Depositional history of the Concepcion de Oro Formation, northeastern Zacatecas, Mexico: Tectonosedimentary implications for the development of the foreland system in northeastern Mexico during the Late Cretaceous
A sedimentological and ichnological analysis carried out in the members Tierras Blancas and Rancho Viejo of the Concepción del Oro Formation (Turonian-Early Campanian), in the region of Concepción del Oro, Zacatecas, allows documenting the sedimentological characteristics, the sedimentary evolution, and its relationship with the orogenic belt. The Tierras Blancas Member (Turonian- Early Coniacian) is made up of successions of deltaic coastlines (i.e., delta fronts influenced/dominated by rivers or by waves/storms), with ichnofaunistic assemblages corresponding to the Skolithos and Cruziana ichnofacies, and a variable Bioturbation Index (BI: 0 – 4), represented by traces of organisms that feed on material in suspension and substrate, with small to moderate traces, controlled by the conditions of salinity, oxygenation, nutrient supply and energy from the sedimentary environment. The Rancho Viejo Member (Late Coniacian-Early Campanian) consists of mixed-type underwater channels, depositional-type submarine channel, channel overflow or abandoned canal, lobe-channel transition, depositional lobe, and mass transport complex (MTC) deposits of type II, characterized by ichnogeneous of the Cruziana icnofacies in its distal variation, Zoophycus and Nereites, with a BI variable between absent and abundant (IB 0 – 5), characterized by traces of organisms of moderate to large sizes that feed on suspended material, which combine the activities of feeding and dwelling.
The average paleocurrent vectors in structures related to wave processes suggest a deltaic coastline with a strike almost SE 20°-NW 20°, while the unidirectional structures associated with sediment transport indicate that the deltaic system progradation was preferably toward the NE20°, perpendicular to the orogenic belt. The orientation documented in flute and tool marks structures in the deep systems (Rancho Viejo Member) determine a preferential strike toward the SE45° and SW30°, indicating that the transport of the sediments was perpendicular and axial to the orogenic belt.