Biostratigraphical and paleoenvironmental changes from the Late Cenomanian to Coniacian are examined mostly based on the planktonic foraminiferal assemblage and a study of microfacies, with emphasis on Oceanic Anoxic Event 2 (OAE2). The OAE2 documented at the Cenomanian–Turonian boundary interval was analyzed, comparing the foraminiferal response from a deep-water deposit and a shallow-water succession. This was evaluated from two sections located in north–central Mexico. The Tlacolula Section located in the Tampico–Misantla Basin and the Sierra de Álvarez Section situated at the western part of the Valles-San Luis Potosí Platform. In the Tlacolula Section, the Rotalipora cushmani Total Range Zone (Dicarinella algeriana Interval Subzone) is recognized based on a scarce association of rotaliporids, dicarinellids, and whiteinellids of late Cenomanian age. Overlying it, the Whiteinella archaeocretacea Interval Zone is preserved as a laminated black shale of latest Cenomanian–earliest Turonian age and is characterized by a foraminiferal association composed of a low planktonic species diversity tolerant of high stress factors such as low oxygen and increased nutrient availability. The presence of filaments and radiolarians is common in this interval, which is known as OAE2. In the Sierra de Alvarez Section in the western part of the Valle–San Luis Potosí Platform (VSLPP), the Whiteinella archaeocretacea Zone is recorded in the Soyatal Formation which consists of a succession of gray limestone laminated with intercalations of thin to thick bedded black marlstone and calcareous shale. This zone represents the flooding of the platform, which was deposited over the El Abra limestone and characterized by the presence of a larger benthic foraminiferal association. Subsequently, a continuous deep-water deposit spanning from the late Cenomanian to late Coniacian interval in the Tlacolula locality was defined by a planktonic foraminiferal assemblage including the Helvetoglobotruncana helvetica, Marginotruncana sigali, and Dicarinella concavata Zones. However, in the shallower water Sierra de Alvarez section only the Helvetoglobotruncana helvetica and Dicarinella asymetrica zones of the late Turonian and early Santonian, respectively, were recognized.