670
Land-Ocean SYstems in the Siberian Arctic: Dynamics and History
Laptev Sector (Laptev Sea and southern Eurasia Basin)
This sector of ERAM is bounded by the Taimyr Peninsula and Severnaya Zemlya Archipelago
on the west and New Siberian Islands on the east (Figure 1). It contains the southern
termination of the Gakkel spreading ridge and thus its geologic structure is the result of a
continental margin/spreading ridge interaction. The new gravity data (Figure 2) confirm the
map-view geometry of the main elements of the rift system, which were previously mapped by
MCS surveys (Drachev et aI., 1995a), and provide more details where the seismic profiles are
lacking.
The Laptev Rift System consists of several deep subsided rift basins and uplifted or highstanding blocks of the basement (Figures 2 and 3). From the west to the east there are: the West
Laptev and South Laptev rift basins, Ust' Lena Rift, Stolbovoi and East Laptev horsts,
Bel 'kov-Svyatoi Nos and Anisin rifts. The structural pattern of the central and eastern parts of
the shelf are clearly expressed in the gravity field with the low-to-high variations from -35
mGal over the rifts to 50 mGal over high-standing blocks. The Ust' Lena, Bel 'kov-Svyatoi
Nos and Anisin rifts are particularly prominent. The total preliminary estimated thickness of the
rift-related sediments varies between 4 and 8-9 km while on the horsts the sedimentary cover is
significantly reduced and its thickness does normally not exceed 2-2.5 km. The rift sedimentary
fill contains several seismic stratigraphic units predicted to be of Late Cretaceous to Early
Pliocene in age and its internal structure reflects the different stages of the spreading
ridge/continental margin interaction (Figure 3). The whole shelf is covered by uppermost
seismic unit. Onshore stratigraphy supports the Late Pliocene to Holocene age for them. This
succession probably reflects a deceleration of the rifting during the last reorganization of the
North AmericanfEurasian plates interaction about 2 Ma as shown by Cook et al. (1986) who
calculated the present-day Euler Pole of the EurasianlNorth American plates to be near the coast
of the Laptev Sea.
The rifts strike SE-NW from the coast toward the shelf edge. The Bel 'kov-Svyatoi Nos Rift
contains a long and narrow axial horst in the southern part that divides it into two parallel
grabens continued on the land. To the north this rift merges the Anisin Rift reaching the shelf
edge at about 77° N 130° E. The northern part of the rift is seismically active (Fujita and Cook,
1990; A vetisov, 1993) and can be considered present-day manifestation of the extension axis of
the Gakkel Ridge on the shelf. The Ust' Lena Rift and South Laptev Rift Basin, however, are
not continuous across entire shelf but are terminated by a NE-SW structural line which is wellexpressed in the gravity field. This line is coincident with the continental slope of Amundsen
Basin, then follows previously outlined Severnyi (Northern) Graben (Vinogradov, 1984) and
extends further toward the Khatanga Bay between Taimyr Peninsula and the mainland (Figure
2). The existence of such lineament was inferred by Fujita et al. (1990) who described it as
Severnyi Transfer. In our opinion this lineament which we call the Northern Fracture could
have acted as a transform fault during some stage of opening of the Eurasia Basin and
displacement of the Lomonosov Ridge relative to the Laptev Shelf.
The decrease of the rift sedimentary fill as one moves eastward from 10-12 km in South
Laptev Basin to 4-5 km in Bel 'kov-Svyatoi Nos Rift and simplification of the structure as a
whole suggest migration of the rifting in an eastward direction. The West Laptev and South
Laptev rift basins may represent failed rifts associated with beginning of the rifting prior the
continental breakup and initiation of sea-floor spreading at about 58 Ma. Such migration of the
rifting could take place since the spreading axis in the Eurasia Basin had to migrate eastward
with respect to the Barents-Kara continental margin.
The structural pattern of the Eurasia oceanic basin and Gakkel Ridge southward of 80° N is
not morphologically expressed as they are buried under a thick sedimentary cover. The first
MCS data were acquired there in 1990 by the Russian Marine Arctic Geologic Expedition
Land-Ocean SYstems in the Siberian Arctic: Dynamics and History
Laptev Sector (Laptev Sea and southern Eurasia Basin)
This sector of ERAM is bounded by the Taimyr Peninsula and Severnaya Zemlya Archipelago
on the west and New Siberian Islands on the east (Figure 1). It contains the southern
termination of the Gakkel spreading ridge and thus its geologic structure is the result of a
continental margin/spreading ridge interaction. The new gravity data (Figure 2) confirm the
map-view geometry of the main elements of the rift system, which were previously mapped by
MCS surveys (Drachev et aI., 1995a), and provide more details where the seismic profiles are
lacking.
The Laptev Rift System consists of several deep subsided rift basins and uplifted or highstanding blocks of the basement (Figures 2 and 3). From the west to the east there are: the West
Laptev and South Laptev rift basins, Ust' Lena Rift, Stolbovoi and East Laptev horsts,
Bel 'kov-Svyatoi Nos and Anisin rifts. The structural pattern of the central and eastern parts of
the shelf are clearly expressed in the gravity field with the low-to-high variations from -35
mGal over the rifts to 50 mGal over high-standing blocks. The Ust' Lena, Bel 'kov-Svyatoi
Nos and Anisin rifts are particularly prominent. The total preliminary estimated thickness of the
rift-related sediments varies between 4 and 8-9 km while on the horsts the sedimentary cover is
significantly reduced and its thickness does normally not exceed 2-2.5 km. The rift sedimentary
fill contains several seismic stratigraphic units predicted to be of Late Cretaceous to Early
Pliocene in age and its internal structure reflects the different stages of the spreading
ridge/continental margin interaction (Figure 3). The whole shelf is covered by uppermost
seismic unit. Onshore stratigraphy supports the Late Pliocene to Holocene age for them. This
succession probably reflects a deceleration of the rifting during the last reorganization of the
North AmericanfEurasian plates interaction about 2 Ma as shown by Cook et al. (1986) who
calculated the present-day Euler Pole of the EurasianlNorth American plates to be near the coast
of the Laptev Sea.
The rifts strike SE-NW from the coast toward the shelf edge. The Bel 'kov-Svyatoi Nos Rift
contains a long and narrow axial horst in the southern part that divides it into two parallel
grabens continued on the land. To the north this rift merges the Anisin Rift reaching the shelf
edge at about 77° N 130° E. The northern part of the rift is seismically active (Fujita and Cook,
1990; A vetisov, 1993) and can be considered present-day manifestation of the extension axis of
the Gakkel Ridge on the shelf. The Ust' Lena Rift and South Laptev Rift Basin, however, are
not continuous across entire shelf but are terminated by a NE-SW structural line which is wellexpressed in the gravity field. This line is coincident with the continental slope of Amundsen
Basin, then follows previously outlined Severnyi (Northern) Graben (Vinogradov, 1984) and
extends further toward the Khatanga Bay between Taimyr Peninsula and the mainland (Figure
2). The existence of such lineament was inferred by Fujita et al. (1990) who described it as
Severnyi Transfer. In our opinion this lineament which we call the Northern Fracture could
have acted as a transform fault during some stage of opening of the Eurasia Basin and
displacement of the Lomonosov Ridge relative to the Laptev Shelf.
The decrease of the rift sedimentary fill as one moves eastward from 10-12 km in South
Laptev Basin to 4-5 km in Bel 'kov-Svyatoi Nos Rift and simplification of the structure as a
whole suggest migration of the rifting in an eastward direction. The West Laptev and South
Laptev rift basins may represent failed rifts associated with beginning of the rifting prior the
continental breakup and initiation of sea-floor spreading at about 58 Ma. Such migration of the
rifting could take place since the spreading axis in the Eurasia Basin had to migrate eastward
with respect to the Barents-Kara continental margin.
The structural pattern of the Eurasia oceanic basin and Gakkel Ridge southward of 80° N is
not morphologically expressed as they are buried under a thick sedimentary cover. The first
MCS data were acquired there in 1990 by the Russian Marine Arctic Geologic Expedition