Nous mettons en evidence une paragenese silico-alumineuse (halloysite, gibbsite, alumohydrocalcite) dans des couches tertiaires alterees impliquees dans des structures cryptokarstiques quaternaires (Normandie, France). Cette paragenese s'est developpee aux depens de gels precipites a proximite de niveaux carbonates ayant participe a la neutralisation de solutions acides chargees en Si et Al. Les gels occupent des fissures millimetriques a centimetriques. Les neogeneses sont un stade precoce d'une evolution pouvant aboutir a une cristallisation complete des gels en halloysite, gibbsite...
We describe a silico-aluminous paragenesis (halloysite, gibbsite, alumohydrocalcite) in weathered Tertiary beds trapped within Quaternary cryptokarstic structures (Normandy, France). This paragenesis was developed from gels neoformed in the immediate vicinity of carbonate levels that acted as neutralizers for (Si, Al)-rich acid solutions. The gels occur in millimetric to centimetric fissures. We refer to these neogeneses as to an early stage of the evolution that may lead to a complete transformation of gels into crystallized halloysite, gibbsite...