Resumé
New occurrences of middle–late Darriwilian (Middle Ordovician) conodonts
are reported from the Nyalam region, southern Tibet. The
conodont-yielding strata, referred to the Chiatsun Group, accumulated on
the north Indian continental margin of northern Gondwana. These Middle
Ordovician conodonts include the informal species Histiodella sp. A in the middle part of the Lower Formation of the Chiatsun Group succeeded by a fauna of the Pygodus serra Zone in the upper part of that formation. Pygodus anserinus
is recorded from the base of the Upper Formation of the Chiatsun Group.
The Nyalam succession and its conodont taxa allow for precise
correlation of the strata preserved on top of Mount Qomolangma (Mount
Everest), eastern Tibet and the Peri-Gondwana Lhasa (north central
Tibet), South China, North China, Tarim Basin and Thailand-Malaysia
(Sibumasu Terrane) terranes and/or microcontinents. The middle
Darriwilian positive increase in δ13Ccarb
values (carbon isotope excursion, or MDICE) is recorded from most
terranes, and can be related to a late middle Darriwilian global
short-term cooling and sea-level drop. The cooling event prompted
temperate- to warm-water taxa to migrate towards the palaeoequator and
constrained the Australasian Province to locations near and at the
palaeoequator. The intensified oceanic circulation and upwelling on
continental margins probably caused some characteristic taxa to become
extinct. The incoming fauna was mainly of cool-water taxa. The conodont
specimens from southern Tibet are black to pale grey, corresponding to
conodont colour index (CAI) values of 5 to 6, which demonstrates that
the host sedimentary rocks were once heated to more than 360°C.
Originalsprog | Engelsk |
---|---|
Sider (fra-til) | 1010-1034 |
Antal sider | 25 |
Tidsskrift | Geological Magazine |
Vol/bind | 158 |
Udgave nummer | 6 |
DOI | |
Status | Udgivet - jun. 2021 |
Programområde
- Programområde 3: Energiressourcer