|North Pacific||AKSR-NASR||Anadyr-Koryak||Verkhoyansk-Chukotka||Okhotsk-Chukotka||N. Alaska||Yukon||Chignik|
The Barykov Phase of Floral Evolution
Herman (1988) was first to distinguish the Barykov phase incorporating the Valizhgen and Verkhnebystrinskaya taphofloras of the Valizhgen Cape in North-western Kamchatka (Herman and Lebedev, 1991) and the Barykov taphoflora of the Ugol'naya Bay locality. The Ugol'naya Bay Barykov taphoflora is the type flora of the Barykov phase.
The boundary between the Kaivayam and Barykov phases is recognizable based on successive taphofloras in the upper part of the Valizhgen Formation exposed in the Valizhgen Cape of Northwestern Kamchatka (Herman and Lebedev, 1991). In this area, the late Kaivayam subcomplex corresponds in age to the second half of the Coniacian age, while the Valizhgen taphoflora can be regarded, though with reservations, as early Santonian in age. Consequently, the Barykov phase base corresponds approximately to the Coniacian – Santonian boundary, or in the lowermost Santonian. The Barykov phase is 8 to 9 m.y. long, and it might be appropriate to try to subdivide into two shorter phases in the future. At present, available data on Santonian floras of the AKSR are insufficient to do this.
Plant taxa of the Barykov floral phase are listed in the panel to the right. Characteristics of the Barykov phase taphofloras are as follows. Their angiosperms represent a little more than a half of all the species, being dominated by Macclintockia (several species, the most widespread M. ochotica included) and Barykovia tchucotica although this is absent from the Valizhgen taphoflora of Kamchatka. The next distinctive feature is persistent occurrence of cycadophytes, which are a noticeable component of floral assemblages after their paucity in terms of diversity and abundance in the Penzhina and Kaivayam floras. Cycadophytes include Nilssonia that occurs frequently and is associated with subordinate Cycadites, Pterophyllum and Encephalartopsis. Paraprotophyllum ignatianum is most widespread species among platanoids, which are less abundant in general than in the Turonian and Coniacian. Representatives of the genus Menispermites occur as single specimens. Floras of the Barykov phase commonly include Magnoliaephyllum, "Zizyphus", Viburniphyllum (especially taphofloras of North-western Kamchatka), Cissites, and Quereuxia. Newcomers to the phase are Aristolochites, Rhamnites, "Vitis", and Barykovia; genera Grewiopsis and Hollickia occur more often than before. Trochodendroides remains are of a low diversity and abundance. Ferns are not abundant. Ginkgo ex gr. adiantoides, the only species of ginkgoaleans, is locally abundant. Sequoia and Cephalotaxopsis, the main representatives of conifers that overall display low diversity, commonly occur in association with Metasequoia and Cupressinocladus. In the Barykov flora, remains of advanced Cenophytic plants are associated sometimes with relict taxa (Hausmannia, Arctopteris, Sagenopteris (?), Pityophyllum, and cycadophytes).
Besides the taphofloras listed above, three other floral assemblages approximately correspond to the age span of the Barykov phase: one from the upper Bystraya Subformation of the Konglomeratovyi Cape area, another one from the Yanranai Formation of the Pekul'nei Ridge western flank, and the third is the “Anadyr flora” (using the nomenclature of Filippova) from a cross-bedded terrigenous member in the Grebenka River basin. The first two are extremely impoverished, however, and cannot be attributed with confidence to any phase in flora evolution.
The Anadyr flora is of a peculiar taxonomic composition. In the opinion of Filippova (1989), Protophyllocladus, Debeya and some other Late Cretaceous taxa present in this flora are indicative of the Early Senonian (Santonian) age, but B.V. Belaya attributed palynological assemblages from the aforementioned plant-bearing member to the Turonian (Shchepetov et al., 1994). It should be noted also that the genus Protophyllocladus occurs in floras of the AKSR from late Turonian time, P. aff. sachalinensis (Krysht. et Baik.) Krassilov is known from the Penzhina taphoflora of the Konglomeratovyi Cape locality, and the Cenomanian genus Sheffleraephyllum from the Grebenka flora is possibly identical to the genus Debeya. Hence, it is possible to state at present that according to its composition and stratigraphic level the flora in question is likely younger than the Grebenka flora found in the same area, although its age and relations with other taphofloras of the AKSR are problematic as yet. In this work, it is regarded as a flora of an indefinite type, which can as yet not be attributed to a particular phase of floral evolution because of a low taxonomic diversity and/or ambiguous composition.