Palaeogeography

Fig. q. The world during the Early Cenozoic. Positions of the continents after Briden et al. 1974.

The palaeolatitude of England and Germany during most of the Palaeogene was approximately 40° N (Fig. q); the climate throughout this time was certainly warmer than the present and, in general, the faunas and floras indicate subtropical and tropical conditions (Fig. r).

Fig. r. Northern Europe during the Early Cenozoic. (Modified after Ziegler, 1975).

The history of the north European Cenozoic is effectively the history of the North Sea Basin, where deposition has occurred almost continuously from the Palaeocene to the present.

In the Mesozoic, rifting occurred in the North Sea area associated with the beginning of the crustal separation of the European and the North American-Greenland plates. When plate separation had taken place, and the North Atlantic rifting was under way in Late Palaeocene and Early Eocene times, rifting in the North Sea ceased. It was probably about this time that the Early Cenozoic basalts of Northern Ireland and north-west Scotland erupted.

Neogene:

Pleistocene

Pliocene

Miocene

Palaeogene:

Oligocene

Eocene

Palaeocene

Table IX Stratigraphic Divisions of the Cenozoic

Many of these lavas have red weathered tops and are overlain by sediments which suggest terrestrial conditions. Thus it can be assumed that during the time of most of this igneous activity the area between the North Sea and the Atlantic was uplifted. Much of Britain has remained above sea level ever since, though the south of England and East Anglia have been submerged from time to time. The North Sea, however, has continued to subside since the Eocene.

In the Palaeogene (Table IX), the sea covered south-east England, northern France and Belgium, and extended into northern Germany, Denmark and Poland. Most of Britain was above sea level, and the North Sea Basin was closed on the south-west, south, and east by several small land areas (Fig. 4), but had periodic connections with the early Atlantic Ocean along the line of the present western English Channel. To the north, in the vicinity of Norway, there was a probably more permanent connection with the Atlantic, but this is not clear.To the south, the Aquitaine Basin, another shallow marine basin, opened on to the Atlantic, which, further south, joined with the Tethys Ocean. The British Isles then were at the western edge of this sea, and in the Palaeogene beds of south-east England we see alterations of fully marine conditions, estuarine deposits and deltaic fluviatile and marsh sediments, as the shore line of the Palaeogene sea oscillated across south-east England (Curry, 1965, 1967).

To the south of the North Sea Basin lay the gulf of Aquitaine and the Tethys Ocean, and there were intermittent connections between these three areas throughout the Palaeocene.

The Tethyean shallow water faunas are characterized by a high diversity and abundance of nummulitic foraminfera of which only a few species penetrated as far north as the North Sea Basin. The molluscan and echinoid faunas of the Tethys were also much more diverse and many genera such as Tridacna, Strombus, Lambis, Cypraea, now typical of the modern tropical Indo-Pacific province, originated at this time. Throughout the Palaeocene of Europe there are beds containing high proportions of Tethyean fossils indicating periodic warming of the sea water.

Hamstead Beds Bembridge Beds and

Osborne Beds Headon Beds Barton Beds

Bracklesham and iVIarine, estuarine and lacustrine clays

Marine and freshwater marls and limestones

Marine and freshwater sands and clays Marine sands and clays Marine and fluvial sands

Bagshot Beds London Clay Oldhaven and

Marine clay witn a basal sand Estuarine sands

Blackheath Beds

Woolwich and Reading Beds

Thanet Beds

Marine and estuarine clays and sands with freshwater clays

Marine sands

Table X The Palaeogene formations of southern England

At the end of the Cretaceous, the sea had withdrawn eastwards from most of Britain, and the Chalk was gently deformed and tilted towards the south-east. Palaeogene sedimentation in England began with a marine transgression when sands were deposited in the London Basin. Further transgression of the sea covered most of south-east England from the Isle of Wight to East Anglia. Large rivers to the west and north-west deposited deltaic and fluviatile sediments in the western and southern parts of the sea (Reading Beds) whilst further to the east were estuarine mud flats followed by offshore sands (Woolwich Beds) (Table X).

Further deposition of estuarine sediments, again showing progressively reduced salinities in the west, is shown in the Oldhaven and Blackheath beds. The transgression which marked the beginning of the London Clay (which consists of sands below and clay above) spread over the whole of south-east England and extended over northern France into north-west Germany and Denmark. The London Clay sea in the London area was at least 100m deep, but to the west, in the Hampshire area, it was much shallower. The north-eastern part of this sea in the vicinity of Denmark was clearly much deeper, and fine laminated clays were deposited containing few benthic animals but abundant plankton. Volcanoes to the north deposited ash layers in the Denmark area, one of these extending as far south as Harwich in Essex. A connection between the London Clay sea and the Atlantic in the south, in the region of the present western English Channel, may have opened in late London Clay times. In the Hampshire Basin, the London Clay was much more sandy and shallow, and its shoreline facies can be recognized in the Isle of Wight. The margins of the London Clay seas were covered with subtropical plants, and land temperatures seem to have been about 20—25° C, although foraminiferal evidence indicates shallow water temperatures of about 16° C.

Towards the end of London Clay times the water became shallower, and fluviatile and deltaic sediments are present over most of south-east England. The succeeding Bracklesham Beds exemplify well the marginal character of the marine environments close to the shoreline, showing interdigitations of deltaic and fluviatile sediments with normal shallow water nearshore shelf sediments. At the end of Bracklesham times a further marine transgression resulted in south-east England being covered by a shallow shelf sea with a water depth up to about 100m and with clay and sand deposits, the Barton Beds. This sea gradually decreased in depth, apparently through silting up, and turned into the shallow lagoons and freshwater lakes of the lower Headon Beds. A further small marine transgression in middle Headon times was again succeeded by estuarine and lacustrine conditions represented by the Upper Headon, Osborne, Bembridge and Lower Hampstead Beds (Daley, 1972).

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