ABSTRACT

Many Gulf of Mexico geologists are aware of the paleocanyons that have been discovered around the margins of the Gulf of Mexico (GOM). Some of these are postulated to be related to a Paleogene drawdown of the GOM. Formation of at least ten of these paleocanyons has been biostratigraphically dated to ∼56 Ma, just prior to the Paleocene/Eocene Thermal Maximum (PETM). An additional nine of the paleocanyons probably formed at that time, but detailed biostratigraphic evidence is not currently available. The key to proving that these nineteen paleocanyons (and possibly more) are the result of the same event, is the detailed paleontology and palynology of the oldest fill sediments within the paleocanyons. As more evidence comes to light, it becomes clear that the PETM sediments are indeed the oldest fill of several of the paleocanyons. This presentation summarizes new evidence from paleocanyons in Mexico, the deepwater GOM, and Belize and how they fit into the GOM Drawdown Theory.

The Acatepec paleocanyon in the Hidalgo and Veracruz states of eastern Mexico is the best documented outcrop example of one of the pre-PETM paleocanyons and has been extensively mapped by two of the authors. The canyon has erosional edges and a dramatic mass transport complex (MTC) and slide blocks filling the basal section. The measured section outcrop has been sampled, studied with gamma ray, δ¹³C, and dated with zircons, palynology, and nannofossils. The oldest fill is of PETM age and the δ¹³C curve can be convincingly correlated to the deepwater Logan well (WR969) in the GOM 525 mi (845 km) away.

Two other paleocanyons (Yoakum and Shenandoah) also show erosion just prior to the PETM and are filled with PETM-age sediments: These three synchronously formed examples have been plotted on paleogeographic maps for the late Paleocene and early Eocene. It is difficult to explain this impressive erosion could happen at exactly the same time, in such widely spread locations and disparate environments, without a Gulf-wide draw-down event.

One would also expect canyon(s) to have been formed when the GOM refilled (probably catastrophically). Some canyons that may have formed during refill of the GOM have been postulated, including a newly-discovered erosional feature in Belize with the characteristics of a refill canyon (Red Bank Canyon) that drained westward towards the GOM. In addition, hardgrounds have been described in samples immediately underlying the PETM in numerous wells of the GOM. It is unclear how both the pre-PETM erosion and hardgrounds can occur without the drawdown in the GOM that created a partially filled basin below global sea-level.