Large-scale, low-angle thrust sheets mapped within a 30,000-sq-mi region have been grouped tentatively into five tectonic units, each characterized by multiple northward thrusting of a distinctive rock sequence.

Rock sequences which distinguish the tectonic units in the De Long Mountains are informally designated as follow:

1. Foothills unit (northernmost and structurally lowest):
Permian(?), Triassic, and Jurassic chert, shale, and limestone, (b) Early Cretaceous (Valanginian) shale with Buchia-bearing coquinoid limestone, and (c) late Early Cretaceous (early? Albian) graywacke and shale.

2. Wulik unit:
(a) Mississippian dark carbonate, chert, and shale, (b) Permian(?), Triassic, and Jurassic(?) varicolored chert, shale, and limestone, (c) Valanginian quartzitic sandstone and shale containing Buchia, and (d) early? Albian graywacke and shale.

3. Kelly unit:
Subunit A: Devonian and Mississippian detrital rocks; Subunit B: (a) Mississippian light carbonate and terrigenous rocks, (b) Permian(?) and Triassic chert and shale, and (c) earliest Cretaceous (Berriasian and Valanginian) graywacke and shale.

4. Ipnavik unit:
(a) Devonian carbonate, (b) Mississippian dark chert, shale, and carbonate intruded by numerous mafic sills (Jurassic?), and (c) Berriasian graywacke and shale.

5. Misheguk unit:
(structurally highest): (a) Jurassic(?) tabular, mafic igneous complex several thousand feet thick, and (b) Devonian carbonate.

The five internally thrust tectonic units are juxtaposed and separated by important low-angle thrusts, some of which have a minimum northward displacement of more than 20 mi. Cumulative northward displacement of all thrusts in the region may exceed 150 mi.

The major episode of thrusting was probably Aptian to early(?) Albian; however, three other phases of less intense Cretaceous deformation also are postulated. All four episodes were accompanied by deposition in adjacent foredeeps (exogeosynclines), which are progressively younger northward. The ages of the preserved foredeep rock sequences are: (1) Berriasian and Valanginian; (2) early(?) Albian; (3) later Albian (Nanushuk Group); and (4) Late Cretaceous (Colville Group).

The contrast between the north-trending grains of the Lisburne Peninsula and the southwest-trending structures of the De Long Mountains may have resulted from latest Cretaceous or Tertiary bending of the regional structural grain.

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