Mid-crustal Late Cretaceous metamorphism in the Nason terrane, Cascades crystalline core, Washington, USA: Implications for tectonic models

Results of comprehensive study of the Kholokhovchan floral assemblage collection is summarized. These plant fossils were collected in 1978 by E. L. Lebedev from volcanogenic deposits in Penzhina and Oklan rivers interfluve, North-Eastern Russia. This assemblage was previously known as a list of Lebedev’s preliminary identifi cations only. He had suggested that the Kholokhovchan assemblage is correlative to the latest Albian — early Turonian Grebenka flora from the Anadyr River middle reaches. However, our study demonstrates that the Kholokhovchan assemblage is most similar to the presumably the Turonian-Coniacian Arman flora of the Okhotsk-Chukotka volcanogenic belt and, therefore, should be dated as the Turonian-Coniacian or Turonian.

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Ginkgophytes of the Ul’ya flora (the Ul’ya depresiion, the Okhotsk-Chukotka volcanogenic belt)

Palaeobotany ◽

10.31111/palaeobotany/2016.7.80 ◽

2016 ◽

Vol 7 ◽

pp. 80-95 ◽

Cited By ~ 2

Author(s):

L. B. Golovneva

Keyword(s):

New Species ◽

Early Cretaceous ◽

Late Cretaceous ◽

Middle Part ◽

Leaf Length ◽

Volcanogenic Belt ◽

Short Shoots ◽

Volcanogenic Deposits

The Ul’ya flora comes from the Coniacian volcanogenic deposits of the Amka Formation (the Ul'ya depression, southern part of the Okhotsk-Chukotka volcanogenic belt). Ginkgoaleans are diverse in this flora and represented by three genera: Ginkgo, Sphenobaiera and Baiera. All specimens have no cuticle and were assigned to morphotaxa. Genus Ginkgo includes two species: G. ex gr. adiantoides (Ung.) Heer with entire leaves and G. ex gr. sibirica Heer with dissected leaves. Genus Sphenobaiera also consists of two species: S. ex gr. longifolia (Pom.) Florin with 4–8 leaf lobes and S. ex gr. biloba Prynada with two leaf lobes. Genus Baiera is represented by new species B. lebedevii Golovn., sp. nov.Leaves of this species are 25–30 cm long and 13–16 cm wide, narrowly wedge-shaped with flat slender petiole, dichotomously dissected 4–5 times into linear segments 3–6 mm wide with 6–12 veins. The length of ultimate segments is equal to about a half of leaf length. Leaves attached spirally to ovoid short shoots about 2 cm long. Among the Late Cretaceous floras similar diversity of ginkgoaleans was recorded only in the Turonian-Coniacian Arman flora from middle part of the Okhotsk-Chukotka volcanogenic belt (Herman et al., 2016). Four species of ginkgoaleans from the Ul’ya flora (except G. ex gr. adiantoides) are considered as the Early Cretaceous relicts.

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