Clay Min. Bull. (1964), 5, 373.
THE
RED
OF
GLACIAL
DRIFT DEPOSITS
SCOTLAND
NORTH-EAST
R. GLENTWORTH, W. A. MITCHELL AND B. D. MITCHELL
The Macaulay Institute for Soil Research, Aberdeen
Read 12th April 1960
ABSTRACT: Extensive deposits of red glacial drift and lacustrine
clay occur along the east coast of Aberdeenshire and constitute the
parent materials of important agricultural soils. The mineralogy of
lacustrine clay at Tipperty, Aberdeenshire, has been determined by
X-ray, differential thermal, and optical methods. General relationships between the mineralogy of this soil parent material and that of
other red drifts in the vicinity are discussed with reference to the glaciology of the region. It is suggestedthat these red drifts were transported
from the bed of the North Sea and not from Strathmore.
INTRODUCTION
For about 25 miles along the eastern coast of Aberdeenshire there
occurs a red-coloured glacial drift deposit occupying approximately 70
square miles and consisting of boulder clay and lacustrine clay. The
latter, which covers about a quarter of the total area, appears to be
derived from the boulder clay. The parent material o f some o f the most
productive agricultural soils of the region is derived from these two
components of the red glacial drift.
In this communication detailed mineralogical data are given for the
fine-textured lacustrine deposit on which the soil of the Tipperty Association is developed, and the general relationships between the
mineralogy of this soil parent material and that of the other parent
materials in the vicinity derived from red glacial drift are discussed with
reference to the regional glaciology.
ORIGIN
AND
DISTRIBUTION
The origin of the red drift has been attributed, from field evidence, to
Old Red Sandstone sediments transported to the Aberdeenshire coastal
plain from the Vale of Strathmore by ice of the second glaciation
(Bremner, 1934). The deposit has in consequence been termed t h e
'Strathmore drift.' The northern deflection of the ice from Strathmore
is thought to have been due to the vast Scandinavian ice sheet which, in
373
374
R. Glentworth, W. A. Mitchell and B. D. Mitchell
the vicinity of the Aberdeenshire coast, was moving in a north-westerly
direction at the time of the glacial maximum (Bremner, 1934; Simpson, 1948, 1955). The distribution of the red boulder clay and the
associated lacustrine clay in eastern Aberdeenshire and the northern part of Strathmore is shown in Fig. 1.
1
ABERDEEN.:.":"[
NEWPITSLIGO
Keyto soil
associations
HATTON~
PETERHEAD~
ll~l~l'r~rr~," ~l~/J
~
/
/
./'
~INVERBERVIE
/"E~E~L
TIPPERTY
/
r/~
~BALMEOIE
O'NTROSE
LAURENCEKIRK
/
.4Miles
ABERDEENI
FXG. 1. The distribution of soils developed on red glacial drifts and clays
in north-east Scotland.
LACUSTRINE
DEPOSITS
Within the area of the red glacial drift lacustrine clays occupy about 17
square miles. These deposits, it is thought, were transported by drainage water from the Scandinavian ice on the seaward side. Occasionally
bands of grey-brown sand are observed interlayered with reddish brown
fine-textured material. This sand is tentatively regarded as a dePOsit
o f water-sorted material from the Scottish ice on the landward side.
The lacustrine deposits lie between the 25 and 300 ft contours, the
majority occurring at about 100 ft. The deepest deposits, however, are
located below the 100 ft contour and constitute the main brick-earth
Red glacial drift
375
spreads. Simpson (1955) considers these to have been deposited in
marine conditions, the sea level at the time standing at about 100 ft.
Numerous meltwater channels running parallel to the coast between
Stonehaven and Peterhead all o p e n out at their northern end at this
level and were cut in succession, the most northerly ones first, as the ice
front retreated southwards, leaving open sea to the north.
The lower-lying clays are varved and in a dried-out exposure the
varves are readily visible on a slicked surface at right angles to the
bedding. They are not visible in the B and C horizons of the soils
developed on these deposits because o f the superimposition o f a pedologically induced morphology. In contrast to the lower-lying lascustrine
deposits, those at elevations above 100 ft are distinctly laminated but
none have been found to be finely varved.
The relief in the areas o f lacustrine material is not flat, as might be
expected, but gently rolling, the deposit apparently following the contour
o f the underlying formations.
THE TIPPERTY
CLAY PIT
The Tipperty clay pit provides an excellent example of the low-lying
phases of the lacustrine material and the greater part o f the mineralogical
data quoted refers to clay samples from this particular locality. The pit
is situated 13 miles north o f Aberdeen and about 1 mile west o f the
Ythan Estuary, at an altitude of approximately 50 ft in a broad valley
drained by the Tipperty Burn.
The present working face consists o f some 12 ft o f remarkably uniform reddish brown (5 Y R 4/3-4/4) varved clay, the imperfectly drained
brown forest soil which predominates on this deposit having been
stripped off. Evidence o f varying appears at about 4 ft--that is, at a
depth outwith the limits of markedly effective pedogenic processes--and
increases with depth. Individual varves are usually from ~ to xs in.
in thickness and are made up of horizontally laminated reddish brown
clay with a parting plane of coarser material which ranges in texture
from silt to fine sand. Occasional strata o f higher silt content are
fairly common; one in particular approximately 3 in. thick was noticed
about 8 ft below the original soil surface. Large vertical cleavages
associated with the coarse prismatic structure of the lower horizons o f
the soil penetrate deeply into the varved clay, and greyish fine-sandy
textured surfaces with occasional dendritic manganese staining are
commonly observed in these large fissure planes. A few live roots
penetrate some distance into the clay deposit, their frequency diminishing
rapidly below 5 ft. Between the varved clay and the underlying boulder
clay there is about 12 in. of water-sorted sand and gravel.
376
R. Glentworth, W. A. Mitchell and B, D. Mitchell
EXPERIMENTAL
Materials
The clay fraction and the light and heavy fractions of the fine sand of
the varved lacustrine material and underlying boulder clay from the
Tipperty pit were examined. Soils of the Tipperty Association are
developed on the varved clay, and the mineralogical composition of
samples from the C horizon of a number of soil profiles representative
of this soil association was determined. In order to ascertain the origin
of the red boulder clay and lacustrine clay, samples of soil parent
materials derived from red glacial deposits in the northern part o f
Strathmore and in the Aberdeenshire coastal plain were also examined.
The soils investigated in the Strathmore Valley were those of the
Laurencekirk and Stonehaven Associations; the former are developed
on a glacial till derived from Old Red Sandstone marl strata, and the
Stonehaven on till from Old Red Sandstone arenaceous sediments
including conglomerate and some lava. In eastern Aberdeenshire,
apart from the Tipperty Association, two other soil associations are
developed on the red glacial material, namely the Peterhead on a red
clayey till containing some igneous and metamorphic stones, and the
Hatton on a stony and very much coarser-textured glacial till. The
Peterhead Association is presumably derived from more argillaceous
rocks. Several samples of each of the soil parent materials were taken
from widely distributed profiles throughout the area to offset local
variations.
Methods
The proportions of sand, silt and clay fractions were determined by
mechanical analysis using a modification of the hydrometer method
(Bouyoucos, 1927). The fine sand (20-150 t~) and clay (< 1.4 .~)
fractions were separated by sedimentation and sieving; the mineralogy
of the light fraction (s.g. < 2-86) of the fine sand was ascertained from
X-ray examination and that of the heavy fraction (s.g. >2.86) ~ by
optical methods. The mineralogical composition of the clay fraction
was determined by X-ray diffraction and differential thermal analysis.
The differential thermal investigations were carried out in a nitrogen
atmosphere using the apparatus described by Mitchell & Mackenzie
(1959).
RESULTS
Samples of the varved material taken from different parts of the Tipperty
pit show a uniform clay mineral composition (Table 1). The illite
content varies between 70 and 80%, all of it being of the dioctahedral
type. The clay mineral assemblage of the boulder clay is closely similar
to that of the overlying varved clay except that the former contains a
Red glacial drift
377
small a m o u n t o f vermiculite. T h e similarity in clay mineral c o m p o s i t i o n
between these two deposits supports the field observations t h a t the
varved clay has been derived f r o m the b o u l d e r clay.
TABLE 1. Clay mineralogy of the red glacial deposits at Tipperty.
No. of
samples
examined
Sample
Varved clay
Boulder clay underlying
varved clay
Percentage
Kandite
Illite
Vermiculite
Quartz
4
15
80
-
5-10
1
15
75
5
5-10
The clay m i n e r a l c o m p o s i t i o n o f soil p a r e n t materials o f the region
d e r i v e d f r o m red glacial drift show (Table 2) that those o f Aberdeenshire,
i.e. the Tipperty, Peterhead, H a t t o n Associations, c o n t a i n considerably
m o r e illite t h a n the p a r e n t materials o f the L a u r e n c e k i r k a n d Stoneh a v e n A s s o c i a t i o n s o f Strathmore. M o n t m o r i l l o n i t e was observed
o n l y in the A b e r d e e n s h i r e p a r e n t materials, a p a r t i c u l a r l y large a m o u n t
TABLE 2. Average clay mineral composition of samples from basal horizons of
soils developed on red glacial drifts.
No. of
Soil
samples
Association examined
Tipperty
Peterhead
Hatton
Laurencekirk
Stonehaven
6
10
6
10
10
Percentage
Kandite
Illite
10
10
10
20
35
70
60
50
40
20
Vermi- Montmorilculite
lonite Hematite
I0
30
35
15
15
25
-
5-10
10
Quartz
< 10
< 10
5
< 5
Trace
(25%) being n o t e d in the H a t t o n Association, a n d significant contents o f
vermiculite are restricted to the red glacial drifts o f the Vale o f Strathmore.
M i n e r a l o g i c a l analyses o f the light a n d h e a v y fractions o f the fine sand
(Tables 3 a n d 4) were carried o u t to p r o v i d e further evidence o f the
relationship between the T i p p e r t y lacustrine deposits, the underlying
b o u l d e r clay a n d the O l d R e d S a n d s t o n e tills o f the Vale o f S t r a t h m o r e .
378
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Red glacial drift
379
F l u c t u a t i o n s in the relative a m o u n t s o f the different minerals d o occur
in the samples o f the varved lacustrine material, but they are o f a m i n o r
n a t u r e a n d the d e p o s i t is r e m a r k a b l y uniform. There are differences
between this m a t e r i a l a n d the underlying b o u l d e r clay. The f o r m e r
contains less quartz, h o r n b l e n d e a n d p y r o x e n e a n d m o r e mica a n d other
TABLE4. Mineralogical composition of the fine sand (20-150/0--light fraction.
Percentage of light fraction
Sample
Light fraction
as percentage
of fine sand
Quartz
•
Felspar
•
Mica
~5~
Kaolin
Tipperty, varved lacustrine
clay from present working
face
96-78
35
30
5
30
Boulder clay
varved clay
underlying
91 '98
65
25
0
5
Stonehaven Association
Tulloch
C horizon
93 "90
35
35
Trace
I0
Stonehaven Association
Uras
C horizon
93"60
35
35
Trace
10
Laurencekirk Association
Northhill Wood C horizon
97'60
35
35
Trace
15
Laurencekirk Association
Lower Powburn C horizon
98"85
35
35
Trace
15
layer silicates t h a n the b o u l d e r clay. These differences c o u l d be due to
c o n t a m i n a t i o n with m a t e r i a l f r o m the west as m e n t i o n e d above. T h e
mineral suite o f the fine sand fraction o f the b o u l d e r clay is in a c c o r d
with that observed for o t h e r red tills in n o r t h - e a s t Scotland, b u t it differs
significantly f r o m that o f the O l d R e d S a n d s t o n e b o u l d e r clays o f
Strathmore. T h e A b e r d e e n s h i r e m a t e r i a l is m u c h higher in the heavy
TABLE5, Mechanical analyses of samples from the basal horizons of soils developed
on red glacial drifts.
Soil 9
Association
Laurencekirk
Stonehaven
Peterhead
Tipperty
No. of profiles Sand (20-2000/0
sampled
(~)
10
10
10
6
56.5
61"3
42.2
14.4
Silt (2-20/z)
(%)
Clay ( < 2 / 0
(~)
16.4
14-1
16.6
30.0
27.1
24-6
41-2
55.6
380
R. Glentworth, W. A. Mitchell and B. D. Mitchell
minerals biotite, muscovite and amphibole, and very much lower in
iron oxides and garnet.
Mechanical analyses (Table 5) show that the red glacial tills of the
Vale o f Strathmore, i.e. the parent materials of the Laurencekirk and
Stonehaven soils, usually have clay contents between 20 and 30%.
The amounts of clay in the parent material of the Peterhead and Tipperty Associations of Aberdeenshire are considerably higher, the average for the Peterhead till being 41% and for the Tipperty 56%.
DISCUSSION
The red varved lacustrine clay at Tipperty has a mineralogical composition very similar to that of the extensive deposits of red boulder clay
in eastern Aberdeenshire and this substantiates the view that the former
was derived locally from the latter.
There are a number of indications, however, that these red deposits of
eastern Aberdeenshire are not derived from the Old Red Sandstone
rocks of the Strathmore valley. The clay mineral composition of the
drifts in the two regions are different, the higher content of vermiculite
in the Stonehaven and Laurencekirk Associations arising probably from
the local lavas. The differences in the fine sand mineralogy are very
striking, especially in the heavy mineral fraction. The textures of the
drifts are quite different; the Aberdeenshire material is much higher in
clay than that of the Strathmore valley. The scarcity of Old Red
Sandstone lavas and conglomerate cobbles in the Aberdeenshire erratics
is also noteworthy as these are a characteristic feature of the red drifts of
Angus and Kincardine.
In the course o f mapping soils in Scotland the Soil Survey has frequently noted a close relationship between the colour, texture and
mineralogy o f the drift and the underlying solid formations. In
general, the boundaries of soil associations--that is, groups of soil
series with parent materials having the same geological origin--are not
usually far displaced from the corresponding parent rock boundaries.
Displacements of the order of half a mile in the direction of ice movement are commonly observed, although local topography will influence
the distance carried. Erratics which have been carried for great distances
are occasionally observed in the glacial drifts, but the bulk of the fine
material is usually of local origin. It therefore seems unlikely that the
huge mass of red-coloured fine-textured material, over 100 ft thick at
Hatton of Cruden, could have been transported over distances of 30-40
miles from the northern end o f Strathmore to the Peterhead district.
It appears to the authors much more likely that the red drifts of Aberdeenshire were derived from red argillaceous rocks on the bed of the
R e d glacial drift
381
N o r t h Sea and were pushed over the present shore-line by the Scandinavian ice sheets. Broken shells and limestone erratics have been found
at Kippet Hills (Simpson, 1955) and oolitic limestone, presumably o f
Jurassic age, soft yellow dolomitic and hard grey and white limestones
occur in the red drift on Fue farm north of Newburgh. F r o m the
abundance of these limestone erratics in the latter area, the source rocks
probably occur along with red argillaceous rocks at no great distance
from the coast. The geological age of these red argillaceous rocks is
unknown, and although they may be of Old Red Sandstone age, i.e.
from an outlier similar to those at Turriff and Rhynie, it is also possible
that they are of Permian or Triassic age. Old Red Sandstone rocks
are known to occur near the Bridge of D o n on the northern outskirts of
Aberdeen, and at Potterton Burn 5 miles further north; also a deep
boring at the Aberdeen beach showed over 500 ft of Old Red Sandstone
sediments underlying recent and glacial deposits. However, these
formations are mostly sandstones and conglomerates and do not seem
to be fine enough in texture to produce the heavy boulder clays of
eastern Aberdeenshire, which can be compared with the boulder clays
from the Keuper Marls or the Permian Marls of north-east England.
To establish beyond doubt the derivation of the red drifts of eastern
Aberdeenshire the nature of the bedrock underlying the North Sea off
the Aberdeenshire coast would have to be ascertained. The evidence
advanced in this communication suggests, however, that these glacial
deposits are of local origin; this is contrary to the hitherto generally
held view that they are derived from the Old Red Sandstone rocks of the
Strathmore valley.
REFERENCES
Bouvoucos G.J. (1927) Soil Sci. 23, 343.
BREMNERA. (1934) Trans. Edinb. geol. Soc. 13, 17.
MITCHELLB.D. & MACKENZIER.C. (1959) Clay Min. Bull. 4, 31.
SIMPSONS. (1948) Trans. roy. Soc. Edinb. 61,687.
SIMPSONS. (1955) Trans. Edinb. geol. Soc. 16, 189.