The Geology Of The Massif Montgris Essay

, Research Paper

The Geology of The Massif Montgris

Declaration

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

Abstract

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

Introduction

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

proposal.

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 Montgr?

produced by the Servei Geol?gic 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 MontPl?, 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.

3.1.4 Orientation

The few dip/strike readings showed the grey to have a dip direction opposite to

that of the red. In this bed there was evidence of an an