--> Stratigraphy and Facies of the Hue Shale in Northern Alaska: Evidence for a Viable Continuous Resource Play in an Emerging Basin

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Stratigraphy and Facies of the Hue Shale in Northern Alaska: Evidence for a Viable Continuous Resource Play in an Emerging Basin

Abstract

The Aptian-Campanian Hue Shale is a major organic-rich formation in northern Alaska and is interpreted to be a source of oil in several North Slope conventional oil pools, including recent giant discoveries in the Aptian-Cenomanian Nanushuk Formation. The Hue also has potential as a self-sourced reservoir. Previous workers have documented multiple lithostratigraphic facies in the Hue, and recent USGS field studies have enhanced this stratigraphic framework. Specific methods currently underway for analysis of the Hue include outcrop sedimentology, measured total organic carbon (TOC), Rock-Eval, thin section petrography, Fourier-transform infrared spectroscopy, inductively coupled plasma mass spectrometry, and uranium/lead geochronology of volcanic ash beds. Conformably overlying the Hauterivian-Barremian pebble shale unit, we have documented that the Hue Shale comprises five distinctive facies, described here in ascending order. (1) The Aptian - Cenomanian high gamma ray zone (GRZ), which has long been recognized as the main organic-rich interval in the Hue. (2) The Inoceramus zone, which consists of mudstone with abundant Inoceramid shells. The Inoceramid zone is recognized in multiple localities from the Arctic National Wildlife coastal plain to an outcrop 100 miles (160 km) to the west, implying that it is a laterally continuous. This interval has been dated as 98-95 Ma at two localities, suggesting that it is a chronostratigraphic marker for a major lowstand in the basin. (3) The middle mudstone unit, which has been dated as 95-88 Ma, making it time - correlative with major source rocks of the Western Interior Seaway. TOC values in the middle mudstone at the Jago River outcrop average over 5 weight percent, with a maximum value over 26 weight percent, suggesting association with the Cenomanian-Turonian boundary Oceanic Anoxia Event (OAE) #2. (4) The tuffaceous mudstone unit, which has individual tuffaceous beds that range in thickness from a few centimeters to over a meter, and commonly show evidence of pervasive fracturing in outcrop. (5) The upper mudstone unit, which is gradational with the underlying tuffaceous mudstone unit and grades upward into distal turbidites of the Canning Formation by 73 Ma. The presence of two significant organic-rich intervals with an overlying brittle siliceous unit demonstrate that key petroleum system elements for a viable continuous resource play are present in the Hue Shale in northern Alaska.