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 Interpreting Geologic Sections  

On the coast of the Chukchi Sea, south west of Point Barrow, Alaska, are sea clifs that expose Pleistocene sediments of the Gubik formation. The section below is on a sea cliff called Skull Cliff, just north of the mouth of Tuapaktushak Creek. The total section illustrated in the schematic section below is about 20 meters high.

Fold in Tuapaktuasak at skull cliff

Soft sediment deformation in late Pleistocene sediments in northern Alaska.
Fold in Gubic formation with amplitude of about 3 meters.

schematic geologic section

Most Recent Event
Event 9:
Event 8:
Event 7:
Event 6:
Event 5:
Event 4:
Event 3:
Event 2:
Event 1:
First (oldest) Event

Unit K is crossbedded Cretaceous sandstones. There is a significant hiatus between their deposition and the deposition of the remander of the late Cenozoic sediments in this section. Units N, T, and Ka are members of the Pleistocene Gubic Formation. Each member represents shallow marine sediments deposited in an interglacial episode of elevated sea level. Unit N is the Nulavik member, and in this section at Skull Cliff does not contain fossils. Unit T is the Tuapaktushak member, it contains fossils and exhibits unusual soft sediment deformation - folds with an amplitude of some 3 meters. The cause of these folds is unclear, though deformation of the sediments by grounded icebergs has been suggested. Unit Ka is the Karmuk member, it also contains fossils in this area. Uint L is a blanket of fine grained recent sediments that has been deformed by the formation of ice wedges W(a cryoturbation feature), and is overlain by a tundra peat Pt.

You can view an animation of the history of this section by pressing the button below

Small image of section

Sources: Stratigraphy of this area worked out by Julie Brigham-Grette, see USGS open file report 85-381. Images and sections shown here by Paul J. Morris.
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Copyright © 1998, 1999 Athro, Limited. All Rights Reserved.
Written by Paul J. Morris
Maintained by Athro Limited
Date Created: 10 Mar 1998
Last Updated: 19 Dec 1999