A new record of early Silurian land plant spores from the Paraná Basin, Paraguay (Malvinokaffric Realm)

Abstract

The first conclusive evidence for Silurian rocks in the Parana Basin, Brazil, was reported in 1985. This evidence was based on organic-walled microfossils, principally spore tetrads, and associated phytoplankton (' acritarchs' and prasinophytes), the first recovered from the Vila Maria Formation on the northeastern rim of the Basin. The spore assemblage was typical of Gray's Microfossil Assemblage Zone I; size-frequency data for the tetrads suggested an early Silurian (early Llandovery; Rhuddanian) age. We now document a new MA Zone I occurrence of spore tetrads together with a few single trilete spores, from the southwestern rim of the Parana Basin, Paraguay. The single spores are among the earliest known to have normally dissociated from a tetrahedral tetrad. Size-frequency data for the tetrads suggest a late Llandovery, pre-C 5 (mid-Telychian) age. These spores, together with phytoplankton and chitinozoans, were recovered from beds laterally equivalent to the Vargas Pena Shale at the type locality from which Llandovery diplograptids and monograptids are known. Llandovery age rocks on the southwestern and northeastern borders of the Parana Basin, c. 1400 km apart, suggest that early Silurian rocks were extensively distributed throughout southern Brazil and adjacent Paraguay. Close conformity between the age reference obtained with graptolites and spore tetrads again demonstrates the stratigraphic utility of early Silurian spores in providing reliable age determinations for otherwise unfossiliferous rocks. Spore tetrad assemblages available from the Malvinokaffric Realm (South America, Africa, Arabia) represent a distinct phytogeographic unit contrasted with spore tetrad assemblages from the North Silurian Realm of North America and parts of Europe.

Silurian and lower devonian chitinozoan biostratigraphy of the paraná basin in brazil and Paraguay

“…The Vargas Pefia Formation in east Paraguay, or the Vila Maria Formation and its equivalents in south Brazil, are now generally considered as Llandovery s.l. in age (Wood and Miller, 1991;Gray et al, 1992;Borghi et al, 1997).…”

Late Ordovician-earliest Silurian palynomorphs from northern Chad and correlation with contemporaneous deposits of southeastern Libya

“…Such assemblages are known from South America in Brazil and Paraguay (Gray 1991;Gray et al 1985Gray et al , 1992Laranjeira et al 1997;Melo 1997;Melo & Steemans 1997;Mizusaki et al 1992;Steemans 2000;Steemans & Pereira 2000), from North America (Strother & Traverse 1979, Miller & Eames 1982, Duffield 1985, Johnson 1985, from Europe in Belgium (Steemans 2001), Bulgaria (Lakova et al 1992), the Czech Republic (Vavrdová 1984(Vavrdová , 1988(Vavrdová , 1989, United Kingdom (Burgess 1991, Wellman 1996, from Asia in China (Wang et al 1997), Turkey (Steemans et al 1996), Saudi Arabia , and from north Africa in Libya (Richardson 1988).…”

“…Littoral to nearshore conditions for the association are proposed in the second assemblage of Moussegouda, but also in the samples from KW-2 in the Kufra Basin, is consistent with significant freshwater input. This is supported by the presence of forms such as Moyeria cabottii regarded to be of freshwater origin (Gray & Boucot 1989, Dorning & Harding 1998. The good representation of miospores, and tubular structures (Tortotubus protuberans) believed to derive from nematophytes (Wellman 1995), is further evidence of deposition in a nearshore shallow water marine environment.…”

Late Silurian-Middle Devonian Miospores

“…Many studies (Gray 1992;Richardson 1988;Steemans 1999a, b) reported possible cryptospores from Middle and late Ordovician. The recorded possible cryptospore assemblages from deposits older than Caradoc are either naked or enclosed within a thin, smooth or variously ornamented envelops.…”

“…However, (Wellman and Richardson 1993;Strother and Traverse 1979;Richardson 1992;Gray et al 1992;Wellman and Gray 2000;Steemans 1999b) believe that the structure and morphology of these early miospores are atypical comparing with existing miospores of younger ages, therefore some times, embryophyte miospores been used as cryptospores. This is due to that the widely spread vegetation was of restricted diversity and diminutive evolutionary change.…”