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The Gulf of Anadyr is underlain by two major sedimentary basins, Kresta basin and East Anadyr trough, that trend east to southeast and contain, in places, more than 9 km (29,500 ft) of fill. The basins are flanked on the east and north by the Okhotsk-Chukotsk volcanic belt, a broad bedrock high composed of plutonic and volcanic rocks that extends from eastern Siberia along the inner Bering Sea shelf at least to St. Matthew Island. The East Anadyr trough extends onshore and connects with the larger Anadyr basin, which underlies the lowlands between the Koryak Range and Okhotsk-Chukotsk volcanic belt of eastern Siberia.
New seismic reflection and refraction data reveal that Anadyr basin is separated from Navarin basin by Anadyr ridge, a southeast-northwest-trending bedrock high that is characterized by high-amplitude, short-wavelength magnetic anomalies. Anadyr ridge may be an offshore extension of the melange belt underlying the Koryak Range. Sonobuoy refraction data indicate that the velocity profile of strata in East Anadyr trough is similar to that in Navarin basin. Structurally, the basins are different: Navarin basin is complex and contains both compressional and extensional elements, whereas Anadyr basin is a simple, broad crustal sag semicircular in outline. Correlation of our reflection data from the offshore part of the Anadyr basin (including the East Anadyr trough and Kresta basin) with d illing data onshore allows us to differentiate three distinct sequences in the offshore portion of the basin. These sequences are separated by two strong reflectors, ^agr and ß, and are tentatively identified with increasing depth as boundaries separating the Neogene and Paleogene, and Paleogene and Mesozoic, respectively.
In the northeastern corner of the Gulf of Anadyr, across the Anaut uplift, shallow beds are folded and broken by faults that commonly offset the sea floor. Furthermore, earthquake epicenters recorded landward of Anadyr basin from Cape Navarin to the southwest and around the Chukotsk Peninsula to the northeast suggest recent tectonic movement in the Gulf of Anadyr near Cape Navarin and near Kresta Bay. We believe that Anadyr basin originally formed as a fore-arc basin during the Cretaceous as a result of underthrusting of the Kula plate beneath Siberia. The collision of the Kula plate with Siberia resulted in the formation of the Okhotsk-Chukotsk volcanic arc north of Anadyr basin and the Koryak melange belt south of the basin. Anadyr basin continued to subside during the Cenozoic and ajor uplift in the Koryak Range occurred in the late Miocene to Pliocene.
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