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  Stop 1: Capitan Reef Overview

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- We are looking at an overview of El Capitan, the Permian reef. This really is a spectacular place because it's one of the few places in the world where you've got original depositional topography preserved. You've got a rimmed attached platform right here. That's the rim. And then, this is rising approximately 600 meters above the valley floor, which was the original topography during the Permian. The basin floor and the reef. Interestingly, what would happen is during lowstands, the platform was covered, the outer platform was covered by sand dunes. And then those sand dunes would come down as sediment gravity flow as turbidity currents and debris flows and deposited these strata down here. During highstands, the platform was producing lots of carbonate. And carbonate-rich sediment gravity flows would come down. It's an excellent example of reciprocal sedimentation in which you get carbonate materials shed from the platform during highstands, and then siliceous material shed from the platform during lowstands. Down here you've got exposures of the famous Brushy Canyon Formation. The best study of deep-water succession in the world. And we'll be looking at some of those turbidites and debrites later on. We'll also be looking at some of the more calcareous sediment gravity flows coming down, including class of the reef itself broken down coming in as debris flows. And then also we'll look at some calciturbidites. But classic example of a rim-attached platform here in the Permian Basin. The other thing to understand is the petroleum system source rocks are down in the basin. Okay, so the marine shales are the source rocks. So oil is generated down here, migrates through the reef. The reef is highly porous, very calcified. But there's no trapping mechanism in the reef. So the oil actually goes through the reef, into the back reef, and in the back reef, you've got evaporites, and those evaporites form illateral seal to oil migration. And that's where it gets trapped. So, the reservoirs are all behind the reef. Actually not in the reef itself.