Amerasia sedimentary basin 

(Early Cretaceous to Quaternary) 

(Canadian Arctic Islands and Beaufort Sea, unit TJs)

Basin, part of which is outside of map area, is separated into two parts by the large, bathymetrically 
irregular Alpha-Mendeleev ridge system. The northern part of the Amerasia basin is the Makarov 
basin that occurs between the Alpha-Mendeleev ridge and the Lomonosov Ridge. The southern 
part is in the Beaufort Sea area between the Alpha-Mendeleev ridge and North America. Adjacent 
to Wrangel Island and the Chukchi shelf, the Amerasia basin contains a cluster of north-trending, 
high-standing, flat-topped ridges separated by narrow, north-trending sedimentary basins. These 
ridges constitute the Chukchi continental borderland and are assigned to the Northwind ridge, 
Chukchi cap, and Arlis terranes that are inferred to consist of continental crust and continental 
margin rocks. The crust of the Amerasia basin is best from seismic-refraction and multichannel 
seismic-reflection data that indicate that the thickness of oceanic layer 3 may range from 4.4 to 6.7 
km, and that oceanic layer 2 is probably less than 2 km thick.

Subsurface geologic and seismic-reflection data from the North Slope of Alaska and the Alaskan 
Beaufort Sea shelf suggest that this region (Canada Basin) opened in two stages. Opening began 
in the Early Jurassic when a series of rifts of unknown width, in part preserved beneath the 
Beaufort shelf and slope, formed between Arctic Alaska and the Canadian Arctic Islands. The 
clastic sedimentary section in these rifts is inferred from seismic data to range from Early Jurassic 
to Neocomian. Renewed rifting in the late Hauterivian led to continental breakup and the initiation 
of seafloor spreading to form the basin. Cessation of spreading is not known but probably 
occurred during the mid- to Late Cretaceous. Oceanic crust beneath the basin in this area is 
interpreted as forming mainly between the Hauterivian and mid- to Late Cretaceous.

The Hauterivian or Barremian to Holocene sedimentary rocks (layer 1) range in thickness from 
about 6 km to the northwest to more than 12 km to the southeast. Seafloor morphology, basin-fill 
geometry, and seismic-reflection character suggest that these sedimentary rocks consist of 
turbidite deposits derived primarily from the Mackenzie delta and the Canadian Arctic Islands, 
with minor contributions from the Alaskan Beaufort Sea and Chukchi Sea shelves. Reflection 
character and tentative extrapolation of continental shelf stratigraphy into the basin suggest that, 
beneath the continental rise north of the central part of the North Slope of Alaska, the Cretaceous 
section in the basin is more than 3.5 km thick, the Tertiary section is 3.0 to 3.5 km thick, and the 
Quaternary section is 1.2 km thick. The Quaternary section locally thickens to about 1.5 km the 
west.

Seismic-reflection and gravity data from the Wrangel Island Abyssal Plain indicates that the 
sedimentary section in the southern part of the Amerasia Basin, west of the Alpha-Mendeleev 
Ridge, consists of turbidite deposits that are more than 3.5 km thick. Gravity modeling suggests 
that the sedimentary rocks may be about 6 km thick and overlie oceanic crust 5 to 7 km thick. 
REFERENCES: Kutschale, 1966; Mair and Lyons, 1981; May and Grantz, 1990; Grantz and 
others, 1990; Grantz and May, 1983