676
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
institutes and published MCS data from the northwestern part of the Chukchi Shelf, gained by
US Geological Survey (Grantz et a!., 1986 and 1990). The surface observations of the gravity
field were compiled by Sobczak et a!. (1990), and the latest tectonic synthesizes were published
by Hall (1990) and Grantz et a!. (1990). The satellite gravity data shed more light on structure
of the region.
The sector has the clear structural boundaries in the northwestern Chukchi Sea. These are the
ViI 'kitskii Rift System on the west and eastern limit of the Listric-normal faults province on the
east. The latter was delineated by Grantz et a!. (1990) and is located along the apparent shelf
continuation of the Northwind Escarpment. The Wrangel Block, North Chukchi rift basin and
North Chukchi Uplift represent the main structural elements of the shelf area which are wellexpressed in the gravity field (Figure 2).
The Wrangel Block represents an uplift (Wrangel Arch by Grantz et a!., 1990) of the folded
basement. Recently it was studied on the Wrangel Island by Russian and Canadian geologists
(Kos'ko et a!., 1993) who reported the island to be composed of pentratively deformed
complexes of Upper Proterozoic metamorphic rocks, Paleozoic (Late Silurian to Permian) and
Triassic clastic, carbonate and flysch strata, overlain by undeformed of tens of meters thick
Tertiary and Quaternary sediments. The main thrust-and-fold deformations are suggested to
have occurred during a Middle Jurassic to Early Cretaceous orogeny. The gravity data suggest
the Wrangel Arch extends northerly and northwesterly of the Wrangel Island up to 73° N.
The 500 km long and 200 km wide North Chukchi rift basin lies north of Wrangel Arch and
represents one of the main negative structural features of the ERAM. It extends nearly W-E
from 180° E toward Barrow Arch and Chukchi Platform of the Alaskan continental margin
(Grantz et a!., 1990). The MCS data show this basin is filled with a very thick, as much as 1214 km, sequence of marine and shelf marine strata, interpreted to be of probable Cretaceous to
Quaternary age (Figure 6B). However, the U.S.G.S. profiles are located on the southern slope
of the basin just southwest of its most subsided part, marked by a gravity low of -40 to -60
mGal around 73° N, 170° W (Figure 6A). This suggests that the sediment thickness is even
higher in the basin depocenter and supports the hypothesis of Grantz et a!. (1990) that an
oceanic or very highly thinned continental crust is present in the base of the North Chukchi
Basin. The northern flank of the basin is marked by a steep gravity gradient. This feature was
noted by Sobczak et a!. (1990) and probably reflects some asymmetry in basin's structure with
a gently sloping southern side and a steep, fault related 0), northern side.
The eastern part of the basin is affected by an array of northerly-striking listric normal faults,
predicted to be of latest Cretaceous or earliest Tertiary age (Grantz et a!., 1990). This Listricnormal fault province is well-expressed in the gravity data and obviously represents a shelf
continuation of the extension-related structures of the Chukchi Borderland.
The North Chukchi Uplift occurs in the outer northwestern Chukchi Shelf (Figure 2). It is
marked by one of the highest gravity peaks, which is as much as 50 mGal in intensity, and
separates structurally the North Chukchi Basin and western part of the Chukchi Borderland
(Chukchi Cap). This structure has not previously been described and there are no data to infer
its geology. We only can suggest some similarity between this feature and Chukchi Cap
(Plateau) since both structures display a similar gravity pattern.
The Chukchi Borderland has the most spectacular expression in the gravity field (Figure 2).
Morphologically it represents an ensemble of the N-S trending narrow ridges and basins,
divided by the steep gravity gradients and marked by gravity highs (40-50 mGal) and lows (40 to -60 mGal), correspondingly. Such a characteristic pattern has previously been established
and has been said to reflect rift-related structure of the borderland (Hall, 1990).
There are two main crustal blocks, which differ significantly in their gravity field. The more
solid western block is represented by the Chukchi Plateau, whose top part consists of a 25 km
wide N-S trending graben, delineated previously (HaJJ and Hunkins, 1968; Hall, 1990). The
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
institutes and published MCS data from the northwestern part of the Chukchi Shelf, gained by
US Geological Survey (Grantz et a!., 1986 and 1990). The surface observations of the gravity
field were compiled by Sobczak et a!. (1990), and the latest tectonic synthesizes were published
by Hall (1990) and Grantz et a!. (1990). The satellite gravity data shed more light on structure
of the region.
The sector has the clear structural boundaries in the northwestern Chukchi Sea. These are the
ViI 'kitskii Rift System on the west and eastern limit of the Listric-normal faults province on the
east. The latter was delineated by Grantz et a!. (1990) and is located along the apparent shelf
continuation of the Northwind Escarpment. The Wrangel Block, North Chukchi rift basin and
North Chukchi Uplift represent the main structural elements of the shelf area which are wellexpressed in the gravity field (Figure 2).
The Wrangel Block represents an uplift (Wrangel Arch by Grantz et a!., 1990) of the folded
basement. Recently it was studied on the Wrangel Island by Russian and Canadian geologists
(Kos'ko et a!., 1993) who reported the island to be composed of pentratively deformed
complexes of Upper Proterozoic metamorphic rocks, Paleozoic (Late Silurian to Permian) and
Triassic clastic, carbonate and flysch strata, overlain by undeformed of tens of meters thick
Tertiary and Quaternary sediments. The main thrust-and-fold deformations are suggested to
have occurred during a Middle Jurassic to Early Cretaceous orogeny. The gravity data suggest
the Wrangel Arch extends northerly and northwesterly of the Wrangel Island up to 73° N.
The 500 km long and 200 km wide North Chukchi rift basin lies north of Wrangel Arch and
represents one of the main negative structural features of the ERAM. It extends nearly W-E
from 180° E toward Barrow Arch and Chukchi Platform of the Alaskan continental margin
(Grantz et a!., 1990). The MCS data show this basin is filled with a very thick, as much as 1214 km, sequence of marine and shelf marine strata, interpreted to be of probable Cretaceous to
Quaternary age (Figure 6B). However, the U.S.G.S. profiles are located on the southern slope
of the basin just southwest of its most subsided part, marked by a gravity low of -40 to -60
mGal around 73° N, 170° W (Figure 6A). This suggests that the sediment thickness is even
higher in the basin depocenter and supports the hypothesis of Grantz et a!. (1990) that an
oceanic or very highly thinned continental crust is present in the base of the North Chukchi
Basin. The northern flank of the basin is marked by a steep gravity gradient. This feature was
noted by Sobczak et a!. (1990) and probably reflects some asymmetry in basin's structure with
a gently sloping southern side and a steep, fault related 0), northern side.
The eastern part of the basin is affected by an array of northerly-striking listric normal faults,
predicted to be of latest Cretaceous or earliest Tertiary age (Grantz et a!., 1990). This Listricnormal fault province is well-expressed in the gravity data and obviously represents a shelf
continuation of the extension-related structures of the Chukchi Borderland.
The North Chukchi Uplift occurs in the outer northwestern Chukchi Shelf (Figure 2). It is
marked by one of the highest gravity peaks, which is as much as 50 mGal in intensity, and
separates structurally the North Chukchi Basin and western part of the Chukchi Borderland
(Chukchi Cap). This structure has not previously been described and there are no data to infer
its geology. We only can suggest some similarity between this feature and Chukchi Cap
(Plateau) since both structures display a similar gravity pattern.
The Chukchi Borderland has the most spectacular expression in the gravity field (Figure 2).
Morphologically it represents an ensemble of the N-S trending narrow ridges and basins,
divided by the steep gravity gradients and marked by gravity highs (40-50 mGal) and lows (40 to -60 mGal), correspondingly. Such a characteristic pattern has previously been established
and has been said to reflect rift-related structure of the borderland (Hall, 1990).
There are two main crustal blocks, which differ significantly in their gravity field. The more
solid western block is represented by the Chukchi Plateau, whose top part consists of a 25 km
wide N-S trending graben, delineated previously (HaJJ and Hunkins, 1968; Hall, 1990). The