LIMNOMA.(II'IETIC STUDIES ON GREEK SEDIMENTS

by

Stavros Papamarinopoulos

submitted

for the degree of

• Doctor of Philosophy

- • S

University of Edinburgh

• 1978 DECLARATION.

1 hereby declare that the work presented in this thesis is my own, unless otherwise stated in the• ... text, and that the thesis h7as bee com osed by myself.

Stavros Papamarinopoulos. 1.

CO1TENTS Page

Synopsis iii

Dedication . :. v Acknowledgements . vi

Abbreviations . Viii 4 List of Figures x

List of Plates__ xvi

Chapter 1 Introduction 0 1.1 On the discovery of the Geomagnetic field 1 1.2 Linmomagne tism 4 Chapter 2 Experiments with magnetic crystals 7 2.1 Magnetic mineralogy 8 2.2 Extraction procedure 8 2.3 Debye-Scherxer X-ray diffractometry 9 2.4 Cryomagnetic and thennomagnetic experiments 10

2.5 'Mössbauer spectroscopy . 11 2.6 Optical microscopy 12 2.7 Discussion and conclusions 14 Chapter 3 The magnetic properties of the fresh water limnic deposits 16 3.1 The Greek lakes 17 3.1 .1 Lake Volvi 17 3- 1 . 2 Lake Begoritis 18 3. 1 -3 Lake Trikhonis 19 3.2 Long core descriptions and measurements - 19 3.3 Single sample measurements jn, k and -ratio 22 3.4 The stability of in 22 3.5 Remanent hysteresis 24 3.6 Significance of jar in lixnnic deposits 25 3.7 Low temperature treatment 25 3.8 Conclusions 26

Li. Page Chapter 4 PDRM 27 4.1 Magnetization processes in sediments 28 4.1.1 Depositional remanent magnetization 28 4.1.2 Post-depositional remanent magnetization 33 4.2 Experimental methods 36 4.3 Jp and its relationship with external applied magnetic fields 39 4.3.1 Presentation and interpretation of the results 40 4.3.2 Inclination error in the Greek lakes 43 4.4 The stability of jp 44 4.5 The growth of jp 44 4.6 Jp undeir controlled conditions 45 4.7 Discussion and conclusions 46 Chapter 5 Limnomagnetic palaeointensities 48 5.1 Introduction 49 5.2 The k, jar and jrs normalization methods for relative palaeointensities 51 5.3 PDEM as a normalization parameter 53 5.4 Discussion and conclusions 54 Chapter 6 Limnomagnetic palaeodirections 56 6.1 Dating controls 57 6.2 Archaeomagnetic and limnomagnetic correlations 57 6.3 Correlation of the Greek and British limnomagnetic master curves 59 6.4 Discussion and conclusions 62 Chapter 7 Speleomagnetism 64 7.1 Introduction 65 7.2 Petralona Cave 67 7.3 Palaeomagnetic sampling 69 7.4 Palaeomagnetic results 69 7.5 The nature of the remanence 71 7.6 Discussion and conclusions 72 7.7 Aragt cave 73 7.8 Palaeornagnetic results 74 7.9 Discussion and conclusion 74 7.10 Ball's Cavern 74 7.11 AFC demagnetizations 76 7.12 Interpretation of the palaeoinagnetic data 76 7.13 Discussion and conclusions 77 Appendix The Mackereth corer 79 8.1 General description 80 8.2 Operation of the corer 81 8.3 Discussion and conclusion 83 Bibliography 84 111.

SYNOPSIS.

Investigations in the whole sediment (reversed isothermal remanence, cryomagnetic experiments, modified Lowrie-Fuller test), showed the pre- sence of fine grained magnetite in dominance of single domain or pseudo- single domain in character, whereas magnetic extracts studies (Debye-

Scherer X-ray d.iffractometry, thermomagnetic experiments, Ml3ssbauer spectroscopy and optical ncroSco) showed the presence of angular fresh magnetite or partially oxidized towards haematite, with size ran- ging from less than 1pm up to few microns. The natural remanence is of stable character producing smoothly falling demagnetization curves, well grouped directions and mediadestructive fields ranging between 200 and

500 Oe after cleaning with alternating magnetic fields. Anhysteretic and isothermal remanence studies showed that the saturating field is 1 ,000 Oe peat field and 1,500-2,0000e direct field respectively. Redeposition with slurries produced remanence of post-depositional origin, which re- corded almost precisely the applied magnetic field without inclination error and of stable character with smoothly falling demagnetization. curves, well grouped directions and mediaj destructive fields of about

200 Oe. Its strength is directly proportional to the strength of the applied magnetic field and its growth remains constant with time. Long column redepositions under controlled conditions produced stable reman- ence when the water content was about 60% with the same characteristics of stability as the slurries, but with an inclination error of about 200, attributed in compactive effects, produced by unnaturally fast rate of deposition and consolidation. Comparison of the post-depositional rem- anent magnetizations produced at 500 and at room temperature showed no difference in their intensities. Susceptibility, anhysteretic, isothermal and post-depositional remanences were used as normalizing parameters to iv. compensate the variations of the magnetic content along the studied limnic cores, but comparisons with the established European archaeo- magnetic intensity curve showed no success. The declination, inclina- tion, geomagnetic variations of the last 2,000 yr. B.P. recorded in the sediments of Lake Volvi correlate with the corresponding European archaeomagnetic records. The same variations recorded in the sediments of Lake Trikhonisof the last 6-7,000 yr. B.P. are correlative with those recorded at Lake Begoritis (Greece), and Lake Winderemere (England) and several other records in central Europe. The declination appears to be periodic having a 2,700 years periodicity while the inclination is oscillatory but aperiodic. - V.

DEDICATION

This work is dedicated with clarity, to all the people who established the ideal of HELLENISM, a way of Olympic life towards perfection with Done simplicity, .a multiple path to the enigmatic unknown, through philosophy and science, through irrational drama and comedy, through geometrized arts or mystisism, a continuous sparkling pass to unity with the HOLON, without fear or hope. vi

ACKNOWLEDGEMENTS

It is more than pleasure to express my-sincere gratitude and thanks to all the people who helped me to achieve this work.

Professor K.N. Creer, Head of the Department of Geophysics and my supervisor, who offered me the opportunity and the topic of the research, helping me, continuously, persistently and invaluably in many ways, from many different directions.

Dr. P.W. Readnian, of the Department of Geophysics, who helped me during the field work in Greece, discussed extensively many palaeomagnetic aspects of my work and took some of the X-ray diffraction photographs.

Dr. R. Thompson and Mr. A. Jackson of the Department of

Geophysics, who helped me during the field work in Greece and especially the latter who helped to solve: many technical problems.

The Institute of Geological and Mineralogical Research (IM) of Greece which offered the permit for the project and, in particular, Dr. N. Apostolidis, Scientific Director, Dr. J. Bornovas

.:and Dr. C. Katsikatsos of the Geology Department who, together with Dr. A. Stavrou and Mr. C. Thanasoulas of the Geophysics Department, offered numerous facilities, help and advice.

Messrs. H. Muir, T. Montgomery, B. Stevenson, I. McDonald who helped me invaluably with enthusiasm and friendliness to approach and solve several technical problems which I face during my experimental work.

Miss J. Neligan who measured many of the samples collected from the Greek cores. vii Dr. R. Gill and Mr. C. Begg of the Department of Geology who had the kindness to introduce me to the aesthetics and science of the optical microscopy of the magnetic crystals and who produced polished sections and took the photographs of them shown in this thesis.

Dr. S. Bottema of the University of Groningen, Department of-Biology-Archaeology who performed the pollen analysis. Dr. D. Harkness of the Scottish University Reactor Research

Centre (StJRRC) who produced the radiocarbon datings of the sediments.

Dr. Y. Naniatis, Dr. T. Simopoulos and Dr. T. Costicas who had the kindness to perform Mossbauer spectroscopy of the magnetic extracts from lake and cave sediments at the Department of Physics of the Democritos Atomic Centre in Athens. Dr. A. Poulianos, Read of the Greek Anthropological Society who made possible through his invitation and the numerous offered facilities the palaeomagnetic study of the excavated site at

Petralona Cave in Greece. Dr. J. O'Donovan of School of Physics of Newcastle University

Upon Tyne who took some of the X-ray diffraction photographs and introduced me in thermoina.gnetic analysis.

Professor S. Kopper, Head of the Department of Anthropology of Long Island University (USA) who helped me sampling in the Greek caves under highly adverse conditions.

Dr. A. Stavrou, who gave me the first stimulus in palaeomagnetism and who, together with Professor J. Drakopoulos, Head of the Department of Geophysics-Seismology of the University of Athens, encouraged me continuously during the years of the research. / vii

Messrs. C. Nakropoulos, co-researcher in Edinburgh and old fellow student from the Physics Department of Athens University, for mathematical and computing analysis of various models in magnetization processes and Y. Liritzis, of the Physics Department of Edinburgh University for useful and critical discussion over the enigmatic cranium found in Petralona cave. Mrs. L. Begg who typed the manuscript with brilliant humour.

My late father Panos from Arcadia and my mother Demetra from Laconia, who supported me and encouraged me throughout the research.

The Ministry of Coordination and Planning which offered me three years' studentship, the Russell Scottish Establishment and, in particular, Dr. D.F.O. Russell who very kindly offered me a studentship during my last year of my research.

The research formed part of a wider research project on the

Greek and on other European Lakes, funded by the National Environment

Research Council (NERc) through Grant No. GR3/22.38 awarded to

Professor Creer. Artemis, who was there and here, always inspiring, introducing fresh ideas, emotions and energy. viii.

BBRE VIAT IONS

in IRM intensity (natural remazient magnetization)

jo Initial NRM intensity

jd. Normalized NRM intensity

jdo Normalized NBM intensity after storage in zero magnetic field

jcr CRM (chemical remanent magnetization)

jd.r : DRM (depositional remanent magnetization)

jp : PDBM intensity (post-depositional remanent magnetization)

jpo : PDRM intensity after storage in zero magnetic field

jpa Normalized PDRM with wet mass

jpb : Normalized PDRM with dried mass

jpc : Normalized PDRM with water content

jar : ARM intensity (anhysteretic remanent magnetization)

jrs : IEIVI intensity (Saturation isothermal rem anent magneti- zation)

jv : VPM (viscous remanent magnetization) k : Initial magnetic susceptibility of naturally deposited sediments kd : Normalized magnetic susceptibility per wet mass of naturally deposited sediments kp Initial magnetic susceptibility of redeposited sediments kpa : Normalized magnetic susceptibility per wet mass of redeposited sediments kpb : Normalized magnetic susceptibility per dried mass of redeposited sediments kpc : Normalized magnetic susceptibility per water content of redeposited sediments

Q (jn/k) Qd : (jd./kd)

QP (jp/kp) ix.

D : NRM declination

Dd. : NRIiT declination after storage in zero magnetic field

Dp : PDEM declination

Dpo : PDI?M declination after storage in zero magnetic field

I : NRM inclination

Id. : NRM inclination after storage in zero magnetic field

Ip : PDRL inclination Ipo : PDRM inclination after storage in zero magnetic field le : Geomagnetic inclination at the spot of the experiment

Ia : Inclination of applied magnetic field

: Inclination error

A95 : Alpha 95 K : Precision parameter R : Length of the vector sum of the direction cosines

N : Number of specimen Wa : Wet mass

Wb : Dried mass

We : Water content

.AF : Alternating field

AFC : Alternating field cleaning

MDF : Medium destructive field

H : Applied direct magnetic field

Haat : Saturating field

Hcr : Coercivity of the maximum remanence

t : Time indays log(t): The logarithm of time

MD Mi.iltidomains

SP : Single domains

PSP : Pseudo single domains X.

LIST OF FIGURES. Chapter 2 (page 7)

Figure 2.1 Automated magnetic separator.

Figure 2.2 Cryomagnetic curves of whole sediment from Lake Volvi.

Figure 2.3 Thermomagnetic curves of extracts, from sediments of the Greek lakes.

Figure 2.4 Mssbauer spectra of extracts, from sediments of the Greek lakes.

Chapter 3 (page 16).

Figure 3.1 Map of Greece with the positions of the main lakes.

Figure 3.2 The geomorphology of the area around lake Volvi.

Figure 3.3 Isobaths and coring stations in Lake Volvi.

Figure 3.4 The geomorphology of Lake Begoritis.

Figure 3.5 Isobaths and coring stations in Lake Begoritis. Figure 3.6 The geomorphology of Lake Trikhonis.

Figure 3.7 Isobaths and coring stations in Lake Trikhonis. Figure 3.8 'Tke of Lake Volvi, core VS.

Figure 3.9 JQi4 o stratigraphy of Lake Begoritis, core B9. Figure 3.10 T rko strati gTaphy of Lake Trikhonis, core T2.

Figure 3. 11 Long core measurements of NEM horizontal intensity from Lake Volvi and their correlation.

Figure 3.12 Long core measurements of NRM horizontal intensity from Lake Begoritis and their correlations.

Figure 3.13 Long core measurements of NRM horizontal intensity from Lake Trikhonis and their correlations.

Figure 3.14 Single sample measurements of NRM intensity, susceptibility and Q-ratio of core V8, of Lake lTolvi.

Figure 3.15 Single sample measurements of NRM intensity, susceptibility and -ratio of core B7, of Lake Begoritis. Figure 3.16 Single sample measurements of NRM intensity, susceptibility and Q,-ratio of core T2, of Lake Thikhonis.

Figure 3.17 Normalized NIUVI demagnetization curves of pilot samples from Lake Volvi, Begoritis and Trikhonis. xi.

Figure 3.18 Normalized NRM demagnetization curves together with stereographic projection of their directions of indi- vidual pilot samples taken from Lake Volvi, core 118.

Figure 3.19 (a, b) Normalized NEM demagnetization curves together with stereographic projections 'of their directions of individual pilot samples taken from Lake Begoritis, core B9.

Figure 3.20 Normalized NBM demagnetization curves together with stereographic projections of their directions of individual pilot samples taken from Lake Trikhonis, core T2.

Figure 3.21 IRM curves of pilot samples taken along cores 118, B9 and T2 of Lakes Volvi, Begoritis and Trikhonis respec- tively.

Figure 3.22 Reversed IBM curves of pilot samples taken along cores V8, B9 and T2 of Lakes Volvi, Begoritis and Trikbonis.

Figure 3.23 ARM curves of pilot samples taken along cores V8, B9 and T2 of Lakes Volvi, Begoritis and Trikhonis.

Figure 3.24 Spectrum of normalized IBM demagnetization curves given to pilot samples (v8-16, .V8-41, V8-65, V8-93), together with their NBM demagnetization curve.

Figure 3.25 Spectrum of normalized ARM demagnetizatiOn curves given to pilot samples (v8-109, V8-140, V8-160, V8-192), together with their I1BM demagnetization curve.

Figure 3.26 ' NEM normalized demagnetization curves before and after cooling, at liquid , €roe'1 temperature ad. ua-i up F%1 ro 9neLic Figure 3.27 ARM normalized demagnetization curves before and after cooling, at liquid ocentemperatureuvid UJ'P$1IIAc u I1 P'rO a9neLic beea, Figure 3.28 IRM normalized demagnetization curves before and after cooling, at 1iquid b 1temperatureorcl ujavhc U ivì e-o ndc etc{. Chapter 4 (page 27) Figure 4.1 Apparatus performing long column redeposition experiments under controlled conditions of temperature, rate of deposition and consolidation.

Figure 4.2 Apparatus performing slurry redepositions.

Figure 4.3 Apparatus performing slurry redepositions with synchronous six specimen sampling.

Figure 4.4 Single sample slurry redeposition apparatus. Figure 4.5 Intensity of PDRM before and after ARC to remove VRMs is plotted against the intensity of the applied magnetic fields. xii.

Figure 4.6 Normalized demagnetization curves, of redeposited specimen, sampled from slurries.

Figure 4.7 Normalized demagnetization curves of redeposited representative specimen for each redeposition experiment performed between 0.20 and 0.80 Oe, with their direction stereographically projected during ARC.

Figure 4.8 Normalized demagnetization curves of redeposited representative specimens for each redeposition experiment performed between 0.40 and 4 Oe with their direction stereographically projected during ARC.

Figure 4.9 The growth of PDRM, before and after AFC to remove superimposed VRMs is plotted against the time. Figure 4.10 Normalized demagnetization curves of specimen sampled along the redeposited column.

Figure 4.11 Normalized demagnetization curves of individual specimens sampled along the redeposited column and their directions of PDRM during ARC is shown in stereographic projections.

Chapter 5 (page 48) Figure 5.1 NRM intensity normalized per wet and dried mass of core VS of Lake Volvi is plotted side by side with the dried, wet mass and the water content along the core.

Figure 5.2 Normalized NRM, ARM, 1PM and PDRIvI curves of pilot specimen taken along core B9 of Lake Begoritis.

Figure 5.3 Normalized IRM intensity plotted against normalized ARM of pilot samples sampled along core B9.

Figure 5.4 The NR/IRM ratio is plotted against the AR of pilot specimen sampled against B9.

Figure 5.5 The normalizing parameters k, ARM, IBM and their ratios upon NRM are plotted side by side against the depth of core B9 of Lake Begoritis.

Figure 5.6 The normalizing parameters k, ARM, 1PM and their ratios upon NRfvt are plotted side by side against the depth of core V8 of Lake Volvi.

Figure 5.7 Normalized NRM is plotted against normalized PDRM of redeposited pilot samples taken along core B9 of Lake Begoritis.

Figure 5.8 I'IBM, PDRM, NBM/FDRM and the ks of the naturally and redeposited samples are plotted side by side against -. the depth of core VS.

xiii.

Figure 5.9 11BM, PDRM, NI1Vr/PDRM and the ks of the naturally and artificially deposited samples are plotted side by side against the depths of cores B9 and Ti, of Lakes Begoritis and Trikhonis, respectively.

Figure 5.10 NRM, NRM,/k, NRM/SARM, NRM/S ThM and NRM/PDRM are plotted side by side against the depth of core B9 of Lake Begoritis.

Figure 5.11 NEM, NRIVI/k, NRM/SARM, M/SIRM and Nfl/PDRM are plotted side by side against the depth of core V8 of Lake Volvi.

Figure 5.12 Normalized archaeomagnetic intensity curve plotted side by side with normalized jn by k, jar, jrs and jp. (Fo is the present day field intensity;. Ft /. S -LkQ.

Chapter 6 (page 56)

Figure 6.1 NRM declination, inclination, intensity and Q-ratio are plotted side by side with their cleaned record after AFC, against the depth of core V8 of Lake Volvi.

Figure 6.2 Limnomagnetic declinationand inclination curves of core V2 after AFC in 200 Oe plotted against the depth of the core and the European (N.L) archaeomagnetic declination and inclination records.

Figure 6.3 NRM declination patterns of single sample measurements plotted against the depth of cores B7, B8 and B9. Co-reEi toi EnQS we re cvcjruc{€ kzbcse o-fl yCo-cJ. Figure 6.4 I'IIM inclination patterns of single sample measurements plotted against the depth of cores B7, B8 and B9.

Figure 6.5 1flM, inclination, declination, intensity and Q-ratio are plotted side by side with their cleaned record after AFC - against the depth of core B9 of Lake Begoritis.

Figure 6.6 NRM declination variation plotted together with its record after six months storage in zero magnetic field and after AFC side by side against the depth of core T2.

Figure 6.7 I'tRM inclination variation plotted together with its record after six months storage in zero magnetic field and after AFC side by side against the depth of core T2.

Figure 6.8 Inclination correlations between core B9 and core T2 of Lakes Begoritis and Trikhonis respectively.

Figure 6.9 Inclination correlation between Lake Trikhonis (Greece) and Lake Windermere (England).

Figure 6.10 Declination correlation between Lake Trikhonis (Greece) and Lake Windermere (England). - xiv.

Chapter 7 (page 64) Figure 7.1 Map of Greece with the main caves with palaeoanthropol- ogical and archaeological interest.

Figure 7.2 The profile of Petralona cave.

Figure 7,3 Schematic cross-section of the excavated section and the site of the fossil.

Figure 7.4 The excavated section and the logs of NRM intensity, magnetic susceptibility and Q-ratio plotted side by side.

Figure 7.5 Orientational sampler for collecting samples along moist core sediments.

Figure 7.6 Normalized. TRM demagnetization curves and stereographic projections of their directions of individual pilot samples, taken along the Petralona section.

Figure 7.7 NPIvI inclination logs plotted together with their values after storage in zero-magnetic field and after AFC in 100 Oe.

Figure 7.8 NRM declinations plotted side by side with their values after storage in zero-magnetic field and after AFC in 100 Oe.

Figure 7.9 Normalized PDRM demagnetization curve and the direction of it during AFC in stereographic projection.

Figure 7.10 Stratigraphy of the sampled section and the plan of Arago Cave in which palaeoanthropological fossils were found.

Figure 7.11 RRM declination, inclination, intensity, susceptibility and Q-ratio logs plotted side by side against the depth of the sampled section.

Figure 7.12a NRM normalized demagnetization curves and stereographic projections of their direction of individual pilot samples collected along the excavated section.

Figure 7.12b NRM normalized demagnetization curves and stereographic projections of their direction of individual pilot samples collected along the excavated section.

Figure 7.13 The stratigraphy of the sampled section and the plan of Ball's Cavern.

Figure 7.14 NBM normalized demagnetization curves of pilot samples from Alpha and Omega sections. xv.

Figure 7.15a NRM normalized demagnetization curves with stereographic projections of their directions of individual pilot samples during .AFC, from Alpha section.

Figure 7.15b NRM normalized demagnetization curves with stereographic projections of their directions of individual pilot samples during AFC, from Omega section.

Figure 7.16 NRM intensities and their cleaned record plotted together side by side with Q-ratio and the magnetic susceptibility, with Omega section in the top and Alpha in the bottom.

Figure 7.17 NRM inclination and declination logs plotted in parallel

- together with their record after AFC with Omega section

- in the top and Alpha section in the bottom. Appendix (page 79) Figure 8.1 Diagrammatic representation of the main features of Mackereth corer.

Figure 8.2a The boat with the corer in a vertical position. Figure 8.2b The boat has moved 40m away and the float holds the nylon rope, which is connected with the boat.

Figure 8-3a Details of the functional procedures during coring. Figure 8.3b A realistic picture of the corer and its major components. :O( -k- Figure 8.4a Phase (A) : The vertical position of the corer on the lake bed.

Phase (B) : The slow penetration into the soft sediment. Phase (C) : The penetration is completed.

Figure 8.4b Phase (D) : The coring procedure is completed. Phase (E) : The corer starts to rise up. Phase (F) : The corer is going to the surface of the lake. xvi.

LIST OF PLATES. Chapter 2 (page 7)

Plate 2.1 X-ray diffraction powder patterns of magnetic crystals extracted from the sediments of Lake Volvi.

Plate 2.2 X-ray diffraction powder patterns of magnetic crystals extracted from the sediments of Lake Volvi.

Plate 2.3 (a) Oxidized angular magnetite towards haematite sur- rounded by fresi magnetite fragments. Lake Volvi (Greece). (Iii çeJ 5 0 0 vrI 1 -eI ti itn'te). - - Plate 2.4 (a) Whole haematite grains with red marginal reflections; (b, c, d.) Clusters of fresh angular fragments of magnetite dominating the field of view. Lake Volvi (Greece).

Plate 2.5 (a) Angular large grain of bright haematite with blood red marginal reflections; (b) Skeletal large magnetite grain; (c) Diamond shaped magnetite fragments. Lake Begoritis (Greece).

Plate 2.6 (a) Composite pyrite rhomboid (aggregate of minute sulphite spheres);(b) Oxidized magnetite fragments towards haematite; (c) Cluster of angular magnetite fragments. Lake Begoritis (Greece).

Plate 2.7 (a) Large diamond shaped magnetite crystal; (b) Composite pyrite rhomboid; (c, d) Haematite grains with tiny magnetite fragments stuck on them; (e, f) Clusters of fresh angular magnetite. Lake Trikhonis (Greece). Plate 2.8 (a) Diamond shaped broken magnetite crystal; (b, c) Clusters of fine grains of bright haematite which dominate the field of view; (d, e) Iydrous iron oxides probably geothite or lepidocrocite with grey-red internal reflections. Canet Cave (Spain).

Plate 2.9 (a) Large titanomagnetite crystal crossed by a distinct unaltered ilmenite lamella along its major axis; (b, c) Titanomagnetites with colour variations. Glacial soil, Balfargh (Scotland).

Plate 2.10 (a) Large titanomagnetite crossed by a distinct unaltered ilmenite lamella along its major axis, partially and heterogeneously oxidized towards a poorly crystalline shaped maghemite, which is recognised by the replacement of the N-E quarter of the host mineral; (b) Broken angu- lar coarse fragments of titanomagnetite. Glacial soil, Balfargh (Scotland).

Chapter 3 (page IG)

Plate 3.1 Sub-sampling of specimens from a sliced core of Lake Trikhonis. Plastic 2.3cm cube-shaped sample holders are pressed serially into the soft sediment. xvii.

Chapter 4 (page 27) Plate 4.1 The long column under controlled redeposition apparatus within the Helmoltz coils system.

Chapter 7 (page 64) Plate 7.1 The fossilized cranium found in Petralona Cave.

INTRODUCTION

1 .1 On the discovery of the Geomagnetic field.

1.2 Limnomagnetism. 1.

1 .1 On the discovery of the Geomagnetic field.

Carlson (1975) established that the Olmec people in San Lorenzo

Verakruz, Mexico 1,000 yr. B.C., were capable of sophisticated work of magnetic minerals, knew the properties of lodestone and in fact the

directive properties of it. He showed that a discovered impure haema-

tite artifact was-indeed a magnetic compass. The properties of the magnetized rocks were first established by the Greeks approximately

600 yr. B.C., who actually gave the names magnet, magnetism, etc. after

the discovery of the lodestone in Magnesia in Asia Minor. The first observations were attributed to Thales. The magnetic compass was also known to the Chinese approximately 200 yr. B.C. (Needham,1962) who con- structed a lodestone spoon rotating on a smooth board. The foundations of geomagnetic studies were probably established in China, where, at least by 1 9 093 A.D. the directive property of a freely suspended magnet was, known at large, (Mitchell, 1932). The Chinese were theorizing about the declination, as well as the polarity of the magnet from 800 to 900 A.D., before Europe knew even the polarity (Smith and Needham,

1 967). By the year 1187 the magnetic compass was in use in northwestern Europe for the purpose of navigation in the primitive form of a suspen- ded lodestone. It was brought by an English monk called Alexander

Necham, who gives the first reference of its arrival in Europe. Roger

Bacon, in 1210A.D. and Petrus Peregrinus, a few years later questioned the universality of the north-south directivity of the compass needle,

(Smith, 1970). Georg Hartmann in 1544 and Robert Norman in 1576 . inde- pendently discovered the inclination. In 1600 William Gilbert establi- shed that the earth itself is a great magnet. In 1.635 H. Gelibrand, by 2 . comparing observations of magnetic declination made in the preceeding

54 years in London, discovered that the declination altered in a regu- lar way with time (Chapman and Bartels, 1940). The secular variation of magnetic direction contradicted Gilbert's hypothesis which asserted that the Earth was a permanent magnet. However Gelibrand' s conclusions have now been verified by numerous observatory records which demonstrate that the geomagnetic field is indeed variable in both time and space.

This result has been active in determining the course of modern theories to explain the source of geomagnetic phenomena.

Two hundred years later, Gauss first mathematically described the earth's magnetic field using potential theory, but another century pas- sed before palaeomagnetism was widely employed to trace field behaviour through geologic time. To a first approximation, the geomagnetic field can be represented by a simple inclined geocentric dipole at the Earth's centre. The increase in the number of magnetic observations and surveys in the last 60 years and more recently, satellite studies, has enabled a better description of the field over the surface of the globe and has improved the estimates of the residual, non-dipole, components. Con- tour charts of the non-dipole field reveal extensive regions of en- hanced or diminished intensity which are also changing and these regions which are entered as "isoporic foci", 'bear no obvious rela- tions to the positions of the continental masses.

This feature, together with the discovery that the foci drift slowly westwards, suggests a deep internal source for the field. A conclusion which is confirmed by spherical harmonic analysis, which shows that more than 99% of the total field is of internal origin and proved by finding field gradient with depth down the deep mines. 3.

Below a depth of about 25 km rocks art a temperature exceeding the

Curie points of all magnetic minerals, so that the mantle and, lower crust can make no permanent contribution to the geomagnetic field.

Following work by Lowes and Runcorn (1951), Alldredge and Hurwitz

(1964) found that they obtained the best fit to the observed field by postulating a central dipole surrounded by eight radial dipoles mid- way between the Earth's centre and the core-mantle boundary. The model proposed a connection between geomagnetic sources and some mech- anism within the core. Seismological indications show strongly' a ouler liquid core, while geochemical and density considerations in high tem- perature and pressure are compatible with a core consisting largely of

iron and nickel. All these facts have led to various proposals of a geomagnetic

dynamo in which the fields are produced by electric currents which are

sustained by fluid motions. Stacey (1969) proposed that the field would decay rapidly with a time constant of roughly 1,000 years. How-

ever, if the liquid core continually undergoes shear flow then toroidal

field lines become trapped in the conducting iron and move with it to

create poloid.al fields, thus resulting in a magnification of any pre-

existing poloidal fields, (Elsasser, 1950). The increase of the magnetic energy reduces the rate of shear flow

which must therefore be sustained if the dynamo is to be continuous.

It is accepted that the energy requirements are very small - about

10 12 watts, something which could be supplied from a lot of available

sources, like heat generated by radio activity in the inarior convec-

tion effects caused by the planet's cooling at the surface and mechan-'

ical torques due to precession of the Earth's axis. The phenomenon

of the geomagnetic reversal, is well established from palaeomagnetic 4. studies (Cox et al, 1967; Bullard, 1968; Cox, 1975; Cox et al, 1975). After the analysis of a large number of data, it was found that the field direction is divided about equally between normal and rev- ersed states, although the, durations appear to be randomly controlled.

Cox (1975) developed a statistical model in which he formulates a distribution function for polarity intervals. In this model, the geomagnetic dynamo is assumed to be steady dipole oscillator which undergoes a polarity reversal only when triggered random fluctuations in the non-dipole field. Kono (1972) analysed Ccx's model and found it inconsistent with the palaeointensity data. An example of simple mathematical models which do not contradict the palaeomagnetic infor- mation was given by him. The model is composed of tens of dipoles in the core with equal movements and directions either parallel or anti- parallel to the rotational axis • The state of the geomagnetic field changes as direction inversion takes place in each dipole in a stochas- tic manner. Advances in the dynamo theory mean that features of the secular variation can now be explained in terms of slow changes in the pattern of convective motions in the core or by the growth and decay of fluid eddies. -

1.2 Limnomagnetism

Limnomagnetism is a branch of palaeomagnetism the scope of which is the recovery of the magnetic signature of the geomagnetic field as it was recorded by limnic fresh-water sediments. The development of the coring procedures and especially of the Mackereth corer,

- '• (Mackereth,1958) has given the possibility of recording the finest fluctuations of the geomagnetic field in a serial manner. Consequently the geomagnetic secular variations can be studied 5. in detail and periods can be identified. The obtained data have region- al and global importance. The regional significance is the establish- ment of the master limnomagnetic curve in a given area, which can be used as dating platform in association with possible archaeomagnetic data. The global significance is the possibility of testing proposed models for the nature of the geomagnetic field, in terms of correlating the regional limnornagnetic curves in a global scale. For example,

Alldredge and Hurwitz (1964) suggested eight radial dipoles placed at 0.3 Earth radii in the outer liquid core and a central dipole to give the best fit for the 1945-U.S. chart. Bochev (1975) proposed a model with six radial dipoles in order to explain the 1942-46 geomagnetic field. These dipoles are unconstrained in position and orientation starting with them being arranged equidistant from each other and ori- entated vertically in the equatorial plane going into an iteration pro- cess. Computerized rapid spinner-magnetometers allowed complete reco- very of the fos.silized !'at closely spaced time strati- graphic intervals. Currently cryogenic magnetometers have improved the sensitivity by a factor of about 100. The used specimen can be as small as 2mm3 allowing detailed study of supposed short period geomag- netic episodes, like the Laschamp event reported to have occurred in

France, Canada, North Atlantic, New Zealand, Czechoslovakia, the

Northern Pacific, the Gulf of Mexico, Japan and Sweden. Thompson and

Berglund. (1976) discredited the event reported in Sweden by Mrner Lanser and Hospers (1971), Mmer and Lanser (1974), Noel and Tarling (1975), Noel (1975) as a result of climatic changes which produced sediments of very variable mechanical properties, particularly at times

of periglacial activity, which were poor recorders of the ambient mag- netic field. 6.

Detailed linu-iomagnetic studies can produce magnetic parameters like k or jrs from which one could obtain the following parameters of limnological interest:

Spatial and temporal variations in rates of accumulation and influx.

Quantifying accumulation and influx on a whole lake/whole drain- age basin basis.

Developing and extending tephro chronologies. ci) Gaining rapid insight into major climatic variations as expressed in changing erosion rates.

Details of sample correlation and combination for further analysis where bulk is needed (e.g. for 140 or for 137Cs in tropics and southern hemisphere.)

Identifying and characterising major influx events (e.g. post- burn erosions). Evaluating the within and between lake consistency of dating techniques. Estimating ancient sedimentation rates.

Estimating palaeolake level fluctuations.

Identifying water quality changes and primary productivity in the lake (Thompson, 1973; Thompson et al, 1975; Thompson, 1977; Winter and Wright, 1977; Wallis, 1977; Oldfield, personal communication).. 7.

[V

EXPERIMENTS WITH MkGI'ETIC CRYSTALS

2.1 Magnetic mineralogy.

2.2 Extraction procedure.

2.3 Debye-Scherrer X-ray diffractometry.

2.4 Cryomagne tic and thermomagnetic experiments.

2.5 MZissbauer spectroscopy.

2.6 Optical microscopy.

2.7 Discussion and conclusions. 8 .

2.1 Magnetic mineralogy.

The mineralogy of magnetic grains extracted from limnic, cave

sediments and soils has been studied, emphasis being given to the ex-

tracts from the Greek limnic sediments, which recorded the geomagnetic

fluctuations (Chapter 6), and which were used for redeposition experi-

ments (Chapter 4).

Identification of the magnetic minerals is based on optical microscopy, Debye-Scherrer X-ray diffractometry, cryomagnetic and

thermomagnetic experiments and Mössbauer spectroscopy. The study cf

the identity of the size and shape was performed with optical micros-

copy.

2.2 Extraction procedure.

Fig. 2.1 illustrates th9 magnetic separator, which is based on

the principle of the attraction of magnetic grains from a water sedi- ment mixture, passing through the high gradient of a magnetic field.

It consists of a commercially available hand magnet with 2kOe initial nominal field which was increased up to 3.5kOe by placing two soft

iron prismatic pieces between its poles, and a peristaltic pump with 25 mi/min rate of flow. The mixture is kept in suspension with a stirrer.

The inclined glass tube with a 8mm internal diameter is connected with

a plastic tubing creating a self-circulating system. The system is

completed with a vibrator, which disperses further the fluid. The sep-

arator works in two stages: a) it extracts magnetic grains continuously

for few hours every day; and b) when enough accumulation of magnetic

grains is observed, the plastic tubing is placed within clean water,

which eventually cleans the extract from the heaviest non-magnetic

minerals or organic compounds. The efficiency of the system is - '- S 9.

= (Jrsl - Jrs2) x 100. calculated as ijrs Jrsl Jrs has been found reduced by 50 and 80% in some cases, whereas the ks has been reduced by 31 and 46% respectively. It is known that k reflects the paramagnetic and diagenetic constituents together with the ferrimag- netic content, whereas the jrs reflects only the ferrimagnetic content.

Thus jrs serves as a better guide to efficiency than susceptibility.

Each sample consisted of up to 20g of dry sediment and the material extracted by this procedure constituted just tenth of one per cent up to 4% in some cases by dry weight, however, this does not mean that all of the extracted material is necessarily ferrimagnetic content.

The purity of the samples is 20-30%, due to contaminants of crystal- line nature like quartz, illite, plagioclase and montOorl om4Q, but probably of amorphous material as well. Assuming that all the magne- tic content of the bulk sediment of the Greek lakes contains magnetite, then its content is ranged between 0.0003 and 0.01% computed from the jre values (chapter 3).

2.3 Debye-Scherrer X-ray diffractometry. Plate 2.1 and 2.2 illustrate the found front and back patterns of the X-ray diffraction of powder magnetic extract from homogenized limnic sediments of Lake Volvi. It was found necessary to dry the extract in 50°C and ground it in an agate mortar in order that each powder specimen might achieve a uniform grain size for a non-orientated powder mount. The analysis was performed by means of the Debye-Scherrer method. The film was left, in each case, for one day's exposure. As

Plates 2.1 and 2.2 show the principal and stronger lines correspond in magnetite and haematite, which is a typical examnpie of the X-ray dif- fraction results for the rest of the extracts, shown in Table I. De bye -Scherrer X-ray diffractometry

Front reflections

0 12 d(A) hkt Mineral

11 1 1.4829 440 Magnetite s

03 333.511 Magnetite S ?

1.6927 116 Haematite v.f

1.7090 422 Magnetite v.f ?

1.8395 204 Haematite v.f

.0963 400 Magnetite f

2.5284 311 Magnetite v.s

27011 104 Haematite v.f

2.9627 220 Mcignetite S

.2173 040 Plagioclase v.f ?

a314.6 006 ILtite v.f 2

5.4822 ? vt

f = faint vi= very faint s= strong v.s= very strong

Plate 2.1 X-raydllffraction powder patterns of magnetic crystals extracted from the sediments of Lake Volvi. Debye -Scherrer X-ray diffractometry

Back reflections

7 d(A) hkt Mineral

5 1.2977 203 Ouurtz

.2635 v.f

12428 0.0.16 Mite v.f ? 3% 1.1206 542 Magnetite v.f

tO 914 553.731 Magnetite $

-1.0478 800 Magnetite f

0.98961 660.822 Magnetite v.f

0

f =faint v.f=very faint S =strong csvery strong

Plate 2.2 X-ray diffraction powder patterns of magnetic crystals extracted from the sediments of Lake Volvi. TABLE I General X-ray diffraction results

Lake Country !gnetite Haematite Qu.rtz Others

Trikhonis Greece coc x P, M, ? Begoritia Greece xxx x M, •,?

Volvi Greece X30C x x I, P, ? Geneva Switzerland xxx trace trace

Le Bourget France xxx trace x • M, trace Ch, ? Annecy France xxx x x M,? 1 Radunskie Poland, x x trace Cave Canet Spain occ x I, ? Petralona Greece cac x I, •? Ball's Cavern (Alpha) U.S.A., xxx xx x Ball's cavern (omega) U.S.A. xxx x x I,?

P - plagioclase; M -montmorillonite; Ch (ic*mosite; I - Illite.,

N. 10.

2.4 Cryomagnetic and thermomagnetic experiments.

Magnetite undergoes a crystallographic transformation from cubic

to orthoriovniCat 120°K. It also exhibits a minimum magnetocrystalline

- anisotropy at about 180 °K. Then pure magnetite is cooled through this temperature in zero magnetic field, it loses some of its remanence.

Similarly it loses some of any remanence acquired at low temperatures,

Ofl warming up through the transition temperatures. Experiments such as

this have been used to identify magnetite as a carrier of remanence.

The transition is suppressed by impurities and very fine grained mag-

netite. Fig. 2.2 illustrates two representative examples characteristic

of several cryomagnetic experiments performed with wet and dried sedi- ments both for the jn and jrs. All the wet sediments sampled from

several horizons in the three representative cores V8, B9, T2, showed a decrease in the horizontal intensity corresponding closely to Morin

transition for coarse haematite, both for jn and jrs, whichmade the

result highly suspicious because it was hardly probable to find haema-

tite in all cases • The horizontal intensity was measured with the

spinner magnetometer and the temperature was monitored with a thermo-

couple attached to the sample, which was rotating in a vertical fashion

within a d.ewar tank full of liquid. nitrogen. To verify or discredit

the supposed Morin transition, several cryomagnetic experiments were

performed. In all cases no Morin transition was found. (Papamarinopoulos and Readinan, 1978a). Pig. 2.2 illustrates the pseudo Morin transition

produced by ice crystals, which randomized. the directions of the mag -

netic crystals locked in the sediment. The jn cryomagnetic curves were

found to be noisy, because of the low sensitivity of the low temperature

magnetometer and most of them did not show the magnetic transition,

THERMOMAGNETIC EXPERIMENTS

MAGNETIC EXTRACT • LAKE VOLVI C ° Mr

a -

4, C 0, 0 E

0 100 200 300 400 500 600 700 8 Temperature 'C

C 0

0 U,

4, C 0, a

Temperature 'C

C 0 a U)

4,

C, U

I ______•

0 100 20) 300 400 500 600 7G0 600 -- Temperature C

Figure 2.3 Thermomagnetic curves of extracts, from sediments of - the Greek lakes. 11

whereas the jrs curves usually showed it for several horizons in all

three Greek linmic sediments. Fig. 2.3 illustrates three thermomag-

netic experiments performed with extracts from the sediments of the

three Greek lakes. The first (Volvi) and the second (Begoritis) were

performed in lOkOe with 20 0 C/min rate of heating and cooling, whereas

the third (Trikhonis) was performed in 4.5kOe with 10 OC/min rate of cooling and heating. The extracts were placed in a tiny quartz bucket

placed in the most sensitive place of a vertical torsion balance.

Each experiment was repeated twice to confirm the initial experimental

results.

2.5 M3ssbauer spectroscopy. Fig. 2.3 illustrates the Mössbauer spectra produced by Maniatis

and Simopoulos, (personal communication), with magnetic extracts from

the sediments of the three Greek lakes. The spectra were obtained at

room temperature and showed three patterns: (I) dominant magnetite in

all three cases; (II) haematite with small contribution, which was

recognizable in the case of the extracts from Lake Volvi and Begoritis;

(III) which probably corresponds to the type of minerals like mica,

M40rillonite, with very small contribution. The spectra of the

Begoritis extract is fairly complex and further work is required at

liquid helium temperature to interpret it fully. Mössbauer spectra

obtained from the sediments of Canet Cave (Spain) and Petralona Cave

(Greece) produced an entirely different picture. Magnetite is absent

in both cases with dominance of haematite and some contribution of

hydrous iron oxides like goethite or lepidocrocite and some iron win-

erals as well (Maniatis and Simopoulos, personal communication). • • • — • ' — L I I — I U

LIMNIC MAGNETIC EXTRACTS

300K

I I I I I I _II II II II I #\ • : •: • • 3 . . . S • 99,0 . ..• •, 0 . S •,S •. . ••• S . • ,,:. ••S S S S S • S.. •. . •• 98.0 • .•% • . . S • • S

Z gj 5 • 0 -- $—•1 - (1) - (I) a I I I I ii 100.0 ,iwj1 LO M • _ : — •. . \. %4 5 S • • . ¼. •' 0 " 990.. 5 • b.? •• • lb • I— 98.0 w .5 > I—I I— 97.0 - • - S W [I I I I II

970

• •IIItIItI'i, •;•• I,,i 111th -10 -8 -6 -4 -2 0 2 4 6 8 10

• • •-. • VELOCITY (MM/SEC)

Figure 2.4 Mössbauer spectra of extracts, from sediments of the Greek lakes. 12.

2.6 Optical rnicroscoPY(YhC'1lov\).

Magnetic extracts from lirnnic and cave sediments in which palaeo- magnetic studies were performed together with extracts from archaeo- logical soils in which magnetometer and magnetic susceptibility surveys were carried out, were studied in detail with optical microscopy, with the purpose of identifying the carriers of the acquisition of the rem- anence locked in the limnic and cave sediments and the source of the magnetic anomalies observed at the sites of archaeological interest.

In all presented illustrations the horizontal field of view is 190um, except for Plate 2.4 which is 50pm. Plates 2.3, 2.4 illustrate a rep- resentative example of magnetic extracts from the sediments of Lake

Volvi. The field of view is dominated by angular fresh and fine grained fragments of pink magnetite (b, c, d) with sizes ranging between less than 1pm and a few microns. In the E-S quarter of the field of view a

12.4pjn angular bright haematite grain with red marginal reflections is located. Plate 2.4 illustrates a 10pm angular oxidized magnetite cry- stal with heavy oxidation towards haematite (a). Plates 2.5, 2.6 illus- trate representative magnetic extracts from the sediments of Lake

Begoritis. Plate 2.5 exhibits a 33pm large angular, bright haematite grain with blood red marginal reflections (a), a 33pm pink, skeletal magnetite grain and several other angular fresh magnetite grains (c, d., e), with sizes ranging between less than 1pm up to a few microns.

Plate 2.6 exhibits a 31pm large composite prite rhomboid (an aggregate of minute sulphite spheres). On the left and above this a 9.6pm haema- tite grain (b) is 'located. On the left and below this a cluster of an-

gular fragments of fresh pink magnetite occur with sizes ranging between

less than 1pm and a few microns. Plate 2.7 illustrates magnetic extracts

from the sediments of Lake Trikhonis. In the centre of the field of Opticcil microscopy of mcigneflc extrctcts

Plate 2.3 (a) Oxidized angular magnetite towards haematite surrounded by fresh magnetite fragments. Lake Volvi (Greece). co

Length of horizontal field of view 190 IPM

Plate 2.4 ça) Vhole harrnatite grains with red marg:iai iliLut1on; (b, c, d) Clusters of fresh angular fignents of magnetite dominating the field of view. Lake Volvi (Greece). Upticat microscopy of magnetic extracts

-i -h cf horizontal field of view 190 pm

Plate 2.5 (a) i1giar laro raii of briit haematite oith blooJ red marginal reflections; (b) Skeletal large magnetite grain; (c) Diamond shaped magnetite fragments. Lake Begoritis (Greece).

Plate 2.6 (a) Composite pyrite rhomboid. (aggregate of minute sulphite spheres); (b) Oxidized magnetite fragments towards haematite; (c) Cluster of angular magnetite Optical microscopy of magnetic extracts Length of horizontal field of view 190 pm

Plate 2.7 (a) Large diamond shaped magnetite crystal; (b) Composite pyrite rhomboid; (c, d) haematite grains with tiny magnetite fragments stuck on them; (e, r) Clusters of fresh angular magnetite. Lake Trikhonis (Greece).

Plate 2.8 (a) Diamond shaped broken magnetite crystal; (b, c) Clusters of fine grains of bright, haematite which dominate the field of view; (ci, e) Hydrous iron oxides probably geothite or lepidocrocito with grey-red internal 13. view a 321.ini large fractured diamond shaped magnetite crystal (a) occurs.

On the left a 19pm composite pyrite rhomboid (b) is located. On the left two 0.6, 0 .8pm angular haematite grains (c) occur. On the right and above this a 1 .2pm angular haematite grain (a) is located. The haematite grains appear with deep brown-red internal reflections hav- ing tiny fragments of angular pink magnetite stuck on them. In the

S-W quarter of the field of view clusters of angular fresh pink magne- tite grains (e, f) occur with sizes between less than 1pm and several microns. Plate 2.8 exhibits magnetic extract from a terra rosa sedi- ment from Canet Cave (Spain). A 21pm diamond shaped broken pink mag- netite crystal (a) is located. The field of view is dominated by an- gular bright haematite fragments (b, c) with sizes ranging between less than 1pm and several microns. The lower reflectivity phases with grey- red internal reflections are most probably hydrous iron oxides (goe- thite or lepidocrocite) with sizes approximately 15pm (a, e), (Gill, personal communication). Plates 2.9, 2.10 illustrate magnetic extracts from archaeological soil in Balfargh (Scotland.). Plate 2.9 exhibits a

large 44pm angular titanomagnetite grain crossed by a distinct pink, unaltered ilmenite lamella visible along its major axis (a) is located.

On the left and above this a 29-pm angular titanomagnetite with colour variations (b) occurs. In the W-S quarter of the field of view several

angular titanomagnetites (c) occur with sizes ranging between few and

several microns. Plate 2.10 exhibits a 36p.m angular titanomagnetite

heterogeneously and partially oxidized. A pink lamella of unaltered

ilmenite crosses the grain along its major axis, whereas the N-E quar-

ter of the grain has been replaced by ma&aemite, which appears with white colourations and poor crystalline appearance (a). On the left

and below this a cluster of angular titanomagnetites with colour Lengthof icrt field of ev 190 pm

Plate 2.9 (a) Large titanomagnetite crystal crosoect by a distinct unaltered ilxnenite lamella along its major axis; (b, c) TitanomagnetiteS with colour variations. Glacial cil, aifar (Scotland).

Plate 2.10 (a) Large titanomagnetite crossed by a distinct unaltered ilxnenite lamella along its major axis, partially and heterogeneously oxidized towards a poorly crystalline shaped maiemite, which is recognised by the replacement of the N-E quarter of the host mineral; (b) Broken angular coarse fragments of titanomagnetite. Glacial soil, • 14. variations (b) occur, with sizes ranging between few microns and

several microns. A.

2.7 Discussion and conclusions.

The reversed Jrs studies of the bulk sediment revealed the pre- sence of fine grained magnetite (chapter 3). The application of the

Lowrie-Puller test with pilot samples, revealed that the magnetite is

SD or PSD in character. Debye-Scherrer X-ray diffractometry illustra- ted that the principal and stronger lines correspond to magnetite and haematite with some contaminants like quartz, c. plagioclase, illite ,whri tonite. Cryomagnetic experiments in dry samples illus - trated magnetite transition when a jrs was given to the samples.

Th ermomagnetic experiments performed in air with extracts showed that the dominant magnetite was oxidized in 350-450°C probably into a cation deficient spinel which was inverted. .into haematite, remaining unaltered

in cooling. Mössbauer spectroscopy showed clearly the presence of mag- netite, haematite and the dominance of the first upon the second.. The

spectrum produced from the extract from the sediments of Lake Trikhon!s

showed no evidence of haematite probably because its content was below

the detection limit of the technique, whereas the detailed study of the

optical microscopy revealed dominant fine grained magnetite, which was

either fresh or oxidized towards haematite. Coarse grains of magnetite

and haematite of crystal or skeletal shape were observed very rarely.

The range of the size which was less than 1.un up to few microns suppor-

ted the results of the Lowrie-Puller test about the SD or PSD character.

of it. The study of the magnetic extracts from the sediments of Caves

Canet and Petra lona (Papamarinopoulos and Readman, 1978b) revealed the

presence of fine and coarse haematite in abundance, whereas magnetite 15.

together with hydrous iron oxides like goethite or lepidocrocite were found very rarely. This does not rule out the possibility that mag- netite could be responsible for the measured high valued magnetic para- meters of naturally and artificially deposited sediments in the labor- atory. Further detailed work should be done to answer the question of the nature of the magnetic carriers responsible for the remanence in cave deposits. The study of the extracts from the glacial soils, which had produced unusual negative anomalies (-200i') showed that the dom-

inant minerals were fine and coarse titanomagnetite, either unaltered

or heterogeneously and partially oxidized towards ilmenite and maghemite. 16.

THE MkGNETIC PROPERTIES OF THE FRESH WATER LIMNIC DEPOSITS

3.1 The Greek lakes.

3-1-1 Lake Volvi. 3.1 .2 Lake Begoritis. 3.1.3 Lake Trikhonis. 3.2 Long core description and measurements. 3.3 Single sample measurements jn,k and Q-ratio. 3.4 Remanent hysteresis. 3.5 Significance of jar in lixnnic deposits. 3.6 Low temperature treatment. 3.7 Conclusions. 17.

3.1 - The Greek Lakes.

All three Greek lakes shown in Fig. 3.1 are of break-tectonic origin.

3.1.1 Lake Volvi.

The Promygdonian basin is located about 10km NE of Thessaloniki in Chalkidiki peninsula. It is the ancestor of the Mygdonian valley (Psilovikos, 19771 which is the deepest part of the present elongated basin, situated between Kamela mountain and Regina village. A system of ridges, low hills and terraces divide the Mygdonian valley into two smaller valleys named Lagatha and Volvi. Exposures in the

Proinygdonian basin reveal torrential, fluvial and limnic sediments including conglomerates, sandstones and silty sands of Miocene age,

(Demopoulos, 1972). Red beds were deposited during the lower Pleisto- cene (Melentis and Koupos, 1977), after the discharge of the lake into the sea.due to a general stadial regression of the area (Psilovikos,

1977). The whole Promygdonian system was deposited into the Promygdon- ian basii between the Miocene and lower Pleistocene (Psilovikos, 1977) when the basin joined Strymonikos gulf by means of two rivers flowing through the old valleys of Redina and Kakia Skala,. The formation of

Mygdonia valley took place, shown in Fig. 3.2 due to the activation of the existing systems of faults in the area (Oswald, 1938; Georgalas-

Galanopo-ulos, 1953; Kochel et al, 1971; Psilovikos, 1977), which occur- red several times during the lower Pleistocene. The joining part bet- ween the new valley of Mygdonia and Strymonikos underwent .a transient interruption during which water was concentrated in the valley and thus the Mygdonian lake came into existence (Psilovikos, 1977). This process was closely related to typical climatic conditions of the lower Pleisto- cene in particular of the first interglacial period (GUnz-Mindel) about • THE GREEK LAKES.

2

L.BO I vo /Iv L.PREPA SALONI

Aegean . . Sea Sea L.TRIK ONIS 3

AThNS

co!e1:5250000 . 'S RTA 9 50 100 150 20C Km Conic Projection • 35•

CRETE

18 2i' 22 24 3

GREECE. . S

\ -

2300 23.430** 24'00 N 400 4100 KILKIS N —a. LAHANAS F I Et IF • - - -._- - -. ' •\.'14170N LAGATHA ____ \ ° V0LVISM0UN1"I', 2 \\STRYMONIKOS THESSA\AGA1

jRIO MARA;HOUSA r.O.30 4039' HOLOMON (1.165m) . \ "IiiiI'\'

GULF OF __ HERMAIKOS X jAGHIO OROS GULF____ 2300 2330' 2400 NORTHEASTERN GREECE ---- Discharge hydrographic Line Mygdonian 0 10 20 30 km

I IIV IZP'.IJUIV.I I VI. (after A. Psitovikos)

Figure 3.2 The geomorphology of the area around lake Volvi. Megcili Volvi

er Loutra Volvis

Lake Vol vi o 2 3 i 5, km The bathymetry Depths (m) After (A.PsiLovikos)

Lake Volvi. Coring Stations

2330' (NT

40045

V32 V4.5 OV2 va

.15.6m, V :20.2m. V 57 :19.5m v 12 :15.3m, V 3 45 V :20.2m. 18.

500,000 years ago. The 500km2 Itygdonian basin followed five distinct phases of development due to activation of faults and the consequent drainage of water, which eventually created the lakes Lagatha and Volvi.

Lake Volvi, shown in Fig. 3.3, occupies the eastern part of the old.

Mygdonian lake. The sediments consist of detritus eroded by rain, which originates from the mountains around the lake. The lake has two outlets which have been artificially enlarged. At its western part it communicates with lake Lagatha through a narrow furrow and at the eas- tern part Rehios river transfers the water into Strymonikos Gulf through the Redina valley. The rate of deposition as an average is 2-3mm/yr,

(Psilovikos, 1977). The geological exposures around the lake reveal basic eruptives and intrusives (Fels, 1950) and metamorphic rocks like gneis$with marble horizons, graphite from Kerdyllia mountains (Demetri- adis, 1974), amphibolites which gave 4.4% in magnetic content (Psilovikos, personal communication).

3.1.2 Lake Begoritis.

The lake shown in Fig. 3.4 has a typical diluvial karst-origin and it is the deepest remaining part of the large depression of Ptolemais (Fels, 1954), vdiich is verified by the numerous large karat-springs occurring in various parts a few kilometres away from the lake, shown in..Fig. 3.5. The sediments reach the lake after rain falls from both torrents and karst-tunnels. The natural outlet of the lake is the sub- terranean river Vodas. Basic eruptives, palaeosoils and limestones are the geological exposures which contribute in the detritus of the sedi- ments. YUGOSLAVIA .(' PAIKON

• c 0 ps ve

EDESSA GIANNITSA VoCa I LAKE-- LL (• MIKRI RESP 'p Loud LAKELAI BEGORITISBEGC Ml 1/.NASA %KRSIt LAKE //olm, 0 • i KASTORIA L 'b STAVRO KHIMADflIS •'% VERROIA , 0

I1 OLEMAIS'?, 04'

KOZANI KATERINI / • —GULF= • //';'-• ______ETHERMA: • /1/4 ______GREVENA .OLYMPUS::

—

NORTHWESTERN GREECE : 0 10 20 30km -p I I • Arnissa t 11 •\ •-k I , I! I•r i'.''''• \ Myti 65 , )

57 Aghios 1 ' Panteteimonof 46

,!(

A

17 Begorci Mciniaki

0 - 0

Lake Begoritis 1 2 3 65. 1-- !-1----1-4 The bathymetry: Depths (m) km

Lake Begoritis Coring Stations 2145 N

6crL5' - (.1IP' B6-9

0 5Km t_____l___I I I I • B6.9 30.8m

Figure 3.5 Isobaths and coring stations in Lake Begoritis. 19.

3.1.3 Lake Trikhonis.

Lake Trikhonis is shown in Fig. 3.6. It is located..within a large depression, which looks like a gigantic moat. It contains the sub-

basins of Agrinio, Lesini.o and the one into which the river Acheloos

flows. It also contains numerous terraces, consisting of deposits

which are remains of a large ancient lake that covered the entire dep-

ression during the Pliocene (Fels, 1952 Leontaris, 1967). The ancient lake was supplied by Acheloos river and rainfalls. Its water level

started falling down and the lake was restricted in area, due to eta-

-- dial overflows and accidental discharge, due to the activation of num-

erous faults existing in the area (Galanopoulos, 1963, 1965; Leontaris, 1967). At first lake Amvrakia became independent of the big lake, because it was on a higher level than the other two lakes, which were split in two stages (Leontaris, 1967). In the course of the first stage Lysirnachia and Trikhonis were separated by deposition of alluvia.

During the second stage lakes Lysimachia and Ozeros were split by means - of'the same mechanism (Leontaris, 1967). The sediments reach the lake mainly from the North eroding palaeolimxiic deposits, pebbles, sandstones

and' geological exposures with a large petrological spectrum. The outlet

of the lake, shown in Fig. 3.7, is a natural furrow westwards of it flowing into lake Lysiinachia.

3.2 ' Long core descriptions and measurements. Fig. 3.8, 3.9 and: 3.10 illustrate the stratigTaphy of three cores representative of the 25 cores taken from the Greek lakes. Core V8 from lake Volvi is divided into five major units with

different distinct colouration. The'first from the top is dark olive

grey, the second light olive grey, the third dark greenish grey, the 210 21°30'

AMPHILOHIA -

3Q ILOzeros • 36' 3 36'

I

WE S 0 0010

PATRAIKos GULF 210 21°30' Western Greece —"—••- The studied area (after S.Leontarjs)

Figure 3.6 The geomorphology of Lake Trikhoni Pcintanosso

Petrohorio

• • Poppadate

Western Greece Depths(m)

1:50,000 •

• Lake Trikhonis

• Coring Stations

216 30 1

71

'

itt I I I

T 123 :50.5m, T 4 : 49.1m. T 55 :31.1mT7 :40.6rn

Figure 3.7 Isobaths and coring station in Lake Trikhonis. LckeVo[vi-CoreV-Greece $J Q DESCRIPTION I The core is divided in five major units with / Dark olive 1c gray different distinct 844±50 _1 colouration.

Tp of sediments Light olive • (Yjy-e gray y-,uO • Colour Thickness(cm) Dark gray Deep brownish (3.2) - 3 'ff (3.2) greenish

16c ' ' _I_• Deep brownish (3.5) ....j1743±55 ____I______3.3 1 1/ •3.2 111111; - I Light olive •ilI gray •

liii]]] • Deep brownish (3.2) Deep greenish (3.3) - • --._- • 5 :—:—: Yellowish dark gray • :-:-:

Pollen 2- • •

6 3000 yrs. B.P • LAKE BEGORITIS CORE B9 -REDEPOSITION IN 040e

NRM PORM NRM/PDRM •k(Nat) k(Redep)o (110) (pG/Oe) 0 20 40 60 80 100 120 0 20 LC) 6070 01 23 1. 56 7891011 0 20 1.0 60 8090

YearsB.P. Magnetic Corr. ages UC 130D 2400

E 2600 U

4050 0. Go 3900

£ 6200 -__ 5300

5I

Pollen 1g 6 1 1' 1 LAKE TRIKHONIS CORE Ti - REDEPOSITION IN 01. Oe

NRM PDRM NRM/PDRM .k(Ncit) k(Redep)o (110) (110 ) (IJG/Oe) 0 10 20 30 40 50 01020300123 1. 5 5 678910111213 Years BP.

ages

14C 1300 2400

E U

3 ASH 0. f C, 2600

5300

C-14 Pollen 6600-5000

Figure 5.9 NRIVI, PDRM, ITR1V1/PDBM and the ks of the naturally and artificially deposited samples are plotted side by side against the depths of cores B9 and Ti, of Lakes Begoritis and Trikhonis, respectively.

-I

5 .J Luke Begoritis-Core B 8 -Greece 0 0E DESCRIPTION

- General colour of the core (Light olive gray) peofsiments L 23±60 - I Colour Thickness (cmj 1 Deep olive greenish (6.0) \\LDeep olive greenish (6.8) \ T 14C \ \LDeep olive greenish (4.8) 3649±60 z:;: 'L4Lg 2mm deep greenish - 2 finely Laminated zone L LjjDeep olive greenish (4.0) L12Deep olive —3 14c : • 51.10±70 IL L14Oeep olive greenish (6.81

• \\\\L15DeeP olive greenish (4.0) \\\\\L16DeeP olive greenish (4.0) - 4 \\\\ L17L302mm. deep greenish ,- • • • \\\\ finely Laminated zone Pollen-- "L Brownish r a 6000-7000 31 coarse L32DeeP olive greenish (5.2)

- • .• 5 • grcined'L33SheLLs •. (8.0)

• • • 640eep dark greenish (24.0) 6

ithostrat1aPhY of Le BeritiS, core B9. Figure 3.9 Te

Lake Trikhonis -Core T2- Greece , -6 co• -0 cLEftjj 2 I . DESCRIPTION ° >' i • General colour of core : (Light olive gray) Tuñeof sediments i 14c :.'::::;• -' '- - Mai-v rnud * - Colour Thckness(cm)

Deep olive greenish (80) - 2 Tephra horizon (18-0) (BrownIsh gray (4.8)

14C F / L3Brownish gray (3.6) - 3 5089± 75 ••:; II L4 Brownish gray (3.2)

• ••f• L5Brownish gray •. (2.4)

L6 Brownish gray (6.0)

1c - 6 15769±90 lPoL1en6500

- 'Figure 3.10 ThQ hostratigraphy of Lake Trikhonis, core T2. 20. fourth lit olive grey and the fifth at the bottom gellowish dark grey.

The sediments are fine-.grained. X-ray diffraction on the samples from depths 96 and 422cm in core V6 showed calcite, siderite, quartz, plagio- clase, illite, chamosite, smec;ite (Readman et al, 1976). Seven deep brownish layers about 3.1 to 3.5cm thick occur at 290, 310 9 340 9 3559

358 9 365, 470cm and one deep greenish layer with 3.3cm thickness occurs at 472cm. Six of them are located in the third unit and the other two near the boundary between the fourth and the fifth unit. Core B8 from lake Begoritis is mainly light olive grey interrupted by 34 layers of different thickness and colour. The sediments are fine- grained. except in the bottom part of the core between layers .31 and 34 at 310 and 370cm respectively. Within this zone a 8cm thick layer con- tains shells. Two zones have distinct characteristics from the rest of the core. The first zone, which is defined between layers 14 and 19 at 10 and 100cm respectively, contains five laminations 2mm thick.

Similarly the second zone defined between layers 17 and .30 at 250 and 285cm correspondingly contains thirteen laminations 2mm thick pro- bably corresponding to cyclic seasonal episodes in the water supply of the lake. The sediments are mainly dolomite, calcite, siderite, quartz, illite, talc, chlorite (MUller, personal communication). Core T2 from lake Trikhonis consists of light olive grey fine- grained. sediments. X-ray diffraction on a sample from depth 145cm in core T3 showed calcite, quartz, plagioclase, illite, interstratified clays (Read.man et al, 1976). The homogeneous clays are interrupted by five deep olive greenish layers with thickness 4.8, 3.6, 3.2, 2.4, 6.0cm at 510, 520, 540, '542.4 and 580cm respectively. J, k and Q-ratio as Pig. 3.16 illustrates at 280cm exhibit,a peak corresponding to a layer, which was visually observed only when the core was left to dry. 21.

This layer is associated with a tephra layer, (Headman et al, 1976) however, MUller has examined thoroughly samples taken from this layer in core T2 and found no direct evidence of glass material coming either from the volcano of Santorini in the Aegean sea or from Italian volcanoes. He does not entirely exclude the possibility of the tephra, because it is possible that an unstable glass component might have been di,enetically altered to crystalline material like silicates (Muller, personal communication).

In Fig. 3.11, 3.12 and 3.13 jnhorizontal intensityris plotted against the depth for all the cores taken from lakes Volvi, Begoritis and Trikhonzis. These figures illustrate the remarkable correlation existing from one part of a given lake to the other. Similar correla- tions have been obtained with long core susceptibility measurements.

To verify and get a more detailed picture of the limnomagnetic para- meters, the cores were cut into sections 150cm long and. then sliced into two halves. One half was preserved for radiocarbon, pollen dat- ing and sedimentological analyses and the other half for palaeomagne- tic sampling. 2.3cm cube-shaped plastic sample holders were pushed centrally into the soft but very firm sediment. Plate 3.1 illustrates

the sampling method. The top of the sample holders had been drilled

to allow easy escape of the trapped air as the sample holders were pressed into the sediment. The holes were later covered with lasso-

tape to avoid partial drying or oxidation. When the sample holders were filled up, they were cleaned and measured with the Digico magnet-

ometers. The declination and inclination patterns are presented in

detail in Chapter 6. Plate 3.1 Sub-sampling of specimens from a sliced core of Lake Trikhonis. Plastic 2.3 cm cube-shaped sample holders are pressed serially into the soft sediment. LAKE VOLVI GREECE NRM horizontal Intensity (piG)

CORE N. (:3) 50 •.d;• 0 . a • -' . 0 30 0 30 0 30 : •.'. . 0 300 p----sO,,, •—g 0. b• • ' •: . 0a II

0• t1, •,00 0•

1

2. 2 2 / 2 '? 2 . • • 2 , 2-.

'.. . •%••' • 3 • . let 3 <.•, 3 •.. '..• 60 • • ... • 0 .. . ••. •,•'• .1 :.' •.

S 9.

•,•• 0 0 . •• . . • • . I . • . 1 • • . H 0 / 000 •• • 5 •,••0 • 000• t ••0 t •0 ..$ 0 7 5'. S 5 .. ) s? S 5 / .•. •' . •:. • :'-. 00:0::. . - 6 .05 .. .:.. •1 :5',:.'. 6.6 • 6 00 ..•. • 0 ,• -. 0 •• 0 6 0 . . •. . .

Figure 3.11 Long core measurements of NRM horizontal intensity and their correlation. . ' • 0' 0 from Lake Volvi

LAKE BEGORITIS- GREECE NRM horizontal intensity (pG)

90 . . I I-I 90 • CORE No. 0 I I I I I 0 o 90 •. . 0 .LIIIIIII 0 iiIIIII . 0 90. .. 0 11111I111 1 • 1. 1 . •.• •

: \. : .5 •• . 3 $ . . . • . . S 4 •z • . . • ......

I • I S • '5 . • as . . C 5 . •. 5 % - .

S • S. t. 5 :•. •1 5 • s.• • f . • . 5 S..... 5t 6. • 6.

Figure 3,12 Long core measurements of NRM horizontal intensity from Lake Begoritis and their correlations.

LAKE TRIKHONIS - GREECE : • • • . : NRM horizontal intensity (p °G) CORE No • . • . •

0 30 0 30g. • o ______30 • . 0. ' ' 0 I.. I I • . 0 • 30 • • . p .) ( • 0 40 0. Or ii. . is .' •s • ii 5 is 5 . • • I •. • • • i) "66 • . $ •. • I • ••:. 1 .5 S . • t• • • ,$• : •: • 2 , - ' ) .• . • . 1 • 2\ • 2• 2 66 t •• • •• • • • .• . .• c.3'' •••.• 31. . • . • 3. . . . • .'. .

: : : :•

• 6 : 5) • • • 5. 9. .6 •'

• • Figure 3.13 Long core measurements of NRM horizontal intensity from Lake Trikhonis and their correlations. • •

22.

3.3 Single sample measurements jn,kand Q-ratio. Jn is the initial measured remanence of a rock or sediment with-

out reference to its mode of origin. Jn is determined by the concen-

tration, composition and physical state of the contained magnetic min-

erals as well as by the geomagnetic field. If this is true, k, which

is almost solely a function of the magnetic mineralogy, should vary

directly with jn. Figs. 3.14, 3.15 and 3.16 illustrate the logs of k - .. and Q-ratio plotted in parallel for cores V8, B9 and T2. As it is shown, the variation in in is matched by a similar variation, however,

- there are also-differences indicating that their relation cannot be

exactly linear. The ratio of in to induced magnetization in .10W field

is called the modified Koenigsberger ratio (Q = jn/k). This ratio

varies from 1 to 5 in these cores as Figs. 3.14, 3.15 and 3.16 illus- trate. It has been suggested that the Q-ratio reflected the changes

of the intensity of the geomagnetic field (Harrison and moyaju1(i,

1966).

3.4 The stability of in. Of more importance from a palaeomagnetic point of view, is not

the absolute intensity of magnetization, but rather the ability of in

to resist change. Fields and laboratory tests are commonly employed

to obtain some indication of the stability of a rock's i• Field tests

(Graham, 1949; Irving, 1964) are never applicable to deep lakes, pri- marily because of the inherently limited lateral sampling of a sedi-

ment horizon at a site and the general restriction of a single rock

type. Johnson et al (1948) applied the test of the coercivity of jn

by measuring the reversed field required to produce a irs equal and

opposite to in• The values that were obtained (2-40 Ce) indicated, that LAKE VOLVI — GREECE

• • • CORE V8

• • WRM Intensity Susceptibility • Q - Ratio PG pG/Oe Oe 30 0 4 • 0 50 0 0 - .

.5 • S S 5. . • S . . 14C ' 844t50 F, I b . • yrS.B.R

• 5 . ( . S.' • - ,. I S'S is 2. 3k .4'. . 4 ?tS•q 1.eS 1.'. • 5* I' . E •'s.'. • - 3 S".'s • /

0.. 0-) %. • e ' . •. • - • 4 1743! 55 . .1 / yrs.B.P. ' 1 1. so .' .• I' • F'. S . •• - . •• D •. see

1,0 • - • • - •"• Pollen 2-3000 . 6 yrs.B.R

Single sample measurements of NBM intensity, Figure 3.14 susceptibility and Q-ratio of core V8, of Lake Volvi.

LAKE BEGORITIS - GREECE CORE 7

NRM Intensity Susceptibility 0 - Ratio PG pG/Oe Oe 0 1600 : 90 0 5 0 -.--.--. ' ' 1 • g •

S .L14C 7 j 2344t60

• 0 yrs.aP • 1 •..,"

Li c - IS? 0 : j 364 8t60 E2 yrs.aP 1..'•'

I S.,, CL .' ' •/ C) 3 ". _5410 t70 5.., .j yrs. BP. • 6 •L 4 46 • 4 • .':-S. • s$ 3 I' •..v •.. ,S• • S. S S. lk Pollen .P, • 6000-7000 yrs.B.P. • - 5

Figure 3.15 Single sample measurements of NRM intensity, susceptibility and Q-ratio of core B7, of Lake Begoritis.

• LAKE TRIKHONIS — GREECE CORE T2

• NRM Intensity Susceptibility 0- Ratio pG pG/Oe Oe 0 50 0 20 0 • 5 -0 , , , •_____ - -. • . • • • • •.:_ • • • • S. • S... ta•. • • • • •.

j •,s$ 228485 • 51 S o yrs.aF • ..!,

'S c •••. 5•S• •6 - • .4 .' - •- 5• • S. • S •• S •

• •S • • . - #• • • . •. • E • . • • .'S :. I - &• • a, _- .•, • IC •I• S • 'a. 14C 508975 .• • *CQ yrs.RP •;_ •• •: . • ' ••, - .5•':.. •. S C) • •' . .. .1 41. •C' . .s:. I •1 • S j. •' • • • •S. . ol •g • p • ,lf • •,•• S • as • '.5 .I. •:. •1. so 4 • S. 5 - • - '.- .• • .i J. • • 46 14C 4C io - 57G9190 5 • 6 ' • I±Pro—I 1 5 0 0 0 - 6 6 00 • • • - yrs.aP • -•

• Figure 3.16 Single sample measurements of NRM intensity, • : susceptibility and Q-ratio of core T2, of Lake Trikhonis. 23.

in of these sediments could not be readily altered by magnetic fields or the magnitude of the geomagnetic field (<10 Oe). However, the cc- ercivity of jn gives a general guide to stability, since low values do not necessarily reflect that stable components are absent. This is because jn is being compared to magnetic components of low coerci- vity that probably do not contribute to it. Better understanding of the stability of jn can be obtained through either AF or thermal demag- netization in stepwise increasing AF or temperature. The main advan- tage of these techniques is that low coercivity magnetizations can be easily removed. The jn of the limnic deposits can be classified as a) stable; b) unstable; and c) multi component. Normalized AF demag- netization curves of selected samples along cores. 118., B9 and T2 are presented in Fig. 3.17. The samples from lake Volvi show IVFs in the range between 200 and 350 Oe, whereas lake Begoritis' MDFs fall in the range between 200 and 400 Oe and those from lake Trikhonis, between

300 and 500 Oe. The results of individual samples are presented in

Fig. 3.18, for lake Volvi, Fig. 3.19 (a, b) for lake Begoritis, and in

Fig. 3.20 for lake Trikhonis. Samples B9 - 1, 5 taken from the top of core B9 of lake Begoritis with initial jn 14.25 and 14.16pG show not smooth demagnetization curves and their directions are not well grouped.

This is explained by the removal of very soft iv components during AFC.

Most of the samples from all three lakes show smooth demagnetization curves and the directions of remanence appear to be well grouped at

least up to 300 Oe and often up to 500 Oe. .F greater than about 500 Oe

could not be used for magnetic cleaning of these specimens due to increa-

sing problems with anhysteretic remanence induced to the specimens.

The stability of jn does not appear to be simply related to the gross

lithology of the sediment nor to the initial jo, nor to the depth. Core V8 N.RM Ot \'A.F.CJ Demagnetizations \0\M.D.E 2OOOe.3OOe)

100 200. 300 400

Lake Baoritis to, Core B9 N.RIt (AFC) DQrnagneElzotions

L OA

0 100 200 300 400 500

Peak Field t Oe 1.2 Lake trikhonis L 101 Core T2 N.RM. 0.8 (A.F.C.)Demagnetizot ions •

J'. 0.6 500 Oe)

OA

0 100 200 300 400 500 600 Peak Field ( Oe )

Figure 3.17 Normalized NRM demagnetization curves of pilot samples • from Lake Volvi, Begoritis and Trikhonis. 08 '\ (pt : \ 70.5cm 06 , JIJo Oi :- i.:1G.521J9' ' • .. : 0 02 MJT:200Oq • tIRM • I I .' W *00 200 300 £00 Peak Field lOel •

L\143.9crn CASS JDO 1.10 . • 'H 02 IAEF= 320 Oct \4J E • : *00 200 300 £03 Peck Fsetd toe)

as 39cm 7NRM 0.4 Mr 7 07 1SQe

at_5...... ).. W E 100 200 300 £00 • !cakFietdt0e)' .

V -12 L 8 : Depth 3386cm ___

':: • , • L _-1_I_ C--V) -1-1-4-1 I_i E 100200330403 • Peak Field tOe) S

•• N •v8_1Lo • 09 Depth )L1.Scrn ól, \ J.:1 6.63 iG ' -

"° : N..,

W _I_1111111 tijilSi_. E 100 200 300 403 500 Peak Field tOe) 0• to N

08 \ O;th27.9cm

06- 'N •' •' J,Jo ' -_ J4RM

02 0Oo1 '

W _ -;--. _ •_i_ E • ' E100 200 •• • . • Peak Fje(d(Oe) •. . . • • N

as \\OePth49SOcm • 06 0 • • ' NRM •' • ••

E • 100 200 Peak Field tOp) •. • .. :

Figure 3.18 Normalized NRM demagnetization curves together with stereographic projection of their directions of individual ii 1 n+ nmrt1 1r fr.nm T.1-o 1Trl',4

V : .V• V De;th2O.5cm 08 J.;14.26 . . V •V V PG 0.6 •. .. .• . V • •. . . JIJo - - - V V .V -

- 2 190 0o • : . . ._____ -• w ,,,,, E • . , too 200 300 £00 500 V .. • . . V . Peak Field tOe)

V . V : . 09-5 V •. -.- V N . Depth300cm

JIJO ..

0. Jq= 14J6 VG TI too 230 300 £00 500 . V V V Peak FleW tOe)

:V V •• .- • V ii 89-30 Depth 97.2cm

• V •V V . ...

OL2fl.flpr, ,. . o2 mu--300 Do I ____ 330 £03 500 • tOO 200 V V V V Peak Fictd(Oe)

• 8-70 • . . V • V - V . .- Depth 202.1cm N

VV O3 L\

JOLS

':: 3:3 i, •. 7. V 'NR4 0.2 MJF2C0Od V V

V _ •_••_ V • . . V 100 200 300 £00 500 . Ptak Field (Oct V

12 8g90 V • . . V Depth 250.5cm -.. 1.0

GLe

JIJ* 06 M_-NIRM

Vt,itiII-I-i-IIIII

100 200 300 £00 500 V V V . • Peak Field tOe) V •• V V

V Depth 298.7cm N 1.0

CLS

42 MW=340 00 E , ,i,...... W •ttsJs-4_ttItI)II 100 200 3•30 £00 Soo.

Peak Fs,ld(Oe) V V

V V V •• Figure 3.19a Normalized NRM demagnetization curves together with

V •. V stereographic projections of their directions of individual pilot samples taken from Lake Begoritis, core B9.

U D9110 • - Depth 3*8.6cm - •- N to

CLS JIJ* 06

I • 111111* 100 20 300 403 500

Peak FieldiOc) U 89-40 Depth 370.6cm N

J130 0S

NRM 0.2 KV-F=3CO

,:., • E . , : ,• I I I I I I. ) . j 103 230 300 403 500 Peak F.ctd tOe)

09 -170 De pt h((.6crn 02

06 7 NRR .JIJo / - . OL i.:f03.4 FG 2l.tQF=37313e1 1 :1

S I !R IIIIIII..tI*III'II IC 100.2'3 301 £30 503 Peck F,etdlOe) 12 69.233 Depth S.5cm N tol

08

0.6 0.4

W. im 100 200 300 03 500

• Peak Field lOel . .

• *2 89-235 Depth 5'36.Lcin • P4 to OLS

JIJO 0.6

0.2 lv~=2900d C

100 200 30 100 500 •

Peak Field (Oc) ......

• Figure 3.19b Normalized NRTvT demagnetization curves together with stereographic projections of their directions of

• . . individual pilot samples taken from Lake Begoritis, core B9. 08

jIii°6 • J.s32.24p0 NRP 02 N.üF.40 Oo

11411111 +4- ItlIll too 200390L00W0 - Peek Field 10.) • U . • 1771 08to Depth 9S.Scin

02 MflF:O0e,

ft I •—i W t 0200XOL0O Soo • Peek Field LOl -- •

T2.S7

NJ* 05

VXF 3W 04

titlilIf 1111111 I ' - 0203t,0L0Soo • Peak Faeld(OeJ

to 12 - 87 08. 1 Depth 234.2an _ 06. ilia

02 %tCLF 3030j

too 200 Peek Field 10.4 wT,\(T11I- • • .

• 12 T.Il1 - - - N Dept h 3 015~. Ccm

02 1,Th - -_ 1_• i_ !._.._.___.+... • I_I_I_I_I_I_I_ i_•_ I Igo M 3Z3 'CO it_ Ptak Field t0e) •

• 10I T2..ILT Depth 37Sict 081 Nit,

967P • NR _____ •

-l-- llll I_i_i_' — W_itIlIll -I,I -. 10D2C030 too W0 Peak Field (Del • • - - -. • 12 • 17101 - N 10 Depth £C65cr •

08

•uJG06 - •

0' 0 J. 56 iD •-•• NR4 • 02MF.300 •

• —4----I W(I t 100 200 300 (00 Soo - Peek Field (0.1 • • • • • . - tfi 12-217 Ca Depth S2S 3c"m 06

100 200 300 400 boo • • Peak Field (Oil Figure 3.20 Normalized NRM demagnetization curves together with ,-s4' +1-.- . ,l, ci rf' 24.

This is not surprising, since there was no simple correlation between gross lithology and magnetic mineralogy. Thermal demagnetization was not performed in order to avoid mineralogical changes during heating.

3.5 Remanent hysteresis. Magnetic hysteresis parameters give important information about the bulk magnetic properties of a magnetic material. The experimental procedure was to take a well-demagnetized specimen and briefly expose it to a direct magnetic field by placing the specimen between the pole pieces of an electromagnet, which could generate fields up to 12kOe.

Fig. 3.21 illustrates the produced curves for pilot samples taken along cores V8, B9 and T2. The Hsat is 1.5-2kOe in all the cases of the ex- amined specimens. Jrs for core V8 is ranging from 0.8-1.9 x 10iG, for core B9 is from 2.6-8.3.x 10 3 iG and for core T2, from 0.3-1.8 x 10 3p.G. Fig. 3.22 illustrates the Hcr required to reduce the reversed jrs to zero. This falls within the range of 300-340 Oe for core V8, except for the case of sample V8 - 145 which shows Ecr - 560 Oe, indi- cating difference in size and shape of the magnetic content in the horizon at 418.2cm, for core B9 falls within the range of 280-300 Oe and for core T2 between 380-440 Oe. The values of Her imply that fine grained magnetite is the dominant magnetic mineral along the core, which masks the possible presence of haematite (chapter 2). The vari- ation of the irs along the cores most likely reflects a variation of the magnetic mineral concentration in each core. This is indicative that perhaps jrs could be a suitable normalizing factor for relative intensity studies in these cores, however, it is necessary that certain criteria should be satisfied before any general conclusion comes out.

In chapter 5 the effect of jrs along two cores is discussed. Lake Votvl CD ci 0 Core Vg Depth (cm) 4 a 53.2 Ix '-I 38 A 136.7 106 + 295.9. 121 0 331.6 158 x. 418.2 19o:o 695.0 - b b 7 U .9 10 . . - Direct Field Mel

9 : . .. . Lake Begoritis

8

6.1

5 .

Cr 3 1 yC

. . - . Direct Field (KOe)

cc Trikhonis

Core T2 Depth )cm) ci 6 0 39.5 0 26 A, 89.8 55 + 163.3 '.4 86 231.8 116 X 304.0 146 0 372.9 186 0 454.3 216 0 523.0 1 2 3. 4 5 6 7 8 9 Direct Fietd(KOe)

Figure 3.21 IRM curves of pilot samples taken along cores VS, B9 icrc 0, i.rp.n 3 2/ LAKE eEGoRITxS

A 4 12.8 V V

+ 86 209 -. J/// as • DIOS 20 • .: . x 14 377.3 . - . .23 • 0160 1206 . . 02 0 • • o203 521.6 0.1 : • . •: •. on' S65 • I .'., Cx

03

• . , . , -1.0 - . - _;.==fr....=-& 1000 S ?.-co LC 3G0 2CCO 13GS.) CO 7C 63 SM LC3 303 200 100 0 - -

— V V Direct Back Field (Oe)

• V • •• V V • Cth CcreTz - LAKE TRIKHONIS 6 39.5 V • . £26 89.8 . Cs • + 55 153.3 . V D85 1318 x116 34 - Jé7/ . as • - 0145 3729 . V • - A/I V • 0.1 : V . . ell

03 0.4 CA

OY 0.8 0.9

tc 5— $ :- O 57 £3 CG 2:O ic 73) S £0 3 200 100 0 • V Deck Field tOe) V V

V V V V • - V 09 coevc L g 0.1 LAKE VOLVI •. as - 532 • .. £ 38 1363 /47 as V V V +106.295.9 • . • as a1.21 331.6 - , • ..... • V. . x 158 £1 a2 7 /A' V olSS 509 • V / If 0.2

03

0.6 0.7

• I200 5033 03 733 Cr00 53.3 0-:1 3:3 10 *X01 t3 1C0 S0 503 L3 . )CO 200 100 0 V • • • V • Direct Back Fled tOe) V . •

Figure 3.22 Reversed IflM curves of pilot samples taken along cores 2.

3.6 Significance of jar in lirnnic deposits Another type of remanence, which can be induced to sediments

without causing any chemical change is jar, the anhysteretic remanence magnetization. Suites of pilot samples taken from cores V8, B9 and T2 were place in an AF demagnetization coil whose axis

was parallel to the geomagnetic field. When the axis of the coil

is aligned perpendicular. to the geomagnetic field the jar is about

a half of that in the parallel configuration. Fig. 3.23 illustrates

the shape of the growth of the jar, which was induced into samples,

which were previously well demagnetized. The Hsat ranges between

800-1000 Oe implying that it is a common parameter for the limnic sediments. The jar ranges for core V8 from 8-10uG, for core B9 from 62-16uG and for core T2 from 9-118uG. The illustrated

variations of the jar along the cores reflect differences of

concentration of magnetite, however, they demonstrate a different

degree of sensitivity in comparison with the jrs for the same

samples. Fig. 3.24 illustrates the effect of the AT in a suite

of samples carrying jar given from 200 up to 1000 Oe. They - also show that the normalized jn are closer to the normalized demagnetization curves of the jar between 800-1000 Oe, which

implies that jar of such a value could be used as normalizing parameters of jn.

3.7 Low temperature treatment Figs. 3.26, 3.27 and 3.28 illustrate normalized demagnetization

curves of pilot samples taken along the core B9 of Lake Begoritis

and normalized demagnetization curves of adjacent samples after low

temperature treatment. Fig. 3.26 illustrates the demagnetization

curves of jn. The appear to be similar in shape and with practically

the same IvtDFs except for samples B9 - 70, 72, in which the NDFs are

20 and 270 Oe 160

150 CoreBj Depth LAKE BEGORITIS 7 160 x 3 25.6 .33 104 130 o89 2(.82 1121 3256 120 113 3898 + 172 649.3 110 a202 519.3 233 5683

70-

50-

'120

110- ;: • 30- ICA

20- 0 25 i7.4

A 65 2215 7 fr.1: 80 + 145 370.6 . 0 100 200 300 400 500 603 709 800 000 1000 —70 f °13 461. .• Peak Field too) 215 520.5 /f . • 50 1.Rk0.350e.16 iso Ccr&.i Depth tc.) 50 7/ 160 15 21.6 LAKE VOLVI ol,3 1487 • S . 40- --O 130 0 55 201.3 A93 2' .64 30 / 120 . 110 3082 / +13!. 3519 20 ho 0 165 4347 a 193 502J. / 10 100 RM0.1.00c.f6 • • • •

o 100 200 300 400 500 600 700 800 90

• Peak Field (00 ) ••... 80 •• . . • •

• • Cx 70 • • . • • 4 60-

so-

40-

30-

20-

10 '1

• • • •. • • • 0 100 200 300 460 503 660 700 800 000 1000 Peak Field (0)

6PM mjrves of Dilot saD1es taken alonr! cores V8. B9

Oeplh S \ . Pjnm to

0.7 ' - H.O.F. Depth ec.ccm Art'1 . 90 (04tO \ \ . . 06 AI'' Q ICO N 700 • S I A!M 19 I • ( Ot) i/..05 A.' 600 - -- - . I I\ AM 240 803 I • - •°' I•sI L!!!! ___..:2J 0 *000 03

• -••• S '\\.\

. 0.0 1.. i -. *30 - • 200 309 tOO boa - (tOO 2CO • 809 Peck FicIdtOt) . • . S •

to Vovi-CociV1 03 somplevs -co Depth 141.Scm

07 fADF(OCj Depth 143.Ocm

\\ 0 leG') - N"4 20 5 S 03

02 \ I -- •; -. • . 0.1

• :; L -. - • Pcli (itidlOc)

• ____

\\S.- • - - . 03 S • . • - Dcth *94.2cc

• • S 08 - S kMI+I

[3 . I0II ft: ;:m / 3E AFM 2$5 803 •-: • 02 I I \\. NRt42.) 0 lt.0'3

• ..:-- , . • 0.2-

• •...• -. __I_'L ______Co *00 200 303 403 03 603 703 (03 Peck Fi,(dtOe) . • S -

S LOk.Vcl.i.COtIV, - -. S S • S 03 • • . _. ______Srp'.V1-93 • - P'(O.F.Met Depth - S • - 06 5 ARM m SO ARM tO.) ARM,00 ISO x 200 02 N170 I (CO MIN 130 A 600

0? \ihj h1" . 5 S--S .l 0 . S • •5 :-.- •• t1'I, ._t - - -. . • 06 • 700 800 100 200 03 (00 • Peck FieId(O,) S S -. • - S

Figure 3.24 Spect'um of normalized. ARM demagnetization curves given to pilot sanp1es (v8-16, 118-41, 118-65 1 118-93), together '(?6L- 9A '09V- 9A 'Ot7-9A 1 6o - 9A) so1dw q.otd o. U8At2 SA.Ifl3 u0izeui3vw9p MJV p3Ziuuotx jo um.ioed ç•ç

(SO) PISIJ IlDad ...... . . ... ' S •C0g cot ' Cog Cos COO ODE rcr1000 0cI Oro . ' • :..:1..':..".'.: ..N"I\' :.',' ' .

0301 0 07 P4N S\ \i 10 • 009 • 07O w7d V J

Cog v CEO 1 •f • c0 %1 - - 07 S 051 • -.. . '...... • . coo x. C91 01mv \ \ . ... ...- . • .•. • (.01 wuv C5 Y w,rzccI5O IaC10 . • . \ '. co . ': . • ' - • \ \ . • . - • . - • • \ \ \ 90 • - w3qdaa

Z61'S • "-. . . .. 63 • ': ••4 • . - 1A6103.IAIOA 03; 01 . 979

li0)P'!i 1d Coa cot 009 Cos Gc7 cE CC I --.

co

VZ1 9 ,10 H to

- -

.- - , C

0t, Z" COt C9 Ct 'Co

co

ws 70 CC3I 0 coo ( j \

ii - \\\ \ too) 111?v S6 OUKEY • W)6C '4 40

60 IA.J_!AGA 61101 . . . . -..-• I 01

(°0JP'!J I(3a4 . • . . . Coe 000 031 . 009 OOL C09 0 _

EV

yo oIy \\ . . . cog- , coo • • \ 7COO • • Olt 'hO1Y . '\ . . • . • - 000 x 071 P*iY \\\ •• - 90 • - I•o Iv 06 °P.UY . • \\ . - - - : 'J'09CC41.'Q POJOW • • ' . .. . '\\ cc • 0t1-% 1:SWDS I. • . S.... • . ... '' w,c0c 'li.0 . . . • • \. • . . . .. 60 -• - . . .. ILO

Bj -70 9 03. 09-900

O.G. 021 OA 0 250.15 B9Depth(cm) 7 02021 Depth(cm)

IV

Oo r 2C0 330 403 S03 600100 a 10 200 300 403 S00 600 700 0 100 • Peak Field (Oe) Peak Field (Oe)

NRM 0 OA 1 0298.72 0318.6 31 8-6 tDepth(cm)thk B9_Oepth(cm)Depth(cm) - 7

42

34.3 400 5 C.) 603 7C - 0 %tQ 203 30 443 sro 603 300 U I0 200

Peak Field (Ce) - Peak Field (Oe)

B9 -140 Ba- 170 B9 41 o (c Depth(CM)-1 Depth(cm) a.373.0ftL37_ 0-6r LTI X 0447.0 CA CA N

J_ to t

• • Peak Field (Ce) - Peck Field (Oe)

• •. • • - B-2000 NRM • • • B2O1o(0ft0r Li) • -

Depth (CM) Lake Begoritis

6A Core B 9

330 400 SCO 600 700 - - - • 0 100 200 • - - - Peak Field (Oe) - - - • ....- -

• Figure 3.26 1'IEM normalized demagnetization curves-before and after cooling, at1iquidfrtD ytemperature- oiw'-si 1049$ . • . - i ,, 2er0 4eQ&t. - • • - - to to

ARM'(af•eLT) • 0 rr2 ' Depth 1cm) : 00L.-TSSS \

ARM ARM B.-ill (Qfter LT) B.7120o (after LT) 0 3is.5 298.7 Depth(cm) Depth 1cm) JAJ. .0 323.2 o 301.6

b00 700 00 1&0 200 300 00 s00 000 10 100 2X 300 C0 - ?C0 Peak Field (Oe) Peak Field (Ce) • • •

Bq_j 71 r\A R AR te370.6 'N J/1 Depth(cm) MB9-V89 -UO. 10 * (af r LY)

6C3 700 200 300 400 - S00 o a t.O 700 0 flO ICO 200 300 Peak Field tOe) • Peak Field tOe)

• 10 •

B9 -200. • • Lake BegoritiS • ARM_2OlotafterLT)

. 5165 • Core Bg. • Dopth ( cm) "1 • • 517.O • ARM 1000 OE

• • tOO Soo 6 Cl700 • •• S 0 • 100 200 300 Peak Field 100) •

curves before and. after • AThM normalized- demagnetization • Figure 3.27 w 'L cooling, at 1iqui14YO4 temperature c4)

zero {tC Stta. • •.•• • •. S • • •• • B-9O.

IRM 1terL) B97 o(after LI) •250:S Depth(cm) 0 255.5

: L.0201

0 0 1W 200 •3C3 400 500 bOO 700 Peak Field (Oe) Peak Field (Oe)

•: B-116. : •. IRM B9_1200(a lter LI) Bg -111 o (alter LT) .298.7 . 318. , J/j• Depth (cm) • Dopthlcm) o 323.2 o30 .5 CA

I I I I I CO 5:3 6 0 703 - 600 703 0 1W 230 0 *00 200 33 co 5;3 0 Peak Field tOe) - Peak Field tOe)

IP • .

ci 40 IR489470 IRM ( 11 • . ) :'(aiter L) 370.610 W.6 Depth (cm) Depth (cm) 3710 J/i o

42

Peak Field tOe) peak Field (Oo)

• . ..\. B-2OO. R • I M Bg _201 o (after LI) Lake Begoritis - • •. • .sIS Oopth(Cm) Core Bg • : . - I R M 10000 OE

£00 700 • • O0 2003ro 400 Sw Peak Field (Oe)

• Figure 3.28 IBM normalized demagnetization curves before and. after V'' Uf 0 cooling, at liquid YøCtemperature U"9

" zero - • 0 0 - 26.

respectively and for samples B9 - 90, 92 the IvEF5 are 310 and 210 Oe correspondingly. It is interesting that the remanence remaining in

samples B9 - 70, 72, was harder than the original in. It is possible

that this harder fraction not removed by the low-temperature treatment

was due to SD magnetic grains attached to parent TvID grains. Fig. 3.27

shows the demagnetization curves of the jar (F = 0.40 Oe, I = 70 ° , D = 00, AF = 1,0000e). In all cases the demagnetization curves look

similar in shape and have similar MDFs except for sample B9 - 90, 92,

which has 300 and 250 Oe, which means that a significant portion of

jar was removed after low-temperature treatment. Fig. 3.28 shows the

d.ernagnetizationcurves of jrs (H = 1Q00 Oe). The demagnetization

curves before and after low-temperature treatment look similar except

in the case of sample B9 - 90, 92, which shows i'1DFs 170 and 120 Oe, which reflects that a significant part of jn, jar, and jrs is removed..

It is interesting that the low-temperature treatment has the same effect

on jr, jar and jrs of sample B9 - 90, 92, whereas only in jn for sample B9 - 70, 72.

3.8 Conclusions.

Jn in all limnic sediments has a stable component with MDFs between

300 and 500 Oe. Jn, k and -ratio can be correlated between cores in a

given lake. Low-temperature treatment in general had the same effect

in samples magnetized with jn, jar or jrs, as AFC showed.

27.

CHAPTER 4

4.1 Magnetization processes in sediments.

4- 1 . 1 Depositional remanent magnetization. 4.1.2 Post-depositional remanent magnetization.

4.2 Experimental methods.

4.3 Jp and its relationship with external magnetic fields. 4.3.1 Presentation and interpretation of the results. - 4.3.2 Inclination error in the Greek lakes. 4.4 The stability of jp. 4.5 The growth of jp. 4.6 Jp under controlled conditions. 4.7 Discussion and conclusions. 28.

4.1 Magnetization processes in sediments.

Depositional remanent magnetization (DBM) is the remanence of the

sediments caused by the statistical alignment of magnetic grains as

they fall through the water of deep lakes and oceans. The acquired

DRM is preserved to some extent when the magnetic particles make con-

tact with the sediment surface. Post-depositional remanent magnetiza-

tion (PDRrvI) may then result from further alignment of the magnetic

particles, after deposition but prior to consolidation of the sediment,

due to rotation within the sediment interstices. In addition to the

above processes, chemical remanen-t magnetization (cRM) is of importance in sediments. These three kinds of remanence magnetization occur either

separately or in combination.

4.1.1 Depositional remanent magnetization.

McNish and Johnson (1938) noted a discord.ence in declinations as recorded by the summer and winter layers of a single varve. The coar-

ser summer layers were found to be magnetized more nearly towards the

present geomagnetic field direction and they attributed this to a re-

alignment of magnetic grains within the pore interstices. Ising (1942) investigated magnetic polarization of recent sediments considered the

magnetization to arise from a preferential alignment of magnetic min-

erals developed while settling through water. Nagata et al (1943) in- vestigated the mechanism of acquisition of jn in sedimentary rocks and

inclined towards the depositional origin of the remanence. Johnson et

al (1948) deposited samples of varved clays from a suspension and found that although. the declination was consistent with the applied field,

the inclination was 200 too shallow. Nagata et al (1950) examined the

mechanism of rem anent magnetization in Pleistocene deposits and concluded 29. in the depositional origin of the acquisition.

Lloyed performed a redeposition experiment with powdered Triassic red. sandstone (quoted in the paper by Clegg et al, 1954), produced art

8° deviation from the inclinati )fl of the ambient magnetic field. This effect was estimated as high as 300 and named inclination error by King

(1955). In addition to this he defined another error, which he named bedding error, which can be 25° steeper than the inclination of the geo- magnetic field. The inclination and bedding errors are expressed by the

equations 5 = If - 10 (i) and 6 = i - 10 (2), when 6 is the in-

clination error, Iis the inclination of the geomagnetic field, 10 the remanent inclination, 6 is the bedding error, I is the remanent inclin-

ation of deposited material onto a. surface sloping at an angle a to the horizontal. He also found that magnetic grains with diameters between

10 and 150uxn are affected significantly by turbulance as they fall. He observed that current velocities as low as 1cm.s could cause sig -

nificant rotations and that velocities about 5 to 10 cm-s-1 could cause declination errors up to 100, while greater velocities could even pro- duce a complete reversal of aeclination. The equation which describes

the angular motion of a magnetic grain of moment of inertia I, magnetic

moment , as it falls through calm and still water at a constant tem- perature in the presence of a magnetic field H and aligned at an angle

Q with H is

I.e+ H. sin e=0 (3.1)

where I . SE)' is the inertia term, x. O the viscous damping torque and a'. H • sin 8 the magnetic torque.

Griffiths et al (1960) showed that natural inclination errors were only half as large as those occurring in laboratory redeposition experi-

ments. Nagata (1962) showed that the time constant describing the 30.

alignment of an assemblage of initially random particles of magnetic

moment in suspension to which a magnetic field H is applied at t = 0

is / a. H. He also showed that equilibria will be established over

an angle of values Q due to the fact that natural magnetic grains will

differ their mechanical, thermal, electric, hydrodynamic and magnetic

properties, so as to limit the efficiency of the alignment process of

a. sediment suspension. - - Rees (1961) found that for near-spherical particles below about

lOum other factors affect the anisotropy of susceptibility. As the

- particles settle through still water the induced magnetization of the grain orientates the axis of maximum susceptibility parallel to the

ambient magnetic field. When these particles reach the sediment/water

interface, they roll into the nearest depression. This produces an in-

clination error in the remanent magnetization. In the presence of

flowing water, shear in the sub-laminar flow layer, rotates the grain

with its maximum susceptibility axis towards the direction of the cur-

rent. This phenomenon is naturally analogous to the current rotation

effect on the remanence. Collinson (1963) found that the term I • e can be neglected due to the fact that the motion is highly damped, in

which case the solution of (3.1) is

tan = tan• e (3.2)

He found that the alignment is largely complete in t 16 15 seconds for most natural grains so that in still calm and thermally stable water

the grains will have optimum alignments long before settling. In

nature the alignment of the magnetic moments will never be complete,

because of the water currents, Brownian motion and gravitational torques. 31.

Keen (1963) describes experiments on graded turbidities taken from

deep-sea sediments, which showed that only sediments with a grain dia-

meter between 0.1 and 50pm could produce reliable palaeomagnetic dir- ections. Hamilton and kir5 (1964) demonstrated that the bedding error is approximately equal to the slope of bedding plane.

Collinson (1965) found that magnetic grains with diameters between

0.1 and 5pm should only be affected by randomization of the Brownian - motion. King and Rees (1966) showed that the lower limiting grain size

which can produce a stable remanence is 0.1pm. They showed that the

orientation of inhomogeneous or non-spherical magnetic grains will be

additionally perturbed by a gravitational torque arising from the sep-

aration of their centres of mass and drag. This gravitational torque

will be proportional to the product of the mass and diameter of the

grain for a given degree of inhomogeneity and increases with grain

size • The inhomogeneity effect appears to be primarily significant

for grains having a diameter between 1 and 10pm.. Harrison (1966) extended Keen's work by showing that samples from 0 38 cores with a latitude range of almost 90 had inclinations which were consistent with a geocentric axial dipole. He also recognised

that bioturbation could destroy any jdr. Nozharov (1966a, b, 1967,

1968a, b) analysed theoretically the mechanism of the acquisition of

jd.r in various conditions and showed the complexity of the phenomenon.

Opdyke and Henry (1969) reported a comprehensive study of 52 cores

from all oceans of the world. Approximately 100 samples representing

the entire Brunhes normal epoch, were demagnetized and measured from

each core. Their mean core inclinations were then compared to those

predicted bya geocentric axial dipole. The excellent agreement led

Opd.yke and Henry to conclude that averaged over periods of a million 32. years, the earth's field was indeed that of a geocentric axial dipole.

Since this conclusion assumes that sediments were accurately recording the earth's magnetic field, Opdyke and Henry were implicitly concluding that there was no inclination error. Dymond (1969) provided strong evidence for the importance of water content when he demonstrated that the Brunhes-Matuyaina palaeomagnetic -boundary was displaced 1 50cm down- ward in a deep sea core with respect to the corresponding radiometric boundary. This distance was well below the limit of bioturbation and the additional depth was attributed to slow dewatering of the disturbéd sediment. Nozharo.v et al (1970) presented a theoretical model with. which he attempted to explaintheorigin.b...... Denham and Cox (1971) who studied liinnic deposits found no evidence.of inclination error.

Stacey (1972) showed that the strength of the ambient magnetic field affects this range of the grain s izes .: liecalcu1ated that the magnet- ization M of a sediment with a uniform distribution of magnetic moments

is given by equation up to a maximum Mmax

M=ln (sinhx . (4.1)

H/)• where Mo is the saturation magnetization and x = max For x>> 1. the magnetization approaches saturation Mo and for x '5 1

reduces to MMO.XM0 •M.Hmax (4.2) OKT Although Stacey was dealing specifically with jd.r, his theory is appli-

cable to jp as well. Several other research workers, who attempted to

see if there is inclination error like Creer et al (1972), Vitorello

et al (1974), Levi and Banerjee (1975) did not find any evidence of it. 33.

4- 1 . 2 . Post-depositional remanent magnetization. Irving (1957) suggested that after deposition the sediments might contain water filled interstices within which magnetic grains would be free to rotate. This hypothesis would imply that when the water con- tent drops below a critical value, characteristic of a particular sedi- ment, the magnetic grains can no longer rotate and the magnetization becomes locked. Granar (1958) who worked with varves from Nyland. Fjord in N-Sweden, suggested that in nature the bedding error rarely exceeds

5_100. This result could be explained if the magnetic grains were able to rotate towards the field direction after deposition. Rouse(1961) showed that the water zone close to the bottom of the lake which is a laminar sub-layer is not turbulent and its thickness depends on the slope of the bottom and the velocity, depth and viscosity of the over- lying moving water. Irving and Major (1964), carried out experiments on synthetic sediments and showed that a jp mechanism produced direc- tions parallel to the induced magnetic field after less than 24 hours.

King and Rees (1966) considered the reduction in inclination error to be due to a jp caused by the upward flow of water through pore inter-

stices during gradual compaction. Geddes (1966) found that in general jp was inclined more steeply than the field as the result of a downward

drainage through the sediments, because the used apparatus allowed the

draining of the water from the bottom of it. Meade (1966) in the re- view of the factors influencing the compaction of certain clays and

sands points out that particle size is the main determinant of water

content although clay mineral composition and shape are also important.

In the case of jp arising from the bodily rotation of magnetic grains

in water filled interstices, the microscopic properties of sediments,

which are likely to be important are sediment particle size, shape and 34. mineralogy, as well as magnetic particle size and composition. In particular, the ratio of sediment size to magnetic carrier size will determine the free volume available to the grains and the ease with which the carriers can rotate. Khramov (1968) deposited red clays from suspension. For some samples he increased, the intensity of the applied field after sedimentation, had been completed.. For sediment with a water content of 70% this procedure incresed the magnetization while for water content of 30% there was no effect. He also found that there was a linear dependence betwéen,intensity and applied field up to 5 Oe. and that the growth of . jp ha.s an exponetia1 shape reaching saturation in less than two days. Wimbush and Mu.nk (1970) showed that the laminar sub-layer close to the bottom of-the lake is created by the damping effect of the lake floor. Kent (1973) who redeposited marine sediment and found that the produced jp is directly propor- tional to the magnetic field in the region between (0.20 and '1.20)Oe.

12hnn (1973) suggested that the jp mechanism can be attributed to burrowing benthic organi6ms, q .whidh..cause a mixing and subsequent remagnetized of the sediment and. to grain rotation in the interstitial pore spaces during post-depositional agitation of the sedimentary de- posits. Davis (1974) working ,on: lirnnic deposits found that some fresh- water organisms are clearly capable of large-scale bioturbation of the

sediments. Løvlie (1974) deposited marine clays from a suspension. Midway through the experiment the magnetic field was reversed and a

calcium carbonate marker horizon was deposited. When the deposited

sediment was sampled, the palaeomagnetic boundary was found to be dis-

placed downward substantially with respect to the marker bed. The

experiment represents the first reported observation of jp in a sedi-

ment suspension. Yaskawa (1974) has attempted to estimate the lock-in 35.

depth of jp based on a simple viscous fluid model in which the viscos-

ity is affected by gravitational compaction. Niitsuma (1974) descri- bes a slump bed in which a portion of the remanenoe appears to be jdr

while the remainder is jp. Although nothing is yet known about the

microscopic properties of this material, it is possible that the range

of carrier sizes is great enough, so that some were able to reorient

within the sediment while others were locked in with their initial

orientation after rolling. Thompson and Kelts (1974) reported that the basal portions of turbidite layers in Lake Zug, Switzerland, have

- lower magnetic intensities and lower inclinations for this is that the

coarser basal portions preserve a jdr while the finer material of the

upper portions reflects a jp. This implication means rapid deposition of coarse material leads to a water content lower than the critical paocj" c4rudure, value. From all these studies the limnic sedijnen]' - which locks the falling magnetic crystals is highly important to be studied, because

its great heterogeneity which results from variations in climate, water'

depth and nutrient supply (Wetzel, 1975). Noel (1975) has offered an alternate explanation for the Swedish results based on a large-scale

fluctuation in the geomagnetic field. He also showed by numerical

approach that inclination could be reduced from 100 to 50 by an increase

of the compaction of only 101o.1 Blow and Hamilton (197) perfonned series of sophisticated experiments with grain-by-grain deposition from

•a dilute suspension which provided a depositional inclination error and

with a slurry deposition, which provided no depositional inclination

error. They estimated that the compactive inclination shallowing exhi-

bited by these laboratory sediments may be associated with the rapidity

of either sediment deposition or compaction or perhaps both of

them. In natural conditions this resulted sediment package might not 36. be produced, consequently the inclination error of such sediments will be significantly modified by compactive effects. Kodama and Cox (1977) gave a jar (D.0 = 1 Oe, AF = 1,000 Oe) to mixture of artificial kaolin- itic sediment containing 0.03% needle-shaped magnetic grains with mean grain size 0.511m. The axis of maximum compression was shortened by

33%, which produced no significant change in the direction of magneti- zation with 'a decrease in intensity of 28%. The proposed discontinuous model explained the results and showed only the magnetic grains in the

shear zones rotate and from symmetry considerations no net change in the direction of magnetization is predicted. The reason of the phenom-

enon is that the magnetic grains rotate in opposite directions in com- plementary sets of the model predicts consequently a-decrease in inten-

sity comparable to that which was observed.. Hamano (1978) working with

artificial sediments proposed that the decrease of the void ratio cor-

responds to the decrease of the blocking temperature is a sum of the

remanence acquired during each step of the temperature decrease. -

Niitsuina (1978) proposed two models of acquisition of magnetization working with deep-sea sediments and attempting to explain the depth

log fixation of jp. The first, the plane magnetization model, 100%

fixation of remanent magnetization occurs in a plane. In the second

zone-magnetization model, magnetization is locked gradually to describe

the experimental procedures and results, which were performed in order

to have better understanding of the mechanism of acquisition of jp.

4.2 Experimental methods.

In order to understand the mechanism of the acquisition of the

magnetic rema.nence in liinnic deposits, several pieces of apparatus

were designed and constructed. Initially apparatus I shown in Fig. 4.1 REDEPOSITiON APPARATUS t Timerl Adjustable 1 Support • 'Disc ....Mixing 1 Tank Water Overflow

Timer2 SUPPO- _ Thermometer

• • Disp:rsior' Head

• : •- - • _____ Circulator

Water

Sediment' Flow Coot er

Figure 4.1 Apparatus performing long column redeposition experiments, under controlled conditions of temperature, rate of •____. .L Plate 4.1 The long column under controlled re-deposition apparatus within the Helm jzcoils system. 37. and on Plate 4.1 were used to determine the nature of jd.r and jp as well. The experiment allowed the acquisition of jd.r and jp under a constant temperature of 5 °C, which is at the bottom of lakes. It con- sists of a im long perspex cylinder with 6cm internal diameter and placed within and co-axially in another perspex cylinder 0.80m long with 15cm internal diameter. The shorter tube was glued to a perspex base 3cm thick. - The longer tube was grooved on a circular groove fit- ting the diameter of it and it was held apart from the shorter tube by a circular locating ring near the top. The internal tube was fil- led up with tap water. The external tube formed a pair of a cooling circuit driven and maintained at constant temperature by a Grant type circulator. The sediment slurry was inserted into the top of the inner tube at a controlled rate by a peristaltic pump using a 2mm plastic tubing leading to a dispersion device consisting of a stain-

less steel tube with numerous tiny holes, producing a cloud of tiny

droplets of falling slurry at the top of the deposition tube. The

reservoir of sediment slurry was kept in suspension by an electric

stirrer. The peristaltic pump was controlled by an electronic timer

so as to pump in a precise amount of slurry for a short time of a few

1 minutes every hour or so. The stirrer was automatically switched on

to disperse the slurry in the reservoir about 10 mm (time adjustable) before such a dose of slurry was injected. -teevnoeLz (OeS\ pro-

duced an 80cm3 volume of field up to ±201. The current throui.each

pair was supplied from a constant current power source. Fig. 4.2 1

4.3 show redeposition apparatus II, which was used strictly for the study of the acquisition of jp. It consists of a plastic beaker of

1,000ml volume with a tap located on its side, 1cm above its bottom.

Inside a plastic perforated platform, covered with filter paper having REDEPOSITION APPARATUS I

V V Lifting V

V V V head[ V J I

Ft It e r paper S -,.Plastic perforated \ plate

Screwy V V Sample holder N o V V V 5 •j: _t 27

V V V V .11 .IJ9 Hi2 V 0 0 0 0 . 10

t Magnetic

V V Meridian TOP VIEW

Figure 4.2 . Apparatus performing slurry redepositiori.

(1OOOcc) 1

• ..• • 2 Sample o 0 - > Sample holders • • . -'holder' II • f / 61 I I Fitter 0 pa per __ • ___ ______ -.- P e r f orated _plate • II _ _.• Beaker. / _ Screw SIDE VIEW .. • TOP VIEW

Figure 4.3 • Apparatus performing slurry redepositions with synchronous six specimen sampling. • 38. a diameter equal to the internal diameter of the beaker, sits on three plastic legs at a height of 5cm from the base. A 15cm brass rod. of

2mm diameter is screwed into the middle of the platform to facilitate lifting the firm slurry containing the marked square-shaped sample holders of side 2.3cm. Orientation lines were marked along the bottom apart down the cylindrical sides of the beaker, which were aligned along marked on the table top. The Förster fluxgate magnetometer was used to measure the components of the geomagnetic field at the position of the beaker. Some experiments were carried out in the earth's magne- tic field, others in a field applied either by a simple pair of EelmhOeLZ coils, 30cm in diameter or by . a set of three pairs of orthogonal alum- inium Helmoltz coils producing a field uniform to within and over a volume approximately 20cm 3 . Three identical single pairs of He1mho({Z coils were built up and each was aligned along the direction of the total intensity of the earth's magnetic field with a jp apparatus at its centre. The three sets of coils were calibrated against one another.

When the water was drained off, the settled wet sediment sample holders were pushed vertically along the marked settling tank into the sediment, which was then lifted gently as a whole. The filled plastic boxes were

then removed, cleaned and immediately measured in the spinner magneto-- meter. Fig. 4.3 shows the same apparatus with modified sampler consisting

of a 6.5 x 7.5cm perspex frame with six windows in which six sample boxes were placed. A hollow plastic tube 10cm long is attached to the

middle of the frame. This fits round the vertical brass rod attached

to the platform on which the sediment was deposited and.' facilitates the

smooth removal of the frame with its six boxes of sediment. Care was

taken not to twist the sampling frame during withdrawal. REDEPOSITION APPARATUS III

a Beaker b Lid - (100cc)_____ I

-I- - - - - - - - ... -. . --- Fitter paper Ptastic • perforated • • • • • .. #ptate

C.. d .

- a

V -

e f N • •.. sample •• • ,holder 'F 0 1 S

Magnet • • • Side View Top View Meridia

• Figure 4.4 Single sample slurry redeposition apparatus. Fig. 4.4 shows redeposition apparatus III, which essentially is a small scale version of apparatus II, consisting of a lOOmi plastic bea- ker, which was designed for carrying out experiments in very small volumes

of sediment taken from successive along the core. Only one standard sized plastic box of artificially deposited sediment could be withdrawn.

4.3 Jp and its relationship with external, applied magnetic fields. Sediments from various lakes studied by colleagues were deposited

in a range of ambient field strengths under controlled conditions in

order to find out whether they could record the applied magnetic field

precisely. Wet sediments from lengths of core of the following limnic

deposits were thoroughly dispersed: (1) Geneva; (2) Vuokon; (3) Morat;

(4) Hjortson; (5) Bourget; (6) Kitteen; (7) Begoritis. 1000ml samples of the mixtures were redispersed for 30 minutes and poured into plastic beakers, which were oriented along the direction of the total inten-

sity of the ambient magnetic field placed at the centre of the set of

three orthogonal aluminium Helmoltz coils. The magnetic field, which

0. was produced by the coils was F = 0.38 Oe, I = 45 0 , D . The slur- ries were left to settle in this field for two days after which 2cm of

water was observed on the top. This was siphoned off with a pipette.

Then the tap was opened and the water drained off.

When firm sampling was performed as described above, sediments

from lakes 5 to 7 were then redeposited under identical conditions. The results are shown in Table I. The jp intensity, declination, inclin-

ation and susceptibility were measured in the usual manner. The weight

and the water content were not calculated in 'the first experiments per-

formed. In Table I all the jp magnetic parameters are presented to-

gether with its statistics. Divergence of the mean direction of jp T.ABX2ZPDRX

DD K N N

Lake Time (e) ( () () () (

1.8 39.5 5.5 6.7 184 5.98373 4 GOflSV$ 9 4.44 -t 0.08 5.17 ±0.30 0.79 ±0.07 0.60 3.36 +0.12 1.5 36.9 8.1 3.1 565 3.99653 4 • Vuokon ( 10 60.20 2.0 17.90 + 2.99426 (14 64.50 + 1.70 19.00 0.10 3.39 0.10 5.2 40.1 4.9 6.6 49 3 964 3.99688 • (10 14.90 + 0.30 5.51 +0.19 2.72 + 0.24 3.60.0 39.1 5.9. .2.9 4 11.0 126 2.984 1 8 3 Morat (top) (14 15.40 0.30 5.89 0.03 2.60 0.08 359.2 39.3 5.7 •. : : 5.0 174 5.97133 6 Ejorteon (top) 13 2.29 t 0.07 3.87 0.17 0.60 ±0.03 1.2 40.9 4.1 • 5.2 39.0 6.0 2.6 442 7.98417 8 • Bourget (top) 13 9.37 + 0.20 11.16 + 0.84 0.84 + 0.02 5.6 2.9 346 7.97977 8 Bourget 13 21.10 * 0.20 10.06 0.39 2.12 * 0.08 3.5 39-4

487 7.98562 • 8 j • Kitteen 13 4.34 t 0.05 7.64 ± 0.35 0.81 ± 0.18 3.9 38.7 6.3 2.5 38.9 6.1 4.0 ..190 7.96308 8 Begoritia (top) 13 12.70 0.30 15.58 ±0.30 0.81 0.02 1.7

PDRM after storage . . j. .. . . Qpo Dco I A95 jPo kp I (0) K •, . (Po/0e) (oe) ( ) (

285 5.98946 4 Geneva 14 4.14 ± 0.61 514 ± 0.30 0 74 ± 0 -07 0.9 37.7 7.3 5-4 39.2 5.8 3.4 702 5.99542 4 (19 53.10 * 1.80 17.90 ± 0.60 2.89 *0.09 559.6 k Ofl 36.2 8.8 7.6 263 2.99241 3 • Vuo (19 55.50 ± 1.20 19,00 ± 0.10 2.89 ± 0.06 2.7 5.51 0.19 1.76 0.05 355.9 40.0 5.0 5.5 683 3.99561 4 . (19 9.73 0.40 t op 36.5 13.6 83 2.97589 3 . S (19 10.00 ±0.60 5.89 ± 0.05 1.73 ± 0.13 1.5 6.5 1.06 ± 0.04 3.80 ± 0.20 0.284 0.02 4.5 36.5 8.5 16.2 230 4.82666 5 HiO1.8Ofl (top) 17 256 7.97266 8 La Bourget (top) 17 7.45 ± 0.23 11.15 ± 0.32 0.67 ± 0.02 3.9 39.2 5.8 3.4

1.88 0.06 38.7 6.5 2.5 488 7.98566 8 • • La Bourget 17 16.86 * 0.36 10.10 ± 0.40 * 7.3 •

8 • • Kitteen .• 17 2.93 * 0.12 7.84 ± 0.35 0.38 ±0.02 356.1 40.7 4.3 3.3 267 7.97378

• 5.2 4.2 7.95971 8 • . Begoritia (top) 17 6.66 t 0.25 15.57 ± 0-30-.0-42 t 0.02 6.8 59.8 174 40. from the declination and inclination of the applied magnetic field can be attributed to experimental error as the A95 shows. In Table II the results of the measurements of jp are shown after storage in zero- magnetic field from 14 to 19 days. Specimen were kept moist, wrapped in wet paper towels and enclosed in polythene bags.

4.3.1 Presentation and interpretation of the results. Comparing the initial jp intensities and direction with those

after storage in zero-magnetic field, it is obvious that a randomiza-

tion process is reflected. For example, the group of samples with

sediments from Lake Geneva in which the jp had been allowed to grow

for nine days, had initial intensity 4.440. Reductions in the inten-

sity after storage in zero-magnetic field by 6.8% shows that jp con- tains an appreciable viscous component. This could be explained by

the rotation of some of the smaller grains into more comfortable orien- tation in the interstices of the mud on removal of the magnetic align-

ing couples. The jp intensity for samples of Lake Vuokon (Finland)

with initial intensities of 10.20 and 14.5 0p.G after being left in zero field 10 and 14 days respectively, decayed by 11.8% and 13.9%. No appreciable further decay was observed on storing period for 19 days.

The experiment was repeated on two groups of samples taken from the redeposited slurry of Lake Morat. After 10 and 14 day periods of dry-

ing in zero-magnetic field, the two groups showed decays of 34.7 and

35.1% respectively, indicating a more marked randomization process

than observed for the lake Vuokon sediments. Samples taken from re-

deposited slurries of Lakes Hjortson, Bourget, Kitteen and Begoritis

sediments with the same drying and storing times decayed by 53.7%,

22.6%, 10.6%, 32.5%, 47.5% respectively. In most cases the A95 increased TABLE IX PDYX intensities Lake )Citteen Core 5 Qp Depth jn 19 jpo Ic lcp N • . cm (uc) (iO) (io) (uc/0e) (uC/Oe) (Oe) (Oe) (8) (82-96) 19.54 t 1.18 3.70 ± 0.14 2.91 ± 0.04 5.84 ± 0.36 6.83 ± 0.14 3.57 ± 0.14 0.54 ± 0.01 7.07 ± 0.06 6 •. (218-232) 19.80 ± 1.46 1.69 ± 0.06 0.96 ± 0.07 4.94 ± 0.43 4.03 ± 0.05 4.01 t 0.12 0.42 t 0.02 5.87 ± 0.04 7 (368-382 ) 27 09 ± 048 1.12 ± 045082 ± 0 1 87 65 ± 021 5.67 10.04 3 54 ± 001 021 ± 006599 ± 0067 (51 8-530) 22.60 ± 0.37 6.99 ± 0.11 6.30 ± 0.11 7.74 ± 0.38 7.84 ± 0.10 2.91 ±0.05 0.88± 0.02 6.39 ± 0.077.:.

• PDEM directions . . . :. Depth Dn • I 7 A9S . cm (0) (O (0) (0) K R N

(82-96) 6,1 67.2 3.8 5-4 152,8 5.96728 6 (21 8-232) 3586 642 6,8 7 7 61.4 690238 7 (318-'82) 358.8 68-3 2.7 11 2 29 7 6 79855 7 (518-530) 357.8 66.1 4-9 3.3 329-4 6 98167 7

Ie.710.0 PRM &ireotions after etorse

Depth Dpa, Ipo A9 K • N

(82-96) 4-6 65.0 6.0 6.2 115.1 5.95658 6 (218-232 ) 358.1 63 1 7-9 10 -4 34.0 6.82577 7 (368-382 ) 3557 66.5 4.5 1 3. 2 21.5 6 72201 7 (518-530) 358 -4 69-4 1.6 3.7 259.2 6-97005 7

Is . 71°.0 41.

after storage in zero-magnetic field (see Table II).

Variations in Q-ratio are attributed to differences in concentra-

tion of magnetic mineral content and differences in the magnetic grains

shapes and sizes and physical state. In Tables II and III the jp re-

suits from Lake Kitteen and Geneva are shown. The sediments of Lake

Kitteen were chosen because they were highly organic (Stober, personal

communication) in opposition with the sediments of Lake Geneva, which

were highly inorganic (Hogg, personal communication), so as to have two

different media for redeposition. 2509 portions of sediment were col- - - lected from specific depths from core 5 of Lake Kitteen and core 3 of Lake Geneva and mixed thoroughly dispersed. with 800m1 of deionized water and then poured into 1000ml plastic marked beakers and left to

settle in the Earth's magnetic field (constant to 2-3%) on a wooden table. / After two days, 2cm of water had been squeezed out to the surface

of the slurry and was siphoned off with a pipette. The rest of the

water was left to drain off through the tap of the apparatus at the

bottom of the beaker. The slurries were allowed to dry for seven days

before being sampled. The mean jn was calculated in each case from

the measured values of the specimen corresponding to the consumed len-

gths of core taken for redeposition. The estimated water content for

the top sediments was 70% and for the rest of the core 60%. It was

found that jp were considerably lower than jn by 81.1%, 91.5%, 95.9%

respectively and 68.8% for the sediments of Lake Kitteen, and 69.0%,

- 80.3%, 60.9%, 69.3% respectively for the sediments of Lake Geneva. These results may be explained by, a) poor disperson due to high

organic content, especially for the sediments of Lake Kitteen, having

caused the formation of clusters of grains resulting in high A95s, and

S .. .

?ABLIII PDBM intenaitiee Lake Geneva core 3

3o k kp 4 ' Depth (o/oe) (ag/Oe) (Oe) (oe) (g) . • cm (no) (pG) (G) ± 0.08 7 ± ± 0.70 1.33 ± 0.05 7.62 e.os ±0.11 8.02 ± 0.34 6.40 ± 0.22 5.83 0.11 4.80 (82-92 ) 26.07 I ± ± 0.09 7 5.51 ± 0.12 5.04 ± 0.17 5.62 ± 0.13 1.27 0.06 7.54 (220-270) 32.30 ± 0.21 6.36 ± 0.30 604 ± 0.30 4.12 0.14 1.75 ±0.12 7.59 ± 0.064 • . 0.27 5.98 ± 0.30 5.20 ± 0.10 ± (370-380) 24.60 ± 1.40 9.61 0-18.9-48 ± * * 0.09 7.37 ;k0.09 ± 0.25 5.15 t 0.27 4.44 ± 0.17 2.02 0.13 0.71 (505-515) 10.40 * 0.66 5.19 ± 0.22 3.18

.PDR2.4 direotione . . I •

• V 95 . S. •• R • •• N • Depth •• • . K .; • . . am (°) • (°) (°) (°) 7.8. : 6.9oo .. . •: 2 ••• • 7.1 .:.: (02-92) 63.9 . 0 8 160.8 6.96257 7 (220-270) 354.6 70.2 4 7 5.8 10-3 167.6 3 98210 4 (370380) 356.5 65.2 5.6 55-9 4.92656 5 (505-515) 1.8 6a.6 2.4

Ic - PDBM direotiona after storage . . •. .. . • V A95 . N • Depth •. po • Ypo N N (0) (Q) (0) (0) cm 11 9 26.5 6-77641 7 (82-92) 8.1 72.3 -1.3 124 7 6 95188 7 (220-270) 355-1 73-4 -2 4 5-4 5.9 7-3 159.0 3-9311 4 4 (370-380) 348.2 651 12.0 41.2 4 90305 5 (505-51 5) 4-4 65.3 5-7

71 -0 42. -. low precision parameter K (see Table,II, III); b) the nine days allowed for the alignment of the magnetic grains of the sediments of the two lakes being sufficient for complete alignment; and c) the water content of the redeposited samples is 40-50% for the sediments of Lake Kitteen and 20-40% for the sediments of Lake Geneva of the total mass, whereas the water content of the naturally deposited samples were found to be

70% for the top of the core and 60% for the rest of the core of Lake

Kitteen (Stober, personal communication) and 60% for all the tore of

Lake Geneva (Hogg, personal communication).

In Tables II, III the results after storage in zero magnetic field are shown. This further decay accompanied by more scattered directions

(higher A95, lower K) due to an increase in magnetic viscosity after redeposition. The ka of the artificially deposited samples appear with higher values than the ks of the natural samples due to hier water content, except for the case of sediments taken between 82-95cm of

Kitteen in which the k of artificially deposited samples is lower, due to experimental error in sampling. Tables IV, V list the results of two experiments, which were performed with sediments from Lake Begoritis, core B8 as it was described in 4.2. The scope of these experiments was to show the relationship of the obtained jp in the laboratory and the applied low (0 - 0.80 Oe) and high (0 - 4 Oe) magnetic field. For both experiments 1Kg portions of sediment was mixed with 8pOOml of water in a big vessel, which was kept covered with a polythene sheet to keep con- stant the initial ratio of sediment upon water. At every step of the experiment the entire mixture was thoroughly dispersed for thirty min- utes and 800m1 of mixture was taken and poured into the settling tanks. The duration of each experiment was chosen to be seven days. Fig. 4.5 illustrates the relationship between the intensity of jp and the Homogenized redeposition experiments . • •. Core B8

Il Mean PDRM • / Least-square test • . . . Slope =2.290.09 4uG.cm?'/0O . / . , Intercept 0.15±0.04j.iG.cm 1 .7' • r = 1.000 / / Prob/ty =0.023% X Mean PDRM C19 1 . • AFC (100 Oe) • Slope =1.96±0.09jG.cm/Oe - - . • Intercept =0.00.04jG.crr? 1 . • . r=0.999 .. Prob/ty =0.11%

I • 0 . 0.20 0.40 0.60 0.80 . • . . . - H (Oe) Direct Field Lake Begoritis 14 Homogenized redeposition experiments .. Core B7 . .

••• :• Mean PDRM 12 •. i f Least-square test Slope =2.72±0.07jG.cmgl/0e . Intercept : 0.71 ±0.08jG.cri' 10 . . . / / J r=0.999 ,f Prob/ty 0.011% • . / Q • Mean PDRM • . . . . AFC (l00 0e) . Slope =2.29±0.07JJG.cm:!/0e o 6 . . Intercept =0.41 ± 0.07jG.cm 1 r=1.000 • . . . . • Probity = 0.00013% )4. . • •

2 • .•. . • . .

0 . I .• .• 1 2 3 4 • 5 . • • H (Oe) Direct Field • • • • Figure 4.5 • Intensity of PDRM before and after AFC to remove VRMs is plotted against the intensity of the applied magnetic

TABLE IV PDRM intenaity ax4 the field. Lake Begoritie core 38 1 )rpa kpb kpo 'i!b Vs H jp jpa 3pb JPO kp . (G . . . o, . 10) (g) (g) (g) (00 (os) () . 10) (10/00) 7.89 ± 0.06 3.84 ± 0.08 4.01 ± 0.08 0.31 ± 0.02 0.20 4.77 ± 0.22 0.61 ± 0.03 1.24 ± 0.06 1.90 ± 0.09 15.42 ± 0.15 1.93 ± 0.06 4.01 ± 0.14 3.84 ± 0.08 0.02 0.40 8.20 * 0.24 1.07 ± 0.03 2.50 ± 0.01 2.18 * 0.06 13.80 ± 0.02 1.60 ± 0.01 3.82 * 0.02 3.36 *0.07 7.68 ± 0.03 3.61 0.02 4.11 0.03 0.65 ±

0.60 12.00 ± 0.36 1.52 ± 0.05 3.01 ± 0.50 2.78 ± 0.09 14.93 ± 0.27 1.86 ± 0.05 3.96 ± 0.07 3.66 10.07 7.89 :t0.05 3.77 ± 0.62 4.08 * 0.03 0.76 * 0.05 0.05 8.04 ± 0.05 4.02 ± 0.03 4.04 ± 0.04 1.00 ± 0.05 0.80 15.61 .± 0.41 1.99 ± 0.05 3.89 ± 0.11 3.87 ± 0.1,1 15.66 ± 0.14 1.99 ± 0.02 3.89 1 0.04 3.89 ±

PDBM directions

H Ia T A9 X R N (0) (0) (00) () () (

0.20 335.3 75-1 71.1 4-0 5.4 80.4 11-85332 12 2 12 0 40 356.9 73,2 70.4 2.8 3.2 188.9 11-9503 160 9 11 0 60 358 2 74 7 69.8 4.9 3.3 10.94983 0 ,, 0, 0 0. •" 0 ,, $ 0 0.80 359-1 74.6 72.0 2.6 3.1 205 4 11 99825 12 p ..0 TABLE V PDRM intensity and the field

H jp jpa kp kpa Wa Qp (Oe) (i.iG) (i.iG.cm3 .1 1 .x10) (iG/0e) (Gcth3 .9.0ex10) (g) (Oe) 0 .40 14.0 ± 0.56 1.92 ± 0.08 14.95 ± 0.10 2.05 t 0.04 7.29 ± 0.12 0.94 ± 0.04 0.85 22.8 ± 0.72 2.89 ± 0.10 15.30 ± 0.12 1.94 ± 0.04 7.90 ± 0.14 1.49 ± 0.05

1.40 34.9 ± 0.84 . 4.41 ± 0.17 15.13 ± 0.14 1.91 ±0.05 7.92 ± 0.22 2.31 ± 0.06 2 .70 64.0 ± 1.32 8.14 ± 0.22 15.08 ± 0.11 1.82 ± 0.03 7.86 ±0.14 4.24±0.09

4.00 93.4 ± 2.06 11 .93 ± 0 .32 15.22 ± 0.16 1.94 ± 0.03 7.83 ± 0.11 6.14 ± 0.15

PDBM d.izeotiona

H Dp I I A95 (Oe) (0) (0 (o) (o) K R N

0.40 355.6 67.1 5.9 4.5 214.4 5.97668 6 0 .89. 359.9 66.8 6.2 4.6 206.6 5.97579 6 1.50 350.3 69.1 3.9 3.2 235.2 5.99352 6 2.70 3599. 64.2 8.8 3.8 222.5 5.98541 6 4.00 356.8 66.4 6.6 4.9 180.9 5.96609 6 Ia = 739.0 43.

intensity of the applied magnetic field. .AFC in 100 Oe removed the jv, which was superimposed upon jp. A weight least-square test was applied IcQ c ± to both cases and showedj linearity between the two parameters. It seems that iv occurs mainly during the period of the sampling which lasts approximately 20-30 minutes due to carefulness and cleaning procedures before the samples are measured.

- - 4.3.2 Inclination error in the Greek lakes. Table VI lists the mean values of inclination of the single earn- pies measurements of three groups of cores from lakes Volvi, Begoritis

and Trikhonis. TABLE VI

Core Y A95 N K R No. (0) () V2 60.12 0.91 112.37 213.10 215 V5 56.87 0.78 148.10 222.49 224 V6 64.00 1.19 66.43 208.82 212 V7 61.74 1.32 50.75 223.53 228 VS 60.47 2.05 21.03 223.87 235

B7 49.95 0.94 114.81 196.27 198 B8 56.07 2.15 20.89 205.71 216 B9 41.83 0.87 112.77 233.92 236 Ti 63.33 0.84 118.36 236.00 238 T2 68.16 0.69 175.69 236.65 238 T3 49.86 0.80 131.17 234.21 236 T5 45.62 0.82 134.30 218.37 220

The present day geomagnetic inclination and declination at the sites of the lakes Volvi, Begoritis and Trikhonis are 57 °17' , 1 °30';

560901, 10091; 54036 1 , 0057' respectively •(Stavrou, personal communica- tion). The deviations of the mean inclinations from the present value 44. of the inclination of the geomagnetic field, shown in Table VI. do not reflect any inclination error but the effect of the tilting of

the coyer which sometimes is accompanied by bending of the PVC core tube distorting anomalously the inclination record. For example the mean inclination record of core B9 is shallower in general than the present value of the geomagnetic inclination at the site of the lake;

in addition it exhibits anomalous low values between 230 and 300cm

in which inclined horizons were observed in the stratigraphy of the

core reflecting bending of the core tube (Chapter 6).

4.4 The stability of Jp. To test the stability of the obtained jp under laboratory condi-

tions pilot samples were progressively demagnetized in alternating

fields. In Fig. 4.6 are shown the normalized demagnetization curves falling smoothly against the increasing AF, with MDFs about 200 Oe.

The jp directions changed minimally on demagnetization, as Figs. 4.7

and 4.8 illustrate.

4.5 The growth of ìp. Mixtures from core B7 of lake Begoritis approximately 1Kg were

mixed with 8000ml of dionized water in a big vessel. The mixtures

were dispersed thoroughly with a stirrer for about two hours. Then

600m1 of the liquid dispersed mixture was poured into 1,000ml plastic

beakers, marked and placed along the magnetic meridian, on a 2 x 1.5m 2

wooden table on which the total magnetic field was different from one edge to the other less than 5%. The beakers were sealed up with thin polythene covers as the slurries were left to settle for logarithmically • 1.0- Lake BegoritiS • (ARC.) Demagnetizations P.D.R.M. 0.8 Homogenized mixtures • CoreBa 0.6 M.D.F.(16OOe2OOOe) • I - O.SOOe\ 0.4 I J0:15.63JGJ • I I fH:O.600e\ • • I I kjo:11.36PGJ I I O.LQOe\ J o== 9.951GJ 0.2 ~ (ii = O.20 0e\ • • I I I i \Jo=4.71P

II . I • 00 • 0 100 200 300 400 500 Peak Field (Oe) 10 Lake Begoritis

(A.F.C) Demagnetizations •.

P.D.R.M. • 0.8.. Homogenized mixtures • • Core B7

• 0.6

- ----\ M.D.F.2OOOe)d • J O (HO.L.00e • 0.4 I\ Jo14.OjJG •. (H:O.9OOe H=2.700e • ) • I \:.: Jo 22.8IJG H 1500e,?f ( • • : (Jo--3,L9,wG (H4.00e 02 I Jo936pG

0.0 0 100 200 • 300 600 500 600

Peak Field (Oe)

• Figure 4.6 Normalized, demagnetization curves, of redeposited specimen, sampled from slurries.

N 1.0 Lake Begorit5

0.8 H:0.200e . . r

- _4.77 1i0 J/JO

clz 120e PrD~R

100200300400 . . Peak Field (Oe) . . . .

1.0- Lake BegoritiS

0.8 0• \ t000e . . ,00.6 J89spG 0.4 YLU 1 PORM E I I I I I 1 Fl- i i i 100 200 300 £00 Peak Fietd(Oe) U t0 Lake Begocitis . 08 \o;6oe

02 180 Oci PDRM _1.L.. W C 4- • 100 230 300 £00 0 Peak F.etd(Oe) 0 0

N 0 1.0 lake Begoritis 0 0.6 II :0800e

KDY (121 200 Oe: W ( I E

• 100 200 300 100 0 • Peak Field (Oe) . • •• . . .

Figure 4.7 Normalized demagnetization curves of redeposited

. representative specimen for each redeposition •0

O experiment performed between 0.20 and 0.80 Oe, .

with their direction stereographically projected • 0 O 0 • during AFC.

ID lake Begoritis • • 08 H:O.LOe \ - \J.:14.0 1iG • JIJ0

0218000

• I I I I I - 100 200 300 LOG 500 •• • • Peak FeLd(OeI

Lake Begoritis

• as - \ H=0.90e • 06 •: - \J.:22.8 110 jM

• 02-180 oe

• • 100 200 300 LOG 500 - Peak Field tOel • 10 Lake Begoritis

• 08 \H1.50e 06 J. = 3 1,9 pG • i/Jo •---, • t4.D.F - 02 2000e'

• - 100 200 300 400 SOO - Peak Field tOe)

10 lake Begoritis 1 08 • - mo06 M.D.F 02j 200 Ce'

100 200 300 400 500 • • Peak Field (Ce)

S\ lake Begoritis • • • • H:40e \ - •: 06 •_ VG • • MDF

• • 02 IF 00e • - • i I I 100 200 300 LOG 500 • • • Peak Field (Oé) • • - • • - •

Figure 4.8 Nonnalized demagnetization curves of redeposited representative specimens for each redeposition experiment performed between 0.40 and 4 Oe With

4 . .

time intervals between two and 24 days. After two days 2cm of water

had been squeezed out to the surface of the slurry. When the beakers

were unsealed at logarithmic time intervals the water was siphoned from the top with a pipette and all the slurries were left for four

days to dry. Table VII lists the jp intensity results which are illus-

trated in Fig. 4.9. When AFC in 100 Oe was applied, the superimposed

jv on jp found in other experiments was removed. Experimental points

- for time <2 days could not be achieved due to rotation of.thentagnetic grains when very moist samples were placed to be measured in the spin-

ner. lthramov (1968) has shown that saturation jp can be obtained in

less than two days probably the same exponential like curve could be the case for the jp growth of the .limnic deposits. AFC 'showed smoothly..

falling demagnetization curves and MDFs about 200 Oe. 4.6 Jp under controlled conditions. - The effect of temperature and rate of deposition on jp was inves-

tigated.. apparatus I (see section 4-1-1) was placed in a- uniform mag-

netic field (F = 0.73 Oe, I = -73 0 9 D = 00 ). The experiment was divi- d.ed into three stages, the depositional stage which consisted of 10

days at 2cm/day, 10 days at 1cm/day and 10 days at 0.5cm/day. The self compaction stage which lasted.. 30 days and the compaction stage in which

excess water was siphoned. off. The top of the sediment was then cov-

ered with 5 x 1 Omi of CaCO3 , followed by the addition of 1 OOml of dried sand at five day intervals, up to a total of 500m1 over 25 days. The

CaCO3 horizons were used as markers indicating the time of the addition at each case. At the end of the deposition a 32.8cm of slurry had

been deposited.. The volume was reduced by 40% after self compaction

and a further 15% compaction occurred under the load of sand.. Sub-

sampling was performed by pushing the core with a piston and getting TABLE VII The owt.h of PDRM Lk. Begoritie Core B8

Qp Tot1 jpa kp kpa Wa (0) I '°) () (no) (z0.cm310) (0.om3.1.01.z10) •.,; 1.76 ±0.05 . 8.71 ±0.11 0.86 ±0.07 - 2 0.3 13.21 ±1.00 1-510-11 15.41 ±0.41 38 177± 005 868±016 066± 006 4 06 1330± 081 153± 010 1538± 0 187±005 856±022 0.62 0.03 6 08 1317*044 1-54 0 - 06 1600*013 8.80 * 0.17 0.87 * 0.03 10 1.0 13.24 * 0.51 1 .50 10.06 15.28 * 0.04 1.74 ± 0.03 ± 0.23 1.78 1 0.03 8.66 0.09 0.87 i- 0-03 14 1.2 13.36 ± 0.41 1 .54 ± 0.05 15.41 8.59 0.23 20 13 13 25± 068 1.54±009 1568*018 1.62 0.05 0-64 0-04 PDEM dirsotiona . .

Total K t) log(t) (g) day (5 9

2 0 3 2.9 71 2 73 6 .2 4 7 6 78 4 5.93624 6

4 9.6 359.3 731 731 0-0 4.9 235-6 4-98304 5

6 08 09 71.5 68.3 32 4.7 2001 597501 6

10 10 07 713 681 32 59 1269 596059 6

14 1.2 2.7 738 67.5 6.3 3.9 284.9 598245 6

20 1.3 0.5 75-0 698 5.2 70 91.7 5-94552 6

• ... . •. TABLE VIII

PDRJI under controlled conditions.

Depth jp jpa W D I & (cm) (hG) ('iG.cm3 .g) (g) (°) (°) (0)

2.3 22.82 30.90 7.39 6.5 -44.8 28.2 4.6 18.74 24.70 7.58 2.6 -49.8 23.2 6.9 19.59 23.90 8.24 3.2 -65.6 7.4 11.5 28.43 33.80 8.43 0.1 -69.6 3.4 13.8 34.23 42.10 8.12 0.9 -70.9 2.1 16.1 28.55 33.90 8.51 9.0 -50.8 22.2

D I & A95 (Q) (Q) K R N () () 4.4 -58.6 12.4 9.6 49.4 5.89897 5

Observed differences in jpa are due to inhomogeneities in the sediment column, produced by the CaCO marker which partly passed through it.. I Luke Begoritis

730e

Core B 5 frtD.F.=(18OOe, 2000e)

0.4

0 100 200 300 400

Peak. Field (Oe)

Figure 4.10 Normalized, demagnetization curves of specimen sampled along the redeposited column. N 1.0 . PORM

=22.82 VO 0.6 FP \Depthl5jcrfl KCLF

I E 103 200 300 400 Peak Fietd(Ce) W('T'T7,I . TT1 N PORM • . i. 2Q42 jG 400 Oe J,Jo 06 (7 KU PORM

11111111 -I--41Il1--- t E 100 200 301 400

Peak Field(Oe) .• . . -

PORM

Depth z 6.9 cm

02 W ( #)DRM

100 200 33 400 Peak Field jOeI Iflj..\ N. PORM

Do pth zf..6cm KOLF

C12 -190 00 , . . . W i t I I I I I 100 200 30 1.00 • • • - Peak Fie(d(C.e) • • •• . . -

s..ept2,3cm • 1°c1 KQF •: 02-130 00: • ( -- .PORM 1001 200 30 • • . • F,r.3(Oe) • . -. •

Figure 4.11 Normalized, demagnetization curves of individual specimens sampled along the redeposited column and their directions of PDRM during AFC is shown in stereographic projections. 46. samples from the bottom by pushing the plastic boxes within the sedi- ment. Fig. 4.10 illustrates the normalized demagnetization having IvtDFs about 200 Oe, and Fig. 4.11 shows the groupings of the obtained direc-

tions. Table VIII lists the obtained results along the core.

4.7 Discussion and conclusions. All redeposition experiments performed in the laboratory under the

described conditions in this chapter showed that ilinnic sediments can

record the direction of external applied magnetic fields almost pre-

cisely. Then the sediments contain organic material in high quantities

an unstable jp was produced, due to the fact that magnetic grains were

mixed with organic material in aggregates which did not allow them free-

dom to align themselves in the water medium along the direction of the

magnetic field. Storage in zero-magnetic fields and AFC removed super-

imposed jvs upon the jp created in the laboratory which is explained by

rotation of the finest grains within the water interstices and the coar-

ser grains and showed that the remanence obtained was of stable charac- ter with smoothly falling demagnetization curves, well grouped directions

and 1MDFs about 200 Oe. The intensity of jp is directly proportional to the intensity of the external applied magnetic field and its growth

remains constant with time. It was found not possible to measure redeposited samples with jp

produced in less than 48 hrs with the spinner magnetometer because the

sediments were not sufficiently solidified and the magnetic grains could

rotate easily in random directions within the water interstices. The

growth of the remanence is most 'probably of exponential character and it

can be studied successfully either by an astatic magnetometer (Collinson, 47. - personal communication), or by a cryogenic magnetometer (B- " ton, The latter case is an excellent opportunity for study-

ing in detail and accurately, the growth of the remanence in small time periods from minutes and hours up to days, with different conditions of

density of sediment, percentages of magnetic content and degree of com- paction, possibly under controlled temperature. In the experiments pre-

sented in this chapter no difference was found between jps produced in

5°C or 230C, however this can be established only if one could measure the growth of the remanence during the actual experimental procedure.

The highly time consuming experiments under controlled conditions illus-

trated unstable remanence when the water content was too high, 80-90% and stable remanence when the water content was 50-60% with smoothly fal-

ling demagnetization curves, well grouped directions and viDFs about

200 Oe, as AFC showed. The observed inclination error was 6 15_200 in some experiments

and it is attributed in to unnaturally fast deposition and consolidation

which produced high rapid compaction effects. Although the redepositions

with slurries did not produce significant inclination error, by no means

reflect that the mechanism of acquisition of the remanence is strictly

of post-depositional character, because they allow the water draining off the bottom of the beaker, while in nature goes most probably upwards

due to gravitational compaction. The long column experiment is a better

simulation to what happens in nature, but still one must avoid fast deposition and take into account possible action of jcr, if oxidation

of magnetic content occurs after deposition (Chapter 2). 48.

CHAPTER 5

LflviNOMG1ET IC PIUEOIWI'ENS ITIES

5.1 Introdu.ction.

5.2 The k, jar and jrs normalization methods for

relative palaeointensities.

5.3 PDEM as normalization parameter. 5.4 Discussion and conclusions.

49.

5.1 Introduction. Attempting to determine the palaeointensity of the Earth's magne-

tic field from the remanent magnetization is one of the most difficult

tasks in palaeomagnetism, because of chemical changes which have taken

place within the rock either since it was formed or during laboratory

experiments carried out to determine the palaeointensity. The most

reliable method described by Thellier and Thellier (1942)/Tor rocks

with therinoremanent magnetization. Although no successful method has been developed to determine the

-- absolute palaeointensity from the remanent magnetization of unbaked sedimentary rocks, many attempts have been made to determine relative

changes in palaeointensity with time from magnetic measurements on

sedimentary sequences. Some liinnic deposits may be well suited for

this purpose, if they were deposited continuously under relatively

stable conditions over long periods of time, in the range of several

millenia, because it could be possible for the record to be compared

with the established archaeomagnetic intensity data. It is necessary (but not sufficient) to compensate for variations in the content of

magnetic minerals in the sediments, isceptibility, vihysteretic rem- anene and saturation isothermal remanence have been used by different

workers to normalize the intensity of the natural remanence, for instance

in deep-sea sediments Johnson et al (1948) first used jrs, Keen (1963),

and Harrison and Somayajulu (1966) used k ; Opdyke et al (1973) compared the variation of k, jar and jrs with the variation of jn in along deep

sea core. However, the advantages, if any, of using one of these para-

. . meters instead of another for the purpose of jn normalization are still

not clear. K and jrs received.isproportionate contributions from dif -

ferent regions of the magnetic grain size distribution. K is most 50.

influenced by very fine, superparamagnetic grains and coarse multi-

domain grains (Nagata, 1961, p.28). It also includes a paramagnetic

or diamagnetic contribution from the matrix. On the other hand., jrs

receives the greatest contribution from stable SD or PSD grains. For

example, the jrs may be as much as half the saturation/magnetization .7

for non-interacting SD grains (with uniaxial anisotropy), but perhaps

several orders of magnitude lower for coarse, MD magnetic grains, and

zero for superparamagne tic grains (Dunlop, 1973). The in of the Greek limnic deposits appears to be carried mainly by SD or PSD fine magne-

tite particles and partly by coarse magnetite grains, which contribute

in smaller proportion (Chapter 2), consequently k, jar and jrs all have

been used as normalization parameters. It is more difficult to choose

• between jar and jrs as the more affect. normalizing parameters, because both the remanences will be most affected. by SD or PSD magnetic

grains, the same magnetic grain size range as is believed to be carr-

ing in in many other cases. Nakajima and Kawai (1974) used jn/jrs as a normalizing parameter

and they obtained a palaeointensity record. from a core from Lake Biwa in Japan and correlated it with the palaeoclimatic record deduced from

pollen analysis studies. H. P. Johnson (1975) preferred to use jar

rather than jrs or k as a normalizing parameter, arguing that the latter two parameters probably over-emphasize the role of multi-domain parti-

cles. Hence he normalized partially demagnetized jnby undemagnetized

jar in order to obtain intensity trends in his cores. Levi and Banerjee (1976) used demagnetized jar as a normalization parameter in

order to obtain palaeointensities from 6m sedimentary cores from Lake

St. Croix, Minnesota and were able to correlate these with the archaeo-

magnetic record which exhibited periods of 300-400 years. Liddicoat 51.

(1976) used jar to normalize in obtained from direct limnic exposures from Lake Mom, U.S.A.

5.2 The k, jar and jrs normalization methods for relative palaeo-

intensities. To interpret fluctuations of the normalized remanence intensity

(usually partially demagnetized in) as flutuations of geomagnetic intensity, it is assumed that the measured remanence of sedimentary deposits is linearly related to the external field fixing the remanence and to the magnetic content of the sediment. It is assumed that fluc- tuations of variables, such as density of sediment, pressure, tempera-

ture of water, together with its content during the acquisition of the

remanence are either very small or else they have a negligible effect on the reinanence intensity. To establish possible fluctuations of the

density of the sediment or of the water content along core V8, samples were weighed, wet and dry and the water content was calculated. All

these three parameters were plotted against the depth, together with

jn normalized per gram of wet and dried mass, all shown in Fig. 5.1.

Sn per gram of dried mass magnifies the fluctuation of the remanence along the core. Below the horizon at 4m an interesting depression is

recognized, which corresponds to an increase in both the dried and wet mass. The water content does not alter along the. 6m core except for

some small variation in the last two meters.

In Chapter 3 it was shown that the pilot samples from core B9 show stable directions with smooth demagnetization curves up to 400 Oe.

Fig. 5.2 illustrates the normalized demagnetization curves of jn, jar and jrs for pilot samples taken along core B9, showing that the magne-

tic carriers are probably of single domain or pseudo single domain LAKE VOLVI-CORE V8

NRM(*Wet,o Dried) Dried mass Wet mass Water content 1jGcrr?gxlO (g) (g) (g) 02 4 6 81012 1 2 3 4 56 7 8 3 4 5 6 .JJIIlIIIIIII. I I I I I I I I &

• 1u

U

• . a-I C)

5

6

Figure 5.1 NTU intensity normalized per wet and dried mass of core YB of Lake Volvi is plotted side by side with the dried, wet mass and. the water content along the core.

Lake Begoritis - Core 09 Lake Begoritis - Core B9 • ••, (AEC.) Demagnetizations . (AEC.] Demagnetizations t &DFOe) ltDF (Oe) 320 NRM 260 NRMo 89-90 200 ARM} 310 ARM Depth 2 1505,M5c m 270 IR+ 202.cm 170 IR4+ 8-90.0-91 .700PDRMo J cm 2

zr.j 3C0 L.3 Sco 0 Zo.. 2CC aw &C IC) (..# 700 IT100 I 6W ,co • . - Peak Field (Oe) Peak Field (Oe) • Lake Begoritis - Core B9 . Lake Begoritis - Core B9 (AF.C.) Demagnetizations (A.F.C.) Demagnetizations 4D F(Oe) ttF(Oe)

: L Depth 3 86cm 17000 IR4+J 296.7cm'pt 11.0 IRM+

CA

• - :- . Peak Fietd(Oc-). •... : Lake Begoritis- Core B9 Lake goritis-CoreB (AF.C.) Demagnetizations (AF.C) Demagnetizations • t4t1F.(Oe) t4D.F.(Oe) • 280 NRM o 280 NRM o 230 ARMA 260 Afl4lT / 170 IRM+ 370.5cm 200 IRM1

Depth372SCM CA 201D0 EIr 007

Peak Field (Oe) . Peak Field (Oe) •

Lake Begoritis - Core B 9 . (EC) Demagnetizations . . . . ,... . . 1D(0e) : . •, . 270 NRM. :. .•. : .- .-.. • - 200 • ...:. •-.. . 240 ARM A Depth 514.5cm •• ..- .. . . . . •, 2201RM+ 09203.692Ol 4, \,,,.r240____ PDR140 Depth00 516.8cm . .

• •. . :-- • .•• . -S • . 00 100 )U tW too we 703 * . Peak Field 100 • . . . .

Figure 5.2 Formalized TRM, ARM, IRM and PDRM curves of pilot specimen taken along core B9 of Lake Begoritis. - 52.

1kg. ARM Ln41 Zo.iO'1 curve £.es c6ove fI%o 19MO na characterf(Lowrie and Fuller, 1971) which is in agreement with the observed mean size of the magnetic crystals (Chapter 2). One could choose any field between 100 and 400 Oe, which would have yielded substantially the same directions.

It seems reasonable that asimilar AF demagnetization level should be used to evaluate the relative palaeointensities. InPig.

5.3 the normalized jn are plotted against the normalized jar for the same P2. It is illustrated clearly that linearity almost exists be- tween the jn and jar except in the low and high AF. To be. consistent with the palaeomagnetic direction data, the relative palaeointensities at AP = 200 Oe should be plotted, however substantially the same results would be obtained by choosing AF anywhere in the range between 100 and

400 Oe. The existing non-linearity in low AF can be explained as the effect of a soft jv. The non-linearity in high AF is due to the fact of the jar imparted with a peak alternating field of only 1,000 Oe. In both cases this can be seen from the intersection of the normalized in and jar. Another way to examine, if there is any linearity between jn and either jar or jrs is to plot their ratios against the AF and see if there is a flat portion of the plotted curve. Fig. 5.4 illustrates the jn/jrs ratio plotted against the P2. It is shown that no flatness occurs indicating that the rapid increase of the ratio reflects the high sensitivity of the jrs to be used as a normalizing parameter.

Similar results have been obtained from core 118 and core Ti • To illustrate all these attempts k, jar, jrs and their ratios with jn are plotted against depth side by side and presented in Fig. 5.5, 5.6 for cores B9 and V8 respectively. In Fig. 5.5 k exhibits three peaks at

180, 250 and 345cm from which it decreases progressively down the core. 15000 47 -

tLS L7000*

: 4vi 50000 Dop!h 202.1cm 42 250.5cm Qi .700e 0.0 I o 02 0.4 0!, 0.8 2.0 0 0.2 ° • ARM Normalised ARM Normalised

250* 49 2500 -- to 111000• o 0-

20000 CLS

0. B9 118 : : : - : 8.7cm troo. Depth 318.6 cm 50000 :

C. CS to o 0.1 CL C6 05 2.0 o 02 Oh ARM Norrnolised ARM Normalised

so 09 A2S01 U 100 Of

lI 20000

E O0i 0$L 9— Clio CLS 3w 00 B070 . B-140 . 03 J -IWO W..6 cm 0. Depth 370.6cm - 02 cc sw 0. 7coO, . I I I I o 0.2 0.4 tO 0 02 Oh 0.6 Cl to ARM Normalised ARM NormaLised

D. O0_ 1 0 fl'2S0. - - Go GA

• Lake Begoritis

0:: Core B /()Do • B-2009 02 Depth 5l4.Scm Z QUO 00 • •. • 0 I I

• 0 0.2 CL 06 01.1.0

ARM Normalised . . .. . . -

Figure 5.3 Noxmalized, IRM intensity plotted against noina1ized. • AIM of pilot samples sampled along core B9.

5 -s • 20 24

20 is N-90 Is 89770 Depth 202J cm Depth 250SCM Ix

203 )CO c0 5.Q SW 103 .9 203 3 103 SW (.10 103 0UO • S. Peak Field (Oo) Peak Field (Oe)

to I Depth 31&6cm L

Peak Field (Oe) -. Peck Field (Oe)

3$ , 2$. • 5•:_ - / • -

21. 21. • S.:

12 to- to 0$/I S07 Peak Field (Oe) Peak Field tOe)

- • - • •.

5. - 2$. - :. • - - S . - • S S • C'_ 241 • 22. • / Lake Begoriis •

Bq - 200 Core Bg Depth cm

0 Ica 200 3CO &W SCO 600 70 Peak Field COo) -

• Figure 5.4 The B/ThM ratio is plotted against the .AP of pilot specimen sampled a€ai.nst B9. .

LAKE VOLVI CORE V6

NRM : k ARM IRM NRM/k N4/ARM NRM/ZRM PO PC/00 0 so 0 30 0 200 0 0 0 1 0 3 • 0 . . . , . . • . ,,..,. I...u.u,.,J.,. , . . .

p ., •.I. S. •. • I So C S .• C . • : • .,' • . NAM ç. .. yrsBR S •: •, • • •.

. . S

46

2 I ) S i,. • • • - - I •. S ••

.••, St

S • • . oo S. ••• •. ) •,•. .•I•I 1 % • SS •, i.:. ••O. •• S N 00 • . • I.... . 5 I ( 0 0 173sSS • .•.• • I' . . . yrsSR 5, :: .. ••I. : / • I), I . S . . (. 4 1 1 % • S 5 ' . S.. •S .s I • • S. •.. S. S - SS . •1 - S I S., '... • %, S • to . 55 • 8 . S..5 S S • .•. t $ • .•. 5 . 55 .S Polish -5 5 . L ?.• • • S S 5 -2000-3000 • • S S .5.

Figure 5.6 The normalizing parameters k; ARM, IBM and their ratios • S S upon NM are plotted, side by side against the depth of • S • 5:... core VS of Lake Yolvi. S LAKE BEGORITIS.CORE B9 ' ..

IRM NRM/k N4/ARM • t4RM/IRM • NRM • k • ARM PO P0/00 P0 pG 0e 3.. 2000 1200 0 ' S 0 3 0 0 1500 90 0 I P V I I I I I • 0 p.,.,., .-,-n,..TvIupluvIug• ' , e - • .. ) . '

uc

00

I — '.• .• .• . 0 0 •.• . j .. 2-

;'6$*6Q yrae s. ' •:

S. S '• •• :.. • S •" . '.2 • .• . •: ' .' . . • • • • . • ç . z . •L :• . . • •: • '3 • '•'•., . . S S • 1., •• • ' • . . s .•• S I•yrss&lots' loSP •

%* . :., • 's '. •' .•. •... : • .'• i'., • •.:. IC> ••S • .• '.s. • •• 00 • ••. • . .. I }I SCOO s 5

• Figure The noiinalizing parameters k, ARM, IBM and their ratios. upon NRM are plotted side by side against the depth of core B9 of Lake Begoritis. , . ,. • . • 53.

Jar exhibits similarly three peaks at 290, 345 and 430cm, from which it decreases progressively down the core. Jrs exhibits two peaks at

180, 345 and below 440cm starts to decrease with depth. The three ratios jri/k, in/jar and jn/jrs exhibit a slow progressive increase up to 510cm, jn/k shows similarities with jn. In Fig. 5.6 k exhibits a slow decrease up to 150cm remaining practically unchanged and a peak at 500cm. The other two ratios show the same pattern with some clear dissimilarities with the jn/k ratio.

5.3 PDRM as a normalization parameter. In Chapter 4 it was shown that PDRM obtained in the laboratory is stable and directly proportional to the applied magnetic fields.

Detailed single sample redeposition experiments were performed along core B9, V8 and TI (Chapter 4). The object of these experiments was to establish whether the ratio jn/jp could produce paiaeointensity geo- magnetic variations. 60g of wet sediment vas sampled every 20cm along

the core and yras11 mixed with BOml of dionized water. From each redepo-

sition lOOml pot a single sample was recovered and measured in the mag-

netometer. The value corresponded to the mean value of two 2 .3cm cube- shaped specimens, which were sampled from the sedimentary horizon from

which the sediment had been collected for redeposition. Pilot samples

from all the cores were subjected to stepwise AF treatment. The normal-

ized demagnetization curves produced are smooth, indicating that jp are

softer than jn, with well grouped directions.

Fig. 5.7 illustrates that jn and jp are linearly pro- porbional to one another through a series of AF demagnetization steps,

so tnat can be used as a normalizing parameter. Fig. 5.8 and 5.9 illus-

trate jn, jp, jn/jp and ks of the naturally and artificially deposited SOO* S009

WO 09 Gas U 10009

V 20000

300 00

- 2000-Depth 318.6 cm _Depth 250.5cm 00 40000 Z Z 2 - 02

. 0D2 Q6 as to 02 U rAb LO

Normalised PDRM Normalised RDRM

ID . __.e .

00 00 10000

Z 200 Ot 10

30000 e-iio 0 B-it.O 5000 2t 10 . / Depth £44.6 cm 0. Depth 370.6 '°°

Oh Oh 02 tO @2 04 Oh 0.0 D 02

NormoUsed PORM . . Normalised P.DRM to SOOO

10000

o.

30000 0h / B9-200 0 Depth 514.5 cm ..

0• api I 02 0* GA 01 ID S S.

• Normalised PORM

Figure 5.7 Normalized. NRM is plotted against normalized. PDRM of redeposited pilot samples taken along core B9 of Lake Begoritia. . LAKE VOLVI CORE V8REDEPOSITIONIN0L

- . KItKA DflOKA .KIDM On DM t,tMf I t/ (r4rr L1III •i%i,4tI . I4flL'I U L_JII9 IILII I

•. ':- io) (0) . (G/Oe) 0203002040 01234.50 10 20 30 I I I I I I

lages Years B.P I 1501 Corr. 1• \ 14C 830 • :- - • . . . 250

2 .2. 800

• U

• .•

3• - 0. 0)

...... . 1200 .

• • • 14C 4 . 1730

• 1700

Pollen 2'-3000

• • Figure 5.8 NRM, PDBM, I'1TM,/PDBM and the ks of the naturally anti - . redeposited samples are plotted side by side against

depth of core V8. . •.. •. •,.• . • • .: .

LAKE BEGORITIS- GREECE CORE B 9

NRM NRM/k NRM/SARM NRM/SrRM NRM/PORM pG pG/Oo

• 02040608010012001 23401230123024 581 - • - 0 iiiiiiiii I I I I • I • I I L I I I I I

1- luc • • \. I-23.h260 - Jjrs&e

2

E \s6O.

LI tic L..5410!70 J yrsB2

5-

Pollan • • 6000yrs BP I •61 IIIIIIIIIIII I I I I I I • I I I I I

-• Figure 5.10 1RM 9 NRM/k, NRM/SARM, NPM/SIRM and. NM/PDRM are plotted • • • side.by side against the depth of core B9 of Lake Begoritie. • • - • •• - • • ;•

LAKE VOLVI - GREECE CORE V8

NRN NAN • NRM NRMc NAM NAN LARM ARM 12000 ' SIRM PORN ,jG.cm.g'x iO 00

A I A 1 fl I 0 0.5 1 0 0.05 0.1 0 4 8 0• '

I

2

:

C

• • .• Figure 5.11 NRM, NRIVT/k, IrRM/SABM, NM/SUM and NRWPDEM are plotted. • • • aide by side against the depth of core V8 of Lake Yolvi. 54. sediments plotted side by side for cores 116, B9 and Ti. The ks show certain similarities and some dissimilarities which are explained by differences in the water content between the natural and artificial samples, ranging up to 10% but also in experimental error which might allow either loss or gain of sediment by sampling not exactly from the depth horizon corresponding in the naturally deposited sample.

All the produced jn/jp ratios are dissimilar to their correspond- ing in curves. They are also dissimilar between representative cores from different lakes, for instance cores B9 and Ti of Lakes Begoritis and Trikhonis respectively. Fig. 5.10 and 5.11 illustrate all the possible ratios which could be obtained as normalizing parameters.

They are plotted against depth side by side with in of cores V8 and

B9 respectively covering 3,000 to 7,000 yr. B.P. Fig. 5.12 illustrates

the European archaeomagnetic intensity curve plotted in parallel with

jn/k, in/jar, in/irs and jn/jp ratios produced from core B9.

5.4 Discussion and conclusions. The detailed experimental work which was performed with the limnic

fresh water deposits from Greece showed that while k, jar, jrs are use-

ful parameters for correlating magnetostratigraphically a number of cores

within a site of a given lake or from site to site in a whole lake, which

is a very rapid inexpensive way for limnological and hydrogeological re- search, none of them is to correct for the different quantities of mag-

netic content contributing in the natural remanence, which is essential

requirement for palaeointensity determination. The reason for which the

normalization parameters are different along the core is because they re-

flect and emphasize variation in magnetic content, its physical state,

its shape and size and the degree of oxidation, with three different ways,

along the length of the sedimentary cores.

NORMALIZED LIMNOMAGNETIC INTENSITY CURVES ARCHAEOMAGNETIC INTENSITY CURVE CZECHOSLOVAKIA LAKE BEGORITIS - GREECE Magnetic ages (after V. Bucha) yr BP .Jn/Jp Jn/Jrs JnIJarx10 Jn/k(Oe) FtIFo Ages - - 1 Z :3 4 5 b 7 U 9 11 1234 ) x1OyraP

1300- 2600- 1

2 3900- 5300- 3 4

Figure 5. 12 Normalized archaeomagnetic intensity curve plotted side by side with normalized in by k, jar, jrs and jp. (Fo is the present day field intensity, whereas Ft is of the past). 55.

The attempt with the new parameter jp appears not to have been successful because the palaeointensity curves produced were not compat- ible with the European archaeomagnetic intensity record. The reason for the disagreement between normalized jn by jp and the archaeomagnetic intensity curve, is either the possible inadequacy of the single sample redeposition slurries technique or that a chemical component acts in parallel or in combination with jp in the form of jcr, in natural condit- ions which cannot be simulated in the laboratory.

For future research%is very importantthe origin and the nature of haematite to be established, because the outcome of this investigation would give light to many problems like the true nature of the magnetic remanence and the acquisition mechanism of it, and probably would help in refining the jp io.malization technique described in this chapter.

Detailed magnetic extractions along sedimentologically homogeneous cores could help to establish the magnetic content itself as a new normaliz- ation parameter.

Another way to approach the problem of normalization is to establish the relationship between the magnetic content and jp. This can be done with redeposition experiments under controlled conditions, by using initially a non-magnetic matrix clay, consisting of known size and shape. natural magnetic grains in which different quantities of known extracted magnetic content can be mixed. The experiments should be performed in

the same applied magnetic field and the strength of the obtained jp should be plotted against the used quantities of the magnetic content. If the

relationship is linear, then the slope of the curve could be used as

another normalization parameter which hopefully could normalize jn. 56.

LIMNOMGI1ETIC PkT,kODThECTIONS

6.1 Dating controls. 6.2 Archaeomagi.etic and liinnomagnetic correlations. 6.3 Correlation of the Greek and British limnomagnetic master curves.

6.4 Discussion and conclusions. 57. 6.1 Dating controls.

Table I lists a suite of radio carbon dates, supplied by Harkness

(Scottish Nuclear Research and Reactor Centre, personal communication) and provisional pollen estimations by Bottema, University of Groningen

(personal communication). The radio carbon dates are in general too old to give the real time controls of the fluctuations of the geomatnetic field recorded in the sediments. This is supported by the pollen analysis of the bottom sediments of the three representative cores V8, B7 and T2, which presuppose a rate of deposition 2-3, 1-1.17 and 1-1.11 mm/yr respectively.

The correction of radio carbon dates into tree ring calendar years was based on McKerrell's conversion tables (McKerrell, 1975).

Radio carbon dates assigned in cores V2, V8, B9, TI, T2, T5, in

Chapter 3 (Fig 3.8, 3.9), 3.10, 3.14, 3.16), Chapter 5 (5.1, 5.5, 5.6,

5.8, 5,9, 5.10, 5.11), Chapter 6 (Fig 6.1, 6.2, 6.6, 6.7, 6.8, 6.9, 6.10), by stratigraphic and palaeomagnetic correlations with cores V, B7, and

T3, in which radio carbon'dates were obtained directly , see (Table I).

6.2 Archaeotnagnetic and litnnomagnetic correlations.

The NRM horizontal and single sample measurements illustrate a remark- able correlation in the three Greek lakes (Chapter 3), however, it is impor-

tant to find out if the palaeodirections show correlation.

Fig. 6.1 shows the NBM inclination, declination, intensity and Q-ratio before and after cleaning in 200 Oe AF. Certain changes in the pattern of

direction of the variations of the geomagnetic field occur; for instance,

the mean NRN inclination was about 700, whereas after cleaning it is about

0 60 for the top 250cm, whichi s closer to the present day value of the axial

geomagnetic dipole at the site, the profound step at 290cm in the NRM,

disappears in the cleaned inclination record. Similarly, the NRN intensity

and Q-ratio are reduced by about 50%. These changes are explained by the

removal of jv soft components during AFC. Similar results have been obtained

after AFC in 200 Oe, with measured samples from the other two lakes.. In additi. TABLE I Radio Carbon Dates

Specimen Lake Core Depth Uncorrected(age) 513C Corrected(age) No. Name No. cm yr. B.P. 8/00 yr. B.P.

SRR-885 Volvi 5 44-80 844±50 -25.6 830 SRR-886 Volvi 5 304-337 1,743±55 -29.4 1,730 SRR-887 Begoritis 7 35-71 2,344±60 -25.4 2,400 SRR-888 Begoritis 7 161-187 3,648±60 -22.2 4,050 SRR-889 Begoritis 7 291-319 5,41070 -34.2 6 9 200 SRR-884 Trikhonis 3 .67-101 2,284±85 -26.8 2,400 SRR-884 Trikhonis 3 249-282 5,089±75 -30.0 5,830 SRR-699 Trikhonis 3 526-559 5,769±90 -26.8 6,600

Provisional Pollen Estimations

Lake Core Depth Estimated (age) Name No. cm yr. B.P.

Volvi 5 bottom .?3. 000 : Begoritis 7 bottom 6-7 1 000 Trilthonis 3 bottom 5-6,600

TABLE II Lake Volvi - Core V2 Depth Magnetic ages cm yr. B.P.

125 150 200 250 260 400 310 800 370 1,200 390 1,300 Core V8

NRM Declination Declination kF.C(2000e) NRM Inclination Inclination A.FC(2000o) • . 400 60° -60° 60° 200 0° 20° 900 0 , i i • ' t i 0. I I I I i

- • • • • •• •S.• • •\• It. . - -T • I 1.1 S 1 1 I4C. • •s•# • . - 844'0 • 4 • • • yrSB.R. • P5 • . • • . • • . • • • • •• 2 2 . 2 f• .. 4.•. __ . •.I • S. I. • . • 5j • S 3-- .P• 3 7 • CL 743t55 at . yrsaP • - .•

sib •••%• 5'• I •, • •• ' -5 5 .t 5 S. 5 'S... S • a.. •• I S.. p • _#•5$ . N I. .• • .• o . • - 6. 6 . . 6's • . . '2000-3000 . -- - - .. - -..,... yrSaR . •.. . • - :- Lake Vo(vi - Greece Core V8

-. Intensity NRM Intensity AF.C(2000e) Q-ratio NRM 0-ratio A.F.C. (2000e) PG 50 pG 20 4 0 2 I I I 0 . $0 I I iO- p.

- - - . •5 . • •• V 14C I 5O yrs. ap

2 2 2 2. : ,0

•1 ,s" ••i • S ,,_ - EIL - . • . • 3 •• . 3 • t•. •.:,... •1 S..., aSs .1I go 14C 1743155 to . "--: . . •-•.• - - :' c'. • 1 .4: a U 5 S.• , 5 4'.. • 5 ' . s..., •-• • .. . •j' • S •• I. •• 'p. a. • . .• . . 5••#55 ••$SS St . S . •., .• . 'a: Pollen 2-30005 . • yrsELP 6 - 6

Figure 6.1 }ffM declination, inclination, intensity and Q-ratio are • • plotted side by side with their cleaned record after • • -. • AFC, against, the depth of core V8 of Lake Vo].vi. 58.

to the reduction of NRM intensity by about 50fo after .AFC, reduction

has been observed during storage in zero-magnetic field up 20-30%

due to partial drying of the samples. Since the azimuthal orientation of the cores is not known the

mean declination for the whole core set to zero and the variations

plotted relative to this arbitrary zero. Fig. 6.1 illustrates the fluctuations of the Earth's field down

core V8, which is a representative example of the rest of the cores, which correlate very well, both palaeomagnetically and stratigraphi- - - cally, by inspecting the same bands and the same changes in the colour down the core. The inclination at the top of core V8 of the cleaned

record is in the range between 56_600 in close agreement with both the

axial dipole field value (-.59 °6') and the present day value of the

geomagnetic inclination in Greece (Chapter 4). - The upper part of Lake Volvi is compared with the archaeomagnetic record, because below 400cm the mean jn makes this part of the record

less reliable for correlation with other records. The correlation is

clear in all cores from Volvi. Fig. 6.2 illustrates the limnomagnetic cleaned declination and

inclination record of Lake Volvi (core V2), showing some similarities

with the archaeomagnetic record. The declination exhibits a broad

and pronounced westerly swing (labelled A) with 20 0 amplitude, followed

by the easterly swing (labelled B) with 15 0 amplitude. Below B two small swings follow (labelled C, D) with amplitude less than 100.

Below D there follows another broad easterly swing (labelled E) in

which archaeomagnetic ages 150, 400, 600,900 and 1,300 yr B.P. are

assigned. The inclination record illustrates four distinct peaks (labelled

• I.. Limnomagnetic Master curves - Greece

.1 Lake Volvi- Core Y2 (•A.F.0 200 Oe) • : Inclination fl Declination (0) • (0)

40 • 50 60 70 W 20 10 0 10 20 E I - • .Years BP. YearsB.R • •. • Magnetic ages - 4U - • • 0 A%I' 150

. • 4f .,c1250 -. •.c 2- •:• - •.:' •400 C) : b.' •0•• 000._ • 0 •b 3 800 •: - •1 -

• • - 'd 1200 • • -14C .'. •-' • • 0 S. - • ••* • 1700 • .• - -. i_t i_i • ______•-

Archueomcignetic - historic curves (N.W.Europe)

Inclination Declination (0) • - 50607080 W 20 10 01020E I I 0 A

b< ,

1000 • 01000 : • :.- .• •

• 2000 • f U I I I I I I I

• • • S • ( After E.&.0.TheUier) (After Ri. Aitken)

• Figure 6.2 Limnomagnetic declination and inclination curves-of core • .• V2 after AFC in 200 Oc plotted, against the depth of the • • - - core and the European (N.W.) archaeoinagnetic declination

• -: and inclination records. 59.

a, b, c and d) which may be compared with features of the archaeo- magnetic record. Hence ages 250 9 700, 800 and 1,200.yr. B.P. are assigned from the archaeornagnetic curve, to the record of core V2. Table II lists all the deduced 'magnetic ages' and the depth to which

they correspond. The limnouiagnetic pattern of the direction of the

geomagnetic field appears to be less sharp in comparison with the

archaeomagnetic one. This is explained by the fact that every 2.3cm

cube-shaped specimen probably needs 3 {Q tOyears to be deposited., whereas the archaeomagnetic record is formed from a series of spot

values each of which was obtained during the short . time taken for a

pot to cool having been taken out from the kiln.

6.3 Correlation of the Greek and British limnomaRnetic master curves. In Chapter 3 it was shown that the obtained pattern of the I'tRM

horizontal intensity of long core measurements of cores collected in

all three Greek lakes, in several sites of them are correlative. Sim-

ilar correlations were observed in the measured magnetic susceptibili- ties of the same cores. However the long core declination data, ob-

tained from the measurements of the cores collected from Lake Begoritis

clearly reveal rotation of the Mackereth core tube during penetration in

the bed of the lake. Pig. 6.3 and 6.4 illustrate the declination and inclination patterns of cores B7, B8 and B9 produced from the measure-

ments of the single samples respectively, in which lines illustrate

the correlation points especially between cores B7 and B8 at any fine

detail. Similarly, the corresponding jn, k and Q-ratio demonstrate

satisfactory correlations (Chapter 3), (Papamarinopoulos, 1977c ]0.

The pattern produced from core B9 appears with shallower inclina-

tion in general, both from the axial geomagnetic dipole field (596')°

- * --- . - • fl •. - - .V

Lake Begontis- Greece NRM Declinations -

-40' 41 ••• . . : •• : . 0- I i i i i • . • • • - • -40' 40 ••• 0 i t s i t • t 40 0 • ': .•', -1'q . 00 I •..• F2344-

- 2-- ••,,. . 14C •••• T s • 3-- :. :I- 3G48

Sc 3 0. % IS 4 .• . . 541017

00 •

Pollen ' • 5 • . • . • •S

5.yrs.aP. .. ..••..... •... •

Core No ®

1BM declination patterns of single sample measurements Figure 6.3 • • ••• • plotted, against the depth of cores B7, B8 and B9. Coreoio i€5 €re c dru€J o o4 k vcQ,10t101 Qco-J

uu %j I • . . - . . . .. I III - Core B8

NRM Declination Declination 200 Oe) NRM Inclination Inclination- AF.(200C 400 -4( 40' 40' 70' 40' 70' 0 . i I - I I 0' * i u i • 0 . S S. • t •. • •• S. S .. • S S . S '.':- St I 4 s•.. . , •5 - 4• . ,• .1 • - •. I . ,•. . ow 5 • . .S S, 5. •: 55 • • - •5 5* • - . .. . ._I ••. . . .. -. ..s • F, lb. 0.1 2 2 2 •. 2 • • .•s... . 4,. . .#• . 55%. •• l% . ...... 5 a .to o0 0 3 3 3 43' 00 .p . OS • .• p SSS.. - G ,• ., • • •. . to ..i. £ . •:.' • ¶1 .

- 6 6 6 6

Lake Begoritis - Greece - Core B8 • ' - Intensity NRM • IntensiyAFC(2000e) Q-ratio NRM a-rctio&F.C(20Oo • . 0 P6 133 0 70 0. 5 0 3 C itit,tjp,ii*C i i * ,0 IC-- i

'5 -.1. ... I $'. I • 1 ?

g o 2 2 .j' 2 3" 2 •ç • --• 5 5 •. •• s. •.• - - • C • .. - ._ 5, •• •. .1. • •• • ••ç - CL

£, 4, • 4:. '1... • • •.:? 55 • . . •• ••4 •.. • S • .- . . . S - - • S • . S . ••• S S L .• . - 5 •• •5 5 • -

6 6

Figure 6.5 - IRM, inclination, declination', intensity and Q-ratio . '- - • are plotted, side by side with their cleaned record after • . . . AFC against the depth of core B9 of Lake Begoritis. M.

and the present day value of geomagnetic inclination at the site of the lake (chapter 4), however it preserves the seine characteristics

as the two other cores. In Fig. 6.5 the NRM and RM after .AFC in 200 Oe, declination and inclination are shown. The records after

cleaning appear slightly scattered especially the top 200cm. The 1IRM

intensity and hence the Q.-ratio are reduced by about 50%, indicating

the removal of soft 'magnetic components. The inclination is charac-

terized with variations over 10 °., which is to be expected as normal,

exhibiting two broad maxima at 250 and 360cm respectively. Fig. 6.6

- and '6.7 illustrate a representative example of correlative single sample measurements of specimens taken, along the collected group of cores from

Lake Trikhonis. They exhibit NEM inclination and declination, together

• with the measurements of them after storage' in éro-magnetic field for

six months and the RM results after AFC in 2000e of single specimen sampled along core T2, are plotted against the depth side by side.

The mean inclination appears to be steeper than the axial geomagnetic

dipole (5707?) and the present day value of the geomagnetic inclination

(Chapter 4) due to tilting of the Mackereth co,'ver. The directions appear slightly scattered, in general, both after storing and PFC. I shows a tendency to become shallower after cleaning.

Fig. 6.8 illustrates the correlation made between the inclination

records of Lake Begoritis (core B9) and Lake Trilthonis (core T3).

Swings b, c and d correspond to those identified with the archaeomag- netic record, but swing a is not observed in the records from. cores

B9 and T3, possibly due to loss of the topmost sediment during coring. Corrected radio carbon dates and pollen estimations are assigned along

the records. Both the records appear with shallower inclinations (see

Chapter 4).

Lake Trikhonis - Greece Core T2 Declinations

I

.- NRM Stored in O-Mcig F1e(d Cleaned in AFC (200'

- -30' 30 -30' 30' -30' ..... .....o 1 0 1 . . • .s • . • - • • • S. • •. • • • I • 1 •.- I 14C I •, . .,.•-: - 1 . • 2284285J.. • - S yrs.B.P. . • • I, . • .1 • • • • --. : - . •. ••, . •. ... .• . S S 2 . 2- 2 - . p I. • •.• 5 •1 1' -' V 1 S .- •••• ,•• .., I .. S 1 •,' . ..: : E - -.,••. , S ..5 3 '.'. S I 14C 3 • • . • 508975 • •• - - . .. • . • yrs.B.P. •• . :0. - S S •' •• • • S S• 0) S - 5. S S • • nfl '. s' • --:. •. . .5. 5 •' 4, 4 •.••'.. 5 S. • •-_ . -.• - : • .• • .\ • • $ •• S S 5 S S SS .- S. • b.' •5 5. • * .5.- % 'S -. . S • •.' , . S 5 • S S ...... S • • - S - S S . •• - S • S • : • 5 • 5-- S .5 .. .. S.., • • % S .5. ' .':' ,.. 5 .: . • , S .5. 5 . •.' 5 5 S. • S S •• ' . S •. . • . • _5 • ' .- - 14C • S .5;. .•-. ,' . •••' , S . 6 6 .5 . 5 . .. '• .'.- -:: • •-. S -. Poll ent5OOO6GOQL 5- . :.- yrs. aP. S S..... S

. NW declination variation plotted together with its • Figure 6.6 S record after six months storage in zero magnetic field. and after AFC side by side against the depth, of core T2.

- S • - _•_••5_ - .5 5-

V .• - . V V

- - --

Luke Trikhonis - Greece

V V Core T2 IndlinationS

- . L_-. . . . V •. -. V

NRM Stored in 0-Mag Field Cleaned in AFC (20( 80 56 80 50 iO— I 0. I . V S . V ...• ••• ., • . S • V. .V - - .$ . V - • • S.. •• S • V VV • •- VV: .• • V •.: .1 . V % .- V 22 4 1 V - B5 yrS,.' . . e s • •. . • .: 8 • . . 00 V• . •' • - • - V V V S •• V V V . S -- - V• • lq S • V •; V 2 ....•'' 2 2 V,555•' .•. ••j • V V•• •SS• - • V - - •S . • S V , •.•.

V V , : •: : ' . ' - :••' . ••'': -• . . 4C S V • . • •,.• • - 3 5C 89 T 3 3 • ' • yrB.P • . c 5.•.: . •, : • •, V • V5 • t5 .•S . 5 s • 0. 0) •. •V 10 S V V 5 V • • •4I •:'• 4 4 . - - V - - . • • l•_ V - go 0 V •% . S .• V • •V • • • S 55 if V V - • - •I.• . •1 I... . - • V •,•• : S 5 600 • 5 ' • •• V V . S .••• •• S 0000S :• . • • 5S • :: . . . . V V. •S • S • S VVV •.. V - •S • •SS•. V V V V . . • 3 . • S S 4C ••• D •S V 569±90 1' • • V ys.B.P. 6.L • S p V V V V . V.. • P11:50006600•• . - - :. -. V• .. : yrs. BP

V V V NW inclination variation plotted, together with its Figure 6.7 six months storage in zero magnetic field. • .• . record after and after AFC side by side against the depth-of co reT2. V

- V -- ...... -... --...... VVV ...... - -----. V

61.

The observed lower inclinations at f, g and h are lower in B9

than in T3, most probably due to the bending of the core tube at 230cm.

Fig. 6.8 illustrates how the rate of deposition may either

exaggerate or reduce the particularly fine details of the fossilized

signature of the geomagnetic field. variations. The mean inclinations

appear to be shallower than both the axial geomagnetic dipole field

at the sites (59 06 1 , 577 1 ) at Begoritis and Trikhonis respectively

- and the present day value of the geomagnetic field at the sites of the lakes (chapter 4). In Fig. 6.10the established pattern of the swings with a period

of up to 2,800 years from Lake Windermere (England.) in parallel with the declination pattern from Lake Trikhonis (Greece) core T5 can be seen.

Swings (labelled A to E) are clear in both records. Swing A is bigger

in Windermere C is bigger in Trikhonis, whereas B, D and E are about the sane. The peaks of the swings appear relatively in the sane chron-

ological order. At the left-hand side of Fig. 6.9, corrected radio carbon ages are assigned according to published data for Windethere (Mackereth, 1971; Creer et al, 1972; Thompson, 1973). The magnetic

age of 150 yr. B.P. has been assigned for swing A from the correlation

of the declination pattern with the British archaeomagnetic record.

In Fig. 6.9 the inclination pattern of the same cores is shown. At the left-hand side of the Figure, the magnetic and radio carbon ages

are assigned, as in the declination record. The inclinations of both the records correlate reasonably well between the depths of tY\CiQ.

swings c and e, they do not correlate between b and c, whereas

above b the Windermere record does not show any - detail. In both cases similar swings are indicated by correlation lines. U • • •• 12400 I ISO.

2 0 .

2 0 481 ~0, ASH $.$v• .c3 CL 0) 0 4 • • • 4

5 - •• 0 5 • 15600 0 : 6 Inctincition

- - - Windermere Trikhonis -- England Greece 4Cr 50° 60° 70° 80° * 0 i 'i 30 40 50 60 70 Magnetic ages 0 .'.. , years BP 150 -© -"'

l4Ccorrected S years B.P.P •.• 14C : 2400yr 1300 •

• • S . • C 5• 2600 .©.....,.o 2 0400

0

3900 2 . 3 •' 5300

6900

6600 000 BR 9600

......

4 - • : . ..

Figure 6.9 Inclination correlation between Lake Trikhonis (Greece) and Lake Windermere (England.). . .. . Declination

- - - Windermere Trikhonis -- En g land. Greece coaT'(j 50° W 0 E50' -- - 0 ' Magnetic ages ' 50' 0 - - sd' -. - - years B.9 •., 0 1— r - .- i • - 150 _®_*_ - __.® 14 C ------l4Ccorrected • s• - - t• years B.F? - 1- 2400yrsBE . . . - lit 1300 __ •, __- - . - -- V• V • - - . .1 V . 2 • - - - . - :- -- -V - - -: 2600- - . V •.

- • V V V- . - - - - - - 3900 '-' - 4- - • 1 CL 2• - - -. • 5 300- E

- ' pollen 6900 , t :• 5000 -- -. -: - •:. 6• 6600yrs BJ - m -.. . - - 8200 3- ® ••• -

9600 '.•

--V -. -..- . • - - - -- . - --. . -. - -, - 4. - : -- - •. - m -

Figure 6.10 Declination correlation between Lake Trikhonis (Greece) -. and Lake V(ind.eriuere (Ragland).. 62.

6.4 Discussion and conclusions. The limnic fresh water deposits in Greece have preserved the fos-

silized record of the geomagnetic declination and inclination variations

during the last 2-3,000 years (14C and pollen) in Lake Volvi, and the

last 6-7,000years (14c and pollen) in Lakes Begoritis and Trikhonis.

The geomagnetic declination and inclination recorded in the limnic de-

posits in Volviechibit features which correlate with both the archaeo-

magnetic pattern of the NW European record (Readman and Papmarinopoulos, 1976; Papainarinopoulos, 1978a) and with individual limnomagnetic curves - from central Europe (Creer et al, 1978) with approximately the same amplitude. The inclination pattern appears to be oscillatory but aper-

iodic, whereas the declination pattern exhibits cyclic shifts of 20 ° -30°

amplitude. The limnomagnetic declination recorded. in Begoritis are not

correlative with the corresponding one of Lake Trikhonis due to distor-

tion of the picture of the first due to rotation of the core tube,

whereas the inclinations recorded in the sediments of both the lakes

are correlative. In addition to this the limnomagnetic declination

pattern obtained. from Lake Trikhonis illustrates cyclic shifts with period approximately 2,700 years and it is correlative with the declina-

tion recorded in Windermere (England), whereas the inclination record appears to be oscillatory and aperiodic but reasonably correlative with

Windermere's corresponding inclination record and the various central

European records. The pollen estimations are consistent with these correlations, ((*Tz) whereas the 14C dates are generally about - years too old. The source which left its magnetic signature at Trikhonis could be either

the main geomagnetic dipole or the non-dipole. The first explanation

would require sinusoidal inclination variations in the Greek and British 63. record, which is clearly not the case.

The second explanation is more plausible as the compelling mechanism, for the recorded geomagnetic secular variation at Trikhonis in the form of two A-H dipoles (Alidredge and Hurwitz (1964), Creer (1977), Hogg (1978))\ which are closer to the European terrain. Fresh data from Windermere

illustrate better and clearer correlation both with the Trikhonis inclin-

ation record and other inclination records from British lakes (Turner, personal communication; Turner and Thompson, 1978), and with the British

and European archaeomagnetic record. 64.

SPE0MAGI]ETISM

7.1 Introduction. 7.2 Petralona Cave.

7.3 Palaeomagnetic sampling. 7.4 Palaeomagnetic results. 7.5 The nature of remanence. 7.6 Discussion and conclusions. 7.7 Arago Cave. 7.8 Palaeomagnetic results.

7.9 Discussion and conclusions. 7.10 Ball's cavern. 7.11 AF demagnetization. 7.12 Presentation of palaeomagnetic data. 7.13 Discussion and conclusions. 65.

7.1 Introduction. This seventh part of the thesis describes the investigation of the author in series of cave sediments, with the hope to get the re- cord of the fossilized geomagnetic field., the origin of the mechanism of the acquisition of the observed remanence, its characteristics and the nature of the magnetic carriers. Cave sediments contain, in general cases, archaeological arti-

facts and palaeontological remains, which can give chronostratigraph-

ical controls together with results from established dating techniques

either in the geological material or in the bone pieces. Reversely, when the magneto stratigraphy is established, it can be used for da-

ting the speleothems or other animal remains. The recovery of the record of the palaeointensity and palaeod.irection of the geomagnetic

field has relied over the last decades on historical records, ancient

kilns, hearths and pottery, for example (Thellier and Thellier, 1959;

Burlatskaya, Nechaeva and Petrova, 1965; Aitken and Weaver, 1965;

Bucha, 1967; Kitazawa and Kobayashi, 1968; Bucha et a]., 1970; Aitken, 1970; Hirooka, 1971; Aitken, 1974; Kobacheva and Veliovich, 1977). It is clear that a serial record cannot be obtained from such a data,

because civilizations had always interruptions intervals and were not

suitably distributed around the globe at any one epoch. An answer to

the problem was the liinnic and cave deposits. The advance of the re-

searchers using limnic sediments as recorders of the, geomagnetic field

havebeen described already in chapter 3. Pioneer research work started. by Kopper and Creer (1973), Creer

and Kopper (1974), Creer and Kopper (1976), who used a variety of Mediterranean cave deposits for palaeomagnetic work. Cave deposits

are characterized by Kukla and Lozek (1957) in two categories: 66.

a) entrance, and b) interior facies. Entrance facies deposits often

contain dateable artifacts or palaeoanthropological and palaeontolo-

gical remains and they record climatic cycles (Sweeting, 1973). They

record cave-wide cycles of erosion, clastic deposition, sta1anitic

formation, calcite-resolution and erosion, together with the magnetic

signature of the field (Creer and Kopper, 1976). They provide sedi-

mentation rates,,-including hiatus and removal episodes with values

- from 0.25 to 1.0 rrim/y -r over the past 50,000 years in the Mediterranean region (Kopper, .1972). Interior facies sediments, on the other hand,

are beyond the reach of surface weathering and accumulate or disperse

only under hydrological controls (Reams, 1972). They are characterized

- by low sedimentation rates, uniform temperatures, high humidities (85-

100%) and a sparse and unique biota (Kopper, 1975). The biomass in

one deep cave zone having been estimated at 20-309.ha (Kopper, .1975).

Clays predominate and sometimes occur in bands with silts and sands

suggesting that sedimentation was controlled by annual or possibly

longer period precipitation cycles (Kopper, 1975). Creer and Kopper . (1976) have shown that Mediterranean cave sediments have recorded geo- magnetic cyclic shifts • For example the palaeomagnetic record for a

2.4m section of interior facies sediments from the Upper Dry Cave,

Jeita, Lebanon, reveals inclination oscillations, which can be corre- lated with those recorded. I ,000Km away in core 1474 from the Black Sea.

The 'magnetic' ages so obtained for the Jeita section are consistent

with the age (0-16,000 yr B.P.) deduced from anthropological and palaeo-

climatic evidence. At Tito Bastillo, Ribad.esella, Asturias, Spain, a

0.54m section was dated palaeomagnetically by Creer and Kopper (1974). The magnetic ages of 11,200-11 ,660 yr B.P. were obtained by correla-

tion. with the limnomagnetic record of Lake Windermere, England. In 67. this way the polychrome famous paintings of this Upper palaeolithic cave were dated independently of stylistic comparison or the radio metric 14C method. At Arbreda Cave, Spain, a 3.4m section from entrance facies sediments with 35,000-50,000 yr B.P. deduced from anthropological and palaeocliinatic controls, gave an abnormally low inclination, which may correlate with a geomaietic excursion reported in an Indian Ocean core at about 40,000 yr B.P.

At Hermit's Cave, Catalonia, Spain, a 1.1m section belonging to the middle palaeolithic, the palaeomagnetic record exhibits large amp- litude swings. In this part of the thesis the palaeomagnetic record. of Petralona Cave, Greece, Arago Cave, Prance and Ball's Cave, U.S.A. is presented and discuèsed in connection with the nature of the reman- ence and the nature of the magnetic carriers locked in the sediments of these caves.

7.2 Petralon.a Cave. Pig. 7.1 illustrates the caves with archaeological interest which were the object of investigation and exploration by Kopper and the author. Extensive work has been done in Prachthi Cave in Pelogenese, but the results are not satisfactory due to the disturbed sediments found in the cave, however another extensive work performed in Petralona 0 cave, located near Petralona village (40011N, 25 3':E)in Chalkidiki peninsula in Northern Greece. The reason of the palaeomagnetic inves- tigation was to date, if possible, the 450cm exposed section within the cave by Poulianos (Poulianos, 1971) containing interesting remains of palaeoanthropological and palaeontological origin. In addition to this, by establishing the magnetostratigraphy, hopefully the recovery

of the BrunlhesMatuyama - geomagnetic reversal, occured 700,000 yr 0 • Greek Archaeological cave sites

Th SI 1' —1

PeP 4rdonaVe

0 kastritscl °Kokinornitc O.Apfchu(ikO

Aegean -

Kits- - - ' Cave

o\ Frachthi Cav0 • a

- -..----

0'

I -

Ot• I I I I Kilometres Crete.

Figure 7.1 Map of Greece with the .main caves with palaeoanthropol- ogical and archaeological interest. •. - 68.

B.P. could be obtained. According to Poulianos (personal communication;

1 978), the bottom layer of the section correlates stratigraphically to the layer in which the cranium was found. If this hypothesis was cor- rect the palaeoinagnetic age would help dating this layer, but not nec- essarily the cranium, shown in Plate 7.1, which was discovered by a local farmer C. Sarianidis in 1960 (Poulianos, 1971) a year after the discovery of the cave in 1959 by another farmer. Poulianos (1971) reported the existence of other anthropological remains relative to the cranium. Fig. 7.2 illustrates the 2Km V-shaped cave situated under- neath the Katsika mountain (642m). The valley in which Katsika mountain lies is 290m above sea-level,

and coincides with the first floor of the cave. The V-shaped cave con-

sists of two elongated corridors which communicate into small or large

chambers of 8-10m height, occasionally with 50m deep precipices. The

floor of the cave is composed of flat, rough travertine layers. The

walls of the cave are covered with layers of red and white stalagmite.

The natural entrance is 170m. N-NE of the artificial entrance, as Fig. 7.2 shows. Petrohelos (1960) first explored the cave speleologically

and constructed the first profile in 1964 9 Kokkoros and Kanellis (1960) identified that the human skull was Homo Nead.erthalensis, Kanellis and

Savvas (1964) agreed, by measuring craniometric indexes. Sickenberg

(1964) studied the palaeontological remains and identified them as be-

longing to the Pleistocene era. Marinos et al (1964) completed

Sickenberg's investigation by finding more palaeontological remains.

They also found human remains like teeth, together with primitive tools.

Poulianos estimated that the section exposed. in 1968 belonged in the

mid-Upper Pleistocene (Courten and Poulianos, 1978). His detailed

study of the craniometric indexes led him to interpret the cranium as Plate 7.1 The fossilized cranium found in Petralona Cave.

PROFILE OF PET R A LO N A C AV E Strata of Urn. Sp.teo- chamber, and corridors

• 007..

350------ z__tfin 345 - __-_-..

r4 a 13 0180 9 283.80

Isohqlghts In meters 325-- Ursus uman

Natural too S2 humai eett 110 Entrance 2990 V-1 2940

Excavat Section - -- 310------ - Artificial J-13-Sites of accumulated fossilised bones hole 1P Entrance 300m above sea-level Depths: above sea-level. • - /' •_ , 300' Source: Greek Speleological Society (After I. Petrohetos) Completion: University of Thessaloniki 0 10 20 30 40 50 60 70 80 90 100 0 (After G.Marinos et at) f •V t 0 Excavated :Greek Anthropological (Motors): Section Society (At ter A.PoutianOS)

Figure 7.2 The profile of Petralona cave. 69. a Homo Erectus which Kokkoros and Kaneflis (1960) concluded to be Neanderthal, consequently any direct or indirect time controls were necessary to approach and hopefully solve the existing controversy.

7.3 Palaeomagnetic sampling. In Fig. 7.3 a schematic representation of the excavated site is shown. The natural former sinkhole entrance, which was a death trap for the animals, was gradually filled up with water transported sedi- ments. The excavated section shown in Fig. 7.4 illustrates the strati- graphy of sediments reflecting the climate and human and animal acti- vities. Breccia in the top layers from triangular small and big stones and occasional very thin travertine layers, did not allow us to get oriented 2.3cm cylindrical samples, which were collected from the moist soft red and brown layers using the orientational device shown in Fig.

7.5, which measures the azimuth and the dip of the cylindrical axis. Samples were pushed out into the plastic containers with a piston.

The sample depths recorded. in Fig. 7.4 were measured by means of a tape placed at the top of the stalanitic column. Duplicate samples were collected at same horizons.

7.4 Palaeomagnetic results. The 120 samples were measured with the spinner magnetometer, they were then stored in zero-magnetic field for 6 months. In the meantime

samples 371, 322, 272, 561, 81 and 731 were subjected to AF. In Fig-7.6

the normalized jn demagnetization curves are plotted and their directions

are shown stereographically. The normalized demagnetization curves

fall smoothly as the AT increased. The directions show good group- ings up to 300 Oe. A peak field of 100 Oe was chosen for the AT of the

FORMER Schematic • SINKHOLE ENTRANCE • '.• Repesntatio

SIDE VIEW . V y : •, -: SEDIMENT .. ) CONE OF . DEPOSIT .,). EXCAVATION

.•.•• 97 • :.. . . .• . - • : : ••'' ....:.,:.. FtJSSI L •:.:...... :..... •• • • ...e .s.: • . . : . • . 100 rr .• • • • • • • • : : : • • • — :

Figure Schematic cross-section of the excavated section and • •• •: : • . S 7.3

• •.• the site of the fossil. .. .. . • • •

• S • .5 S •' \

V

(?1300000 Intensity . Susceptibility . 0k-Ratio • : PG/00 00 650CC 0 600 70 0 2. 1111.11 4111111: 1 0 T . S •5 • .• S • S 0 0

. . .. •• _.• •. • . S S . . • . S• ••S •••• S . •• • . S . 5 . S • II . •. . . .1: • 0 •. • • S • S I S ...... I • 5 . . 0 U/Th . •• •t. .-. • ....,. _.90000•_ : :. •. . . •. . •0 • •••.• yrsBi? . . • 0 . .

.... . S 0 . S. -S S • 0• . i. •• . i 0o •5 . % l . S. . 00 S . •. I: • 0 : • SI, •.. ..: S • S S • . $ ...... • 51 • .'' e • •• •. H S. . 55•5 • • • •J• •. . S • . .'•• . . . • I S 5 • . • S •. •. S . .5 • . •0 ••S S . . . S .1 • . • ••••• 4 . . .

0 (iced)-oarth lays M 15 Stalagmitic material. Breccia • Terra rossa . PetraLona Cave-Greece. . Argil Excavated section (After A.Poulianos) L'sa. Ashes? Animal & human bones & teeth V al Im l Q m o nts of stone A bone

Figure 7.4 The excavated section and the logs of NRM intensity,., . magnetic susceptibility and Q.-ratio plotted side by • • S aide. • • . . . .

• $peleomciçjnetic orienfcltiQflQt sctmpl.er

Aluminium Spirit Levels in right angles frame-7 / coinciding with the axes - of the compass / Flexible rotating . . .. .perspex plane . . • Compass

N Axes compass • Magnetic needle

• Slot coinciding

• with the axis S • of the compass

• ..: . Protractor • Window

4—Sampler. S

• • .

•:'

. Piston S NSedimentary . sample / . Mark produced

• :. • • S // along the slot / coinciding with the

• . .• S . •• mark of the sample • . . holder. .

S .. • Marked sample holder

Figure 7.5 Orientational sampler for collecting samples along • moist core sediments. • 10. 0 Pet 56* 10t Pet 272 Depth 242.0cm Co- Depth 3230cm

,,,O6 Jos12.73jO .100 Jo:1L.OSPG .2S 10. CL CL ND.EI\ Pet 322 ISOOcI \•%% 02 - o2t*0r\.S.% I 061 \ .Jo:7.31iG 3D0 L03 SCO 100 200 303 LCO ¶C) ° 100 200 Peale Field (Oct OL - Peak fit' d tOe) • j!Do 9e \ .

• 100 2-3) 30 3 500 - -- - Peak Field (Oct : . •1 •• S000e

.sa .-...

- V• V 10i. 101. Pet of Pet 73* V Depth 3400cm -- 08 oej \ Cepth 3560n -05' \JQ16Vl5J..G Ji.o !3o:765iG Jlio CL 0LIt4OI". • V \ Pet 371 MOE CS Depth 166.0cm •_. o4 00 CS 103 Icr) 3L3)5C • .V Q It MDF V V

V ISO • 02 - : •-..-_. V • V V V to 7o3 3:3 L03 500 V • PCQ7,t Field (Oct scoo • -

s50000

JEouh ut > W(- o 00 3 ) V V Normalized NIM demagnetization curves and. stereographic Figure0 7.6 projections of their directions of individual pilot V V V samples, taken along the Petralona section. 70. bulk of the samples. The deposits of Petralona cave possess a stable remanence. Poulianos' thesis was based on the observation of many palaeontological finds belonging to the Pleistocene epoch and in re- cent dating of the top stalagmite column, which gave two dates of

260,000 and 300,000 yr B.P. (nceya, 1977; Schwarcz, 1977), respect- ively. The latter are not considered reliable in the first, case, because the method of the electron para.magnetic resonance used requires the rate of growth of stalagmite to be known and that it remains con- stant during its formation. It also presupposes known background ra- diation. In the second case, the uranium content was found. very low

(Liritzis, personal communication). The new u/Th dates which were obtained, the first from the top stalagmite, gave an age of 65,000 yr

B.P. and the second., from a travertine layer located at 185cm, gave

90 9000 yr B.P. (Schwarcz ,et al, 1978) shown in Fig. 7.4. In Fig. 7.7 the NRvT inclination together with those after storage in zero-magnetic field and after .AFC are plotted against the depth of the section. In

Fig. 7.8 similarly the declination log is shown. Both logs appear to be scattered and they do not show any significant improvement after

AFC. The presented palaeomagnetic data show that no evidence of the

Brunhes.Matuyama geomagnetic reversal is present. Taking into account the estimated rate of deposition to be 50,000 yr/rn, (Kopper, personal communication) together with the u/Th dates, it is conceivable that the deposits span an age approximately 200,000 years. Another major point of Poulianos' thesis is the existence of ashes within the studied sec- tion (Poulianos, 1971, 1977). One would expect that jn and k would be clear indicators of the ash remains mixed with sediments. As Fig. 7.4 shows the first peak at approximately 80cm coincides with the layer

containing ashes (Poulianos, 1971) whereas the second peak at 330cm is

PETRALONA CAVE- GREECE

Inclinations

NRM Stored in 0-Mcig.Fietd Cleaned in A.F.C(10OOe) 30 801 30 8C 0 ' 0 I I I I I

40 • . . - S - • S • V --V . V S S • • • S •. • . •. S • S -- ••• S. S •S . S . S • 5 • • S 1 • 1- •• • : '• : ::'. . •. 0.

- • . • U/rh , • 5 S • - 90000 • • •., • • . ,yrsBi? : •• 2 2- V _ 2

E V ___ 5S S • S • • . . S V S - S S V •S S CL • -V . S S •• S. S • 5 3 • 55 V 3 - 3 •5 • S .: - S •• . S • • . % . .5 5 . S • 5 5 •5 - • S 5 V S - V 0% V S • V • • •• • • • S S• • V V S • S S • •• 5 V S S V V S S _V_V S • - • - V •• 4 - 4• • - 41 - . • • V •. . .

V V V Figure 77 IM inclination logs plotted together with their values V V after storage in zero-magnetic field and after AFC in V -: - 100Cc. V V V

PETRALONA CAVE- GREECE

DecLinations

NRM - Stored in0-Mcig.Field Cleaned in AFC (l000e) _60h1 6cr 6b' -60' 6(1 0 I I I I I I I I I I 0 I I I I I I I - I I I I 0 • • . --- . • . . S S. • •• • . • . • • . • . • . •

• • S

• - . S • . S - S •- S • • S S S S S • .• . • 5 • . •5 . . S • S • • S • S. . • . S • 55 5 S. S •5 - 5• S S.

fl/TI-. _ S 'lS III S. •• oo too -90000 • • • e• 4__ - S... S • •• yrsBP . .• .. 2- 2• .

• • • S • S S -4—. S CL S • S S

Ca • S - . S • ._ . S S S S 55 S • S S. S S. • % • S • S S •5 •• S •• S S S • • S • • •. S -----S

4- S S S

51 I 51 - I

Figure 7.8 }11M declinations plotted side by side with their values - after storage in zero-magnetic field and after AFC in -- 1000e. . - - - - • - 71. is 10-15cm higher than the layer with the ashes. Liritzis (personal communication) attempted to characterize burnt and unburnt soil from these layers by using thermoluminescence but the glow curves produced by the' soil overmasked the glow curves of the feldspar and quartz at

350 and 365°C.

7.5 The nature of the remanence. To test if jp could be accounted for the mechanism of acquisition a redeposition experiment was performed and six samples were, sampled in the way described in Chapter 4. The geomagnetic field measured on = 750, the spot of the experiment was (F 0.38 Oe, I D = o°). It lasted seven days. At the end of the second day, 2cm of water was siphoned from the top, then the tap of the settling tank was opened to allow a slow drainage of the water during the next five days. On the last day of the experiment the volume of the slurry had been re- duced by 50%. Table I illustrates the obtained results of the mean values of the measured parameters.

TABLE I

jp jpa k kpa Q. Wa (pa) (iG.cm3 .9x10) ()iG/Oe) (G.cm3 .g.0ex10) (0.e) (g) 9.80±0.30 1.06±0.03 3.60±0.30 3.91±0.07 0.27±0.01 9.21±0.09

'I o A95 K R N (0) (0) (0) (0)

3.5 73.2 1.8 6.9 93.4 5.94648 6

Fig. 7.9 illustrates AFC of a representative redeposited sample, which shows smooth demagnetization curve with MDF = 120 Oe and satisfactory

grouped directions.

72.

7.6 Discussion and conclusions. The deposits of Petralona cave possess a stable remanence as the

.AFC showed and they are probably of PDRM origin as the redeposition

experiment demonstrated. They contain fine grained haematite and mag-

netite with Hcr45O Oe, as the reversed jrs studies showed. The scat- tered.inclinations due to possibly disturbed sediments showed no nega-

tive values after .AFC which means that the earth's magnetic field had

rlozTnal polarity up to 410cm depth. Taking into account the U/Th offered

dates and the estimated rate of deposition 50,000 yr/rn, the total time

span of. the 450cm section is estimated to be 200,000 years. The existence of a large variety of palaeontological remains within the

layers of the section clearly of the Pleistocene period does not neces-

sarily rule out the possibility that the age of these remains cannot

be less than 100,000-200,000 years because it is generally assumed that

the animals of the Pleistocene had a progressive extinction up to

50,000 years. The dating techniques on bones like the epimerization

of amino acids, 14C of the new advanced type and thermoluminescence,

could help to characterize all these remains. The lithotechnic speleo-

thems clearly demonstrate activity of the occupants of the cave,, how-

ever, they are vague indicators of the age in which they were used.

The susceptibility peaks are indicative towards the ashes hypothesis,

however only optical and electron scanning microscopy for fused mat-

erial sampled exactly from the horizons with the supposed ashes mixed

with soil could be the direct proof (t'lckerrell, personal coinmunica-

t ion) . 73.

7.7 Arao cave. Arago cave is located. (42 082 1 N, 2'851E) near the town of Tautavel in France, 19Km north-west of Perpignan, Pyrenees Orientales, France. It is one of the most important Palaeolithic,archaeological and an- thropological sites in airope, containing the partial remains of at least three early Homo Sapiens (Preneand.erthal) who lived in the cave

300,000 yr B.P. Evidence of lengthy human occupation in the form of stone tools (Archaic Tayacien) and the bones of hunted animals occur as layers in the entrance facies deposit of the cave. These layers are well dated by lower Palaeolithic standards providing cultural- stratigraphic and bio-stratigraphic controls for the sediment samples through the upper 240cm of the excavation. In Fig. 7.10 the cave plan and the stratigraphy of the excavated section are shown. It contains, in addition to the other controls, chronostratigraphic controls, pro- viaed by uranium disequilibrium series dating of the upper travertine at 95,000 yr B.P. 10,000 yr (Tuxekian and Nelson, 1976) and emer- ization of amino-acids dating technique of bone in the Sol F layer at

220,000 yr B.P. and Sol G at 320,000 yr B.P. (Bada and Masters Helfman,

1976). The cave lies more than lOOm above the Verd.ouble River in the flank of a bare, heavily Karsted ridge. The cave cannot be dated mor- phologically, but the fill of travertines, wind deposited sand and silty sand have been assigned to the Hiss I and Hiss III glacial stades of the penultimate glacial period of the Alpine sequence (Miskovsky,

1976). Several palaeosols have been identified and other alterations of the soft sediments have occurred due to prolonged exposure to wea-

thering in the layer open cave mouth. One of these weathering effects

under dry hot conditions was the formation of several zones containing

high concentrations of Fe.

VV V V V - V V V V •V V V V•

V -. •V V - -V • V•V V V VS V V • •:- / ..-.

V V•

V VV V CAUNE DE LARAGO V V I TAUTAVEL I PROVENCE .

V V .-• V -STRATIGRAPHY

3- 4er Breccia 951000Th/U GAVE PLAN V V V V 4 Zone of a -ral- ion. 5 high FeMn J V

6 Pateosot F vo 220000 BP AA I ..:p.::.. J '7 •. "O\:-. - rmeoso

V V - V V V

V

8 V 0 V 9V VIEW 2700 • -• meters V • V PaLeosotF

V •• • V -. - V

-.-'aeotian sand G)7 eCD

V V V_V VIEW 00 V V

Figure 7.10 Stratigrathy of the sepled section and the plan of Ara€o Cave in which palaeoanthropological fossils were

V

• LARAGO CAVE-FRANCE : ••

NRM H Declination Inclination Intensity . Susceptibility QRatio • pG/Oe ..• '. Oe is o • 2 0' los 0 _15 11151$-I -I •4d' 40' 0 -4 O s-i_II_III_111111_i 0- iii_iii_ 0 I % 95000yrsBR •' . • .•' . • , • U/Th • e I , I •. I I • • •' • : , . 1. .' . I I • •,I - I •• • S .. .. S • . . SI . • I • S. S • •• . S S. I • •• S. • 5• • . S S S I • • •• S S •I •. I. • . •i I.. 1. . 1 •.. :• i 1 , . • S • 5 1 • • S • I, • • I S •S • gI I ,? .5 . • S S • 's •• • . .' , . I. . # 4 •'l • • S I •S• •5, • •S •• • • • • CL I:. • •S •' S • C) • ' •• . • . . • • •',. • 2 2 • • 21 • 2• • • 2 • I. • •. . I $ . S '5 S 'S • . %. • . • • • • •.• S • • \ • S SI •. • • . I •' •. ,• - . . ••• I

• .. . . • • • • • •. •1' • : • •.,. 31 • • 31. 3 3 3.

• Figure 7.11 ?RM declination, inclination, intensity, susceptibility . and Q-ratio logs plotted side by aide against the depth • • of the sampled section.

AraS - - Am 16 •OB. Depth 1&Ocm Depth L.8cni Jo = 7.23pG Jo: 10.35 pG 06 J/JO •_MiiF.:900 CkI.

• :

1 t I I Ii I I I I 100 203 300 L00 500 100 203 330 40 500 Peck Field(Oe) Peck Field tOe)

• N

• ______ .-4JRM I • till,' III. t it .5000.It E j'500Oe C

S - -

• • • - -..

Ara 2C -. Depth 67.2cm • Depth 92Lcm Jo:5.3Sj.iG '. Jo:6.2j.iG - CS :90 C. 05 • •• Jfj jKOF =900* .

:.

•

. , - , 100 203 3,j3 403 500 ICO 203 3) £00 500 Peck Field tOe) - • Peck Field tOe)

N N

SOOOO

Figure 7.12a IRM nomalized de.aetization curves and stereogratihic

- projections of their direction of ir.d.ivid.ua.1 pilot -. • saiples collected along the excavated section. :

-.------... ---.---..--.

•tO Ara 42 - tO • 1\ Depth 117.6cm Ara60 • . \ Jo:6.OlpG •\ Depth 168.0cm 06 \t.tD.E=8000 Jo:7.42pG =700e -OL I. We • I •.....•. W. 02 I I -I - O.2• I I I t I I 100 200 300 LOU 500 , I Peak Field (Oe) 100 200 300 WO 500 Peck Field (Oe)

N

10 10 Ara85 Am71 08- Depth 2352cm - Depth 151.8cm - cc Jo:7.51j.3 Jo:5.683. G ,06 I oF.=eooe \.tDF 7O0e • - tio • 06 M •-: r -- ;; _ II I I I 100 200 300 LOU 500 100 233 333 403 SCO A Peck Fie' d (Oe) Peck Fie'd (Oe) _4•. . . _N---- ..

MM 4 S. ... • •1111I1; I -11111117 I E j) 5000e

Figure 7.12b IM oralized deaetization cues and stereographic projections of their direction of individual pilot sles collected along the excavated section. • ......

74.

7.6 Palaeomagnetic results.

Approximately 86 square-shaped 2.3cm samples were collected by

Kopper, by pushing 0.50cm rectangular containers, in which empty

0 sample-holders had been placed tightly covering the space of the steel

container. The logs of inclination and declination are presented in

Fig. 7.11. No geomagnetic reversals are present. The susceptibilities are low and the remanence appears to be unstable with MDPs between

70-100 Ce, as it is shown in Fig. 7.12 (a, b), which represents the

group of the demagnetization curves. A viscous component is present

causing the directions to change as Fig. 7.12 (a, b) clearly show.

7.9 Discussion and conclusion. The sediments collected from Irags cave possess a weak and

unstable reinanent magnetization. The viscous probably grew during

transportation from the site to the laboratory. These sediments

are classified as bad geomagnetic recorders.

7.10 Ball's Cavern. Ball's (or Gage's) Cavern is located. (42067 1 N, 74°28'W) on Barton

Hill about 7Km northeast of Schoharie, New York, U.S.A. It contains no archaeological materials and its only cultural significance is that

it supplies, indirectly, part of the town of Schoharie's water supply.

The cave is situated about 13m below a heavily Karsted sinkhole plane

and trends in a NE-SW direction. Its known length of approximately

650ni is entirely developed in a Devonian limestone. Like most caves in the region it consists mainly of a single level linear solution tube

of small cross section with occasional sinkholes connecting it with the 75.

surface. Ball's Cavern is unique in the immediate area in having

several large rooms in its system and one of these, the "Rotunda

Room" contains about 8m of soft sediments deposited in it. These

sediments were chosen by Kopper for palaeomagnetic study. They were

sampled with the same technique that has already been described in

the case of Arago cave.

Ball's Cavern has striking similarities with Jeita Cave in

Lebanon (Creer and Kopper, 1976) in that it contains very thick sedi- ments which are presently accumulating due to its location below the

- water table, though deposition has not been continuous in the past, having been controlled by it. The strata consist of finely laminated

tan silty clays, sandy layers, gravel aboulis and finely laminated

reddish-brown silts. Two sections, Omega and Alpha, banked at oppo-

site sides of the main chamber were sampled. It is quite certain

that the cave did not accumulate deposits during the UjLsconsin Stadials, because it is located in a formerly glaciated area. The

cave plan and the stratigraphy of the sampled area are shown in Fig.

7.13. No estimations of the rate of deposition or chronostratigraphic evidence are available. The cave carries a free surface stream that

disappears into a fissure in another lower room that also contains

sediment. It would first appear that this stream carried the accumu- lated sediments into the' cave as suspended load but this is decidedly

not the case. In fact the sediments were brought in through small dia-

meter vertical openings communicating with the surface by a separate,

low energy hydraulic system. Both fine material from the surface,

silts and clays, as well as coarser detritus from freeze-thaw (mechan-

ical) weathering of the cave ceiling are present in the deposit as

distinct layers of one or another of the grades. These layers measure 76. from 1mm to several mm and more in thickness and consist predominantly of one grade of sediment, sand, silt or clay.

At the top of the Rotunda Room deposit a thick layer of large angular cryoturbated blocks are lying near the surface, undoubtedly the result of glacial action. The sinkhole plane under which the cave lies is known to have been covered by the Wisconsin and Illinoian ice sheets and probably by earlier Pleistocene glaciers.

7.11 AFC demagnetizations.

In Fig. 7.14 the demagnetization curves for Alpha and Omega section are presented. The IvlDFs of the Alpha samples are extremely high, in the range of 450-800 Oe while those of the Omega samples are in the range of 120-200 Oe. In Fig. 7.15 (a, b) the same samples are plotted individually in two parallel columns. In the first column the normalized jn demagnetization curves are shown, while in the second their directions during AFC are shown stereographically. The direction of magnetization show remarkable groupings between 0 and 600 Oe for Alpha samples while for Omega samples the groupings are formed up to 300 Oe. It is clear that in the case of Alpha section, we deal with magnetic carriers of high coercivity. The magnetic carriers of Omega appeared with lower coercivity.

7.12 Interpretation of the palaeomagnetic data.

Fig. 7.16 illustrates the NRM declination and inclination, together with those after AFC in 100 Oe, plotted against the depth,

side by side with Omega section in the top and Alpha in the bottom.

Both the records appear scattered, with the inclination having a

CALLS CAVERN SCHOHARIE.NEW YORK - •. .- - STRATICRAPHY -

- Streom - - ceiling

I-i • Finely laminat tan silty clays uncon iormi ty F-i Sandy layer • Entrance 1zzJ Silty clays N (1 W '-1' I =-- Gravel Ebouus

• - - - - . -; 3- _ -= Samp!es(' - - L-- Finely larninat - reddish-browi silts

0102030 5 -- - • - - - meters -water flow ft - .CAVE PLAN -. - 6- i Gravel - • - -- - VIEW 9O° - - Piguxe 7.13 The I tiaphyof the sampled section and the plan of Ball's Cavern. - - • -

• 10 - -

J/i 0 OA-- 1pha Section

V Bat's Cavern V N.M. -V - V - .02• (AF..C.) Demagnetizations'

V V - -M.D.F.:(L5OOe,8OOOe) V V

- 00 V 0 100 200 300 400 500 . 600 700 630 V - Peak Field (O e)

V V VVV VV V • 10 - Bat's Cavern V V

Omega Section V V • • \\\ M.D.F:(1200e,500 Oe)

Si, )_V V•_____ J0 V - V V

02 1 N.RM (AEC) Demagnetizations

V V 1 - 0.0 V 100 200 300 400 V V Peak Field (Oe) --

Figure 7.14 NM noimalized demagnetization curves : V V of pilot samples from Alpha and Omega sections.

- SV V_•VSVVVSVVV Orr 09 94A I Depth, I&ACES

V V V 400 no 330 'CO .0O - we - Peak Field c -.

FWFX SSG 00

sat 78 Depth S60CM LI V 400 r3 30 93 30WO V - - -- - Peak field Joel - • V V V to - - w , V 1111111 I i-:- •V V

8"C4 442 Depth ea.-am

V -- 403 j_3 330 tC3 !.6-3 100 - - - V V Peak Field 10.1 V

*V'JrIFeI&2C Do

balsa Depth 116Akm J.*ISAB PG

• V - leek F..t4 tees -. V - t IEt • 7 V KCLF. S60 00

-

V VV peak f ie ld Joe l

03

oaf $I Depth 1760ces CL2 A- C20 pG

100 2CO 300 too -,ao 609 Peak IseId0e)

-. Figure 7.15a V V NRM nomalizeci demagnetization curves with stereograplijc projections of their directions of individual pilot • V - samples during AFC, from Alpha section.

V V - -.

- 1J1Fit0OOo , : • i V

WiD 04 Dat7 Depth Mom 02r P

100 200 300 L(.3 WO (413 - - Peek fseldtQcj

to 650 00 G

rewgot--S650 ;~78 S~ 00 Ir

100 233 323 £33 33 600 - - Peek Field ICe) - -: - - -- -

- I tulilti- titliSt I -. to - kflFL03 0. RRH

D"4C Dot t2 Depth MCCIft 02

- _ - 100 203 230 ((.3 33 COO - - - Peek Field tOe) - - -

rJ1F&20 Os NRI4 Owl 06

DEC Dot ss~ - - Depth 1160cs -

- 3.. IS-Be 1jG - V - - V - 233 323 £.3 tZo C.O • V - Peek F.etdtOeI - - • 10 - - w IIIIIIii -1 -IfIllI, .. - S - KrXF- S60 00 08 IMH 06 V :. 044 Dal 70 • V V - V

;' . - V 100 230 3C0 L0 S00 COO

V . Peak Feld(Oc) V •, , - Vt I I I - 1-4SiF 720 Oe I I I • • Him ,,0:

) 67 - - V Depth 1760cm -• V

02L V lCD 200 303 (0) SOO 600 • V • - P(QII I seld tOe) -

V Figure 7.1 5b NRM normalized demagnetization curves with stereographic

V V V projections of their directions of individual pilot V

V samples dung AFC, from Omega section. V VV

S - • VV -- - V SV• V V V • 0 ,,

BALL S CAVERN SCHOHARIE (NEW YORK) -USA • . . 0 . . . . . . Intensity 0-ratio Susceptibility • '. °° A.EC(100 Oe) •• : NRM A.RC(100 Oc) NRM 30 60 0 500 . 500 .30 0 0 0 t I 0 •. I $ $ 0 • ..., . 0• . . • £ —r-T-

•: • •... . • :. :. •' 0• .,. .: •. . S • . . . . • • 4 1 .11 S • ••• ••. • •

:.• . I

% •'i

as a sa. eases. sea a.aeeaa. - - — a.. - aecas • • ea - sea a a Cs — a y • e :15._s E • S. • 0•• •. — Ill 2. 2 .2,." 2 ,2 asaysa aeae — pS ea55 aaaaeSS•5SC ..eaeaea5 0 0 0 s.• %I. • ..• • 0 • %. • •j .1 • ••l• 0 I • I • • • • I •. • •• . . .' •

• s%;::.: • • • : f • ' I •• •. S • I 0• 0 . 0 • s.:..' . S.: • • . 1 II . S S .• 0 • . S ,1 SO • •, II.SI • •• l, . Cl. •• •0 •'S .. • . S •0• 1,. •.• 5 ,• I • . •: . # • •' '• . • • • 0 •• •l I, I. SI 0 . • • . •.

Figure 7.16 NMI intensities and their cleaned record plotted together •. • side by aide with Q-ratio and the maetio soeptibility, 0 . •,, •o •, •• • . with Omega seotion in the top and Alpha in the bottom. • 5 •• • 0 -

• - - BALLS CAVERN -SCHOHARIE (NEWYORKJ -U.SA Declination - Inclination - - -- • - AFC (100 Oe) - NRM AFC 1100 Ce) • - NRM - -LO - - 63 -L0 60 I 0 S3 I & 0 t • . .• / - - - • •e. - S - •e•. - •. - •• • . - - -- V - - - ; . - • •• .5 - S 8 . .S• - ••. .: • • - C •. •.. C. •__ - -. Ce •. • - - - - • .8. - -- . S.-- • .•. I I i • • I - ••,

2 2.. : 2.. :;::iz CL

- .- - •:. S : .. - - 3 • • 3 8_C. 3 •.. • % • • • . •. • • - -- -. • - . .•.• •• - S - C - I s - • :- •. •% • • • - • • •• . . - - - e - C C • - . • S • -. • - - . • - - - • •. • - •:.. • • - - •• • • - &••. S • 6 • -•• &_ •. '-:

Figure 7.17 • 1iBM.iiiclination and declination logs plotted in parallel- . •• together with their record after .AFC with Omega section S •• in the top and Alpha section in the bottom. - - - -- - - - • - S

. - - • • - . -S - - S - -- - - -

- 77.

tendency towards shallower values after AFC. The declination record 0 exhibits profound swings with 10-20 amplitude, whereas the inclina- tion.recoiü exhibits two broad maxima at 130 and 255cm respectively.

Fig. 7.17 illustrates the NRM intensities, together with their

cleaned values after AFC plotted against the depth side by side with

the Q-ratio and the ks. The intensities and hence the s-ratios of

the Omega section are reduced by about 60-70% whereas those of the. - . Alpha are reduced by 10-15%. The differences in jn, k and Q-ratio - between the two deposits are explained by differences in the concen-

tration .of the magnetic content. The jrs of. Omega and Alpha are in

the range of 1 ,000 and 1,700 pG respectively, reflecting higher con- centration of ma,gne.ticccntent in the Alpha deposit.

- 7.13 Discussion- and conclusions. - The deposits of Ball's Cavern show highly stable remanence whichprobablyis-of:PDRM origin, as the conditions of sedimentation

in the cave, and the redeposition experiment showed. The sediments

ard deposited in 'a gigantic settling tank and the acquisition of the remanence is fixed when the water goes upwards as it occurs in

the lakes due to gravitational compaction of the newly coming sedi- ments. The settling tank is the entire "Rotunda" chamber. The Q..-

ratios follow the usual pattern of the low values, which can be ex-

plained as contribution of other magnetic minerals different from

magnetite. The existence of magnetite is assumed from the Hcr45 0

Oe obtained value and from the X-ray diffraction data, however detailed

Mossbauer spectroscopy, at room temperature and at liquid helium should

be performed to specify in detail the nature of the magnetic carriers

locked in these cave sediments, together with the thermomagnetiC, 78. cryomagnetic experiments and optical microscopy. The observed swings cannot be dated or associated with other existing serial geomagnetic records in U.S.A., due to lack of both archaeological controls and direct. ratiometric ages on travertine layers.

79.

THE MA.C}RETH CORER

8.1 General description. - 8.2 Operation of the corer.

8.3 Discussion and conclusion. • V V 80. V

8.1 General description. - V The corer invented by Mackereth (Mackereth, 1958) consists of V. two PVC plastic tubes approximately 6m long, one tube within the other,

• and a 1.20m long drum with 0.40m diameter. The entire system weighs

only 30kg. The external tube has 7.2cm diameter and an 0.105cm wall

thickness. The internal hollow core-tube has a 5.3cm diameter and 0.45cm wall thickness. The outer tube (A) engulfs the inner tube (B). The inner tube is attaàlied to a piston (C) and can slide past an inner • piston (D) which is attached to the top of the outer tube by means of

a narrow innermost tube (E). The drum (F) is fixed to .the lower part is attached V V of the outer tube. In operation an air pressure hose (G)

V to the top of the outer tube aiii a hose (H) which is connected to a V

V V V pump, is attached to the top of the drum. A short pipe (I) leads from the lower part of the outer tube to the top of the anchor chamber and a release valve () is also fitted to the top of the drum.

V •V V 1 I

V Figure 8.1 Diagrammatic representation of the main features of

V V Mackereth corer. V • V V 81.

C 8.2 Operation of the corer.

The corer is lowered to the lake bed by means of a nylon rope. The hoses (1) and (2) are payed out.at the same time. Small floats can be added to facilitate the operation. Then the corer has reached

the lake floor a slight tension is retained on the rope; this tension and the attached floats maintain the corer in a vertical position, as is shown in Fig.8.2a. Once the corer is settled, a buoy is attached to the taut tether. The line and tether are then let out and the boat

is anchored, some 40m away, as is shown in Pig. 8.2b.

AIR vROPE "V .PUMP

&.s . •..• • I&)t.,• '••r•.•,..•.I : . \1 .. ;• .. . .,•

Figure 8.2a - Figure 8.2b The boat with the corer in The boat has moved 40m away and a vertical position. the float holds the nylon rope, connected with the boat. which is The water in the drum is now pumped out through the point (4)1 as is shown in Pig.8.3(a, b) of the hose (2) extending to the top of the corer. This occurs by passing compressed air to the drum from the hose (1). The compressed air is supplied by air bottles laid on

the boat. ; Consequently the hydrostatic forces act on the drum and. push it 82. into the sediment. This procedure lasts approximately ten minutes at low pressure. It is highly important that the drum is completely pumped out. After the completion of the slow-penetration of the sediments from the drum, air is passed down from hose (2) causing the main piston with

the hollow core tube to be pushed out of the corer into the soft sedi- ments. The rate of coring can be monitored by observing the amount of water which comes-out of the retract tube (attached to point (3)).

This water is displaced from inside the core tube (B) and passed back up to the retract tube. Once the core is fully extended, that is when the main piston

passes outlet (4), the coming air is by-passed through (4) into the drum and the retrieval process is enacted. The bypass of air through

(4) causes the drum to fill with air. This causes the drum to lift from the sediment and when sufficient buoyancy is reached the whole

corer is propelled to the lake surface for retrieval. The assemblage

is kept afloat by the continuing passage of air keeping the drum posi-

tively buoyant. The sequence of events is illustrated in Fig.8.4(a, b).

A. The drum rests in contact with the sediment on the lake floor. The corer is supported by a nylon rope and the hoses from the drum and the top of the corer are connected to a pump and to a supply of compres-

sed air in the boat. The water is pumped out and the drum penetrates vertically

the soft top sediments. The water trapped in the drum has been pumped out and the

hydrostatic pressure has pushed the chamber into the sediment. The hose

used to pump out the water is sealed out the core is about to be taken.

Compressed air has been admitted into the space between the

piston at the top of the core tube and the outer tube and the core tube

'is being pushed into the sediment.

I 3

Figure 8.5a Phase (D) : The coring procedure is completed.. Phase (z) : The corer starts to rise up. lake. Phase () : The corer is going to the surface of the

• V V • V • The Mackereth corer • V V V

V C

-- 1' -- - -

____

•.:

Figure 8.4a • Phase (A) : The vertical position of the corer on the lake bed.

V Phase (B) : The'slow penetration into the soft sediment.

V • Phase (c) : The penetration is completed.. 83.

The core has been taken and compressed air has entered the drum from the outer tube by means of the short pipe shown in Fig. 8.3a.

The air pressure being greater than the hydrostatic pressure is raising

the drum from the lake bed. The corer is now rising to the surface being lifted by the buoyancy of the air trapped in the drum. Some of the air is escaping

from the drum through the air release valve. Figures 8.1, 8.2 and 8.4 are mod.ificatiors of drawings based on

Smith's schematic representation of the corer (Smith, 1959).

8.3 Discussion and conclusion. The main profound advantage of the pneumatically operated corer

are the portability of it on the roof of a Land. Rover, its independence from big depths (.. 300m limit), the easy operational procedures requir-

ing only two people and an outboard motor, the very low construction

and running costs together with new improvements which do not allow

rotation during coring and the possibility of taking oriented cores

by placing a submarine camera on the top of the drum which would give

precise photographs of a compass and the degree of tilting of the corer

by measuring the degree of deviation of the bubble from the centre of

the spirit levels, are intriguing prospects for new advances in palaeo-

magnetic research, Jackson(çerScDy\ci - 64.

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