Abstract

The Paleogene Chicontepec Formation of the Tampico-Misantla Basin (TMB) in eastern Mexico contains numerous forms of bitumen, such as clasts within debrites, fault and fracture fillings, dikes, mounds, and depositional beds. A sampling program was conducted within the basin to investigate the sequence of migration events using the geological setting and geochemical characteristics of the bitumen. We analyzed a selection of these bitumens from 19 locations within the basin in order to reconstruct the migration history during and after the Paleogene and to identify the active source rocks. Other workers have described three phases of hydrocarbon migration after the lowermost Eocene based on one outcrop in the basin, but we conclude there may be more events. There are four main pre-Paleogene source rocks in the basin. The main source is thought to be the Jurassic (Tithonian and Kimmeridgian) Pimienta and Taman formations, which basin modeling using one nearby well indicates only started to expel oil at ∼80 Ma and stayed in early maturity (0.5 to 0.7 %Ro) until 48 Ma. Our samples from this study were all obtained to the west of and shallower than the modeled well. We interpret that the main source is from the Pimienta and Taman formations, but at least three samples indicate that a deeper source (probably the Callovian/Oxfordian Santiago Formation) was mature and actively migrating at 56 Ma. The most anomalous sample from a large NE–trending fracture plane is highly degraded but may indicate that the source is an even older (possibly the Liassic Huayacocotla Formation) algal limestone, which was deposited in a hypersaline, non-lacustrine, anoxic marine environment.