New Zealand Journal of Geology and Geophysics abstracts
Late Triassic–Jurassic bivalves from volcanic sediments of the
Lhasa block, Tibet
Jiarun Yin
China University of Geosciences
29 Xueyuan Lu
Beijing 100083, China
yjr@cugb.edu.cn
J. A. Grant-Mackie
Geology Department
The University of Auckland
Private Bag 92019
Auckland, New Zealand
j.grant-mackie@auckland.ac.nz
Abstract Mesozoic volcanic sediments known as the
Yeba Formation are widespread in the northeastern region of Lhasa.
Recent fossil collections in the formation allow the establishment of a
biostratigraphic framework for the volcanic sediments; bivalves are
assigned to 21 genera and 22 species including a new genus and 5 new
species: Lhasanella lhasaensis (gen. et sp. nov.), Trigonodus
xiabolangensis (sp. nov.), Isocyprina lhasaensis (sp.
nov.), Gervillaria tibetica (sp. nov.), and Jurassicorbula
fuersichi (sp. nov.). Three benthic assemblages have been
recognised: the Trigonodus-Isocyprina assemblage
(Rhaetian–Hettangian), the Lhasanella-Propeamussium assemblage
(Toarcian–Bajocian), and the Jurassicorbula–Neomiodon
assemblage (Middle Jurassic). The Yeba Formation ranges in age from
latest Triassic to Middle Jurassic. Volcanism in the Lhasa block
occurred frequently during this period, corresponding to the
fragmentation episode in eastern Gondwanaland and to the northwards
drift of the Lhasa block. A strong faunal affinity between the Lhasa
block and southern Qinghai, Japan, and Vietnam suggests that the Lhasa
block had been located within the northern marginal region of the East
Tethys since Toarcian times. The existence of a deep ocean which might
serve as a barrier to fauna dispersal between the Lhasa and Qingtang
blocks remains questionable.
Keywords Eastern Tethys; Lhasa block; volcanism;
Yeba Formation; Rhaetian; Hettangian; Toarcian; Aalenian; Bajocian;
Bathonian; bivalves; new taxonomic names; benthic assemblages; Lhasanella
lhasaensis (gen. et sp. nov.); Trigonodus xiabolangensis
(sp. nov.); Isocyprina lhasaensis (sp. nov.); Gervillaria
tibetica (sp. nov.); Jurassicorbula fuersichi (sp. nov.)
G04005; Received 30 January 2004; accepted 25 January 2005; Online
publication date 22 August 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
555–576
0028–8306/05/4803–0555© The Royal Society of New Zealand 2005
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