Mississippian-Lower Pennsylvanian foraminifers from the Sierra Nacimiento and San Pedro Mountains, North-Central New Mexico, USA

• This study presents foraminifers from the Mississippian Arroyo Peñasco Formation and basal Log Springs Formation, and the lower Pennsylvanian Osha Canyon Formation of north-central New Mexico, USA. • Foraminifers of the Arroyo Peñasco Formation (Espiritu Santo Member) indicate a Tournaisian age (MFZ 1–8). • Reworked limestone clasts of the basal Log Springs Formation contain foraminifers of late early Viséan age. • The Osha Canyon Formation contains a small foraminiferal assemblage indicating Morrowan age. In the Sierra Nacimiento-San Pedro Mountains-Jemez Mountains of north-central New Mexico (USA), the thin succession of Mississippian sediments is termed the Arroyo Peñasco Formation, overlain by the Log Springs Formation. The Arroyo Peñasco Formation is subdivided into Del Padre Member composed of siliciclastic sediments and the overlying Espiritu Santo Member composed of carbonate sediments. Foraminifers of the Espiritu Santo Member at Lion Spring in the northern San Pedro Mountains indicate a Tournaisian age. The lower Tournaisian (= Hastarian = biozones MFZ1-4 of Poty et al., 2006 [Geological Magazine 143, 829-857]) is locally characterized by Septaglomospiranella ex gr. primaeva, Septabrunsiina minuta and Tournayella sp. The upper Tournaisian (= Ivorian = biozones MFZ5-9 of Poty et al., 2006 ) is characterized by Spinoendothya, Inflatoendothyra and Tuberendothyra. In the Sierra Nacimiento-San Pedro Mountains-Jemez Mountains, the sediments of the Arroyo Peñasco Group are unconformably overlain by nonmarine redbeds of the Log Springs Formation (Serpukhovian/upper Chesterian). Some of the carbonate clasts of the basal conglomerate of the Log Springs Formation at Lion Spring contain late early Viséan (biozone MFZ11B of Poty et al., 2006 ) foraminifers and algae, including Koninckopora and Paraarchaediscus. These carbonate clasts are reworked from the underlying Arroyo Peñasco Formation (Espiritu Santo Member). In north-central New Mexico, a transgression during the Early Pennsylvanian (Morrowan) caused deposition of the shallow marine sediments of the Osha Canyon Formation. The Morrowan age of the Osha Canyon Formation is based on Nigrispiroides nov. gen., Iriclinella, Globivalvulina, and Millerella.