The 3,000-ft-thick Carboniferous section in Atlantic Richfield/Humble Prudhoe Bay State 1 is divided into two groups. The older rocks in the section, Endicott Group, are 1,200 ft thick and unconformably overlie argillites of the pre-Mississippian Neruokpuk Formation. Within the Endicott Group, the Kekiktuk Conglomerate is 600 ft of gray to dark-gray sandstone, shale, and thin-bedded coal, deposited in a paralic environment. The overlying Kayak(?) Shale is 620 ft of quartzitic and calcareous red sandstone, siltstone, shale, and arenaceous to ooid limestone; it represents transition to marine sedimentation and contains microfossils of Zone 16s (Chesterian). Overlying the Endicott Group, the Lisburne Group is 1,770 ft thick. Within the Lisburne Group, the Alapah Limestone, 1,050 ft thick, includes arenaceous bryozoan-echinoderm wackestone and packstone to lime mudstone and microdolomite with gypsum. The age of the Alapah Limestone ranges from Zones 16s through 18 (Chesterian). The overlying Wahoo Limestone, 720 ft thick, is a series of cyclic glauconitic-bryozoan-echinoderm-ooid packstone and grainstone capped by lime mudstone and arenaceous microdolomite. These are interpreted to represent cyclic deposition of tidal-flat lime mud developed directly over ooid tidal bars. The age of the Wahoo Limestone ranges from Zone 20 to Zone 21 (Pennsylvanian).

In comparison with the section penetrated by this well the outcrop data 75–112 mi southeast show that the Endicott Group is diachronous because, in the Franklin Mountains, it has a lithology similar to that found in the Prudhoe well but contains (Meramecian) Zone 11 marine microfossils. During the Meramecian the Sadlerochit Mountains were high; the Endicott Group is either absent or less than 50 ft thick here. The Alapah Limestone of Prudhoe Bay State 1 is more dolomitic and arenaceous than its equivalent in the Franklin or Sadlerochit Mountains. The Wahoo Limestone of the Prudhoe Bay subsurface is similar in lithology and in environments of deposition to the outcrop sections in the Sadlerochit Mountains.

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