--> Abstract: Insights into the Cretaceous–Tertiary Thermal History of the U.S. Chukchi Shelf from Apatite Fission Track Samples in Exploration Wells, by William Craddock; #90177 (2013)

Datapages, Inc.Print this page

Insights into the Cretaceous–Tertiary Thermal History of the U.S. Chukchi Shelf from Apatite Fission Track Samples in Exploration Wells

William Craddock

The U.S. Chukchi Shelf, a ~125,000 km^2 region covered by less than 100 m of water, is estimated to hold a huge endowment of undiscovered oil and gas. The geologic framework of the shelf is known from extensive seismic reflection, gravity and magnetic surveys, and five exploration wells drilled more than twenty years ago. Those wells proved the presence of multiple viable petroleum systems, as demonstrated by at least one non-developed discovery and many oil and gas shows. The Chukchi Shelf shares many geological attributes with the Alaska North Slope, including multiple oil-prone source rocks and a generally similar Phanerozoic history, but it also displays key contrasts in both stratigraphy and structure. Therefore, the burial, uplift, and hydrocarbon generation history of the Alaska North Slope may not be an accurate analog for the Chukchi Shelf. Similar to Arctic Alaska, preserved stratigraphy indicates episodes of Aptian-Albian and Paleocene-Eocene burial across the shelf. An apparent break in vitrinite reflectance (VR) across the Cretaceous-Tertiary unconformity also hints at an intervening episode of burial/exhumation, but the timing and magnitude of these various events are not well resolved. Thus, to better understand the Cretaceous-Tertiary evolution of the Chukchi Shelf, we present new apatite fission track (AFT) data from the five exploration wells on the Chukchi Shelf. Most samples are in the oil window or immature based on depth-VR profiles, though a few deep samples are in the gas window. Generally, AFT central ages date to the Cretaceous and Tertiary, although some samples appear to contain multiple kinetic populations. New inverse models of time-temperature history, constrained by AFT, stratigraphic, and VR data, integrated with new interpretations of seismic reflection profiles, reveal several important contrasts between the Cretaceous-Tertiary basin evolution and thermal history of the Chukchi Shelf vs. Arctic Alaska. First, Aptian-Albian sediment burial proximal to the Herald Arch thrust belt is modest in comparison to Arctic Alaska to the east, perhaps accounting for ~80 – 100 ° C of heating at most. Second, Late Cretaceous burial and heating by an additional ~20– 30°C is required to achieve maximum temperatures in some parts of the shelf, a result consistent with the little-known local preservation of Upper Cretaceous strata along the flanks of the Herald Arch. Third, subsequent to Late Cretaceous burial, as much as 20 - 40°C cooling occurred across the shelf, during the latest Cretaceous and/or the middle Tertiary. The latter event appears to be associated with exhumation of the North Chukchi high during north-vergent, basement-involved thrusting. Around the Chukchi shelf, Paleocene-Eocene burial appears to be modest and nearly indistinguishable from isothermal holding in time-temperature models, although thick Tertiary successions in North Chukchi Basin onlap structural lows in the northern shelf.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013