674
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Uplift on the south. The MCS profile LARGE 8901 (by Laboratory of Regional Geodynamics,
Moscow) crosses this area and provides more details about internal structure and relationship
between structural elements displayed in the gravity field (Figure 5). The southwestern part of
the shelf is occupied by a structural terrace that represents a gently northward dipping of the
acoustic basement and seismic reflectors toward the East Siberian Basin. Previously this area
was suggested to be the deep subsided Blagoveshchensk sedimentary basin underlain by
thinned continental or even oceanic crust and separated by a linear basement uplift (Anzhu
Ridge) from the New Siberian Basin (Fujita and Newberry, 1982; Kos'ko, 1984; Fujita and
Cook, 1990). Our data show neither Blagoveshchensk Basin nor Anzhu Ridge in this area.
The East Siberian Basin is bounded by the normal faults both from the shelf terrace and De
Long Uplift (Figure 5B). The marginal parts of it are the deeper with the top of the acoustic
basement at a depth of 3.5 s TWT, whereas in the central part of the basin the basement is
occurred at 2.0-2.3 s TWT and affected by the numerous low-amplitude near-vertical normal
faults (Figure 5B). A boundary between the De Long composite terrane and the rest of the basin
basement is well expressed in the MCS data. It is a narrow (about 5 km) zone consisting of
several anticline-shaped folds accompanied by thrusts and reverse faulting within the lowermost
part of sedimentary cover. It can be considered either a compression or transpression fracture.
The sedimentary cover of the basin is composed of 5 to 7 seismic stratigraphic units which
were suggested to be Cretaceous to Holocene in age (Drachev et aI., 1995b). The two
uppermost units form an uninterrupted cover while others were deposited by both northward
(from the mainland) and southward (from the De Long Uplift) sediment transport.
The eastern part of the East Siberian Shelf is occupied by the ViI 'kitskii Rift System
comprised of several NE-SW trending rifts. It has not been studied by offshore MCS profiling
but can be delineated by satellite gravity and airborne magnetic data (Figure 2; for magnetic field
see Macnab, 1993; Verhoef et aI., 1996). The previously delineated Vil'kitskii Trough
(Vinogradov, 1984; Fujita and Cook, 1990) is one of the most prominent members of the rift
system and represents a natural boundary between East Siberian and Chukchi sectors of
ERAM. There are no data to infer the age of the sedimentary fiII of this rift system and the
nature of the basement. However, by an analogy with the East Siberian Basin, we suggest the
former to be of a Cretaceous (Middle to Late Cretaceous ?) to Quaternary age and the latter to be
composed of deformed complexes of the Late Mesozoic New Siberian-Chukchi Fold Belt.
The southern Makarov Basin appears gravitationally as a smooth, low area, outlined by the
2000 m isobath (Figure 2). It does not reveal any clear structural zonality and is probably
underlain by a thinned continental crust covered with a thick (8-9 km) sedimentary cover as it
shown by seismic refraction and MCS data (Gramberg et aI., 1993; Sekretov, 1993a). The
southeastern wedge-shaped end of the basin separates the continental margin and Arlis Plateau
(southern part of the Mendeleev Ridge). Further to the southeast, there is a prominent linear
gravity low in the area of the continental slope. We consider this feature to be an expression of
an extensional structural feature that we call the Toll' Rift (Figure 2). This rift is structurally
bounded by the Arlis Plateau on the NE and De Long Uplift on the SW and merges the
Vil'kitskii Rift System on the shelf.
Chukchi Sector (Northwestern Chukchi Sea and Chukchi Borderland)
The Chukchi Sector spans the eastern part of the ERAM and adjacent territories of the Alaskan
continental margin, surrounded on the north by high-standing submarine blocks of the
Amerasia Basin: Arlis Plateau and Chukchi Borderland (Figures I and 2). The principal source
of the present-day geological understanding of this area is the ice- and aircraft based
geophysical measurements carried out during many years by U.S.S.R., US and Canadian
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Uplift on the south. The MCS profile LARGE 8901 (by Laboratory of Regional Geodynamics,
Moscow) crosses this area and provides more details about internal structure and relationship
between structural elements displayed in the gravity field (Figure 5). The southwestern part of
the shelf is occupied by a structural terrace that represents a gently northward dipping of the
acoustic basement and seismic reflectors toward the East Siberian Basin. Previously this area
was suggested to be the deep subsided Blagoveshchensk sedimentary basin underlain by
thinned continental or even oceanic crust and separated by a linear basement uplift (Anzhu
Ridge) from the New Siberian Basin (Fujita and Newberry, 1982; Kos'ko, 1984; Fujita and
Cook, 1990). Our data show neither Blagoveshchensk Basin nor Anzhu Ridge in this area.
The East Siberian Basin is bounded by the normal faults both from the shelf terrace and De
Long Uplift (Figure 5B). The marginal parts of it are the deeper with the top of the acoustic
basement at a depth of 3.5 s TWT, whereas in the central part of the basin the basement is
occurred at 2.0-2.3 s TWT and affected by the numerous low-amplitude near-vertical normal
faults (Figure 5B). A boundary between the De Long composite terrane and the rest of the basin
basement is well expressed in the MCS data. It is a narrow (about 5 km) zone consisting of
several anticline-shaped folds accompanied by thrusts and reverse faulting within the lowermost
part of sedimentary cover. It can be considered either a compression or transpression fracture.
The sedimentary cover of the basin is composed of 5 to 7 seismic stratigraphic units which
were suggested to be Cretaceous to Holocene in age (Drachev et aI., 1995b). The two
uppermost units form an uninterrupted cover while others were deposited by both northward
(from the mainland) and southward (from the De Long Uplift) sediment transport.
The eastern part of the East Siberian Shelf is occupied by the ViI 'kitskii Rift System
comprised of several NE-SW trending rifts. It has not been studied by offshore MCS profiling
but can be delineated by satellite gravity and airborne magnetic data (Figure 2; for magnetic field
see Macnab, 1993; Verhoef et aI., 1996). The previously delineated Vil'kitskii Trough
(Vinogradov, 1984; Fujita and Cook, 1990) is one of the most prominent members of the rift
system and represents a natural boundary between East Siberian and Chukchi sectors of
ERAM. There are no data to infer the age of the sedimentary fiII of this rift system and the
nature of the basement. However, by an analogy with the East Siberian Basin, we suggest the
former to be of a Cretaceous (Middle to Late Cretaceous ?) to Quaternary age and the latter to be
composed of deformed complexes of the Late Mesozoic New Siberian-Chukchi Fold Belt.
The southern Makarov Basin appears gravitationally as a smooth, low area, outlined by the
2000 m isobath (Figure 2). It does not reveal any clear structural zonality and is probably
underlain by a thinned continental crust covered with a thick (8-9 km) sedimentary cover as it
shown by seismic refraction and MCS data (Gramberg et aI., 1993; Sekretov, 1993a). The
southeastern wedge-shaped end of the basin separates the continental margin and Arlis Plateau
(southern part of the Mendeleev Ridge). Further to the southeast, there is a prominent linear
gravity low in the area of the continental slope. We consider this feature to be an expression of
an extensional structural feature that we call the Toll' Rift (Figure 2). This rift is structurally
bounded by the Arlis Plateau on the NE and De Long Uplift on the SW and merges the
Vil'kitskii Rift System on the shelf.
Chukchi Sector (Northwestern Chukchi Sea and Chukchi Borderland)
The Chukchi Sector spans the eastern part of the ERAM and adjacent territories of the Alaskan
continental margin, surrounded on the north by high-standing submarine blocks of the
Amerasia Basin: Arlis Plateau and Chukchi Borderland (Figures I and 2). The principal source
of the present-day geological understanding of this area is the ice- and aircraft based
geophysical measurements carried out during many years by U.S.S.R., US and Canadian