GL4023 Mapping Report finalised

University of Aberdeen

Geological Map Project 2015-2016

GL4023

A Comparison of the Minor Structures within the Igneous Layered Sequence and the Torridonian Sedimentary Group on the Isle of Rum,

Inner Hebrides. Peter J. Denheen

Student number: 51227548

B.Sc. Petroleum Geology (2015/2016)

2

University of Aberdeen

Geological Map Project 2015-2016.

Declaration of academic integrity

I declare that this piece of work is my own and does not contain any unacknowledged work from other sources.

Signed: ……………………………………………………………………………………..

Name: PETER J. DENHEEN Date: 01/02/16

GL4023 Geological Map Project – Peter J. Denheen

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CONTENTS:

ABSTRACT 4

INTRODUCTION 5

LITHOLOGICAL DESCRIPTIONS 7

GEOLOGICAL HISTORY 29

LITERATURE REVIEW 31

CRITICAL STUDY – MINOR STRUCTURES WITHIN THE ILI AND MAF 36

CONCLUSION 44

REFEENCES 45

APPENDIX 1 – SEDIMENTARY SYMBOLS FOR STRATIGRAPHIC LOGS 47


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ABSTRACT:

The Isle of Rum is a perfect example of a Paleocene Igneous Complex in Britain. It is an island

split in two distinct geological halves, with the mountainous landscape of the Igneous Complex

to the south incorporating the major peaks of Hallival and Askival, and the flatter, undulating

topography of the various sedimentary successions to the north. During a seven-week period

in the summer of 2015, fieldwork was carried out on a section of the east coast of the island

and a geological map of the various lithologies within an area of around 10km2 was produced

(see plate 1 (attached)). As a result of this fieldwork, it became possible to separate these

lithologies into three separate special groups; these included the sedimentary Mullach Ard

Formation (MAF), the Cnapan Breaca Assemblage (CBA) which is itself composed of the

sedimentary Cnapan Breaca Formation (CBF) and the Cnapan Breaca Conformable Sequence

(CBCS), and the Igneous Layered Intrusion (ILI). Furthermore, both the MAF and CBF are

themselves grouped into the East of Rum Group (EoRG). From measurements of the

orientation and the analysis of lithological boundaries, it became possible to produce a series

of cross sections of the area as well as a basic interpretation of the geological history. In

addition, detailed comparative analysis was carried out on the minor structures within the

igneous lithologies of the ILI and the sedimentary member of the MAF.


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INTRODUCTION:

The Isle of Rum is situated within the Inner Hebrides in the north-west of Scotland. It is a

National Nature Reserve (NNR) owned and managed by Scottish Natural Heritage (SNH) with

a small community located at the east coast of the island in the village of Kinloch. Within the

mapping area the topographical scenery is profoundly affected by the lithologies present (see

fig. 1 and 2). The main purpose of this fieldwork was to provide a geological map showing the

spatial distributions of these lithologies with cross-sections portraying an interpretation of the

relationship of these lithologies in the subsurface in order to understand the geological history

of the area. The main problem that was faced during the majority of the project was to provide

an interpretation of the interactions between the lithologies present. This was most apparent

with the interaction between the ILI and the surrounding lithologies which were separated by

intrusive boundaries which showed no clear orientation of dip. Complex faulting within the

area also made the organisation of the lithologies into a plausible stratigraphic order difficult.

Figure 1: Topographical sketch map of Rum with key localities included. Red box indicates extent of fieldwork area. (Adapted from Emeleus et al. 2014).


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Figure 2: Generalised map showing the 3 main spatial lithology groups present within the mapping area. To the south-west, the barren, irregular topography of the area surrounding the peak of Hallival is formed as a result of the sequential layering of resistant plagioclase-rich units with easily weathered pyroxene-rich units which form the ILI. In contrast the flatter, marshy areas of Fearann Lamhrige, Mullach Ard, An Uamh and Raonapoll to the north-east comprise the sedimentary members of the MAF, which is interrupted to the north-west by the abrupt raise in elevation of the exposed outcrops of the CBA (note: the CBA does not represent a conformable stratigraphic sequence from the Cnapan Breaca Mudstone (CBM) to the Cnapan Breaca bedded Dacite (CBDb) it is used to show the relationship between rock units through a post-depositional major structural event (see table 1)).


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LITHOLOGICAL DESCRIPTIONS:

Note: The nomenclature used to describe

the various lithologies present within the

mapping area were invented by the author

during fieldwork. Please see tables 5-7 for

a comparison between fieldwork and

literature nomenclature of lithologies and

faults as well as the full names of

abbreviated fieldwork lithologies.

IGNEOUS LITHOLOGIES:

Cnapan Breaca Dacite (CBD):

With Bedding (CBDb):

Lithology: Rectangular, stubby, lath-

shaped, (1-3mm) milky-white plagioclase

crystals are present within a melanocratic,

aphantic fine-grained matrix. These

plagioclase crystals are consistent

throughout the entire lithology as well as

within the lenticular bedding features

present. Smaller whiter crystals (<1mm)

which appear more fractured are also

present which are thought to represent

quartz.

Major faulting: None.

Orientation: Layered structures present dip

moderately to the south-west.

Minor structures: Layering structures (see

fig.2).

Boundaries: Fourth member of the CBCS

(see table 1). Intruded by intrusions of IBM

and OG on the margin of the ILI (see

fig.12).

Inferred genesis: Due to the presence of

fine grained layering features within an

igneous lithology it is inferred that the

CBDb formed as a result of an ash flow

deposit from some form of volcanic

eruption.

Without Bedding (CBDw):

Lithology: Similar base lithology to CBDb

with euhedral plagioclase feldspar present

within a fine-grained, melanocratic,

aphantic matrix. Only difference is the

presence of some rare small, pinkish

crystals that may possibly represent K-

feldspar.


Orientation: No preferential orientation

due to inferred vertical intrusive nature of

lithology.

Minor structures: None, uniform intrusive

structure. Fragments of basic material

similar to the basaltic dikes are visible.

Boundaries: The lithology cross-cuts the

CBS to the north and the CB-SDBu to the

south as a singular, narrow, winding

intrusion. There are visible signs of thermal


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metamorphism within the country rock into

which the CBDu has intruded.

Inferred genesis: It is inferred that this

lithology formed as an intrusion, possibly

from the same or similar source material as

the CBDb.

Figure 3: Bedding structures within the CBDb (NM 39366 47736). These 1-4cm thick lenticular shaped layering structures are visible in all CBDb outcrops and are the main feature used to differentiate them from outcrops of CBDw. 15cm long pencil for scale.

Table 1: Representation of lithology groups within the Cnapan Breaca Assemblage

(CBA) (in stratigraphic order).

Lithology Group: Lithologies present:

Cnapan Breaca Conformable

Succession (CBCS):

Cnapan Breaca Dacite with bedding (CBDb).

Cnapan Breaca sandstone

Debris Breccia (CB-SDB):

Unbedded (CB-SDBu).

Bedded (CB-SDBb).

Cnapan Breaca Sandstone (CBS).

Cnapan Breaca Formation

(CBF): Cnapan Breaca Mudstone (CBM).

Note: There is no conformable boundary between the CBS and the members of the CBCS, which form from the brecciated remains of uplifted CBS.


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Igneous Layered Intrusion (ILI):

Plagioclase-rich olivine basic (PlROB):

Lithology: Contains a high proportion of

milky-white plagioclase feldspar relative to

the amount of lustrous dark pyroxene and

olivine (lime-green in samples unexposed

to weathering, orange in weathered

outcrops), resulting in a general leucocratic

appearance. Crystal of all sizes range from

1-3mm in size, with plagioclase normally

remaining the largest in outcrop. Regions

of higher concentrations of olivine can also

be identified by slightly weathered orange

outcrops. The crystal size and percentage of

plagioclase feldspar can also fluctuate

within sub layers. An increase in the

percentage of pyroxene and/or olivine

within sub layers is identified in outcrop by

the presence of vesicle-shaped weathering

patterns.

Major faulting: There appears to be no

major faulting associated with this

lithology, however the presence of a single,

continuous NW-SE OG layer dipping to the

NE could indicate a line of weakness within

the ILI area.

Orientation: Layers generally dip gently to

the SW, however this degree of dip varies

slightly throughout the area of the ILI,

possibly due to the conductive environment

in which the alternating layers were

deposited.

Minor structures: Layers are divided into

many sublayers with differing

concentrations of plagioclase, pyroxene and

olivine. Within these sub layers planar,

wavy and convolute lamination is visible.

In addition, there are many examples of

density related structures within and

between sublayers that resemble soft-

sediment deformation structures seen in the

MAF, these include pseudonodules, flame

structures and load casts (see fig. 19-21).

Boundaries: This lithology is sequentially

layered with the PyROU within the ILI, in

which boundaries are easily visible by the

presence of resistant outcrops of PlROB

and sparser, heavily weathered outcrops of

PyROU which are largely obscured. The

majority of the boundary between the ILI

and the surrounding lithologies is defined

by marginal IBM. The only exception to

this is an intrusion of marginal OG at

around NM 39400 97350 which separates

the CBD to the north and associated ILI

layers to the south. A NE dipping OG

intrusion through the ILI is also present at

around NM 39280 96584. At around NM

41000 96650 the ILI was mapped as being

in straight contact with the DMM due to the

lack of evidence of intermittent IBM,

however it is possibly that the IBM is

present as a very thin intrusive layer at this

locality.


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Inferred genesis: It is possible that the ILI

formed within an upwards intruding, dome-

shaped conductive magma chamber of

some form, in which periodical pulses of

magma of varying mineralogical content

formed the alternating layers of PlROB and

PyROU.

Pyroxene-rich olivine ultrabasic

(PyROU):

Lithology: Identified mainly by the high

proportion of lustrous, dark pyroxene in

relation to the amount of plagioclase

feldspar resulting in a general melanocratic

appearance. There is also an increased

concentration of olivine compared to

PlROB.

Major faulting: (See entry for PlROB).

Orientation: (See entry for PlROB).

Minor structures: Although PyROU is seen

to interlay within the major PlROB layers

there are no visible PlROB sublayers

visible within the major PyROU layers,

however this may be simply due to the

erosion of the majority of PyROU outcrop.

In addition this large-scale erosion of many

layers makes identification of internal

structures difficult, however cross-cutting

10-30 cm thick vein structures of PlROB

from overlying and underlying layers are

visible at some localities.

Boundaries: (See entry for PlROB).

Inferred genesis: (See entry for PlROB).

Olivine-Hornblende Dolerite (OHD):

Lithology: Mesocratic, phaneritic medium-

grained lithology containing the same

minerals seen in the ILI; milky-white

plagioclase feldspar, shiny pyroxene and

lime-green olivine. Some additional dull,

earthy hornblende is present in small

concentrations. There are two different size

variants of pyroxene present; smaller 1-

3mm crystals and larger 1-2cm crystals. It

is observed that only OHD identified as

orientated dikes contain both pyroxene

types whereas the intrusive plugs only

contain the smaller variety.


Orientation: The OHD dikes dip

moderately to the SW in a similar

orientation to the surrounding basic dikes.

The intrusive OHD show no evidence of

orientation, therefore they are assumed to

have intruded vertically.

Minor structures: Within the OHD dikes

coarser grained minerals are present in the

middle of the intrusion between finer

grained materials at the edges, a similar

structure seen within the basaltic dikes.

Boundaries: OHD dikes intrude into the

DBM at NM 41028 98366 and the CBM at

NM 39973 97883. Intrusive OHD plugs

present within the DMM at NM 41424


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96979 and NM 41712 96521 and on the

outer faulted boundary between the DBM

and the CBM at NM 41000 97830.

Inferred genesis: The two slightly different

varieties of OHD suggests that they could

have possibly intruded into the system at

different times but from a similar source

material, the order of which is unclear as

there are no cross-cutting relationships

present. The presence of an OHD intrusive

plug on the outer fault between suggests

that it postdates the activation of major

faults in the region.

Olivine Gabbro (OG):

Lithology: Coarse-grained melanocratic

lithology containing a high proportion of

milky-white plagioclase feldspar, alongside

lower concentrations of dark, glassy

pyroxene and lime-green olivine. The

noticeably larger grain size is the main

criteria used to differentiate it from the

members of the ILI (see fig.4).

Major Faulting: None.

Orientation: The inclined intrusive layer

mentioned above is the only example of OG

in the mapping area with visible bedding

which dips moderately to the NE. The

marginal OG shows no signs of orientation,

however due to its emplacement at the edge

of the ILI it is inferred to have intruded

upwards in a curved path along the edge of

the domed ILI magma chamber. In

addition, the lack of solid outcrop could

also have concealed bedding features. The

OG intrusive plugs are assumed to have

intruded vertically upwards.

Minor structures: The intrusive plugs of

OG as well as the marginal OG contains no

visible structural features and crystals are

arranged uniformly. The layering within

the inclined OG intrusion within the ILI is

identified by faint, distorted thick regions of

aligned plagioclase feldspar.

Boundaries: Intrusive plugs of OG are

visible within the DBM (NM 39620 98450)

and DMM (NM 41200 96900). As

mentioned above there are two example of

intrusions of OG within the ILI which are

inferred to be interconnected; one at NM

39280 96584 and another at the northern

ILI margin at NM 39400 97350 (see fig.12).

Inferred genesis: All OG examples are

inferred to have intruded from the same

igneous source, either vertically, or along

possible major lines of weaknesses in the

case of the marginal and layered OG.


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Figure 4: Hand sample of OG from intrusive plug at NM 41200 96900. Note difference in colour between rock appearance in weathered and unweathered surface, most likely due to the weathering of olivine. Coarse grained chalky-white plagioclase and dark pyroxene are clearly visible. Pencil for scale.

Basic Dikes (BD):

Lithology: Aphantic, melanocratic basalt.


Orientation: Varies with respect to

location. Dikes in the vicinity of Cnapan

Breaca are commonly NE-SE trending (see

fig.5) however at the coastline of An Uamh

and Fearann Laimhrige this orientation

changes to N-S trending (see plate 1). This

curvature could indicate the presence of a

cone structure radiating outwards from the

vicinity of the SW corner of the mapping

area.



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Figure 5: Dike orientations within the mapping area (top left: CBS, top right: CBM, bottom left – CBDb, bottom right – CB-SBD). Black arrow represents mean orientation. There is a majority NW-SE orientation although a slight deviation from this trend is present within the CB-SDB. There also appears to be two main groups of orientations in each data set; the majority NW-SE and a less common SW-NE which could imply two separate periods of dike intrusion.


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SEDIMENTARY LITHOLOGIES:

East of Rum Group (EoRG):

Dobhrain Bhig Member (DBM):

Lithology: The large majority of this

member is composed of a conglomeritic,

coarse-grained, medium-poorly sorted,

sub-angular-angular, arkosic sandstone

assemblage. The major visible minerals

include opaque, sub-rounded – sub-angular

quartz and sub-angular clasts of pinkish K-

feldspar. Some fine-grained sandstone and

siltstone interbeds are also present.

Within around 9km distance from the

boundary of the ILI, the K-feldspar grains

have undergone a bleaching effect and are

visible as dull white grains having lost their

characteristic pinkish tinge. This boundary

of bleaching can be traced around the

circular outline of the ILI. This effect is

only visible within sandstone layers and is

also present in the DMM within the

bleaching radius (see fig.11). In addition

within the vicinity of the immediate

boundary with the ILI the DBM is bleached

and baked.

Major faulting: Exposure of major low

angle Cro nan Laogh Fault (CnLF) at NM

42118 98924 in which DBM from the west

has been faulted over DMM resulting in a

major lateral eastwards displacement of the

DBM. Intensive SW dipping fracture

planes are visible in the DBM to the east of

the fault. The CnLF can be traced around

the peninsula of the Mullach Ard to Bàgh

na Uamha where the fault is seen to cut

perpendicularly in map view through

conformable successions of DMM and

AUM (see fig. 9).

Structural Integrity: All members of the

MAF weather normally with good coastal

exposure and sparser exposure inland.

Orientation: The majority of beds within all

members of the MAF dip at around 25° to

the west. The exception to this in the DBM

is the area north of the outer fault with the

CBM in which there is a gradual steepening

of the dip of DBM bedding towards the

boundary.

Minor Structures: The majority of layers

show examples of soft-sediment

deformation structures, such as flame

structures and chaotic bedding. Cross-

bedding is also widely visible within cosets

of about 10-50cm in thickness. This

evidence was used to infer that the DBM

represents the paleoenvironment with the

highest energy input out of the three

conformable sedimentary lithologies.

Boundaries: To the SW there is a

conformable boundary with the DMM in

addition to faulted contacts with the DMM,

AUM and CBM. IBM is present on contact

with the ILI.


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Inferred genesis: It is likely that the DBM


highest energy input in the MAF, possibly

forming as rapidly deposited sandy river

channels

Dobhrain Mhor Member (DMM):

Lithology: Fine grained arkosic medium-

very fine-grained sandstone interbedded

with siltstone.

Major faulting: Affected by CnLF. An

anticlinal structure with its axial plane

inclined to the W is present directly to the

west of the fault. This is interpreted to have

formed due to interaction of the

sedimentary faults with fault movement

(see fig. 8).

Orientation: (See entry for DBM).

Minor structures: Layers of medium

sandstone contain similar features found in

the DBM such as cross-bedding and

convolute layers (albeit on a less chaotic

scale). Finer layers show planar lamination,

asymmetric ripples, cross bedding and

desiccation cracks as well as examples of

soft sediment deformation such as

pseudonodules, flame structures, graded

bedding and load casts (see fig. 6 -7 and

18).

Boundaries: Conformable boundaries

present with the DBM and AUM, which

define the stratigraphic top and base of the

DMM in addition to the faulted contact with

the DBM. Also in contact with some of the

eastern margin of the ILI as well as a faulted

contact with the CBM.

Inferred genesis: The lack of mudstone

within the DMM represents an increase in

energy input to the paleoenvironment

compared to the AUM. The presence of

cross bedding and river channels suggests a

sinuous sandy river formation

interconnected by sand bars.

An Uamh Member (AUM):

Lithology: Medium-very-fine grained

arkosic sandstone interbedded with

siltstone and mudstone. The proportion of

mudstone is far greater at the stratigraphic

base of the member than at the top.

Major faulting: Affected by the CnLF

which cuts the member at a right angle at

An Uamh with a visible contact of the fault

present in a cave at Bàgh na Uamha (NM

42281 97362).

Orientation: (See entry for DBM).

Minor structures: Cross bedding, ripples

and wavy lamination are present. Within

outcrops exposed at the beach at An Uamh

the 3-D outlines of river channels are

visible. Evidence of soft-sediment

deformation is present in the form of load

casts. At the base of the sequence the


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member is dominated by asymmetrical

ripples (see fig. 7 and 17).

Boundaries: Conformable boundary with

the DMM as well as the faulted contact at

with the DBM at Bàgh na Uamha.

Inferred genesis: The high proportion of

mudstone indicates that the AUM


lowest energy input. Presence of laminated

mudstone/siltstone near the base of the

exposed member indicates that the

succession is possibly deep marine or deep

lacustrine with the top of the sequence

representing a transitional phase from

deeper paleoenvironments into the river

deposits of the DMM and DBM.


17

Figure 6: Stratigraphic log of minor structures within the DMM. Note: see APPENDIX 1 for key to log symbols).


18

Figure 7: Stratigraphic log of minor structures and a possible boundary within the AUM and DMM.


19

Figure 8: Analysis of the anticlinal structure within the DMM.


20

Figure 9: Stereonet and cross-section of the CnLF exposed at the South coast of Loch Scresort separating the DBM and DBM


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Cnapan Breaca Formation (CBF):

Cnapan Breaca Mudstone (CBM):

Lithology: Finely laminated (0.2 – 1mm

thick) mudstone.

Major faulting: At Cnapan Breaca the

CBM is affected by two major faults; the

Cnapan Breaca inner (CBFSi) and outer

(CBFSo) faults. It is also affected by the

Fearann Laimhrige Fault (FLF) to the

south. All of these faults are assumed to be

vertically orientated.

Orientation: CBM bedding dips steeply to

the SW at the eastern edge of Cnapan

Breaca and transits to vertical and steeply

dipping to the NE at the vicinity of the

hydroelectric dam at Allt Slugan a’

Chollich. The bedding exposed at Fearann

Laimhrige dips to the NW and becomes

increasingly steeper towards the ILI

margin.

Minor structures: Parallel and wavy

lamination is visible in all CBM outcrops.

Overturned, stretched and broken

lamination suggests that they have been

subjected to localised structural effects

related to the faulted boundaries.

Laminations are also seen to become

increasingly fractured and broken with

increasing proximity to fault boundaries

and are affected by ductile deformation

nearer to boundaries with the ILI and other

intrusions.

Boundaries: In addition to the faulted

boundaries with the DBM, CBS and DMM

the CBM is intruded by the ILI and

associated IBM (see fig.. 10-11).

Inferred genesis: Due to the highly

deformed nature of some strata is difficult

to identify particular structures that could

be used to identify the paleoenvironment. It

is assumed that before deformation, the

strata was planar and continuous mudstone

that could suggest a deep marine/lacustrine

low energy environment. Due to the outer

fault boundary with the MAF it is difficult

to determine whether it relates conformably

with the base of the AUM.

Cnapan Breaca Sandstone (CBS):

Lithology: Very fine-coarse grained

sandstone containing visible quartz.

Major faulting: The CBS is affected by the

vertical CBFSi (see fig.10).

Orientation: On average, most bedding

dips steeply to the SW, however strike

direction can varies from SW to SE

throughout the lithology, especially in the

central area of Cnapan Breaca bordering the

OG in which most bedding is randomly

orientated and dip varies from moderate to

vertical. Strike of bedding is also seen to


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‘curve’ in a wide arc around the north of

Cnapan Breaca (see fig.10).

Minor structures: Normal and reverse

grading can be seen in outcrop. The vast

majority of layers and lamination are

strongly curved and convoluted. However

as with the CBM, the high amount of

structural deformation of layers makes it

difficult to identify particular structures

used to determine paleoenvironment. Large

fractures (1-3m wide) infilled with CB-

SDB are present which often cut strata at

right angles.

Boundaries: Separated from the CBM by

the CBFSi. First in the CBCS (see table 1

and fig.12). Intruded by a thin, nodular

section of CBDw.

Inferred genesis: As with the CBM, the

high amount of structural deformation of

layers makes it difficult to determine the

paleoenvironment, however the presence of

graded layers as well as fine and coarse

grains of the only identifiable mineral grain,

quartz, could signify an environment of

fluctuating energy input which was

deposited far from its source material.


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Figure 10: View of the north-west area of Cnapan Breaca showing the difference in bedding strikes between the CBS and CBM on either side of the CBFSi.


24

Figure 11: View of the east section of the fieldwork area from Mullach Ard. The extent of the ILI/MAF boundary is clearly visible due to the sudden change in topography. Note the constant distance maintained between the ILI margin and the extent of bleaching of the MAF which indicates the ILI was most likely the source of the alteration affect.


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BRECCIATED ROCK UNITS:

Igneous Breccia Matrix (IBM):

Lithology: The IBM lithology itself is

composed of an aphantic, melanocratic

igneous matrix of very small (<1mm)

crystals of plagioclase feldspar and

pyroxene. The area of the country lithology

into which the IBM intrudes is commonly

deformed and thermally affected normally

with features such as deformed layers, dike

fragments or angular/sub-angular clasts

(1cm – 5cm) present within a replacive

IBM matrix. There also appears to be

various magnetic anomalies present within

the IB.


Orientation: There is no evidence of

orientation present within the IBM.

Minor structures: A faint form of bedding

(usually incorporated from the country rock

into which the IB has intruded) is very

wavy and deformed in a ductile manner. At

one locality (NM 40465 97396) criss-

crossing patterns are visible within clasts

with a weathering appearance similar to

that seen in members of the ILI.

Boundaries: The IBM itself acts as a

boundary lithology between the ILI margin

and the surrounding lithologies with some

exceptions (see entry for PlROB) (see

fig.11).

Inferred genesis: Due to the lack of any

features that could be used to deduce

orientation of intrusion, the IBM is assumed

to have intruded vertically along the

curvature of the hypothetical ILI magma

dome, much like the marginal OG.

Cnapan Breaca sandstone Debris Breccia

(CB-SDB):

Unbedded (CB-SDBu):

Lithology: Contains a variety of clast sizes,

and shapes, all of which appear to have

originated from the CBS to the NE. Clasts

are supported within a fine grained matrix


Orientation: None visible, clasts all appear

to be randomly orientated.

Minor structures: (See table 2 for clast size

distribution).

Boundaries: Second member of the CBCS

(see table 1 and fig. 12). A small section is

intruded by the marginal OG.

Inferred genesis: Clasts originate from the

underlying CBS. The boundary with the

CBS is very irregular most likely due a high

intensity of fracturing and brecciation of the

CBS. This could be related to the fault

activity of the CBFS.

Bedded (CB-SDBb):

Lithology: (See entry for CB-SDBu).


26

Major faulting: The distribution of major

and minor faults is the same as in the CB-

SDBu.

Orientation: None.

Minor structures: Linear bedding-like

features are present within the CB-SDBb.

The vast majority of these lineations have a

similar strike and dip orientation to that of

the CBDb however a small number are

orientated at right angles to these. The two

orientations of lineations also appear to

conjoin rather than cross-cut one another.

These features are the main criteria used to

distinguish the CB-SDBb from the CB-

SDBu. Various clast types and sizes are

also present, like the CB-SDBu (see table

2).

There are also noticeable 20-40cm wide

intrusion-like features that cross cut the

NW-SE orientated intrusions at right

angles. They contain more clasts of CBS

than the surrounding breccia.

Boundaries: The CB-SDBb is the third

member of the CBCS (see table 1 and

fig.12).

Inferred genesis: A continuation on from

the brecciation of the CBS. The presence of

layering features could suggest coeval

activity of the same process that led to the

deposition of the CBDb.


27

Figure 12: View of Cnapan Breaca from NM 39532 97640 showing contacts between members of the CBCS. Note the nodular intrusion of OG that branches off from the main marginal intrusion as well as the difference in thickness between the CB-SDBu and CB-SDBb.


28

Table 2: Comparison of clast count within the CB-SDBu and CB-SDBb.

CB-SDBu (data collected as SDB boundary): CB-SDBb (data collected at CBDb boundary):

Comparison: Size: The data from the CB-SDBb contains a higher percentage of smaller (<1cm) grains than that of the CB-SDBu which contains larger grains. It also contains very large (>10cm) clasts that are not present in the CB-SDBb. Shape: The CB-SDBu contains more angular /sub angular clats whilst those in the CB-SDBb are mostly rounded/sub-angular. Structures: Both contain mostly non-layered clasts but there are more layered in the CB-SDBb than the CB-SDBu. Grains within clasts: Medium-fine is the most common in both lithologies althought there is a higher number of fine in the CB-SDBb. General comments: Indication of normal grading in which coarser clasts are deposited first, followed by smaller, rounded clasts as energy imput diminishes

Size

<1cm1cm-5cm5cm-10cm>10cm

Size

<1cm1cm-5cm5cm-10cm>10cm

Structures

Layered

Non-layered

Structures

Layered

Non-layered

Grains within clasts

Very fineFineMedium

Shape

RoundedSub-roundedSub-angularAngular

Shape

RoundedSub-roundedSub-angularAngular

Grains within clasts

Very fine FineMedium Coarse


29

GEOLOGICAL HISTORY:

Table 3: Interpretation based on fieldwork observations of the relative timing of

geological events within the mapping area from oldest (bottom) to youngest (top):

Formation of lithologies: Major structural events:

Intrusion of minor igneous intrusive lithologies (e.g. basaltic

dikes, OG, OHD, CBDu).

N/A

Vertical intrusion of ILI magma chamber, with associated

IBM intruding into country rock at its boundary.

Possible input of volcanic ash or associated volcanic event to

form layering in CB-SDBb and CBDb.

Brecciation of SBS to form CB-SDBu.

N/A Occurrence of a major

uplift event. Formation of

CBFSi, CBFSo and FLF

and exhumation of CBM

and CBC. Bedding of DBM

is deformed and curved.

Lateral movement of DBM

via CnLF possibly related

to instability caused by

uplift event.

Major structural event

resulting in the tilting of the

deposited sedimentary

members to the NW.

Deposition of the EoRG Deposition of the DBM

Deposition of the DMM

Deposition of the AUM

Deposition of the CBM.

Deposition of the CBS.


30

Table 4: Geological sequence in Rum (oldest at base to youngest at top) within the

literature (adapted from Emeleus, 1997 to include only the lithologies present within

the mapping area).

Major Geological Events

Generalised Thickness

(m) Unconformity Subaerial erosion of the Rum Central Complex

Pale

ocen

e

RUM CENTRAL COMPLEX

Stage 2: Emplacement of the Rum Layered Suite.

a. Eastern Layered Intrusion.

Gabbro and dolerite plugs were probably coeval with Stage 2

intrusions.

Regional NW-trending dyke swarm (probably continuous through

much of Stage 1, with sporadic dykes to the end of Stage 2), intrusion

of basaltic cone-sheets and radial basaltic dikes (probably overlaps

(c) below).

Stage 1: Ring-faulting, caldera formation, intrusion and effusion

of silicic magmas.

(c) Second, final phase of uplift on Main Ring fault; basal

Torridonian reverse-faulted.

(b) Subsidence on the Main Ring Fault; Coire Dubh Breccias

(Volcanic Mesobreccia).

(a) First phase of uplift on the Main Ring Fault, accompanied by

doming of the country rocks.

Mullach Ard fault (probably coeval with (a) above).

Unconformity Erosion of intermittent sedimentary successions.

Prot

eroz

oic

Torridon Group:

Applecross Formation

Diabaig Formation

Sandstone, pebbly sandstone,

siltstone

Sandstone, siltstone, shale,

sedimentary breccia

c.2000

500+

Note: This table does not assign an age to the tilting event of the Torridonian strata. For a comparison of lithology nomenclature with fieldwork results see tables 5-7.


31

LITERATURE REVIEW:

Through consultation of literature based on

past fieldwork of the mapping area there

has been some notable correlation with the

findings of this fieldwork. For a

comprehensive layout of this comparison

see tables 3-4 for the geological history,

table 5 and 7 for lithology nomenclature

and table 6 for fault nomenclature.

The most outstanding difference is the

alternate criteria used to differentiate the

members of the ILI (see table 4). The

difference in nomenclature and distribution

of some of the lithologies in the CBCS (see

fig. 14 and 15) as well as the stratigraphic

arrangement of some of the sedimentary

members (see table 5 and fig.13) is also

noticeable.

Previous studies have also been very useful

in understanding the true depositional

environments of the sedimentary

lithologies. Within the Diabaig formation,

the Fiachanis member was deposited in

channelised flows on alluvial fans, which

explains the presence of grading. The

Laimhrig member is believed to have

formed in lakes into which these fans fed

into which was the predicted fieldwork

paleoenvironment (Stewart, 1982; 1988b;

Stewart and Parker, 1979), with the

laminated silt-mud alternations

representing seasonal varves in a deep

lacustrine setting below wave base (Rodd,

1983). Personally I am sceptical about the

decision to combine what I believed were

two different members in the case of the

Laimhrig as I saw only one lithology and

structure present in the CBM whilst the

AUM was more varied in its appearance.

However due to the constraints of the

mapping area size I may not have seen other

examples of outcrops on Rum that could

connect these lithologies.

The Applecross formation is interpreted as

fluvio-deltaic in origin and the Scresort is

believed to have formed on a major fluvial

braid plain filled with sandy-braided rivers

(Nicholson, 1992a; 1992b; 1993). This is

similar to the expected paleoenvironment

based on fieldwork findings.

These interpretations correlate with the

inferred increasing energy

paleoenvironment noted within the MAF

during the fieldwork, with a movement

from deep marine/lacustrine to continental

fluvial.


32

Table 5: Comparison of the Field work and Literature Nomenclature of Rock Units. Lithology type:

Name applied to Lithology by author during field work:

Formal British Geological Survey (BGS) name given to Lithology:

Igneous Lithologies:

Olivine Gabbro (OG). Gabbro. Olivine-hornblende dolerite (OHD). Dolerite. Igneous Layered Intrusion (ILI):

• Plagioclase-rich olivine basic (PlROB).

• Pyroxene-rich olivine ultrabasic (PyROU).

Rum Layered Suite; mapping area falls into area of Eastern Layered Intrusion (ELI):

• Troctolite. • Peridotite.

Cnapan Breaca Dacite (CBD): • With Bedding (CBDb). • Without Bedding (CBDw).

Porhypritic Rhyodacite: • Extrusive ash flows. • Intrusive bodies.

Brecciated Lithologies:

Igneous Breccia matrix (IBM) containing brecciated remains of:

• Cnapan Breaca Dacite (IBM-CBD).

• Dobhrain Bhig Member (IBM-DBM)

• Dobhrain Mhor Member (IBM-DMM).

• Cnapan Breaca Sandstone (IBM-CBS).

• Cnapan Breaca Mudstone (IBM-CBM).

• An Uamh Member (IBM-AUM).

• Cnapan Breaca Sandstone Debris Breccia (IBM-SDB).

Intrusion Breccia within microgranite groundmass (mapped as one unit but composition differences when in contact with different lithologies described in more detail in literature).

Cnapan Breaca sandstone Debris Breccia (CB-SDB):

• Unbedded (CB-SDBu). • Bedded (CB-SDBb).

Volcanic Mesobreccia.

Sedimentary Lithologies:

Member: Formation: Group: Member: Formation: Group:

Dobhrain Bhig Member (DBM).

Mullach Ard Formation (MAF).

Ea

st o

f Rum

Gro

up (E

oRG

).

Scresort Sandstone Member (TCAS).

Applecross Formation.

To

rrid

on G

roup

.

Dobhrain Mhor Member (DMM).

Allt Mór na h-Uamha Member (TCAM).

An Uamh Member (AUM).

Laimhrig Shale Member (TCDL).

Diabaig Formation.

Cnapan Breaca Mudstone (CBM).

Cnapan Breaca Formation (CBF).

Cnapan Breaca Sandstone (CBS).

Fiachannis Gritty Sandstone Member (TCDF).

Note: Nomenclature for BGS lithologies taken from the ‘1:50 000 Geological Sheet 60 (Scotland)’ and associated memoir (Geology of Rum and the adjacent islands, 1997). Note: see table 4 for more detailed comparison of ILI.


33

Table 6: Comparison of the Field work and Literature Nomenclature of Major Faults. Name applied to fault during field work: Formal British Geological Survey (BGS)

name given to fault : Cnapan Breaca Fault System (CBFS):

Inner (CBFSi)

Main Ring Fault (MRF):

Inner

Outer (CBFSo)

Outer

Fearann Laimhrige Fault (FLF) Cro nan Laogh Fault (CnLF)

Mullach Ard Fault (MAF)

Note1: Nomenclature for BGS fault names taken from the ‘1:50 000 Geological Sheet 60 (Scotland)’ and associated memoir (Geology of Rum and the adjacent islands, 1997).

Note2: The CBFSo and FLF were inferred during fieldwork to be the same fault as both appear to affect the CBM and members of the MAF. All fieldwork faults with the exception of the CnLF are inferred to be vertical or near vertical.

Figure 13: Stratigraphy of the sedimentary Torridonian group present on Rum. (After Nicholson, 1992, taken from Emeleus et al. 2008) (Note: Lewisian Gneiss and Sgorr Mhòr Member not present within the mapping area).


http://earthwise.bgs.ac.uk/images/c/cd/EGS_RUM_03.jpg

34

Table 7: Comparison of Fieldwork and Literature Mineralogical Criteria used to Differentiate the Lithologies within the Igneous Layered Sequence.

Fieldwork Lithologies Literature Lithologies (based on McClurg, 1982, taken from Emeleus, 1997).

Lithology name Mineral Characteristics

Rum name used here

Standard name Mineral characteristics (approximate modes in vol. %)

PlROB >50% plagioclase feldspar

Anorthosite Anorthosite >95% total plagioclase

Bytownite-troctolite (formerly allivalite).

Bytownite-troctolite, gabbro.

Plagioclase-olivine cumulates with total plagioclase 95%-50%, cumulus clinopyroxene <5% to c.35% (rare).

PyROU >50% pyroxene. Feldspathic peridotite.

Troctolite and gabbro. Melatroctolite.

Olivine cumulates with 50%-30% post-cumulus plagioclase.

Peridotite. Melatroctolite

Feldspathic peridotite.

Olivine-cumulates with 30%-5% post-cumulus plagioclase.

Dunite. Dunite. >95% cumulus olivine, <5% combined post-cumulus clinopyroxene and plagioclase.

Note: Clearly the criteria possesses a far higher degree of variation and complexity than that of the fieldwork. Whilst the criteria used for defining PlROU correlates with the literature the PyROU does not, with the main alternating mineral being olivine rather than pyroxene, however the mapping of these two lithologies is still consistent due to the erosive nature of pyroxene/olivine. Please note that this has a direct implication on the stratigraphic logs of the ILI (see fig. 18-20)


35

Figure 14: Stratigraphic column of the Coire Dubh intra-caldera succession (just to the west of Cnapan Breaca). Note the grading within the mesobreccia which was observed in the clast count of the CB-SDB (table 2). The interpretation of the Rhyodacite as lithic tuff from the Caldera also correlates with the fieldwork interpretation of the formation of the CBDb through some form of ash flow. (Simplified after Troll et al. 2000, taken from Emeleus et al. 2008).

Figure 15: View of Coire Dubh from Meall Breac, with elements of the Northern Marginal Zone (CBA) and the Eastern Layered Intrusion (ILI) marked. The area at the far middle of the picture comprises fig.12 as viewed from the opposite orientation. Note the similarities of the placement of lithologies such as the extrusive and intrusive Rhyodacite (CBDu and CBDb) and the uplifted Torridonian members (CBS and CBM). The main difference is the lack of a boundary between the bedded and non-bedded CB-SDB, which is simply known as mesobreccia here. The presence of Epiclastic Sandstone was also not noticed during fieldwork however this could possibly be another interpretation of the CB-SDBb. These features are interpreted to show the component of caldera formation and collapse, which was also responsible to the major uplift event that formed the Major ring fault. (Taken from Emeleus et al, 2014).


http://earthwise.bgs.ac.uk/images/b/b2/EGS_RUM_15.jpg

http://earthwise.bgs.ac.uk/images/5/58/EGS_RUM_20.jpg

36

CRITICAL STUDY – MINOR

STRUCTURES WITHIN THE ILI AND

MAF:

The lithologies within the ILI and MAF

both appear to contain similar minor

structures which show characteristics of

having been formed by the process of soft-

sediment deformation (SSD). These

structures include:

• Load casts.

• Flame structures.

• Pseudonodules.

• Distorted/ wavy lamination.

Within the clastic sedimentary members,

these features are known to form due to the

load of sediment on interfaces between

sediments with different physical

properties. For example a material of higher

density (e.g. sand) on a less dense material

(e.g. mud). According to (Lucci, 1995) A

convective-like motion starts, but the

attempts of the two "fluids" to overturn the

bedding and replace each other abort at a

certain stage owing to frictional resistance,

effectively freezing the deformation.

This principle also applies to

pseudonodules, distorted lamination and

flame structures, however these features

cannot form by load and inverted density

gradients alone and require the liquefaction

of both the substratum and the sand as well

as fluidisation through groundwater flow

(see fig.18).

In the ILI I believe that a similar

gravity/density driven process has occurred

during the formation of the alternating

layers, with the density differences of

plagioclase and pyroxene resulting in the

formation of these SSD features with wavy

lamination forming due to the convective

nature in which the alternating beds are laid

down on the floor of the intrusive magma

chamber. However, there were also

examples of cross-cutting relationships

within some of the logs constructed (see fig.

19 and 21) that do not appear to have been

formed through the same processes as

clastic sediment SSD and appear more to

have been formed by intrusions, possibly

due to pulses of late ILI layers through

those already lithified .

For many years most academics held a

similar interpretation that the deposition of

the Layered Suite was through a

sedimentary-like process, with early-

forming crystals and crystal aggregates

settling in less dense magma at rates that

depended on densities and sizes. In

addition, the accumulation and deposition

of these crystals was facilitated by

convectional magmatic currents which,

according to (Brothers, 1964), were also a


37

major contributor to the strong lamination

found in many troctolites.

However, in addition to this gravity-driven

method of crystal settling and deposition,

Bédard et al (1988) introduced a

replacement origin in which metasomatism

occurs via the movement of pricritic

magma from intrusive sheets of peridotite

into the partly solidified troctolite layers

resulting in the formation of overprinting

peridotite veins and undulating, wavy

contacts

Holness (2005) identified that the concept

of an intrusion of peridotitie as a sill sheet

into the system was limited only to unit 9 of

the ELI (see fig. 16). Within this layer there

is a feature known as the ‘Wavy Horizon’

which contains load casts and flame

structures that are pyroxene rich. Previous

researchers such as Young and Donaldson

(1985) identified these and related forms of

structures as products of loading. However,

building on the replacement interpretation

by Bédard et al, (1988), further work done

by Holness et al. (2007) led to the

proposition that these structures formed

from the ascension of residual fluids from

the crystallising unit 9 peridotite sill

upwards through the semi-lithified

troctolite. As the fluid moved it

incorporated clinpyroxene from the

surrounding troctolite until saturation of the

invading liquid occurred, and a reaction

front formed at which the characteristic

SSD structures within the Wavy Horizon

developed.

Figure 16. Schematic showing the arrangement of units within the layered sequence. Unit A represents the intrusive sill of peridotite as referred to (taken from Holness, 2007). The log from fig.18 is from unit 5 and those from fig.19 and 20 are from the overlying unit 10.

The logs made of the layered sequence

during the fieldwork are not from unit 9 (see

fig.16), however both logs show signs that

they may have been influenced mainly by

SSD via the effects of gravity and density

differences as well as some localised

examples of what appears to be cross

cutting relationships that could indicate

upwards vertical fluid movement. This

could imply that the processes outlined in

both interpretations are present throughout

the layered sequence, with possibly smaller

intrusions of peridotite resulting in


http://minmag.geoscienceworld.org/content/78/4/805.full%23ref-2

http://minmag.geoscienceworld.org/content/78/4/805.full%23ref-2

38

localised metasomatism rather than the

intrusion of sheet like sills affecting whole

layers. This could explain why another

‘Wavy Horizon’ has not been noticed

elsewhere is the layered sequence.


39

Figure 17: Log of the AUM showing an example of a loading structure. Note the sinking of denser silt into less dense mud at around 1m.


40

Figure 18: Log of the DMM showing examples of load casts, pseudo nodules, flame structures and convolute bedding. Note the sinking of denser sand into less dense mud. It is possible that upward fluidisation of the sandstone at ~2m caused the flame structures present. Distorted lamination at the top of the log also appears to have been affect by possible fluidisation.


41

Figure 19: Log within a major layer of PlROB showing examples of flame structures, and loading. With reference to table 7 the orange layers that show examples of SSD consist of mostly plagioclase in addition to a noticeably high proportion of olivine (which gives the distinctive orange weathered colour) whereas the plagioclase poor layers ae also olivine poor. For this log it may be the case that the orange layers represent examples of peridotite and the yellow layers are examples of a variation of troctolite. Therefore it may still be possible to view these deformational structures as possible intrusive peridotite formations as well as possible SSD structures. The cross cutting relationship at around 0.4m resembles upwards fluidisation of the underlying bed, although the thinner layers directly below it are intruded through rather than deformed as would be expected..


42

Figure 20: Log of ILI within a layer of PlROB near a boundary with underlying PyROU showing loading structures, flame structures and planar and wavy bedding. Interpretation of this log appears to favour a gravitational, sedimentary-like origin of formation with a distinct lack in cross cutting relationships and visible loading of bedding and disturbed lamination. This could suggest that vertical fluid movement is not continuous throughout the whole layer, affecting only certain localities. Note: dashed lines at the edge of the log represent the size of clasts.


43

Figure 21: Log of the PlROB showing examples of pseudo nodules, flame structures, loading structures and convolute bedding. This log appears to support the idea of possible fluid intrusion within partly lithified plagioclase rich layers, with veining at around 0.7m and 1.5m. There is also some possible example of SSD deformation with loading at around 1.2m.


44

CONCLUSION:

This study has managed to provide a limited interpretation of the spatial variations and

relationships of the lithologies present, with some findings correlating well with past fieldwork

undertaken in and around the mapping area. However there are some differences, as discussed,

which would most likely have been avoided by the more experienced geologist.

Through the creation of the map and cross section (see plate 1 (attached)), an interpretation of

features in map view and in the subsurface such as the dome-like magma chamber of the ILI

and the north-westerly dipping members of the MAF has been successfully produced. This in

turn has allowed for the creation of a general geological history of the area which has been

separated into separate geological events leading to the creation of different lithology groups

(e.g. the CBCS, the ILI etc.).

The study of the similar features within the igneous ILI and sedimentary MAF, whilst

recognising that the process of soft sediment deformation may be prevalent within both

lithology groups, indicates an additional unique vertical fluid injection component within the

ILI which is most likely related to post depositional intrusions of peridotite (or PyROU) into

the layered sequence, resulting in a cross-cutting rather than deformational effect on the

surrounding troctolite (PlROB) that would be expected in sedimentary deformation. Bearing

these features in mind, it is clear that the formation of the layered sequence on Rum is still an

area that is contested in the academic world and would benefit greatly from further detailed

study.


45

REFERENCES:

BÉDARD et al. (1988). Peridotite sills and metasomatic gabbros in the Eastern Layered Series of the Rhum complex. Journal of the Geological Society, London, 145, 207-224.

BRADWELL, T and GOODENOUGH, K. (2004). Rum and the Small Isles: A Landscape Fashioned by Geology. Scottish Natural Heritage, Perth.

BROTHERS, R.N. (1964). Petrofabric analyses of Rhum and Skaergaard rocks. Journal of Petrology, 5, 255-274.

EMELEUS, C.H. (1994). 1:50 000 Solid and Drift Geology Map of Rum. Sheet 60 (Scotland) British Geological Survey, Keyworth, Nottingham, UK.

EMELEUS, C.H. (1997). Geology of Rum and the Adjacent Islands. Memoir of the British Geological Survey, Sheet 60 (Scotland) Brtitsh Geological Survey, Keyworth, Nottingham, UK.

EMELEUS, C.H. and TROLL, V.R. (2008). A geological excursion guide to Rum: the Paleocene igneous rocks of the Isle of Rum, Inner Hebrides. Edinburgh Geological Society, Edinburgh.

EMELEUS, C.H. and TROLL, V.R. (2014). The Rum Igneous Centre, Scotland. Mineralogical Magazine, 79, 805-839.

FRANCO, R.L. (1995). Deformation Structures. Sedimentographica: photographic atlas of sedimentary structures. New York: Columbia University Press.

HOLNESS, M.B. (2005). Spatial constraints on magma chamber events from textural observations on cumulates: the Rum Layered Intrusion, Scotland. Journal of Petrology, 46, 1585-1601.

HOLNESS, M.B. (2007). Textural immaturity of cumulates as an indicator of magma chamber processes: infiltration and crystal accumulation in the Rum layered suite. Journal of the Geological Society, London, 164, 529-539.

HOLNESS, M.B. and WINPENNY, B. (2009). The Unit 12 allivalite, Eastern Layered Intrusion, Isle of Rum: a textural and geochemical study of an open-system magma chamber, Geological Magazine, 146, 437-460.

MCCLURG, J.E. (1982). Petrology and evolution of the northern part of the Rhum ultrabasic complex. Unpublished PhD thesis, University of Edinburgh, 2 volumes. (As seen in Emeleus, 1997).

NICHOLSON, P.G. (1992a). Precambrian: Upper Proterozoic Torridonian Group. 5-7 in Atlas of palaeogeography and lithofacies, Memoir of the Geological Society of London, 14. (As seen in Emeleus, 1997).


https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj1v4Wr08_KAhXGWxoKHUzWAcoQFggkMAA&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2F%25C3%2589&usg=AFQjCNHIlipNWqn6nB0Y69YnSiZzUN_m3Q

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NICHOLSON, P.G. (1992b). Sedimentation of the fluvial ‘Torridonian’ Applecross Formation, NW Scotland. Unpublished PhD thesis, University of Glasgow. (As seen in Emeleus, 1997).

NICHOLSON, P.G. (1993). A basin reappraisal of the Proterozoic Torridon Group, north west Scotland. 183-202 in Sedimentation and tectonics, Special Publications of the International Association of Sedimentologists, 20. (As seen in Emeleus, 1997).

STEWART, A.D. and PARKER A. (1979). Palaeosalinity and environmental interpretation of red beds from the Late Precambrian (‘Torridonian’) of Scotland. Sedimentary Geology, 22, 229-241. (As seen in Emeleus, 1997).

STEWART, A.D. (1982). Late Proterozoic rifting in NW Scotland: the genesis of the ‘Torridonian’. Journal of the Geological Society of London, 139, 413-420. (As seen in Emeleus, 1997).

STEWART, A.D. (1988b). The Sleat and Torridon groups. Later Proterozoic stratigraphy of the North Atlantic regions. Blackie, Glasgow. (As seen in Emeleus, 1997).

STOW, D.A.V. (2005). Sedimentary Rocks in the Field: A Color Guide. Manson Publshing, London.

RODD, J.A. (1983). The sedimentology and geochemistry of the Type Diabaig Formation in the Upper Proterozoic Torridonian Group of Scotland. Unpublished PhD thesis, University of Reading. (As seen in Emeleus, 1997).

WAGNER, L.R. and BROWN, G.M. (1968). Layered Igneous Rock. Oliver and Boyd, Edinburgh.

YOUNG, I.M. and DONALDSON, C.H. (1985). Formation of granular-textured layers and laminae within the Rhum crystal pile. Geological Magazine, 122, 519-528.


47

APPENDIX 1 – SEDIMENTARY SYMBOLS FOR STRATIGRAPHIC LOGS:

(Note: Adeapted from Stow, 2005)


Documents

GL4023 Mapping Report finalised