8/21/2019 BCRA 15-1-1988

1/40

  a

Science

The Transactions

o f the British

Cave Research

ssociation

BeR

I

o lume

15

Number 1

Apr

i

I

1 9 8 8

Sed iment Pa leomagne t i sm

at L langa t twg

Natura l Tunnel

Vi rg in ia

Tufas and

Traver t i nes

f rom Yorksh i re

Pigments in ave

Organisms

Survey

Reduc t i on by

Least

Squares

8/21/2019 BCRA 15-1-1988

2/40

  aveScience

The

Transact ions of

the

Br i t i sh

Cave

Research

covers

a l l

aspec ts of spe leologica l

s c i e n c e ,

including

geology  

geomorphology, hydrology,

chemist ry  

physics ,

archaeology

and

biology in t he i r appl i ca t ion to caves.

I t a l so

publishes

ar t i c

l es on t echnica l matters

such

as exp lo ra t ion  

equipment

  d iv ing , surveying,

photography

and documentat ion

 

as

well

as

exped i t ion

r epor t s and

h i s t o r i ca l

or

b iograph ica l s tudies .

Papers

may

be

read a t

meetings held in

various

par t s

of

Br i ta in

 

but

they may be

submit ted

for publ ica t ion without

being read

.

Manuscr ipt s should be sen t to the Edi to r   Dr T . D. Ford   a t

the Geology

Department

  Univers i ty o f

Leices te r

 

Leices te r LEl

7RH.

Intending

authors

are

welcome

to

con tac t

e i t h e r

the

Edi to r

or the Product ion

Edi to r

who

wi l l

be

p leased

to advise in any

cases

of doubt concerning the prepara t ion o f manuscr ipts .

NOTES FOR CONTRIBUTORS

These notes

are intended

to help

the authors

to

prepare their material

in

the

most

advantageous

way so as

to e xped i t e publica t ion and

to reduce

both

their

own

and e d i tor ia l labour

.

I t

saves a

l o t of

time i f the rules below are

followed.

All

material should be presented

in

a

format

as

c lose

as possib le

to

t ha t of C VE SCIENCE s i n

ce

1985. Text should be typed double - spaced

on

one

s ide o f the paper

only .

Subheadings within an

art i c l e

should

fol low

the

system used in CAVE

SCIENCE a

system of

primary, secondary, and i f

neccesary,

tert iary subheadings

should be

c learly

indicated .

Abstrac

t :

All

ma te r i a l should be accompanied

by

an abstract stat ing the

essential results o f

the invest igtation

for use

by abstracting

, l ibra

ry

and other

services .

The abstract may

also be

publ i shed in C VES ND C VING .

References to

previously

published work

should be given in

the

standard format used in

CAVE SCIENCE . In the t e x t the s tatement

r e f e r r

ed

to should be followed by the re levant au th o r s

name and

date (and page number, i f approp

r i at e )

in

bracke ts .

Thus:

Smith,

1969, p . 42). All such

references ci ted in th e te x t should be given in

fu l l in alphabet ical order, at the end. Thus:

Smith, D.

E.,

1969. The speleogensis of the Cavern

Hole. Bul le t ing Yorkshire Caving Assoc .

Vol.

7,

p. 1-63 . Books

should

be

c i ted

by the author ,

date

,

t i t l e publ i

s

her

and

where

published.

Periodical

t i t l e s should

be abbreviated in

standard

s ty l e or, where doubt

ex i s t s should be

writ ten out in fu l l .

Acknowledgements:

Anyone who has given a

grant

or helped wi

th the

in v es t ig a t io n , or with

the

prepara t ion

of the a r t i c l e , should be

acknowledged

br ie f ly . Contr ibuto rs in

Univer s i t i e s and other ins t i tu t ions

are

reminded

that

grants towards

the cost of

publication

may

be

availab le and they should make the

appropria te

enquiries

as

ear ly

as poss ible .

Expeci t ion

budgets should

include

an element

to help

publ icat ion

and

the edi tor should

be informed at

the

time of

submission .

I l lustration:

Line diagrams

and drawings must

be

in BLACK ink on e ither clean white

paper or

card, or on trac1ng

paper

or

such materials as

kodatrace.

Anaemic grey

ink

and pencil

wil l

not

reproduce I l lus tr a t ions should be designed to

make maximum use of

page

space . Maps must

have

bar scales only . I f photo - reduction

i s

contemplated a l l

l ines

and

l e t t ers must

be

large

and thick

enough

to al low

for the ir reduction.

Let ters

must be

don e by

s t e n c i l l e tr as e t or

s imi lar

meth

ods, not

handwritten. Diagrams

should

be

numbered in

sequence as f igures and re ferred

to in the te x t where necessary, by insert ing

Fig. 1)

e t c

in bracke ts . A fu l l l st of f igu r e

captions should be

submitted

on a separate sheet .

Photographs are welcome. They

must

be

good

clear black and

white

prints , with sharp focus and

not too much contrast ; prints about 15 x 10

cm

(6

x 4 inches) are best ; i f in doubt a se lect ion may

be submitted.

They

should be numbered in

sequence , but normally

not

referred to in

the

text . A fu l l l i s t of plate capt ions

with

photographer credits

where

relevant should

be

submitted on

a

separate sheet .

Tables: The

se

should not be included

in

the

t ex t but should be typed,

or

c lea r ly handwri t ten  

on separate sheets . They should be numbered in

sequence, and a

l i s t

of captions , i

ne

cessary

should be

submit ted

on a separa te sheet .

Approximate

locat ions for tables plates and

f igures

should

be

marked in

penci l in the

manuscript

margin, unless already

clear from

the

t ex t

.

Copyright: I f

any

te x t

dialJrams

or photos

have been

published elsewhere

,

i t

i s

up

to

the

author to clear

any

copyright or

acknowledgment

matters.

Speleologica l expedi t ions have a moral

obl iga

t io n to

produce repor ts (contrac tua l in the

cases

of

rec ipients

of

awards fr

o m the

Ghar

Parau

Foundation) .

These

should

be

concise and cover

the results o f the expedit ion

as

soon

as

poss ible

a f te r the

return

from

overseas

,

so

that l a t t er

expedi

t i

ons are informed for

their

planning.

Personal

anecdotes

should be kept to a minimum,

but useful advice such as locat ion o f food

suppl ies medical services e t c . may be included.

Authors

may order reprints of their

contribution

for the ir own private use. The order must be

not i f i e d to

the

Editor at the time of submission.

I f

you have

any problems

regarding

your

material

, please consult e ither o f

the

Editors

in

advance

of submission.

8/21/2019 BCRA 15-1-1988

3/40

  ave

Science

TRANSACTIONS OF THE

BRITISH CAVE

RESEARCH ASSOCIATION

Volume 15

Number

1

Apr i l

1988

Contents

Paleomagnetism

of Cave

Sediments

from Mynydd Llangat twg

Mark

Noel

Natura l Tunnel Virg in ia

Tony Waltham

P o s tg l a c i a l

Tufas

and

Traver t ines from

the

Craven

D i s t r i c t

o f Yorkshi re

Al lan Pen tecos t

and

Tom Lord

Pigmenta ry Development of Cavernicolous Organisms

Mark F Chapman

The

Least

Squares

Method

of Cave Surveying

Data

Reduct ion

based on a Micro

Computer

S Kel ly

and

P B

Warren

Forum

Cover: The

mass ive f o s s i l t runk passage o f

Qian Dong

in the

Bama kar s t of western Guangxi

China.

By J e r r y

Wooldridge.

This

i s

one

of

the

many spec tacu la r

photographs of the Guangxi caves

and

kar s t in the

r e p o r t

o f

the

1987/88 phase of the China Caves P r o j e c t

a v a i l a b l e

t h i s summer fo r £4 inc lud ing

UK

postage from

BCRA

S a l e s .

Edi to r : Dr T . D. Ford Geology

Dept .

Leices te r Univers i ty Leices te r LEI 7RH

3

11

15

21

9

35

Product ion Edi to r : Dr. A.C. Waltham

Civ .

Eng.

Dept .

Tren t

Poly techn ic

Nottingham

NGI

4BU

Cave Science

i s pub l i shed by the Br i t i sh Cave Research Assoc ia t ion and i s i s sued to

a l l

pa id

up members

of

the

Assoc ia t ion

1988

subsc r ip t ion r a t e s a re :

Ind iv idua l £10.00 I n s t i t u t i o n or Club

£12.50

Membership

Secre ta ry :

N.

Br iggs 68 P o i t i e r s Road Cheylesmore

Coventry

CV3

5JX

Ind iv idua l cop ies and

back numbers

of

Cave

Science a re ob ta inab le from:

B.C.R . A. S a l e s 20 Woodland Avenue Westonzoyland Br idgewate r

Somerset

TA7 OLQ.

The

permanent address

fo r

B.C.R.A.

i s : B.C.M.-B.C.R.A. London

WClN

3XX

Copyr i gh t t he B r i t i s h Cave Research

Assoc ia t ion

1988. No pa r t

of

t h i s publ ica t ion may be

reproduced in

any othe r

pub l i c a t i on used

in

a dve r t i s i ng s tored in

an

e l e c t r on i c

r e t r i eva l

sys tem

or o therwise

use d

fo r

commercial

purposes

wi thou t

the pr io r

wr i t t e n

consen t of the

au thors

and

of the Assoc ia t ion .

ISSN

0263-760X

8/21/2019 BCRA 15-1-1988

4/40

8/21/2019 BCRA 15-1-1988

5/40

C VE SCIENCE

Vol. 15, N o . 1 ,

Apri l 1988

Transact ions of the Bri t i sh

Cave

Research Associat ion

Paleomagnetism

of ave Sediments from Mynydd Llangattwg

Mark NOEL

Abstract : The palaeomagnetic

study of

Br i t i sh cave

depos i t s began

with

an

examination of sediments

within Mynydd

L1angattwg,

Powys.

This paper

reviews

the

r esu l t s

obtained from a t o t a l of 77

specimens col lec ted in

the

Agen

Allwedd and Pwll y Gwynt cave systems . The evidence suggests

that

these

s i l t s

and clays

acquired

a s tab le remanent

magnet isat ion

through the

alignment

of

magnetic minerals ,

by

the geomagnetic f ie ld , dur ing

deposi t ion.

Similar i t ies in remanence di rec t ions within

the Cap Mud'

a t

f ive

s i t e s in

Agen Allwedd suggests

t ha t

deposi t ion of th i s

uni t was

simultaneous throughout the cave dur ing a per iod of normal

geomagnetic

polar i ty .

A

sediment

secton

near the top of the

5th

Aven in Pw11 y Gwynt

includes

a

clay

hor izon wi th reversed magnet isat ion

implying

that

these

sediments

record

e i ther

a recen t

geomagnetic

excursion or

f ie lds

dur ing the

reversed Matuyama chron (>720 Ka). Magnetic

fabr ic data provide

evidence

fo r di rec t ions of water currents and mass f low

in

these cave

sediments

INTRODUCTION

Sediments formed

by

slow deposi t ion in water

often contain a weak remanent

magnet isat ion.

This deposi t ional remanent

magnet isat ion

can

therefore

provide a record of

geomagnetic

secular

var ia t ion extending

beyond

his tor ica l observat ions.

This concept

has been

applied to palaeomagnetic

studies

of

glacial varved sediments

from

Scandinavia and North

America

(Noel 1975;; Johnson

e t a l . 1948). Lake and marine sediments (Creer

1974, 1981) and

surface

t e r r e s t r i a l depos i t s

(eg.

Heller Tung-Sheng 1982). These s tudies have

provided important

palaeomagnetic

cons t ra in t s on

models for the geomagnetic dynamo; they have led

to the dat ing and cor re la t ion

of

Quaternary

sediments (eg. Creer

1982)

and

they

have helped to

re f ine and ver i fy

a

reference curve for

archaeomagnetic

dating

(Aitken 1974).

Due to the

glacial

erosion which af fec ted

many lake basins dur ing the Devensian and the

problems

of

re t r i ev ing

longer core samples,

t

has

proved di f f i cu l t to extend exis t ing lake

sediment

magnetostrat igraphies much beyond 13000 yr BP.

Although marine sediments

have

the potent ia l for

providing a much longer t imesca le ,b io turba t ion and

slow sedimentat ion

rates .severely

l imi t the

resolut ion

a t ta inable with t h i s

material ,

Final ly, surface t e r r e s t r i a l deposi ts seldom

provide

the

long

sequence

of

unweathered mater ia l

which

is

a

prerequis i t e for

accurate

palaeomagnetic s tudies . Cave

sediments, on the

other

hand,

are usual ly preserved under favourable

condit ions of low weather ing, wi th l i t t l e

bioturba t ion

or

desiccat ion, par t i cu la r ly

in the

i n t e r io r zone. They therefore

have

a capabi l i ty

f o r deta i l ed palaeomagnetic studies of the

Quaternary geomagnetic f i e ld . Evidence from U/ Th

dating

of

assoc ia ted speleothems

suggests

that

cave

sediments,

a t

some

l oc a l i t i e s ,

may

have

ages

in

excess

of

350 Kyr BP (Atkinson

e t a l . 1978)

.

Cave sediment palaeomagnetic research has

been

slow to

develop largely due

to the

log is t i ca l

problems

of

sampling. The

potent ia l

of th i s

mater ia l

was f i r s t confirmed

in s tudies of

sediments

from

caves in

Spain,

Majorca

and the

Lebanon

(Creer

Kopper 1974, 1976; Kopper

Creer

1973, 1976) .

The ea r l i e s t invest igat ion

in

Bri ta in

concerned

rhythmites from the entrance to

Vic tor ia Cave, Yorkshire (Stober 1978; Homonko

1978) but

Agen Allwedd provided

the

f i r s t

palaeomagnetic

da ta

for sediments

from a

deep cave

environment (Noel e t a l . 1984; Noel 1986; Noel

St .

Pierre 1984; Noel

Bull

1982; Schmidt

1982).

There i s now evidence to suggest the

speleothems

may also

contain r e l i ab le

records

of the

geomagnetic

f i e ld (Latham e t

al . 1979).

This paper

summarises

the

palaeomagnetic

r esu l t s

obtained from

samples

of s lt

and

c lay

from f ive s i te s in Agen

Allwedd and

one

s i t e

in

Pwyll

y

Gwynt.

Further de ta i l s are

given in

Noel

3

(1983,

1986). The r esu l t s provide evidence

for

the

relat ive

ages of the deposi ts and for a

palaeocurrent

di rec t ion in Agen

Allwedd.

METHODS

Lightweight, robust sampling equipment was

developed to overcome the

special

di f f icu l t i e s of

sampling underground.

The ent i re

apparatus,

including a camera, can be car r ied in a standard

7.6cm

wide ammunition case

and weighs

approximately

2 kg.

A clean, hor izonta l or

ver t i ca l

sediment

surface

i s

f i r s t

prepared wi th a brass

scraper

blade. 2.54 x

2.54 cm

p las t i c tubes are then

pressed

into

the sediment using an angle

plate

f i t t e d with a bullseye sp i r i t l eve l . The

or ienta t ion

of

each

tube is then recorded in s i t u

and the

di rec t ion

of

down (or magnetic

nor th)

scr ibed on

the

sample tube.

The specimens

are

then

extracted,

trimmed and

placed

end

to

end

in

sealed s torage tubes

for

t ransport

to the

laboratory .

The natural remanent

magnet isat ion of

the

specimens is

measured

in

a

f luxgate spinner

magnetometer (Molyneux

1971). The r esu l t s

are

expressed

in

terms of

the magnitude

and di rec t ion

decl ina t ion ,

incl inat ion)

of the remanence

vector . The s t ab i l i ty of the magnet isat ion in

representa t ive samples i s then examined using

a l te rna t ing f i e ld

demagnet isat ion. For

fur ther

de ta i l s

of

th i s and other

laboratory techniques

the

reader

i s referred

to Coll inson

(1983). On

the bas is on the demagnetisation

t e s t s , each

sample i s next exposed to an a l te rna t ing magnetic

f ie ld

chosen to i so l a t e

the

primary

component

of

magnet isat ion in the

sediment. This

is

f inal ly

measured in the magnetometer.

The

magnetic

suscept ib i l i ty

anisotropy

(magnetic fabr ic ) of the

sediments has

also been

examined.

In

a sediment which contains the

mineral

magnet i te , the

magnetic fabr ic can provide

an

indicat ion of

the

degree

of prefer red

or ienta t ion

of

non-spherical

magnetic gra ins .

This or ienta t ion ar i ses

from the

in te rac t ion

of

magnetic

gravi ta t iona l

and

hydrodynamic forces

on

the se t t l ing

par t i c l es (Hamilton

Rees

1970).

Hence

the

s ty le

of the magnetic fabr ic can

be used

to

in fer

the di rec t ion and the

veloci ty

of flow

through a flooded passage

or

to

indicate

the

nature of gra in

in te rac t ions which occurred

dur ing

a mudflow.

The suscep t ib i l i t y

anisot ropy

i s measured in

modified spinner

magnetometer (Collinson 1983) .

This inst rument measures

the

di rec t iona l var ia t ion

of

suscept ib i l i ty within the specimen and

expresses the

resu l t s

in

terms

of

an

el l ipso id

of

suscept ib i l i ty specif ied

by the

magnitude

and

di rec t ion

of

three pr inc ipa l axes. These

are

general ly displayed on a stereographic projec t ion .

8/21/2019 BCRA 15-1-1988

6/40

R SULTS

Ogof

Agen

Allwedd

As par t

of

a prel iminary

study

in

1979;

t en

specimens

of

horizontal ly

bedded sur face

s lt

( Cap

Mud ) were obtained near the

northern

end of

Main

Passage

(Fig.

1) .

This f ine ly laminated s lt

was probably derived from surface

per ig lacial

weather ing

of

Mills tone

Grit

on Mynydd

Llangattwg

which then en te red

the flooded cave

via

ver t i ca l

jo in t s and f i ssures .

These samples

were found

to

contain

a

s tab le

magnetisat ion recording

a

period of Normal

geomagnetic f i e ld

polar i ty

(Noel e t a l . 1979).

The mean remanence inc l ina t ion ,

(40.7°; Fig.

2),

i s

somewhat shal lower than would be

expected for

geomagnetic secular

var ia t ion

a t th i s

l a t i t ude .

However, th i s

can

be

explained

in terms

of an

i n c l i n a t ion e r r o r ,

d,

which

ar ises

from

the

ro l l i ng

of

par t i c l es as

they

come to r es t on the

sediment

sur face

(King 1955).

A Primary Style

of

magnetic fabric

(Hamilton Rees 1970)

was

found

in

these

sediments. This

i s character ised

by

a

near-hor izonta l

magnetic

fo l i a t ion plane

(minimum

axes ver t i ca l ) . The maximum axes

def ine

a

l ineat ion which

i s deviated

away

from

the

remanence di rec t ion ,

implying that

water flow

down

the passage

has

been an important cont ro l on the

magnetic

fabr ic .

The r esu l t s

of

thermomagnetic

measurements on a magnetic

ext ract

from

the

Cap

Mud ,

(Fig.

3) , suggested t ha t

the

main magnetic

mineral

in

the

sediment

was magnet i te .

Encouraged

by these ear ly

r esu l t s , a fur ther

30

samples were obtained from three s i t e s

in

Main

Passage

and

a s i t e in

Keyhole Chamber, (Fig.

1;

Noel e t a l . 1981). Si

es

4 and 5 were

again

located on hor izonta l ly bedded Cap Mud but s i t e s

2 and 3

were

a t two levels on

the

f lanks

of

a

STREAM

N

STREAM

I

PASSAGE

0

25

5

SCALE : metres

Figure

1. The Agen

Allwedd

cave system showing

the

location

of the

sampling

s i tes .

Si te

5 was in the

upper level

of

Keyhole Chamber.

4

SITE 2

200 0 .

SITE 4

200

0 .

- " I

':

.

 

SITE 1

350 Oe

, ,

i

..

SITE 5

2000.

SITE 3

2 0 0 0 .

Figure

2.

Remanence

directions for the five

Agen

Allwedd

s i tes

after

par t i a l demagnetisation in the alternating

magnetic f ields shown.

steep

sediment connected

to

twin

ver t i ca l cracks

in

the western wal l of Main Passage, (Fig. 4).

The samples

contained

a

s tab le primary

component

of

magnetisat ion. Fig. 2 shows the

di rec t ions

of

remanence

af te r pa r t i a l

demagnet isat ion

in a peak al ternat ing f ie ld

of

200

Oe

(20 mT). The

magnetic fabric r esu l t s

are

shown

in

Fig.

5. The sediments

again contained

a

primary

depos i t ional

s ty le

of magnetic

fabr ic

but

the s i l t s on

the

f lanks

of the

cone

have

a fabric

re la ted to the s t r ike

and dip of the

sloping

surface.

The fo l ia t ion

planes are

t i l t e d in the

downslope di rec t ion , al though a t lower angles than

the

bedding,

thereby causing an imbricat ion in to

the s lope. The

maximum

axes

of

suscep t ib i l i t y are

scat tered within the

fo l ia t ion

plane a t s i t e 2 (8°

slope) but are

more t i gh t ly grouped a t s i t e 3 (29°

slope) . These r esu l t s

conform

c lose ly

with the

6

·c

5

z

0

4

n

i

w

z

( l

3

ct

C

2

w

U

:::>

0

o 100

1( 1

?9

\

200 300

400

500

o

TEMPERATURE

C

600

700

Figure

3. Changes in the

in tensi ty of induced magnetisation

in a

maonetic

extract from

the

Cap Mud

during

a cycle of

heating-and cooling.

8/21/2019 BCRA 15-1-1988

7/40

Figure 4. Plan

vi

ew of the

sediment

cone

near

two

f issures

in the western wall of Ma i n

Passage wi

th

the

posi t ions of

s i t es 2 and 3. The

arrows

are

the

in ferred directions

of

current

flow

based on the

analysi s

of

magnet

i

remanence

and

suscept ibi l i ty anisotropy.

F

igure

S.

Directions

of the

three principal

axes of magnet i c

suscept ibi l i ty in the Cap Mud'

samples. The

dashed

l ines

i ndicate the downward direction

of bed slope .

=

maximum,

.. = intermediate

and

• = mi nimum

axes.

Closed

symbols = posit ive

i nclination ; open symbo ls

=

negative incl inat ion

m tr

' ,

::

.

 : ;.  :

.

 :

 

+ ~ z

j

; f 0

- 0

0 - 0

Oem

,

: q , '

•

3

,

,

\

\

\

\

\

\

\

I

f indings

of Rees (1966) who

redeposi ted

medium

sands

onto varying

slopes in

the

laboratory.

The sediments a t s i t e s 4 and 5 contain two

or thogonal

l inea t ions

causing

a c lus te r ing of

maximum

and

intermediate di rec t ions

(Fig.

5).

This

unusual

r esu l t was

confirmed

using a low

f ie ld torque

magnetometer

and

is therefo re

not

instrumental

in

or ig in . Hence t

is

probable

that

these sediments

contain

two par t ic le l inea t ions ,

only the

dominant one of which can be resolved by

the

magnetometer . These l inea t ions

are

para l l e l

and

t ransverse

to the

current

flow

di rec t ions

as

defined

by the or ienta t ions

of

the passage

a t

the

two

s i t e s .

A

magnetic fabric

with

l ineat ion transverse

to

the

presumed flow

direct ion

has

been

reported

by Rees (1965) in Eocene sandstones which contain

two grain alignments and

by

Granar (1957) in

Swedish

varved clays. Grain or ienta t ion

perpendicular to the current has also been noted

by Hand

(1961)

.

I t

i s possible t ha t

these Cap

Muds

contain magnetite

grains

whose

shapes

enable them to take

up

one of two

hydrodynamically

s tab le

posi t ions

on a hor izon tal

bed.

The sets of remanence

vectors

for each s i t e

are

well grouped but there is a s igni f icant

disagreement

in

the mean di rec t ions

for

the

two

s i t e s on the cone (

Fig.

2). This

can

be explained

in

terms of the tendency for

s e t t l i ng

magnetic

grains

to ro l l systemat ical ly downslope

before

coming to

r es t thus causing a

ro tat ion

of the

f inal

remanence vector. From the r esu l t s of

laboratory deposit ion experiments in control led

magnetic

f ie lds ,

an

empir ical

correct ion

has been

derived for the '

bedding

er ror ' (Hamilton King

1964). When th i s correct ion i s applied to s i t e s 2

and 3 ,

(Fig.

6) , the mean

vectors

become

5

:-

0.

..... .

..

h

0

, .

, ,

4

3

. , If , ,

5

CURRENT

ROTATIONS

Figure 6.

Correction of

the s i tes 2 and 3 r emanence vectors

f or

bedding

error

fo

and incl ination

error I i

The re

su l t

i ng

vectors

are

then

onnecte

d to

the

estimated

f ie ld

direct ion

by small

ci

r cles (dotted)

which

indic ate the degree of

rotation due to

current

shear

ind is t ingu ishab le

(wi thin

sample

errors) from

the

palaeomagnetic di rec t ions a t other s i t e s in the

cave

(Fig. 7)

. This strongly

suggested

that

deposi t ion of these surface s i l t s has been

simultaneous throughout the cave .

By considering the

hyrdodynamic informat ion

contained

in

the

magnetic fabric

t

i s

possible

to

apply a fur ther

correct ion

to the remanence

vectors for the

ef fec t of water flow. For each

sample,

the

di rec t ions

of

maximum

suscept ib i l i t

y

and remanence are joined by a small c i r c le which

represents the ro ta t ion of grains, about

horizontal axes , due to

f lu id

shear

_ When the

8/21/2019 BCRA 15-1-1988

8/40

small c i r c le

for a su i te of samples are

extrapolated,

they

should converge on the

palaeofield direct ion . Further de ta i l s of th i s

method are

given

by Rees

(1961) and Noel

(1986).

In Fig.

8

th i s technique

i s

applied to s i t e

1. The zone of small c i r c le in te r sec t ions defines

a range of di rec t ions within which

t

i s assumed

the

palaeofield

vector

l ies .

In Fig.

6

th i s is

compared to the

mean

remanence di rec t ions for

s i

es

2 and 3 ( a f t e r correct ion for

incl inat ion

and

bedding

er rors ) . The remaining

angular

discrepancy

may

be

explained

by

current rotat ions

caused by f low over and around the

cone.

The

small c i r c les correspond to the cur rent ro ta t ions

shown,

indicat ing t ha t water flowed up the cone

and

into

the wall

f i ssure .

10

0

20

20

30

30

.0

50

- . 1

Figure 7 . Mean palaeomagnetic directions in sediments from

the five s i t es in Agen

Allwedd.

Corrections

have been

applied for bedding error a t s i t es 2

and 3.

Fi gure 8 . Est i mate of the t rue palaeomagnetic f ie ld

d

i r ec

t io n dotted box) by combining the remanence (circles)

and

maximum

suscept ibi l i t

y

directions (squares).

The solid

l i n es

re

s

  ir le

s  

SECTION

A S C

I I I

: SITE I I \ I I

I '

6

Ogof Pwll y Gwynt

Pwll y Gwynt i s a

small

cave 213m long)

developed

beneath

Mynydd Llangattwg

near the

upper

l imi t

of the Avonian l imestone sequence and about

8 m above Agen Allwedd (Fig . 9). The

cave

consis ts of a

ser ies

of narrow foss i l phreat ic

passages l inking

large

ver t ica l avens and

probably

represents

the

ea r l i e s t

stage

of

kars t development

in the area.

In common

with

Agen Allwedd (Bull 1976;

1981), Pwll y Gwynt contains an

extensive

sediment

i n f i l l

and

in

places

th i s

has been exposed

in

natu ral stream sect ions to

reveal

a complex

succession

of layered s i l t s and clays.

Fig.

10

shows an approximately

1m

thick sequence

of

sediments

deposi ted

in a

small passage leading

to

the

Fif th

Aven.

These sediments

occur a t

one

of

the highest

levels

in the

cave

and hence almost

cer tain ly predate the deposits in Agen

Allwedd.

The

lower hal f of

the

sect ion comprises a mud

flow, as

shown by the contorted

r e l i c t

laminat ions

and random in t r ac las t s of layered clay .

These

sediments are over la in by nine l i t ho log ica l ly

dis t inc t uni t s of laminated clay , stalagmite

and

homogenous

clay

with

sand. The

presence

of

desiccat ion cracks and the th in

stalagmite

layer

a t a depth of 12cm i s evidence for prolonged

breaks in sedimentation. A prel iminary

in terpretat ion of the sect ion suggests that these

sediments

record

changes

in

surface

cl imat ic

condit ions

which might be equated

with

a

g lac i a l

/ i n t e rg l ac i a l sequence. Unfortunately,

because of de t r i t a l contaminat ion, the speleothem

mater ia l was unsuitable for radiometr ic dating. A

minimum of seven samples

were

obtained from each

of

layers

2,

6

and

9

(Fig.

10). A

ver t ica l

su i t e

of

th i r teen

samples was

also

obtained from the

slump deposit .

The di rec t ions of remanent magnetisation

before

and af te r par t i a l

demagnet isat ion

in

al ternat ing magnetic f ie lds

are shown

in

Fig. 10.

Detai ls of the pi lo t

sample

behaviour dur ing

demagnetisation are given in Noel

(1986).

The

di rec t ions of maximum

and

minimum magnetic

suscep t ib i l i t y in layers 6, 9

and

10

are presented

in relat ion

to the

passage or ien tat ion in

Fig.

11.

The

in tensi ty

of the natural remanent

magnet isat ion

was

in

the

range

7

.7-4

2 . 2 x 10-

7

Am2 / Kg.

Normal

polar i ty

remanence vectors

were

found

in layers 2

and

6

but

a

reversed

polar i ty

magnet isat ion

was found

in layer

9.

Shallow

values of remanence

incl inat ion

again suggest the

presence of an i nc l ina t ion e r r o r .

The disturbed clay records an

i r regular

prof i le of

remanence

di rec t ion

(Fig.

12). With

the

exception

of the shal lowest sample, the

vectors are of

normal polar i ty , however,

and

within 38° of the present geomagnetic f ie ld.

Three

contrast ing s ty les

of

magnetic

fabric

are present in the Pwll y Gwynt sediment

(Fig.

N

I

10m

Fi

g

ur

e

9.

The

Pw

l l

y G

wyn

t c a

ve

s ystem

sh

owi ng the sampl i ng

lo c a t io n i n

the Fif

t h Aven .

8/21/2019 BCRA 15-1-1988

9/40

Figure 10. Stra

t igraph y

of

the

sediment

section in the

Fifth

Aven with

remanence

direct ion s

in layers 2 . 6

and

9 before

and

a f te r demagnetisation in the

f ie lds shown . Li t hologies a re

as fo l l ows:

1) s talagmite

;

2)

mottled blue-brown

clay

; ( 3)

dr y .

black

an d white

laminate

d

s

la y

; 4) clay and sand; 5)

s talagmite;

6)

br own

laminate

d

c l a

y;

7) dry . orange laminated

c l ay; 8)

clay

with sand

pa r t ings ; 9) laminated

clay;

(

10) slum

p with c la s ts o f

laminated

clay

. Present f i e l d

d ir e

c t i

on i s

ind icate

d by the

s tar .

DEPTH

em.

5

10

15

20

25

30

35

45

5 ~ ~

LAYER

.

o

NRM

.

.

.

:

>II

. .

o 0

A.F

.

7·5mT

-

.

.

:'

15mT

, .0,

+ .

o

o o ·

10mT

i

SEE

FIG.

~

5

100

11) . The suscept ib i l i ty anisotropy of layer 6

contains

a

l i ne a t i

on

para l l e l to the dip di rec t ion

of

the

clay

with

an

imbricat ion

which

i s

upslope

with respec t t o th e

bedding dip-20

0

  .

A

similar

s ty le

of fabr ic is

seen

a t Agen

Allwedd

s i t e 3

Fig. 5 ) and in laboratory deposi t ion

experiments

Rees

1966).

A down

-d

ip l inea t ion i s also s e en

in

l ayer

9

Fig

. 11) .

0;'

The

slumped

sediments

contain a well-defined

hor izonta l

magnetic

l inea t ion in a di rec t ion

approximately para l l e l

to

the

passage

axis

Fig.

11).

The

minimum

suscep t ib i l i t y

axes sh ow a

gi rd led

dis t r ibu t ion .

since magnetic reor ient ing

forces

appear

to have

been unimportant in

governing

the

remanent

magnet isat ion

of

the

depos i t it

seems

l ikely that

the magnetic fabr ic

/

/

,/

/

•

. .

,

\

\

LAYER 9

Figure 11 . Direc t ions of

maximum Ie )

and

minimum Ie )

axes

o f ma gnetic s uscept i bi l i t y in

t

hree

of

the

Pwl l y Gwynt clay

la yers . Orienta t io n of t he c ave

passage

i s

shown by the

arrows

.

Sol id symb

o

l s

l ow

er hemisphere,

open symbols upper hemi sphere .

LAYER

6

o

8

o

7

I I I

o

Q)

o

0

o

0 -

0

0

LAYER

1

I I I

8/21/2019 BCRA 15-1-1988

10/40

DECLIN TION

180

220

260

300

3.

0

70

E

u

r

80

Q..

w

0

90

-   0

has

been dominated by the

ef fec t s

of

viscous

f lu id

forces

o r

gra in co l l i s ion

dur ing

the slump event .

This caused

the g ra ins to

ro tate about

axes

perpendicular

t o

the flow di rec t ion .

The girdled d i s t r ibu t ion

of minimum

axes

can

then be explained by considering the veloc i ty

dis t r ibu t ion in

the

sediment

as t

flowed through

the

narrow passage

(Fig.

13). The

di rec t ion of

the veloc i ty gradient and hence the shor tes t

axes

of the

moving gra ins

must have been ho

r izontal

near the walls and

approximately ver t ica l

near the

cent re of

the

r i f t .

Since the samples

span a

width

~ 1 0

cm)

which

i s

a

s igni f icant

f rac t ion

of

the wall spacing (15-4) cm) they wi l l , therefore,

contain minimum suscep t ib i l i t y di rec t ions

which

depar t

appreciably

from the

ver t ica l but

which are

conf ined

to

a plane

perpendicular

to the

flow

di rec t ion .

CONCLUSIONS

These

r esu l t s

from Agen

Allwedd

and Pwll y

Gwynt

confirm

the value of deep cave

sediments

for

palaeomagnetic s tudies

of the ear th s

magnetic

f i e ld . Moreover,

since the cave

sediments

were

formed

in

condit ions

analogous

to those crea ted

in

l abora tory flumes, t

has

been poss ib le to compare

equivalent depos i t ional

magnet isat ions

in na tura l

and

a r t i f i c i a l

sediments.

The palaeomagnetic

data suppor t

the

conjec ture ,

based

on

laminat ion matching,

t ha t

depos i t ion of the Cap Mud

was

s imultaneous

throughout

Agen

Allwedd (Bull

1978).

I t would be

in teres t ing

to extend th i s t e s t to

similar

depos i t s

in Darren

Cilau, Eglwys Faen and

other

caves beneath

Mynydd

Llangattwg.

In the

absence

o f rad i ometr ica l ly dateable

material ,

palaeomagnetism i s probably the only technique

which can prove contemporaneity

of

cave

sedimentat ion

on

a regional

scale.

The

discovery

t ha t some

sediments in

Pwll y

Gwynt date from a period

of

reversed geomagnetic

polar i ty ind ica tes t ha t these

clays must have

an

age well

in

excess of the 11000 yr

BP

conjectured

for the Cap Mud

in

Agen

Allwedd (Bull

1980).

The sediments may be contemporary

with

the

Laschamp

Geomagnetic

Event a t -47 Kyr BP

(Hall

&

York

1978). Alternat ively, the

c lays may have

recorded

an

older

Brunhes

geomagnetic

event

or may

da te

from

the

Matuyama

Magnetic Epoch (>720 Kyr).

Cave s i l t s

with a reversed

remanence polar i ty

have

also been found

in Masson Mine, Derbyshire

(Noel,

Shaw and

Ford 1984).

INCLIN TION

8

o

70

80

90

0

80

0

m

Figure

12. Prof i les of

remanence

directions in

the

slumped clay

before (0

) and

after

(e)

demagnetisation

in

a peak

alternating

f ield of SmT.

SLUMPE

[

20

em

Figure 13 . Sketch i l lus t ra t ing t he posit ions of samples in

the

s l umped

clay

and

the

form

of the

a l

ong-passage

velocity

dis t r ibut ions , V in the deposit during the flow . The

shor test axes of moving

grains were

aligned paral lel

to

the

velocity

gradient

giving r i se

to

the directions of minimum

suscept ibi l i ty in the

samples

shown

by

the diametric l ines .

REFERENCES

Ai tken, M J . , 1974 . Physics

and

Archaeology . Clarendon

Press, Oxfo

rd.

Atki

nson

T. e . armon , R.So Smart P.L. Waltham, A.C.

1978. Pal aeoc

l i

matic

and

geomorphic

implications

of

23

0Th/ 234U

dates on

speleothems

from

Br i tain,

Nature,

2

72-24-

28 .

Bull, P.A.,

1976.

An

electron

microsco

pe

study of cave

sediments f r om Agen

Allwedd,

Powys ,

Trans. Bri t

i sh

Ca

ve

res

. Ass . , 3, 7-14.

Bull,

P.A . ,

1976. Observations on small sedimentary

qua r

tz

part icles analysed by scanning

electron

microscopy,

Scann.

Electron. Microsc., 1,

821-828.

Bull,

P .

A., 1980.

The

antiq

u

i ty of caves and dolines

i n t

he

Bri t ish Is les , Z. Geomorph., 36, 217-232.

Bu l

l , P . A. ,

1981.

Some f i ne -gra i

ned

sed i mentat ion phenomena

caves , Earth Surf. Proc.

La

ndforms,

6,

11-22 .

8/21/2019 BCRA 15-1-1988

11/40

Collinson,

D.W., 1983. Methods

in

rock

magnetism and

palaeomagnetism,

Chapman and Hall, London.

Creer,

K.M., 1974. Geomagnetic var iat ions for the interval

7000-25,000 yr BP as recorded in a core of sediment from

stat ion

1474 of

the

Black Sea Cruise of Atlant is I I .

Earth

Planet. Sci.

Lett . ,

23, 34-42

.

Creer,

K.M.,

1981. Long-period

geomagnetic secular

var ia t io

ns since 12,000

yr BP, Nature,

292, 208-212.

Creer

K.M. 1982. Lake

sediments

as recorders of

geomagnetic

f ield variations - applicat ions

to dating

post-Glacial sediments, Hydrobiologia, 92, 587-596.

Creer,

K.M., Kopper, J .S

. ,

1974. Palaeomagentic dating of

ca ve paintings in Tito Busti l lo Cave, Asturias, Spain,

Science,

186, 348-350.

Creer, K.M., Kopper J .S . , 1976. Secular osci l lat ions of

the

geomagnetic

f ield recorded

by

sediments deposited in

ca v

es in

the

Meditteranean

region,

Geophys. J.R. as t r .

Soc . ,

45,

35-58.

Granar L.

1958

.

Magnetic

measurements on

Swedish varved

sediments,

Ark.

Geofys., 3, 1, 1-34.

Hall, C.M. York, D., 1978. K-Ar and 40-Ar /

39-Ar

age of

the Laschamp geomagnetic polari ty reversal ,

Nature,

274.

462-

464.

Hamilton,

N

King,

R.F.,

1964.

Comparison

of

bedding

errors

of ar t i f i c ia l ly

and natural ly deposited

sediments

with those

predicted

from a simple

model, Geophys, J .

8,

370-374.

Hamilton, N Rees,

A. I . , 1970. The use of magnetic

fabric in

palaeocurrent estimation, In :

Palaeogeophysics,

ed.

Runcorn S.K. Academic Press London.

Hand

8 .M.

1961. Grain orientat ion in

t urbi d i t e s

Compass

Cambr., 38,

133-1444.

Heller, F. Tung-sheng,

L., 1982.

Magnetostratigraphical

dat ing of loess deposits

in

China,

Nature, 300,

431-433.

Homonko, P., 1978. A palaeomagnetic

study

of cave and

lake

deposi ts in Bri tain

M.Sc.

T h es i s

Univers i ty

of

Newcastle upon Tyne.

Johnson, E.A., Murphy,

T. Torreson,

O.W.,

1948.

Pre-history of the Earth s magentic f ield ,

Terr. Mag.,

53, 349-372.

King, R.F., 1955.

The

remanent magnetism of

ar t i f i c ia l ly

deposited

sediments, Mon

Not.

R

ast r . Soc. Soc.

geophys .

Suppl., 7,

115-134.

Kopper,

J . S . , Creer, K M . , 1973. Cova

dets

Alexandres,

Majorca:

Palaeomagnetic dating and archaeological

in terpretat ion of i ts

sediments,

Caves

Karst, 15, 13- 18 .

Kopper, J .S . ,

Creer, K.M.,

1976.

Palaeomagnetic

dating and

s t rat igraphic

interpretat ion in archaeology,

MASCA

Newsl., 12,

1-3, University of Pennsylvannia.

Latham', A.G., Schwarz, H.P . Ford, D.C., 1979.

Palaeomagnetism of stalagmite

deposi ts ,

Nature,

280,

383-385

.

Molyneux,

L.,

1971. A

complete

resul t magnetometer

for

measuring

the

remanent

magnetism

of rocks,

Geophys.

J.R.

as t r . Soc., 24, 429 -

434.

9

Noel, M., 1975. The palaeomagnetism of varved clays from

Blekinge, southern Sweden, Geol. Foren. Stockh. Forh.,

97,

357-367.

Noel, M., 1983. The

magnetic remanence

and anisotropy of

suscept ibi l i ty of cave sediments from Agen

Allwedd,

South

Wales ,

Geophys.

J.R. as t r .

soc. , 72,

557-570.

Noel,

M., 1986 . The

palaeomagnetism and magnetic fabric of

sediments from Peak Cavern,

Derbyshire, Geophys .

J.R.

astr .

soc. , 84,

445-454.

Noel,

M.,

198?

The

palaeomagnetism and

magnetic

fabric of

cave sediments from Pwyll y Gwynt, South Wales , Phys.

Earth

Planet. Int . ,

(in

press) .

Noel, M Bull, P.A.,

1982.

The palaeomagnetism of

sediments

from

Clearwater

Cave,

Mulu,

Sarawak,

Trans.

Bri t ish Cave Res. Assn.,

9, 134-141.

Noel,

M., Homonko,

P, Bull,

P.A.,

1979.

The

palaeomagnetism of

sediments from Agen

Allwedd,

Powys,

Trans

. Bri t ish Cave

Res. Assn.,

9,

134-141.

Noel, M , Retall ick, W

G

Bull,

P.A.,

1981. Further

palaeomagnetic

studies

of sediments from Agen

Allwedd,

Trans.

Bri t ish Cave Res. Assn., 8, 178-187.

Noel, M., Shaw, R.

P. Ford,

T.D., 1984. A palaeomagnetic

reversal

in ear ly

Quaternary sediments

in

Masson Hill,

Matlock,

Derbyshire,

Mercian

Geologist,

9, 235-242.

Noel,

M 

St Pierre, S. , 1984.

The

palaeomagnetism and

magnetic

fabr ic of cave sediments

from

Gronligrotta and

Jordbrugrotta, Norway, Geophys. J.R.

astr .

Soc., 78,

231-239.

Rees, A.I., 1961. The

effect

of water currents on the

magnetic

remanence

and anisotropy of suscept ibi l i ty of

some sediments, Geophys. J.R. astr . Soc., 5, 235-251.

Rees,

A.I.,

1965.

The

use

of magnetic suscept ibi l i ty in the

estimation

of

sedimentary fabr ic, Sedimentology, 4,

257-271.

Rees,

A. I . ,

1966.

The effect

of depositional slopes on

the

anisotropy

of magnetic

suscept ibi l i ty

of

laboratory

deposited sands, J . Geol. , 74, 856-867.

Schmidt, V.A.,

1982.

Magnetostratigraphy

of sediments in

Mammoth

Cave, Kentucky, Science, 217, 827- 829.

Schmidt, V.A., Jennings, J . Bao

Haosheng,

1984. Dating of

cave sediments

a t

Wee

Jasper,

New

South

Wales, by

magnetostratigraphy,

Australian

J . Earth Sci . , 31,

361-370.

Stober, J.C., 1978.

Palaeomagnetic secular var iat ion studies

on

Holocene

lake sediments,

Ph.D. Thesis, University of

Edinburgh.

Received December 1987

Mark

Noel,

Department

of

Geology,

University of

Sheffield,

Sheffield

S7 3HF

8/21/2019 BCRA 15-1-1988

12/40

8/21/2019 BCRA 15-1-1988

13/40

CAVE

SCIENCE

Vol. 15, No.1 ,

Apri l

1988

Transact ions of

the

Bri t i sh

Cave Research

Associat ion

Natural

Tunnel Virginia

Tony WALTHAM

Abstract :

Natural

Tunnel, in Virgin ia , U.S.A.,

i s a 260m long

cave

t raversed

by

a standard

gauge

rai lway

from

sink

to

resurgence.

I t

is

a

spectacular cave

cur iosi ty ,

yet t remains in

r e l a t ive

obscur i ty .

The cave

i s the rejuvenated remains of a

phreat ic

loop ins t iga ted

by

underground

capture of a surface stream.

Natural

Tunnel

l i e s

in the Allegheny

Mountains about

5 km southeast of

the

small town

of Duff ie ld ,

in

the western

t i p

of Virgin ia ,

U.S.A., where t pinches

out

between

Tennessee and

Kentucky.

I t

i s

therefore in the hear t

of the

Valley

and

Ridge

kars t

region of

the

grea t

Appalachian

fo ld mountains and

should

not be

confused with the

wel l

- known but much

shorter

Natural

Bridge, which

l i e s

300

km to the

eas t .

The Tunnel has dimensions which are

hardly

remarkable, though

t i s a

passage of considerable

cross -sec t ion ,

and t would probably receive few

vis i to r s

t t

did

not

happen

to

have

a

main- l ine

rai lway

l a id throughout i t s length.

History of the cave

I t appears

that

Indians

used

the cave

long

ago

as

a

route between hunt ing grounds, for

a

complete t r averse

i s

j u s t poss ib le

without leaving

a t l eas t

a ves t ige of dayl ight . But t i s

speculateG

t ha t

the f i r s t white man

through

Natural

Tunnel was Daniel

Boone,

soon af te r 1769

when he l ived in the area br i e f ly and was

exploring west in to

Kentucky. Writ ten

descr ipt ions

of

the

cave

date

from as ear ly

as

1832,

but t then seems to have sunk

back

in to

obscur i ty unt i l 1880,

when

an engineer , J .H. McCue

came across

t

while surveying

a route for

the

South Atlant ic and Ohio

Rai l road l a te r

to become

par t of

the Southern Railway .

Figure 1 The area of Purchase Ridge and Natural Tunnel

11

Purchase

Ridge i s a subs tant ia l topographic

feature,

essen t i a l ly composed of sync l ina l

limestone escarpments or iented NE SW in l ine with

the Appalachian

s t ruc tu ra l

t rend. I t separates

the val leys of

the

North

Fork

of the

Clinch River

and the main Clinch

River

f igure 1) , both of

which dra in southwest eventual ly in to

the

Tennessee River. The Ridge r i ses to cres t

elevat ions of

about

600m 200m

above

the

Clinch

Rivers,

and the

modern

highway has

to climb to

500m to cross the r idge. However, the narrow

val ley of Stock Creek

cu ts

r ight through the r idge

a t around the

400m

l eve l ,

and

t h i s was the

route

chosen

by Mr. McCue.

But

par t way

through

the

Ridge, Stock Creek goes underground,

leaving a

dry

saddle cres t ing a t 448m.

This

i s where Mr. McCue

found

that

Natural

Tunnel,

the cave which

Stock

Creek t raverses almost beneath t h i s dry saddle,

was also spacious enough

to take

his

rai lway.

A

l a rge

amount of brushwood

and

debr i s had to

be cleared out of the cave, and a kink, par t way

through, demanded

30m of

blasted

tunnel .

Otherwise,

a

low embankment was bui l t on the f irm

sands

and

gravel

of

the cave sediment to

keep the

rai lway above f lood l eve l s , and, with a gentle

reverse curve

in

i t s

t racks,

the rai lway gained an

underground route 250m

long

for minimal cost .

The

rai lway

through

Natural

Tunnel

i s st ll

in use

today.

This in i t s e l f

i s f a i r ly

remarkable

The caboose of a northbound f reight t ra in

disappears

nto

atural Tunnel

8/21/2019 BCRA 15-1-1988

14/40

in America, but the

l ine

t raverses the

great

Appalachian

coal f ie lds and

has

been kept

al ive

by

coal. There have been no regular passenger t r a ins

for many years ,

but

about 10 t r a in s per day

st ll

pass

through

the

Tunnel, mostly diesel-hauled

very

long l ines

of

coal

trucks .

Since 1971,

Natura l

Tunnel

has

been a s ta te

park, though i t s

vis i to r

centre and

tour i s t

f ac i l i t i e s

are only

cur rent ly being developed,

and

An empty coal t ra in rolls into the

south

end of Natural

Tunnel, as seen from the top of the limestone c l i f fs

Elevation

on 75

plan scale

5

amphitheatre cliffs

Entrance

Exit

par t

of

i t s

a t t r ac t ion l i e s

in

the campgrounds and

foo t - t r a i l s on the wooded

ridge, This

does make

the s i t e very accessible , with l a id paths to

c r i t i ca l

poin ts

including a spectacular viewpoint

above the c l i f f s around the cave

exi t . A path

descends through

the

woods

and reaches the

cave

af ter

pass ing

through another

short

railway

tunnel .

Perhaps

surpr i s ingly in a society

normally zealous over safe ty cont ro l s ,

vis i to r s

can

wander along the ra i lway

t rack through

Natura l

Tunnel,

a l l of which is a t l eas t gloomily l t by

daylight.

Signs

warn

to

beware

of

t ra ins ,

but

the sound ef fec t

of an

approaching

t r a in

makes

an

accident a

th reat

only to someone completely

devoid

of ears or

brain.

There

i s

l i t t l e

exis t ing

l i t e r a ture

on

Natura l

Tunnel. Together

with Natura l

Bridge

(a lso in

Virginia) t

was described by Woodward

(1936), but

he lacked

cave

surveys and

was

a

l i t t l e

over-enthusiast ic about

collapsed caverns .

Since then

t

has

achieved passing mention in

various

ra i lway

journals , textbooks

of

engineering

geology

and items

of tour i s t l i t e r a ture

(with much

of

the

l a t t e r

containing grossly dis tor ted

s t a t i s t i c s ) . Then in

1977,

a very deta i l ed survey

was prepared by W C. Douty and others for the

Virg in ia

Cave Survey.

The cave today

Stock

Creek i s

entrenched about

100m

in

a

narrow winding ravine

which

cuts through

the

l imestone of

Purchase

Ridge. The stream

enters

Natura l

Tunnel where

t

swings gent ly

l e f t

into

the

c l i f f

forming the eastern ravine

wall .

The entrance i s over 20m wide

and

15m

high,

and the railway

enters on the s tream's l e f t bank,

which has

been modified

with a low concrete wall

to

prevent

erosion beneath the t racks. The cave

is a simple arched tunnel

with

minimal breakdown

and

an undula t ing roof

l e f t

from

i t s phreat ic

o r ~ g ~ n s No rock f loor i s vis ib le , and the stream

i s

s l igh t ly entrenched in beds of sand, gravel

and cobbles ; there are

no s igni f icant

ca lc i te

deposi

t s .

There i s a very gentle overa l l

gradient, but the roof fa l l s to a low poin t on

an

overdeveloped l e f t bend. There the

modern

vadose

stream

swings through

a meander notch cut

in

the

rock

wall .

A

short cut sect ion

of ra i lway

tunnel

avoids both the bend and the low roof.

The downstream hal f

of

the cave i s more

spacious , wi th

the

ra i lway

on

a

low bank almost

down i t s

centre. The

roof r ises in to a shallow

dome, blackened

by smoke from by   gone stream

t ra ins , and then r ises towards the exi t . The

resurgence of the cave i s a splendid

arch

25m high

Figure 2 Survey of Natural

Tunnel

NATURAL TUNNEL

Virginia U.S.A.

o

m 1

cliffs

Stock

Creek

~ 4 = ; ; 0 = ; ; 0 : = = = = = = = = = = = = = = = = = ~ r ~ a ~ I I ~ W ~ ~ Y : : : 1 Downst

ream

cr bed

CW

12

8/21/2019 BCRA 15-1-1988

15/40

and

wide, which appears to have been

hardly

trimmed

to take the ra i lway agains t the

l e f t

wall .

Above

the

cave

exi t ,

a ver t i ca l l imestone

c l i f f r i ses

about 80m,

wall ing

a

f ine

natural

amphi thea t re . Stock Creek swings round

the

edge

of

t h i s rock bowl,

before

rounding a spur in to a

more open

val ley

beyond . The

railway

uses a

shor t

tunnel

through

the spur , and

then re jo ins

the

creek on

a

dayl ight course .

Total

length

of

the

Natural Tunnel

cave i s

260m,

and it

descends only a few metres. The

survey

(

f igure

2

i s

a

low-grade,

one-man

product ion, but,

because

of the

simplici ty

of the

cave, it

i s

probably

a very

f a i r representa t ion .

Origins of Natura l Tunnel

Purchase

Ridge i s

a

narrow

syncl inal

core

preserved in massive l imestone with outward-facing

escarpments

of which the nor thern

s ide r i ses to

the h igher

cres t

f igure

1) . I t

is par t of

a be l t

of su b - para l l e l s t ruc tu ra l ly control led

r idges,

whose pat te rn

i s

complicated

a

l i t t l e by

some

cross - faul t ing and over

-

th rus t ing . Northeast of

Stock Creek, Purchase Ridge

widens

in to a pla teau

as

the

syncline opens

out

. Both

pla teau and

r idge , and also the other

l imestone

r idges

in

the

area ,

are

r iddled with dol ines , b l ind val leys and

sinkholes, and comprise f ine kars t landscapes.

Both the Clinch River

and

i t s North

Fork

are

t runk streams flowing

para l l e l

to

the

s t ruc tu ra l

controls . The

headwaters of

Stock Creek

or ig inal ly

drained

into

the

North

Fork, and an

obvious wind gap survives

a few

ki lometres

nor theas t of Duffield f igure 1) .

A t r ibu tary

of

the

Clinch River then eroded headward into

Purchase

Ridge and eventua l ly captured the

head

of

the

North Fork -

to form Stock Creek

along

most of

i t s

present

l ine .

There

i s

no c lear remaining

evidence

that

th i s i n i t i a l

capture

involved

any

underground cu t

-

offs , but the poss ib i l i t y cannot

be

ru led

out. And

the

present

drainage

pat te rn

i s

probably

superimposed from

a landscape

of

much

l ess re l i e f .

The or ig inal route

of

Stock Creek took

it

j u s t west

of Natura l

Tunnel, along a

still

well-defined val ley, now followed

by

a

minor road

over a

dry saddle f igure 3).

A

sec t ion of val ley

lS00m

long

was

then

abandoned

when

another capture

took the water through Natural Tunnel;

the wind

gap now

l i e s 4 m

above

the

present stream l eve l .

This

capture

c lear ly

was

underground, as water

leaked through

the i n i t i a l opening

of

Natura l

Tunn 

e l and

in to a

shor t

t r ibu tary

val ley enlarging

headwards from the

eas t bank.

of the val ley lS00m

downstream. Development of t h i s underground loop

offered

hardly any shor ten ing of the

surface

route, but

was probably aided

by

fol lowing bedding

The railway track

inside

the Natural

Tunnel

cave

13

m

Figure

3

Surface

features around

Natural

Tunnel

planes

r igh t

across the syncl ina l core.

The

or ig ina l sink in to t h i s phrea t ic loop

was

very c lose to

the

present

northern entrance of

Natura l

Tunnel. The or ig ina l resurgence

was

a

vauclus ian

r i s ing

with

a

phrea t ic li t of c lose

to

40m, as

indica ted by the

level of

the wind gap,

and

appears

to have been

some

shor t way downstrea

m

8/21/2019 BCRA 15-1-1988

16/40

14

of the present cave

exi t .

Subsequent regional

lowering of

both Clinch

River

and

Stock Creek

el iminated th i s phrea t ic loop and l e f t the

roof

of Natural Tunnel

above

water

level .

Vadose

modificat ion of the cave since then has

been

minimal

except

for an element

of

collapse

back

from the or ig inal resurgence.

There i s no

evidence nor any apparent s tructural

control

to

suggest that the i n i t i a l phreatic cave rose

sharply

to i t s

resurgence a t

the s i t e

of the

present cave

exi t .

The rock

amphitheatre

a t

the

exi t

has

ver t ical

walls

and

almost

cer ta inly

formed by

collapse

of the

cave

where

t

wrapped

round an

exceedingly

sharp l e f t

bend

perhaps

leaving a cave pi l la r of

inadequate

strength.

Fai lure

of the

roof i t se l f thinning as the

surface

slope

descended to

the south occurred a

long

time ago.

Stock Creek has since removed the

breakdown and graded i t s course to leave a

spectacular

exi t to

Natural Tunnel.

ACKNOWLEDGEMENTS

The author thanks Tammie

Heazlit

for

chasing various

reference items in

America

nd

acknowledges source

data from

the NSS f i les .

REFERENCE

Woodward H.P.

1936.

Natural Bridge and Natural

Tunnel

Virginia. Journal of

Geology

v.

44

pp

604-616

.

Received January

1988

A C Waltham

Trent

Polytechnic

Nottingham

NGl

BU

Looking

out

of

the

south end of

Natural

Tunnel

8/21/2019 BCRA 15-1-1988

17/40

CAVE

SCIENCE

Vol

.

15, No.1 ,

Apri l

1988

Transact ions

of

the

Bri t i sh Cave Research

Associat ion

Postglacial

Tufas

and

Travertines

from

the raven

District

of Yorkshire

Allan

PENTECOST

and

Tom LO

RD

Abstract : Pos tg lac ia l tufas , t r aver t ines and

cemented

gravels

are

described

from 29 s i te s .

The

depos i t s are c la s s i f ied

according

to

t he i r

assoc ia ted f lora ,

where t h i s i s present . Most depos i t s exposed to l i gh t were assoc ia ted with

bryophytes ,

cyanobacter ia

and

higher

plant s . Archaeological evidence was

obtained

a t

some s i te s suggest ing a

phase

of

rapid

or

more extensive deposi t ion

pr ior to

or dur ing

the Atlant ic Per iod 6000-8000

years BP)

and t h i s was

suppor ted by the l a rge number of

pos tg lac ia l

s i t e s where there is

l i t t l e

act ive

depos i t ion today. Nineteen s i t e s are described for the f i r s t time.

INTRODUCTION

Tufa

deposi t ion can

occur

in any region

where

l imestones are

over la in

by so i l .

The

so i l

atmosphere , which contains 10-50 times more

carbon

than the

a i r

i s pr imar i ly responsible for the

disso lu t ion

of l imestones

and

subsequent

de-gassing

and

re -

precip i ta t ion

of much of

the

carbonate as

speleothems

and tu fa . The chemistry

of

the process

is

f a i r ly well understood although

the

mechanism of

the r ec rys t a l l i za t ion and

the

s igni f icance

of bac ter ia

and algae requ i res

fur ther study.

Tufa

deposi t ion can

r esu l t

from

several unre la ted changes

occurr ing

in the

percola t ing

water .

Previous stud ie

s

in

the Craven

d i s t r i c t

have

shown t ha t the major

change i s

the

di f fus iona l

loss of

carbon

dioxide to the

atmosphere Pentecost ,

1981).

However, there i s

some

evidence to

suggest

t ha t the uptake

of

carbon

dioxide

by

photosynthesizing

plant s , temperature

ch

an g

es and

water loss by

evaporat ion

also play

some par t

in tufa

deposi t ion

Barnes, 1965),

though genera l ly on a

smal ler

sca le .

Tufa,

when f i r s t

formed, may

be e i ther so f t

and

with

a

mealy

or crumb-like

t ex ture ,

or

massive

and

s tone- l ike .

Several at tempts have

been

made

to

c lass i fy the

var ious

types, though

none

appears

to

be sa t i s f ac to ry when

applied to the range of

depos i t s

found

in

Craven. Gruninger 1965) and

Frey

Probst

1974) have followed

a

system

descr ibed by

Klahn 1923) for tufas

of the

Schwabische

Alb. This

c lass i f i ca t ion i s

based

upon the shape of the depos i t which i s

inf luenced

by

the angle of slope . Although useful , these

def in i t ions do not consider the small

-

sca le

s t ruc ture

of

the

depos i t s .

I r ion Muller 1968),

attempted a biogenic

c lass i f i ca t ion into

s in t e r or

t raver t ine,

which i s predominantly inorganic , and

var ious

c lasses

of

organic a lga l and moss

tufas

.

In

th is paper we

place

emphasis

on

the

inact ive

s i te s of

the

d i s t r i c t because

of

t he i r

potent ia l value as sources of palaeoenvironmental

data

Kerney e t

aI ,

1980)

and

as

a

medium

for

the

preserva t ion of archaeological

material .

Figure 1 .

I l lus t ra t ions ot

moss-tufa

fabr

ics found in

Craven.

a) cascade

tufa

Rhynchoste g ium

r ipar ioides ),

arrow

shows direct ion o f

water

flow

. b) hummock tufa plumose

ratoneuron commut tum nd

Pell ia) .

c)

stromatoid

tufa

TGYrnnOstomum) Bar 1 cm.

15

CLASSIFICATION

The

scheme

adopted

i s

based

upon the

predominant vegetat ion,

where

present

Table

1) .

As plants become

encrusted by the depos i t , they

eventual ly decay but leave t he i r or ig ina l

s t ruc ture

impr inted

on

the

mater ia l

.

Consequently, the tufa fabr ic

i s l a rge ly

determined

by them. Plants are general ly absent

only where l igh t in tens i t i e s are

low

or

nonexistent .

Such

condit ions occur

in

caves

and

in deep t a lu s .

We

have

reserved two

terms

for

abio t ic

mater ia l ;

t raver t ine

for porous

i r regular ly

laminated depos i t s

formed

within

caves, and clas t - suppor ted

brecc ia

for cave

deposi ts

containing >50

brecc ia by

volume with

the i n t e r s t i ces

f i l l ed

with

t raver t ine.

Some doubt remains concerning the def in i t ion

of

t raver t ine.

The term

was

or ig inal ly

used to

describe

depos i t s occurr ing

near Tivol i

in

I ta ly

and

there i s some

evidence indicat ing that

much

of

the mater ia l i s of

bac te r i a l or ig in Chafetz

Folk,

1984).

I f t h i s proves to be cor rec t , the

term calcareous s in te r , which i s also

used

to

denote

abio t ic

depos i t s ,

may

be

more

acceptable .

Bryophytes are

the

most conspicuous plants

associated with

the

i l luminated

and

act ive Craven

tufas

and there are a

number

of

charac te r i s t i

c

species .

The

plumose var ie ty of

Cratoneuron

commutatum

f or

ms yellow-brown

mats

in seepages

or

slow-flowing water and

i s

the charac te r i s t i c moss

of hummock tu fa .

This tu fa

i s found around small

springs

as

i r regular

unlaminated

mounds, sometimes

dissec ted by

narrow

channels Fig.

lb ) .

In par t s

of Belgium such

depos i t s

are

known

as crons

Symoens,

1951).

In

shaded seepages, tufa

- encrusted mosses

with a

radiat ing

cush ion- l ike stromatoid)

s t ruc ture

occur

Fig. l c ) . Two important

genera

forming t h i s type

of

tu fa are

Eucladium

and

Gymnostomum.

Final ly

there are bryophytes which

grow in turbulent condit ions

where

the moss stems

become

al igned

with

the

di rec t ion

of water

f low.

As

t h i s

tu fa

forms, a

ser ies

of l ayers is

b

8/21/2019 BCRA 15-1-1988

18/40

 

low

regl me

assoc

iate

d

vegetat1 n

Table 1 Tufa classificat ion

absent

cyanobacted a

bryophytes hlghe r plants

c sc de

tufa

turbulent

l aml na

ted tu f

a

Rh:z:nchosteslum

non  plumose

Cratoneuron

Ho  o

thr1

x

travert1

ne

Sch1z o

th r 1x

lam:1nar

l s  

supported

R:1vular1a

hummock tufa

breccia

pl u ose

C

raton

eur

on

unconsolida t ed

tufa

SCItonema

stramatoid tufa Carex

u

ncus

seep ge

s

Eu c1adlum

produced.

The

layers are approximately 2-10 m

thick and cons i s t s of

s lan t ing

moss

stems

similar

in appearance

to

a

sect ion

through a thatched

roof.

This

is

defined

here

as cascade

tu fa .

Three

moss species

are associa ted with th i s tufa:

Cratoneuron commutatum non-plumose

var iety) ,

Rhynchostegium

r ipar io ides

and Eucladium

ver t ic i l la tum Fig. 1a) .

I t

should be

noted

t ha t

the flow

regime l a rge ly

determines the

type of

vegetation

presen t

Table

1) .

Cyanobacterium tu fas also

occur. These

consis t

of ser ies of

th in

encrusting

layers.

The

cyanobacterium colonies formerly known as

blue-green algae)

are usually

nodular

and rarely

exceed

10

in

diameter

resu l t ing

in

a

rugose

surface. These tufas are

less common

than

bryophyte tu fas but occur

in

f as t - and

slow-flowing

water

Table 1) . In some s i t e s ,

cyanobacter ia overgrow bryophytes and here tu fa

formation

must be

inf luenced

by

both

groups of

organisms

Pentecost 1978

,

1981,

1987).

Unconsolidated

tu fa or spring chalk

forms

in

mires

where

higher plant s are of ten

dominant.

16

The

deposits often

form

around the

bases

of Carex

and other

wetland

species , o r produce a marl

between

the tussocks.

Animal remains may be a

conspicuous featu re and

some species

of gastropods

of narrow ecological amplitude can be preserved in

this tu fa . These have proved

to

be usefu l

environmental indicators Kerney

e t

a l . , 1980).

I t

i s

important

to

real ise that in any

s i tuat ion , intergradat ions

occur between

these

types of

tu fa .

With

act ively forming deposi ts ,

t

is

easy

to

ident i fy

the dominant form of

vegetation but

with

foss i l ised mater ia l

th i s

i s

of ten

not possib le .

Most

modern

tufas

in

the

Craven d i s t r i c t

cons i s t of micri te . The calc i te crys ta ls are

of ten l

l -defined

,

anhedral

and 5

um

or

less

in

diameter. Bryophyte

stems

and

leaves

are

sometimes

encrusted

wi th

ca lc i e pal isades

consist ing

of

crystals 50-100

um

in

length with

their long axes perpendicular

to

the moss surface .

Microspars

are

also

found, with euhedral ,

drusy

crystals

occurr ing

in

small

cavi t ies ,

probably as

a resul t

of

recrys ta l l izat ion or l a t e r in f i l l i ng .

U

ncon

s o

l idated tufa

on

the

east

bank of Clapham Beck s i te 7 .

The beck has

expcsed

a 2 m

section through the

depcs

i

t , top

marked by arrows .

8/21/2019 BCRA 15-1-1988

19/40

75

Figure 2. Map of s i t e s

.

Numbered s i t e s with large

circles are described in

the

t ex t .

Small

c i r c l e s

without

numbers

depict o ther act ive

s i tes .

Circle s ize is

not

related to deposit s ize .

Faul ts : NCF North Cr av

en:

MCF

Mid Craven: SCF South Craven.

65

76

72

68

t

-

7 J

'

~ 9 1 1

'

-

 

80

Microspars

with

crys t a l s up to 60 urn in

diameter

are

often found cementing scree . Older tufas

generally

have a

similar

petrology

to act ive s i t e s

although organic mater ia l i s usual ly absent . The

tufas of

Gordale

are

exceptional

for t he i r

pronounced laminations and

apparent

r ec rys t a l l i za t ion .

Here

,

microspar

i s

found

al ternat ing

with large ca lc i te

pal isades up

to

3mm

in length. Ser ies of these

laminae

are found

sandwiched between micri

tes bui l

up around

Eucladiurn.

The petrology of some Craven s i t e s i s

described

in

more de ta i l elsewhere

(Pentecost,

1978, 1981, 1985) .

DESCRIPTION

OF

SITES

For

s i t e

posit ions re fe r to Figure 2. All

gr id references

are in square

SD(34)

.

1.

695754

a

l t .

230

m Cascade tufa

2 m

high, jus t eas t of

Thornton Force.

2. 698735 a l t . 130

m

Bench

of cemented r ive r gravel 1 m

above the

R.

Doe,

20 m in l ength wi th

act ive

rimstone

t r ave r t ine nearby. Meal Bank Quarry, adjacent to th i s

Ingle ton s i t e may have s t a r t ed as a tu fa quarry .

3.

757714 a l t . 290 m.

Rel ic t

hummock t u fa ,

extending 15

m

down

slope of eas t

s ide

of dry

valley

above

Ingleborough

Cave.

4. 757713 a l t .

285

m

Rel ic t hummock t ufa extending 10 m

down s lope

o f

eas t

s id e o f

dry va l l ey with protuberant

r e l ie f

.

5. 756713 a l t .

280 m Rel ic t hummock tu f a

jus t below s i t e

4.

An active

Cratoneuron

tu fa

occurs

100m lower down

the

valley near

Ingleborough

Cave. ,

6.

754711 a l t .

265 m Hummock tufa grading

i n to

t rave r t ine

a t the entrance

of Ingleborough Cave.

The

t r ave r t ine bar r i e r

j us t within the cave was removed

by

bl as t i ng in c .

1837

(Dawkins,

1874). Impressions of l iverworts

and mosses

cf .

Conocephalum,

Cratoneuron

occur .

7. 752707 a l t . 250 m Layers of

unconso

l i d a ted and hummock

tu fa exposed in

west

bank of

Clapham

Beck . Exposures up to

50 cm

th ick

extend l a te ra l ly

for

30 m

8 .

751706

alto

indurated blocks,

Beck.

235 m Small bank

of

hummock t u fa with

in

woodland

by the footpa th along

Clapham

9. 788663 a l t

. 245

m

Cave

Ha 1. Large

l imestone rock

s he l t e r

with

f loor deposits

of t ravert ine and

clas t -suppo

r t ed

breccia McKenny

Hughes, 1874)

. Indura ted

cushion

-

l ike

(s t romatoid) tu f a bosses up to 20 cm wide underneath western

extremi ty

overhang.

Some of the t r ave r t ine i s reported to

have a high phosphate content

resu lt ing

from

in f i l t ra t ion

of

water

through

a layer of

guano

(Marr ,

1876).

17

MalhamJ;:?

- ._Tarn

'---.

'-

- t i F ~

- .- .

t K E ~ _

5km

85

90

95

10.

788663

a l t . 245 m Cave Ha 3. Limestone rock she l t e r

with f loor deposits of t ravert ine and clas t-suppor ted brecc ia

over lain by uncemented ta l us. A few s t romatoid tu fa bosses

on the wall. The sit has yielded archaeologica l mater ial

sealed within

travertine

and finds

include

numerous human and

animal bones, a

few

chipped stone too ls

and charcoal . The

bulk of

the t r ave r t ine formation had preceeded the depos i t ion

of

the occupat ion horizons From the typology of the

stone

to o ls and the composit ion

of

the fauna, the occupation

horizons are

most

l i ke ly Atlantic / Su