Drachev et al.: Main Structural Elements of East em Russian Arctic Continental Margin
673
(Sekretov, I 993b) but they are not published yet. The new gravity data give an unique insight
into structure of this very interesting spreading ridge/continental margin conjugation.
The Gakkel Spreading Ridge is sharply displayed in the gravity field by a narrow low about
-20 to -50 mGal and surrounding gravity highs of 10 to 30 mGal, which reflect an axial rift
valley and both uplifted flanks of the buried ridge correspondingly. The rift valley is traced onto
the continental slope up to 78 0 30' N 126 0 15' E, where it is cut by a set of oblique lineaments
which appear to be transform-like fractures. Several transform faults can also be recognized
within the ridge. They segment the ridge but do not reveal a visible offset and can be considered
zero-transform faults.
The southern Eurasia Basin has been crossed by several MCS profiles in 1990 (Sekretov,
1993b). These data show a thick (about 5-8 km) sedimentary sequence suggested to be a Late
Cretaceous to Cenozoic in age. The Gakkel Ridge is buried under its upper (Miocene to
Holocene) part.
East Siberian Sector (East Siberian Sea and Southern Makarov Basin)
This sector is located between 140 0 and 180
0
E and thus is the central part of the ERAM. There
is a limited amount of available MCS and seismic refraction data obtained by the Russian and
German scientists in 1989-1994 in the western part of the East Siberian shelf, mainly
northward of New Siberian Islands (Gramberg et a!., 1993; Sekretov, 1993a; Drachev et a!.,
1995b; Roeser et a!., 1995). Satellite altimeter data give us the opportunity to extend the
structural contours, localized previously by seismic surveys, and to provide a preliminary
delineation of the structure of the seismically unstudied areas (Figure 2).
The 500 km long and 100-120 km wide New Siberian Rift is a most prominent negative
gravity feature of the East Siberian shelf. It occurs between the De Long and Kotel 'nyi uplifts
extending NW -SE toward central part of the shelf where it merges with the East Siberian
sedimentary basin. The triangle-shaped Kotel 'nyi Uplift separates the New Siberian Rift from
the Laptev Rift System and consists of folded Paleozoic to Mesozoic clastic and carbonate
complexes covered with thin, less than 1 km of thick, Upper Cenozoic sediments. The northern
part of the rift was studied by joint German-Russian geophysical survey in 1993 (Roeser et a!.,
1995). It includes two deep subsided parallel grabens divided by a narrow horst, as shown on
Figure 4. These features are well distinguished in the gravity field (Figure 4A). The preliminary
estimated thickness of the Cenozoic sediments within the rift exceeds 5 km.
De Long Uplift, the large ellipsoid-shaped positive feature of the region, occurs between 145 0
and 175 0 E extending northward of 75
0
N up to the shelf edge. It comprises high-standing block
of the folded basement (Bennett and Henrietta terranes; for more details see Fujita and Cook,
1990) covered by subaerial Cretaceous (Albian) and Late Cenozoic basaltic flows and Upper
Cenozoic sediments. The boundaries and internal structural pattern of the uplift are clearly
expressed both in gravity (Figure 2) and magnetic (Macnab, 1993; Verhoef et aI., 1996) fields.
The latter reveals a pattern typical for a volcanic plateau consisting of high amplitude short
wavelength anomalies. Gravity and MCS data show small grabens and horsts which complicate
the internal parts of the plateau (Drachev et aI., 1995b; Roeser et aI., 1995). In the northeast the
uplift is bordered by the ViI 'kitskii Rift System, whose western branch enters the uplift and
merges with the East Siberian Basin. The northeastern slope of the uplift has been crossed by
Marine Arctic Geologic Expedition MCS profile (Sekretov, 1993a). According to these data,
the thickness of the sediments in the area of the continental slope northward of the uplift reaches
6-8 km and their age is predicted to be Aptian to Cenozoic.
In the area between 150 0 and 160 0 E the New Siberian Rift joins the East Siberian sedimentary
basin. The latter occupies the central part of the East Siberian Shelf, bordering the De Long
673
(Sekretov, I 993b) but they are not published yet. The new gravity data give an unique insight
into structure of this very interesting spreading ridge/continental margin conjugation.
The Gakkel Spreading Ridge is sharply displayed in the gravity field by a narrow low about
-20 to -50 mGal and surrounding gravity highs of 10 to 30 mGal, which reflect an axial rift
valley and both uplifted flanks of the buried ridge correspondingly. The rift valley is traced onto
the continental slope up to 78 0 30' N 126 0 15' E, where it is cut by a set of oblique lineaments
which appear to be transform-like fractures. Several transform faults can also be recognized
within the ridge. They segment the ridge but do not reveal a visible offset and can be considered
zero-transform faults.
The southern Eurasia Basin has been crossed by several MCS profiles in 1990 (Sekretov,
1993b). These data show a thick (about 5-8 km) sedimentary sequence suggested to be a Late
Cretaceous to Cenozoic in age. The Gakkel Ridge is buried under its upper (Miocene to
Holocene) part.
East Siberian Sector (East Siberian Sea and Southern Makarov Basin)
This sector is located between 140 0 and 180
0
E and thus is the central part of the ERAM. There
is a limited amount of available MCS and seismic refraction data obtained by the Russian and
German scientists in 1989-1994 in the western part of the East Siberian shelf, mainly
northward of New Siberian Islands (Gramberg et a!., 1993; Sekretov, 1993a; Drachev et a!.,
1995b; Roeser et a!., 1995). Satellite altimeter data give us the opportunity to extend the
structural contours, localized previously by seismic surveys, and to provide a preliminary
delineation of the structure of the seismically unstudied areas (Figure 2).
The 500 km long and 100-120 km wide New Siberian Rift is a most prominent negative
gravity feature of the East Siberian shelf. It occurs between the De Long and Kotel 'nyi uplifts
extending NW -SE toward central part of the shelf where it merges with the East Siberian
sedimentary basin. The triangle-shaped Kotel 'nyi Uplift separates the New Siberian Rift from
the Laptev Rift System and consists of folded Paleozoic to Mesozoic clastic and carbonate
complexes covered with thin, less than 1 km of thick, Upper Cenozoic sediments. The northern
part of the rift was studied by joint German-Russian geophysical survey in 1993 (Roeser et a!.,
1995). It includes two deep subsided parallel grabens divided by a narrow horst, as shown on
Figure 4. These features are well distinguished in the gravity field (Figure 4A). The preliminary
estimated thickness of the Cenozoic sediments within the rift exceeds 5 km.
De Long Uplift, the large ellipsoid-shaped positive feature of the region, occurs between 145 0
and 175 0 E extending northward of 75
0
N up to the shelf edge. It comprises high-standing block
of the folded basement (Bennett and Henrietta terranes; for more details see Fujita and Cook,
1990) covered by subaerial Cretaceous (Albian) and Late Cenozoic basaltic flows and Upper
Cenozoic sediments. The boundaries and internal structural pattern of the uplift are clearly
expressed both in gravity (Figure 2) and magnetic (Macnab, 1993; Verhoef et aI., 1996) fields.
The latter reveals a pattern typical for a volcanic plateau consisting of high amplitude short
wavelength anomalies. Gravity and MCS data show small grabens and horsts which complicate
the internal parts of the plateau (Drachev et aI., 1995b; Roeser et aI., 1995). In the northeast the
uplift is bordered by the ViI 'kitskii Rift System, whose western branch enters the uplift and
merges with the East Siberian Basin. The northeastern slope of the uplift has been crossed by
Marine Arctic Geologic Expedition MCS profile (Sekretov, 1993a). According to these data,
the thickness of the sediments in the area of the continental slope northward of the uplift reaches
6-8 km and their age is predicted to be Aptian to Cenozoic.
In the area between 150 0 and 160 0 E the New Siberian Rift joins the East Siberian sedimentary
basin. The latter occupies the central part of the East Siberian Shelf, bordering the De Long