Todilto Formation: A Jurassic Salina and Its Petroleum Potential in East-Central New Mexico: ABSTRACT

Abstract

Todilto Formation of northern New Mexico and southwestern Colorado was deposited during the Middle Jurassic (middle Callovian) by a landlocked, saline lake (salina) developed in the Entrada erg. Evaporative pumping drew marine water from the Curtis sea in eastern Utah, which percolated through porous Entrada dune sands into the salina basin. The Todilto salina deposited organic-rich limestone (source rock) within a porous eolian sandstone (reservoir rock). In the San Juan basin, organic-rich Todilto limestones are a primary source of Entrada oil. There, the Todilto Limestone is generally overlain by a thick, impermeable gypsum sequence that allows Todilto hydrocarbons to migrate only into the underlying Entrada. In east-central New Mexico, the Todilto limestones pinch out into the Entrada and are not overlain by gypsum. Therefore, Todilto hydrocarbons should migrate either into the main Entrada body below the Todilto or into the Exeter member of the Entrada above. The Todilto/Entrada in east-central New Mexico has generally been overlooked in oil exploration because of its limited outcrop area and because burial depths did not seem sufficient for hydrocarbon maturation. However, until the late Cenozoic, the Todilto probably was continuous from western Quay County to the Four Corners, and east-central New Mexico was coveredmore » by a thick sequence of Cretaceous marine rocks. Furthermore, migrating Todilto hydrocarbons need not be restricted to existing Todilto outcrops, but may be expected up Entrada paleodip wherever porosity and stratigraphic traps allow accumulation.« less