PALYNOLOGICAL ZONATION OF MID-PALAEOZOIC, NW SPAIN 



125 



LP19), Geras (sample Ger 1 2) and La Vid (sample LV 10). This spore 

 event occurs in England in sections from Hereford and Worcester in 

 strata below the micrornatus - newportensis (MN) Zone. Although 

 the Aneiiwspom Sub-Biozone in the Cantabrian Mountains occurs a 

 little below (c. 5 m) the occurrence of the typical Lochkovian 

 chitinozoans Eisenackitina hohemica and Angochitina tsegelnjucki 

 (Geras), we regard the base of this Sub-Biozone as close to the 

 Silurian/Devonian Boundary (Richardson. Rodriguez & Sutherland, 

 2000). This correlation is based partly on comparisons with material 

 from Podoliadescribed by Arkhangerskaya( 1980). In Podolia, below 

 the base of the equivalents of the MN Biozone (Chortkov Group), there 

 is distinct spore assemblage in the Mitkov Formation (Borshchov 

 Group). This lower assemblage probably contains non-papillate 

 spores of the gtnu?, Aneurospora and is above the first occurrence of 

 the graptolite Mo/!Og ra/j?(M (//ir/o/v);/^ H/!//bn«/.y providing support for 

 the idea that the Anewrospora (A) Sub-Biozone is Devonian. Based on 

 the distribution of key chitinozoan species, Paris & Grahn ( 1 996) used 



the base of Motwgniptiis unifonnis unifonnis. the higher of the two 

 critical graptolite subspecies, to mark the base of the Devonian. In 

 particular Eisenackitina hohemica. also found by us in the Cantabrian 

 Mountains, and other restricted chitinozoan species occur in the upper 

 Tajna Formation along with M. unifonnis unifonnis. Although it is 

 difficult to be certain, because of the nature of the spore illustrations 

 (Arkhangel'skaya, 1980), this Lower Podolian spore assemblage 

 appears to include non-papillate species/varieties oiAneurospora and 

 may, therefore, be equivalent to the Aneurospora Sub-Zone. Assem- 

 blages with tripapillate spores (Aneurospora/Streelispora'l) occur in 

 the Chortkov Group c. 70 m above the Mitkov assemblage. The 

 Silurian/Devonian Boundary is currently placed at the first appear- 

 ance of M. unifonnis angustidens at base of the Borshchov Group 

 (Tajna Formation, Nikiforova, 1977) but no spore assemblages have 

 been described from the lower part of the Borshchov Group. Even so, 

 the position of the Silurian/Devonian boundary as determined by Paris 

 & Grahn seems reasonable from the spore evidence currently available. 



Pacific 

 Ocean 



Positive areas 



• Convergence i 



Fig. 7 Pfi'dolf palaeotectonic-palaeogeographic map. Simplified from Ziegler (1988). 



