The Orera section (Calatayud Basin, NE Spain) - Universiteit Utrecht

More documents

Recommendations

Info

confirmed by magnetostratigraphy, resulted in the construction ofthe Orera Composite Section (OCS). In this OCS, four - hierarchically arranged - sedimentary cycles of different scales are recognised. Basic small-scale cycles are the most prominent and are characterised by an alternation ofgrey and/or red mudstones with white carbonate beds. At least 91 basic small-scale cycles are recognised in the OCS. Large-scale cycles are marked by an alternation of dark intervals comprising weakly developed (i.e., indistinct carbonate beds) small-scale cycles, with overall lighter intervals consisting ofregular and well-developed (distinct carbonate beds) smallscale cycles. Short intemlediate-scale cycles are marked by an alternation ofthick-thin carbonate beds in successive basic small-scale cycles. Long intermediate-scale cycles are represented by clusters of five to six well-developed basic small-scale cycles. The OCS magnetostratigraphy is unambiguously correlated to the GPTS resulting in an age of ro.7 to 12.8 Ma for the composite section. Using this age constraint, a first approximation is made to determine the average duration of the cycles and to determine the link with astronomical parameters. The average duration of a basic small-scale cycle turn is arrived at 23 kyr, while the large-scale cycle has a periodicity of-400 kyr. The short- and long-term intermediate-scale cycles have periodicities of about 41 and roo kyrs, respectively. All these values are in good agreement with the periods of the orbital cycles of precession (basic small-scale cycles), obliquity (short intermediate-scale cycles) and eccentricity (long intermediate- and large-scale cycles), and strongly suggest an astronomical origin of the cyclicity in the OCS. Hence, the OCS provides an opportunity to extend the astronomical polarity time scale into the middle Miocene. The importance of recognising and understanding the role of astronomical forcing, and consequently climate change, in continental settings is emphasised in Chapter 2. Also the significance of studying cyclostratigraphic correlations between continental and marine sequences, necessary for detailed comparisons of (regional) paleoclimatic changes in the Mediterranean, is outlined. The good magnetostratigraphy, the presence of astronomically forced cyclicity and the prospect of extending the APTS, all indicate the high potential of the Orera section - and the adjacent area - for multidisciplinary studies and led us to propose Orera as a geological heritage site to ensure its preservation and protection. In Chapter 3 a detailed sedimentological description of proximal to distal alluvial fan and shallow lacustrine deposits in the prera area and its surroundings is presented. The aim of this study is to reconstruct the paleoeuvironment of these deposits and to develop a depositional model for the cyclic successions. the sediments are divided into four lithofacies associations: i) proximal and medial alluvial fan facies; ii) distal alluvial fan facies; iii) lake margin facies; and iv) cyclic shallow lacustrine (and floodplain) facies. The cyclic facies comprises the mudstonecarbonate cycles. The mudstones are red, reddish-brown or greyish-green in colour and are composed mainly of clay minerals, which are dominated by illite, illite-smectite mixed-layers and subordinate kaolinite. Minor amounts of dolomite occur, particularly in the greyish-green mudstones. The carbonate beds are mainly dolomitic. The paleoenvironment in which the cyclically bedded succession was formed is associated with a low gradient, shallow lacustrine basin that developed in a "shadow zone" between two major alluvial fans. The measurements of the isotopic compositions of carbonate beds from the various lithofacies display the lateral variations in the paleoenvironments from marginal to more central lake areas. Although the mudstone-carbonate cycles are attributed to lake-level variations caused by penodlc changes in climate, two depositional models are presented in this chapter to explain the formation ofthese cycles. The reasons for the difficulty in assessing a single model are due to the lack of clear 17
sedimentary features in the mudstones but also to the absence of well-developed models that adequately can explain cyclicity in continental settings. Therefore, two depositional models that have an opposite relation with climate are presented. The lacustrine Model-I depicts that mudstones are deposited in a shallow lake during lake-level highstands and wet climate conditions whereas carbonates are deposited during low lake-levels and dry climatic circumstances. The lacustrine-floodplain Model-II implies that mudstones accumulated on vegetated mudflats of the alluvial-fan floodplain at times of relatively dry climate. Carbonates thus would have accumulated in a shallow lake that developed on the floodplain of the alluvial fan during periods ofwet climate. In Chapter 4, the astronomical forcing ofthe sedimentary cycles in the OCS is demonstrated and, subsequently, the two depositional models formulated in chapter 3 are evaluated in relation to astronomically induced climate change. To determine the periodicity - in metres and in kyrs - of the different scales of cycles, spectral analysis and bandpass filtering of high-resolution carbonate and colour reflectance records of the OCS are performed. The results in the depth domain indicate that the dominant peak at ~I.7 m corresponds with the average thickness ofthe basic small-scale cycle. Other significant peaks correspond to the large-scale cycles and to the short- and long-term intermediate-scale cycles, respectively. The GPTS-based age model, established in chapter [, is used to transform the proxy depth-records into time series. Spectral analysis ofthe time-series revealed periodicities ofabout 23, 41, 100 and 400 kyr, for respectively the basic small-scale, short-, long intermediate-scale and the large-scale cycles. Thereby the relationship of the OCS cycles to precession, obliquity and eccentricity is unambiguously demonstrated. By employing well-known phase relations for marine (and continental) sequences in the Mediterranean, inferred phase relations for the OCS cycles with the astronomical parameters are established; these phase relations are consistent with the lacustrine-floodplain Model-II outlined in chapter 3. Consequently, the OCS cycles are tuned to the precession and eccentricity curves of La93 (Laskar, 1990 and 1993). This resulted in an APTS for the time interval 10.6-12.9 Ma and provides astronomical ages for the sedimentary cycles and hence also for the polarity reversals (and cryptochrons). However, a discrepancy of I or 2 precession cycles may be present in certain intervals. Finally, the accuracy of the OCS tuning is tested in two ways. Firstly, spectral analysis and bandpass fIltering demonstrate a remarkably good coherency and in-phase relation with obliquity and eccentricity. Secondly, the newly acquired ages of polarity reversals are examined with respect to constancy in sea floor spreading rates and confirm that the new APTS is in good agreement with the sea floor spreading rate ages. In Chapter 5, it is demonstrated that astronomical forcing ofsedimentary cycles is also present in late Miocene distal alluvial fan to lacustrine deposits ofthe Teruel Basin. In the Cascante and Caiiizar sections, the cyclically bedded mudstone-carbonate alternations are more easily interpreted in terms of astronomically induced climate variations than the mudstone-carbonate cycles in the OCS. The phase relations are similar to those from the lacustrine-floodplain Model-II in the OCS. Furthermore, the correlation ofthe Cascante magnetostratigraphy to the GPTS of CK9S is elaborated. Because of an uncertain polarity in the top parts of the Cascante and Caiiizar sections, two age models are presented. The age models show consistent spectral analysis results. Combined with the integrated magneto-, bio- and cyclostratigraphic results, errors are inferred in the duration of subchrons, particularly in the younger part of Chron Csn and the older part of Chron C4Ar, occur. Because of these uncertainties, and because of the necessity to investigate the lateral consistency of the Cascante cycle patterns in more detail, 18
Page 2 and 3: GEOLOGICA ULTRAIECTINA Mededelingen
Page 4 and 5: Astronomical forcing in continental
Page 6 and 7: Voor mijn ouders
Page 8 and 9: Contents Bibliography II Introducti
Page 10 and 11: Introduction and summary During the
Page 12 and 13: common and many of these repetitive
Page 16 and 17: especially related to obliquity and
Page 18 and 19: Chapter [ Introduction Time control
Page 20 and 21: Chapter l and L6pez Martinez, 1985)
Page 22 and 23: Chapter T VT-III 91 90 VII 88 86 84
Page 24 and 25: Chapter 1 Overlap LY The short subs
Page 26 and 27: Chapter I Cycle hierarchy Visual ch
Page 28 and 29: Chapter [ The natural remanent magn
Page 30 and 31: Chapter I maximum unblocking temper
Page 32 and 33: Chapter I enables us to define the
Page 34 and 35: Chapter I the astronomical polarity
Page 36 and 37: Chapter [ Valdelosterreros I (VT-I)
Page 38 and 39: Chapter 2 The Orera section (Calata
Page 40 and 41: The Orera section Orera section is
Page 42 and 43: The Orera section 20 ~ 10 Om ocs I
Page 44 and 45: Chapter 3 Paleoenvironmental reCOll
Page 46 and 47: Paleoenvironmental reconstruction R
Page 48 and 49: Paleoenvironmental reconstruction (
Page 50 and 51: Paleoenvironmental reconstruction m
Page 52 and 53: Paleoenvironmencal recon)trllction
Page 54 and 55: Paleoenvironmental reconstruction o
Page 56 and 57: Paleoenvlronn1ental reconstruction
Page 58 and 59: PaleoenvIronmental reconostruction
Page 60 and 61: Paleoenvironmental reconstruction N
Page 62 and 63: Paleoenvironmental reconstruction c
Page 64 and 65:
Paleoenvironmental reconstruction 1
Page 66 and 67:
Paleoenvironmental reconstruction r
Page 68 and 69:
Paleoenvironmental reconstruction p
Page 70 and 71:
Paleoenvironmental reconstruction r
Page 72 and 73:
Paleoenvironnlental reconstruction
Page 74 and 75:
Chapter 4 An astronomical polarity
Page 76 and 77:
APTS for the middle Miocene ages fo
Page 78 and 79:
I APTS for rhe middle Miocene Des C
Page 80 and 81:
Depth domain Entire records Cycle i
Page 82 and 83:
APTS for the middle Miocene The fil
Page 84 and 85:
APTS for the middle Miocene saprope
Page 86 and 87:
APTS for the middle M,occne L*-valu
Page 88 and 89:
APTS for the middle Miocene 165 ,.,
Page 90 and 91:
APTS for the middle Miocene The int
Page 92 and 93:
APTS for the middle Miocene though
Page 94 and 95:
Chron Lithology and cycle Stratigra
Page 96 and 97:
APTS for the middle Miocene Ages of
Page 98 and 99:
APTS for the middle Miocene interpr
Page 100 and 101:
APTS for the middle Miocene Finally
Page 102 and 103:
Chapter 5 Introduction Sedimentary
Page 104 and 105:
Chapter 5 ofthe Iberian Chain and t
Page 106 and 107:
Chapler 5 Canizar 25 * 20 g~~:~ _ 3
Page 108 and 109:
Chapter 5 Figure 3b. indicated Phot
Page 110 and 111:
Chapter 5 multierestatus, which are
Page 112 and 113:
Chapter 5 above 600°C, to a maximu
Page 114 and 115:
Chapter 5 80 Cascante Depth domain
Page 116 and 117:
Chapter 5 Figure 6. Correlation of
Page 118 and 119:
Chapter 5 ' l 46 L'-value maximum t
Page 120 and 121:
Chapter 5 Cascante Age Model-1 9.4
Page 122 and 123:
Chapter 5 points ofthe base ofC5n.r
Page 124 and 125:
Chapter 5 Phase relationship The pa
Page 126 and 127:
Chapter 6 One new subchron (Csr.2r-
Page 128 and 129:
New subchron and cryptochrons requi
Page 130 and 131:
New subchron and cryptochrons Corre
Page 132 and 133:
NRM New subchron and cryptochrons (
Page 134 and 135:
New subchron and cryptochrons throu
Page 136 and 137:
New subchron and cryptochrons Figur
Page 138 and 139:
New subchron and cryptochrons Linea
Page 140 and 141:
New subchron and cryptochrons 6 (Fi
Page 142 and 143:
New subchron and cryptochrons hemat
Page 144 and 145:
New subchron and cryptochrons I ~g:
Page 146 and 147:
New subchron and cryptochrous prefe
Page 148 and 149:
References Abdul Aziz, H., Calvo, J
Page 150 and 151:
Calvo,].P., Abdul Aziz, H., Hilgen,
Page 152 and 153:
Dekkers, M.J., 1989. Magnetic prope
Page 154 and 155:
Hilgen, FJ., Krijgsman, W., Raffi,
Page 156 and 157:
Earth from -20 Myr to +IO Myr. Astr
Page 158 and 159:
Pisias, N.G, Dauphin, J.P. and Sanc
Page 160 and 161:
Shackleton, N.J., Crowhurst, S., Ha
Page 162 and 163:
ecord. Rev. Ceophys. Space Phys. 15
Page 164 and 165:
correspond to periods of prolonged
Page 166 and 167:
extending the APTS further down int
Page 168 and 169:
- op basis van multidisciplinaire e
Page 170 and 171:
van polariteit verwisselde heeft ge
Page 172 and 173:
en In meren. Acht, gedeeltelijk ove
Page 174 and 175:
In hoofdstuk 4 wordt het bewijs gel
Page 176 and 177:
Acknowledgements Many (ex-)colleagu
Page 178:
Curriculum Vitae Hayf;la Abdul Azi7
show all

The Orera section (Calatayud Basin, NE Spain) - Universiteit Utrecht

Create successful ePaper yourself

Delete template?

Save as template?