Microplankton changes through the early Silurian Ireviken extinction event on Gotland, Sweden

D.N Gelsthorpe

doi:10.1016/j.revpalbo.2003.12.003

Abstract

This paper documents and analyses the extinction and origination patterns of acritarchs and prasinophyte algae at the Llandovery/Wenlock boundary transition in the Lower Silurian on the island of Gotland, Sweden. Closely spaced samples were collected from two parallel sections: Lusklint 1 and Lickershamn 2, spanning the upper part of the Lower Visby Beds and almost all of the Upper Visby Beds (i.e. the uppermost Llandovery and lowermost Wenlock). At least eight extinctions affecting the conodont record have been reported at these levels. This turnover (named the Ireviken Event) has been interpreted as an example of the change from a P to an S climate state, reflecting large changes in the ocean/atmosphere system. The palynomorph data show a significant turnover in the phytoplankton, with most of the extinctions at the end of the event (85.3% in the top 4 m of the Lusklint 1 section). The originations are more numerous than the extinctions and they are distributed through the whole of the Ireviken Event. There is an uneven distribution across the event with more originations in the Lower Visby Beds forming a convex pattern. Comparison of these data to other palynological studies suggests that there was a slightly higher number of migrations out of Gotland than in. The P and S model does not successfully explain all the changes recorded, but is the model most inclusive of all the climatic variables available at this time.

Highlights

This chapter begins with a description of the sampling technique, goes on to describe in detail the processing technique used and outlines previous research
DGOOLKl.257 yielded 33 acritarchs (0.8 < 7 pm acritarchs per gram of sediment), of which 24 were Leiosphaeridia spp., the remainder consisting of Domasia trispinosa, Veryhachium trispinosum, Diexallophasis gotlandica, Micrhystridium stellatum and Cymatiosphaera aff. ledburica
Two important points that emerged from Colbath’s (1985) investigations still remain: consistency of technique and the trade-off between the accuracy of results and the time incurred in obtaining them. 100% repeatability of results is unlikely to be achieved; repeat sampling of modem biological communities gives a certain percentage of random variation (Watkins et al 1990, Muylaert et al 2000)

Summary

Introduction

This chapter begins with a description of the sampling technique, goes on to describe in detail the processing technique used and outlines previous research. The processing method is often tailored to the sample being analysed and the equipment available, it is important to maintain some constant factors and to quantify the losses experienced. Consistency of processing technique is the most important factor, so that samples can be compared. Several publications outline techniques used in extracting palynomorphs from rock. These reviews include Funkhouser & Evitt (1959), Gray (1965), Barss & Williams (1973), Forster & Flenley (1989), Litwin & Traverse (1989), and Wood et al (1996). Colbath (1985) is the only author who used Silurian material to compare some of the extraction techniques available These reviews include Funkhouser & Evitt (1959), Gray (1965), Barss & Williams (1973), Forster & Flenley (1989), Litwin & Traverse (1989), and Wood et al (1996). Colbath (1985) is the only author who used Silurian material to compare some of the extraction techniques available

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Conclusion