The discovery of a Middle Eocene diatom flora from Whitecliff Bay, Isle of Wight, England

Author(s):  
Alexander G. Mitlehner ◽  
Malcolm B. Hart
2021 ◽  
Author(s):  
Malcolm Hart ◽  
Pritpal Mangat ◽  
Meriel Fitzpatrick

<p>The Paleogene section of Whitecliff Bay (Isle of Wight) is one of the most complete onshore successions in North West Europe (see Curry, 1965, 1966). The microfossil assemblages have been investigated by many micropaleontologists and the succession of foraminifera, ostracods, calcareous nannofossils, pteropods, diatoms, charophytes and dinocysts have been described in varying levels of detail. The planktic foraminiferal datum (Wright, 1972; Murray et al., 1989) in the Lower Eocene and the occurrence of larger foraminifera in the mid-Eocene provide evidence of incursions of warm water taxa that may be recording the presence of the Early Eocene Climatic Optimum (EECO) and the Middle Eocene Climatic Optimum (MECO) although these occurrences could equally be caused by changes in palaeogeography, glacio-eustasy and the general depositional environment.</p><p>Over a period of over 40 years samples have been collected from both the cliff succession and, at times of lowered sediment levels, on the foreshore which can often provide 100% exposure of the succession. Preservation of microfossil assemblages in samples is always better when collected from the foreshore while the cliff succession often records no calcareous (e.g., foraminifera) or siliceous microfossils (e.g., diatoms).</p><p>Both EECO and MECO are recorded as being brief, transient events while the palaeontological variations look to be of an altogether longer duration. Stable isotope data are limited (Dawber et al., 2011) and, at the present time, do not provide precise confirmation of isotope excursions precisely synchronous with the palaeontological distributions. Nevertheless, the evidence of northward migration by warm-water taxa is quite distinctive and worthy of still further investigation. In the case of MECO, the presence of Nummulites spp., Alveolina fusiformis and corals is certainly suggestive of warm-water migration into the northern confines of the Anglo-Paris-Belgian Basin.</p><p>Curry, D., 1965. The Palaeogene Beds of South-East England. Proceedings of the Geologists’ Association, 76(2), 151‒173.</p><p>Curry, D., 1966. Problems of correlation in the Anglo-Paris-Basin. Proceedings of the Geologists’ Association, 77(4), 437‒467.</p><p>Dawber, C.F., Tripati, A.K., Gale, A.S., MacNiocaill, C., Hesselbo, S.P., 2011. Glacioeustasy during the middle Eocene? Insights from the stratigraphy of the Hampshire Basin, UK. Palaeogeography, Palaeoclimatology, Palaeoecology, 300, 84–100.</p><p>Wright, C.A., 1972.  The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proceedings of the Geologists’ Association, 83, 413‒419.</p><p>Murray, J.W., Curry, D., Haynes, J.R., King, C.,1989. Palaeogene. In: Jenkins, D.G., Murray, J.W. (eds), Stratigraphical Atlas of Fossil Foraminifera [2<sup>nd</sup> Edition] (eds), British Micropalaeontological Series, Ellis Horwood Ltd, Chichester, 490‒536.</p>


2011 ◽  
Vol 122 (3) ◽  
pp. 472-483 ◽  
Author(s):  
Alex De Jonghe ◽  
Malcolm B. Hart ◽  
Stephen T. Grimes ◽  
Alex G. Mitlehner ◽  
Gregory D. Price ◽  
...  
Keyword(s):  

A study of rock-samples collected at 26 stations and continuous seismic profiles taken over a distance of 2000 km in the eastern part of the English Channel reveals the existence of a large flat-floored Tertiary syncline which forms an easterly extension of the Hampshire Basin of Southern England. The newly delineated basin, which is here referred to as the Hampshire—Dieppe Basin, forms part of the well-known Palaeogene Anglo-Paris-Belgian depositional basin. The total thickness of Palaeogene strata in the eastern part of the basin is about 380 m and the youngest beds present are probably of Upper Eocene age. Upper Cretaceous strata are exposed around the edges of the basin; the thickness of the Chalk varying from about 250 m in the south and east to 420 m in the northwest. The basin is bounded to the northeast by the Weald—Artois anticline and a strong flexure, the Bembridge—St Valery line, which is a continuation of the Isle of Wight monocline, controls the position of much of its southwestern boundary. To the south of the Hampshire-Dieppe basin lies the Baie de la Seine Tertiary syncline. Here, freshwater limestones of presumed Oligocene age overlie a Middle Eocene marine sequence. Lithologies and microfaunas of the samples are described and related to those of sequences of similar age on nearby land, and some conclusions are drawn about the palaeogeography of the area. The geological structure of the area is elucidated, the paths of faults and fold axes are traced and a geological map is presented.


In 1863, Heer and Pengelly published in the ‘Phil. Trans.’ an account of these lignite-beds and their flora. Heer classed the lignite as Lower Miocene, considering it equivalent to the Aquitanian of Prance and to the Hamstead Beds of the Isle of Wight. These latter are now referred to the Middle Oligocene, and many of the other deposits called Lower Miocene in Heer’s day are now classed as Upper Oligocene. A statement by Mr. Starkie Gardner, that Heer’s Bovey plants are the same as those found in the Bournemouth Beds (Middle Eocene), has caused the Bovey Beds to be classed as Eocene in recent text-books and on recent maps of the Geological Survey, leaving a great gap in the geological record in Britain. Every division, from Upper Oligocene to Upper Miocene, was supposed to be missing.


The lignite of Bovey Tracey, in Devon, was fully described by Oswald Heer and Pengelly in these ‘ Transactions,' and there is no need to repeat their description. The conclusion Heer came to, from the study of the fossil plants (except a single beetle there were no other fossils), was that the deposit “must be referred to the Lower Miocene division and to the Aquitanian stage of it,” or as we should now put it, the strata were Upper Oligocene or, perhaps, Lower Miocene. Heer also considered it to be equivalent to the Hamstead Beds of the Isle of Wight, which we now know are somewhat earlier than the Aquitanian and are of Middle Oligocene date. Doubt has since been thrown on these conclusions by Mr. Starkie Gardner, who considered that the flora collected by Heer and Pengelly is identical with that of the Bournemouth Beds (Middle Eocene). Mr. Gardner appears to have made no collections at Bovey, and in his Bournemouth collections (now in the Museum of Natural History) we can find nothing to justify this statement. Perhaps this extreme view is somewhat modified by later changes in the identification of some of the plants.


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