Abstract:
The Lomonosov Ridge (LR) transects the Arctic Ocean between the North American and Siberian margins via the North Pole. The LR was formed by rift events first during formation of the oceanic Amerasia basin in the Early Cretaceous and later during opening of the Eurasia basin in the Paleocene. The LR is extremely remote, lying beneath pack ice in the Arctic Ocean, making petroleum assessment challenging. Seismic data collected from ice islands and ice breakers and a few scientific cores offer an opportunity for an initial evaluation of the petroleum potential of this area. Seismic profiles show that LR consists of at least three stratigraphic sequences overlying continental crystalline and/or metamorphic rocks. The oldest sequence is poorly to moderately reflective with seismic velocities suggestive of consolidated sediments or carbonate rocks. The middle sequence is highly reflective, 0.5 to approximately 2 km thick and is flat layered in the crestal part of LR but progradational along the Amerasia basin margin. The uppermost sequence, which averages about 500 m thick, rests on a regional angular unconformity. Scientific (ACEX) coring indicates this unit consists of Paleocene to Holocene mudstone that is organic-rich in its lower half. The oldest unit is interpreted to consist of Proterozoic to Jurassic platform rocks of northeast Baltica, whereas the overlying reflective unit represents the Cretaceous shelf and passive-margin succession of the Barents shelf prior to formation of the Eurasia Basin. Following rifting, uplift-related erosion, and separation from the Barents shelf, the uppermost sequence was deposited mainly under pelagic conditions on an intraoceanic plateau that subsided below sea-level at about 50 Ma. Source rocks are inferred from regional relations to possibly include Triassic and/or Jurassic organic-rich marine shale present on the Barents shelf and Albian to Turonian high-stand condensed intervals known from marginal areas of the Amerasia basin in Alaska and Canada. Good quality source rocks are present in the Paleogene section in ACEX cores on the LR but these are probably thermally immature nearly everywhere in the province. Reservoirs are hypothetical but could include shelf-margin clastic units, especially those overlying the Early Cretaceous and Paleocene breakup unconformities, and low-stand turbidites along the Amerasia basin margin. Traps are probably largely stratigraphic, although unconformity and half-graben structural traps could also be present. Peak generation probably occurred during Paleocene rifting when high heat flow conditions prevailed. Our initial look suggests that most of the key elements for a petroleum province may exist on the LR but that large uncertainties about the stratigraphy, reservoir quality, traps, and thermal history remain. In addition, preservation of any accumulated hydrocarbons may be compromised by large displacement rift- and post-rift extensional faults.