Ichnology of the Cenomanian Buda Formation, USA: assessing environmental and taphonomic controls on carbonate trace-fossil assemblages

The Buda Formation is a coccolith-rich carbonate unit deposited in lagoonal waters of the Comanche Shelf during the early Cenomanian. This unit constitutes a long-lived hydrocarbon reservoir and an important regional marker in the Texas Gulf Coast Basin. Several sedimentological and stratigraphic studies have been carried out on this formation but debates regarding its depositional conditions persist. The Buda Formation is characterized by a high degree of bioturbation intensity; however, comprehensive ichnological analyses focused on elucidating its depositional conditions have not been performed yet. Here, we report the Buda Formation ichnofauna comprising twenty ichnotaxa and widely dominated by Thalassinoides isp. and Chondrites isp. The ichnological analysis allowed us to recognize nine ichnofabrics, which reflect changing palaeoecological and palaeoenvironmental conditions during the deposition of this unit. In general, the different ichnofabric expressions throughout this formation reflect fluctuating levels of exchange of waters between the Buda lagoon and the open sea, based on the inherent changes in physicochemical parameters, such as oxygenation levels and salinity. In addition, the concept of taphonomic pathways is underscored for accuracy in palaeoecological reconstructions, as well as the need for integrating diagenetic processes, particularly when applying this concept to carbonate rocks.