Debatable questions of Boreal Triassic stratigraphy: boundary between middle and upper series

Abstract

Various opinions on the position of the Middle/Upper Triassic boundary have been concisely reviewed. The lower boundary of the Carnian Stage is accepted at the base of the Trachyceras aon Zone. The recentmost data on biostratigraphy of boundary beds of the Ladinian and Carnian Stages of the Southern Alps, Himalayas, British Columbia, northeastern Asia, Svalbard, and Arctic Canada have been considered and critically analyzed. Using sections of British Columbia with mixed Boreal and Tethyan fauna of Ammonoidea, we compared biostratigraphic schemes of the Middle/Upper Triassic boundary interval of the Boreal and Tethyan regions. On the basis of correlations and paleontological data, the lower boundary of the Carnian Stage in Northeastern Asia is suggested to be drawn at the base of the ammonoid “Protrachyceras” omkutchanicum Zone and its equivalents in other Boreal regions.

A revision of the Early Carnian Trachyceratidae (Ammonoidea) of Northeastern Asia

“…indet., but it is similar in the number of spiral of nodes to species known from the aon Zone of the Alpian Region. This allows a direct correlation of the omkutchanicum Zone with the aon Zone, which was previously correlated using the ecotonic sections of British Columbia (Konstantinov, 2008).…”

Triassic ammonoid biostratigraphy: an overview

“…From the Early to Late Ladinian (Fassanian -Longobardian), the faunal similarity between western Tethys and North America is impressive, with assemblages showing the same kind of structure and genera. The Boreal assemblages are poor and dominated by 'leiostraca' long-ranging ammonoids in the Early Ladinian (Tozer 1981b;Dagys 1988), whereas the Late Ladinian shows the development of extremely similar faunas from the Canadian Arctic to eastern Siberia, wholly consisting of nathorstitids (Nathorstites and Stolleyites) with some 'leiostraca' long-ranging forms (Tozer 1981b(Tozer , 1994Konstantinov 2008). Correlations with Tethyan successions are allowed by Nathorstites, which occurs also at mid-palaeolatitudes in northeastern British Columbia (Tozer 1981b(Tozer , 1994.…”

Middle Triassic ammonoid fossils from Aring, Kelantan, Malaysia

“…Geological Society of Malaysia, Bulletin 56, December 2010 menghasilkan zon-zon ammonoid piawai relatif terhadap usia geologi yang agak jitu dan mantap yang dapat digunakan dengan darjah keyakinan yang agak tinggi sehingga ke hari ini. Bagaimanapun, penzonan ammonoid masih mengalami pengubahsuaian kecil berdasarkan penemuan dan pengenalpastian spesies-spesies ammonoid baru dan penafsiran semula spesies-spesies lama seperti yang dibincangkan oleh Balini & Jenks (2007), Balini (2008), Konstantinov (2008) dan Meitto & Manfrin (1995) dalam kertas kerja mereka.…”

“…B. balatonicus (Mojsisovics). Berdasarkan skala piawai amonoid yang disediakan oleh Mietto dan Manfrin (1995) dan disokong oleh Konstantinov (2008) kehadiran Balatonites cf. B. balatonicus (Mojsisovics) dan himpunan ammonoid yang wujud bersamanya mencirikan Subzon Balatonicus yang merupakan salah satu daripada tiga subzon dalam Zon Balatonites (Rajah 5).…”

“…Pada tahun 1971, Tozer telah mengkaji semula genus Paratrachyceras dan menamakannya sebagai Frankites. Berdasarkan skala piawai ammonoid yang disediakan oleh Mietto & Manfrin (1995) dan disokong oleh Konstantinov (2008) (Mietto & Manfrin 1995). Dari segi korelasi biostratigrafi pula, kedua-dua spesies ammonoid indeks yang dikenalpasti iaitu Balatonites cf.…”