| Summary: | Analyses carried out on benthonic foraminiferal assemblages of the Puentedey-Hornillalatorre formations (Norcastilian Platform) are part of a multidisciplinary research with the main subject of understanding the palaeoceanographic events that took place at the end of the Cretaceous within the Basque-Cantabrian Basin. The study sections have been dated from the late Cenomanian to the late Turonian. A total of 98 benthonic species have been identified, which clearly correspond to shallow marine water microfauna. In this context, some of the aspects about the palaeoenvironmental variations detected in Puentedey-Santelices area are crucially provided by changes of the foraminiferal assemblages (Units 1 to 3), specific diversity changes of the microfauna, the rate between different type of tests of benthonic, percentage of keeled, incipiently keeled and globular planktonic foraminifera and oceanicity index. Thus, the dominant foraminiferal assemblages, the great percentage of agglutinated tests, and the lower values of the oceanicity index suggest a cool, acid, and bad-oxygenated internal platform (<100 m) waters palaeoenvironment (Units 1-2). The inoceramid bivalves I. (Mytiloides), with thinner shells and grey colour are well-developed. The Unit 3, marked by oxygenated internal platform waters palaeoenvironment, where I. (Mytiloides) are replaced by I (I) lamarcki, with thicker shells and caramel colour
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