Chukchi shelf stratigraphy: core study reveals pre-Cenozoic bedrock.

• Author: Stricker, Julie
• Position: SPECIAL SECTION: Petroleum Geology

[ILLUSTRATION OMITTED]

With the warming of the Arctic, more focus has been put on the potential for resource development off the northern coast of Alaska in the Chukchi Sea. In February 2016, USGS (US Geological Survey) released a report titled "Upper Cretaceous and Lower Jurassic Strata in Shallow Cores on the Chukchi Shelf, Arctic Alaska."

David W. Houseknecht, William H. Craddock, and Richard 0. Lease conducted the study, which was backed in part by Statoil. They studied six cores taken during USGS exploration cruises between 1977 and 1985. The cores were extracted using either rotary or vibracore technologies.

During later expeditions, USGS captured high-channel, high-resolution, shallow seismic-reflection data, which was correlated with the cores. Since then, several newer seismic studies of the area have been taken, adding more information to the physical layers recovered in the samples.

65 Million Years and Older

The sample area is in the Chukchi Sea off the northwest corner of the North Slope. The Chukchi Shelf is a major feature of the area. Its waters are relatively shallow, about 160 feet deep. The cores were drilled to study the characteristics of the seafloor and the shallow subsurface layers of rock.

Most of the cores were taken in a region called the Hannah Trough, a Jurassic riff basin believed to have high petroleum-charging potential. Three of the cores were sampled along the northern limit of the Cenozoic fold belt, another to the northwest. One core was taken on the western rim of the Hannah Trough, all in a formation called the Herald Arch foreland. A sixth was sampled to the west of the Wrangel-Herald Arch.

The locations from which the cores were taken were selected based on the geology revealed by single-channel, high-resolution seismic reflection data. Rotary cores were taken in 1983 and vibracores in 1985. The study analyzed them to determine the presence of fossils, potential for petroleum sources, thermal maturity, and dating. The study contained detailed descriptions of each core, compared with an image of the correlating shallow seismic data to determine the age of the layers.

The cores sample pre-Cenozoic layers, 65 million years and older. The region is thought to contain large oil and gas prospects, but despite the importance of the strata in determining the geologic framework, little has been published regarding the pre-Cenozoic bedrock.

Five of the cores contain layers about 86 million to 100 million years...