" Tubotomaculum " et nodules de manganèse - Comparaison d'objets énigmatiques fossiles avec des concrétions marines et lacustres

Tubotomaculum are cylinder-shaped bodies a few centimetres long which can be found in pretty large quantities in the "numidian clays" of the upper Cretacean to Oligocene Mediterranean boundary. We present the observations conducted with electron microscopy. Geochemical and mineralogical analyses have been carried out. The manganese and iron contents are similar to the polymetallic nodules covering the bottom of today's oceans. We continued the comparison with the transition element contents (copper, nickel, cobalt). The Tubotomaculums' core is composed of rhodocrosite and siderite, while their cortex is made of non crystallised iron and manganese. The deposition localization is discussed through the analysis of the surrounding sediments. Different hypothesis on the nature and origin of Tubotomaculum are discussed: epigenesis of digging animal lairs, mineralised faecal pellets, rolled mud fragments, specific iron and manganese oxide concretion figures.