Sunday, October 14, 2012

geology of massif montgris


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 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 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.

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

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