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The Geology of The Massif Montgris

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The Geology of The Massif Montgris Empty The Geology of The Massif Montgris

Post  MBAstudent on Tue Feb 23, 2010 1:08 am


This report entitled "The Geology of the Massif Montgris" was composed by me and
is based in my own work. Where the work of others has been used, it is fully
acknowledged in the text and in captions to tables and illustrations.

Signed …………………………………….

Date ………………………………………..

Chapter 1.0


This is a study of the Massif Montgris, it is based on evidence gathered in the
field over 21 days of field work. To supplement this data I have looked at
papers and works by previous visitors to the Montgris. The units within the
area are from the Upper Cretaceous the Tertiary and the Quaternary. I aim to
give an overall guide to the geology on a smaller scale than has previously been
accomplished. This study is mainly aimed at correctly dating the units of
limestone using micropalaeontological data. The micropalaeontological data has
also given light into the palaeoenvironment/geography during deposition.

Chapter 2


2.0.1 Introduction

Between the 24th of June and the 24th of July 1995 Glen Burnham and I ventured
to Catalunya. More precisely to Torroella de Montgris. Torroella is in the
North East of Spain, just inland of the Mediterranean sea. This remarkable old
town lies at the foot of the rather imposing Massif Montgris.

Locally known as "El Montgris" (literally the grey Mountain) the massif rises up
over the town and dominates the skyline. Torroella sits on quaternary
conglomerate deposits. These are easily eroded, hence the valley between Pals
(10Km to the south) and Torroella is extremely flat. The valley is bisected by
the river El Ter, which flows at a leisurely pace from the foothills of the
Pyrenees. The river flows to the south of Torroella and winds it's way to its
conclusion in the Playa de Pals (6Km east of Torroella).

El Montgris has been known to humans since prehistoric times. It has some large
caves on its slopes that served as a shelter to prehistoric man. The area was
very popular with the Romans who cultivated the local area, built roads and
towns (many of which still stand to this day) such as Peretelada to the south
adjacent to Pals.

Since the time of the Romans Torroella has grown into a thriving market town.
It has always had close links with the Montgris which until recently still
served a purpose as a shelter, not , however, against the elements but against
Pirates and marauders from the sea. In fact, on top of the Muntanya Santa
Catherina stands the remains of a thirteenth century castle (the last castle
ever built in Spain).

El Montgris has provided for the local commerce since it was first settled.
The local people value the Mountains greatly and still use them today. The rock
from which our dwelling was made was quarried from the mountain, the castle rock
was quarried on the mountain.

2.0.2 Aims of Study.

When I first considered the Montgris as a project area I realised that
information would be sparse and that the project would be more complicated than
a similar project in the U.K because the environment is so very different and
resources would be a great deal more difficult to access (due to the language
barrier). I also realised the project would probably be very different to the

Before Glen and I left England we attempted to research the Massif Montgris
through the usual channels in order to get an idea of what we would be facing.
The research lead to a few vague leads, we new the rock was sedimentary and most
likely limestone. Having visited the area previously I could recall a little
about the rocks but was certain of their sedimentary nature.

Our first lead came from an unexpected source. My parents had vacationed in the
area and upon my request had asked locally about any information pertaining to
the Geology. The result was that they brought back a research map that dated
the Massif as Cretaceous but suggested it was composed of 1 massive bed. We
loosely agreed our study areas and arranged our projects accordingly. The local
guide books and map had supplied us with information about the palaeontology
(macro fossils) which suggested the rock was full of bivalves, brachiopods,
corals and belemnites.

Before leaving we were unable to unearth much more information BUT seemingly at
the last minute we were able to make contact with Dr. David Brusi from the
Universidad de Gerona(departament del geophysica) who reassured us that upon our
arrival in Spain he would brief us on geology of El Montgris.

Therefore, with very little in the way of successful research we traveled to
Spain. Upon our arrival we immediately made our way to the city of Gerona and
to the University. Our meeting with David Brusi and his team proved very
productive indeed as they gave us a couple of papers about the area as well as
providing us with a geological map of the Montgris. The most important
information they gave us was about our working environment and how to "survive".

2.0.3 Methodology.

Previously, we have been taught to outcrop map. These skills were honed in the
inhospitable environment of the Highlands of Scotland, where one can actually
draw outcrops onto the map. It was, therefore, it was the intention to use this
technique over approximately 6km2 .

In order for this mapping technique to work you have to know what it is you are
looking at. With this knowledge in mind one set out to spend most of the first
week exploring the area and identifying the different strata, and their
relationships. This as you will see proved most difficult for various reasons.
The plan had been to have the Muntanya de Santa Catherina as common ground, but
after 3 or 4 days we came to the conclusions were made that there was a need for
safety equipment. There were reports of packs of wild dogs patrolling the area
also the terrain was at best rugged and challenging and at worst moderately
dangerous. On top of all this it was understood that work would have to be
completed in temperatures of up to 40 0 Celsius, every day with the
possibility of hotter/muggier weather to come.

Each day would begin with plotting a starting position, when the castle was
obscured an estimated position would be used to locate a specific point. Most
dip/strike readings are estimated as there were not many bedding planes level
enough to use the compass clinometer accurately . The local geological map
(296-2-2[78-24]) gave an indication to the geological relationships present,
however, even though the map is a 1:25,000 it is quite ambiguous with the
position of some boundaries and faults.

In order to cross reference the different strata, samples were taken and labeled.
So further samples could be identified. This was assisted by the geological
map and by referring to the map it was possible to take samples away from faults
and boundaries to ensure correct identification.

Chapter 3

The Rocks

This is an in depth study into the locations, ages and natures of the rocks that
were studied. These have included both observations from the field and later
observations made in response to new evidence, which was forthcoming after thin
sections of the different units were made in the laboratory.

Whilst in Spain Glen and I only had each other to consult on the more difficult
matters of El Montgris. This led to a subtle stagnation of ideas towards the
end of the trip. Therefore, on our return we were most grateful for the
assistance of various members of the faculty in gently pointing us in different
directions which proved to be pivotal. I have attempted to bring together
various different sources of data in the study of the individual rock types.

Limestone diferention between facies variations was exceedingly difficult in the
field. Therefore, it was necessary to use external references these resources
have been the 1994 1:25,000 scale geological map of Torroella de Montgrí
produced by the Servei Geològic de Catalunya. This provided gives basic
framework in the field and also a foundation with which to begin research upon
the return to England. The main tool in discovering the nature of the rocks was
micropalaeontology. The mainstay of this evidence is the study of the
Foraminiferida within the thin sections of each unit. The most useful resource
in this respect was: Loeblich A. R. Tappan H., Foraminiferal Genera and their
classification plates 1988 Van Nostrand Reinhold.

This book gives an accurate correlation and measuring device. It gave in all
cases a link between the framework in the map and the actual rocks we
encountered. This in turn has allowed us to build up a stratigraphy as well as
helping to formulate our ideas with respect of the structural relationships
within the Massif. In addition to all the less obvious links it gave a very
exact view of the palaeoenvironment during deposition.

Chapter 3.1

The Rocks

Grey Limestone

3.1.1 Location

The grey unit occurs at the very base of the limestone succession. In the area
that was mapped the grey unit is found adjacent to the underlying thrust plane.
The unit is best exposed within the study area on the south slope of Mt. Santa
Caterina between the 170-200m contours. The unit is also supposed to appear on
the south slope of MontPlà, also within the area under study. Evidence for this
outcropping is less obvious and difficult to locate.

3.1.2 Age/Thickness

The grey unit is thought to be as being from the Turonian stage. Subsequent
data has confirmed this evidence to corroborate this with microfossil data. As
for thickness, the unit appears to be up to 45m thick.

3.1.3 Field Description

This was one of the first units encountered, as with the red limestone. This
unit was grey on the surface and slightly darker when a fresh surface was made.
As with the red unit it effervesces on the application of dilute hydrochloric
acid, thus showing it to be of carbonate nature. Another correlation to the red
unit was the fact that veining increased in coverage, the closer you get to the
North-South faults. It should be noted that most of the information about grey
was collected on Mt. Santa Caterina. The unit was for the most part very
accessible there because of paths made by tourists/shepherds over recent years.
The grey was no different to the other units in as much as it has been attacked
by surface erosion. This has left it in the early stages of karstification.
The grey did not have many joints within it therefore it was nearly impossible
to measure the dip/strike. The grey unit is cut by two faults with north east
south west orientation in Mt. Santa Caterina.


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