Eifelian-Givetian diversity trends in palynofloras of northwestern Argentina.

NOETINGER, S.; DI PASQUO, M.M.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IANIGLA

This study aims to elucidate diversity trends during the Middle Devonian in northwestern Argentina through the characterization of palynological events. A dataset of spore genera counts from two boreholes (San Antonio x-1, Santa Victoria x-1), ranging in age from the Eifelian to Givetian, was analyzed. Several measures of diversity were compiled and contrasted with the composition of the floras. The Simpson, Shannon-Wiener and standing diversity indices together with Pielou and Hurlburt?s evenness measures were calculated. The standing diversity reaches its maximum during the Eifelian and rapidly decreases towards the Givetian. This tendency is also supported by the other computed parameters. The floras, during the Eifelian, are composed of apiculate, cavate and boldly sculptured spores represented mainly by the genera Apiculiretusispora, Grandispora and Verrucosisporites respectively. The decline in the evenness, towards the top of the sections, is shown when the Verrucosisporites genus outnumbers in the assemblages. This pattern is seen in other parts of Gondwana during the same time frame, where the increment of this particular genus, associated with filicopsids, co-occurs with the inception of Geminospora lemurata and Biharisporites parviornatus. The latter species have a well defined onset worldwide during the late Eifelian ? early Givetian and are known to have affinities with archaeopteridales. Both, marine and continental elements, support a marginal depositional setting, with little shoreline shifts for both assemblages during the Eifelian. By the early Givetian there is a significant increment of the marine components. Changes in the diversity and palaeoenvironment suggest that stressed environments occurring during the late Eifelian - early Givetian led to the predominance of few existing species and the inception and establishment of new ones in the floras of this region.