Cryogenian - Ediacaran to Cambrian Stratigraphy and ...

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Cambrian Stage 2 - Aldanella attleborensis and Watsonella crosbyi. Pavel Yu ... STAGES. STAGE 4. STAGE 3. TOMMOTIAN. NEMAKIT-. DALDYNIAN. STAGE 2.
Cryogenian - Ediacaran to Cambrian Stratigraphy and Paleontology of Guizhou, China

The 17 th Field Conference of the Cambrian Stage Subdivision Working Group, International Subcommission on Cambrian Stratigraphy and Celebration of the 30 th Anniversary of the Discovery of the Kaili Biota

Guizhou

2012

Edited by Yuanlong ZHAO, Maoyan ZHU, Jin PENG, Robert R. GAINES, Ronald L. PARSLEY

Journal of Guizhou University Natural Sciences

Cryogenian - Ediacaran to Cambrian Stratigraphy and Paleontology of Guizhou, China

Stratigraphic distribution of two potential index species for the GSSP of Cambrian Stage 2 - Aldanella attleborensis and Watsonella crosbyi 2

Pavel Yu. PARKHAEV 1 , Calina A. KARLOVA and Alexei Yu. ROZANOV 1 1. Borissiak Paleontological Institute of the Russian Academy of Sciences 2. Trofimuk Institute of Oil and Gas Geology of the Siberian Branch, Russian Academy of Sciences

In the lower half of the Cambrian, the time of initial diversification of skeletal Metazoans, recognition of correlative levels basing on single species is a challenge. Their FADs in remote regions are doubtfully synchronous or evidently asynchronous. For more precise correlations, entire fossil assemblages should be

considered. However, the formal rules of GSSP substantiation compel us to choose a single species. During the last years two mollusk species were suggested for determining the base of Cambrian Stage 2, i. e. Aldanella attleborensis (Parkhaev et al. , 2011; Parkhaev, Karlova, 2011) and Watsonella -

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Journal of Guizhou University (Natural Science) , Vol. 29 (Supplement 1)

crosbyi (Li et al. , 2011). Both species have rather wide geographical distribution providing good correlation potential for major regions of the world and from this point of view, these mollusks seem to be to be index species. The FADs of both species lie very close to each other and, in the terms of the Siberian stage standard, correspond to the base of the Tommotian Stage. However, the entire stratigraphical range of these species are not comparible in terms of their duration, i. e. A. attleborensis is a rather short - lived species, occurring only in the lower part of the Tommotian Stage (Parkhaev, Karlova, 2011), whereas W. crosbyi is extremely long - lived form, ranging from the beginning of the Tommotian up to the middle of the Botomian (Esakova, Zhegallo, 1996; Gravestock et al. , 2001; Rozanov et al. , 2010) (Fig.

1) . It is certainly evident, that short - ranging fossil has much higher significance for practical stratigraphy than the long - ranging one, because it provides more accurate age estimation (one of the main goals of the stratigraphy). In other words, any new find of A. attleborensis in any new section provides grounds for age determination as Early Tommotian equivalent, and it is rather good resolution. Any new find of W. crosbyi in any new section suggests that the age is within the limits of two and a half stages, i. e. Early Tommotian Early Botomian, and obviously such estimation is Siberian standard STAGES

Sib e ria

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not sufficiently accurate. Thus, we consider that Aldanella attleborensis a more preferable index species for the GSSP of Cambrian Stage 2 than Watsonella crosbyi. References Gravestock D I, Alexander EM, Demidenko Yu E, et al. The Cambrian Biostratigraphy of the Stansbury Basin, South Australia. Moscow: MAIK Nauka I Interperiodica, 2001. 344 p. Esakova N V, Zhegallo E A, 1996. Lower Cambrian Biostratigraphy and Fauna of Western Mongolia. Moscow: Nauka, 214 p. [in Russian]. Li G X, Zhao X, Gubanov A, et al. , 2011. Early Cambrian mollusc Watsonella crosbyi: a potential GSSP index fossil for the Base of the Cambrian Stage 2 II Acta Geol. Sin. , 85 ( 2) : 309 ~ 319. Parkhaev P Yu, Karlova G A, 2011. Taxonomic revision and evolution of Cambrian mollusks of the genus Aldanella Vostokova, 1962 (Gastropoda, Archaeobranchia) II Paleontol. J. , 45(10) : 1145 - 1205. Parkhaev P Yu, Karlova G A, Rozanov A Yu, 2001. Taxonomy, stratigraphy and biogeography of Aldanella attleborensis - a possible candidate for defining the base of Cambrian Stage 2 II Bull. Museum NOlthern Arizona, 67:298 - 300. Rozanov Yu, Parkhaev P Yu, Demidenko Yu E, et aI, 2010. Fossils from the Lower Cambrian stage stratotypes. Moscow: PI RAN, 228 p. [in Russian].

REGIONS NE America E u r 0 peW Mongolia S Australia

BOTOMIAN

I SC STAGES

STAGE 4

w ATDABANIAN

w

STAGE 3

TOMMOTIAN

STAGE 2

NEMAKITDALDYNIAN

FORTUNIAN

Figure 1. Stratigraphic ranges of Aldanella attleborensis (A) and Watsonella crosbyi (W) in regions of the world.

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