Neogene

During the Miocene and most of the Pliocene, the shores of the North Sea Basin lay to the east of Britain, and marine deposition took place in northern Germany and Denmark. The shoreline advanced westwards again in the late Pliocene and early Pleistocene.

From the Miocene onwards, marine faunas consist increasingly of extant species, including, in the north-west European deposits, species found today in the west Atlantic and the Mediterranean. The present day latitudinal sequence of faunas, or provinces, in the west Atlantic was more or less in existence by Pliocene times.

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However, the position of the province boundaries fluctuated to the north and south with climatic warming and cooling.

Pliocene and Pleistocene marine sediments in Britain are represented by a series of deposits in East Anglia. These are often small in area, fragmentary, and difficult to relate to a coherent sequence of events or paleogeographic reconstructions. The best known of these deposits are the Coralline Crag of late Pliocene age which occurs in a small area of Suffolk, and the Red Crag which occupies a wider area of East Anglia and Essex.

117 Pliocene Marine Gravel Communities

Bryozoans were particularly abundant in these deposits, and among the species were forms normally found encrusting gorgonian corals. Flat-conical free-living colonies of Cupuladria canariensis were common; they were raised clear of the sediment on stilt-like setae. Another bryozoan, Hippoporidra, formed botryoidal growths on shells inhabited by hermit crabs (Fig. 117, 7). The molluscs were extremely diverse. They make up the first community we have considered in which many of the species are still living in the northwestern Atlantic and the Mediterranean. The epifaunal species included the byssate Cardita senilis. The scallop Chlamys opercularis was common; it lived on the sediment surface, but was a very active swimmer if disturbed. The brachiopod Terebratula maxima was common; it was the largest terebratulid ever known, reaching a length of 1 lcms.

Infaunal bivalves included the shallow-burrowing gravel-dwelling Glycymeris, Astarte, Arctica and Venus casina. Deeper bur-rowers included Phacoides borealis and Mya truncata. An even deeper burrower, Panopea, was common in places. Gastropods are represented by the ciliary suspension feeder Turritella communis, the scavenger Hinia reticosa, the bivalve predator Natica and the ascidian-feeding Trivia arctica.

Similar bryozoa-rich communities to this are found today in shelf environments at depths up to about 50m, on sandy substrates and hardgrounds. The bryozoan Cupuladria is restricted today to waters with a mean temperature in excess of 14° C, and thus equivalent to a latitude south of Portugal. The molluscan fauna in general confirms this estimate of palaeotemperature.

Fig. 117 Pliocene Marine Gravel Communities a Arctica islandica (Mollusca: Bivalvia: Veneroida)

b Mya truncata (Mollusca: Bivalvia: Myoida)

c Astarte omali (Mollusca: Bivalvia: Veneroida)

d Chlamys opercularis (Mollusca: Bivalvia: Pterioida)

e Glycymeris glycymeris (Mollusca: Bivalvia: Arcoida)

f Venus casina (Mollusca: Bivalvia: Veneroida)

g Lucinoma borealis (Mollusca: Bivalvia: Veneroida)

h Cardita senilis (Mollusca: Bivalvia: Veneroida)

i Terebratula maxima (Brachiopoda: Articulata: Terebratulida)

j Turritella incrassata (Mollusca: Gastropoda: Mesogastropoda)

k Emarginula fissurata (Mollusca: Gastropoda: Archaeogastropoda)

1 Natica millepunctata (Mollusca: Gastropoda: Mesogastropoda) m Hinia reticosa (Mollusca: Gastropoda: Neogastropoda)

n Trivia coccinelloides (Mollusca: Gastropoda: Mesogastropoda)

o Temnechinus excavatus (Echinodermata: Echinoidea)

p Balanus crenatus (Arthropoda: Crustacea: Cirripedia)

q Sphenotrochus intermedia (Coelenterata: Anthozoa: Scleractinia)

Gastropoda

t gorgonian (Coelenterata: Anthozoa: Octocorallia) u alcyonarian (Coelenterata: Anthozoa: Octocorallia) v bryozoan (Bryozoa: Ectoprocta) w sponge (Porifera) x bryozoan (Bryozoa: Ectoprocta) y Hippoporidra (Bryozoa: Ectoprocts) encrusting a shell inhabited by hermit crab

The fish faunas found here are largely similar to those of the north-west Atlantic of the present day, and include forms such as the cod which feed mainly upon benthic invertebrates such as molluscs and Crustacea. These deposits are found only in a restricted area of Suffolk; they consist of cross-bedded gravels and coarse calcarenites, made up largely of bryozoan fragments and broken mollusc shells. Fossils are extremely rich and diverse, but it is obvious that the beds consist of post mortem accumulations and represent a variety of actual communities.

118 Pleistocene Sublittoral Sand Community

The community illustrated represents a shallow sublittoral habitat perhaps from 10 to 15m deep, with a sandy substrate and abundant shell debris. Epifaunal animals included clumps of suspensionfeeding Mytilus, the scallop Chlamys opercularis and Balanus crenatus. Common gastropods were the scavenging Nassarius granu-latus, Nassarius reticosa, the predatory Neptunea antiqua and the sinistrally coiled Neptunea contraria which today feed largely on polychaetes and bivalves. The infauna was both abundant and diverse, chiefly suspension-feeding bivalves; particularly abundant were Glycymeris, Macoma, Arctica, Spisula and the deeper-burrowing Phacoides borealis. Other communities were represented in the Red Crag deposits, and at some horizons an abundance of the cockle Cerastoderma, the winkle Littorina littorea and the dog whelk Nucella indicate intertidal conditions.

A large proportion of the species found in the Red Crag are found in British seas today; some species such as the large whelk Neptunea despecta are found in colder Arctic waters, whereas Neptunea antiqua is found around British shores. The sinistrally coiled Neptunea contraria is found off the Atlantic coast of France, Spain and Portugal and in the Mediterranean. The changing proportions of these three species at various horizons in the Red Crag deposits, with Neptunea contraria becoming less abundant higher in the rock sequence as Neptunea despecta appears, has been interpreted as indicative of a cooling of seawater temperatures.

The Red Crag sea covered most of East Anglia; the deposits consist mainly of cross-bedded sands with abundant disarticulated bivalve shells. Several divisions of the Red Crag have been recognized, and these follow one another in a progressive sequence from south to north, which probably represents a retreating shoreline. The fossils were obviously transported by the sea from a variety of communities of the intertidal to nearshore shelf.

Fresh Water Fossils Cromer Forest Bed

Fig. 118 Pleistocene Sublittoral Sand Community a Glycymeris glycymeris (Mollusca: Bivalvia: Arcoida)

b Yoldia oblongoides (Mollusca: Bivalvia: Palaeotaxodonta)

c Macoma obliqua (Mollusca: Bivalvia: Veneroida)

d Mytilus edulis (Mollusca: Bivalvia: Mytiloida)

e Chlamys opercularis (Mollusca: Bivalvia: Pterioida)

f Spisula solida (Mollusca: Bivalvia: Veneroida)

g Arctica islandica (Mollusca: Bivalvia: Veneroida)

h Phacoides borealis (Mollusca: Bivalvia: Veneroida)

i Neptunea antiqua (Mollusca: Gastropoda: Neogastropoda)

j Neptunea contraria (Mollusca: Gastropoda: Neogastropoda)

k Nassarius granulatus (Mollusca: Gastropoda: Neogastropoda)

1 Nassarius reticosa (Mollusca: Gastropoda: Neogastropoda)

m Balanus crenatus (Arthropoda: Crustacea: Cirripedia)

n cod — Gadus callarius (Vertebrata: Osteichthyes)

Fig. 118 Pleistocene Sublittoral Sand Community a Glycymeris glycymeris (Mollusca: Bivalvia: Arcoida)

b Yoldia oblongoides (Mollusca: Bivalvia: Palaeotaxodonta)

c Macoma obliqua (Mollusca: Bivalvia: Veneroida)

d Mytilus edulis (Mollusca: Bivalvia: Mytiloida)

e Chlamys opercularis (Mollusca: Bivalvia: Pterioida)

f Spisula solida (Mollusca: Bivalvia: Veneroida)

g Arctica islandica (Mollusca: Bivalvia: Veneroida)

h Phacoides borealis (Mollusca: Bivalvia: Veneroida)

i Neptunea antiqua (Mollusca: Gastropoda: Neogastropoda)

j Neptunea contraria (Mollusca: Gastropoda: Neogastropoda)

k Nassarius granulatus (Mollusca: Gastropoda: Neogastropoda)

1 Nassarius reticosa (Mollusca: Gastropoda: Neogastropoda)

m Balanus crenatus (Arthropoda: Crustacea: Cirripedia)

n cod — Gadus callarius (Vertebrata: Osteichthyes)

119 Pleistocene Freshwater Sand and Clay Community

This community lived in a deltaic environment where the deposits consisted of sand, gravel, laminated clay and peat layers. Some horizons contain shallow water marine mollusca, and are the result of marine incursions. The peaty sands and organic-rich clays are thought to have been laid down in a slow-moving river or lake rich in plant debris. The lakes were surrounded by mixed oak forests, containing also elms and limes, and inhabited by deer. Temperatures were thought to have been approximately similar to those experienced in southern Britain today, although lower parts of the sedimentary sequence are dominated by pine and birch forest, and were obviously cooler.

The major elements in the community were freshwater mol-lusca; Viviparus and Valvata lived upon the sediment surface and the aquatic plants, whereas Succinea is found near the lake edges which periodically would have dried out. Viviparus is a detritus-feeding gastropod which ploughs along the substrate surface stirring up the sediment; particles are drawn across the gills and collected in a mucous string which is then drawn into the mouth. Both Viviparus and Valvata incubate eggs within the oviduct which functions as a uterus from which the young snails emerge, hence the name Viviparus.

The infaunal components of the community consisted of the sluggish suspension-feeding bivalve Unio tumidus, and the small siphonates Corbicula fluminalis and Pisidium amnicus. Unio and other members of the family Unionidae have an interesting mode of development; the eggs are initially fertilized and incubated within the mantle cavity and gills of the mussel but are soon expelled into the water where they attach themselves by spines or byssal threads to the fins and gills of fish. The fish tissue forms a cyst within which the Unio larva develops for up to 36 days; after this period it emerges to begin life as a benthic animal. Pisidium, a small bivalve with a single siphon, also incubates its eggs within the mantle cavity, whence they emerge as miniature adults.

The river was also inhabited by giant beavers and by voles; occasionally beaver dams are revealed as the Norfolk cliffs are eroded. This community occurs in the Upper Fresh Water Beds near Cromer, Norfolk.

Neogene Period

Fig. 119 Pleistocene Freshwater Sand and Clay Community a Unio tumidus (Mollusca: Bivalvia: Unionoida)

b Pisidium amnicus (Mollusca: Bivalvia: Veneroida)

c Corbicula fluminalis (Mollusca: Bivalvia: Veneroida)

d Viviparus gibbus (Mollusca: Gastropoda: Mesogastropoda)

e Valvata antiqua (Mollusca: Gastropoda: Mesogastropoda)

f Succinea putris (Mollusca: Gastropoda: Pulmonata)

g beaver (Vertebrata: Mammalia)

h roach (Vertebrata: Osteichthyes)

i gudgeon Gobio gobio (Vertebrata: Osteichthyes)

Fig. 119 Pleistocene Freshwater Sand and Clay Community a Unio tumidus (Mollusca: Bivalvia: Unionoida)

b Pisidium amnicus (Mollusca: Bivalvia: Veneroida)

c Corbicula fluminalis (Mollusca: Bivalvia: Veneroida)

d Viviparus gibbus (Mollusca: Gastropoda: Mesogastropoda)

e Valvata antiqua (Mollusca: Gastropoda: Mesogastropoda)

f Succinea putris (Mollusca: Gastropoda: Pulmonata)

g beaver (Vertebrata: Mammalia)

h roach (Vertebrata: Osteichthyes)

i gudgeon Gobio gobio (Vertebrata: Osteichthyes)

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