A
PLANT-
B E A R I N G H O R I Z O N IN T H E I C E N I A N OF EASTON BAVENTS AND
CRAG
COVEHITHE
P . CAMBRIDGE
Fragments of plant-bearing beds were first seen by the author on the beach below Covehithe Warren (Nat. Grid. TM 522803). The samples varied from thin-bedded ironstone to hardened clay or sandstone. Some samples, especially the sandstones, contained only badly preserved fragments of wood or twigs. Others contained numerous elongate leaves, preserved as dark films or impressions. Associated with these were casts of small coiled 'shells', which Dr. M. Kerney kindly identified as tubes of spirorbid worms. So far no other fossils have been identified. The appearance of the specimens suggested material from estuarine beds, in some ways similar to those from the Cromer series of the North Norfolk coast. Since they were not in situ, an attempt was made to locate the source. As regards the origin there were several possibilities. First, was that the slabs came from the base of the Holocene sediments in the nearby broad. Ironstone can form rapidly in such conditions. However, it is possible to examine the broad's material which outcrops on the beach and this source was eliminated. The next possibility was derivation and long shore drift from the Forest bed deposits of Kessingland and Pakefield. Samples were submitted to Prof. R. West of Cambridge University who discounted a Forest bed source. This left the probability that the samples were from the local Crag No plant beds could be located in the cliffs but they could have come from exposures under the beach or below low water mark, below the Baventian Clay. A t a later date Mr. H. D. Collings of Southwold informed me that he had found similar material in a stone layer below the Easton Bavents Clay, and allowed me to examine examples. At a meeting of the Geological Society of Norfolk in 1979 I was able to collect examples from the beach below Easton Bavents Cliffs (TM 515787). Mr. Collings pointed out the stone layer and several further examples were collected from this bed. Unfortunately, the plant beds were not in situ, but occurred in a bed with much derivative material, with many pebbles, fish remains and fragments of mammal bones. This means that the plant remains must be older than the Easton Bavents Clay but have moved from their original position. It is unlikely that they were transported any great distance. Can anything be deduced from the meagre fossil remains of the plant beds? The worm Spirorbis attaches its tube to marine shells, polyzoans, seaweeds and other objects. The elongate leaf impressions which are the commonest plant remains are not seaweeds and such a combination points to an estuarine deposit. The leaves are long, with parallel sides and rounded tips, and the most likely plant seems to be one of the Eel Grasses (Zostera spp.) which live
>
Specimen of Zostera beds, Covehithe Warren beach, Suffolk. Specimen size 9 x 12 cm. Author's collection G7789. at half- to low-tide in estuarine muds. Although a botanist might not make a definite identification from the material available, in the absence of anything more likely, this seems the most probable genus. The petrology of the plant beds would also be consistent with estuarine conditions. These Zostera beds may have been fairly widespread. A small Hat ironstone pebble from the Stone Bed of the Norwich Crag at Caister-St.-Edmunds, near Norwich (TG 240048) when examined closely showed impressions of similar leaves and suggests that examples may be found elsewhere. However, it is probable that suitable conditions for the growth of these plants may have been repeated several times during the deposition of the Icenian Crag. Such fine-grained, shallow-water deposits are
256
Suffolk Natural History, Vol. 18, Part 3
ideal for the preservation of fragile material and fragments of the Zostera beds should be examined for other fossils. T h a n k s are due to Messrs. H. D. Collings and R. Winyard for allowing me to examine their material and to Mr. P. Laurance of Castle Museum, Norwich, for allowing me to examine recent Zostera specimens from the herbarium.
Philip Cambridge, 258 Bluebell Road, Norwich, NR4 7LW.
Trans. Suffolk Nat. Soc. 18 part 3.