Faunal shifts and climatic changes in the Upper Ordovician of South America (W Gondwana)

BENEDETTO J.L.; SANCHEZ, T.M.; CARRERA, M.G.; HALPERN K.; BERTERO, V.

Alcalá de Henares

Congreso; International Symposium on the Ordovician System; 2011

Instituto Geológico y Minero de España

According to the microcontinental model the Precordillera terrane rifted off Laurentia in the late Early Cambrian and then drifted through a relatively narrow Southern Iapetus Ocean to finally collide with the Andean margin of Gondwana during the Late Ordovician (Benedetto, 2004 and references therein). Such a trajectory from low to intermediate/high southern latitudes has been well documented by a progressive decrease of Laurentian faunal affinities and a correlative input of Gondwanan taxa. By the end of the Ordovician the Precordillera basin was inhabited by the typical Hirnantia Fauna which occurs immediately above the glacigenic deposits (Benedetto, 1986). Such paleogeographic changes took place under highly variable climatic conditions at global scale documented by lithologic, biological and stable isotopic data (mainly delta13C and delta18O). Most evidence used hitherto to establish global paleoclimatic models for the Late Ordovician comes from the continuous, essentially carbonate successions of Laurentia, Báltica and China, as well as from high-latitude basins of North Africa and perigondwanan terranes such as Iberia, Sardinia, Armorica and Perunica (e.g. Boucot et al., 2003; Fortey and Cocks, 2005; Ainsaar et al., 2010). In this paper we analyze paleoclimatic evidence from the well-known Precordillera terrane compared to the autochthonous Central Andean basin of NW Argentina and Bolivia. Since carbon isotope data from the Precordillera are still limited (Marshall et al., 1997), we use lithofacial, stratigraphic and paleontologic evidence in order to infer (1) a relatively warm paleoclimate during the Late Sandbian, (2) a probable Katian (Ka2- Ka3) warming interval partially equivalent to the Boda Event , and (3) a cool-water postglacial transgression recording the first stages of development of the Hirnantia Fauna.