The Common Association of Giant Oil Fields with Evaporites: Linked by Both Pull Apart & Collision of Continents, Climate, Basin Position & Sea Level
Over 50% of world's most easily accessible hydrocarbon reserves are trapped in carbonates; over 60% of these beneath evaporite seals. The seals are distinct widespread stratigraphic markers capping evaporite successions that accumulated during Wilsonian plate motion cycles of extension & compression. Hydrocarbon prone succession architecture is driven by base level change during deposition; juxtaposing source, reservoir, & seals, & favoring hydrocarbon exploration & exploitation in Arabian Gulf, Central Asia, Atlantic, & the Cordilleran & Appalachian Mountains.
Critical to these settings are high rates of organic production, accumulation & preservation; a response to widespread enveloping continental plates windward of rain shadowed lea shores of restricted anoxic & saline basins behind structural &/or depositional barriers. Internal drainage &/or limited access to open ocean waters are products of linear belts of uplifted crust marginal to depressed crust, often below sea level & so favoring evaporites & organic matter preservation. The upper bounding surface of updip supratidal sabkha evaporite cycles is found in regressive coastlines, matching sea level positions of late high stand system tracts while surfaces of downdip restricted playas & basin evaporites matches the sea level position of lowstand system tracts.
Common updip shallow water carbonate platform play elements include sabkhas, salinas, & mudflats with near-shore & tidal flat reservoirs sealed by lateral & top seal sabkha facies, & offshore bar & shoal complexes capped by tight peritidal carbonates. Examples include Central Basin Platform Upper Permian San Andres, Arabian shelf Permian Khuff & Devonian Dolomitized Wabamun ramp. Downdip carbonate platform play elements include subaqueous salterns with platform margin buildups; isolated buildups on platform; & nearshore/tidal flat plays. Examples include Eastern Arabian Basin Arab D & Eastern Siberian Basin Lower Cambrian Osa grainstone play.
Common basins play elements from shallow &/or deep basins include platform margin buildups; isolated buildups, & allochthonous mass gravity deposits. With no structure, platform margin buildups often lack top & lateral seal probability but Iranian & Iraqi Asmari & Main Limestone plays have structure & potential. Smaller isolated buildups are the most successful play & include the Paradox Basin porous algal buildups, Western Canadian Middle Devonian Keg River play, & Michigan Basin Niagaran plays.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009