ABSTRACT VOLUME
~..t: .'
.~.~~.. International Symposium ~-
•
on the
Ediacaran-Cambrian Transition
20 17
Convened by: Dr. A. Liu, Prof. D. McIlroy, Prof. G. Narbonne & Dr. M. Laflamme For: The International Subcommission on Ediacaran Stratigraphy (ICES) The International Subcommission on Cambrian Stratigraphy (ISCS)
GEOLOGICAL SURVEY NEWFOUNDLAND AND LABRADOR - - - - Founded 1864 - - - -
D. McIlroy (ed.)
Critical review of C-isotope data across the Precambrian-Cambrian boundary on the Siberian Platform P.Yu Parkhaev', Yu V. Shuvalova Borissiak Paleontological Instilute o/the Russian Academy o/Sciences *
[email protected]
The Cambrian is the only system in the International Stratigraphic Chart still without a complete stage subdivision. Recent studies have focused on selection of the GSSP for missing stages. Another urgent problem is reconsideration of the lower Cambrian boundary (Babcock et aI., 2014), since the existing GSSP does not provide necessary correlation potential (Rozanov et aI., 1997). The predominantly carbonate Cambrian sections of the Siberian Platform with continuous sequences and rich fauna are classic 'testing grounds' for Precambrian-eambrian paleontology and stratigraphy (e.g. Rozanov et aI., 1969; Shergold et aI., 1991). Ol3 C oscillation can be an important correlation tool in addition to the biostratigraphy (Peng et aI., 2012), and a number of C-isotope curves of various reliability for all major facial regions of the Siberian Cambrian have been published, i.e. (1) Lena-Aldan Region: Aldan river (Kirschvink et aI., 1991; Magaritz et aI., 1991; Brasier et aI., 1993), Lena river (Parkhaev et aI., 2016), (2) Igarka Region: Sukharikha river (Kouchinsky et aI., 2007), (3) West Anabar Region: Kotuy and Kotuykan rivers (Knoll et aI., 1995a; Landing, Kouchinsky, 2016), (4) East Anabar Region: Bol'shaya and Malaya Kuonamka rivers (Kouchinsky et aI., 200 I), (5) Olenek Uplift, Khorbosuonka river (Knoll et aI., 1995b; Marusin, 2016), (6) Uchur-Maya Region (Kouchinsky et aI., 2005; Zhu et aI., 2017). Due facies differences, calibration and correlation of these curves is only possible against evolutionary events within the studied interval: (I) FAD ofeloudina-type fossils in the Vendian/Ediacaran; (2) FAD of tubular SSF and protoconodonts in the late Precambrian (base Nemakit-Daldynian); (3) FAD of diverse SSF assemblages, including halkieriids, chancelloriids and the first molluscs, in the terminal Precambrian (end Nemakit-Daldynian); (4) FAD of taxonomically diverse skeletal fossils, including tommotiids, brachiopods and first archaeocyaths at the beginning of Cambrian; (5) FAD of arthropods, including trilobites, in the first half of the Early Cambrian (at the beginning of Atdabanian). We analysed the above mentioned ol3 C curves and can emphasize a prominent positive peak (up to +4-6 %0) in the following sections: lower Pestrotsvet Fm at Selinde, lower Emyaksin Fm at Bol'shaya Kuonamka, middle Medvezhya Fm at Kotuy and Kotuykan, upper Kessyusa Fm at Khorbosuonka. This peak in most sections is slightly above the FAD of mollusc Aldanella attleborensis, suggesting that it is already Tommotian in age (Parkhaev, Karlova, 2011). This level can be correlated with the similar excursion in the upper Yudoma Fm of reference curve on Aldan. The lower part of Pestrotsvet Fm at Selinde should be correlated with the upper part of Yudoma Fm on Aldan. In such a case there is no need to draw so-called 'subTommotian unconformity' (e.g. Knoll et aI., 1995a; Landing, Kouchinsky, 2016). The difference in lithology and fossil composition can be explained by the facies change and 'sliding' age of base of the Pestrotsvet Fm (slightly younger to SW). These assumptions corroborate the biostratigraphic data on SSF (Khomentovsky, Karlova, 2002, 2005; Parkhaev, Karlova, 20 II) and newly developed sedimentology model of for the Cambrian basin on the Siberian Platform (Sukhov et aI., 2016). A new detailed Ol3 C data from Yudoma section (Zhu et aI., 2017) with the prominent positive plateau in the upper Precambrian Yudoma Fm, contrasting the high amplitude oscillation pattern of corresponding part of Aldan or Sukharikha curves, suggest a necessity in high-resolution restudy of C-isotope characteristic of the Aldan type sections. 95
