This document discusses geological formations in the Stonehaven area, focusing on sandstone and flood deposits shaped by historical river activity and tectonic forces. It describes the geological structures created during the continental collision between Avalonia and Laurentia, including the Highland Boundary Fault and the associated metamorphosed rocks. The paper highlights various rock types, their characteristics, and the effects of folding and shearing in the region's geology.

1. Stonehaven Exercise using FieldMove 388800
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The paler section in this image
are sandstones deposited within
active channels near their mar-
gins. The reddish-brown oxidized
rocks are sheet flood deposits
which“represent sediment that
was deposited in times of flood
when the river overflowed its
channels” (Craig, 2009) and
spread sediment onto an alluvial
flood plain.
From the stereonet 1, the ORS to the
south of the area dips very steeply to the
south-east. This is due to strong compres-
sive forces that tilted the strata between
400-500Ma during the continental colli-
sion of Avalonia and Laurentia. This area
constitutes the northern side of the
Strathmore Syncline, where the axis runs
relatively parallel to the HBF. The degree
of tilting decreases further up the beach
toward the pillow lavas (as low as 36
oriented south-west)
This image shows pale-grey sandstone
with trough cross bedding that distorts
lamiations due to dewatering. The base
of the cycles represent erosion,
followed by depositon of sand bars.
These fluvial sandstones contain
pebbles at the base of packages.
Mudstones with ripples and desicca-
tion cracks are also common.
The ORS unit contains
packages of siltstone
and sandstones, with
sub-rounded clasts of
various sizes. These are
clasts of overbank mud-
stone that were eroded
and deposited within
the channel sandstones.
At Craigeven Bay, the steep Highland
Boundary Fault (HBF) oriented NE-SW cuts
through the outcrop forming a contact
between the Dalradian metamorphic rock
within the bay and HBC at the headlands.
These are deep marine deposits meta-
morphosed to schists, phyllites and slates
during the Caledonian Orogeny. From
satellite imagery, the HBF appears as a
linear feature representing a near-verticle
fracture zone. There are small zones of
transitional facies sandwiched in between
the pillow lavas at Ruthery Head.
Ruthery Head
Craigeven Bay
Cowie
The Dalradian originally erupted
underwater as basalt and accu-
mulated as a pillow-shaped
structure on the ocean floor.
There is minor tight folding in the
image. Some parts of the expo-
sure seem more metamorphosed
than others (changing grade).
Parts appear fissile like a slate. It is
likely a phyllite formed by region-
al metamorphism, with regularly
spaced cleavages
The HBC has interesting features around the fault zone.
Detailed images reveal a green tinge of this “carbonate
serpentinite spur” (McKay et al., 2019). It looks fine-grained,
heavily fractured and has a green-grey-buff colour with
shearing adjacent to the HBF. The transitional HBC facies in
contact with the Dalradian have olive surfaces termed green-
stone (chlorite schist) by Trewin et al., (1987). There is also
evidence of unit brecciation and mineraliazation of quartz in
the dolimitized pillow lavas along fractures, but no bedding
structures. In 2019, McKay et al identified 4 distinct clay-rich
units of the HBC. Some parts have a beige colour and are a
“dolomitic and siliceous carbonate,” (MacGregor, 1996) now
highly altered serpentine that is cross-cut by numerous
carbonate veins. The band of darkness in site 7 resembles
metabasalts and metasediments interbedded with black
siliceous shale no more than 1m thick and may yield fossils.
The pillow lavas show evidence of ductile deformation and
reverse motions. The transitional facies have experienced
more shearing and fractures.
Old Red
Sandstone
(ORS)
N = 46
Bedding is quite variable
but generally steep to the
SE. The unconformity is
above site 5, where ORS
meet HBC rocks with a
clevage that dips steeply
to the NW. The rocks likely
suffered from rotation
adjacent to the HBF.
1
References
1: Craig, P., 2009. Teachers' Guidecowie, Stonehaven,
Aberdeenshire. [online] Geowalks.co.uk. Available at:
<http://www.geowalks.co.uk/eso/CowieTeachersGuide-v4.pdf>
[Accessed 17 March 2020]. 2: MacGregor, A., 1996. Fife And
Angus Geology. 3rd ed. Edinburgh: Pentland Press, pp.30-36.
3: McKay, L., Shipton, Z., Lunn, R., Andrews, B., Raub, T. and
Boyce, A., 2019. Detailed internal structure and along-strike
variability of the core of a plate boundary fault: the Highland
Boundary fault, Scotland. Journal of the Geological Society,
177(2), pp.283-296. 4: TREWIN, N.H., KNELLER, B.C. and GILLEN,
C. (Eds.), 1987. Excursion guide to the geology of the Aberdeen
area. Scottish Academic Press, Edinburgh.
GrampianOrogeny
(460-480Ma)
Acadian Orogeny
(420-390Ma)
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Key
Old Red Sandstone (ORS: Lower
Devonian)
Highland Border
Complex (HBC:
Ordovician) -
Highland Border
Complex (HBC:
Ordovician ) - Pillow
Dalradian
Highland Boundary Fault (HBF)
Contact
There is internal deformation of the ORS
associated with the unconformity of the HBC.
On the beach 100m south of Ruthery Head,
there is an immediate change of strike (SE to
SW) closer to the volcanic units possibly due
to minor faulting or shearing. These sand-
stones and conglomerates unconformably
overlie the HBC rocks.
HBC: Transitional
Facies
Dalradian
HBC: Pillow Lavas
N = 49
Foldiation is generally
toward the north-west
with variable dip.
The volcanic units have an apparent dip to the north-west, likely due to
the“shear planes parallel to the plane of the main Highland Boundary
Fault”(MacGregor, 1996) 100 meters to the north-west.
73
Way up
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2
2
3
4
5
6
3
4
5
6
7
7
Stereonet 2
Stereonet 1
Unconformity
Unconformity