V. the Cretaceous and Tertiary Formations of the Mons District
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J. CORNET, V. THE CRETACEOUS AND TERTIARY FORMATIONS OF THE MONS DISTRICT. By J. CORNET, Professor of Geology at tho School of Mines, Mons. THE PALlEOZOIC FLOOR. THE region which geologists call the "Bassin de Mons" corresponds approximately to the hydrographic basin of the little River Haine, which flows into the Escaut at Conde. The Palseozoic floor presents in this region a very peculiar form, which is reflected not only in the disposition of the Cretaceous and Tertiary beds, but also in the surface-topography of the country. Between the source of the Haine to the east, and the Escaut to the west, the sub-Cretaceous surface of the Coal Measures forms a long and deep valley running in an east and west direction, that is to say, almost in the direction of the Palceozoic synclinal basin of Namur. In this valley are accu mulated the Cretaceous and Eocene sediments which have, at the same time, a synclinaldisposition. The valley-bottom drops from a height of room. above sea-level to the east of Anderlues, to om. to the south of Haine-St.-Pierre; -loom. near St. Vaast ; -250m. to the south of Havre; ---315m. at Nimy; -319m. between ]emappes and Ghlin; -327m. at Hautrages; below -394m. at Pommerceul; --333m. at Harchies (Preau) : -320m. at Bernissart ;-224m. at Thivencelles and-I25m. at Onnaing, where the valley ends. Thus it rises at both ends. The pre-Cretaceous valley of Hainaut is certainly due, chiefly, to erosion; but it is difficult to explain it as a result of the action of running water. It presents some characters which recall a glacial valley, comparable with those of certain Alpine lakes. It is not possible to enlarge on this subject here. In order to give an idea of the relative importance of the depression of the valley, one may mention that at only three kilometres (less than two miles) from the point where the bottom descends to belOW-394m. (about I,300 feet) Palaeozoic rocks of the northern slope of the valley outcrop at the surface at a height of +63m. (about 200 feet). This corresponds to a slope of about 152 metres per kilometre (about I in 6.5). The Cretaceous rocks of the Mons Basin, which fill the pre-Cretaceous valley, overstep considerably southwards to the south of Mons and west of Dour. With reference to the Paris Basin and the main Anglo-Franco Belgian Basin, the Mons" Basin" is an annexe sometimes called the" Mons Gulf." It is connected with the main basin towards the Franco-Belgian frontier. It is evident that the existing limits of the Cretaceous, both to the north and to the south of Mons, are the result of denudation, and originally the Cretaceous. LA TROu,l.l.E. STRE.RIY\ I SECTION ACROSS THE ('BASSIN DE MONS') o-l ::z: FROM CEN LY (SSW) TO THE CAMP ttl DE CASTEAU (NNE) o ot:1 I"" - L. OvDL.£Y STflMP ~l-t,. J. CO,.,fV£,T - o o 8T LAZARE HILL ><: o "'l t:X1 ttl I"" £) c:: ~ SCALE HORIZONTAL 1 :+0,000 Z.on~ (APPRQX.tMAl E L'f Ii,,. .. , MU,.£,) z'one oJ Mi.cra.stel" co...·te!>h... d~na.l"luJn VE~TIC~L. I I\) : a O OO ~ CEo N 0 M"'N I~ N AND TURONIAN FIG. 5. 28 J. CORNET, beds, at least in the upper part, extended without a break north and sout h of the basin. The expression " Mons Gulf " is th ere fore somewhat incorrect. One may add that the knowl edge of the geology of the Mons district rests not only on surface observations, but also on a study of more than 1,000 borings and min e-shafts. The figure (Fig. 5, page 27) represents a section of the Cret aceous and Tertiary rocks of the Mons Basin , t aken through the t own of Mons and at right angles to the pre-Cretaceous valley. Pressure of space has necessit ated the diagram being printed in two halves. The position of the various un con formities and the overlap of successive beds are well shown. GENERAL TABLE OF THE TERTIARY AND CRETACEOUS STRATA OF THE MONS BASIN. TERTIARY-EOCENE. Paniselian. 2. Glauconitic sands , slightly or non-argillaceous, with thin bands of lustrous hard green grits or quartzites (with an opaline cement) containing Pinna margari tacea, Cardita planicosta, etc. 1. Glauconitic, clayey sands with thin beds of fossiliferous argillaceous sandstone . Locality .-Mont Panisel, near Mons, British Equivalent.- The Paniselian is considered by the majority of Belgian geologists as a stage intercalated between the Ypresian and Bruxellian. F or others, the Paniselian is only a west ern facies, formed under somewhat different condi tions, of the Bruxellian. The Bruxellian corresponds to the lowest beds, or zone of M aretia Omaliusi, of the Lutetian of the Paris Basin. In England, it has its equivalent in the Bracklesham Beds. Ypresian. 2. Fine-grained, glauconitic sand, slightly micaceous. Nummulites planulatus-elegans, Turritella hybrida, Turritella Solanderi, Xanthopsis Leachi, et c. 1. Dark blue-grey clay. Localities.-Mons, Cuesmes and Mont Panisel. British Equivalent.-The London clay. Landenian. II. Upper Landenian (continental facies). White sands with white sa nds tones (" gres mamelonnes" or "sarsens " ) and lenticular beds of gravel, clay and lignit e. Coryphodon eocenus, Pa chynolophus M aldani, Trionyx levalensis, Champsosaurus, Crocodilus, Lepi- THE GEOLOGY OF BELGIUM. 29 dosteus, Amia, Eriocaulon porosum; Arundo groenlandica, etc. Localities.-LevaJ, Grand-Reng and ]eumont. British Equivalent.-The Reading (freshwater) type of the Woolwich and Reading Beds. 1. Lower Landenian (marine facies). 6. Slightly glauconitic sand, greyish green. Gres de Grandglise with Cyprina scutellaria. 5. Glauconitic sand, dark green, with Turritella bello vacensis. 4. Glauconitic sand, with an opaline cement (Tuffeau d'Angre), Pholadomya Konincki. 3. Argillaceous sand, calcareous and very glauconitic, often pyritous. Cyprina M orrisi. 2. Very calcareous, glauconitic sand; sandy, glauconitic marl or a sandy, glauconitic limestone with foramini fera. 1. Argillaceous, glauconitic sand, slightly calcareous. Lucalities.-Mons, Cuesmes, Ciply, Mesvin, S1. Symphorien, Elouges, Angre, Grandglise. The beds I and 2 do not crop out at the surface. British equivalents.-The Thanet Sands; and the Marine Bottom-Bed of the Woolwich Series (=zone of Cyprina scutel laria.) Montian. II. Upper Montian (continental). Marls, clays, lacustrine limestones and lignites. Physa, Paludina, Bithinia, Ancylus, Sphcerium, Chara, etc. 1. Lower Montian (marine or estuarine). The famous "Calcaire grossier de Mons." A friable or coherent limestone with foraminifera and Litho thamnion. A very rich fauna with marine species, brackish-water species (Potamides, Cyrena, etc.), species of littoral pulmonate gasteropods (Alexia, M elampu«, Blauneria), fresh-water species (Limncea,Physa, etc.), and terrestial species (Cyclostoma, Scarabus, etc.) Localities.-There is now no good section. British equivalent.-None. CRETACEOUS. Danian. 2. Tuffeau de Ciply. Soft, yellowish limestone with grey flints. Campanile Briarti. Formerly regarded as a lateral equivalent of the Calcaire de Mons (Montian). I. Basal conglomerate, consisting of phosphatic nodules. 30 J. CORNET, and rernanie Maestrichtian and Senonian fossils (= Poudingue de la Malogne, pro parte). Locality.-The quarries of Ciply. British equivalent.-None. .Maestrichtian (sensu stricto). 2. Tuffeau de St. Symphorien. Soft whitish limestone with grey flints. Trigonosemus pectiniformis, Hemi pneustes striato-radiatus, Thecidea papillata abundant. I. Basal Conglomerate of phosphatic nodules (=Poudingue de la Malogne, pro parte). Locality.-The quarry of S1. Symphorien. British equivalent.-None. Senonian. IV. Assise de Spiennes, a Trigonosemus Palissyi. 2. Phosphatic chalk of Ciply, with flints towards the top and towards the base. Pachydiscus neubergicus, P. colligatus, Ostrea lunata, Trigonosemus elegans; Pecten pulchellus abundant. The Poudingue de Cuesmes occurs locally at the base. I. Chalk (" Craie grossiere") of Spiennes, with brown and black flints. Localities.-The quarries of Ciply, Spiennes, S1. Symphorien and Baudour. British equivalent.-The Trimingham Chalk (zone of Ostrea lunata.) III. Assise de Nouvelles, a Magas pumilus. 2. Nouvelles Chalk, with Magas pumilus. I. Obourg Chalk, often with black flints. At the base is a conglomerate with Belemnitella mucronaia and with rolled specimens of Actinocamax quadratus. Localities.-The quarries of Harmignies, Nouvelles, and Obourg. British equivalent.-The Norwich Chalk (zone of Belemnitella mucronata). II. Assise de Trivieres, a Actinocamax quadratus. Trivieres Chalk, without flint. Actinocamax quadratus and Inoceramus balticus. There is a conglomerate at the base. Localities.-The quarries of Obourg, Trivieres, St. Vaast, etc. British equivalent.-The Newhaven Chalk (zone of Actina camax quadratus). I. Assise de St. Vaast, a Inoceramus involutus. St. Vaast Chalk, with mottled flints and grains of glauconite towards the base. Inoceramus inoolutus. At the base are beds of remanie glauconite. Localities.-The quarries of St. Vaast, etc. British equivalent.-The Dover Chalk (zone of Micraster cor testudinarium [Micraster decipiensJ). THE GEOLOGY OF BELGIUM. 3I Turonian. II. Upper Turonian. 3. Glauconitic chalk of Maisieres with Ostrea semiplana, O. canaliculata, Neoptychites peramplus and Actino camax Strehlenensis (the Gris). 2. Marly chalk with flints (the Craie a comus of the north of France); Meuliere of Maisieres and St. Denis. Micraster Leskei (the Rabots). I. Chalky or glauconitic marls with siliceous concretions. Micraster Leskei (the Fortes-Toises). Localities.s-Ttxe quarries of Maisieres, St. Denis, etc. British equivalent.-The zone of Micraster Leskei and Holaster planus, including the Chalk Rock and usually placed in England at the base of the Upper Chalk. 1. Lower Turonian. 2. Whitish marls with Terebraiulina rigida (= Ter. lata?) (the upper Dieves). Localities.-Autreppe, Hautrage, etc. British equivalent.-The zone of Terebraiulina lata. I. Clayey blue or green marls with Inoceramus labiatus, Rhynchonella Cuvieri and Mammites nodosoides (the middle Dieves), Locality.-Autreppe. British Equivalent.-The zone of Rhynchonella Cuvieri and Inoceramus labiaius. Cenomanian. II. Upper Cenomanian. 2. Clayey blue or green marls with Actinocamax plenus (the lower Dieves).