The Cenomanian–Turonian (ca. 94 Ma) interval of the Western Interior Seaway (WIS) of North America hosts a critical record of changing marine shelf environments during greenhouse conditions. In this paper, we compile a detailed study of lithofacies, calcareous nannofossil biostratigraphy and elemental geochemistry from outcrops and cores of mid-Cenomanian to lower Turonian strata in Kansas, eastern Nebraska, and western Iowa, along the understudied eastern margin of the WIS. The Graneros Shale was constrained as a generally non-calcareous heterolithic unit deposited in vigorous bottom waters. We suggest that the contact between the Graneros Shale and overlying Greenhorn Limestone can be readily identified with a shift to more calcareous lithofacies, increase in Ca/Al and increase in calcareous nannofossil recovery. The uppermost unit of the Greenhorn, the Bridge Creek Limestone, was noted by widespread chalk deposition. Our combined use of lithofacies, biostratigraphy and elemental chemostratigraphy provides better constraint on these units on the eastern margin of the WIS, especially for units in which contacts are currently uncertain due to their gradational nature. Our results provide a more detailed assessment of depositional environments along the eastern margin of the WIS and improved comparison to the western margin. We show that, during Graneros time, there was substantial detrital sediment input from the North American Craton to the east. The transition towards pelagic carbonate sedimentation, especially in northeastern Nebraska, and a concomitant decline in detrital sediment, may have resulted from rising eustatic sea level and the transgressive landward retreat of detrital facies tracts, unconstrained changes in shelf currents or physiography and/or changes in climate that decreased detrital sediment delivery during the late Cenomanian to early Turonian. We also show that the critical Oceanic Anoxic Event 2 (OAE2) was captured in our studied sections. Along the eastern margin of the seaway, OAE2 corresponds to overall dry climate conditions, widespread chalk deposition and possible bottom water dysoxia. Such records have been lacking from nearshore shelf settings, especially in the eastern margin of the WIS, and the discovery opens future research that can better constrain the event in neritic environments.