Member 1217 exposed in the Ampe pit (Crepin et al. ,2004). Towards the top, the sediment 1218 becomes coarser and more homogeneous with numerous nummulites. A 1219 detailed section of the Egem Member in the Ampe quarry and corresponding 1220 grain‐size data (Geets, 1991) in the Tielt borehole 068E0169, are shown in 1221 Steurbaut (1998, p 117). Subdivisions of the Egem Member can be regionally 1222 followed in CPT logs and borehole descriptions (Jacobs et al., 1996a, b). On 1223 geophysical logs the base of the Egem Member can generally be recognised 1224 by a sharp increase in resistivity as it generally overlies the clay‐rich 1225 Egemkapel Member.

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1226

1227 Regional occurrence and previous names:

1228 The Egem Member occurs over most of the provinces of West and East 1229 Flanders (Steurbaut & Nolf, 1986; King, 1991 p370) and its extension 1230 northeastwards into the Antwerp province has been interpreted in many 1231 publications although an identification as Hyon Formation is probably more 1232 prudent . On regional profiles the base of the Egem Member is clearly erosive 1233 into underlying units (Vandenberghe et al., 1998; King,1991).

1234 The Ledeberg sand and Evergem sand are synonymous for the Egem Member 1235 (Geets et al., 2000).

1236 In the legend of the 1:40 000 maps the Egem Member is representing the Yd 1237 and the P1b units and in the stratigraphic register (1929, 1932) the Y1b 1238 division (Geets et al., 2000).

1239

1240 Stratotype:

1241 The Ampe extraction pit ‐ 053W0060 in Egem (Pittem) (mapsheet 21/1 1242 Wingene x= 70.150, y= 190.150, z= +44m) between +39.5 m to +19 m T.A.W, 1243 between the Egemkapel Member below and the X‐sandstone (in this review 1244 named the Hooglede Bed) bed underlying the Pittem Member above (Geets 1245 et al., 2000).

1246 A detailed description of the Ampe extraction pit anno 1994‐1995, comprising 1247 the Egemkapel, Egem and Pittem Members can be found in Willems (1995) 1248 and Steurbaut (2015).

1249

1250 Geophysical borehole references 1251 In the central West Flanders type area of the Egem Mbr several boreholes can 1252 be used as reference for the Egem Mbr and its Yd4, 5, 6 subdivisions: Tielt 1253 053E0061, Gent – 055W1020, Brugge – 023W0454, Torhout – 052E0195, 1254 Oosterzele – 070E0237, Kruishoutem – 084E1412.

1255

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1256 Mont‐Panisel Member and the Bois‐la‐Haut Member.

1257 Authors: d’Omalius d’Halloy (1862, p 536 & 625), Steurbaut & Nolf (1986), 1258 Steurbaut & King (1994), Steurbaut (1998), Geets et al. (2000).

1259 Name : The Mont‐Panisel hill is the twin hill of Bois‐la‐Haut in the village of 1260 Hyon, near Mons (map figure 1 Steurbaut & King, 1994).

1261

1262 Description:

1263 Poorly sorted, faintly laminated, prominently glauconitic and highly 1264 bioturbated clayey fine sand occur in the reference borehole section of this 1265 unit at the Mont‐Panisel (151E0340) (Steubaut & King, 1994). A separate 3,6 1266 m thick layer at the base of the section in the Mont‐Panisel borehole 1267 (151E0340, between 18 and 21,58m), is highly glauconitic, highly bioturbated, 1268 rather well‐sorted fine to medium sand with clayey patches in contrast to the 1269 finer and less‐sorted sand above (see section in Steurbaut and King, 1994 1270 fig.3). The lower part is named the Bois‐la‐Haut Member and the main upper 1271 part is called the Mont‐Panisel Member. The latter contains also numerous 1272 irregularly shaped siliceous sandstone concretions and locally poorly 1273 cemented nummulite‐bearing sandstones occur (Steurbaut, 2006). Maximal 1274 thickness is 20 m.

1275 Geets et al. (2000) report that somewhat coarser glauconite‐rich sand in 1276 boreholes between Aalst and Brussels could correspond to the Bois‐la‐Haut 1277 Member. The X‐stone bed , named Hooglede Bed in this review, underlying 1278 the Pittem Member in the Ampe quarry has also been tentatively suggested 1279 to be a lateral equivalent of the Bois‐la‐Haut Member by Steurbaut (1998) 1280 although in Steurbaut (2011, fig.8 p 255) the X‐stone bed is again included in 1281 the base of the Pittem Member. Although the Bois‐la‐Haut Member is until 1282 now only clearly identified in the Mont Panisel borehole, it is ranked as a 1283 member seen its thickness of several meter ,more than the normal thickness 1284 for a lithostratigraphic bed.

1285

1286 Regional occurrence and previous names:

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1287 These deposits were originally described by d’Omalius d’Halloy (1862) as 1288 ‘psammites, sables et argiles du Mont‐Panisel’ at the Mont‐Panisel near 1289 Mons. The Mont‐Panisel Member occurs in the area Gent‐Brussel‐Mons‐ 1290 Kortrijk. The Mont‐Panisel Member overlies the Aalbeke Clay in clay pits 1291 around Kortrijk (e.g. Mulier clay pit) (Steurbaut 2006).

1292 The sands correspond to the previously used unit ‘Panisel sand’ in Steurbaut 1293 & Nolf (1986) and this Member corresponds to the ‘Unnamed Sand member’ 1294 in the top of the Mouscron borehole and the Kortrijk outcrops of King (1991 p 1295 365). It also occurs in the hills of North France. It corresponds to the term 1296 ‘Paniselien’ used by Gulinck in his profiles around Brussels ( Archives Belgian 1297 Geological Survey,MG/00/250‐329‐547;MG/53/327;MG/55/335; MG/56/176‐ 1298 177‐313‐316;.MG/58/249).

1299 Whereas in the Gent (055W1020) area the Egem Member subdivisions Yd4, 1300 Yd5, Yd6 (sensu Bolle & Jacobs, 1993) can be recognised between the 1301 Egemkapel (Yd3 unit sensu Bolle & Jacobs,1993) and the Merelbeke Clay, such 1302 identification becomes difficult to the east near the boundary with the 1303 Brabant province. It seems that in this latter area and more to the east, the 1304 Mont‐Panisel Member replaces the Egem Member. Jacobs et al. (1996a p 28) 1305 have reported that the Egem Member becomes more clayey to the south.

1306 In the southeast of East Flanders and the neighbouring eastern Brabant 1307 province, about 6 to 11 m of glauconitic sand occurs containing sandstone 1308 layers and overlies the Aalbeke clay Member in Kerksken (086E0340) and 1309 Kattem (087W0479) boreholes; its description corresponds to the Mont‐ 1310 Panisel Member (Geological Service Company, 2003). The typical Mont‐ 1311 Panisel sand in the borehole is overlain by a clayey sand of about 11 m which 1312 in its turn is capped by the Merelbeke clay Member. The lithostratigraphic 1313 position of this clayey sand unit overlying the Mont‐Panisel sand is further 1314 discussed under the Kwatrecht Member.

1315 The implication of this succession is also that towards the east, the Kortemark 1316 Member and the Egemkapel Member have disappeared. Also on the map 1317 sheet 23 Mechelen, Buffel et al. (2009) note that the Kortemark Member 1318 disappears to the east and is only present in the western part of the map.

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1319 More northwards in the Brabant province (east of Aalst), the Merchtem 1320 borehole (072E0229) (Buffel et al., 2009) shows above the Aalbeke Member 1321 and below the Merelbeke Member, the same twofold borehole geophysical 1322 log signature and thickness as the Kerksken – 086E0340 and Kattem – 1323 087W0479 boreholes, with the lower part being the typical Mont‐Panisel 1324 Member below a more clayey glauconitic sand without sandstones (see 1325 Kwatrecht Member). This pattern can also be observed further west and 1326 north‐westwards in geophysical logs (Meise borehole 073W0394 in 1327 Welkenhuysen & De Ceukelaire, 2009) and in grain‐size analysis of the Zemst‐ 1328 Weerde borehole (073E0359) (Buffel et al. 2009). The presence of Merelbeke 1329 clay in the Zemst‐Weerde ‐ 073E0359 borehole was confirmed by 1330 micropaleontological data (Buffel et al., 2009). Note that in the Zemst‐ 1331 Weerde‐ 073E0359 interpretation by Buffel et al. (2009) these two units 1332 together were named Egem Member, an interpretation not followed in the 1333 present review. Also, just north of Brussels in Vilvoorde, Gulinck described in 1334 his profile MG 00/504 ‘Paniselien’ above a clay rich top of the ‘Ypresian’ and 1335 below the Brussel and Lede Formations; this ‘Paniselien’ is characterised by 1336 stone layers in its lower part.

1337 Over a short distance to the east, between Zemst‐Weerde (073E0359) and 1338 Zemst‐Hofstade (073E0397) the Mont‐Panisel sand and the overlying clayey 1339 sand have disappeared, except maybe for a very thin remnant, and it appears 1340 that the Aalbeke and the Merelbeke clay Members are almost superposed 1341 (interpretation Johan Matthijs), although this needs micropaleontological 1342 confirmation. This superposition would imply the wedging out of the Mont‐ 1343 Panisel and Kwatrecht units by erosion before the deposition of the 1344 Merelbeke Member rather than their later erosion before deposition of the 1345 overlying Zenne Group as would be the case if only Aalbeke clay is present 1346 (see also Merelbeke Member).

1347

1348 On the other hand in the Kallo wells (027E0148/014E0355), more north‐ 1349 westwards, the Kortemark and Egemkapel Members can be recognised and 1350 between the Egemkapel and the Merelbeke clay Members the sandy unit is 1351 often interpreted as Egem Member, although identification as Hyon 1352 Formation is probably more prudent. The same log signature of the Hyon

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1353 Formation interval in the Kallo well 014E0355 is also recognised in the 1354 Rijkevorsel 007E0200 borehole.

1355 Stratotype:

1356 The section between 0 and about 21.58m depth in the borehole of the Mont‐ 1357 Panisel (151E0340) (topographic map sheet 45/7‐8 Mons‐Givry, (x=122.300, 1358 y= 125.375, z= +102m).

1359 As the Mont‐Panisel borehole is located in an outlier area of the Mont‐Panisel 1360 Member, the interval 46‐54 m in the borehole Zemst‐Weerde (073E0359) can 1361 be considered a parastratotype of the Mont‐Panisel Member (verslag Zemst, 1362 FV Matthijs‐Buffel, 2000; Steurbaut et al., 2015).

1363

1364 Geophysical borehole references 1365 Typical log signature of the Mont‐Panisel Mbr can be observed in the 1366 reference borehole logs: Merchtem ‐ 072E0229, Zemst‐Weerde ‐ 073E0359, 1367 Wieze ‐ 072W0159, Wortegem – 084W1475, Kerksken – 086E0340, Kester – 1368 101W0079.

1369 Often it is not possible to distinguish Egem and Mont‐Panisel Mbrs. In that 1370 case the signatures are best described as Hyon Fm such as a prudent 1371 interpreter could do in the case in the reference logs Rijkevorsel – 007E0200, 1372 Mol – 031W0237, Kallo – 014E0355,...

1373 In the Kallo well – 014E0355, and eventually the Rijkevorsel borehole – 1374 007E0200, the subdivisions Yd4,5,6 are still recognisable and could be 1375 assigned to the Egem Mbr as has commonly be done in the Mol well – 1376 031W0237 (M. Gulinck) although in this Mol well, Steurbaut (1988) has 1377 differentiated Kortemark and Egem above the Aalbeke Mbr.

1378 The Egem Member in the Knokke well 011E0138 is intriguing as the Yd4,5,6 1379 subdivisions on the geophysical logs are apparently identifiable although only 1380 Yd6 is a sandy deposit but Yd4,5 are reliably described as clay deposits in the 1381 cores; only the Yd6 interval is therefore considered as the Egem Mbr in the 1382 Knokke Memoir (Laga & Vandenberghe, 1990; King, 1990; Welkenhuysen & 1383 De Ceukelaire, 2009 p. 72). The profile designed by Van Burm and Bolle (in

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1384 Jacobs et al, 1996a) indicates the appearance of a clay‐layer above the 1385 Egemkapel Member; this clay layer called Yd5 is clearly increasing to the 1386 west. Apparently in the Brugge‐Knokke area the lower part of the Egem 1387 Member is developed as a clay whereas it was a sand, subdivided in Yd4‐Yd5‐ 1388 Yd6, in the Tielt‐Gent area (Jacobs et al, 1996a‐b). A provisional informal 1389 name could be used for this clay unit in the Brugge‐Knokke area, the 1390 Hazegraspolder unit referring to the location of the cored Knokke borehole.

1391

1392 Differentiation between the Mont‐Panisel and the Egem Members: 1393

1394 The Mont‐Panisel Formation consists of poorly sorted clayey glauconitic 1395 sands in which the glauconite can make up to 15%. The Egem Member 1396 consists of well sorted laminated fine sands in which also somewhat thicker 1397 clay layers can occur. In this sense, the Mont‐Panisel Formation is more 1398 homogeneous than the Egem Member.

1399 The Mont‐Panisel Member, in contrast to the Egem Member, contains 1400 numerous irregularly shaped siliceous sandstone concretions whilst 1401 sandstones in Egem are rare.

1402 In the practice of the 1:50 000 mapping, the Egem Member was identified 1403 whenever it could be subdivided in the subunits Yd4,5,6 introduced by Jacobs 1404 & Bolle (1993) and Jacobs et al.(1996a,b); towards the east, in the 1405 neighbourhood of Aalst, the sediment became more clay‐enriched and the 1406 traditional Egem sand subdivisions could no longer be followed in the 1407 mapping; consequently, this more clayey unit in the east, which also 1408 contained sandstones, was mapped as the Mont‐Panisel Member (see Jacobs 1409 et al., 1996, a /Fig.15 showing this transition).

1410

1411 Gentbrugge Formation 1412 Author: see also Geets (1988) and Steurbaut (1998). 1413 The formation is also discussed by de Heinzelin & Glibert (1957), De Moor & 1414 Geets (1973), De Moor & Germis (1971), Fobe (1986), Geets (1979), Gulinck

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1415 (1967), Gulinck & Hacquaert (1954), Kaasschieter (1961), Maréchal (1993), 1416 Steurbaut & Nolf (1986) and Wouters & Vandenberghe (1994). 1417 1418 Description: this formation of marine origin consists at the base of a very fine 1419 silty clay or clayey, very fine silt. To the south and upwards, it is followed by 1420 an alternation of layers of glauconiferous, clayey silty, very fine sand and 1421 clayey sandy, coarse silt, disturbed by bioturbation. The clayey members are 1422 covered by fine sand, clearly horizontally bedded or cross bedded. The 1423 sediments contain different layers of sandstones. 1424 1425 Stratotype: stratotypes have only been designated for the members. 1426 1427 Area: the formation mainly outcrops in the centre of East‐ and West‐Flanders 1428 and on the hills in the southern part of East‐ and West‐Flanders. It occurs also 1429 in the subsoil of the province of Antwerp and northwest Belgium. Some 1430 outliers can be observed to the south till northern Hainaut and eastwards 1431 from the Senne River. 1432 The regional distribution map of the Gentbrugge Formation is figured in 1433 Maréchal (1993, p 222) as understood at that time; the extension mapped on 1434 the 1:50 000 geological maps can be consulted on 1435 https://dov.vlaanderen.be/dovweb/html/geologie.html. 1436 1437 Thickness: maximum 50 m in the north and decreasing to the south and the 1438 east. 1439 1440 Members: the formation is subdivided into the Kwatrecht, Merelbeke, Pittem 1441 and Vlierzele Members. Note that in the present review the now more 1442 generally recognised, Kwatrecht Member is ranked in the Gentbrugge 1443 Formation because of its more clayey nature compared to the sediments in 1444 the Hyon Formation. 1445 1446 The Vlierzele Member has been traditionally included in the Gentbrugge 1447 Formatie of the Ieper Group. It could be argued that the Vlierzele unit as a 1448 sand unit would be better ranged in the sandy Zenne Group. However it is 1449 also argued that the Vlierzele unit also contains clayey parts and therefore

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1450 should remain in the Ieper Group. However, taking into account the full 1451 significance of the clayey parts of the Vlierzele unit led Fobe (1995, 1997) to 1452 differentiate different members in the Vlierzele unit and to rank the Vlierzele 1453 unit as a Formation (see further/ to be discussed). In the present review the 1454 Vlierzele is kept as a Member and ranked in the Gentbrugge Formation (see 1455 below). 1456 1457 1458 Age: late Ypresian. 1459 1460 Remark: the Gentbrugge Fm is called Gent Fm on the 1:50 000 geological 1461 maps. The name Gent Fm was changed to Gentbrugge Fm since it was 1462 already in use for Quaternary eolian cover‐sand deposits in Flanders (Paepe & 1463 Vanhoorne 1976, see website NCS Quaternary subcommission). 1464

1465 Kwatrecht Member 1466 Authors: De Moor & Geets (1973)

1467 The occurrence described in the Gent area (Merelbeke) as reported by De 1468 Moor & Geets (1973) is only documented in this one section (boreholes 1469 DB11&12) as alternating clayey and sandy sediments in contrast to the more 1470 well‐calibrated fine sand of the Egem Member below. No further 1471 sedimentological details can be derived from this description and the 1472 suggestion for a fill of erosive channels as figured on the De Moor and Geets 1473 (1973) profile is not considered justified by the existing borehole data. An 1474 analogue profile in the same area around Gent (Jacobs et al. 1996a fig. 9) 1475 omitted the Kwatrecht unit below the Merelbeke Member. Vandenberghe et 1476 al. (1998 & 2004) have suggested this Kwatrecht unit could be an erosion 1477 remnant as a consequence of intense erosion phases in the late Ypresian and 1478 early Lutetian.

1479 However a review of the original documentation and biostratigraphic 1480 information (dinoflaggellate data) suggests that this clayey sand unit can be 1481 maintained as a separate unit. Furthermore a detailed analysis of the Zemst‐ 1482 Weerde borehole (Steurbaut et al. , 2015) seems to confirm a more regional 1483 extension of this lithological unit at the same biostratigraphic level.

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1484 Therefore it is justified to introduce the Kwatrecht Member as aformal 1485 lithostratigraphic unit.

1486

1487 Description:

1488 A layered complex of greenish glauconitic and micaceous bioturbated sand 1489 and sandy clays, without stone beds, originally indicated as the Kwatrecht 1490 Complex, has been described underlying the Merelbeke Member and 1491 overlying the Egem Member in the Gent area near Merelbeke by De Moor 1492 and Geets (1973, see 2.2.3.3).

1493 In regional sections, the Kwatrecht Member is geometrically positioned 1494 between the Egem and Merelbeke Members by Steurbaut & Nolf (1986), 1495 Steurbaut (1991) and Willems & Moorkens (1991). Based on geometry and 1496 biostratigraphy the Kwatrecht Member has been related to the Hyon 1497 Formation by Vandenberghe et al. (2004). However more recently the 1498 Kwatrecht Complex is ranged in the Gentbrugge Formation by Steurbaut 1499 (2006, 2011).

1500 Regional occurrence and stratigraphic position:

1501 Original description by De Moor and Geets (1973) in the Gent area. Steurbaut 1502 (2006, p 79) has reported the presence of the Kwatrecht Member in the 1503 Zemst‐Weerde borehole (073E0359, Buffel at al., 2009); according to the 1504 description of this borehole in the present review (see Mont‐Panisel 1505 Member), the about 5 m clayey sand between the Mont‐Panisel Member and 1506 the Merelbeke Member, are meant as Kwatrecht Member by Steurbaut 1507 (2006). Consequently this Kwatrecht Member is now also recognised in the 1508 east of the Brabant province (boreholes Kerksken – 086E0340, Kattem – 1509 087W0479, Meise – 073W0394, Merchtem ‐ 072E0229.see Mont‐Panisel 1510 Member).

1511

1512 Stratotype:

1513 The Gent area (Merelbeke) section as described by De Moor & Geets (1973). 1514 As data from this stratotype are not easily accessible, the 41‐46 m interval in

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1515 the Zemst‐Weerde (073E0359) borehole could be considered as the 1516 parastratotype.

1517 1518 Geophysical borehole references 1519 A twofold subdivision of a sand layer between the Aalbeke and Merelbeke 1520 Mbrs allows to distinguish an upper Kwatrecht Mbr signature above a Mont‐ 1521 Panisel Mbr signature in the reference boreholes Merchtem – 072E0229, 1522 Zemst‐Weerde – 073E0359, Kerksken – 086E0340, Wortegem – 084W1475, 1523 (Wieze – 072W0159?) and in the analysis of the Kattem borehole – 087W0479 1524 (Geological Service Company, 2003) and the published Meise borehole 1525 (073W0394) (Welkenhuysen & De Ceukelaire, 2009 Fig. 32). 1526 1527

1528 Merelbeke Member 1529 Authors: De Moor & Germis (1971,p 57), Steurbaut & Nolf (1986, p 128), 1530 Geets et al. (2000).

1531 Description:

1532 The Merelbeke Member is a compact heavy to silty clay; it is a marine 1533 deposit, although some periods with fresh water algae influx have also been 1534 observed. Thin sand laminae with organic matter and small pyritic 1535 concretions have been described by De Moor & Geets (1974). The Merelbeke 1536 Member thickness is generally limited to about 6 to 7 m but exceptionally up 1537 to 14 m near Melle in the profile 3 by De Moor & Geets (1973). The thickness 1538 variations as figured in the profile by DeMoor and Geets (1973) are most 1539 probably due to the lack of borehole sample quality although they may also 1540 be the result of strong erosion at that stratigraphic interval (Vandenberghe et 1541 al. 2004).

1542

1543 Regional occurrence and previous names:

1544 The Merelbeke Member occurs in the western part of the Brabant province 1545 and in the north of the provinces of East and West Flanders. Its distribution is

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1546 irregular because of erosion by later Eocene deposits (Vandenberghe et al., 1547 1998, 2004).

1548 Where the Merelbeke Member occurs, it overlies either the Egem Member or 1549 the Mont‐Panisel Member as in the Ronse‐Aalst‐Brussel area or the 1550 Kwatrecht Member in the east. The Member is overlain by the Pittem 1551 Member.

1552 On the 1:40 000 maps the Merelbeke Member is mapped as P1m, a code also 1553 often used in borehole descriptions. In the stratigraphic register (1929, 1932) 1554 it is part of the Y2 division. In the 1:40 000 mapping, Merelbeke and Aalbeke 1555 Members have been confused in the southwest of Flanders.

1556 In the area west of Mechelen (Hombeek, Zemst...), the Merelbeke Member 1557 has been confused in some borehole descriptions with the P1n clay (1:40.000 1558 map legend), which is a unit occurring above or in the top of the Vlierzele 1559 Member (Buffel et al., 2009). This confusion in North Belgium was already 1560 pointed out by Fobe (1995).

1561 Stratotype: 1562 The section described between +5,6 and ‐4,9 m T.A.W. in the borehole Melle 1563 (055E0783) (222/E3/SWK/F/DB11), topographic map sheet 22/1‐2,Gent‐Melle 1564 (X= 109.125, Y = 188.775, Z = + 12.6 m) (Geets et al., 2000).

1565

1566 Geophysical borehole references 1567 The Merelbeke Member signature in the reference borehole logs can be 1568 observed in many boreholes: Merchtem – 072E0229, Zemst‐Weerde – 1569 073E0359(confirmation by biostratigraphy in Buffel et al., 2009), Kerksken – 1570 086E0340, Brugge – 023W0454, Knokke – 011E0138, Kallo – 014E0355, 1571 Rijkevorsel – 007E0200, Oosterzele – 070E0237, Kruishoutem – 084E1412, 1572 Merksplas – 017W0280.

1573 The Zemst‐Hofstade – 073E0397 borehole presents an interesting case. The 1574 top clay unit, consisting of two parts on the log, is either entirely the Aalbeke 1575 Clay or it might be composed of the Aalbeke Clay overlain directly by the 1576 Merelbeke Clay, or with only a very thin remnant about 1m Mont‐Panisel 1577 Sand in between (interpretation Johan Matthijs); the latter case implies the

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1578 erosion of the Mont‐Panisel, and probably Kwatrecht, units before the 1579 deposition of the Merelbeke Member rather than their erosion before 1580 deposition of the overlying Zenne Group as would be the case if only Aalbeke 1581 clay is present.

1582 It should be noted that in the reference borehole Knokke – 011E0138, and 1583 also Mol‐SCK15 – 031W0237, also a similar two fold Aalbeke Mbr signature is 1584 observed.

1585

1586 Pittem Member 1587 Authors: Geets (1979), Geets et al. (2000), Steurbaut et al. (2003)

1588 Description:

1589 The Pittem Member consists of a bedded alternation of thin, dm scale, layers 1590 of silty clay and clayey fine glauconitic sand, locally cemented into thin 1591 sandstone and siltstone beds which can be microporous after dissolution of 1592 sponge spiculae and fossils. Bioturbation is common. Tidal gullies have been 1593 reported by Geets et al. (2000). The thickness of the Pittem Member is about 1594 15 to 20 m. Traces of lignite have been reported in the Pittem Member 1595 occurring between Knokke and Kruibeke in the north of West and East 1596 Flanders by Fobe (1993).

1597 The lower boundary is easily distinguished from either the underlying 1598 Merelbeke Member, the Egem Sandstone Bed or the Egem Member. The 1599 often reported gradual transition between Pittem Member and the overlying 1600 Vlierzele unit in boreholes, is erroneous and due to a confusion between the 1601 Pittem Member and clayey parts of the Vlierzele unit sensu Fobe (1995) 1602 (Fobe, 1995 p 143).

1603 Also, in typical cases, the limit between the clayey sediment of the Pittem 1604 Member and the overlying Vlierzele Sand can be traced with reasonable 1605 confidence in the geophysical log correlation profiles by Welkenhuysen and 1606 De Ceukelaire (2009).

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1607 Fobe (1997) reports that in the subsurface of northwest Belgium the upper 1608 part of the Pittem Member is a conspicuous horizon, brown coloured by 1609 lignitic material.

1610 Regional occurrence and previous names:

1611 The Pittem Member occurs almost continuously in a small zone north of a line 1612 Torhout‐Tielt‐Oudenaarde‐Ninove and in West Brabant but subcrops over a 1613 larger area north of this line. South of this line it occurs only in the South 1614 Flemish hills. Towards the south the Pittem Member becomes more sandy.

1615 On the geological maps 1:40 000 the Pittem Member is represented by the 1616 P1c unit and in the stratigraphic register (1929, 1932) as part of the Y2 1617 division. On the 1: 40 000 maps of the Kortrijk area, clayey deposits of the 1618 Tielt Formation have been incorrectly interpreted as P1c. The name ‘sandy 1619 clay of Anderlecht’ is a synonym.

1620 Stratotype :

1621 Geets (1979) considered the now abandoned Claerhout extraction pit in 1622 Pittem (topographic map 21/5‐6, Izegem‐Wakken, X = 74.250, Y = 187.540, Z = 1623 + 46 m) as the reference section for the Pittem Member. An identical section 1624 is exposed in the Ampe pit – 053W0060 between +43.5 and +40 m T.A.W 1625 (topographic mapsheet 21/1 Wingene x= 70.150, y= 190.150, z= +44m) above 1626 the X‐stone Bed.

1627

1628 Geophysical borehole references 1629 The Pittem log signature can be observed in the reference boreholes of the 1630 type area of central Flanders such as Tielt 053E0061, Brugge – 023W0454, 1631 Knokke – 011E0138, Oosterzele – 070E0237, Kruishoutem – 084E1412 but also 1632 in the borehole logs of Merchtem – 072E0229, ON‐Kallo‐1 – 014E0355, 1633 Rijkevorsel – 007E0200 and Merksplas – 017W0280.

1634

1635 Hooglede Sandstone Bed 1636 Authors: Bolle & Jacobs (1993), Fobe (1997b), Steurbaut et al. (2003, p 33, 34)

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1637 Description:

1638 A pale yellowish brown, limonite stained, about 40 cm thick, cemented and 1639 originally shelly coarse‐grained sandstone layer; most shells have been 1640 dissolved and left large voids. Typically, numerous very coarse glauconite 1641 grains are dispersed across the sandstone and sometimes glauconite staining 1642 occurs in the dissolved shell voids. The fossils in the layer are bivalves, 1643 oysters, nautiloids and shark teeth; also phosphatic nodules are reported 1644 (Steurbaut, 2006). The sandstone bed overlies the Egem Member and 1645 underlies the Pittem Member.

1646 Because of its characteristic aspect, it is preferred to attribute a bed status to 1647 the stone bed. It has been named bed X in Steurbaut (1998, fig. 5), bed 22 in 1648 Steurbaut (1998) and Steurbaut et al. (2003, p34). It is proposed in this review 1649 to name the bed the Hooglede Sandstone Bed of the Pittem Member after 1650 Fobe (1997b).

1651

1652 Regional occurrence and previous names: 1653 The bed occurs in the classical Ampe extraction pit – 053W0060 at Egem and 1654 is named bed 22 in the classical section of the pit published by Steurbaut 1655 (1998). Lithotratigraphically, the Egem Sandstone Bed has generally been 1656 considered as the base of the Pittem Member (a.o. Steurbaut, 2003) as 1657 several thin and fine‐grained sandstone beds also occur in the Pittem 1658 Member ; it was tentatively suggested to be a lateral equivalent of the Bois‐ 1659 la‐Haut Member by Steurbaut (1998) (reported also in Geets et al., 2000), 1660 although in Steurbaut (2011, fig.8 p 255) the Egem Sandstone Bed (X‐stone 1661 bed) is again included in the base of the Pittem Member.

1662 Stratotype :

1663 The Ampe extraction pit – 053W0060 in Egem (Pittem) (mapsheet 21/1 1664 Wingene x= 70.150, y= 190.150, z= +44m) between the Egem Member and the 1665 Pittem Member.

1666 Vlierzele Member 1667 Comment on the stratigraphic ranking:

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1668 In the recent literature, the Vlierzele Member has been included in the 1669 Gentbrugge Formation of the Ieper Group. However it could be argued that 1670 the Vlierzele Member as a sand unit better fits in the Zenne Group overlying 1671 the clay dominated Ieper Group. This would be partly in line with Fobe (1995) 1672 who argues that the Merelbeke and Pittem Members as clayey units should 1673 be united in the Gentbrugge Formation and distinguished from the sandy 1674 Egem and Vlierzele units, respectively below and above. 1675 As the lower part of the Vlierzele unit can also be clayey (see Jacobs et al., 1676 1996a Fig. 13; Lochristi unit sensu Fobe, 1995 p 142), and also for continuity 1677 reasons, the present review keeps the Vlierzele unit in the Gentbrugge 1678 Formation as a Member. 1679

1680 Authors: Kaasschieter (1961), Geets et al. (2000), Fobe (1995, 1997)

1681 Description:

1682 In the recent literature, based on outcrop observations, the Vlierzele Member 1683 is described as consisting of a lower part of mostly bioturbated, slightly 1684 clayey, glauconitic sand and an upper section of alternating units of tidal 1685 cross‐bedding with mud drapes and structureless intercalations; the upper 1686 section may contain lignite lumps (Houthuys, 1990).

1687 In the recent literature, based on outcrops, the Vlierzele Member is described 1688 as consisting of fine glauconitic green‐grey mostly bioturbated sand, finely 1689 laminated horizontally and in cross stratification. Towards the base the sands 1690 becomes clayey and more homogeneous. Towards the top individualised clay 1691 layers occur together with humic intercalations. Macrofossils are very rare. 1692 Thin cemented siliceous sandstone beds commonly occur (Geets et al., 2000); 1693 irregularly shaped siliceous sandstone concretions are also common. The 1694 maximal thickness is about 20 m; in the type locality the cross bedded sand 1695 above is 7m thick and the lower homogeneous sand at least 5 m (see sections 1696 in Houthuys & Gullentops, 1988 p 142).

1697 Fobe (1995), after reviewing information available from more than 25 1698 localities, considers the ‘traditional Vlierzele sand sensu stricto’ as only one of 1699 5 members in a formation between the Pittem Member and the Aalter Sand

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1700 in the Zenne Group. Steurbaut (2006) reports erroneous correlations in Fobe’s 1701 (op.cit.) subdivisions ; the Beernem sand, traditionally a member of the Aalter 1702 Formation of the Zenne Group (Maréchal & Laga,1988 p 120‐121; Geets et al., 1703 2000), is included in the Vlierzele unit by Fobe and the existence of a distinct 1704 Aalterbrugge unit is refuted by this author. Therefore the present review is 1705 not following the interpretations by Fobe (1995, 1997) but recognizes that the 1706 clayey basis, a 3‐10m very fine clayey sand with mm‐thick clay layers, 1707 (Lochristi layer sensu Fobe) and locally a thin coarser basal layer (Hijfte layer 1708 sensu Fobe) merit a separate mention aside the traditional Vlierzele sand 1709 sensu stricto (which according to Fobe 1995,1997 could be named Oosterzele 1710 unit). 1711 1712 Regional occurrence and previous names:

1713 The Vlierzele Member outcrops in the northern and central parts of the 1714 provinces East and West Flanders and in the western part of the Flemish 1715 Brabant province. It also occurs as outliers in the top zones of the South‐ 1716 Flemish hills. On a regional scale the base of the Vlierzele is erosive into 1717 underlying strata (see also Fobe, 1989b, 1995). In northern Flanders the grain‐ 1718 size properties of the Vlierzele Member seem to be more variable (Laga & 1719 Vandenberghe, 1990 p 1; Fobe, 1993, 1995). The boundary between the 1720 clayey sediment of the Pittem Member and the overlying Vlierzele Sand can 1721 mostly be traced with reasonable confidence in the geophysical log 1722 correlation profiles by Welkenhuysen and De Ceukelaire (2009).

1723

1724 On the legend of the 1:40 000 maps the Vlierzele Member is coded P1d and 1725 P1n for the upper clayey facies. In the stratigraphic register (1929, 1932) the 1726 Vlierzele Member is included in the Y2 division.

1727 The P1n‐clay, defined by Rutot (1890) and described as a local top clay in the 1728 Vlierzele Sand (Gulinck & Hacqaert, 1954) is believed to correspond in fact to 1729 the Merelbeke Clay (Fobe, 1995; Buffel et al., 2009).

1730

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1731 Stratotype: The Vlierzele locality is part of the Sint‐Lievens‐Houtem 1732 municipality in the East Flanders province where several extractions have 1733 been active in the past. The sand pit, formerly known as the Verlee or 1734 Balegem sand pit (at present Balegro sand pit)– 070E0050, is the stratotype; it 1735 is located on topographic map sheet 22/7‐8, Oordegem‐Aalst (X = 116.650, Y 1736 = 181.725, Z = + 45 m) (Geets et al., 2000).

1737 However this stratotype is limited to the Vlierzele sand sensu stricto. 1738 Following Fobe (1995), as far as the Vlierzele sensu stricto, the Lochristi and 1739 Hijfte layers are concerned, the Ursel borehole (039W0212 x= 87.910, y= 1740 204.260, z= + 29 m TAW) shows the Vlierzele Member between 58 and 69,3 m 1741 with the Vlierzele sand sensu stricto between 58‐63 m, Lochristi layer 1742 between 63‐66 m and the Hijfte layer between 66‐69,3 m.

1743

1744 Geophysical borehole references 1745 The Vlierzele Mbr has been identified on top of the Pittem clay Mbr in the 1746 following reference borehole logs: Brugge, Merchtem, Knokke (comprising 1747 the Hijfte, Lochristi and Oosterzele units sensu Fobe 1995,1997), ON‐Kallo‐1, 1748 Rijkevorsel.

1749

1750 Aalterbrugge Bed 1751 Authors: Hacquaert (1939); Gulinck & Hacquaert (1954); De Moor & Geets 1752 (1973); Fobe (1995); Van Simaeys (1999).

1753 Description:

1754 The Bed consists of clays and sand occurring in a complex geometrical 1755 relationship like usually encountered in continental deposits; also lignite beds 1756 and drift wood, sometimes silicified, occur. It occurs between the Vlierzele 1757 Member and the Aalter Formation (Zenne Formation) (Maréchal & Laga, 1758 1988; Steurbaut, 2006), both more homogeneous, glauconitic, marine 1759 sediments.

1760 In the synthesis on Belgian geology (P.Fourmarier, 1954, Prodrome d'une 1761 description géologique de la Belgique, Soc. Géol. Belg.) Gulinck & Hacquaert

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1762 (1954) describe in the chapter XIV the Complexe d'Aalterbrugge occurring in 1763 the top of the Vlierzele sand unit as follows : " Ces sables prennent souvent 1764 dans les zones supérieures, quelquefois aussi dans les parties moyennes, un 1765 facies plus grossier, pauvre en galuconie, parfois ligniteux, avec bois flottés 1766 percés de tarets et souvent silicifiés. On y rencontre également des niveaux 1767 de galets de glaise, spécialement dans la région de Torhout (Rutot 1768 [explic.carte géologique 1:40 000]) et d'Aalter (Hacquaert, [1939]).

1769 Les bois flottés sont parfois très volumineux. Leur nature fragmentaire 1770 permet rarement une détermination précise, mais on a pu y distinguer une 1771 dizaine d'espèces (F. Stockmans [région de Bruxelles])".

1772 The Aalterbrugge unit as represented on the section in De Moor & Geets 1773 (1973, fig.4) attains 10m thickness. The temporary exposure described by 1774 Jacobs (2015 p 137) was at maximum 3m thick (Steurbaut or. com.). Van 1775 Simaeys (1999) shows the presence of the Aalterbrugge Complex in the Hijfte 1776 borehole (040E0373) section between 46.1 and 53.1 m depth.

1777 No Aalterbrugge unit is reported in Geets et al. (2000) and also in the 1778 explanatory notes of the 1:50 000 map sheet 22 Gent, the Aalterbrugge unit is 1779 not reported (Jacobs et al., 1996).

1780 From his extensive data review, Fobe (1995) even concludes that the 1781 Aalterbrugge layer does not exist as a separate facies and has been confused 1782 with lignitic rich zones occurring at different levels in the Vlierzele unit.

1783 The Aalterbrugge unit is well documented and analysed by Van Simaeys 1784 (1999) in the Hijfte borehole 040E0373 in which it is 7m thick. Because of this 1785 thickness the member rank is justified for the Aalterbrugge Member. A 1786 several meter thick similar unit was also exposed during the construction of 1787 the pedestrian bridge over the E40 motorway in Wetteren.

1788 Boundaries:

1789 The section in De Moor & Geets (1973, fig.4) suggest an erosive base into the 1790 underlying Vlierzele Sand. Also Hacquaert (1939) reports intraformational 1791 clasts at the lignite level, suggesting erosion during the complex formation. 1792 Also Steurbaut (2015 p132) suggests that with the regression after the 1793 Vlierzele Sand deposition gullies were formed in the area of Aalterbrugge.

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1794 Maréchal & Laga (1988, p 119) attribute a bed status to the Aalterbrugge 1795 layer between the Gent Fm and the Aalter (at that time named Knesselare) 1796 Formation and note that the transition between the Aalterbrugge bed and 1797 the overlying marine Aalter Sand is continuous. Jacobs (2015, fig.3.21 p 137) 1798 shows the Aalterbrugge unit in Wetteren as a continuous transition between 1799 the Vlierzele and Aalterbrugge unit, but reports that the top of the 1800 Aalterbrugge unit is eroded.

1801 Regional Occurrence:

1802 The Aalterbrugge Bed is most often reported between Aalterbrugge and 1803 Beernem (Jacobs, 2015). It was also described in the Hijfte borehole ‐ 1804 040E0373 northeast of Gent. A recent outcrop along the E40 in Wetteren also 1805 showed the presence of the Aalterbrugge Bed.

1806 Roche (1988‐1991, p 375) and DeConinck (1988‐1991, fig. 9 p 304) report the 1807 presence of the Aalterbrugge Complex in the boreholes Kallo ‐ 027E0148 1808 (level 203 m) and Woensdrecht (NL) (level 385 m).

1809 Stratotype:

1810 sections along the Gent‐Brugge canal (Hacquaert 1939 section).

1811 Parastratotype in the Hijfte borehole (040E0373) section between 46,1 and 1812 53,1 m depth (Van Simaeys, 1999).

1813 Remark : The ‘Aalterbrugge Member’ of the Hijfte borehole (Van Simaeys, 1814 1999) contains isolated records of the freshwater fern Azolla sp. which occurs 1815 massively in the North Sea and even the Atlantic Ocean at the base of chron 1816 C21r (Vandenberghe et al., 2004).

1817

1818

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1819 COMPENDIUM OF REFERENCE LOGS WITH COMMENTS 1820

1821 GR and RES geophysical logs from a selection of boreholes are interpreted in the 1822 lithostratigraphic terms outlined in the present review, dated May 2016. The selection of the 1823 boreholes is made to illustrate the geographical variations observed. The location of the 1824 reference boreholes in this compendium is shown in the map. More borehole data than 1825 those represented in the compendium are available and have been used in the discussions 1826 by the working group. However the selection does represent the present state of knowledge 1827 and also illustrates the still remaining correlation issues. It is not yet well understood how 1828 the Kortemark, Egemkapel, Egem (Hyon Fm), units … a succession so typical for the west and 1829 central Flanders area is replaced laterally over a fairly short distance to the south, east and 1830 the northeast by the undifferentiated Hyon Formation and Mont‐Panisel and Kwatrecht 1831 Members. It is suspected that tectonic tilting rearrangements in the area play a more 1832 important role than previously estimated.

1833 To make progress in these issues, it is imperative to have more combined sedimentological 1834 and biostratigraphic analyses on representative borehole samples from carefully chosen 1835 localities selected after the study of the geophysical borehole patterns.

1836 In the comment section of each borehole only those issues are addressed that make the 1837 proposed interpretation debatable, eventually referring to other boreholes. If the given 1838 interpretation straightforwardly follows from the definitions explained in the text no further 1839 comments are given.

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1840 1841

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1842 Brugge (023W0454) 1843

1844 The threefold subdivision of the geophysical log pattern in the Egem Mbr interval 1845 (‘Yd4’,’Yd5’,’Yd6’) terminology for respectively the sandy lower part, a clayey middle part 1846 and a sandy upper part) can be recognized as determined in the area of the reference Egem 1847 sand and clay pit in central Flanders where the unit is about 20m thick (....14m in Tielt 1848 borehole). However on the Brugge borehole log, only the upper sandy part is expressed as a 1849 manifest sand layer which is the main lithology defining the Egem Mbr. This log pattern is 1850 similar to what is interpreted in the present review as the Egem Mbr interval in the Knokke 1851 borehole (011E0138) (see Knokke borehole) although the Yd4 and Yd5 parts are about 10m 1852 thick compared to almost double in Brugge while the sandy Yd6 part has comparable 1853 thickness of about 10m in both the Knokke and Brugge boreholes. In previous studies of the 1854 Knokke borehole (011E0138) (see a.o. King, 1990 ; Welkenhuysen & De Ceukelaire, 2009 p. 1855 72) only this upper about 10m thick sandy part is identified as the Egem Sand Mbr.

1856

1857 Gent (055W1020) 1858 The presence in the top of the Kortemark Member of a sandy package identified as Yd2 on 1859 the log pattern seems to be a common feature of the Kortemark Member (compare to Tielt, 1860 Kruishoutem, Knokke boreholes...). The Egem Member section is comparable to the lower 1861 subdivisions of the threefold subdivision in the Brugge (023W0454) borehole but the upper 1862 most sandy part, and genuine Egem Sand Mbr (see comment Brugge, Knokke boreholes) is 1863 missing under the erosive base of the Quaternary deposits.

1864

1865 Hijfte (040E0373) 1866

1867 The stratigraphic position of the succession of the upper part of the Vlierzele Member, the 1868 Aalterbrugge Member and also the Aalter unit, already part of the Zenne Group, is taken 1869 from the work of Van Simaeys (1999, fig.2.2). This borehole is shown in the compendium 1870 because it is the only available geophysical log signature associated with a reliably identified 1871 Aalterbrugge Member ( see text Aalterbrugge Member). The interpretation of the boundary 1872 position between the Pittem and Vlierzele Members is according to the lithological 1873 interpretations of Van Simaeys (1999) and Fobe (1997,fig.3) located at about 68m depth; a 1874 marked geophysically change is also observed at about 62m depth the meaning of which is 1875 not clear. Fobe (1997) has identified between 58 and 59m depth a lithological boundary 1876 between the Lochristi and Oosterzele units within the Vlierzele unit of this author.

1877 The top of the Aalter unit is also taken from Van Simaeys (1999); this author interprets the 1878 sand unit above the Aalter unit as Lede Sand in comparison with the Lede Sand in the

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1879 Woensdrecht (Nl) borehole whilst Fobe (1999) interprets this sand as a few meter of lede 1880 Sand overlain by Wemmel Sand .

1881 ON‐Kallo 1 (014E0355) 1882 The Mont Héribu Mbr is recognised by the thin silty basal sediment also containing 1883 glauconite recognised in the cores of the borehole.

1884 The boundary levels between Orchies and Roubaix Members a proposed by Steurbaut (1988, 1885 1998) in the BGD Kallo 027E0148 borehole, with cores but without geophysiscal logs, can be 1886 approximately transferred to the ON‐Kallo‐1 borehole(014E0355), with cores and 1887 geophysical logs, using the depth conversion formula: m(ON‐Kallo)=1.0016(Kallo BGD) + 1888 23,638 (courtesy Peter Stassen) although it must be warned that comparing depth values 1889 from core descriptions and geophysical well logs has some inherent inaccuracies.

1890 The top Aalbeke Mbr is following the silting‐up trend till the first sandy interval (RES curve) 1891 marking the start of the overlying Kortemark Mbr.

1892 The top and base of the Egemkapel Mbr, could be interpreted with some degree of freedom 1893 if solely based on GR,RES; however the boundaries are chosen based on the published grain‐ 1894 size data by Geets (1988) and the grain‐size and geophysical‐log response in the reference 1895 area of the Egem clay and sand pit and the Tielt borehole (Steurbaut, 1998).

1896 The core description of the Hyon interval corresponds to a carbonate containing sand in 1897 which stone layers are absent. A threefold subdivision can be made in the Res pattern in the 1898 Hyon Fm interval, somewhat comparable to the threefold subdivision of the Egem Mbr 1899 interval in the Knokke borehole (011E0138); however, in the Knokke well only the upper 1900 subdivision consists of fine sand and is considered Egem Sand (Laga & Vandenberghe, 1990) 1901 (see comment Brugge and Knokke boreholes). In the ON‐Kallo‐1, additionally a subdivision 1902 could be made based on the GR curve reflecting the lithology observed in the cores: the 1903 lower part being a fine sand and the upper part a very fine sand and glauconitic fine sand. 1904 However it is not possible to unequivocally identify this unit as the Egem Member and 1905 therefore it is more prudent to describe this unit as the Hyon Fm of which the Egem Sand is a 1906 Member.

1907 Based on the log readings,the sediments above the Merelbeke Mbr are clayey over about 1908 5m followed by sand. Fobe (1995, Fig.5) describes in the nearby Kruibeke borehole 1909 (042E0314) 5m Pittem Mbr sediment overlying 12m Merelbeke Mbr, and overlain by at least 1910 10m Vlierzele Sand Mbr (top of the ‘sensu Fobe Oosterzele facies ‘).

1911

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1912 Kerksken (086E0340) 1913 The log pattern of the Mont‐Panisel and Kwatrecht Members is very comparable with the 1914 interval in the Weerde‐Zemst (073E0359) borehole in which the interpretation of the Mont‐ 1915 Panisel and Kwatrecht Members is discussed by Steurbaut et al. (2015).

1916

1917 Kester (101W0079) 1918 Different stratigraphic interpretations exist of this borehole(see Houthuys 2014; see also a 1919 reinterpretation discussion of the borehole by Houthys and Matthijs , 2016 posted on DOV ) 1920 and available on http://mars.naturalsciences.be/geology/boreholes/110w0079‐ 1921 kesterberg/view

1922 The sandy clay base of the Ieper Group (105‐111m) is unusual. The low GR at the base is 1923 maybe comparable to the lower GR at the base of the Merchtem borehole (072E0229) log. 1924 The Lower Orchies unit is about 15m thick.

1925 The interpretation of the Aalbeke Mbr overlain by the Mont‐Panisel Mbr is based on the 1926 similar pattern observed in the Merchtem borehole (072E0229).

1927 The lithology between the Aalbeke and the top of the Upper Orchies Member seems more 1928 clayey at its base and more sandy towards the top. Based on the expected vertical 1929 succession of lithostratigraphic intervals, this interval could be interpreted as the Roubaix 1930 Mbr or as the Mons‐en‐Pévèle Fm. The Roubaix Mbr interpretation could be supported by 1931 the GR signal which is not so different from the signal in the Orchies section below. The 1932 lithological description of the section in the Kester borehole however (Archives Belgian 1933 Geological Survey) reports a very dominantly sand lithology, confirmed by grain‐size analyses 1934 in Geets (2001, p68) and hence the interval corresponds to the Mons‐en‐Pévèle Fm 1935 according to the criterion outline above in the text (>50‐60% sand layers). The geophysical‐ 1936 log pattern events in that interval can be interpreted as similar to those observed in the 1937 boreholes Merchtem (072E0229) and Zemst‐Hofstade (073E0397) : in the former the pattern 1938 is considered transitional between Roubaix and Mons‐en‐Pévèle (see Merchtem log in the 1939 compendium) and in the latter the pattern is interpreted as Mons‐en‐Pévèle ( see log in 1940 compendium).

1941

1942 Knokke (011E0138) 1943 The Zoute Mbr is defined (Steurbaut, 1988) between 283,4‐288m.

1944 The top of the Aalbeke Mbr is consistent with a clay mineralogy boundary as published by 1945 Mercier‐Castiaux & Dupuis (1988).

1946 The GR and RES log signatures between 154 and 157,5m are interpreted as the level 1947 corresponding to the Egemkapel clay Member. In

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1948 Plates 2 and 3 in Laga & Vandenberghe(1990) illustrate brecciation in the intervals 153.20‐ 1949 153.40m, at 154.20m and also at 170‐171m and 180‐180,90m which could represent 1950 submarine erosion levels associated with low sea‐level positions.

1951

1952 Unfortunately biostratigraphic data are missing in this interval (nannoplankton of the Knokke 1953 borehole in Steurbaut (1990,p48); dinoflagellates (see De Coninck, 1991), and the few 1954 dinoflagellate marker horizons by Hochuli (in Vandenberghe et al. (1998, fig.7)) are probably 1955 lacking precision).

1956 The practice of considering the sediment interval between the Egemkapel and the 1957 Merelbeke units as the Egem Member is the basis of the present interpretation which seems 1958 supported by the consistent correlation of subunits in the Egem Member Yd4‐Yd5‐Yd6 which 1959 is exemplary demonstrated in the Tielt‐Gent area (legends geological maps Tielt and Gent, 1960 Jacobs et al, 1996a‐b); however it seems that towards the north‐west in the Brugge‐Knokke 1961 area, the lower part of the Egem Member is developed as a clay. This is also observed in the 1962 Brugge borehole. In previous studies of the Knokke borehole (011E0138) (see e.g. King, 1963 1990; Welkenhuysen & De Ceukelaire, 2009 p. 72), the identification of the Egem sand Mbr 1964 is logically limited to the upper about 10m thick sand layer (‘Yd6’) in the interval (see also 1965 Comment, Brugge borehole).

1966 The profile designed by Van Burm and Bolle (Jacobs et al, 1996a), reproduced below, is 1967 already an indication of the appearance of a clay‐layer above the Egemkapel Member. The 1968 layer called Yd5 is clearly increasing to the west. It is proposed to call informally the clayey 1969 lower Yd4 and Yd5 part the Hazegraspolder unit, referring to the location of the deep cored 1970 Knokke borehole (Laga & Vandenberghe (1990).

1971 The intervals of the Merelbeke, Pittem, and Vlierzele Mbrs are in accordance with core 1972 descriptions (see Laga & Vandenberghe, 1990) and with the Fobe (1995,1997 fig.3) 1973 interpretation, if this last authors’ Beernem unit ‘ with base at 116m, is considered part of 1974 the Aalter Fm of the Zenne Group as discussed in the text under Vlierzele Member.

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Yd5 clay

1975 1976

1977 Kruishoutem (084E1412) 1978 In the Hyon Fm interval (8‐18,2m), absence of stone layers and a log pattern having a good 1979 resemblance to the Tielt, Brugge .. boreholes, suggests that the Egem Sand Mbr is present.

1980 The top of the Aalbeke Mbr is based on the GR pattern but the base of the unit is more 1981 arbitrary and could be a few m lower.

1982

1983 Merchtem (072E0229) 1984 An inspection of the original lithological description of the borehole (DOV) shows less than 1985 25% of the interval between about 76‐118m is described as sandy and therefore, according 1986 to the criterion discussed in the text, the interval has to be considered as the Roubaix Mbr 1987 rather than the Mons‐en‐Pévèle Formation. However referring to the discussion about this 1988 criterion in the text and the relatively high values both GR and RES in the interval 76‐118m, 1989 make a distinction between Roubaix Mbr and Mons‐en‐Pévèle Fm doubtful. From the 1990 traditional events in the Roubaix Mbr only the 4,5,6 labeled events can be identified.

1991 The 2 units between the Aalbeke and Merelbeke clay Members have an almost identical log 1992 signature to a pattern recognized in the Kerksken (086E0340), Weerde‐Zemst (073E0359) 1993 (see discussion in Steurbaut et al. , 2015) and even maybe Wieze (072W0159) borehole logs 1994 and are therefore interpreted as the Mont Panisel and Kwatrecht Mbrs.

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1995 The Gentbrugge Fm above the Merelbeke unit is interpreted as the Pittem Mbr below and 1996 Vlierzele Mbr above, and the log seems similar to the Kallo (014E0355) and maybe even 1997 Rijkevorsel (007E0200) borehole logs. In the Kallo (014E0355) borehole the Pittem Member 1998 identification is in line with the about 5m Pittem Member identified in the nearby Kruibeke 1999 borehole by Fobe ( 1995,fig.5).

2000

2001

2002 Merksplas (017W0280) 2003 The presence of just a few meter of the Mont Héribu Mbr cannot be excluded as it is present 2004 in the nearby Kallo (014E0355) and Rijkevorsel (007E0200) wells; however it is estimated too 2005 thin to be positively identified on the Merksplas log.

2006 The Kortemark Mbr is identified as the unit between the Aalbeke and Egemkapel clay 2007 Members, although it has become thin in this borehole and the log pattern is not very 2008 charactersitic.The pattern is comparable to the nearby Rijkevorsel borehole.

2009 No further specification of the Hyon Fm is possible; the GR pattern is quite comparable to 2010 the Kallo borehole.

2011 Mol SCK 15 (031W0237)

2012 This well is included in the compendium because it is cored, reliably described (Gulinck & 2013 Laga, 1975) and many biostratigraphic work was done on samples from this well. More 2014 recent cored boreholes with geophysical wells were drilled and cored in the Mol‐Dessel 2015 area in the framework of the ONDRAF‐NIRAS research related to radioactive waste.

2016 The top of the Orchies Member corresponds with the base of the Mons‐en‐Pévèle Sand Fm 2017 above according to a detailed core description by Gulinck and Laga(1975) showing at that 2018 level the boundary between fine sand and clay.

2019 The fine sand above the Aalbeke Mbr has clay laminations in the middle as observed in the 2020 cores. It is interpreted as the Hyon Fm because of its sandy nature while the Kortemark Mbr 2021 is more clayey. No stone layers have been reported in the interval.

2022 Steurbaut (1988) has interpreted this interval as consisting of the Egem Mbr above 355m 2023 and the Kortemark Member below 355m; this could be supported by the somewhat similar 2024 borehole pattern as in the Merksplas borehole where the pattern is interpreted as the 2025 Kortemark, Egemkapel , Hyon succession. The clay laminations could then be considered the 2026 equivalent of the Egemkapel unit.

2027 Steurbaut has reviewed the nanoplankton data of this interval for the purpose of the present 2028 review; he concludes that the top of the Hyon Fm interval above 354,2m corresponds to the

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2029 Mont‐Panisel Mbr whilst the lower part cannot be attributed with certainty to any known 2030 unit, and neither to the Kortemark nor the Egem Member.

2031 Oosterzele (070E0237) 2032 The Hyon Fm between the Egemkapel and Merelbeke Mbrs lacks stone layers and its log 2033 pattern is comparable the pattern of the Egem Mbr in the nearby Gent borehole.

2034 The Gentbrugge Formation consists entirely of the Vlierzele Member which is consistent 2035 with the observation from field and borehole data of the absence of the Pittem Member in 2036 the area (see text).

2037

2038 Pittem (053W0073) 2039 The borehole is close to the nearby Tielt borehole (053E0061) and the Egem clay and sand 2040 pit (see Steurbaut, 1988, Fig. 5). The more clayey log pattern at the base of the Kortemark 2041 Member compared to the Kortemark Member log pattern of the Tielt borehole may be an 2042 indication of the lithological variability within the Kortemark Member.

2043

2044 Rijkevorsel (007E0200) 2045 Log patterns in the Rijkevorsel and Kallo (014E0355) wells are very similar for the Kortemark 2046 Mbr, Hyon Fm, Gentbrugge Fm... Subdivisions within the Orchies Member have been 2047 interpreted by Steurbaut (1998, Fig.10). The base of the Gentbrugge Fm probably consists of 2048 a few meter of the Pittem Member.

2049 Tielt (053E0061) 2050 Note that the borehole represented in the Compendium is a different borehole than the 2051 classical 068E0169 borehole from which grain‐size data are available (Geets 1988; and used 2052 in the interpretations by Steurbaut, 1998, Fig16). Distance between the two boreholes is 2053 more or less 2 km. Tielt is located close to the Egem clay and sand pit.

2054 The top of the Aalbeke Mbr is interpreted at 49,5m below which heavy clay was described in 2055 the borehole (De Geyter, Archives Belgian Geological Survey); on the GR and RES log pattern 2056 this level corresponds to the coarsening of the sediment in the top of the Aalbeke Mbr (see 2057 discussion in text).

2058 Torhout (052E0195)

2059 Although the geophysical logs are not of very good quality, a reasonable interpretation with 2060 typical log signatures can be made, based on a comparison with the Tielt borehole 2061 (053E0061).

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2062 Wieze (072W0159) 2063 The identification of the 3 sub‐members of the Orchies Member is straightforward, as is the 2064 labeling in the Roubaix Member and the identification of the Aalbeke Mbr.

2065 Above the Aalbeke Mbr, the RES and GR log pattern resembles the twofold subdivision 2066 pattern as in Kerksken (086E0340), Zemst‐Weerde (073E0359)…. and consequently can be 2067 interpreted as Hyon Fm/MontPanisel Mbr overlain by the Kwatrecht Member. However, the 2068 clay intervals at about 8 and 20 m depth could equally well be interpreted as respectively the 2069 Merelbeke and Egemkapel Members. In the latter interpretation the unit above the Aalbeke 2070 Clay would be the Kortemark Member instead of the Mont‐Panisel Member and above the 2071 Egemkapel Clay would occur the Egem Member instead of Kwatrecht Member. The 2072 signature of the possibly Kortemark Member is comparable to the Kortemark Member 2073 signature more to the west but the supposed Egem Member on the other hand would then 2074 appear to be more clay rich according to the logs than the Kortemark Member below it. It is 2075 hard to make a final choice without more sedimentological and biostratigraphic analyses in 2076 the area and in the reference areas.

2077 Both possible interpretations are shown on the log while in the log correlation figure by J. 2078 Matthijs, the Kortemark to Egem interpretation is represented.

2079 Wortegem (084W1475) 2080 The top Orchies Mbr corresponds to the systematic description by De Geyter (1990) as the 2081 limit between overlying silty clay and heavy clay below. The Roubaix Member log pattern is 2082 analoguous to the Roubaix section in the Oosterzele borehole.

2083 The Aalbeke Mbr GR, and also RES, pattern is comparable with its equivalent in the 2084 Kruishoutem borehole.

2085 The Mont‐Panisel and Kwatrecht Mbrs patterns are comparable to the patterns of these 2086 units in the Kerksken (086E0340) and Wieze boreholes

2087

2088 Zemst‐Hofstade (073E0397) 2089 The pattern of the Orchies and Mons‐en Pévèle section is comparable to the pattern of the 2090 Orchies‐Roubaix interval in the Merchtem log. The identification as Mons‐en Pévèle Fm is 2091 preferred over the Roubaix Mbr as the RES values are nearly double the ones in the 2092 Merchtem borehole, in which borehole the interval is considered transitional Roubaix to 2093 Mons‐en Pévèle (see Merchtem in the compendium) . In the Zemst‐Hofstade borehole the 2094 amount of sand layers, apparent from the RES log, are estimated to be about 50% of the 2095 total, which according the specified criterion (see text) is characteristic for the Mons‐en 2096 Pévèle Mbr.

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2097 The top clay unit consists either entirely of the Aalbeke Clay (see comparable signal in the 2098 Knokke and Mol‐SCK15 boreholes) or it might be composed of the Aalbeke clay overlain 2099 directly by the Merelbeke clay , an interpretation suggested by Johan Matthijs; in the latter 2100 case the Mont‐Panisel and Kwatrecht units wedged out or were eroded before the 2101 deposition of the Merelbeke Mbr, while in the former case, if only Aalbeke clay is present, 2102 the Mont‐Panisel and Kwatrecht units could have been eroded in a later were stage.

2103 Zemst‐Weerde (073E0359) 2104 The log pattern below the Merelbeke Mbr is very comparable with the pattern of the Mont‐ 2105 Panisel and Kwatrecht Mbrs in the Kerksken (086E0340) borehole.

2106 The stratigraphy of this borehole, including biostratigraphy and grain‐size analyses, has been 2107 elaborated in detail by Steurbaut et al. (2015). Below the Mont‐Panisel Fm occur a few 2108 meter of the Tielt Fm: from the log correlation by J. Matthijs , the Aalbeke Mbr is expected 2109 to occur below the Mont‐Panisel Mbr.

2110

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2111

2112 Referenties: 2113

2114 Ali, J., King, C., Hailwood, E.A., 1993. Magnetostratigraphic calibration of early Eocene 2115 depositional sequences in the southern North Sea Basin. In: Hailwood, E.A. & Kidd, R.B. 2116 (eds), High Resolution Stratigraphy. Geological Society Special Publication, N°70 : 99‐125.

2117 Bolle, I. & Jacobs, P., 1993. Lithostratigraphy of the Egem Member (Ypresian) South‐East of 2118 the Gent agglomeration (Belgium). Bull. Belg. Ver. Geol. 102 : 258‐260.

2119 Buffel, P.,Vandenberghe, N., Vackier, M., 2009. Toelichtingen bij de Geologische kaart van 2120 België, Vlaams Gewest Kaartblad 23 Mechelen Schaal 1:50 000. Vlaamse Overheid 2121 Departement Leefmilieu, Natuur en Energie, Ondergrond en Natuurlijke Rijkdommen, 2122 Brussel.

2123 Cornet, F.L., 1874. Compte‐rendu de l’excursion du 31 août aux environs de Ciply. Bull. Soc. 2124 Géol. France, (3), 2, 567‐577.

2125 Crepin, N.,Vandenberghe, N. & Thimus, J.‐F., 2004. A quantitative interpretation of a 2126 paleoseismite in the Eocene of Belgium. I.A.S. Regional Meeting, Oman. Abstracts.

2127 Databank Ondergrond Vlaanderen https://dov.vlaanderen.be

2128 De Ceukelaire, M. & Jacobs, P., 1998. Indeling van de Formatie van Kortrijk op basis van 2129 kwalitatieve interpretative van reistiviteitsmetingen. Natuurwetenschappelijk Tijdschrift, 2130 78, p 27‐51, 13 fig.,1 tab.

2131 De Coninck, J., 1975. Microfossiles à paroi organique de l’Yprésien du Bassin belge. Belg. 2132 Geol.Dienst, Professional Paper, 1975/12, 151p.

2133 De Coninck, J.,1991. Ypresian organic‐walled phytoplankton in the Belgian Basin and 2134 adjacent areas. Bull. Belg. Ver. Geol. 97 (1988): 287‐319.

2135 De Coninck, J. 1996. Phytoplankton à paroi organique et phases transgressives vers la 2136 transition Paleocene‐Eocene dans la partie méridionale du Bassin de la Mer du Nord. Bull. 2137 Belg. Ver. Geol. T 105 (3&4) : 139‐169.

2138 De Coninck, J., Geets, S. & Willems, W. 1983 ‐ The Mont‐Héribu Member: Base of the Ieper 2139 Formation in the Belgian Basin. Tertiary Res., 5 (2), 83‐104.

2140 de Heinzelin, J. & Glibert, M., 1957. Lexique Stratigraphique International. Vol. I. Europe, 2141 Fasc. 4a: France, Belgique, Pays‐Bas, Luxembourg. Fasc. 4a VII: Tertiaire. 217 p., 15 maps. 2142 Congrès Géologique International ‐ Commission de Stratigraphie, Mexico, 1956. Centre 2143 National de la Recherche Scientifique, Paris, VIIe, 1957.

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2144 de Lugt, I., 2007. Stratigraphical and structural setting of the Paleogene siliciclastics 2145 sediments in the Dutch part of the North Sea basin. Geologica Ultraiectina,N°270 112p.

2146 De Moor, G. and Geets, S., 1973. Sedimentologie en litostratigrafie van de eocene 2147 afzettingen in het zuidoostelijk gedeelte van de Gentse agglomeratie. 2148 Natuurwetenschappelijk tijdschrift, 55: 129‐192.

2149 De Moor,G. & Geets, S., 1975. Application de quelques méthodes sédimentologiques à 2150 l’étude des dépôts éocènes du Bassin flamand. In : Synthèse des bassins sédimentaires. 9 2151 ième Congrès International Sédimentologie 2 : 305‐ 312.

2152 De Moor, G. & Germis, A. 1971 ‐ Hydromorphologie du Bassin de la Molenbeek (Melle). 2153 Bull. Soc. belge Etud. Géogr., 40, 29‐68.

2154 d’Omalius d’Halloy, J.J. 1862 ‐ Abrégé de Géologie, 7e édit., 626 p.

2155 Dupuis ,C. , Brych, J., Laga, P. , Vandenberghe, N. , 1988. Sondage stratigraphique au Mont‐ 2156 Panisel: premiers resultants géologiques et géotechniques. Bull.Soc. belge de Géologie t 97 2157 /1 :35‐46)

2158 Fobe B., 1986. Petrografisch Onderzoek van de Coherente Gesteenten van het Eoceen in 2159 Laag‐ en Midden‐België. Doctoraatsproefschrift, R.U.Gent.

2160 Fobe, B., 1989a. Het Eoceen tussen Mol en Beringen. Belgian geological Survey Prof. Paper 2161 nr 239 9p 5 fig.

2162 Fobe, B., 1989b. Some recent borings in the Ypresian and Lower Lutetian of Northwestern 2163 Belgium. Belgian geological Survey Prof. Paper nr 240 7p 5 fig.

2164 Fobe, B., 1993. Ypresian lithostratigraphy in Northern Belgium. Bull. Belg. Ver. Geol. T 102 2165 (1‐2), 254‐257.

2166 Fobe, B.,1995. Lithostratigraphy of the Vlierzele Formation (Ypresian, NW Belgium). Bull. 2167 Soc.Belge. Géol. t 104 (1‐2) : 133‐149.

2168 Fobe, B., 1997. Review of the lithostratigraphy of the Middle Eocene in Northern Belgium. 2169 Contr. Tert. Quatern. Geol. 34 (3‐4): 53‐67.

2170 Fobe, B., 1997b. Lithostratigrafische betekenis van een zandlaag tussen de Klei van 2171 Merelbeke en de Klei van Pittem (Eoceen‐België). Natuurwetenschappelijk Tijdschrift, 76 : 2172 94‐99.

2173 Geets, S. 1979 ‐ De overgang Ieperiaan‐Paniseliaan in de streek van Roeselare en Tielt. 2174 Natuurwet. Tijdschr., 60, 41‐69.

2175 Geets, S., 1988. Ieper Groep. In: Maréchal, R. & Laga,P. (eds) Voorstel Lithostratigrafische 2176 indeling van het Paleogeen. Nationale Commissie Stratigrafie. Commissie Tertiair p 81‐113.

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2177 Geets, S. 1990 ‐ The evolution of the grain‐size distribution in the sediments of the Ieper 2178 Formation in Belgium. Bull. Belg. Ver. Geol., 97 (1988), 3‐4, 451‐456.

2179 Geets, S., 1993. The “abnormal” heavy‐mineral distribution at the base of the Kortrijk 2180 Formation (Ieper Group). Bull. Soc. Belg. Geol., 102 (1‐2), pp.165‐173. 2181 Geets, S. & De Geyter, 1990. Grain‐size and heavy minerals of the Tertiary strata in the 2182 Knokke well. In: Laga P. & Vandenberghe, N., The Knokke well (11E/138) with a description 2183 of the Den Haan (22W/276) and Oostduinkerke (35E/142) wells. Mem. Expl. Cartes Géol. 2184 et Min. Belgique, N°29 :19‐26.

2185 Geets, S., Maréchal, R., Laga, P., 2000. Lithostratigrafie van het Paleogeen (Nl/Fr). 2186 Stratigrafische Commissie Tertiair. 2187 2188 Geets,S., 2001. Sedimentpetrologisch onderzoek in de boringen van Oedelem en Gooik‐ 2189 Kesterberg. Geological Survey of Belgium, professional Ppaer 2001/1 N°293 90p. 2190 2191 Geological Service Company, 2003.Geologische beschrijving en interpretatie van de 2192 kernboringen te Kerksken en Kattem (in opdracht Ministerie Vlaamse Gemeenschap, 2193 ANRE) 32p. 2194 2195 Gosselet, J. 1874 ‐ L’étage éocène inférieur dans le nord de la France et en Belgique. Bull. 2196 Soc. Géol. France, 3e s., 2, 598‐617.

2197 Gulinck M., 1965. Aperçu général sur les dépóts éocènes de la Belgique. Bull. Soc. Géol. 2198 France, 7ième série, t.VB, p.222‐ 227.

2199 Gulinck, M. 1967 ‐ Profils de l’Yprésien dans quelques sondages profonds de la Belgique. 2200 Bull. Soc. belge Géol., 76, 109‐113.

2201 Gulinck, M., 1969. Le Sondage de Kallo (au Nord‐Ouest d’Anvers). Mém. Expl. Cartes Géol. 2202 et Min. de la Belgique, 11, 42p. 2203 Gulinck M. and Hacquaert A., 1954. L'Eocène. In: P. Fourmarier (ed). Prodrome d'une 2204 deseription géologique de la Belgique. Soc. Géol. Belg., Liège 1954, chp.XIV, p.451‐493.

2205 Gulinck, M. & Laga, P., 1975. Boring SCK te Mol 31W 237. Archives Belgian Geological 2206 Survey, Brussels.

2207 Hacquaert, A., 1939. De overgang van Ieperiaan to Lutetiaan te Aalter (Kanaal). 2208 Natuurwetenschappelijk Tijdschrift p 323‐325. Gent.

2209 Houthuys, R., 2014. A reinterpretaion of the neogene emersion of central Belgium based 2210 on the sedimentary environment of the Diest Formation and the origin of the drainage 2211 pattern. Geologica Belgica 17/3‐4 : 211‐235.

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2212 Houthuys, R. & Gullentops, F., 1988. The Vlierzele sands (Eocene, Belgium) : a tidal ridge 2213 system. In : P.L. De Boer et al. (eds) Tide‐Influenced Sedimentary Environmenst and Facies 2214 : 139‐152. D. Reidel Publishing Company.

2215 Jacobs, P., 2015. 4.Het midden‐Eoceen en laat‐Eoceen, in : Borremans(ed.), Geologie van 2216 Vlaanderen, Academia Press, p. 136‐146.

2217 Jacobs, P., De Ceukelaire, M., De Breuck, W., De Moor, G., 1996a. Toelichtingen bij de 2218 Geologische kaart van België Vlaams Gewest Kaartblad 22 Gent,1:50 000. Belgische 2219 Geologische Dienst & Min. Vlaamse gemeenschap, Natuurlijke Rijkdommen en Energie, 2220 Brussel.

2221 Jacobs, P., De Ceukelaire, M., De Breuck, W., De Moor, G., 1996b. Toelichtingen bij de 2222 Geologische kaart van België Vlaams Gewest Kaartblad 21 Tielt,1:50 000. Belgische 2223 Geologische Dienst & Min. Vlaamse gemeenschap, Natuurlijke Rijkdommen en Energie, 2224 Brussel.

2225 Kaasschieter, J.P.M. 1961 ‐ Foraminifera of the Eocene of Belgium. Verh. Kon. Belg. Inst. 2226 Natuurwet., 147, 271 p.

2227 King, C., 1990. Eocene stratigraphy of the Knokke borehole(Belgium). In: Laga P. & 2228 Vandenberghe, N., The Knokke well (11E/138) with a description of the Den Haan 2229 (22W/276) and Oostduinkerke (35E/142) wells. Mem. Expl. Cartes Géol. et Min. Belgique, 2230 N°29 :67‐102.

2231 King, C., 1991. Stratigraphy of the Ieper Formation and argile de Flandres (Early Eocene) in 2232 western Belgium and Northern France. Bull. Belg. Ver. Geol. 97 (1988): 349‐372.

2233 Laga P. & Vandenberghe, N., 1990. The Knokke well (11E/138) with a description of the 2234 Den Haan (22W/276) and Oostduinkerke (35E/142) wells. Mem. Expl. Cartes Géol. et Min. 2235 Belgique, N°29

2236 Laga,P., Geets, S., Moorkens, T., Nolf,D., 1980. A lithostratigraphic scheme for the NW‐ 2237 European Tertiary Basin. In : Kockel (ed), Subgroup Lithostratigraphy and Maps (IGCP124), 2238 Newsletter Stratigraphy, 8(3), 236‐237.

2239 Laga,P., Louwye, S., Geets, S., 2001. Paleogene and Neogene lithostratigraphic units 2240 (Belgium). Geologica Belgica 4/1‐2 : 135‐152.

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2242 Maréchal, R., 1993. A new lithostratigraphic scale for the Paleogene of Belgium. Bulletin 2243 Belgische Vereniging voor Geologie, 102 (1‐2), 215‐229.

2244 Maréchal, R. & Laga,P. (eds) 1988. Voorstel Lithostratigrafische indeling van het 2245 Paleogeen. Nationale Commissie Stratigrafie. Commissie Tertiair

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2246 Mohammad, W. (ed.), (2009). The NIRAS‐ONDRAF Kallo 1&2 boreholes: the Ypresian cored 2247 section 254‐410m depth. KULeuven Report 120p.

2248 Nolf, D. & Steurbaut, E. 1990 ‐ Stratigraphie de l’Eocène en Flandre occidentale et dans les 2249 régions limitrophes. Bull. Inform. Géol. Bassin de Paris, 27, 3, 9‐36.

2250 Ortlieb, J. & Chelloneix, E. 1870 ‐ Etude géologique des collines tertiaires du Département 2251 du Nord comparées avec celles de la Belgique. Quarré & Castiaux, Lille, 228 p.

2252 Roche, E. (1988). Sporopollinic biostratigraphy and Ypresian paleoenvironment. Bull. Soc. 2253 Belg. Géol. 97 3/4 (1988 : 373‐383 publ. 1990).

2254 Rutot, A., 1890. Constitution géologique des collines d’ Hekelgem et d’Esschene entre 2255 Assche et Alost. Bull. Soc. Belge. Géol. 4 : 33‐58.

2256 Smith,T & Smith,R, 2003. Terrestrial mammals as biostratigraphic indicators in Upper 2257 Paleocene‐Lower Eocene marine deposits of the southern North Sea 2258 Basin.Geological Society of America, Special Papers,369:513‐520.

2259 Smith,T & Smith,R, 2013. A land micro‐mammal fauna from the Early Eocene marine Egem 2260 deposits (NP12, Belgium) and the first occurrence of the peradectid marsupial 2261 Armintodelphys outside North‐America. Geologica Belgica, 16 (4): 302‐310.

2262 Steurbaut, E., 1987. New Early and Middle Eocene calcareous nannoplankton events and 2263 correlations in the middle to high latitudes of the northern hemisphere. Newsl. Strat. 18 2264 (2), 99‐115.

2265 Steurbaut, E., 1988. The Ypresian in the Belgian Basin. Bull. Belg. Ver. Geol. T 96 fasc 4 2266 (1987): 339‐351.

2267 Steurbaut, E., 1991. Ypresian calcareous nannoplankton biostratigraphy and 2268 paleogeography of the Belgian Basin. Bull. Belg. Ver. Geol. 97 (1988): 251‐286.

2269 Steurbaut, E., 1998. High –resolution holostratigraphy of Middle Paleocene to Early Eocene 2270 strata in Belgium and adjacent areas. Palaeontographica Abt.A, Bd 247, Lfg.5‐6: 91‐156.

2271 Steurbaut, E., 2006. Ypresian. Geologica Belgica 9/1 : 73‐93.

2272 Steurbaut, E., 2011. New calcareous nannofossil taxa from the Ypresian (Early Eocene) of 2273 the North Sea Basin and the Turan Platform in West Kazakhstan. Bulletin de l’Institut royal 2274 des Sciences naturelles de Belgique, Sciences de la Terre, 81: 247‐277,2 pls, 26 figs.

2275 Steurbaut, E., 2015. 3.Het vroeg‐Eoceen, in : Borremans(ed.), Geologie van Vlaanderen, 2276 Academia Press, p. 125‐135.

2277 Steurbaut E. & Nolf, D., 1986. Revision of Ypresian stratigraphy of Belgium and 2278 northwestern France. Meded. Werkgr. Tert. Kwart. Geol. 23, 4: 115‐172.

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2279 Steurbaut E. & Nolf, D., 1991 (1988). Ypresian Teleost otoliths from Belgium and 2280 northwestern France. Bull. Soc.belge de Géol. 97 3/4 : 321‐347.

2281 Steurbaut,E. & King, C., 1994. Integrated stratigraphy of the Mont‐Panisel borehole section 2282 (151E/340), Ypresian (Early Eocene) of the Mons basin (SW Belgium). Bull.Soc. Belg Geol., 2283 102,1‐2,175_202.

2284 Steurbaut,E., Dupuis, C.,Jacobs, P., 2003. Field guide to the Ypresian stratotype. 2285 Symposium on the Paleogene 25‐30 August 2003, Leuven, Belgium.

2286 Steurbaut,E.,King,C., Matthijs, J., Noiret, C., Yans, J., Van Simaeys, S., 2015. The Zemst 2287 borehole, first record of the EECO in the North Sea Basin and Implications for the Belgian 2288 Ypresian‐Lutetian stratigraphy. Geologica Belgica vol 18, n°2‐4 :147‐159

2289 Stratigrafisch register refers to :

2290 CONSEIL GEOLOGIQUE, 1929. Légende générale de la carte géologique détaillée de la 2291 Belgique. Annales des Mines de Belgique, 30: 39‐80.

2292 AARDKUNDIGE RAAD, 1932. Algemeen stratigrafisch register van de uitvoerige 2293 aardkundige kaart van België. Imprimerie des Travaux publiques, Bruxelles, 46 p.

2294 Vandenberghe, N. & Gullentops, F., 2001. Toelichtingen bij de Geologische kaart van 2295 belgië. Vlaams Gewest, kaartblad 32 Leuven, 1: 50.000, 77p. Belgische Geologische Dienst 2296 & Min. Vlaamse gemeenschap, Natuurlijke Rijkdommen en Energie, Brussel

2297 Vandenberghe N., Laga P., Vandormael C. and Elewaut E., 1991. The geophysical log 2298 correlations in the leper Clay sections in Belgium. In: Dupuis C., De Coninck J. and 2299 Steurbaut E., 1991. The Ypresian stratotype. Bull. Soc. belge Géol., (1988) v.97, fasc.3‐4, 2300 p.437‐440, 8 plates.

2301 Vandenberghe, N., Laga, P., Steurbaut, E., Hardenbol, J. & Vail, P.R. (1998). Tertiary 2302 Sequence Stratigraphy at the Southern Border of the North Sea Basin in Belgium. In: (Eds): 2303 de Graciansky, P.C.,Hardenbol,J.,Jacquin, Th. & Vail, P.R., Mesozoic and Cenozoic Sequence 2304 Stratigraphy of European Basins. SEPM Special Publication, 60, 119‐154.

2305 Vandenberghe, N.,Van Simaeys, S.,Steurbaut, E., Jagt, J.W.M. & Felder, P.J., 2004. 2306 Stratigraphic architecture of the Upper Cretaceous and Cenozoic along the southern 2307 border of the North Sea Basin in Belgium. Netherlands Journal Geosciences/Geologie & 2308 Mijnbouw Vol 83, N°3 :155‐172.

2309 Vandenberghe N., Hilgen F.J., Speijer R.P., with collaboration of Ogg J.G., Gradstein F.M., 2310 Hammer O., Hollis C.J., Hooker J.J. (2012) The Paleogene Period. In: Gradstein F.M., Ogg 2311 J.G., Schmitz M.D. & Ogg G.M. (eds), The Geological Time Scale 2012. Vol 2, 855‐921.

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2312 Van Marcke, P. & Laenen, B., Wouters, L. (contr.),2005. The Ypresian Clays as potential 2313 host rock for radioactive waste disposal: an evaluation. NIROND TR 2005‐01 149p.

2314 Van Simaeys, S., 1999. Dinoflagellaten van de Ieperiaan‐Lutetiaan overgang in het Belgisch 2315 Bekken. Lic. Thesis,Vakgroep geologie en bodemkunde, Universiteit Gent, Belgium

2316 Walstra, J., Dusar, M. & De Ceukelaire, M., 2014. Geological Model of the Ypresian Clay. 2317 Report ONDRAF‐ NIRAS by GSB, Brussels, 77p.

2318 Welkenhuysen, K. & De Ceukelaire, M., 2009. Tertiair lithostratigrafische interpretatie op 2319 basis van geofysische boorgatmetingen van de boringen van meetnet 1 VMM‐afdeling 2320 Water uitgevoerd in 2005‐2006. Geological Survey of Belgium. Professional Paper2009/2 2321 N°306.

2322 Willems, A., 1995. Groeve‐opname te Egem (Ypresiaan). Sedimentologische en 2323 sequentiestratigrafische interpretative. Lic. Thesis., Geologie, KU Leuven, 92p.

2324 Willems, W., 1982. Microfossil assemblages, zonations and planktonic datum levels in the 2325 Ieper Formation (Ypresian s.s.,Early Eocene) in Belgium. BGD Professional Paper 1982/8, 2326 194: 1‐17.

2327 Willems, W. & Moorkens, T., 1991. The Ypresian stage in the Belgian Basin. Bull. Belg. Ver. 2328 Geol. 97 (1988): 231‐249.

2329 Wouters L. & Vandenberghe N., 1994. Geologie van de Kempen.Een synthese. NIRAS‐ 2330 ONDRAF, Brussel pp 208.

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