Spore-pollen biostratigraphy of the English Jurassic
Srivastava, Satish K.
published: Jun 27, 2011
An analysis of 204 samples collected from 34 localities, representing almost all Jurassic ammonite zones of England, yielded 63 species of 51 spore-pollen genera and one species of a fungal genus Annella. The appearance of various spore-pollen taxa characterizes all the Jurassic Stages. Gliscopollis meyeriana and Heliosporites altmarkensis occur first in the Hettangian. Bisaccate pollen and Classopollis classoides form the major part of the assemblage in the lower part of the Sinemurian. Fern spores Cingutriletes, Deltoidospora, Dictyophyllidites, Hamulatisporis, and Retitriletes also appear in the Sinemurian. Dinocysts appear abundantly in the upper part of the Sinemurian indicating an increased marine influence. Baculatisporites comaumensis, Ceratosporites sp., Duplexisporites problematicus, Gleicheniidites senonicus and Obtusisporis juncta make their first occurrence in the Pliensbachian. Most of the specimens of almost all the species recovered in the Pliensbachian are corroded and show circular degraded areas which are considered to have been formed by the fungal species Annella capitata and A. pulchra. The triangular or polygonal degraded areas are probably formed by pyritic inclusions. Only corroded and poorly preserved spore-pollen were recovered from the Toarcian except the appearance of Matonisporites phlebopteroides from the basal ammonite zone of the Toarcian. No well preserved spore-pollen occurred in the Aalenian. Araucariacites australis, Balmeiopsis turbata, Callialasporites dampieri, Concavisporites twentianis, Densoisporites velatus, Laevigatosporites ovatus, Leptolepidites major, Retitriletes singhii and Vitreisporites pallidus appear in the Middle Jurassic at the base of the Bajocian. The Bajocian spore pollen assemblages also show biogenic degradation. The appearance of genera Foveosporites, Klukisporites, Lycopodiacidites, Sestrosporites and Uvaesporites distinguishes the Bathonian Stage and shows an increase in diversity of fern spores in this Stage. Most of the Callovian samples, particularly those from the Yorkshire localities, are dominantly rich in dinocysts and bisaccate pollen. Samples from the Dorset locality are rich in well preserved spores and pollen. The genera Biretisporites, Camarozonosporites, Coronatispora, and Neoraistrickia appear in the upper Callovian, indicating a progressive increase in fern species. The occurrence of Densoisporites, Kraeuselisporites, Matthesisporites, Staplinisporites and Trilites differentiates the Oxfordian Stage. Spore-pollen assemblages of the Oxfordian are also biogenically degraded. Converrucosisporites exquisitus occurs at the base and Contignisporites cooksoniae at the top of the Kimmeridgian. No new spore-pollen appearance was noted in the Portlandian. The appearance of Cicatricosisporites mohrioides, C. venustus, Coronatispora valdensis, Distaltriangulisporites perplexus and Ruffordiaspora australiensis in the Cypridea granulosa fasciculata Zone of the middle Purbeckian marks the Jurassic/Cretaceous boundary. A comparison of assemblages of the Jurassic stages of England with those of France and Germany shows considerable differences in the yield of spores-pollen despite the depositions being generally in a deep marine realm.