Samenvatting van de lezing op 8 januari 2000 The Quaternary Geology of East Anglia

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71 AFZETTINGEN WTKG 20 _(4), 1999

Samenvattingvandelezing op 8januari 2000

The

_{Quaternary Geology}

of East

Anglia

Richard Hamblin*

The BGS East

Anglia

teamare

currently completing

the

resurveyof the classic Cromerareaof North

Norfolk,

and this is

_leading

to_a_{considerable revision of}_ourideason

the

_{glacial stratigraphy. Traditionally}

_aNorth Sea Drift FormationandaLowestoftFormationare

recognised,

with the latter

_overlying

theformer, but both

_{being Anglian}

(Oxygen Isotope Stage 12)

in age. Within the North Sea Drift Formationtherearethreetills

_{(Happisburgh,}

Walcott and Cromer diamictons of

_Lunkka).

Howeverour

map-ping

is

demonstrating

that theLowestoftFormation passes into the North Sea DriftFormation,andmost

likely

equates

directly

tothe Walcott Diamicton. Thuswe have abol-ished thetermNorth Sea DriftFormation: the middle third of it

_clearly

should betermedLowestoft

Formation,

the lowest thirdweterm Corton

Formation,

since it correlates with that formationatCorton in

_Suffolk,

and the

upper-mostthird

requires

a newformationname.

The

_splitting

_{up of the North Sea Drift Formation raises} doubtsas tothe

_Stage

_{12 age of all of the}

_deposits,

_and

unfortunately

little direct evidence is

_currently

available. It is still

_possible

that the Corton and Lowestoft forma-tions both date frotn

_{Stage 12,}

but

_{altematively they}

may

be fromstages12 and

_10,

or14 and 12. The third

forma-tion is howevermost

likely

of

_Stage

_{6 age,}

_confirming

thata

major glaciation

did reach the United

Kingdom

at

this time.

*Richard

Hamblin,

British

Geological Survey, Kingsley

DunhamCentre,

Nottingham

NG12

_5GG,

United

Kingdom,

email

_{RJOH@wpo.nerc.ac.uk}

The RedCragFormation(Pre-LudhamiantoThumian,

tentatively Praetiglian

to

_Tiglian

_B)was

deposited

in

struc-turally-controlled

basins.

_{Afteraregression,}

it is followed

unconformably

by

the Norwich

_Crag

Formation

_(Antian/

Bramertonianto

Baventian, tentatively Tiglian

Clto

_C4c).

A

regression during

the Baventian ledtothe formationof shoreface

_{gravels (Westleton Beds)}

and intertidal

_clays

(Baston

Bavents

_Clay)

atthe mouth of the

Bytham

River which flowed frontthe

_English

Midlands. TheChillesford

Clay

was

similarly

formedatthe mouth of the proto-Thames.

Sandsand

_gravels

in north-eastem Suffolk and eastem

Norfolk,

characterised

_by

the inclusion of

_pebbles

of

quartz, quartzite

and Welsh volcanic

_rocks,

have

previ-ously

been considered

_deposits

of the

_proto-Thames

(Kesgrave Formation).

Howeverwe now know theseto be

_{largely marine,}

anda new

formation,

the Wroxham

Crag,

has beensetup within the

Crag Group.

This includes

the

Bure

_Valley

Beds and

_Weyboume

_Crag

of earlier

au-thors,

and is of Pre-PastoniantoPastonianage. The

trans-gressions

atthe bases of the

_Red,

Norwich and Wroxham Cragformationsare

tentatively

correlated with reflectors atthe base of the

Westkapelle

Ground,Smith’s Knoll and Winterton Shoal formationsof thesouthemNorth Sea.