7212- Geological notice Saint Laurent
A. Movable formations due to periglacial solifluxion. These silts are of very complex formation in terms of their composition: on the one hand they come from the alteration of the underlying rock, but also a part derives from a loessic origin; at the base there is a "head". These silts cover the terrace of the Bas Normannien.
A,. Furniture formations, of older age but still poorly defined (pliocene or quaternary), were distinguished from the previous ones. But this is also a silty flow.
a1b. Limons of the trays. The extreme abundance of precipitation and the low thickness of deposits has generally left only lehms. The distinction between these lehms and the products of the decomposition of the underlying rock is sometimes difficult.
an. Norman. The Norman Bas (or Normannian II) exists in lsigny, Grandcamp and Mesnil-Vigot (not figured: southern region of the leaf whose contours have not been modified compared to the previous edition) where it forms a terrace of average altitude of 7 m with sand and gravel and pebbles. The presence of an erratic block, brought by the floating ice, was reported there.
The Haut Normannien (or Normannien I) is formed between Criqueville and Grandcamp, at an average altitude of 20 m, by a sea terrace,
a1a Old alluvions. The relative permanent isostatic mobility of the Cotentin region explains the relative abundance of quaternary alluvian formations of fluvial origin.
po. Pliocene. Plyocene transgression begins with a poudingue on which rest sands partly reworked by the winds: they are coastal deposits. These fine sands, without fossils, occupy fairly large areas on the outskirts of the Gulf of Cotentin. A. Bigot assimilated them to the Sables de Saint-Vigor (near Bayeux).
p1 Green clays at Nassa prismatica var. limata, 5 to 6 m thick, surface in Bosq-d'Aubigny (municipality of Marchésieux).
R. Redonian. Calcareous sands (Gourbesville) from the on-site rearrangement of the underlying Eocene, as evidenced by the ravine; at the base, there is a conglomerate with pebbles of Paleozoic and Mesozoic rocks. In addition to the mixture of the faunas of Eocene and more recent Foraminifers, the presence of rolled bones of Dinotherium and of Halitherium as well as was reported.
A. Bigot (2nd ed.) considered that the ferrous conglomerate of Saint-Georges-de-Bohon must be a Redonian facies. According to the macrofauna, it is probably Pliocene, More likely the coarse and quartz facies of Saint-Georges-de-Bohon should be considered to be contemporary with the Pliocene marls of Bosq-d'Aubigny.
m. Faluns Helvetian. As for Saint-Georges-d'Aubigny, these formations could not be revised, the contours and ratings of the previous
c4 Cenomaniac. Some discontinuous shreds of 4 to 5 m of power are outcropping in the region of Orglandes and Fresville. They are hardened limestones, even silicified, containing Orbitolina concava, transgressive on the Lias or even the Paleozoic.
jII. Medium Bathonian. it is formed of coarse limestone, in thick banks of about thirty meters of power, where beds of blond flint are interstratified; no fossils have been reported. They are well exposed in the cliffs between Pointe de la Percée and Grandcamp.
jIII. Lower Bathonian. These are marls and gray clays (Marnes de Port-en-Bessin on the Caen leaf) whose power reaches 50 meters. Fossiliferous towards the base: there are two fossiliferous banks of marly and hard limestone, containing oppelia aspidoides, Morphoceras pseudo anceps, Belemnopsis bessinus, Good outcrops are formed by the cliffs, from the Pointe de la Percée towards the East.
jIV Bajocien. We find from the top:
‐ the white Oolite in Spongiaires, well visible in the cliffs between Port-en-Besin and Sainte -Honorine -des- Perthes; the power of this seat is slightly less than 15 meters: they are marly limestones with nodules, rich in Calcisponges (Cupulospongia, Amorphospongia),
‐ the ferrous Oolith, low-power horizon, usually less than 1 meter. At the top is a level of transition with the White Oolith in Spongiaires, where a mixture of ferrous ooliths and white ooliths occurs. This level is rich in Ammonites: Cadomoceras cadmense, Morphoceras defrancei, StriJ~ceras truelli, Polyplectites gracilis. Below, in a yellow-gray marno-limestone, with relatively calibrated ferrous ooliths, we find Parkinsonia parkinsoni, Lytoceras eudesianum, Calliphylloceras heterophylloides. Under the previous levels of the area at Parkinsonia, the ooliths are no longer calibrated at all and the main types of Ammonites are: Garantiana garantiana, Cadomites deslongchampsi, Spiroceras bifurcatum. The base of the ferrous Oolith is represented by the Bayeux Conglomerate with ferruginous concretions of variable dimensions. These nodules have as their nucleus either a fossil or a fragment of limestone in the substrate. This level rests on a hardened, perforated and ravined surface.
‐ Under the Green layer, as the level of the previous conglomerate is sometimes designated, there are blue gray limestones, with flint and chaile banks with Cancellophycus. These limestones are frequently decalcified and transformed into a grayish clay where some fossils and flints remain; it is from this facies that the local terminology of malière given to the whole level derives. There is Otoites sauzei.
Some more distant witness flaps of White Oolith and Ferruginous Oolith meet on the plateau of Sainte-Mère-Église above the Toarcien (Boutteville, Sainte-Marie-du-Mont). In La Galie (Sainte-Marie-du-Mont), the malière the layers without fossils and blond flint that accompany the white Oolith and the ferrous Oolith have been reported.
I2. Synemurian. The upper Sinémurian consists of numerous and thin banks of marly limestone, dark gray, separated by thin clay layers. The fossils found there are: Oxynoticeras oxynotum and Liogryphoea obliqua. This floor is widely represented in the Bessin and north of the Carentan basin, especially on the Sainte-Mère-Église plateau where its alteration has given a soil particularly favorable to grasses of reputed quality.
I1 Hettangian. This floor has three levels: at the top, hard limestone, limestone in Cardinies, sometimes siliceous, dotted with ooliths. In Osmanville, near Isigny, only this Hettangian level is present. The cut of the Hettangian ends with a large bank of limestone with many Cardinies. The hard limestones of the Hettangian were exploited in Valogne (Valogne stone) and Yvetot (Yvetot marble).
Under the limestone, we see marls with Mytilus minutus (uncharacteristic fossil) and sea urchins (Diademopsis serialis in the state of debris).
In surveying, the lower Hettangian is known in the Valogne region, it is formed of sands and dolomitic limestones with plant footprints.
Marls retain an important water table and an artesian nappe exists at the base of the Hettangian.
t. Upper Triass - infralias. The conglomerate formations with rolled pebbles of Paleozoic or Precambrian rocks are widely distributed around the Carentan Basin and continue towards the Southeast. These layers are based on red layers once brought back to the Pem-ùen, today to the upper Keuper. A more complete cartographic correction would have been necessary, but could not be carried out; consequently, retaining the notations and contours of the previous edition, the notation t represents the Keuper and pro parte the Rhetian.
rt Keuper superior. For the reasons mentioned above, although it could not be represented, it will be considered that this notation corresponds to the superior Keuper, due to paleontological data, including a microflora of Gymnosperms and the presence of Semionotus.
H3-rII,,. Autunian ‐ Superior Stephanien. Lower Normandy Houiller (once exploited by the first mining company established in France) was deposited in a tectonic ditch in formation whose sinking was more or less fast depending on the points (characters highlighting the difference with the slow and regular isostatic subsidence of the bases and platforms) and where the evolution of the various elongated cuvettes varied from one to the other. At the beginning of this sedimentary cycle, most likely linked to the reaction of an older accident, active volcanism intervened, whose effusions filled the depressions.