Foraminiferal Biostratigaphy and Sequence Stratigraphy of the Cenozoic Lower Magdalena Valley, Colombia
Ignacio Martinez and Martha Beltran
Statistical treatment (RASC program) of planktonic and benthonic foraminiferal populations and (cluster analysis) of benthonic forams were applied to 18 wells from the Lower Magdalena Valley in northern Colombia. A scaled optimum sequence containing a succession of 31 planktonic species (last occurrences) common to at least 6 wells was determined. Seven zones ranging in age from the latest Oligocene(?) to the Pliocene, with a resolution comparable to the duration of Cenozoic stages were found. A sequence stratigraphy scheme, based on the counting of benthonic and planktonic foraminiferal species and the GR signal, is proposed. A thick section of deep water deposits characterized by a NW prograding wedge and slope fan complexes in the Media Luna/1 and Ligia/1 well areas du ing the middle Early Miocene, was found. The prograding complex is dominated by agglutinated foraminifera, higher abundance of benthonic foraminfera and predominance of Gaudiyiana pyramidata, Gupyella pozonensis, Guttullina irregularis, Haplofragmoides campester, Hoeglundina elegans, Martinotiella petrosa, Plectofrondicularia yumuriana (Cluster C); Towards the top, the prograding complex is characterized by Alveovalvulllnella pozonensis, Ammonia beccari, Cassidulina punctuata, cibicidoides mantaensis, Epistominella vitrea (cluster A) suggesting shallow water conditions. Cluster B characterized by Uvigerina carapitana, Textularia excavata, nonion costipherus, Clavatorella bermudezi and bulimina pupoides is dominani along flooding surfaces during the late Early M ocene; whereas cluster A is dominant again during the Middle Miocene to Pliocene.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California