Geology and assessment of undiscovered oil and gas resources of the Lomonosov-Makarov Province, 2008

The Lomonosov-Makarov Province lies in the central Arctic Ocean and encompasses the northern part of the oceanic Amerasia Basin (Makarov and Podvodnikov Basins) and the adjoining Lomonosov Ridge and Siberian continental margins. The Amerasia Basin is thought to have been created in the Jurassic and Early Cretaceous by rotational rifting of the Alaska-Siberia margin away from the Canada margin about a pivot point in the Mackenzie Delta and an associated continental-scale transform fault along the Lomonosov Ridge. The province is bounded on the south by the Cretaceous Alpha-Mendeleev Ridge, an undersea ridge composed of plume-type volcanic rocks that obliquely crosses the Amerasia Basin, dividing it into northern and southern parts. The thickest passive-margin succession in the province lies along the Siberian margin, where sediments thin from a maximum thickness along the continental margin to less than 2 km in the basin. The northern part of the province consists of the Lomonosov Ridge, which was rifted away from the Eurasia Plate in the Paleocene during formation of the oceanic Eurasia Basin, creating an isolated, narrow, submerged, but highstanding microcontinent. This part of the province contains sediments that were shed from the Eurasia Plate in the Mesozoic and covered by pelagic and hemipelagic sediments in the Cenozoic, creating depositional successions with thicknesses ranging from about 1 to more than 5 km. This tectonic framework provides the basis for division of the province into four assessment units (AUs), including (1) Lomonosov Ridge AU, (2) Makarov Basin Margin AU, (3) Siberian Passive Margin AU, and (4) Makarov Basin AU. The Lomonosov Ridge and Makarov Basin Margin AUs compose a displaced part of the Cretaceous shelf and slope, respectively, of the Eurasia continental margin with a covering drape of pelagic Cenozoic sediments. The Siberian Passive Margin and Makarov Basin AUs represent the slope of the Siberian continental margin and adjoining basin plain deposits, respectively, deposited on oceanic crust of the northern Amerasia Basin. All of the AUs are entirely submarine and covered by the polar icecap, and consequently have not been explored for petroleum. Petroleum source rock units considered in the assessment of the province are mostly hypothetical, and include Triassic and Jurassic platformal marine shale units on the Lomonosov Ridge, and province-wide Lower Cretaceous synrift, Lower and Upper Cretaceous postrift, and Paleogene organic-rich shale intervals. The most prospective reservoirs and traps are envisioned to include base-of-slope turbiditefan complexes, slope channels and basins, extensional and growth fault structures, and other stratigraphic, structural, and composite trap features typically present on clastic-dominated continental passive margins. Because of concerns about reservoir quality in the Makarov Basin AU and the detrimental effect of Paleocene rifting in the Lomonosov Ridge AU, these units were not quantitatively assessed, as they were judged to have less than 10 percent probability of containing at least one accumulation of hydrocarbons equal to or greater than 50 million barrels of oil equivalent (MMBOE). The mean volumes of undiscovered resources for the Makarov Basin Margin AU are estimated to be 0.12 billion barrels of oil and 0.74 trillion cubic feet of nonassociated gas, whereas the undiscovered resources for the Siberian Passive Margin AU are estimated to be ~1 billion barrels of oil and 4.7 trillion cubic feet of nonassociated gas. Introduction The U.S. Geological Survey (USGS) in 2008 completed an appraisal of undiscovered, technically recoverable, conventional oil and gas resources north of the Arctic Circle. Results of that Circum-Arctic Resource Appraisal (CARA) include aggregate resource estimates for the entire Arctic region (Bird and others, 2008; Gautier and others, 2009, 2011a) and documentation of the geologic framework and resource estimates for specific Arctic provinces (Bird and Houseknecht, 2011; Gautier and others, 2011b; Houseknecht and Bird, 2011; Houseknecht and others, 2012a, b; Klett and Pittman, 2011; Klett and others, 2011; Moore and Pitman, 2011; Moore and 2 The 2008 Circum-Arctic Resource Appraisal others, 2011; Schenk, 2011a, b; Sørensen and others, 2011). The procedures and methods used in conducting the CircumArctic Resource Appraisal were documented by Charpentier and Gautier (2011) and the location and extent of the basins were delimited by Grantz and others (2010; 2011a). The purpose of this chapter is to provide a synthesis of the petroleum geology of the Lomonosov-Makarov Province, to present the reasoning and input parameters used for petroleum assessment of its constituent assessment units, and to report the complete results of the resource assessment for the province. Lomonosov-Makarov Province Description Boundaries The Lomonosov-Makarov Province of the CircumArctic Resource Appraisal (CARA) encompasses the northern part of the Amerasia Basin and its margins, comprising a wedge-shaped area of about 715,000 km2 in the central part of the Arctic Ocean (fig. 1). The province includes the continental Lomonosov Ridge, oceanic Makarov and Podvodnikov Basins, and the outer shelf and slope of the Siberian continental margin (fig. 2). The province is bounded by the Amundsen Basin of the Eurasian ocean basin, the Canadian and Greenland margins in the Lincoln Sea, the Alpha and Mendeleev Ridges, and the Siberian continental shelf. In detail moving clockwise around the province, the province boundaries were placed at the (1) continent-ocean transition between continental crust of the Lomonosov Ridge and oceanic crust of the Amundsen Basin, (2) transform faults bounding the Lomonosov Ridge against oceanic crust and Greenland continental crust in the eastern Lincoln Sea, (3) depositional limit of volcanogenic deposits of the Alpha Ridge on the Lomonosov Ridge north of Ellesmere Island, (4) edge of onlap and (or) interfingering of sedimentary deposits of the Makarov and Podvodnikov basins onto volcanic rocks of the Alpha and Medeleev ridges, (5) downlap limit of continental slope deposits of the Siberian continental margin onto the Mendeleev Ridge, and (6) southern limit of the Siberian passive margin against the Vilkitski Basin and DeLong Massif on the Siberian Shelf. Boundaries delimiting the lateral extent of the Siberian passive margin deposits along the continental margin were arbitrarily placed at the termination of the Mendeleev Ridge in the east and at the termination of the Lomonosov Ridge in the west. The province boundaries were drawn entirely from geologic observations without regard for the political boundaries in the region. The entire province lies north of the Arctic Circle. Tectonic Evolution of the Central Arctic Ocean Region The Lomonosov Ridge is a high-standing submarine ribbon microcontinent that extends from northern Greenland to Siberia via the North Pole and divides the Arctic Ocean into two separate ocean basins: the younger Eurasia Basin and the older Amerasia Basin (figs. 2 and 3). The Eurasia Basin was formed during the Cenozoic by seafloor spreading at the active Gakkel Ridge (Vogt and others, 1979; Brozena and others, 2003; Cochran and others, 2003; Jokat and Micksch, 2004). Magnetic anomalies from the Eurasia Basin indicate that the seafloor spreading began in the late Paleocene (Chron 24 or Chron 25; ~56–58 Ma) and show that the basin developed by nearly orthogonal rifting of the Lomonosov Ridge away from the northern margin of the European continent (Brozena and others, 2003; Glebovsky and others, 2006). The origin and tectonic development of the Amerasia Basin is less certain because of its thick sedimentary and volcanic fill and because magnetic anomalies are absent or poorly developed over large parts of the basin. The anomalies observed in the basin are geometrically simple and limited to a narrow triangular region having an apex in the Mackenzie Delta in the western Canada Basin (Grantz and others, 2011b). The magnetic anomalies are associated with gravity anomalies that together suggest a rotational mechanism of seafloor spreading, with the Alaska-Siberia margin having been rifted away from the Canadian margin in the Hauterivian (Early Cretaceous, ~135 Ma) about a pivot point in the Mackenzie Delta (Grantz and others, 1990; 2011a). This model requires transform motion along the opposing margin to resolve the plate tectonic geometry of the basin, probably at the boundary between the Lomonosov Ridge and the Amerasia Basin. The geometry of bathymetric features along the western margin of the Lomonosov Ridge suggest they were deformed by translational shearing and are similar to bathymetric features at other sheared transform margins, supporting the rotational interpretation (Cochran and others, 2006) (fig. 4). Opening of the Amerasia Basin by counterclockwise rotation is not universally accepted, however, and a number of other mechanisms for the tectonic development of the Amerasia Basin have been proposed. The most popular alternative models are sea-floor spreading parallel to either the Alaskan margin or alternatively, parallel to the Canadian margin (see, for example, Lawver and Scotese, 1990). Other recent suggestions include simultaneous rotational openings about opposed poles of rotation in the Mackenzie Delta and near the New Siberian Islands (Kuzmichev, 2009) and separate phases of opening for the Canada Basin and Makarov-Podvodnikov Basin, with the latter having opened in the Late Cretaceous (Alvey and others, 2008). We note that (1) the magnetic and gravity anomalies of the western Canada Basin are fan-shaped and oriented Geology and Assessment of Undiscovered Oil and Gas Resources of the Lomonosov-Makarov Province, 2008 3