PALYNOLOGICAL ZONATION OF MlD-PALAEOZOlC. NW SPAIN 



Leonispora argovejae Cramer & Diez 1975: pi. 1, fig. ^ (PI 7 

 fig. 5). 

 Reference section for base of sub-biozone. San Pedro For- 

 mation, Geras section, 70. 1 m above the base of the section (sample 

 Gerl4). 



Description. First appearance of tripapillate species of the 

 Aneitrospora - Streelispom complex {S. newporteiuis and Leonispora 

 argovejae), the non-papillate species A. richardsonii, and the 

 murornate and apiculate patinate species, Chelinospora cassicida, 

 C. media and Cymbosporites dittonensis. Spores with a well-devel- 

 oped zona first appear within the zone. Persistence of/?, coronadus 

 and appearance of spores with curvatural spines and a narrow 

 curvatural zona (Breconisporites'l sp. C; PI. 4, fig. 3) at the base of 

 the MN Biozone. 



Accessory species. In Britain the MN Biozone is divided into 

 three sub-biozones (Richardson, Ford & Parker 1984). With the 

 exception of A. richardsonii (Rodriguez) comb, nov., R. coronadus 

 Rodriguez 1983, and Breconisporites'l sp. C all the species listed 

 above occur also in the lower MN Sub-Biozone of the Anglo- 

 Welsh area and consequently the NA Sub-Biozone can be used 

 there also. 



Remarks. The MN Biozone is widely distributed. It is found in 

 England, Scotland, Wales, Belgium, Poland, Podolia (Ukraine), 

 Baltic States, northwest Spain and North Africa (Libya & Morocco), 

 northwest and southern China (Richardson & McGregor, 1986), 

 Poland (Turnau, 1986), and the U.S.A. (Wood, pers. comm.). 



Rare specimens of Telisporites sp. A and Emphanisporites cf. 

 decoratus (PI. 3, figs 2, 6) occur in the highest productive sample of 

 the La Vid section, also high in the Argovejo section ( sample Arg 14). 

 Raistrickia sp. (PI. 3, fig. 4), a taxon not found in England and Wales 

 at this level, also occurs in the Geras section. 



Occurence. The MN Biozone occurs in the upper San Pedro 

 Formation in the Argovejo, Geras, and La Vid sections. 



Age. Lower but not lowermost Devonian (Lochkovian) based on 

 spores, probably lowermost Devonian based on chitinozoans. 



AGE OF THE BIOZONES AND INTER- 

 REGIONAL PALYNOLOGICAL 

 CORRELATION 



Palynological correlation reveals several anomalies between the 

 ages based on chitinozoans and those on spores in three of the four 

 sections examined from the Cantabrian Mountains. There is evi- 

 dence for considerable reworking in three of the sections. In other 

 parts of the sections the data are consistent between the two fossil 

 groups and the sequence of spore zones can be traced throughout the 

 study area. All but the lower two zones in La Peral are found in at 

 least three localities. 



In spite of regional differences there are a number of species that 

 are found both in the Silurian type area of England and south Wales 

 and the current area of study. Of the four sections, that at La Peral is 

 farthest offshore and perhaps represents a more continuous spore 

 sequence less disturbed by reworking than the sediments in the 

 Argovejo, Geras and La Vid sections where the San Pedro Formation 

 is marginal marine in part. For this reason the La Peral section is 

 taken as our basis for correlation of our sections with those from the 

 Anglo- Welsh type area, and, although the preservation of the spores 

 is not as good in the La Peral section, it is nevertheless sufficient for 

 correlation with Britain up to the Aneurospora Sub-Biozone. 



123 

 La Peral Section (Figs 5, 6) 



LPl, LP2. These samples belong to the lowermost part of the San 

 Pedro Formation . The assemblages are relatively poor with only 

 thirteen cryptospore and miospore taxa recorded so far. (N.B. the 

 spore range charts are not published in full at this time and only 

 those important for local zonation are included in Fig. 5). 

 Chitinozoans indicate a Llandovery age for this interval and, al- 

 though some of the spore species also occur in the Upper 

 Llandovery they are long ranging forms. Sculptured spores e.g. 

 Scylaspora spp. have not been found in the type area below the 

 upper part of the Homerian Stage. This discrepancy between the 

 spore and chitinozoan data may be due to reworking of the 

 chitinozoan Spinachitina, as the transition from the underlying 

 formation to lower part of the San Pedro Formation constitutes a 

 regressive-transgresive cycle across the whole area. Thus, the 

 lower part of the San Pedro Formation in this area may represent a 

 transgressive cycle where reworking may be prevalent. Reworking 

 of Upper Llandovery spores would be practically invisible in im- 

 poverished younger assemblages as the spore records of 

 Ambitisporites spp. found in these samples range from the Upper 

 Aeronian (Llandovery) into the Devonian. 



LP3-LP5. This assemblage of sculptured cryptospores includes 

 typical Upper Homerian and Lower Gorstian forms such as 

 Artemapyra brevicosta, A. radiata, Hispanaedisciis lamontii and H. 

 verriicatiis. 



LP6-LP9. Stellatispora inframurinata var. camhrensis and spores 

 similar to Chelinospora obsciira. appear in LP6 and they are both 

 typical Gorstian species. The miospore species Concentricosisporites 

 Sagittarius (LP8) first occurs at the base of the Ludlow Series (basal 

 Gorstian) in the type area. All three taxa are key species in the Anglo- 

 Welsh area. This age is consistent with that indicated by chitinozoans 

 in sample LP8 dated as Middle Gorstian to Middle Pfi'doli age. 

 Stellatispora inframurinata is used as a zonal species in England and 

 Wales and is found in the Upper Gorstian and Ludfordian stages. 

 With the exception of 5. inframurinata, none of these forms has been 

 found above the Ludlow in the type area. In sample LP 10 (10 m 

 higher than LP 8) C. hemiesferica occurs for the first time, marking 

 the base of our H Biozone. 



LP12-LP16. The first appearance of Amicosporites splendidus may 

 mark either the uppermost Ludfordian or the lowermost Pfi'doli. 

 There were no chitinozoans in sample LP 12 but in the overlying 

 sample (LP16) chitinozoans typical of the Middle Pfi'doli have been 

 found. 



LP19. According to our research the genus Aneurospora marks a 

 level at, or near, the base of the Devonian. Unfortunately chitinozoan 

 evidence is limited and suggests a Lower to Middle Pfi'doli age. 

 However, in all the other sections studied the Aneurospora Sub- 

 Biozone is followed by the MN Biozone, which is found only in 

 Lower, not basal, Lochkovian. LP20 may belong to the MN Biozone 

 but lacks the nominal species. 



SPORE BIOZONES 



Scylaspora vetusta (V) Spore Biozone. This biozone has been found 

 only in the La Peral Section samples (LP 1 , LP2). The assemblage is 

 limited but contains Scylaspora vetusta and Retusotriletes abundo. 

 Both these species were found in North Africa (Richardson & 

 loannides, 1973) but the latter occurs 60 m above Wenlock/basal 

 Ludlow graptolites. Scylaspora and Synorisporites sp. indicate an 

 age not older than late Lower Homerian. 



