Proxies for Climatic and Paleogeographic Evolution Geologica Acta: an International Earth Science Journal, Vol
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Geologica Acta: an international earth science journal ISSN: 1695-6133 [email protected] Universitat de Barcelona España AKHMETIEV, MIKHAIL A.; BENIAMOVSKI, VLADIMIR N. Paleogene floral assemblages around epicontinental seas and straits in Northern Central Eurasia: proxies for climatic and paleogeographic evolution Geologica Acta: an international earth science journal, vol. 7, núm. 1-2, marzo-junio, 2009, pp. 297- 309 Universitat de Barcelona Barcelona, España Available in: http://www.redalyc.org/articulo.oa?id=50513109018 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Geologica Acta, Vol.7, Nos 1-2, March-June 2009, 297-309 DOI: 10.1344/105.000000278 Available online at www.geologica-acta.com Paleogene floral assemblages around epicontinental seas and straits in Northern Central Eurasia: proxies for climatic and paleogeographic evolution MIKHAIL A. AKHMETIEV* and VLADIMIR N. BENIAMOVSKI Geological Institute RAS Pyzhevsky 7, Moscow 119017, Russia. * Corresponding author. E-mail: [email protected] ABSTRACT Paleogene connection of Tethyan and Paleoarctic water masses and biotas was largely enhanced by a N-S trend- ing epicontinental seaway in northern Central Eurasia, which extended from the Aral Sea to the Amerasian deep basin of the Paleoarctic. This seaway enabled warm waters to impinge into polar latitudes, being a kind of “radi- ator” for the Arctic. Its closure had immediate effect on climatic conditions and terrestrial flora in the Arctic and entire North Eurasia. The Kara and West Siberian epicontinental seas, which were the major components of this N-S trending seaway, were connected to adjacent oceanic basins by a system of straits. Opening, closure, nar- rowing and widening of these straits in the Early Cenozoic determined the evolution of the marine ecosystems and current development, as well as the related depositional processes and biota (especially flora). The evolu- tion of these straits also influenced on the Northern Hemisphere climatic fluctuations that took place during the Paleogene transition from a warm to a colder paleoclimatic state of the Earth system. KEYWORDS Paleogene. North Central Asia. Sea straits. Flora. Climate. INTRODUCTION field work and collection of plant fossils have continua- lly been carried out since the late seventies in a vast area The relevance of the Paleogene flora from Northern that comprises the Volga River and Aral Sea areas, the Central Eurasia was put forward during the 80–90’s of the Turgai Trough, the South and East Transuralian, the past century, when the Turgai Strait area was studied in Western Siberian Plate, the Zaisan Lake Basin and other detail in the frame of the IGCP Projects 174 (Terminal parts of Kazakhstan and Middle Asia (Fig. 1). In addi- Eocene Events) and 326 (Oligocene–Miocene Transition tion, private collections from many reference sections and in the North Hemisphere). These studies showed that the localities, such as Taizhuzgen, Kara-Biryuk and Kiin- Cenozoic floral record of this area is more complete Kerish (Zaisan Lake Basin), Romankol and Baky (South than that of West and Central Europe. However, many Ural and South East Transuralian), Zhaman-Kaindy and other localities from Northern Central Eurasia that are Tortmolla (Turgai Through), the Amur River area (many equally important remain less poorly known, although localities of Tsagayan–type Flora), the Volgograd district © UB-ICTJA 297 M.A. AKHMETIEV and V.N. BENIAMOVSKI Paleogene floral assemblages in Northern-Central Eurasia Gelinden Pripyat River Koryak Land East Ukraine Tastakh Kamchatka European Lake Dnieper River Black platform Lena River DonVoronezh River sea West Scythian MountainsSiberian plate Caucasus K Ural plate sea as Turanian Kivda plate akh Aral sea Amur River Turkmenia Caspian Belaya Gora s (Tsagayan) ta Mongolia Badkhyz n 0 400 km FIGURE 1 General map of North Eurasia showing geographic and tectonic elements mentioned in the text. Boxed area is that of Figures 2 to 4. Main localities of Paleogene flora are shown: Gelinden, Badkhyz, Belaya Gora, Kivda and Tastakh Lake. (Kamyshin) and some North Siberian localities have also Gulf of Mexico to the Beaufort Sea; and (2) the West been studied (Figs. 1 and 2). On the basis of this informa- Siberian–Turgai Basin in northern Central Eurasia. tion, Paleogene stratigraphic schemes of the Central and South Russian Plate, the West Siberian Plate and the In the Paleogene, after the Western Interior Basin was Transuralian area were established between 1997 and closed in the Maastrichtian, only the northern Central Eura- 2002, and the correlation of their main stratigraphic sub- sia epicontinental seaway remained (Figs. 1 to 3). These divisions was specified. marine zones, which included the Kara and West Siberian seas, as well as the straits connecting them with the oceans, As a result of all this work, Akhmetiev (1987, 1990, extended for 3,500 km from the Aral Sea in the south to the 2004 and 2005) described the Paleogene flora of the recent Franz Josef Land and the Severnaya Zemlya in the Northern Central Eurasia and compared it with other ana- north (Fig. 1 and 2). This N-S trending seaway defines a logues within the context of the Paleogene phytostratigra- boundary between palynologically established paleophyto- phy and palaeoclimatology. Unfortunately this informa- geographic subdivisions (i.e., kingdoms of Normapolles tion is not easily accessible, far less understandable, to and Aquilapollenites; Zaklinskaya, 1977). non-Russian researchers. Therefore, this paper deals with providing a comprehensive and updated summary that The strait system also controlled the surface and bot- might eventually prove useful to improve the knowledge tom marine currents, as well as Arctic upwelling. The cur- of the Paleogene global climate and distribution of floras. rents played a decisive role in life, dispersion and migra- tions of planktonic and benthic marine organisms. Water depth, shoaling and the total or partial desiccation of the PALEOGEOGRAPHIC SETTING seaway directly depended on differently oriented tectonic structures and paleogeographic rearrangements. Opening In the Late Cretaceous connections between Paleoarc- or closure of straits and the consequent reorientation or tic and Tethyan water masses and biotas were provided disappearance of currents influenced exchanges of water mostly by two N-S trending epicontinental seaways: (1) masses and biotas. Variations in biotic endemism deter- the Western Interior Basin of North America that mined similarities and distinctions of regional biostrati- stretched for 4,800 km along the Cordilleras from the graphic zonations and zonal correlations. Geologica Acta, 7(1-2), 297-309 (2009) 298 DOI: 10.1344/105.000000278 M.A. AKHMETIEV and V.N. BENIAMOVSKI Paleogene floral assemblages in Northern-Central Eurasia When the straits became closed or transformed into Arctic connections, as well as the evolution of sedimenta- gulfs, land bridges were formed and connected neigh- tion, flora and climate were determined by successive bouring areas. These bridges allowed animal and plant changes in sea and strait configuration, sea current direc- communities to migrate to the west and east of Eurasia tion, transgressive-regressive cycles and varying interaction (Shatsky, 1978; Akhmetiev and Beniamovski, 2006). of boreal, subboreal and subtethyan water masses and bio- tas. The most important moments and intervals of bios- pheric changes are summarized below (Fig. 3). Evolution of the Paleogene seaway in Northern Central Eurasia 1. The Cretaceous–Paleogene boundary time, when most of Eurasia and adjacent areas were above the The Paleogene history of the northern Central Eurasian sea level (Beniamovski, 2003, 2007) (Figs. 3 and system of epicontinental seas and straits and the Tethys– 4A). 80 0 20 40 60 80 100 Franz Josef Severnaya Land Zemlya 70 Novaya Zemlya 60 Ivdel Volga River Ul’yanovsk Ufa Kurgan Irtysh River Samara Ural Mountains Saratov 50 Volgograd Arkalyk Pavlodar Volga River Semipalatinsk Caspian syneclise 0 550 km Ashzheiaryk Chu-Sarysu Northern Zaisan Lake Ustyurt depression Plateau Aral Sea Balkhash Lake Chu-Balkhash 1 Kyzylkum threshold 2 depression 40 Dzhungar Alatau Caspian Sea FIGURE 2 Paleogeographic map of the Paleogene N-S trending system of epicontinental seas and straits in Northern Eurasia (modified from Beni- amovski, 2007). Location of paleogeographic features and geographic localities referred to in the text is shown. Key for Figures 2 to 4: 1 (grey): marine zones; 2 (white): emerged land. Geologica Acta, 7(1-2), 297-309 (2009) 299 DOI: 10.1344/105.000000278 M.A. AKHMETIEV and V.N. BENIAMOVSKI Paleogene floral assemblages in Northern-Central Eurasia 2. The Middle Danian transgression after the Creta- widespread, and bottom and subsurface currents existed ceous-Paleogene boundary regression. It resulted in a sys- (Fig. 3). The northern system of seas and straits supplied tem of sea-straits and different gulfs, which formed the the Kara–West Siberian Basin with boreal water masses N-S trending epicontinental seaway connecting the containing siliceous and organic-walled biota from the Tethyan and Arctic oceans and transported low-latitude, North Sea and Danish basins, whereas the southern sys- warm water masses into northern basins (Beniamovski, tem