Silurian Palynomorphs

The data obtained from an independent study of acritarchs, chitinozoans and miospores enables the determination of maximum age ranges of samples taken from three wells. These are shown in Fig. 8. ACRITARCHS At present, samples have been examined from six wells – A1-46, Core 2; E1-81, Cores 3, 4; F1-46, Core 3; D-31, Core 1; A1-81, Core 3 and C1-31, Core 8. The last mentioned is considered no further here as all samples have to date proved barren. The oldest of the acritarch assemblages are recorded from E1-81, Cores 3, 4 between 1850ft. and 2340ft. (Fig. 8) and from A1-81, Core 3 between 3750ft. and 3773 ft. These are dominated by the polygonomorph acritarchs, Veryhachium trispinosum and V. valiente but also include acanthomorphs such as Diexallophasis and Multiplicisphaeridium. The lack of diagnostic acritarchs of post convolutus zone would indicate the age of the samples as Rhuddanian to Early Aeronian but no higher than convolutus zone. Wells A1-46, Core 2 between 9710 to 9721 ft. (Fig. 8); D1-31, Core 1, 6105 to 6160ft. (Fig. 8) and F1-46, Core 3, 8852 to 8858 ft. all yield rich assemblages dominated by Multiplicisphaeridium, Diexallophasis and Veryhachium and characteristic species of Visbysphaera, Cymbosphaeridium, Oppilatala and ?Dateriocradus. The presence of forms such as Oppilatala eoplanktonica, ?Dateriocradus monterrosae, Multiplicisphaeridium arbusculiferum, Diexallophasis caperoradiola and Visbysphaera gotlandicum indicate the assemblages are of post-convolutus zone age, thus late Aeronian, as an oldest date. Regional palynological differences in the acritarch assemblages are observed between North Africa and Great Britain, which are consistent . . .

Neoveryhachium carminae is recorded sporadically in most of the samples under study and is a dominant form in Well C1-44, located in Sirte Basin west of the study area.
Formigoso Formation (Cramer & Diez, 1978). From these data it seems likely that the Silurian samples from Wells El-81, A1-81 and D1-31 (except in D1-31,6105 to 61 06 ft., where Cyarhochitina was not recorded) are not younger than the early Telychian. In addition, in Well D1-3 1 the occurrence of a few individuals of Conochitina proboscifera and C . (Densochitina) densa is noted, both species are well represented in the uppermost Llandovery and early Wenlock of Gotland (Laufeld, 1974).
On the basis of chitinozoans, the age assignment of level 9710ft. in Well A1-46 is more difficult to establish. Indeed the individuals are rare and the occurrence of a form, closely related to Margachirina feonensis from the Pridoli of Spain (Cramer, 1964), in association with Early Silurian taxa (P. deichaii and C . edjelensis elongatu, and a form quite similar to P . spongiosa), is still unexplained, even though a late Llandovery age is expected for this assemblage.

MIOSPORES
Silurian miospores have been obtained from core material of two wells, El-81, (1968 and A1-46 (9710 to 9721 ft.). The assemblages from the two wells are distinct although showing some features in common. The older of the two miospore assemblages (Well El-81) consists entirely of dyads and tetrads with some possible alete spores. Dyads e.g. Dyadospora rnurusdensa, and 'permanent' tetrads, Nodospora sp., are the most common. Some of the dyads are surrounded completely by a diaphanous sheath. In these respects, and in the absence of single grain trilete miospores (i.e. those separated from tetrads), the Well El-81 assemblages resemble those from the Medina Group (Rhuddanian, early Llandovery) of the Niagara Gorge (Miller & Eames, 1982). However, the North African assemblage contains occasional specimens of "loose" tetrads, which may suggest a younger age, but is otherwise less diverse than the Niagara Gorge assemblages. The provisional age for this level is early Llandovery and probably Rhuddanian. The basis for this age is partly the close similarities with the Rhuddanian assemblages from Niagara Gorge. In addition Hoffmeister's (1959) Libyan assemblages containing Arnbitisporites were dated on graptolites as early to middle Llandovery and the Well El-8 1 assemblage is therefore probably older but few well-dated spore assemblages have been described of this age.
A more varied and younger assemblage occurs in the sample from Well A1-46 (9710 to 9721 ft.). Two species of dyad are present Dyadospora rnurusdensa and D . murusattenuata, associated with "permanent" tetrads Nodosphaern sp., and Rugosphaeru sp., and trilete spores Arnbitisporites dilutus. The age of this assemblage is post Rhuddanian to earliest Telychian, approximately Aeronian but probably not earliest Aeronian. This correlation is made on the assumption that the early/middle Llandovery age of Hoffmeister's material (Berry, in Gray and Boucot,197 1) is roughly equivalent to the middle of the magnus zone (early Aeronian).
onniensis ranges from Late Caradoc up to Ashgill).

Explanation of Plate 16
All figures are X 1000 Fig. 1. Archaeozonotriletes cf.