The uppermost Cretaceous sedimentary sequence (Umir and Cimarrona Formations) is exposed in the Honda-Guaduas area (Middle Magdalena Valley, Colombia) and have supplied an abundant association of planktonic foraminifera which shows strong affinities with Tethyan paleofaunas. In these associations, the biozones of Gansserina gansseri and Abathomphalus mayaroensis have been identified. In agreement with biostratigraphic zonations of the western Tethys realm (Gulf Coast, Trinidad and Caribbean Sea), these zones could represent Middle and Late Maastrichtian. The time-space relationships among the facies of the upper part of the Umir, Cimarrona and the lower portion of the Seca formations indicate that their lithostratigraphic limits are diachronous. In other words, the vertical profile of these facies is the result of the lateral migration of contiguous sedimentary environments. In this indirect way, an upper Maastrichtian age is suggested for the lower portion of the Seca Formation.