Thesis Compleet

FACULTEIT WETENSCHAPPEN Vakgroep Geologie en Bodemkunde

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Thomas Vandorpe

Academiejaar 2009–2010

Scriptie voorgelegd tot het behalen van de graad Van Master in de Geologie

Promotor: Prof. Dr. D. Van Rooij Begeleider: L. De Mol Leescommissie: Prof. Dr. M. De Batist, Prof. Dr. J. Henriet, Prof. Dr. P. Van Rensbergen

FACULTEIT WETENSCHAPPEN Vakgroep Geologie en Bodemkunde

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Thomas Vandorpe

Academiejaar 2009–2010

Scriptie voorgelegd tot het behalen van de graad Van Master in de Geologie

Promotor: Prof. Dr. D. Van Rooij Begeleider: L. De Mol Leescommissie: Prof. Dr. M. De Batist, Prof. Dr. J. Henriet, Prof. Dr. P. Van Rensbergen

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Preface

Hij is af!

Een grote opluchting! Ongeveer een jaar geleden kon ik enkel maar dromen van het moment waarop ik deze magische woorden zou kunnen typen. Nu ik dit eindelijk kan doen laten ze toch enigzinds een wrang gevoel na, want ongetwijfeld volgt hierna een groot gat. Zeker het laatste half jaar was de thesis zo goed als het enigste waar ik aan kon denken bijna. Dit valt nu allemaal weg. Toch ik ben ik heel trots mijn eigen onderzoek hier te kunnen presenteren.

Natuurlijk heb ik dergelijk iets niet alleen kunnen doen. Vele mensen hebben mij met raad en daad bijgestaan. Hen zou ik dan ook zeer graag bedanken.

Ten eerste zou ik uitdrukkelijk mijn promotor, David Van Rooij willen bedanken. Deze heeft mij uitstekend begeleid, stond altijd klaar om mijn vragen vrijwel onmiddellijk te beantwoorden en zorgde voor een uistekende, snelle feedback. Ik weet dat het op tijd afkrijgen van mijn thesis voor een groot deel aan hem te danken is.

Ten tweede zou ik Lies De Mol willen bedanken voor de meer praktische hulp. Het inladen van de profielen in Kingdom en mijn weg vinden in de (voor mij) nieuwe software was zonder haar nooit zo vlot verlopen.

Ten derde zou ik de vele mensen van de “Mariene gang” willen bedanken voor de vele hulp met al mijn vragen, in het bijzonder professor Henriet en professor De Batist. Professor Henriet voor de hulp bij enkele lastige geofysische problemen en professor De Batist voor het beantwoorden van vele van mijn (waarschijnlijk soms wel stomme) vragen.

De studenten die hun thesis op de mariene gang deden (Anouk, Joris, Myriam, Nele en Robbert) en Willem wil ik zeer graag bedanken voor de deugddoende ontspanning en afleiding tijdens het vele werk (met een bijzondere vermelding voor de “voetballers”). Hun aanwezigheid maakte het werk soms veel minder zwaar. Het is waar wat ze zeggen: in groep werken is zoveel plezanter en geeft veel meer moed om verder te doen.

Ten slotte (maar zeker niet het minst belangrijk) zou ik mijn ouders willen bedanken voor de mogelijkheid om hogere studies aan te vatten en om te zijn blijven geloven in mijn kunnen.

Voor al deze mensen nog één maal:

BEDANKT!

Tables

Table of content

PREFACE ...... 1

1 INTRODUCTION & OBJECTIVES ...... 10

2 GENERAL SETTING ...... 12

2.1 Geomorphology ...... 12

2.2 Geology ...... 16 2.2.1 Basin Evolution ...... 16 2.2.2 Stratigraphy and sediments ...... 27

2.3 Hydrography ...... 40 2.3.1 Present-day hydrography ...... 40 2.3.2 Paleoceanography ...... 46

3 MATERIAL AND METHODS ...... 50

3.1 Geophysical dataset ...... 50

3.2 Multibeam bathymetric data ...... 52

3.3 Methods ...... 52 3.3.1 Seismic processing ...... 52 3.3.2 Seismic interpretation ...... 53 3.3.3 Description of seismic data ...... 54 3.3.4 Map making ...... 56

4 RESULTS ...... 60

4.1 Multibeam bathymetry ...... 60 4.1.1 Mallorca channel ...... 60 4.1.2 Southwestern shelf and shelf break of Mallorca ...... 62

4.2 Seismic stratigraphy ...... 62 4.2.1 Northern Grid ...... 62 4.2.2 Connection profiles ...... 67 4.2.3 Southern Grid ...... 68

5 DISCUSSION ...... 92

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

5.1 Reef ...... 92

5.2 Depositional history Plio-Pleistocene sequence ...... 93 5.2.1 General ...... 93 5.2.2 Sequence 1 ...... 94 5.2.3 Sequence 2 ...... 97

5.3 Plio-Pleistocene Stratigraphy ...... 99 5.3.1 Discontinuities ...... 99 5.3.2 Sequences ...... 101

5.4 Sedimentation rates ...... 104

6 CONCLUSIONS ...... 106

6.1 Summary ...... 106

6.2 Recommended future reearch ...... 107

6.3 Dutch summary/Nederlandse samenvatting ...... 109 6.3.1 Doelstelling...... 109 6.3.2 Materiaal en methode ...... 109 6.3.3 Situering ...... 109 6.3.4 Evolutie ...... 109 6.3.5 Hydrografie ...... 110 6.3.6 Rif ...... 111 6.3.7 Multibeam ...... 111 6.3.8 sedimenten ...... 111 6.3.9 Seismische stratigrafie ...... 112 6.3.10 Afzettingssnelheid ...... 113

REFERENCES ...... 114

Table of figures Fig. 1: The seas of the Mediterranean and some important basins...... 12

Fig. 2: Major islands of the Balearic Promontory and important seas and basins...... 13

Fig. 3: A) Balearic Promontory as a prolongation of the Betic Cordillera. B) Bathymetry of the bordering regions of the promontory...... 14

Fig. 4: Topographic map of Mallorca with its most important topographic charateristics...... 15

Fig. 5: Tomographic figure showing subducted lithosphere below the western and central Mediterranean...... 17

Fig. 6: Oligocene to present evolution of the Western Mediterranean area...... 19

Fig. 7: Evolution of the western and central Mediterranean during the Neogene...... 20

Fig. 8: A) Betic and Rifian corridor at the Late-Miocene. B) Gibraltar Strait nowadays...... 21

Fig. 9: Position of the Betic and Rifian corridor ...... 22

Fig. 10: Distribution of the evaporites formed during the MSC...... 23

Fig. 11: Polar glacial conditions induced from marine isotopic records in the left panel. In the right panel, observed deposits and changes in the Mediterranean area are given ...... 24

Fig. 12: Location of different important land-sections ...... 25

Fig. 13: Seismic profile through drill site 975, ODP leg 161...... 28

Fig. 14: Seismic profiles in the Balearic region. After Stanley et al (1976)...... 29

Fig. 15: Geological map of the Balearic islands ...... 31

Fig. 16: part of the ESCI profile showing the southern Balearic platform...... 32

Fig. 17: Distribution of the Middle-Upper Miocene reefs of the Western Mediterranean...... 33

Fig. 18: LLucmajor platform and platform margins inferred by Hüssner et al., 2001...... 34

Fig. 19: Hypothetical section through a Miocene reef from the Llucmajor platform ...... 35

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 20: Real transect through the Llucmajor platform on Mallorca...... 35

Fig. 21: Seismic profile from the Almeria Turbidite System ...... 37

Fig. 22: Two examples of contourite deposits...... 38

Fig. 23: An example of a Mounded and confined drift ...... 39

Fig. 24: Anti-estuarine circulation pattern through the Gibraltar Strait...... 40

Fig. 25: Salinity transect across the Mediterranean...... 41

Fig. 26: Current pattern in the western Mediterranean ...... 43

Fig. 27: Present-day currents around the Balearic Promontory...... 44

Fig. 28: Surface currents in the studied area...... 46

Fig. 29: Reconstruction of the paleo-circulation in the Eastern and Central Mediterranean during the Miocene...... 47

Fig. 30: δ 18 O-curve for the last 2000 ka...... 48

Fig. 31: δ 18 O –curve for the last 5.2 Ma...... 49

Fig. 32: Left: an example of a seismic wave. Middle: Seismic wave going through a high density contrast boundary, giving multiple lines for 1 reflector. Right: wave going through a low contrast boundary, leaving 2 lines per reflector...... 51

Fig. 33: When the template is loaded, “The Kingdom Suite” can interpret the navigation file...... 53

Fig. 34: Profile 02 from the northern grid...... 55

Fig. 35: Parameters used for isopach maps...... 56

Fig. 36: Overview of the seismic reflection configurations ( ...... 57

Fig. 37: Position of the seismic profiles in the northern grid...... 58

Fig. 38: Position of the seismic profiles in the southern grid...... 59

Fig. 39: Multibeam map of the Mallorca Channel...... 61

Fig. 40: multibeam map of the southern and southwestern shelf and shelf break of Mallorca...... 63

Fig. 41: Multibeam imagery showing the seismic canyon, seen from the west...... 64

Fig. 42: Depth of the seafloor in the northern grid...... 65

Fig. 43: Profile 30 in the northern grid, showing small channels...... 65

Fig. 44: Part of profile 06...... 66

Fig. 45: Parts of profiles 22_out and 28...... 67

Fig. 46: Grid of the seafloor ...... 69

Fig. 47: Depth at which the reef occurs in the southern grid (boundary R)...... 70

Fig. 48: Thickness of the post-reef deposits in ms TWT...... 72

Fig. 49: Thickness of unit 1A ...... 73

Fig. 50: Profile 45_out ...... 75

Fig. 51: Base map of unit 1B (boundary D1)...... 77

Fig. 53: Profile 32_out...... 78

Fig. 54: Base map of unit 2A (boundary D2)...... 81

Fig. 55: Thickness of unit 2A...... 82

Fig. 56: Profile 38_out...... 83

Fig. 57: Seismic profiles through the most western depression...... 84

Fig. 58: Base map of unit 2B (boundary D3)...... 85

Fig. 59: Thickness of unit 2B...... 86

Fig. 60: Profile 34_out ...... 88

Fig. 61: The thickness of each sigmoidal unit has been measured along of the red line...... 89

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 62: Plot showing the amount of alternations counted in the SE-NW-orientated profiles...... 89

Fig. 63: Seismic profile 34_out with the double reflection...... 91

Fig. 64: Davie drift ...... 95

Fig. 65: Abstract picture of a channel-related drift ...... 95

Fig. 66: Two seismic profiles of the Vema fan...... 96

Fig. 67: The Le Danois drift in the Gulf of Biscay...... 98

Fig. 68: Summary of the sedimentary sequences and units on the southwestern Mallorca shelf,) ...... 100

Fig. 69: Correlation of the small units of sequence 2 to the δ 18 O-curves...... 103

Fig. 70: Evolution of the sedimentation rate during the Plio-Pleistocene...... 105

Fig. 71: Proposed grids for future research ...... 108

Fig. A1: Paleogeographic maps of the Tremadoc, Llandovery and Ludlow ...... 121

Fig. A2: Paleogeographic maps from the Early Emsian, Early Givetian and Famennian ...... 122

Fig. A3: Paleogeographic maps from the Early Visean, Bashkirian and Kasimovian...... 123

Fig. A4: Paleogeographic maps from the Sakmarian, Late Wordian and Permian-Triassic boundary ..... 124

Fig. A5: Paleogeographic maps from the Anisian, Ladinian and Early Norian ...... 125

Fig. A6: Paleogeographic maps from the Sinemurian, Aalenian and Oxfordian ...... 126

Fig. A7: Paleogeographic maps from the Valangian, Aptian and Santonian ...... 127

Fig. A8: Paleogeographic maps from the Late Lutetian, Eocene...... 128

Fig. A9: Paleogeographic maps from the Late Rupelian, Oligocene...... 129

Fig. A10: Paleogeographic maps from the Early Burdigalian, Upper Miocene...... 130

Fig. A11: Paleogeographic maps from the Early Langhian, Middle Miocene...... 131

Fig. A12: Paleogeographic maps from the Late Tortonian, Late Miocene...... 132

Fig. A13: Paleogeographic maps from the Piacenzian/Gelasian, Pliocene...... 133

Fig. B1: Profile 03...... 135

Fig. B2: Profile 22_out...... 136

Fig. B3: Profile 23_out...... 137

Fig. B4: Profile 27_out...... 138

Fig. B5: Profile 43_out ...... 139

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Table of tables Table 1: Summary of the geological evolution of the Western and Central Mediterranean ...... 26

Table 2: Summary of lithostratigraphic units for site 975...... 30

Table 3: Source specifications of the seismic survey ...... 50

Table 4: Penetration from the signal in relation to the depth of the seafloor and reef...... 50

Table 5: Receiver specifications of the seismic survey ...... 52

Table 6: Number of the profiles that underwent the above described processing ...... 52

Table 7: Thickness of the sigmoidal or divergent units in profile 34_out ...... 90

Table 8: The sigmoides in unit 2B and their associated MIS and assumed age...... 102

Table 9: The units in unit 2A, their associated MIS and estimated age...... 102

Table 10: Depth of the upper boundary and thickness of every unit occurring in the area...... 104

Table 11: Thickness, age and sedimentation rates of every unit occurring in the area...... 104

Table 12: Thickness, MIS, age and sedimentation rate of the units of sequence 2...... 105

1 Introduction & objectives

“The Mediterranean Sea can be considered as the Mare Nostrum (‘our sea’) of Earth sciences.” (Krijgsman, 2002).

The Mediterranean area was and still is the geological natural laboratory for investigating: 1) Geodynamic processes: It is an area of continued convergence between Africa and Eurasia. Though convergence may be the main plate tectonic feature, lots of extensional basins (through slab roll-back) characterize the Mediterranean ((Krijgsman, 2002) and (Carminati et al., 1998b)b). 2) Paleoclimatic processes: Its landlocked configuration and latitudinal position make sure the Mediterranean preserves orbitally-induced climatic changes rather well in its sedimentary record (Krijgsman, 2002). One example is sapropels. Many deposits around the Mediterranean contain sapropel layers, especially in the Eastern Mediterranean (Cramp and O'Sullivan, 1999) and these are used as important proxies (like δ 18 O) which give paleoclimatic information. 3) Hydrographic conditions: The Mediterranean is an unique sea, almost completely closed off from other seas and evaporates more water than water running into it via river-runoff (Frigola et al., 2008).

The RCMG (Renard Centre of Marine Geology) of the University of Ghent, has been working on various areas the last years: Lake Baikal, Porcupine Basin, Chili, Antarctica, … In the summer of 2003 however, the RCMG and the Vrije Universiteit Amsterdam conducted a survey, in cooperation, offshore southwestern Mallorca. The Vrije Universiteit Amsterdam wanted to compare sequence anatomy and boundaries with the spatial variability of acoustic properties from outcrops and offshore seismic data. The seismic data (obtained during that survey) will be compared with synthetic seismograms, created from petrophysical and geological data. Ultimately, this study will aid in the understanding of reflections across a carbonate platform and relationship with geological properties.

The seismic data cover an area of about 1250 km 2 and were shot in the sedimentary sequence above the prevailing Miocene reefs at the shelf off southwestern Mallorca (just west of the island of Cabrera). These seemed to be display many depositional features and the decision was made to investigate them further. The goal of this study is to investigate the obtained seismic data, together with multibeam bathymetric data, for being able to reconstruct paleoceanographic conditions, study the hydrodynamics of the Mallorca shelf and gain more insight into the sedimentary processes on and near the Mallorca shelf.

Chapter 2 introduces the geography of the studied area (going from Mediterranean over Balearic Promontory to Mallorca), the geology of the western Mediterranean (the Phanerozoic evolution of the basins to which it belonged, including description of the Messinian Salinity Crisis), the prevailing rock- and/or sediment sequences in the area (including general information about turbidites and contourites, as they have been reported in the area) and describes the current hydrography of the Mediterranean

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain with a focus on the Western Mediterranean. Some paleoceanographic features are described in this chapter as well.

Chapter 3 describes the materials and methods used in order to conduct this study. A short review of the characteristics of the source and receiver of the seismic sparker are given together with the used processing techniques and computer programs for processing the data.

Chapter 4 describes the results of the seismic study and an overview of the features seen on the multibeam bathymetric data. The seismic data are divided into sequences and units and of each of them, isopach and isochron maps are made. Each sequence is discussed based on its seismic characteristics, shape and occurrence.

In chapter 5, the results are discussed based on the literature study (chapter 2). The prevailing sequences are trying to be linked to sequences of the surrounding regions and a stratigraphy is being developed for them. The depositional system of each unit is discussed and finally, sedimentation rates are estimated.

Chapter 6 gives an overview of the most important discoveries of this study with some advice on future research. A short summary in Dutch is presented.

2 General setting

2.1 Geomorphology The investigated area is located on the continental shelf of south-eastern Mallorca, known as the Balearic Promontory, a part of the Mediterranean Sea (Fig. 1 and Fig. 2).

2.1.1.1 Mediterranean Sea

Fig. 1: The seas of the Mediterranean and some important basins. Adapted from http://upload.wikimedia.org/wikipedia/commons/6/61/Mediterranian_Sea_16.61811E_38.99124N.jpg

The Mediterranean Sea is a marginal sea (a partially enclosed basin separated from other waters by islands or peninsulas) which is divided into several basins, according to the International Hydrographic Organization (IHO, 1953) (Fig. 1). The Mediterranean Sea is connected to the Atlantic Ocean through the Gibraltar Strait, to the Black Sea by the Sea of Marmara and the Bosphorus and to the Red Sea via the Suez channel (Fig. 1).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

2.1.1.2 The Balearic Promontory

Fig. 2: Major islands of the Balearic Promontory and important seas and basins. The Emile Baudot Escarpment is the steep edge south of Mallorca. Two investigated areas on the southwestern shelf of Mallorca are indicated.

The Balearic Promontory is a structural elevation including four island: Eivissa (Ibiza), Formentera, Mallorca and Menorca (Fig. 2). The Promontory is a NE-wards prolongation of the Betic Range (or the “Cordillera Betica” in Spanish) (Fig. 3A). The mountain range, Sierra Nevada, is part of this elevation. The Promontory is 348 km in length, 105 km wide and rises 800 to 2600 m above the surrounding basins (the Balearic-Provençal basin, the Algerian Basin or the Valencia Trough, Fig. 2 and Fig. 3B), depending on the depth off those basins. In the southwest, the Promontory is attached to the Iberian Peninsula, but further northeast, it gets detached and separated from Iberia by the Valencia Trough, an aborted rift zone (Roca, 1992). In the east, the Promontory is bordered by the Balearic-Provençal Basin, as the Valencia Trough terminates into this basin. The Promontory separates the Balearic-Provençal Basin and the Valencia Trough in the north from the Balearic-Algerian Basin in the south (Fig. 3B). In the south, the Promontory is bordered by a steep NW-SE-orientated, 14 to 16 km wide slope, the Emile Baudot Escarpment (EBE). Multibeam data of Acosta et al. (2002) show a drop in height over the EBE of an average 1500 meters (going from 800-1000 m to 2225-2600 m). The data also show a rough surface; due to multiple incisions by 4 major canyons. At the base of the escarpment, unchannelled narrow aprons are found, bordered by a 25 m deep low, the Southeast Mallorca Trough. This low is the seaward extension of a canyon draining the Mallorca Shelf. The massive erosion associated with these canyons made the escarpment less steep and created slopes ranging from 7° to 9° (Acosta et al., 2001).

The Promontory can be divided into three blocks: Eivissa-Formentera, Mallorca and Menorca (Acosta et al., 2002). Eivissa (Ibiza) and Formentera are separated from Mallorca by the Mallorca channel (MCH), containing the Central Depression (CD), an elliptical depression almost separating the Promontory in two, which is over 1000 meters deep. This depression almost connects to a northwest orientated embayment at the southeast side of the Valencia Trough (Acosta et al., 2002). The islands of Mallorca and Menorca are separated by a shallow shelf-sea, called the Menorca channel (MNCH), with no major topography in it. Regarding the shelf itself, we can divide the promontory into two different parts: Mallorca-Menorca, whose shelves are connected and Ibiza-Formentera, of which the same can be said.

Fig. 3: A) Balearic Promontory as a prolongation of the Betic Cordillera. PB= Provençal Basin, TB= Thyrrenean Basin, AB= Algerian Basin, BP= Balearic Promontory. B) Bathymetry of the bordering regions of the promontory. VT= Valencia Trough, EBS= Emile Baudot Scarp, CD= Central Depression, ICH= Ibiza Channel, MCH= Mallorca Channel, MNCH= Menorca Channel (Acosta et al., 2002).

2.1.1.3 Mallorca Mallorca (or Majorca, as it is written in Spanish) is the biggest island of the Balearics. Its capital is Palma de Mallorca, which is also the capital of the entire Balearics. The island covers a surface of about 3640 km² and consists out of the main island and two very small islets: Dragonera in the northwest and Cabrera in the southwest (López-Jurado et al., 2008). The island has two elevated regions: the Llevant ranges in the south and the Tramuntara ranges in the north. In between those regions, there is a depression, which is called the central rift (CR) (not the same topographic expression as the central depression in the Mallorca channel). The climate prevailing on the island is Mediterranean, a subtropical

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain climate. It is characterized by warm, dry summers and wet, mild winters (in the classification of Köppen, this climate is indicated by the letters Cs). Mean annual temperatures are 17°C, mean precipitation is about 600 mm/year and about 60% of that occurs during spring and autumn (Candela et al., 2009). As the climate is rather extreme, vegetation has to be adapted to those kind of conditions. The natural vegetation than also consists out of pines, tough grasses, herbs like lavendel and olive and citrus fruit trees.

Fig. 4: Topographic map of Mallorca with its most important topographic charateristics.

2.2 Geology

2.2.1 Basin Evolution

2.2.1.1 Paleo- and Mesozoicum An overview of the Paleo- and Mesozoic evolution of the Tethys region (to which our study area used to belong) is given in Stampfli and Borel (2002). Here, we present a summary of it. The origin and evolution of the Tethyan seas can be seen on the figures in appendix A, all of the names in the following text are in those figures.

The Paleo-Tethys originated due to the slab roll-back of a subducting Rheic Ocean (ocean between Gondwana and Avalonia/Laurussia) under Gondwana during the Late Ordovician and the Silurian. Partial closure of the Paleo-Tethys due to collision of Gondwana with Laurussia happened in the Late Carboniferous. Pangea blocked the eastern edges of the ocean. The Neo-Tethys opened due to large slab-pull forces from subduction of the mid-ocean ridge of the Paleo-Tethys under northern Pangea during the Late carboniferous to Late Permian.

The final closure of the Paleo-Tethys occurred during the Triassic and is associated with northward drift of the Cimmerian superterrane, due to progressive opening of the Neo-Tethys. At the Triassic-Permiam border, the Paleo-Tethys was closed. The subduction of the Neo-Tethys under northern Pangea during the Early Jurassic was one of the causes for the break-up of Pangea. It started in the east (around Australia) and went westwards. Also the break-up of Gondwana is related to the opening of the Neo- Tethys in the Late Jurassic to Early Cretaceous. A north-south connection was established from Mozambique up till the Neo-Tethys, separating Antarctica, Australia and India from Gondwana. The orogenic system that originated in the east (Carpathians), due to southwards subduction of smaller back-arc basins that originated during closure of the Paleo-Tethys, moved westwards towards the Alps in Late Cretaceous times, creating the Alpine orogen.

2.2.1.2 Cenozoicum A review of the Cenozoic evolution of the entire Mediterranean can be found in Meulenkamp and Sissingh (2003). In this section, there will be a focus on the development of the Western and Central Mediterranean. The Cenozoic evolution of the Peri-Tethys region, the region south and north of the Alpine orogen (to which the studied area belongs), can be seen on paleogeographic maps in appendix A.

In the Cenozoic, this region shows a trend towards decreasing marine influence, due to the Alpine orogen (Meulenkamp and Sissingh, 2003). The Tethys had, at the start of the Cenozoicum, marine connections with the Northern Atlantic via a connection across the Aquitane Basin and to the Arctic Ocean via the West-Siberian Basin and the Turgaj Strait (Meulenkamp and Sissingh, 2003). The Alpine orogen also created the Para-tethys, a semi-seperated part of the Tethys due to the enhanced uplift of Alpine orogen (present-day remains of the Paratethys are the Black Sea, the Caspian Sea end lake Aral).

From the Late Cretaceous to the Eocene, the peri-Tethys region underwent progressive regression with some Alpine tectonic pulses, creating the configuration of a Neo- and Paratethys region, each with a different evolution (Meulenkamp and Sissingh, 2003).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

After the main Eocene uplift, Oliogocene to Late-Pliocene differentiation off the Peri-Tethys occurred, with an eastward moving locus of uplift, creating the many Mediterranean basins and seas (Meulenkamp and Sissingh, 2003).

The Cenozoic evolution of the western and central Mediterranean (Neo-Tethys region) is controlled by the convergence of the African and European plates (with an anti-clockwise rotation of the African and Arabian plate throughout most of the Cenozoicum (Meulenkamp and Sissingh, 2003)). The opening of basins in the western and central Mediterranean can all be attributed to the result of back-arc extension due to roll back towards the southeast of a northwestwards subducting African plate (Carminati et al., 1998b). The evidence of a north-west dipping convergence during the Neogene is numeral (Carminati et al., 1998b):

1) Volcanism in the southern parts of the European plate 2) Evidence of subduction complexes 3) Tomographic evidence (Fig. 5)

From the late Cretaceous to the Oligocene (Campanian-Rupelian) the western Mediterranean experienced a compressive stage which gave rise to the Pyrenees, the Iberian Range and the Catalan Coastal Ranges due to convergence of the Eurasian Plate and the Iberian Microplate. Carminati et al. (1998b) also claim that the evolution of the western and central Mediterranean is strongly influenced by slab detachment processes. This process occurs in slow converging areas or in areas where a final stage of subsidence takes place, the last one certainly accounting for the Mediterranean. Three certain slab detachment are recognized.

The first one occurs during the Early Oligocene in the Alpine area. After this detachment, a rift phase initiated in the Gulf of Lyons (more a collapse, according to Hippolyte et al. (1993)), the Camargue and Corsica and Sardinia (Fig. 6). From the Late Oligocene to Early Miocene, movement of the Balearic Islands (than however, still under water) away from the Spanish mainland induced the formation of the Valencia Trough through thinning of the lower crust (rift phase one from Comas et al. (1992)) (Sabat et al. (1995) and Carminati et al. (1998b)) (Fig. 6b). During this event, folding and thrust-faulting occurred in Mallorca up to the Middle Miocene.

Fig. 5: Tomographic figure showing subducted lithosphere below the western and central Mediterranean. Each subfigure has two models, EUR89B on top and BSE beneath (Carmintati et al. (1998a) for information about the two models). 7a shows a section through the Alboran and Betics region. 7b shows a section through the Balearic-Provençal basin and 7c shows a section through the Tyrrhenian basin and Appenine region. 7d shows a slice of the entire western Mediterranean at 400 km depth. Positive (blue) values are regions with faster P-waves, whereas negative (red) regions have slower P-waves. Regions with subducting lithosphere have colder temperatures, leading to faster movement of P-waves and thus negative relative values (red colors). The white dots on the little maps represent earthquakes (Carminati et al., 1998b)

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 6: Oligocene to present evolution of the Western Mediterranean area. Location of the area during the first slab detachment on figure A. On figure B, movement of the Balearic Islands created the Valencia Trough in the Late-Oligocene to middle-Miocene. Also the Corsica and Sardinia block moved eastwards, creating the Balearic-Provencal basin. Figure C: from the Middle Miocene onwards, the area resulted in about its current shape. BP= Balearic Promontory, NB-P= North Balearic- Provencal Basin, SB-A= South Balearic-Algerin Basin, ALB= Alboran Microplate, EBE= Emile- Baudot Escarpment. VT= Valencia Trough, CA= Calabria microplate, KA= Kabylies (Mountain range in northern Algeria/Tunesia) (Acosta et al., 2001).

A second slab detachment might have occurred around the Betic Cordillera in the Aquitanian (Mattei et al., 2006).The reorganization associated with this slab detachment is coeval with the beginning of major active extension and subsidence in the Valencia Trough (Fig. 6b). From the Chatian to the Burdigalian, the region underwent a mostly WNW-ESE extension associated to the anti-clockwise rotation of Corsica and Sardinia. Extensional faults attributed to this event are seen in the Pyrenees, the Iberian Chain and in the Betic area (Carminati et al., 1998b).

The Alboran microplate moved westwards along the EBE during this period (Fig. 6b). This favors the hypothesis of the EBE being a transform fault, as another hypothesis was that the EBE was a structure resulting of NW-SE rift/drift (Acosta et al., 2001). Massive erosion (in two phases, one during the Miocene, which is a fluvial erosion and one during the Pleistocene, which is a marine erosion phase, (Acosta et al., 2001)) resulted then in the gentle slopes observed on the EBE nowadays. Further proof of the EBE being a transform fault is its linearity and internal and external morphology (Acosta et al., 2001), while step-like morphologies (associated to extensional regimes) are not recognized.

The eastwards movement of the Corsica-Sardinia block continued until a continental collision occurred in the Late Oligocene between the active margin of the islands and the passive Adriatic margin. The anti- clockwise rotation of the islands however continued until the Langhian, it is then that spreading in the Balearic-Provençal basin stopped (Vigliotti and Langenheim, 1995). In the Early-Miocene (Burdigalian, 18 Ma) underthrusting of the African plate under the European ends and soon, detachment faults are recognized in the Edough massif area (Northern Africa) (Monie et al. (1992) and Carminati et al. (1998b)). While in the Balearic-Provençal basin, the rift evolved into an oceanic stage, in the Valencia Trough, no oceanization occurs and the activity gradually stops during the Early Miocene-Langhian (Banda and Santanach (1992) and Meulenkamp and Sissingh (2003)). The extensional phase found in northern parts of the Valencia Trough (rift phase 2 in Comas et al. (1992)) is also found in the southeastern parts (Balearic area), but at the same time, this region underwent a compressional stage (NW-SE orientated) responsible for the formation of the Betic Ranges and the rise of some parts of the Balearic Promontory above sea-level (Early Langhian, Middle-Miocene). The extensional phase

19 originated probably from thinning of the lower crust and the compressional phase from thickening of the upper crust (Sabat et al., 1995). The thickening was the result of a tectonic phase recognized in Northern Africa and the Balearic islands (the Tell orogen) and can be attributed to the still ongoing convergence of the two continents although subduction had already ceased (Carminati et al., 1998b).

Fig. 7: Evolution of the western and central Mediterranean during the Neogene. Open triangles indicate slab detachment places, filled triangles the retreating subduction and no triangles indicate collisional stages. The long dashed lines indicate the position of the Balearics, Corsica, Sardinia and the North African coastline at 30 Ma, the short dashed at 21 Ma, the solid lines at 18 Ma and the grey filled are the present positions. The red line indicates the transition from the first opening stage to the second. After Carminati et al. (1998a).

The Early Langhian marks the beginning of a major tectonic reorganization, resulting in the end of the opening of the western Mediterranean basins and a more intense opening of the Central Mediterranean, due to the third slab detachment (Carminati et al., 1998b). The end of the opening of the Western Mediterranean is coeval with the end of the rotation of Corsica and Sardinia. At the same time, the main rifting phase in the Alboran Sea occurred (Comas et al., 1992).

This third slab detachment occurs at the end of the early Langhian along the northern African margin. This detachment resulted in the beginning of the extensional tectonics in the central Mediterranean, as a shift off active expansion occurs from the western to the central Mediterranean (Tyrrhenian Basin) due to this event. This is known as the second opening phase of the Mediterranean. While extensional

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain features were already recognized in the Late-Oligocene in the Tyrrhenian basin, subsidence didn’t occur until the Langhian, starting at the eastern coast of Corsica. The major rifting phase in the Tyrrhenian basin is of Tortonian-Middle-Pliocene age and the place of maximum extension shifted towards the southeast during the Plio- and Pleistocene. As a consequence, oceanic expansion shifted along. Extension occured in the Vavilov (northern Tyrrhenian) (4,3-2,6 Ma) and the Marsili basin (southern Tyrrhenian) (1-0,1 Ma). This last oceanization phase is induced by the translation of the Calabria block, detached from the Sardinia basement as rifting initiated. As extension occurs in these basins, compression is registered in the Apennines. This whole process creates the opening of the central Mediterranean (Carminati et al. (1998a), Carminati et al. (1998b) and Meulenkamp and Sissingh (2003)).

2.2.1.3 Messinian Salinity Crisis

1) Gibraltar arc The Gibraltar arc comprises the Rifian and Betic Cordilleras and is very important for the development of the Messinian Salinity Crisis (MSC). During most of the Miocene, exchange between Atlantic and Mediterranean water went via a broad Gibraltar arc (Paleomaps in appendix A). Extensional tectonics during most of the Miocene made sure that the passage remained. During the Late-Miocene (Tortonian) however, the region underwent a drastic change in tectonic regime: from extensional to a complex pattern of compressional and strike-slip tectonics (Mattei et al. (2006) and Comas et al. (1999)). This was due to the change in convergence direction between the Eurasian and African plate from N-S (about 200 km of convergence according to Comas et al. (1999)) to NW-SE (50 km of convergence according to Comas et al. (1999)) and the accompanying stop in roll-back processes (Mattei et al., 2006). This process resulted in the gradual uplift of the Betic and Rifian belt systems, blocking eventually the inflow of Atlantic water.

Fig. 8: A) Betic and Rifian corridor at the Late-Miocene. B) Gibraltar Strait nowadays. Kouwenhoven et al. (2003) after E. van Assen (personal communication, 2002).

Fig. 9: Position of the Betic and Rifian corridor, the two connections with the Atlantic Ocean of the Mediterranean during the Messinian (Warny et al., 2003).

2) Messinian Salinity Crisis During the MSC, which lasted only 640 ka (Rouchy and Caruso, 2006), the connection between the Mediterranean Sea and the Atlantic Ocean was closed off, so that the Mediterranean Sea almost completely dried out, creating huge evaporitic deposits within its basins. No climatic role is believed to have played a role in the causes of the MSC (Fauquette et al., 2006).

Rouchy and Caruso (2006) identified two big episodes in the MSC, corresponding to respectively deposition of the Lower and the Upper evaporarites (Fig. 11).

The first stage (6.3-5.6 Ma) consists of thick (up to 1600 m) homogeneous halite deposits in the deepest basins, deposited during a glacial period (Fig. 11 and Fig. 10). Early evaporitic deposition in Sicily coincides more or less with the beginning of glacial conditions around 6.2-6.1 Ma. Although glacial influence is a factor that contributed to the first stage (as there are several glacial low-stands during the period between 6.22 and 5.55 Ma), it was not the main cause, as there is a lag of about 200 ka between maximum glacial stages (TG22 and TG20) and the onset of evaporitic deposition. A global sea-level drop of about 30-100 meter together with the uplift of the Betic and Rifian corridors is one of the main reasons for the MSC (see further), certainly for the first stage, which is accompanied by the largest drop in sea-level (about 1000m) of the Mediterranean. The first stage ended with a last glacial peak (TG12).

The second stage (5.6-5.3 Ma) is associated with a rise in freshwater contribution, culminating during the Lago Mare-event. The deposits from this period are mostly freshwater, with some marine interruptions (the marine episodes decreased in occurrence towards the end of the Messinian). This increase in freshwater input is due to the tighter closure of the oceanic gateways (discussed later) and

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain the wetter conditions prevailing, delivering more freshwater through runoff. The second stage ended abruptly (and thus ending of the MSC was abrupt) at the beginning of the Pleistocene (Zanclean), when a new oceanic gateway was established, which flooded the Mediterranean practically instantaneous.

According to Fauquette et al. (2006), three phases have been recognized in the MSC. The first phase is from 5.96-5.80 Ma and involves a global sea-level drop. A second one (5.80-5.70 Ma) is a sea-level rise and the third is the actual desiccation of the Mediterranean (5.70-5.33 Ma), associated with a sea-level fall of about 1000 meters.

Fig. 10: Distribution of the evaporites formed during the MSC. Note that the area studied does not contain any evaporites (Rouchy and Caruso, 2006).

The mechanism responsible for the MSC is the tectonic uplift of the Rifian and the Betic corridor (Fig. 9), leading to fragmentation and constriction of the connection between the Mediterranean and the Atlantic Ocean (Krijgsman et al. (1999) and Warny et al. (2003)). The constriction started already before the Messinian: Kouwenhoven et al. (2003) believe it started in the Late-Tortonian, but according to Seidenkrantz et al. (2000), it started much earlier. The problems with determining the exact onset of the process are dating problems and the complexity of the Betic and Rifian Cordilleras.

A) Betic and Rifian corridor Three phases are recognized in the closure of the Betic and Rifian corridors:

1) 9.8-9.3 Ma: Shallowing of the corridors (Betic and Rifian) due to tectonic uplift. 2) 9.3-7.17 Ma: Especially between 9 and 7.5 Ma, closure of the Betic Strait occurring gradually, with the western parts closing earlier than the eastern ones. This caused lower oxygenation of the Mediterranean waters, resulting in more low-oxygen benthic fauna, found in sections described in Seidenkrantz et al. (2000). According to these authors, the most severe restriction

of the Betic Strait occurred at 8.5 Ma. Restriction of the Betic Strait caused the TSC (Tortonian Salinity Crisis, discussed later). 3) 7.17-6.7 Ma: At 7.16 Ma, several benthic foraminifera indicating well-oxygenated bottom- waters disappear throughout the Mediterranean (p.e.: Monte Del Casino (Kouwenhoven et al., 1999) and Metochia Section in Gavdos (Seidenkrantz et al., 2000), Fig. 12). The cause for this shift is believed to be the partial closure of the Rifian corridor, causing the onset of the real MSC.

Fig. 11: Polar glacial conditions induced from marine isotopic records in the left panel, TG are the isotopic stages inferred from general isotopic curves. In the right panel, observed deposits and changes in the Mediterranean area are given (Rouchy and Caruso, 2006).

B) Betic corridor Vertical uplift along faults due to compression caused the differentiation of the Betic corridor into different basins in the Tortonian. Micro-basins connected to the Mediterranean had already evaporite deposits in the Late-Tortonian (7.8 Ma) due to evaporation of the enclosed sea water, called the Tortonian Salinity Crisis (TSC) (Krijgsman, 2002). The Betic corridor was certainly entirely blocked at 6.1 Ma (certainly the central and eastern parts), as there are land mammal exchanges between Spain and Morocco at that time (Kouwenhoven et al. (2003), Garcés et al. (1998) and Krijgsman (2002)).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

C) Rifian corridor Further closure of the Rifian Belt is described in Warny et al. (2003). He found that tectonic uplift exceeded glacio-eustatic sea-level rise and inhibited the influx of Atlantic waters. He recognized two steps in closure of this gateway. The first one occurred between 6.8 and 6.26 Ma due to a gradual tectonic uplift of the region causing shoaling of the corridor. From 6.26 Ma onwards (second stage), the passage was so shallow, that minor glacio-eustatic changes affected the entering of Atlantic waters greatly (Kouwenhoven et al., 2003). After 5.4 Ma, tectonic uplift had made sure that almost full continental conditions were present at the Rifian corridor, deducted from pollen analysis (Warny et al., 2003). The re-entering of Atlantic waters went most likely via a breach elsewhere, the Gibraltar arc (Warny et al. (2003) and Fauquette et al. (2006)).

Fig. 12: Location of different important land-sections for investigating the Mediterranean area during the MSC (Kouwenhoven et al., 2003).

2.2.1.4 Plio-Pleistocene evolution of the Balearics The present physiography of the Balearic region is a result of structural displacement from the Late- Miocene to recent. The Balearic region knows two main structural directions: NE-SW (due to movement of the African Plate with respect to the Eurasian plate) and NW-SE, which are along reactivated Hercynian faults (Stanley et al., 1976). The NE-SW-faults record important vertical displacements from the Miocene (Obrador et al., 1971). Afterwards, in general, the region underwent foundering during the Pliocene and more gentle subsidence during the Pleistocene. Some places were more affected by these processes than others, e.g. the Mallorca Channel is a result of this large-scale subsidence (Stanley et al., 1976). As a consequence, a thick Plio-Pleistocene sequence was able to develop in this region, with on its surrounding slopes and shelves, expression of Plio-Pleistocene eustatic changes. The canyons in the region (e.g. the Cabrera Canyon (Stanley et al., 1976)) therefore have both a tectonic and sedimentary origin. The canyons are mostly positioned along pre-existing faults.

ernand Mediterranean Central 1: Summaryof the evolution West theof geological Table

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

2.2.2 Stratigraphy and sediments

2.2.2.1 Balearic Promontory and surroundings

1) Local seismic stratigraphy Stanley et al. (1976) described the Balearic Rise and its surrounding regions based on seismic profiles and correlation with ODP-site 124 (located in the Balearic-Provençal basin, about 200 km S-SE of Menorca, Fig. 10). These authors observed in general 5 different seismic units (Fig. 14):

1) The lower one is the acoustic basement (B). The unit is mostly present between the islands, but sometimes, this unit occurs as pinnacles of intrusive volcanics in overlying units, especially on the shelves. 2) The second unit includes the N-reflector and usually consists out of 3-5 reflectors. The nature and age of this unit is unknown. Stanley et al. (1976) think it is post-Oligocene in age. Also, it is quite rare, as it does not occur at most places. 3) A third unit, acoustically transparent, is commonly present. The upper boundary is unconformable. It used to be called “couche fluante” and although no halite was recovered at site 124, it has been interpreted as a salt layer, because of observation of “plastic tectonics”. This unit occurs however more in the Algerian basin than on the Balearic platform. 4) The fourth unit is a very expressive and important one, called the M-reflector sequence. It usually comprises six to nine reflectors, is very extensive and ranges in thickness, when present, between 100 and 300 meters. Drilling shows that it consists out of alternating layers of dolomites and gypsum or anhydrite of Messinian age (although it has to be noted that the unit is not synchronous throughout the entire region). Sometimes, this unit reaches the sea-floor, but mostly a fifth and final unit lies unconformable above. 5) This fifth unit is the Plio-Quaternary unit (consisting of 10 to 20 reflectors) and has bottom layers which are more transparent (Pliocene age) and evolve upwards into layers with high- amplitude reflectors (Pleistocene age) (Fig. 14d). Thicknesses vary between 100 and 700 meters, when present. On the Balearic Rise, thickness will be more in the order of 100 meters and the lower layer of this unit does have reflectors (Fig. 14d). The lithology consists out of fine to medium grained turbidites of hemipelagic (sediments from continental shelves or rises) origin. The more undeep the setting is, the coarser grained the sediment is.

Some of these units are also recognized by other authors. One of these is Acosta et al. (2001), he has seismic profiles cutting the central depression in an east-west direction. In these profiles, the unit containing the M-reflector is present, followed by a Plio-Quaternary unit. This last unit has the same subdivision as observed by Stanley et al. (1976), which is a more transparent lower part, which evolves into a higher-amplitude upper part. Also, volcanic pinnacles cutting through the upper units are found, in this case on the EBE.

Seismic profiles shot across site 975 are displayed in Curzi et al. (1985). The profiles have a Plio- Pleistocene sequence with a lower, more transparent unit (Pliocene) and an upper, high-amplitude unit (Pleistocene) (Fig. 13).

Fig. 13: Seismic profile through drill site 975, ODP leg 161. Above the M-reflector, a Plio- and Pleistocene sequence is present, with the Pliocene being way more transparent than the Pleistocene (Curzi et al., 1985).

In Acosta et al. (2004), description of the Plio-Quaternary cover in the area is performed in more detail. This unit rests on the unit containing the M-reflector. These authors recognized U- to V-shaped features in this unit, interpreted as erosive features from the MSC. As a result, these features must be paleo-river valleys. The transparent unit above, is inferred to be a fine-grained deposit, rapidly deposited, with its age being Messinian to early-Pleistocene. The unit is found in seismic profiles from cores from deep sea drilling sites (DSDSP leg 124, leg 134, sites 371 and 372 and ODP leg 161, site 975; for location of these sites, Fig. 10) around the Promontory. The cores display a lithology of calcareous silty clay and ooze. The sediments are hemipelagic, gravity-driven deposits, containing sapropels (discussed below). This unit smooths the irregular surface of the eroded M-horizon and leaves a quit smooth upper boundary. Thought of being a fine-grained soft mud, this unit has the possibility of sliding along the underlying M- horizon. Finally, the upper unit of well-stratified layers is interpreted as being a Plio-Quaternary turbidite sequence. The overall lithology is carbonate-rich sediments, going from fine-grained muds in deeper parts to coarser turbidites on slopes. In this unit, transparent lenses are present which may represent buried debris flows. Faults have affected the sediments and have created an undulating surface and scarps due to slumps. This makes sure that thickness of the Plio-Quaternary cover increases down-slope.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 14: Seismic profiles in the Balearic region. The upper boundary of the acoustic basement (B) is indicated in red, the M- reflector in orange and the N-reflector in blue. Above the M-reflector usually lies a thick Plio-Pleistocene sequence. In profile D (in our investigated area), the border between the Pliocene and Quaternary sequences is indicated in pink. A huge offset crossing the Miocene strata is present. After Stanley et al (1976).

Table 2: Summary of lithostratigraphic units for ODP site 975; mbsf= meters below seafloor (Comas et al., 1996).

Uni t Age Lithology Sedimentary structures Interval (mbsf) I Pleistocene to Major: Nannofossil or Alternating dark and light bands, 0-305.2 (*) Pliocene- calcareous clay and through Core975B-18X Miocene silty clay

Nannofossil ooze Foraminifer -rich silt laminae, through Core 975B-18X Bioturbation, common throughout; large burrows especially noticeable in Cores 975B-18X through 33X Slumps in Cores 975B-13X and 975C- 13Xand26X Minor: Organic -rich Color banding layers II Pliocene - Major: Micrite and Thinly interbedded and finely 305.2 -307.0 (*) Miocene? micritic silty clay laminated

Minor: Calcareous silty Thin beds; graded or laminated sand III Miocene Gypsum and Finely laminated, nodular, and coarse 307.0 -317.1 (*) gypsiferous chalk grained with micrite matrix

Minor: Clay to micrite - Thin beds rich clay Foraminifer- Thin laminae in Section 975B-34X-CC rich gypsum silty clay Thin laminae in Section 975B-33X-CC Anhydrite (*): Depth varies depending on the cores

2.2.2.2 Mallorca-Menorca and its shelves In the vicinity of the investigated area, fewer groundtruthing is available. Therefore, an exact knowledge about the nature and the age of the prevailing sediments (especially the Plio-Pleistocene) is not possible. Acosta et al. (2002) stated that the sediments present on the Balearic shelf consist out of biogenic sands and gravels with high percentages of carbonates (77-84%), but this is of course being very general.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 15: Geological map of the Balearic islands, with in detail, the map of Mallorca, indicating the Miocene Llucmajor platform. The position of the two grids is displayed. Source: http://servicios3.mma.es/siagua/visualizacion/lda/images/mapa-geologico-g.jpg

The basement of the Balearic Promontory crops mostly out on Menorca, but is present on all of the islands. A Silurian to Permian succession is overlain unconformable by carbonates from the Triassic to Lower Cretaceous. Lower to Middle Miocene limestones cover the southwest side of the island and mark the most recent member of the basement successions. Above these Miocene limestones, the reef deposits are positioned. The reef deposits have a basal unit (about 200m thick on Mallorca) consisting of Heterostegina Calci-siltites (Heterostegina is a foraminifer and the most important fossil in this unit). This indicates towards an open shelf environment (Pomar, 1991). The ESCI (Earth Sciences Incorporated) profile described in Sabat et al. (1995) shows deformed Middle-Upper Miocene deposits which thicken basinwards (Fig. 16). The units occurring in these deposits are Upper Miocene reefal deposits (consisting of Lower Tortonian ramp and Tortonian-Messinian coral-reef deposits according to Pomar (2001)) and thus again carbonates. The reefs present on Mallorca are locally very wide (up till several tens of kilometers of multiple-phase reefs) with a reef front and a lagoon.

Fig. 16: part of the ESCI profile showing the southern Balearic platform. This profile shows deformed Middle-Upper Miocene strata beneath a Plio-Pleistocene cover (Sabat et al., 1995).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

The Upper Miocene reefs are not only present on Mallorca and Menorca, but in other western Mediterranean sites, Fig. 17 (Pomar, 1991).

Fig. 17: Distribution of the Middle-Upper Miocene reefs of the Western Mediterranean. The position of the two grids is displayed. After (Pomar, 1991).

The Lower Tortonian Ramp mainly crops out on Menorca, where it is described as the lower Bar Unit (Obrador et al., 1992). On Mallorca, this unit is only known from boreholes and does not crop out (Emeis et al. (1996) and Pomar et al. (1996)). Above this unit lies the Upper Tortonian-Lower Messinian coral- reef platform. This consists of progradational reef-rimmed deposits on all Balearic Islands and has an extensive outcrop around the Llucmajor area, southwestern Mallorca, bordering the northern grid and only 40 km off the southern grid (Fig. 18) (Pomar (1991), Pomar et al. (1996) and Hüssner et al. (2001)). Fig. 18 shows the border of the reef platform on Mallorca, clearly indicating that the northern and southern grid are located on its edge.

Fig. 18: LLucmajor platform and platform margins inferred by Hüssner et al., 2001. The position of the two grids is again displayed. After Hüssner et al. (2001).

According to Pomar (1991), the different lithofacies present in this unit are (Fig. 19):

1) Open-platform facies: calc siltstones which grade into reef-slope facies (laterally and vertically) 2) Reef-slope facies: calc siltstones and calcarenites at distal slopes and clinoforms (up to 100s meters) calcarenites and interbedded red algal biostromes. 3) Reef-front facies: Present at Cap Blanc (just north of the northern grid). It consists of coral framestones. 4) Lagoon and back-reef facies: Not always present. Consists of bioturbated calcarenites or bioclastic sediments, depending on its position (respectively outer or inner lagoon).

The reef mainly consists of just three reef-builders: Porites, Tarbellastreae (both scleractinian corals with a tube-like morphology, Tarbellestrae is the last reef-builder present in the area before the MSC) and Siderastreae (only in the reef crest). Also reef terraces are present, one reef has been built over the previous one (Pomar (1991) and Hüssner et al. (2001)), Fig. 20.

Above the reef deposits, sediments of Pliocene and Pleistocene age are observed, as the reef deposits are of Late-Miocene age. In seismic profiles in the vicinity of Mallorca, Acosta et al. (2001) recognized Pliocene-Quaternary sediments consisting of Pliocene marls and Quaternary calcarenites and marls. These sediments have been affected by destabilization and slumping in areas where steep slopes occur, producing downlapping layers or turbidites, depending on the region (slumps/canyons) (Acosta et al., 2002).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 19: Hypothetical section through a Miocene reef from the Llucmajor platform (Pomar, 1991).

Fig. 20: Real transect through the Llucmajor platform on Mallorca. Progradational reefs are visible, divided into three major facies with a Quaternary cover. After Pomar (1991).

2.2.2.3 Turbidites and contourites

1) Turbidites Turbidity currents are mostly periodic currents, consisting of sediment-loaden water, that move rapidly downslope in another fluid (in this case, seawater). Turbidites occur frequently along convergent plate margins, submarine trenches or submarine canyons. All of them are hyperpycnal flows, flows whose gravity is higher than that of the surrounding water mass. The term turbidite for a deposit is however used too quickly in some cases. One has to make a distinction (where possible) between debris flows and turbidity currents. A cohesive flow type is a characteristic of a debris flow, while turbidity currents have a non-cohesive flow type (Haughton et al., 2009). Several classification schemes have been proposed, with one of the most recent that of Mulder and Alexander (2001).Their scheme is based on

35 the cohesivity of particles, flow duration, sediment concentration and particle-support mechanism. They distinguish:

1. debris flows (which are cohesive and matrix-supported due to the high amount of particles) 2. hyperconcentrated density flows 3. concentrated density flows 4. turbidity flows

The last three are non-cohesive flows, mentioned in order of decreasing cohesivity. The first one is supported by particle-interactions, while the last three are supported by fluid turbulence. The boundary between the different subdivisions is not conclusive and depends on the situation. What’s more, one type can evolve into another type, for example when sediment supply decreases or when more and more fluid is incorporated, cohesive flows can evolve into non-cohesive ones. Also within the non- cohesive flows, one type can grade into another. Post-depositional changes (soft-sediment deformation, erosion, …) may even make an interpretation more difficult.

Turbidites have three major possible origins according to Piper and Normark (2009):

1. Transformation of failed sediment 2. Hyperpycnal flow due to river discharge or glacial meltwater release 3. suspension of sediment due to oceanographic processes (currents, storms). This may have been important in periods of low sea level.

Turbidites preferentially build up sediment to the right (on the northern hemisphere) of their channel once velocities have decreased or when slopes have diminished, this due to the Coriolis force, deflecting them to the right. The preferential sediment deposition to the right induces a channel migration to the left (again, only in the northern hemisphere, in the southern, the opposite occurs) (Faugères et al., 1999).

Channels and levees, lenticular facies, chaotic facies, parallel facies, … all of these features are recognized in turbidite systems (e.g. Alonso and Ercilla (2003)). They are difficult to determine solely based on seismic profiles, as other mechanisms (e.g. contourites) can cause the same deposits.

An example of a turbidite system is given in Fig. 21.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 21: Seismic profile from the Almeria Turbidite System with channels and levees in a Plio-Quaternary sequence (1: Lower Pliocene, 2: Upper Pliocene, 3: Lower Quaternary, 4: Upper Quaternary). BA= acoustic basement (Alonso and Ercilla, 2003).

2) Contourites Contourite drifts originate due to sediment accumulations by a current. Many types of currents can cause them: a bottom current as well as a wind-driven current can be the source. Contourite drifts deposits have a wide variety of dimensions, going from <100 km 2 to over 100.000 km 2 (Faugères et al., 1999). Faugères et al. (1993) state that they are commonly formed during high-stand system tracts and during a fall of sea level (when turbidity currents are less common). Based on the bathymetric framework, current velocity, sediment and time of deposition, five categories of drift deposits can be discerned (Table 1 of Faugères et al. (1999)):

1) Contourite-sheeted drift: broad, low amplitude-configuration basin floor “carpet”. Sediment waves are present. 2) Elongate-mounded drift: Elongation mostly (sub) parallel to the margin. Perpendicular orientation is possible in some cases (margin trend change and current interaction). This type resembles turbidite deposits and the two are thus often confused (Fig. 23). 3) Channel-related drift: Small, erosional flows with discontinuities. At the channel exit, a chaotic fan is mostly present. Discerned from turbidites as they are way thinner and contain erosional discontinuities. 4) Confined drift: Present in any morphological “confined” setting. Two topographic highs is enough to create a confined drift, an example is noticed by Van Rooij et al. (In Press) in the Danois drift in the Bay of Biscay (Fig. 23).

5) Modified drift-turbidite systems: An interplay between turbidite and contourite deposits is possible. Downslope turbidites can for instance be modified by contour currents and vice versa.

Observed seismic facies of contourites include transparent layers, parallel reflectors of low amplitude, chaotic, discontinuous reflectors, sigmoidal progradating reflectors, wavy reflectors and horizontal layers truncated by an erosional surface. Examples are given in Fig. 22.

Fig. 22: Two examples of contourite deposits. A) The Flemish drift (northeastern New foundland margin) shows a burried channel-levee system. B) Contourite drift from northeastern Brazil showing an alongslope progradation and a canyon filled with gravity deposits (g) and contour current deposits (c). tc= turbidity current and bc= bottom current (Faugères et al., 1999).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 23: An example of a Mounded and confined drift (Van Rooij et al., In Press).

3) Distinction Discerning contourite from turbidite deposits is difficult, as they share a lot of characteristics. The seismic facies described above for contourite drifts are also found in turbidites, implying that looking at seismic facies along is not enough. However, some seismic facies are more characteristic for turbidites than for contourites:

- Well-stratified, horizontal, parallel reflectors - Progressive channel-levee migration, channel switching and channels having two levees - Deep erosion in channels (contourite drift deposits have less erosion in their channels) - Facies deposited on a steep slope are naturally more indicative of turbidites than contourites (characteristics are chaotic reflectors, scars and lenticular transparent seismic facies)

One has to look at the entire picture though to make a sure distinction. Prevailing currents, slopes, geometry, sediment migration, sea level, climate, … All of them have to be taken into account and even then, an interpretation is difficult, as combined or alternating contourites and turbidites are also known. Especially along western margins of oceans, where western boundary currents can interfere with downslope turbidites, for instance, the eastern margins of the USA (Faugères et al., 1999).

2.3 Hydrography

2.3.1 Present-day hydrography

2.3.1.1 Mediterranean Sea The Mediterranean Sea has a negative hydrological balance because evaporation exceeds the hydrological inputs (Lacombe (1983), Frigola et al. (2008) and Millot (1999)). Thereby, if the Mediterranean would not receive water from the Atlantic Ocean, it would dry out. The Mediterranean has an anti-estuarine circulation pattern (Kouwenhoven and van der Zwaan, 2006). Estuarine circulation is the pattern in which water flows out of the basin at the surface and in the basin at greather depths. Anti-estuarine circulation thus involves shallow-water inflow and deep-water outflow (both of them via the Gibraltar Strait in this case (Fig. 24) (Bardají et al. (2009) and Pierre (1999)). It is now believed that this anti-estuarine circulation persisted throughout the last glacial cycle. Sea level has a big impact on the exchange of water between the Mediterranean and the Atlantic Ocean, for example when sea level was down by 120 meters (during the last glacial period) advection (exchange of heat with the Atlantic waters) of the MOW was reduced by 30-50% due to the reduced exchange via the Gibraltar Strait (Bethoux, 1984).

Fig. 24: Anti-estuarine circulation pattern through the Gibraltar Strait. AW= Atlantic Water, MOW= Mediterranean Outflow Water, LIW= Levantine Intermediate Water and WMDW= Western Mediterranean Deep Water.

The water masses pattern in the Mediterranean can be seen in general as a superposition of three layers: surface waters (0-200 m maximum), intermediate waters (200-2000 m on average) and deep waters (below 2000 m). The surface waters flow, generally spoken, east- and northwards, the intermediate flow westwards, as do the deep waters (Pierre, 1999).

1) Surface waters In the Mediterranean, surface waters consist of Modified Atlantic Water (MAW) entering the Mediterranean via the Gibraltar Strait. They flow in the upper 200 meters of the sea eastwards along the

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

African coast (in the Algerian current) forming a series of clockwise eddies (Bardají et al., 2009). The Algerian current flows into the Eastern Mediterranean via the Sicily Strait (a narrow, 460m deep, passage between Sicily and Africa, preventing deep water exchange between the western and eastern Mediterranean) or gets diverted towards the north via the Tyrrhenian Sea, Ligurian Sea, Gulf of Lyons eventually all the way into the Valencia Trough (Bardají et al., 2009), Fig. 26. The surface waters are located at a maximum depth of about 200 meters (Fig. 25) (Klein et al., 1999). As the surface waters move eastwards, their salinity increases (with almost 2‰), as evaporation rates increase also (Fig. 25) (Pierre, 1999).

Fig. 25: Salinity transect across the Mediterranean. Salinity increases from west to east by more than 2 ‰. Two deep waters are recognized: Western Mediterranean Deep Water (WMDW) and Eastern Mediterranean Deep Water (EMDW). The Levantine Intermediate Water (LIW) is present at lower depths. Annual mean evaporation rates are indicated at the top (Comas et al., 1996).

2) Intermediate waters Four types of intermediate waters are recognized in the Mediterranean, three according to Send et al. (1999) and one found by several authors (e.g. Malanotte-Rizzoli et al. (1999) and Millot et al. (2006)):

1) Levantine Intermediate Water (LIW) (200-1000m average depth range, but extremer depths to 1800m can be observed (Millot, 1999)) has a high salinity and temperature. Its origin lies in the eastern Mediterranean. The LIW is formed as a consequence of evaporation and thus sinking of MAW (Modified Atlantic Water), water originating from the AW. Mostly in the winter, when temperatures are down, cooling induces denser waters and thus more sinking (Pierre, 1999). It flows towards the west, where it enters the western Mediterranean through the strait of Sicily, flowing just below the surface waters (200-460 meters deep), known as the Eastern Outflow Water (EOW). It is though not the only intermediate water running through the Strait of Sicily. The LIW increases in salinity and temperature in the western Mediterranean (Millot et al., 2006). LIW used to be formed only in the Levantine Basin, but some quit recent changes made sure that LIW is formed in multiple places in the Eastern Mediterranean. The Southern Aegean Sea disturbs the pathway of the LIW by producing the Cretan Intermediate Water, a water mass that is positioned deeper than the LIW itself. This makes sure that LIW is positioned higher than it

used to (Klein et al., 1999). CIW spreads partially into the Levantine Basin, partially blocking the exit of the LIW towards the west (Malanotte-Rizzoli et al., 1999). 2) Winter Intermediate Water (WIW) (100-300m depth range) is formed in the Gulf of Lyons, Ligurian Sea and along the Catalonian coast when waters gain a larger density due to cooling. As it name implies, this water mass is formed only in (some) winters, depending on the mean temperature of that winter. After a cold winter, WIW is present, after a warm one, it is not. When this water mass is formed, it flows towards the Valencia Trough, where it can disturb the outflow of other intermediate waters (like LIW) towards the Algerian Basin (across the Ibiza Channel) as the WIW occurs as lenses and sometimes blocks other flows (Fig. 27). For instance, WIW makes sure that LIW is positioned in deeper parts of the basin and is deflected into the Balearic current (see further). The WIW does not penetrate to depths where the LIW flows, but flows above it. Its temperature is below 13°C, which is among the lowest temperatures measured in the Mediterranean (Table 1 of López-Jurado et al. (2008)). 3) Adriatic/Aegean Intermediate Water (500-1200m depth range) incorporates water, as its name implies, from the Adriatic and/or Aegean Sea. They flow into the Western Mediterranean through the Strait of Sicily, together with the LIW. Millot et al. (2006) state that in the 1990s, due to a succession of exceptional meteorological conditions (known as the Eastern Mediterranean Transient), the Aegean Water became more dense than the Adriatic and replaced it as a constituent of the EOW. 4) The Cretan Intermediate water (CIW) spreads from the western Cretan Sea into the Ionian Sea. Malanotte-Rizzoli et al. (1999) state that during 1991, the CIW replaced the LIW in the Ionian Sea and thus took over the EOW that year. The part of the CIW flowing towards the east re- enters the Cretan Sea by being diverted by an anticyclone, just east of Crete.

3) Deep waters Two big types of deep water masses are recognized in the western Mediterranean according to Send et al. (1999):

1) Western Mediterranean Deep Water (WMDW) (beneath 2000 meters) originates in the Gulf of Lyons through deep convection. The WMDW is mainly formed in the winter, when cold and dry winds (northwesterlies) cause loss of surface buoyancy (the water gets colder and thus denser, sometimes only a few days is enough) so that mixing at greather depths can occur (Send et al. (1999) and Bardají et al. (2009)). These newly formed waters cause spreading of these heavier waters in the deep parts (estimates say that about 75% of the water formed eventually sinks) (Send et al. (1999) and Frigola et al. (2008)). The WMDW remains in the deeper parts of the western Mediterranean, except in the Gibraltar Strait, where it rises to about 300 meters, to exit the Mediterranean (Bardají et al., 2009). 2) Tyrrhenian Deep Water (TDW) (about 2000 m and deeper) is formed in the Tyrrhenian basin and it is now thought that most of the deep waters in the western Mediterranean are of this origin. It is formed through mixing of the upper parts of the inflowing WMDW (from the Algerian Basin (Millot, 1999)) with the lower parts of the LIW (coming from the Sicily Strait and cascading into the Tyrrhenian Sea, thereby reaching depths up till 2000 meters (Millot, 1999)) and flows out of

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

the basin via the Sardinia Channel, together with the remaining LIW (1900 m water depth). TDW is of equal importance in the Algero-Provencal Basin as is WMDW, formed in the Gulf of Lyons.

Fig. 26: Current pattern in the western Mediterranean with named currents relevant for the next section. G.S.=Gibraltar Strait, S.S.=Sicily Strait. Solid lines are strong currents, dotted lines are gyres or less strong offshoots. After Bardají et al. (2009).

In the Eastern Mediterranean, deep waters were formed in the Adriatic Sea. The Adriatic Deep water (ADW), formed in the southern edges of this basin by convection, flows over the sill of Otranto (The sea between the heel of Italy and Albania) into the Ionian Sea and spread as a bottom-hugging water mass. As it goes into the Eastern Mediterranean (especially, the Levantine Basin) the current is called the Eastern Mediterranean Deep Water (EMDW) (Malanotte-Rizzoli et al., 1999). However, in 1999 discovered, the Aegean Sea is also a big source for the EMDW (Klein et al. (1999) and Malanotte-Rizzoli et al. (1999)). Water that flows out of the Cretan Strait is denser and spreads west- and eastwards. The eastward push, into the Levantine Basin, creates the EMDW nowadays (Malanotte-Rizzoli et al., 1999). This change in source for the EMDW shows us that the circulation patterns are very dynamic and constantly changing in the Mediterranean.

Eventually, the WMDW (now TDW) and the LIW join in the Alboran Sea to leave the Mediterranean via the Gibraltar Strait as the MOW (Millot (1999) and Millot et al. (2006), Fig. 24).

2.3.1.2 Area around Balearic Promontory The Balearic Promontory is the scenery for the exchange between the cooler, more saline waters from the north (originating from the Gulf of Lyons) and the southern, warmer waters (originating from MAW) (Pinot et al., 2002).

Fig. 27: Present-day currents around the Balearic Promontory. Black lines are superficial currents, grey lines are deep water currents. The grey area is the Gulf of Lyons, where the WMDW is partially formed. AC stands for the anticyclonic gyre which blocks the northern current, depending on the climatic conditions (see text for further info). Adapted from Frigola et al. (2008)

The WMDW is formed partially and the WIW almost completely, in the Gulf of Lyons due to sinking of shelf waters in the winter (Monserrat et al., 2008). These deep waters then flow westwards towards the promontory where they get diverted due to the sudden steep rise of this structure (bathymetry in Fig.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

27). The WMDW gets diverted towards the south and eventually continues flowing westwards south of the promontory as can be seen on Fig. 27 (Frigola et al., 2008).

Surface waters and intermediate waters flow into the Valencia Trough, coming from the southern coasts of France. Once they enter the Valencia Trough, they enter the Northern Current. The current can leave the basin via two ways (Fig. 27):

1) The current can flow through the Ibiza Channel (which is mostly used for southward movement of saltier waters) towards the Algerian Basin, where it loses its expression (Bardají et al., 2009) due to the occurrence of more recent inflowing MAW. 2) The current can get diverted along the north side of the promontory (at that moment it is called the Balearic current) and flow into the Balearic-Provençal Basin (Pinot et al. (2002) and Frigola et al. (2008)). This last current receives not only its strength from the Northern current, but also from north moving water masses (originating from anticyclonic gyres in the Algerian basin, consisting of MAW) across the Mallorca channel (Bardají et al. (2009) and Monserrat et al. (2008)).

The strength of the Balearic current is controlled by the strength of the anticyclonic eddie occurring in the Gulf of Valencia. This eddie consists of WIW, formed in the Gulf of Lyons and lies at depths of about 100-300 meters (a typical value for WIW in the region). A strong anti-cyclonic eddie is generated in the spring and summer after a relatively cold winter, a relatively weak one after a mild winter (Monserrat et al., 2008). When the eddie is strong, it blocks the Northern current heavily and most of it gets diverted into the Balearic Current. On the other hand, when the eddie is weaker, most of the current passes through the Ibiza Channel into the Algerian Basin (Pinot et al., 2002), leaving a weak Balearic Current.

Werner et al. (1993) studied the surface currents on the southwestern coast of Mallorca. They concluded that during ideal summer sea-breeze conditions (this breeze comes from the SW), the studied area is an area of very weak currents, while when storm conditions prevail (storms are mainly from the WSW), the area undergoes northwesterly currents with strengths varying between 30 cm/s in the south and up till 50 km/s in the north, Fig. 28. As storms occur more during glacial periods (Einsele, 1993), the currents during storm conditions characterize these periods better and summer-breeze conditions characterize interglacial periods better.

Fig. 28: Surface currents in the studied area. During wind-still conditions (A) and during storm conditions (B). Again, the two grids have been indicated (Werner et al., 1993).

2.3.2 Paleoceanography

2.3.2.1 Paleocurrents Kouwenhoven and van der Zwaan (2006) reconstructed the circulation pattern prior to the Messinian Salinity Crisis. The basin had then already the same anti-estuarine circulation pattern as nowadays. These authors developed their own paleo-oxygenation-index, using benthic foraminifera exceeding 125 µm. An increasing trend towards heavier oxygen isotope composition has been found, indicating increasing bottom water salinity after 7.2 Ma. Pierre (1999) concluded that in the Mediterranean, the salinity and δ 18 O values have the following relationship:

δ18 O= 0.25*S-8.2 where S = salinity

This correlation is specific for the Mediterrranean (as it has higher salinities than other waters). Due to the uplift of the Rifian corridor (after closure of the Betic corridor (Fig. 9)), deep waters could not flow into the Atlantic anymore, preventing flushing of the deeper parts of the Mediterranean and thereby increasing its oxygen isotopic signal (Kouwenhoven and van der Zwaan, 2006). The same authors found no exceptional change in isotopic composition of intermediate water depth sections, thereby implying that intermediate waters were not affected and may have become decoupled from the deep water masses. The authors also suggest a more or less same three-layered water flow system as today with formation of LIW in the east, deep water formation in the proto-Adriatic and superficial inflow from the Atlantic (Fig. 29). In Fig. 29, the Paratethys is the shallow sea positioned from the Alps over Romania, all the way to Lake Aral.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 29: Reconstruction of the paleo-circulation in the Eastern and Central Mediterranean during the Miocene. More or less the same circulation pattern as nowadays ruled, with exception of an offshoot of superficial currents in the Paratethys (Kouwenhoven and van der Zwaan, 2006).

Frigola et al. (2008) described variations in circulation patterns based on a sediment core (IMAGES core MD99-2343, 32.44 m long in a water depth of 2391 m; 40°29.84’N, 04°01.69’E) offshore northwestern Menorca for the last 50 ka. They concluded that WMDW was controlled by fluvial runoff (and thus freshwater lenses). This was in turn determined by long-term precipitation records and thus insolation changes. The WMDW has three modes: weak, intermediate and strong. Which mode the WMDW is in, depends on the factors just mentioned before. When lots of freshwater enters the Mediterranean, like after a GIS (Greenland warm Interstadial), stratification increases, density of the bottom waters increases and the WMDW goes into a strong mode. During GS (Greenland cold Stadials), less freshwater enters the basins, surface waters get denser and mixing can occur, which results in a less strong circulation.

2.3.2.2 Sea level Cores have been taken in the surroundings of the study area which can yield us a regional δ18 O-curve. Pierre et al. (1999) deducted one from drill site 975, about 200 km south of Menorca (Fig. 10), the curve can be seen in Fig. 30.

The variations in δ18 O represent the changes in the Northern Hemisphere ice volume between glacial and interglacial conditions (about 1.2‰ in the North Atlantic) plus a local (Mediterranean) multiplier (for further information about this, see Pierre et al. (1999)). These changes in ice volume (preserved in e.g. foraminifera shells) induce a change in sea level. Low δ18 O values represent warmer, interglacial stages and thus high sea levels, while high δ18O represent cold, glacial stages and thus low sea levels (as 16 O preferentially goes into the ice and leaves 18 O in the oceans). Miller et al. (2005) state that other factors affect the δ18 O-signal in sediments as well: temperature, evaporation-precipitation effects and postdepositional alterations. Thereby, correction factors have to be implemented if a sea level curve is derived from δ18 O-measurements.

Pierre et al. (1999) recognized four major intervals in the record based on frequency of glacial periods and the amplitude between glacial and interglacial period:

1) Interval 4 (1900-1700 ka): The amplitude of sea level was very smal (about 1‰). 2) Interval 3 (1700-900 ka): A slight increase in amplitude (0.3‰), a 40 ka (obliquity-controlled) periodicity. 3) Interval 2 (420-900 ka): The amplitude in sea level increases substantially (from 1.9 to 3.5‰), but an eccentricity-periodicity (100 ka) starts. 4) Interval 1 (0-420 ka): High amplitudes and 100 ka-periodicity (eccentricity) of sea levels are recognized.

Fig. 30: δ18 O-curve for the last 2000 ka. Black numbers indicate the isotopic stages. Red numbers indicate the different intervals. Interval 1 goes from 420 ka till recent, interval 2 from the MPR till 420 ka, interval 3 from 1700 ka till MPR and interval 4 from 1900 till 1700 ka. More explanation is given in the text above and below. After Pierre et al, (1999).

Lisiecki and Raymo (2005) published a global benthic δ18 O curve for the last 5.2 Ma. Fig. 31 is constructed with their data and focuses on the Plio- and Pleistocene. Sea-level-correlations were made based on correlations of Miller et al. (2005). These authors published sea-level curves for the entire Phanerozoic based on backstripping and δ 18 O values. The δ 18 O values are derived from Pacific and Atlantic cores and a 0.1‰/10 m correlation has been used. Although the Mediterranean has a slightly different evolution with respect to a global curve, the correlation has still been used, bearing in mind that a small error thus is implemented.

The obtained curve shows a gradual decline in climate and sea level from the Latest Miocene to present. During the Lower Pliocene, the curve shows a more or less stable, high sea level, but other authors (e.g. Haq et al. (1987)) state that the sea level kept rising untill 4.2 Ma. A drastic cooling around 3.5 Ma, induced by the glacio-eustatic climate variations, itself due to periodic growth of northern hemisphere ice sheets (which we still know today) is observed. From that moment onwards, a gradual decline is observed in sea level, which lasted till about 1.6 Ma. After 1.6 Ma, sea levels are extremely variable.

The Upper Pliocene Revolution (UPR) indicates the moment at which permanent ice sheets are present on the northern hemisphere and is associated to a drastic cooling. In the curve, this cooling lies at about 2.5 Ma, but consensus is at 2.4 Ma. From that moment onwards, drastic climate changes are characteristic and are caused by the changing amount of northern hemisphere ice sheets.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

From 2.4 to 0.9 Ma, the changes are obliquity-controlled (Ruddiman, 2008). The last 0.9 Ma (after the MPR, Mid-Pleistocene revolution), they are eccentricity-controlled (100 ka) (only in the Alboran Sea, 42 ka alternations are observed till 420 ka (von Grafenstein et al., 1999)). The MPR is coincident with a large cooling, due to permanent ice sheets on Antarctica. The sea-level amplitudes rose from 50 meters before to 100 meters after the MPR (Ruddiman, 2008). The 420 ka-boundary represent the onset of the maximum extent of this ice-sheet on the northern hemisphere (Pierre et al., 1999).

Fig. 31: δ18 O –curve for the last 5.2 Ma. Data are from Lisiecki and Raymo (2005) and correlation with sea levels is based on Miller et al. (2005). The UPR indicates the first occurrence of permanent northern hemisphere ice sheets and the MPR a change in controlling orbital parameter. The dotted line indicates the large drastic cooling event after which glaciations occurred in the northern hemisphere. MPR= Mid-Pleistocene Revolution, UPR= Upper Pleistocene Revolution.

3 Material and Methods

3.1 Geophysical dataset The seismic data were acquired by the Renard Centre of Marine Geology (RCMG), Ghent University (as subcontracter of the Vrije Universiteit Amsterdam), during a seismic survey off the southwestern coast of Mallorca in 2003. 46 lines were shot divided into a northern and a southern grid (Fig. 37) using a SIG sparker with Applied Acoustic CP1000 powersupply.

Table 3: Source specifications of the seismic survey

Source specifications Name SIG sparker Number of Electrodes 100 Voltage Pulses 3.8 kV Energy Pulses 0.3 -0.5 kJoule (Applied Acoustic CP1000 Powersupply ) Frequency 300 -1200 Hz, average: 700 Hz Shot increment 2 meters Speed of boat 4 knots(or about 6.5 km/h)

The record length of the profiles is 700 milliseconds (ms) TWT, both for northern and southern grid. The penetration is locally variable as it depends not only on the source itself, but also on the substrate through which the waves go. From the obtained profiles, some values of three parameters (registered at random points in random profiles) are registered in Table 4. Table 4 shows that the penetration depends on the depth at which the reef occurs. As the reef consists of hard carbonates, which attenuate most of the seismic wave in their upper parts, the penetration is not very deep. The waves that go through soft sediments penetrate deeper as they attenuate less. This makes sure that in the northern grid (where the reef is almost at the seafloor), not much observations can be made, while in the southern grid (where the reef is positioned deeper), they can.

Table 4: Penetration from the signal in relation to the depth of the seafloor and reef.

Depth of seafloor (ms TWT) Penetration (ms TWT) Depth of reef (ms TWT) 250 550 520 21 0 340 315 200 500 470 160 300 270 150 290 260 70 100 80

A sparker source sends a propagating sound wave trough the water and rock sequences beneath. The shape of such a wave can be seen in Fig. 32. The reflectivity (R) depends on the contrast in acoustic impedance (Z) between the two sequences:

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Z − Z R = 2 1 + Z 2 Z1

−1 ≤ R +≤ 1 The acoustic impedance in turn depends on the density of the substrate and velocity of the propagating waves.

When the wave travels through a boundary between two sequences with highly contrasting acoustic impedance, the reflection will consist of multiple “lines” (Fig. 32). How many lines depends on the threshold value, which is a set value. When the contrast in impedance is smaller, the reflection will be much thinner and contain less “lines” (Fig. 32). The highest contrast in density is noticed at the seafloor, where water has a density of about 1030 g/m 3 and the sediment on average 1650 g/m 3. This gives a reflector of mostly 2 dual lines (two blue and two orange ones, Fig. 32), as can be seen on every profile (e.g. Fig. 34). The contrast in the sediment itself is way smaller than that at the seafloor and thus at most 1 dual line per reflector occurs (Fig. 32).

Fig. 32: Left: an example of a seismic wave. Middle: Seismic wave going through a high density contrast boundary, giving multiple lines for 1 reflector. The seafloor is an example. Right: wave going through a low contrast boundary, leaving 2 lines per reflector. The boundary between units in the sediment itself is an example.

The receiver is a single channel SIG streamer. This receiver is capable of amplifying the received signal up till 40 times its original value.

Table 5: Receiver specifications of the seismic survey

Receiver specificatio ns Name Single channel SIG streamer Number of hydrophones 10 analogues ones Amplification 40x Record length 0.7/0.5 seconds

3.2 Multibeam bathymetric data The multibeam bathymetric data were obtained during several cruises (from 1974 to 1998 during the Spanish Exclusive Economic Zone Program surveys) and are the same as those discussed by Acosta et al. (2004). The data were collected with a Simrad EM-12S (a full ocean echosounder) and an EM-1000 system (works in depths between 3 and 1000 meters). 100% of the seafloor was covered with a 33% overlap between adjacent tracks. The navigation was done using a double differential GPS system. The accuracy of the data is ± 10 meter. The data were progressed using the Neptune and Roxar’s Cfloor software (editing grid generation) and IberGIS (Digital Terrain Model and morphometric treatment).

3.3 Methods

3.3.1 Seismic processing The obtained profiles were processed by the VU Amsterdam, according to the following work-flow:

1. The data were converted from an ELICS format (a Delph software format, used to acquire high- resolution seismic data of mostly shallow water settings) to SEGY (Motorola 2 bit format). This last format can be loaded into the “The Kingdom Suite” software packet. 2. A swell filter (to correct for the up- and downward movement of source and receiver) and a bandpass filter (retaining frequencies between 0 and 1350 Hz) have been used. 3. Multiple reflections were removed 4. The initial data have finally been converted to data shot at assuming a constant velocity (1500 m/s). The signals shot, travel at different speeds at different depths; thereby it is difficult to determine the exact depth at which the reflectors occurs. By assuming a constant velocity, one can know the exact depth of every reflector.

Not all of the data has been processed, below a list with all of the profiles that have been. When a profile is processed, the name of the profile is added with “_out” (for example: 45 becomes 45_out).

Table 6: Number of the profiles that underwent the above described processing

09 17 23 32 36 41 11 19 24 33 37 43 13 21 25 34 38 45 15 22 27 35 40 46

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

3.3.2 Seismic interpretation

3.3.2.1 Loading profiles into “The Kingdom Suite”. First of all, when loading profiles into the “The Kingdom Suite” (Seismic Micro-Technology, Inc.), the world coordinates have to be inserted, so that the profile can be located exactly. This is performed by loading the .NAV-files (coordinate files) into “The Kingdom Suite” (an example of how such a .NAV file looks like is given below in the upper part of Fig. 33). The positioning of the profiles can be done by “The Kingdom Suite” by loading a template, guiding the program through the navigation file.

Fig. 33: When the template is loaded, “The Kingdom Suite” can interpret the navigation file.

The second step is inserting the actual seismic data. The profiles (both processed and non-processed) were loaded into the program as a SEGY-format (.tra). The data are in Big Endian (a term indicating how the bytes are organized in bigger computer units, as for example bits), meaning that the most significant bytes come first. The data have time intervals instead of depth intervals. Fig. 37 shows all of the lines with a multibeam background.

In total, 46 lines have been acquired, 2 of them could not be loaded into “The Kingdom Suite” software packet, which leaves us 44 workable profiles. These 44 profiles are divided into two grids, a northern (10) and a southern (34) one, the southern grid contains all the processed profiles.

The northern grid is located in the north, closest to the coast. It consists out of 10 profiles which were not processed by the steps described above and as a consequence, lots of multiples are visible (Fig. 34).

On most of the profiles from the southern grid (located close to the shelf edge, west of Cabrera), the corrections have been applied. Penetration in these profiles goes to a depth of about 400-500 ms (while record length always remains 700 ms TWT), at these depths, multiples are found deeper and leave more room for expression of the sediments.

The seafloor reflector consists out of multiple lines (mostly 3 to 4), this due to the strong difference acoustic impedance between the water and the sediments. Conversion of milliseconds TWT into meters water depth can be done by applying the mean values op propagating waves in water and sediment, respectively 1450 (global average value for water) and 1650 ms TWT (average value from boreholes in ODP leg 161, site 975 (Comas et al., 1996)).

3.3.3 Description of seismic data After having loaded the profiles into Kingdom, units and sequences can be discerned on the base of their seismic characteristics. Seismic data can be discerned based on reflection terminations or reflection configuration (Mitchum et al., 1977). This allows us to properly describe the obtained seismic data.

Sequences consist of concordant layers bounded by discordant ones above and below or consist of concordant layers finishing laterally against a discordant boundary. These boundaries can consist of top- discordant relations (erosional truncation or toplap) and of base-discordant relations (onlap and downlap). Offlap occurs when layers fade out internally in a sequence (due to thinning of the layers below the seismic resolution) (Mitchum et al., 1977).

Once a sequence is defined based on its boundaries, its internal configuration can be described based on seismic reflection parameters: configuration, continuity, amplitude, frequency and interval velocity. Especially the reflection configuration gives valuable information of each sequence. Common configurations are parallel (subparallel), divergent, prograding (sigmoid, oblique, shingled and hummocky), chaotic or reflection-free. Examples can be seen in Fig. 36 (Mitchum et al., 1977).

The external form of sequences is also a discerning characteristic, containing information on the depositional environment and area of sediment of source. One of the factors influencing the external form of the sequence is sea level. The different external forms recognized are: sheet (drape), wedge, bank, lens, mound, fan and fill. This last one can further be subdivided, they display a large range of internal configurations as can be seen on Fig. 36. (Mitchum et al., 1977).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 34: Profile 02 from the northern grid. The white numbers indicate some of the multiples observed in this profile.

A clear definition of what exactly is a sequence and what is a unit does not exist. Several authors tend to give their own interpretation to that (e.g.: A seismic sequence is a group of reflections that share the same characteristics and are distinctly different from the other sequences (John et al., 2005)). Therefore, it is might be difficult to know what is exactly meant by these names. In our paper, a unit is deposited due to one depositional regime. For instance: a eustatic unit (due to a rising and falling sea level), a seismological unit (due to an earthquake), and so on. A sequence consists out of several units and originates from a marked change in depositional regime. For instance, deposits from the UPR (Upper Pleistocene Revolution) till present comprise 1 sequence (but consist of several units). The UPR indicates a change in controlling factor of the sedimentation and thus a marked change in depositional regime.

3.3.4 Map making Maps of the seismic data were mostly made in “The Kingdom suite”, by computing the isopach map in between two horizons. The assumed interval velocity is 1700 ms TWT (the average value of propagating waves through sediments). Smoothing is kept low, so that sharp boundaries do not lose their expression. All the used parameters can be seen in Fig. 35. Afterwards, the maps were adapted in “CorelDRAW X3”.

Maps from the multibeam data are from “GlobalMapper” (Global Mapper Software LLC). Exporting the entire multibeam data (or a part of it) into “CorelDRAW X3” (Corel) (and adapting them) generated the maps necessary. A small amount of maps originate from “Fledermaus” (“A powerfull interactive 3D data visualisation system”, according to the website of the manufacturer, IVS 3D). Exports were made to adapt them in “CorelDRAW X3”.

Some of the multibeam maps have been processed in “Surfer 9” (Golden Software) to add isopach contours to them.

Fig. 35: Parameters used for isopach maps.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain after Mitchum al.(1977)). et after Mitchum ns ns Van (seeRensbergen forexplanation) text (1996 36: Overview of the reflection seismic 36: Overview configuratio Fig.

Fig. 37: Position of the seismic profiles in the northern grid.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 38: Position of the seismic profiles in the southern grid.

4 Results

4.1 Multibeam bathymetry

4.1.1 Mallorca channel In the Mallorca Channel (diameter of about 60 kilometers), consisting of the Central Depression (CD) and the Northern Incision (NI), depths of just over 1000 meters are obtained (in the CD in its most central part and in the NI in its northern parts, Fig. 39). The two depressions almost connect, a small ridge (Ibiza-Mallorca ridge, named by Stanley et al. (1976)) separates them. The centre of the Mallorca Channel is quite flat without major topographies, apart from one ridge (R1 in Fig. 39). The deepest parts of the CD are N-S aligned and form a major canyon: the Cabrera Canyon (name from Stanley et al. (1976)).

Towards the west, two guyot-shaped (a guyot is a flat-topped mountains) heights are observed: Mont de Ausias Marc and Mont dels Olivia. They have height differences in the order of 300 meters. In the south, another major topographic expression is noticed: the Emile Baudot Seamount (EBS). The height difference with the surrounding area is in the order of 500 meters. Several cone-shaped mounts are present around the EBS. They are on average 2 kilometers wide and have a height difference of about 100-150 meters (10 have been indicated on Fig. 39). The EBS forms, together with the outstanding part of the southern Mallorca shelf and the Island of Cabrera, the Cabrera Ridge (name from Stanley et al. (1976)).

The shelves of Mallorca and Ibiza are cut off in the south by the Emile Baudot Escarpment (EBE) (direction NE-SW). It has a very clear expression, as height differences over 1500 meters are observed. The distance between head and toe of the EBE is on average 10 kilometers and slopes range between 10° and 18°. Lots of canyons cut the EBE (indicated in red in Fig. 39). The direction of these canyons is always about NW-SE, more or less perpendicular to the EBE.

The shelf break is indicated by the red 200 m-contour line. The northern Mallorca shelf, north of the Ibiza-Mallorca ridge is cut by several canyons (also indicated in red). Their direction is more or less E-W. The shelf and shelf break south of this ridge will be discussed in the next section.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

and are explained in the text. CD= Central yed the following figure.in thern thern Incision. displa area the is The white boxin . The most important structures have been indicated : : Multibeam map of the Mallorca Channel 39 Fig. Depression, EBS=Seamount,Nor EmileBaudot NI=

4.1.2 Southwestern shelf and shelf break of Mallorca Fig. 40 displays a zoom from the large multibeam data set, covering the studied area and its relevant surroundings to the west. This allows us to describe the area in greater detail.

The southwestern and southern shelf of Mallorca varies greatly in width. The western shelf is about 20 kilometers wide, while the southern shelf is over 40 kilometers (including Cabrera). The average slope is 0.5°. The shelf does not display many topographic features. In the northern grid, three small heights are observed (diameters just under 1 kilometer), with heights of 5 (most northern), 15 (most eastern) and 10 (most southern) meters above the surrounding area (labeled P in Fig. 40). West of these depressions, a couple of minor drops in height are observed on the shelf (labeled D).

In the shelf break just west of Cabrera, a canyon system is observed (C in Fig. 40). This canyon system cuts into the shelf and moves the 200 meter contour-line landwards (making sure that some profiles of the southern grid are positioned within the canyon: Fig. 37 and Fig. 38) and seems to have two channels (seismic profiles show this as well: Fig. 50). Channel 1, the northern one is more or less E-W-orientated and has a deeper thalweg than the second channel (which is NE-SW-orientated). Both of them drain towards the deeper parts of the CD.

The shelf break north and south of canyon C has a totally different appearance. To the south of C, a clear shelf break and a steep slope, basinwards of this shelf break, is observed. The shelf break in and south of this canyon shows four closely-packed, step-like, lowerings (dotted white lines in Fig. 40). North of C, no clear shelf break is noticed and the shelf gradually goes into the slope and eventually the CD. Some minor steps are though observed on the shelf (labeled D on Fig. 40). The shelf break in the north has multiple mass transport deposits (MTD) (M 1-6 in Fig. 40). All of these MTD’s and even canyon C drain towards the deep parts of the CD, towards the Cabrera Canyon. One other feature present in the shelf break north of canyon C are small depressions, ten have been recognized in Fig. 40 (S). They occur up till 20 kilometers north of canyon C.

4.2 Seismic stratigraphy

4.2.1 Northern Grid

4.2.1.1 Seafloor Numerous multiples are observed in the northern grid and this due to the fact that this grid has been shot in very shallow waters (50 to 100 milliseconds (ms) TWT) (an example can be seen in Fig. 34), very close to the coast of Mallorca (Fig. 37), and thus causes the seafloor-reflection signal to be received multiple times.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

. Discussed structures have been indicated. S are t the the and M1-6 shelf aredeposits. the Mass transport elf and shelf break of Mallorca -like features-like the and, areon threeP depressions : multibeam map of the southern and southwestern sh 40 Fig. depressions,C the canyon, is the are step D

Fig. 41: Multibeam imagery showing the seismic canyon, seen from the west. Two different channels are discerned.

The seafloor in the northern grid (1 to 15 km away from the coast) moves basinwards with a gentle slope gradient, no major topographies have been observed, except for a high “platform” in the middle of the grid (B in Fig. 42). Only at the intersection of lines 05 and 06, a sudden lowering of the seafloor (about 15 ms TWT in 150 meters, which gives a slope of about 7°) is observed (A in Fig. 42, profile: Fig. 44). In these profiles, the Miocene reef is present very close to the surface (at most 20 ms TWT beneath the surface), which leaves very little space for post-reef deposits. Even the depressions observed on the multibeam data do not leave an imprint on the profiles, as no profiles cut them. The observed deposits in this grid are an amalgamation of sediments. Almost no units can be distinguished (all profiles, but one (profile 03), have almost no horizontally continuing reflectors).

The structures observed in the sea, just above the seafloor (Fig. 43 and right part Fig. 45) could be due to escaping gas or a school of fishes. As no underlying sources of gas and conduits on the seafloor are observed, fishes are the most likely.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 42: Depth of the seafloor in the northern grid. A indicates the lobe that has is situated higher and B indicates the place where the small leap in seafloor is observed, discussed in the text and visible on Fig. 44.

Fig. 43: Profile 30 in the northern grid, showing small channels. A is the biggest of them and mentioned in the text. The structure in the left could be due to escaping free gas or a school of fishes.

Some smaller channels are present in the seafloor in the northern grid (for instance, the biggest in profile 30 is 100 meters wide and has a height difference of 4 ms TWT, A in Fig. 43). Small levees to the southwest and northeast are observed along these channels.

4.2.1.2 Seismic results At the intersection of profiles 05 and 06 (Fig. 44), the reef is situated deeper, which leaves room for some post-reef deposits. In profile 06 (partially displayed in Fig. 44) the post-reef deposits are situated between 105 and 160 ms TWT. Two units can be recognized within; unit N1 and N2. The first one, just above the reef edge (purple reflector), has a chaotic appearance (at some places it is almost reflection- free), with some small continuing reflections within. The second unit is situated between the black and red reflector and has higher amplitudes. It consists out of more continuing, wavy, (sub) parallel reflectors in the northwest, while in the southeast, a small more or less fill structure is observed with a gentler slope in the northwest than in the southeast. An erosional contact with the seafloor marks the upper boundary.

Fig. 44: Part of profile 06. The seafloor is indicated in red, the reef edge in purple. The black reflector shows the lower boundary of the laterally continuous reflectors. The multiple occurs already at a depth of about 220 ms TWT. The leap in the southeast is discussed in the text.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

4.2.2 Connection profiles Although a connection profile has been shot between the two grids (profile 28), it does not contain any transition. All it contains are reefs almost reaching the seafloor, a small amount of sediment on top and lots of multiples. Profile 22_out (Fig. B2) (having overlap with profile 28) shows different sequences: the reef gently going upwards and decreasing amounts of post-reef sediments. The overlapping parts of profiles 22_out and 28 are displayed in Fig. 45. Obviously, the supposedly overlapping parts are different (black boxes in Fig. 45). This implies that either profile 28, either profile 22_out contains wrong data. As profile 23_out (Fig. B3) (perpendicular to 22_out and 28) shows an excellent correlation with profile 22_out and not with profile 28, conclusion can be that probably profile 28 contains wrong data. This means that no connection profile can be presented and that correlation of the two grids is not possible.

Fig. 45: Parts of profiles 22_out and 28. The black boxes in each profile indicate the parts that normally should overlap. As can be seen, there are no similarities at all. In profile 22, a channel in the seafloor is observed (described in the text below). In profile 28_out, the circled features could again be due to fishes or escaping gas.

4.2.3 Southern Grid The depth of the seafloor in the southern grid is displayed in Fig. 46.

The reflection of the seafloor consists out of multiple reflectors (on average 4-5) in every profile (processed and non-processed), the explanation for this phenomenon has been given in Material and Methods.

The seafloor in the southern grid displays a more intense morphology than the one in the northern grid. In general, an increase in depth from the seafloor occurs from northeast to southwest, with an amphitheatre-like scarp in the west-southwest (A in Fig. 46). This scarp gradually fades out, depths within it reach 450 ms TWT. Slopes of the scarp are in the range of 19.5° for its southern border, 8.7° for its eastern border and 13.1° for its northern (these values have been obtained after conversion of ms TWT) (Fig. 46).

On profile 45_out (Fig. 50), a bifurcated channel in the seafloor is observed, just above the position of the steep reef edge. Other SE-NW-orientated profiles show only one channel, decreasing in channel depth eastwards (e.g. Fig. B5 and Fig. 56). The same channel has been observed on the multibeam data and correlation of the bifurcated channel can be done (Fig. 50).

1.5 kilometers from the eastern border of profile 22_out, a channel is observed in the seafloor (see part profile 22_out in Fig. 45), it is too small to be recognized on the multibeam. Its width is about 250 meters and depth about 4-5 ms TWT. Northeast and southwest of the channel, small levees are observed. Profile 23_out (which cuts the channel, Fig. B3) also displays a levee (thickness of 7 ms TWT) to the northwest of profile 22_out

4.2.3.1 Units The units in this chapter are discussed from old to young, based on Steno’s law of superposition.

1) Reef The reef is present in all seismic profiles, where they set the lower boundary for every subsequent deposit on top. It may be considered as an acoustic basement, as no strata are observed below. The reef reaches its highest positions (less than 200 ms TWT below sea level) in the south and southeast of the grid and its lowest in the northwest (more than 600 ms TWT deep). A steep WSW-ENE edge is present in the middle of the southern grid with height differences in the order of 300 ms TWT, slopes are in the order of 0.2 - 0.3 ms TWT/meter. The edge diminishes in height to the east-northeast. The deepest positions of the reef (Fig. 47) show a small depression along the steep edge (arrow in Fig. 47) that goes into a little amphitheatre-like scarp (in the outermost western part, A in Fig. 47) at about the same position as the one in the seafloor. Depths here go to 609 ms TWT. South of the reef edge, two circular areas are observed where the reef is positioned deeper (up till 300 ms TWT) (B in Fig. 47).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 46: Grid of the seafloor, showing a gentle increase in depth towards the southwest and the canyon in the west- southwest (A). The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Fig. 47: Depth at which the reef occurs in the southern grid (boundary R). A indicates the canyon and the reef edge is indicated by the dotted white line. Two depressions south of this reef are observed as well. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

The reef is a homogenous unit with a chaotic configuration, having very few reflectors, sometimes even being nearly transparent (visible on every profile). Only at its upper boundary (R), reflections are abundant and strong (although not being laterally continuous) and they have a chaotic appearance. This upper boundary (R) has a huge contrast with the more transparent units above (e.g. Fig. 53), which leaves a good marker for the upper boundary. The boundary itself has a very irregular surface, with many V-shaped wedges (V-shaped depressions with height differences ranging from 10 to 70 ms TWT) and sudden steep falls (with the most extreme one, the steep edge (Fig. 50)). The biggest wedges are indicated in Fig. 50, Fig. 53 and Fig. 56.

2) Post-reef deposits The deposits above the reef are mainly concentrated in the west and the north, in the places where the reef has its deepest positions. In Fig. 48, two areas are recognized in the southern grid: an area where the reef almost reaches the seafloor (the dark blue and black areas) and an area where there is a thick sedimentary cover (the green and light blue area). The boundary between the two is sharp and steep in the southeast, while in the northeast, there is a more gradual transition. In the southern part, two small places where more deposits are present are observed (1 in Fig. 48). Thicknesses up till 100 to 150 ms TWT are present in these places.

In general, 2 major sequences can be discerned in the profiles from the southern grid. A more or less transparent lower sequence and a well stratified upper sequence, the latter having reflectors with higher amplitudes (e.g. Fig. 50, Fig. 53 and Fig. 56).

A) Sequence 1

Sequence 1 is characterized as an almost acoustically transparent sequence, deposited mostly on top of the reef. Thicknesses vary between 70 and >150 ms TWT. Based on its transparency, two units can be recognized.

1) Unit 1A a) Base and isochron map (Fig. 47 and Fig. 49)

The base of the unit is formed by the reef (boundary R), thereby its base map is Fig. 47. The base for this unit is a very irregular surface consisting of lots of wedges. The unit is observed only in the west- southwestern parts of the grid (e.g. in Fig. 56, the unit is not observed anymore). The thickest deposits are close to edge, just northwest of it (thicknesses up till 100 ms TWT thick), it fills the small canyon observed in the reef (zone 1, Fig. 49). Northwest of these thickest parts, a zone of thinner deposits is observed (on average 25 ms TWT, zone 2, Fig. 49). The boundaries of zone 2 with 1 and 3 are both parallel to the reef edge (Fig. 49). Northwest of this zone, a zone is observed containing thicker deposits in the west that thin gradually eastwards (zone 3, Fig. 49). The part where the unit disappears in each profile is almost always consistent with overlap of the multiple from the seafloor (e.g. Fig. 53)

Fig. 48: Thickness of the post-reef deposits in ms TWT. To the south of the reef edge, almost none are present, while in to the north, there are a lot. Two circles south of the edge with more deposits are observed. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 49: Thickness of unit 1A. The deposits lie to the north of the reef edge, where three zones are discerned: zone 1 with thicker deposits, zone 2 with thinner deposits and zone 3 with a more or less gradual decline northeastwards. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

b) Seismic facies

The internal configuration of the unit is in general wavy to hummocky, (sub) parallel strata which fade out northeastwards (e.g. Fig. 50), but sometimes a chaotic facies is observed (Fig. 53). They seem to drape the underlying reef deposits. In profile 34_out (Fig. 60), reflectors of higher amplitudes are observed than elsewhere in the unit. The unit disappears in this profile, but due to the expression of the nearby multiple in the profile, the point of disappearance cannot be observed.

The reflectors in the unit are disrupted by sediment movement along vertical faults, especially close to the steep reef edge (Fig. 50). Profile 34_out (Fig. 60), just northwest of the reef edge, displays as well lots of vertical faults. No consistent pattern of lowering or rises across the faults is observed, offsets are in the order of 1-2 ms TWT, at most.

The upper surface (D1) has a quit sharp surface in the west (western part Fig. 50). The surface is though still far less sharp than the reef border. In the eastern parts, a less sharp boundary is observed (e.g. Fig. 53), as the unit gently fades out eastwards.

2) Unit 1B a) Base and isochron map (Fig. 51 and Fig. 52)

The unit is deposited on the erosive boundary of unit 1A (1D) in the western parts of the grid, but in the eastern parts, it covers the reef directly (boundary R) (Fig. 60). The boundary between the two is not visible due to the strange high amplitude reflector in Fig. 60 and in other profiles, the multiple inhibits the observation of the transition (e.g. Fig. 53). The deepest parts of the base are observed along the reef edge (values around 500 ms TWT, number 2 in Fig. 51) and in the west (same values). A gradual rise towards the east is observed, with a major topography in the eastern part (number 1 in Fig. 51), going to depths of about 480 ms TWT.

Unit 1B has its thickest deposits in the northeast. Generally seen, an increase in thickness is observed going from southwest to northeast (±50 to >100 ms TWT). A depression is present in the east, about 1 km northwest of the reef edge (thicknesses are reduced in this depression to values of 25 ms TWT, 1 in Fig. 52). Along the reef edge, thicknesses are reduced as well, sometimes almost no deposits are observed (southwest).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 50: Profile 45_out showing the two channels from the canyon and the four different units present in the area. The pink bold line is the boundary between Sequence 1 and 2 (the same colors are used for every profile in this chapter). The numbers in unit 1B refer to the same subunits as numbered in Fig. 53 and Fig. 56. The numbers in the canyon refer to the two channels observed in the multibeam as well. The dotted black line is the place where the thicknesses of the four units have been measured. AG= aggradation, PG= progradation, C.C.= Contourite Current,. R, D1, D2 and D3 are the names of the boundaries.

b) Seismic facies

Unit 1B is the most transparent unit in the sedimentary deposits. The unit can be divided into three parts:

1) Part 1 has wavy, semi-continuous strata. In general they dip towards the reef edge (e.g. Fig. 53 and Fig. 56). 2) Part 2 has a chaotic configuration with inverted lenticular, discontinuous, hummocky strata. Channel-like features are observed. Profile 45_out (Fig. 50) shows at least ten changes of depositional regimes (small “cut and fill” structures). Onlap, downlap and toplap are all observed. These small channels have a prograding infill. 3) Part 3 has about the same configuration as the reef: almost transparent, with just a couple of reflectors (northeastern part profile 32_out (Fig. 53)).

The boundary between part 1 and 2 is well expressed, with a sharp change in deposit. An exact boundary between parts 2 and 3 is not noticed, but a gradual transition is observed with deposits from part 2 changing gradually into those of part 3 (Fig. B2). In general, the first part occurs just northwest of the steep reef edge, while part 2 occurs 2-3 kilometers to the northwest of part 1 (Fig. 53 and Fig. 56). Profiles which cut the steep reef edge show these two parts (apart from profile 45_out (Fig. 50)). The boundary between the two is sometimes visible, sometimes it is not. Part 3 is observed in the northeastern part of profile 32_out (Fig. 53).

The SE-NW-orientated profiles display the aforementioned parts 1 and 2, but the SW-NE-orientated profiles show only deposits resembling part 1 (Fig. 53). In profile 32_out (Fig. 53), 7 depositional systems (cuts and fills) are observed, divided into two groups: a lower group containing three of the seven and an upper group containing four of the seven systems. A continuous dotted black line marks the boundary. The three lower ones belong to part 1, the four upper ones to part 2. The upper group cuts the lower group. Correlation of some of the cuts was done with those of profile 45_out (Fig. 50) and Profile 38_out (Fig. 56) (they have the same numbering).

Some of the deposits are affected by vertical faults, mostly close to the steep reef edge. The offset along these faults is small, in the order of 1-2 ms TWT.

The upper surface of 1B (D2) is generally quit smooth, sloping. Deep depressions (close to the reef and in the northwest) indicate towards an erosional phase. Again, the boundary in the west-southwest is located deeper, but especially in the canyon, the boundary goes to relatively large depths.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 51: Base map of unit 1B (boundary D1). 1 is the depression in the east and 2 the lower base along the reef edge. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Fig. 52: Thickness of unit 1B. 1 refers to the large depression observed at the top of the unit in the profiles. It is filled with deposits from 2A. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Fig. 53: Profile 32_out. The numbers in unit 1B indicate the cut and fill structures and correlation with profiles perpendicular to this one has been done (Fig. 50 and Fig. 56). The dotted blue line indicates about the boundary between parts 2 and 3 of unit 1B. C.C.=contourite current. R, D1, D2 and D3 are the names of the boundaries.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

B) Sequence 2

The second sequence has a large contrast in amplitude compared to the underlying almost transparent sequence 1. The thickness of this sequence varies between 10 and >200 ms TWT. The increased thickness of this sequence is located in the east of the grid. Again, two units can be discerned based on their amplitudes.

1) Unit 2A a) Base and isochron map (Fig. 54 and Fig. 55)

Northwest of the reef edge, the unit is deposited on an irregular surface (D2): a depression in the eastern part of the grid (depth difference of about 130 ms TWT, number 2 in Fig. 54), a steep decline in the western part (depth difference of about 140 ms TWT, 1 in Fig. 54) and a channel-like feature along the reef edge (diminishing depth difference when going from west to east) are observed. In other parts, a gentle upward gradient is observed going from west to east.

Southeast of the reef edge, two smaller circular depressions (diameters of almost a kilometer, 3 in Fig. 54) are observed, depth differences with the surrounding reef are in the order of 70 ms TWT.

The thickness of this unit varies between 10 and 170 ms TWT. Outside the big depression and the outermost western part, thicknesses are in the range of 20-75 ms TWT. In the depression and the steep western decline (1 and 2 in Fig. 55), the thickness reaches about 150 ms TWT. The two smaller depressions have thicknesses of 50 to 75 ms TWT (3 in Fig. 55).

b) Seismic facies

Unit 2A is the unit with the lowest amplitudes of sequence 2, although the contrast in amplitude with the underlying unit 1B is still huge. This unit mostly fills the large depression in the east and the steep decline in the west of the grid and drapes the other places (Fig. 56). Alternating combinations of units of reflectors having higher and lower amplitudes (on average 5 of them) are observed outside the depression (e.g. Profile 34_out (Fig. 60), where six are observed and Profile 45_out (Fig. 50), where there are 4). These are characterized by (sub) parallel reflectors.

In the depression, an irregular prograding depositional pattern is observed: its northeastern border has a steeper slope than its southwestern one (Fig. 53). In several NW-SE orientated profiles, one or two (depending on the profile) smaller units are recognized, showing a change of direction of deposition in the draping part of this unit (e.g. Fig. 50, Fig. B5 and Fig. 56). Reflectors from the upper smaller unit show onlap onto the ones from the lower one. Both of the units have wavy parallel reflectors.

In the canyon (visible in e.g. Fig. 50), layers display an angle of about 45° in regard to lower boundary (which is about horizontal).

The upper boundary of unit 2A (D3) has a more or less constant slope, going up towards the northeast. One depression is present, in the pathway of the canyon, with depth differences around 100 ms TWT.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 54: Base map of unit 2A (boundary D2). 1 is the depression in the west, 2 is the depression in the east and 3 are the two minor depressions south of the reef edge. See text for further explanation. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Fig. 55: Thickness of unit 2A. The depressions observed in the previous base map have the same expression here, as they are filled with deposits from unit 2A.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 56: Profile 38_out. Numbers in unit 1B correspond to numbers in profile 32_out. The line containing the question marks indicates about the boundary between 1 and 2, inferred from Fig. 53. In this profile, it is not entirely clear. C.C.=contourite current, AG=aggradation, PG=Progradation. R, D2 and D3 are the names of the boundaries.

Fig. 57: Seismic profiles through the most western depression. The dotted, vertical black lines indicate the crossing line of the two profiles.

2) Unit 2B a) Base and isochron map (Fig. 58 and Fig. 59)

The base of the unit (D3) resembles a lot like the seafloor (Fig. 46). Differences are, besides the obvious depth of the base, the two small depressions about 2 km southeast of the reef edge. Depth differences in these depressions go to about 100 ms TWT. Besides these, the canyon system has an expression just northwest of the reef edge and an amphitheatre like scarp is observed in the west of the grid, close to the reef edge.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 58: Base map of unit 2B (boundary D3). Two peculiar features are observed: the depression in the west (1) and the two smaller ones south of the reef (2). Apart from 2, the base map resembles the seafloor a lot. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Fig. 59: Thickness of unit 2B. The two smaller depressions show thicker deposits (2), as does the western depression (1). Along the reef, an increase in thickness is observed (3). 4 shows the part where gradual declines in every direction are observed. The little numbers next to the profiles indicate the depths (in milliseconds TWT).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

This unit is present on top of all of the previously mentioned deposits. In the northwest and west, the unit lies above unit 2A, in the northeast, east, southeast and south, the unit lies on top of the reef (this is in fact the first unit (except for the two small circular depressions south of the reef edge) observed on top of the reef deposits in these places and on top of the reef edge).

Thickness of the unit varies between 10 and 110 ms TWT, the average is about 50 ms TWT. Thicker deposits are present in:

1) In the amphitheatre-like scarp (up till 100 ms TWT) (1 in Fig. 59) 2) The small depressions (about 100 ms TWT) (2 in Fig. 59) 3) In the middle of the grid, along the reef edge (up to 120 ms TWT thick) (3 in Fig. 59) 4) In a large area in the northwest of the grid (thickness between 75 and 100 ms TWT on average) (4 in Fig. 59)

b) Seismic facies

Unit 2B is the unit having reflectors of the highest amplitudes. Most of the reflectors can be perfectly followed along each profile, thus being continuous. An alternation of smaller units with higher and lower amplitudes can be seen. Depending on the profile, up till 10 alternations are present (e.g. Fig. 50 and Fig. 53). Close to the reef edge, they have a sigmoid shape (Fig. 60) (these layers are discussed in the next paragraph).

As in unit 2A, the northwestern parts of NW-SE-orientated profiles display two to three (again depending on the profile) asymmetric channel-like structures (visible in Fig. 50, Fig. B5 and Fig. 56). The channels’ northwestern sides are steeper than their southeastern. In profile 45_out (Fig. 50), one of the channels is part of the lower boundary and two are within the unit. These have a prograding infill. In some profiles, a thick sedimentary cover can be observed on top of the alternating sequences, especially in Profile 32_out (Fig. 53).

This unit also fills the canyon (Fig. 56). Steep dipping reflectors are observed in it, with the dip diminishing upwards, as the canyon gets filled.

The internal configuration of the draping part is characterized by parallel reflectors, which display onlap onto the (rising) reef towards the east. In the southwest, a depression is present, which eroded most of the unit. This is a canyon.

In profile 34_out (Fig. 60), a thin (15 ms TWT) top layer of continuous (sub) parallel reflectors is observed, draping the sigmoidal units. It covers only a small area (about 1 X 1.5 km), as it is only present outside the canyon. On Fig. 60, this is evidenced by being present only on top of the upper parts of the sigmoidal units.

Fig. 60: Profile 34_out showing the sigmoids in units 2A (6) and 2B (12). The reef reflector due to the double profile, the thick black line (explained further; Fig. 63) can be ignored in this case. R, D1, D2 and D3 are the names of the boundaries.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

3) Sigmoidal units

Sequence 2 and especially unit 2B displays a distindistinctictiveve feature: alternating small units of higher anand d lower amplitudes. They have been briefly discussed in the sections above, but will be discussed in detdetailail now. In unit 2A, the difference in amplitude between the units is nonott that big and the amount of alternations depends on whether a depression is filfilledled or not. In unit 2B however, the difference in amplitude is bigger and clear alternations are prespresepresenent.nt.t. In the southwest, the layers are better discernable and more important, more alternations aarere present there than in the northeast ( Fig. 62).

Fig. 61: The thic kness of each sigmoidal unit ha s been measured along of the red line.

Only in profile 34_out (Fig. 60 ), the units have a sigmoidal shape and display onlonlapap (onto the re ef), downlap (onto a lower base in the west) and have totopplaplap (by the seafloor or by the top sediment layer)layer).. The thickness of each sigmoidal unit varies between 5 and 25 ms TWT (measured at the place of the dotted black line in Fig. 61 ). Profile 34_out ( Fig. 60 ) shows that the each sigmoid is deposited in greatgreaterer depths than the pr evious one, thus moving westwards. Most of the sigmoids have some reflectors at their outer parts, but with its internal part being vveryery chaotic and sometimes even reflection -free. The upper surface can be erosive, especially in the northnortheeast.ast.

Alternating layers 12

2 Number of Numberalternations 0

Fig. 62: Plot showing the amount of alternations counted in the SE-NW-orientated profiles. Profile 27_out (Fig. B4) lies in the western part of the southern grid , profile 9_out in the east ern part.

In profile 34_out (Fig. 60), 12 sigmoidal (unit 2B) and 6 divergent (unit 2A) units are counted. The thickness of each small unit has been measured (at the place of the dotted black line in Fig. 60) and is displayed in Table 7. They were divided into categorie s; which have been listed below .

Category A 1-5 ms TWT Category B 6-10 ms TWT Category C 11-15 ms TWT Category D 16- … ms TWT

Table 7: Thickness of the sigmoidal or divergent units in profile 34_out. The numbers with an apostrophe are from unit 2A, the other from 2B.

Sigmoid Thickness (ms TWT) Category Sigmoid Thickness (ms TWT) Category 1’ 20 (*) D 4 7 B 2’ 12 C 5 10 B 3’ 13 C 6 8 B 4’ 7 B 7 8 B 5’ 12 C 8 15 C 6’ 15 C 9 7 B 1 12 C 10 6 B 2 17 D 11 6 B 3 5 A 12 5 A (*): Fills the irregular lower surface

4.2.3.2 Special profile In profile 34_out (orientation from southwest to northeast), we observe an inverse lenticular, very high amplitude reflector cutting through the sedimentary deposits (Fig. 60 and Fig. 63). This reflector fades away into deeper parts. This reflector (and what is beneath it) shows characteristics just like the reef (almost transparent with a very high amplitude upper reflector).

This phenomenon is due to the spherical shape of the waves. As seismic waves propagate, they go in all directions (Huygens principle). The receiver thus gets information from both sides of propagating waves, thereby, it is possible to receive information from two different deposits when the line is shot just at its intersection.

This profile is shot at the intersection of two completely different geological sequences (the intersection between the Miocene reef and the sedimentary cover) and thus a double profile was obtained. In Fig. 63, the yellow line indicates the reef from the southeast, the deposits between the purple and red line are the sedimentary deposits from the northwest (units 1A, 2A and 2B).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. 63: Seismic profile 34_out with the double reflection. The red line is the seafloor. The yellow line is the edge of the reef in the south. The purple line is the edge of the reef from the north. Figure b shows how deep the reef is below the water surface. Figure c shows how thick the post-reef deposits are. In part B and C, the red or white line is the position of the reef edge. The double occurs just at the edge, indicated on B and C by a dashed double arrow.

5 Discussion

The origin of, and the implications on the area of the presence of, the reef and its steep edge (observed in the seismic data, e.g. 45_out) will be discussed, along with the sedimentary cover, observed to the northwest of the edge (its stratigraphy and depositional history). The base for the Quaternary and the Pliocene is still under discussion and has shifted many times in recent years. In this discussion, the assumption is made that the Quaternary and Pliocene have the same base at 2.588 Ma.

5.1 Reef The reef is part of the Middle-Upper Miocene reefs present throughout the Balearic Promontory and even in many parts of the Western Mediterranean (Pomar, 1991), Fig. 17. Fig. 18 tells that the studied grids mostly belong to the platform margin of the Late-Miocene reefs, associated to the Llucmajor platform. The Llucmajor platform has been divided into four parts (Fig. 20). Based on the transect described in Pomar (1991) and the position of the northern grid, it is very likely that the reefs present beneath the northern grid are the open platform and slope facies, consisting of calc siltstones, calcarenites and biostromes. The southern grid is situated about 30-50 km south of the transect and thereby, it is more difficult to know the composition of the reef beneath it, as no drill sites are present in the vicinity as well. Based on the same transect (Fig. 20), either open platform and slope facies, either Heterostegina calci-silites are inferred to be present. As most of the southern grid is supposed to be positoned on the reef platform margin, the southern grid contains most likely the open platform and slope facies.

The described seismic data indicate a huge reef edge, vertically offsetting the Miocene reef deposits (visible on almost every NW-SE-orientated profile), that has a NE-SW orientation. The reef deposits north of this structure are positioned much deeper (about 250 m deeper). Stanley et al. (1976) stated that this structure was an erosional feature, dissected by fluvial erosion. This is consistent with the observations done in this study:

1) The edge has only a small expression, it diminishes northeastwards and eventually fades out entirely. Southwestwards, its expression just stops when the reef platform takes a turn southwards (Fig. 40). 2) A small linear depression along the reef edge is observed cutting into the lower reef deposits. This is a possible fluvial pathway. 3) Steep slopes (which are observed, about 25°) are more consistent with fault origins. However, reefs can contain steep slopes as well, e.g. Webb (2001) described slopes of 20-30° in reef deposits. This is consistent with our slopes. 4) The deposits beneath the sedimentary cover to the north of the edge have exactly the same characteristics as those south of the edge and no boundary between the deposits (no change in characteristics) is observed along the edge.

On the multibeam bathymetric data, a marked change in shelf-break characteristics is observed when going from north to south (Fig. 40). In the north, mass transport deposits (MTD) are ubiquitous and no

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain clear shelf break is present, while in the south, a sharp shelf break and no MTD’s are observed. The change is coincident with the funnel-shaped canyon C, which runs along the edge and separates reef deposits in the south from sedimentary sequences in the north (observed on many profiles, e.g. Fig. 50, Fig. B5 and Fig. 56). This implies that lithology of the underlying units determines the seafloor morphology. A large sequence of soft sediments creates vulnerable shelf breaks, affected by many MTD’s, while hard carbonate reef deposits prevent massive erosion of the shelf break and create a clear shelf break and steep slopes.

The upper surface of the reef is incised by many U- to V-shaped incisions (for instance, Fig. 56). These are likely erosive features, originated during the Messinian Salinity Crisis (MSC), when sea levels were down over a 1000 meters (Fauquette et al., 2006). This left the shelf containing the grids completely open and vulnerable for subaereal erosion. The linear depression observed along the reef edge (depths of about 50 meters) was the most likely pathway for transporting sediment from land towards the deeper Central Depression. This implies that canyon C (Fig. 39) originated already at the end of the Miocene and remained active till now.

The two circular depressions southeastwards of the reef edge have a hemispherical shape (Fig. 57) and are filled with a transparent facies and unit 2B on top of it. The most likely origin for these depressions is during the MSC: subaerial erosion created karstic holes in the carbonate reef, which have been filled during the Plio- and Pleistocene. The high position of the depressions made sure that during these periods, the sediment in the depressions was prone to subaerial erosion, leaving mostly the last unit (2B) in it.

5.2 Depositional history Plio-Pleistocene sequence

5.2.1 General The northern grid only contains some reef deposits and a small amount of sediments on top, presumably of unit 2B. This is concluded based on the fact that only unit 2B is deposited on top of the reef edge (Fig. 56) and the characteristics of the deposits observed in the northern grid resemble those of unit 2B (Fig. 44).

No groundtruthing is known on the Mallorca shelf and thereby, an exact knowledge about the prevailing sediments is not possible. According to Acosta et al. (2002), the sediments prevailing are biogenic sands and gravels that have about 80% carbonate content. This is the probable composition of both sequences.

The observed facies show characteristics that are associated to turbidite and/or contourite deposits:

1) Profile 34_out (positioned just north of the reef edge, almost on top of it) shows (in its northeastern part) sigmoids in unit 2B on a steep lower platform (Fig. 50). 2) Buried (sub) parallel prograding deposits, with some small local cut-and-fill structures are found (for instance Fig. 56 and Fig. B5)

3) All of the seismic facies associated to these kind of deposits (chaotic discontinuous, prograding sigmoidal, low amplitude wavy parallel and erosional features (Faugères et al., 1999)) have been observed in the two sequences.

5.2.2 Sequence 1 The lower unit 1A follows the erosional surface of the Miocene reefs. This is a draping unit with close to the reef small faults, which may have two causes: sediment failure due to the steep reef edge or differential movement due to subsidence as reported by Stanley et al. (1976). The unit is not omnipresent (only in the deeper parts) and has an erosive upper surface (D1), meaning that it either was not deposited, or has been eroded, above a certain depth.

The seismic pattern of part 1 of unit 1B (transparent zones with intercalated low amplitude, wavy, (sub) parallel layers) and a small depression along the reef edge can be interpreted in two ways:

1) Mounded drifts with a moat along the reef edge can account for the observed seismic pattern. Mounded drifts can occur on shelves and upper slopes (which is exactly the depositional setting of this study) and wavy (sub) parallel reflectors have been observed in these deposits. The Faro drift and Davie drift (Fig. 64) are two examples where mounded drifts and moats occur together (Faugères et al., 1999). The faults in unit 1B occur in the depression along the reef edge and could be the result of sediment destabilization on its slopes. The causing contour current (implied to flow parallel to most continuous layers) should have a more or less NW-SE orientation, as NW-SE-orientated profiles (e.g.Fig. 53) display more continuous reflectors than NE-SW-orientated ones (e.g. Fig. 56). 2) Turbidity currents can produce levees on their sides that have the same characteristics as observed in this part of unit 1B. If a turbidity current is causing these deposits, the sediment source should be in the northeast, landwards. Turbidity currents mostly occur however on steeper slopes and slopes are almost absent in this part of the base of unit 1B (Fig. 51).

As the distinction between the two is not possible on seismic data alone (Faugères et al., 1999), favoring one of the two hypothesis is difficult. However, contourite drift deposits are more likely, as NW-SE currents are already observed in the area:

1) The permanent offshoot-current of the Balearic Current flowing southwards across the Mallorca Channel towards the Algerian Basin 2) The semi-permanent NW-SE storm currents inferred by Werner et al. (1993) are possible sources.

The deposits from part 2 occur in the middle of the southern grid, about 2-3 km northwest of the reef edge. The observed seismic facies (nearly transparent, short chaotic discontinuous cut-and-fill structures) are characteristic of channel-related drift deposits. They can be very erosive and are usually confined to a smaller area (a few tens of km 2) (Faugères et al., 1999), this is consistent with the observation that deposits of part 2 cut deeply in those of part 1. A non-consistent switching of channel- structures is observed as well (Fig. 56) which is a characteristic of these kind of deposits as well (Fig. 65)

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

(Faugères et al., 1999). The deposits can be compared to those of the Vema fan (South Brazilian Basin), which have a variety of seismic facies cutting into the lower deposits (Fig. 66).

Fig. 64: Davie drift with a buried channel migration pattern (moat) with next to it, wavy (sub) parallel reflectors of an elongated mounded drift deposit (Faugères et al., 1999).

Fig. 65: Abstract picture of a channel-related drift, showing the switch in channel. (Faugères et al., 1999).

Some factors do however not support a channel-related drift. For instance, these kind of deposits require a channel or two topographic features in between which it can be deposited, however evidence of a paleochannel is not observed. Furthermore, with the reef edge being nearby, a channel-related deposit would be more likely close to the reef edge, as in sequence 2, and not a few kilometers away from it.

Fig. 66: Two seismic profiles of the Vema fan. The red boxes indicate channel-related drift deposits. Numbers indicate different deposits: 1= parallel continuous, 2= chaotic, 3= climbing hummocky, 4= sigmoidal, 5= semi-continuous, 6= onlap fill (turbiditic channel), b.e.d.= basal erosive discontinuity. After Faugères et al. (1999).

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

5.2.3 Sequence 2 Sequence 2 can be divided into three parts: cut-and-fill structures in the northwest, continuous (sub) parallel reflectors in the middle of the grid and sigmoidal, steep dipping layers close to the steep reef edge.

The lateral continuous (sub) parallel reflectors of the second part are probably due to contourite currents. They resemble elongate mounded drifts (e.g. those described by Van Rooij et al. (In Press), Fig. 67). Elongate mounded drifts can occur almost anywhere and are mostly elongated parallel to the margin (Faugères et al., 1999). Here, the elongation (about NW-SE) is indeed parallel to both the land and shelf margin, observed due to the parallel character of the second part in the NW-SE-orientated profiles and their dip and termination basinwards on NE-SW profiles. Cut-and-fill structures (1-1.5 km in diameter) are observed in the elongate mounded drifts. The presence of cut-and-fill structures in elongate mounded drifts is also observed by Van Rooij et al. (In Press) in the Le Danois drift. The existence of cut-and-fill structures infers the presence of a moat, filled afterwards by sediment- delivering currents. A stronger current may induce the erosion necessary for creating the moat. The infill probably happened when currents eventually slowed down and erosion stopped, allowing depositing of sediment again. As several cut-and-fill structures are observed (almost) on top of each other, several periods of intensified currents must have occurred, eroding sediment at the same place.

The infill of the cut-and-fill structures displays onlap onto the southeastern border of these structures (Fig. 50) and therefore indicates towards a northwestern source of sediment. On NW-SE-orientated profiles, the (sub) parallel deposits lay horizontally parallel, while in NE-SW-orientated profiles, they dip basinwards (southwestwards) and have a more convex appearance. This is consistent with a more northeastern source of sediment. Combining the two leads to a current, delivering sediment from the north (northwest to northeast). This current orientation is consistent with 2 known current directions:

1) The permanent offshoot current of the Balearic Current flowing southwards across the Mallorca Channel towards the Algerian Basin 2) The semi-permanent storm-driven current calculated by Werner et al. (1993).

One of these two (or both) can be responsible for the above describe deposits.

Towards the reef, the aggradational (sub) parallel layers are replaced by steep downward facing layers on NW-SE-orientated profiles (Fig. 56) and the basinward-dipping reflectors on NE-SW profiles are replaced by sigmoidal to divergent units (Fig. 60). The deposits are positioned in a steep depression, running along the reef edge (depths differences are in between 85 and 130 meters, Fig. 56). This depression is coincident with the observed canyon C on the multibeam data (Fig. 40). Therefore, canyon C may still have existed during the Pleistocene and the deposits close to the reef edge are probably deposited in its paleo-channel.

The steep dipping layers in NE-SW-orientated profiles suggest a current coming from the northwest, depositing sediment in canyon C. Most likely, the contour currents (causing the (sub) parallel deposits and cut-and-fill structures) were deflected against the steep reef edge and intensified. Contour currents deflecting against topographic heights have been reported before, e.g. by Faugères et al. (1999) and Van

Rooij et al. (2003). They ran parallel to the edge after deflection and eroded almost completely unit 2A, creating a channel. Afterwards, currents must have been reduced and sediment was again deposited in the channel (sediments of unit 2B). The steeper slope in canyon C (5° in it instead of 0.3° outside it) could have created occasional sediment failures, generating sigmoidal units. Destabilization of sediment on steeper slopes has already been reported in the region (Acosta et al., 2002).

Fig. 67: The Le Danois drift in the Gulf of Biscay. The setting resembles the southwestern Mallorca shelf during the Pleistocene. The high reef edge can be compared with the Le Danois bank. The mass movement slump deposits can be compared with the deposits closest to the reef edge and units Ua, Ub and Uc are elongate mounded drifts resembling the (sub) parallel deposits.

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Alternating units of differing amplitudes may indicate towards small variations in lithology. This may be due to changes in oceanography (changing current strength) or sediment supply (Faugères et al., 1999). As the alternations are also associated to eustatic sea-level variations, each subunit was deposited under different oceanographic conditions than the previous one.

5.3 Plio-Pleistocene Stratigraphy The data set shows 2 sequences, each with 2 units, thus 4 major depositional units. Each of them is bounded by erosional boundaries (R, D1, D2 and D3, visible on all profiles).

The lower sequence in the stratigraphy (sequence 1) has low amplitude-reflectors and many different seismic facies (the last one being a characteristic of its unit B, which is most of the sequence). These low amplitudes have been recognized in other seismic profiles throughout the area (Balearic Promontory and adjacent seas), for instance in Curzi et al. (1985), Stanley et al. (1976) and Alonso and Ercilla (2003) and they have been interpreted as Lower- to lower Upper-Pliocene in age. The age for sequence 1 is thus inferred to be the same.

The upper sequence has high amplitudes and (sub) parallel layering, with some localized deviatory facies. Only close to the reef edge, other seismic facies have been observed. These high amplitudes deposits have been recognized as well, on top of a sequence of low amplitudes (Curzi et al. (1985), Stanley et al. (1976) and Alonso and Ercilla (2003)). The age for these sediments has been inferred Upper-Pliocene to Holocene and will be refined in the next section.

In the Alboran Sea, sediments have been divided into four units by Alonso and Ercilla (2003) (for slope turbidites) and by Hernández-Molina et al. (2002) (for shelf and shelf-break deposits, which is the same setting as in this area): two units of Pliocene age (having lower amplitude reflectors in general) and two of Pleistocene age (higher amplitude reflectors). The lower boundary for the deposits is each time formed by the M-discontinuity, the reflector of Upper-Miocene age. The units of low amplitudes are separated by a discontinuity of the Lower-Pliocene (LPR), the discontinuity between the units of low and high amplitude reflectors is Upper-Pliocene in age (UPR) and the discontinuity between the units of higher amplitude reflectors is of the middle-Pleistocene (MPR).

The deposits from the southwestern Mallorca shelf can be correlated with those of the Alboran shelf by Hernández-Molina et al (2002). This is done in Fig. 68. This leaves us with a Lower Pliocene age for unit 1A, an upper Lower Pliocene to Upper Pliocene age for 1B, an Upper Pliocene to Middle-Pleistocene age for 2A and a Middle-Pleistocene to recent age for unit 2B. These larges depositional cycles are formed by 3 rd –order sea-level cycles with durations of about 1.4-1.6 Ma, according to Hernández-Molina et al. (2002).

5.3.1 Discontinuities The Late Messinian (M) discontinuity is due to the very low relative sea levels at the end of the Messinian, caused by the MSC. Sea levels were down over a 1000 meters at some places (Fauquette et al., 2006). Fig. 10 shows however that MSC deposits (evaporitic deposits) do not occur on the southwestern Mallorca shelf and they have not been observed on the seismic data. The base on the Mallorca shelf is thus not formed by the M-reflector, but by a reef. The data show a highly erosive

99 surface (R) between the reef and the overlying deposits (e.g. the deep depressions southeast of the reef edge (Fig. 57)).

Fig. 68: Summary of the sedimentary sequences and units on the southwestern Mallorca shelf, positioned above the reef. Colors used in this figure are related to the used colors in the results. After Hernández-Molina et al. (2002)

The boundary between units 1A and 1B (D1) is sharp in the west and becomes less sharp eastwards. If the boundary is erosive or not, can not be determined on the base of the seismic data alone. It is associated to the large sea-level fall in the Lower-Pliocene (4.2 Ma) (Hernández-Molina et al., 2002).

The boundary between unit 1B and 2A (D2) is an erosional one, indicated by the depression in the east of the southern grid or the erosion of unit 1B at the reef edge. It is associated to the large sea-level fall in the Upper-Pliocene (2.4 Ma) of about 50 meters. This fall is caused by an important climatic change due to the first existence of major ice sheets on the northern hemisphere, causing glacio-eustatic variations (in the order of 50 meters) from then onwards (Hernández-Molina et al. (2002) and Ruddiman (2008)). The huge difference in amplitude of the reflectors between sequence 1 and 2 indicates a change in depositional regime, probably coincident with this sea-level fall. Now, the sequence-boundary lies at depths which would not have been affected by a sea-level fall of 50 meters. But during the Pleistocene, constant subsidence has taken place (Stanley et al., 1976) and thus, during the UPR, the area will have been positioned at higher levels, probably being prone to erosion due to sea-level variations.

The seismic data reveal also an erosional contact between unit 2A and 2B (D3). It can best be noticed at the steep reef edge, where unit 2A was eroded and filled by 2B. This boundary is associated to the MPR

100

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain discontinuity, a boundary due to a major sea-level fall at about 920 ka. It is associated with the shift from obliquity-controlled glacio-eustatic variations (41 ka) to eccentricity-controlled variations (100 ka), causing the large temperature and δ 18 O- amplitudes, marking the onset of the large glaciations (Hernández-Molina et al. (2002) and Ruddiman (2008)). The sudden change in amplitude of the reflectors indicates again a different depositional environment accompanying the major sea-level fall.

5.3.2 Sequences The last unit (2B) shows sigmoidal units and alternating units of reflectors of lower and higher amplitudes. This is also observed in the Alboran Sea (and the Gulf of Cadiz) by Hernández-Molina et al. (2002) and in the lithology of shelf-outcrops in southern Italy by Massari et al. (1999). Ten different small units are discerned by Hernández-Molina et al. (2002) based on seismic lines and well-log data, while we observe in unit 2B 12 sigmoids (in the canyon) or 9-10 alternating layers (outside the canyon). Several authors (e.g. Hernández-Molina et al. (2002) and Massari et al. (1999)) state that most of the small units (65-80% according to Hernández-Molina et al. (2002) and 85-90% according to Massari et al. (1999)) were deposited during low sea levels and thereby have a strong asymmetrical shape. They can be associated to 4 th –order sea-level cycles of 100-120 ka. These strong similarities make us conclude that the sigmoids, observed here, are probably a characteristic of the Pleistocene shelf/shelf break of the entire Western Mediterranean (as they occur as well in the west (Alboran Sea) as in the east (Southern Italy) and originated due to the same glacio-eustatic variations.

A more precise age of the small units in the unit 2B can be estimated by correlating the sigmoids with δ18 O- curves (Fig. 69). Sigmoid 1 (the lower one) is thus associated with the first lowstand after the MPR (920 ka), marine isotopic stage (MIS) 20. MIS 18 poses a problem: it has a two-fold nature with a first large drop in δ 18 O, followed by a small rise and a small fall. This can be associated to sigmoids 2 and 3: sigmoid 2 (which is thicker, D in the classification scheme, Table 7) is associated to the initial large drop and sigmoid 3 (A in the classification scheme) to the minor drop afterwards. The next seven sigmoids are correlated to the next seven lowstand MIS (16-4). The last two sigmoids are considered to have originated during MIS 2. Sigmoid 1 is among the thinnest (A in classification scheme, Table 7) and together with sigmoid 2 is has the shape of one sigmoid. Thereby, it is considered as one and associated to MIS 2. The ten remaining sigmoidal units are consistent with the observation of 9-10 alternating units of higher and lower amplitude reflectors in the draping part of unit 2B. A summary of the sigmoids, their associated MIS and age can be seen in Table 8. These ten sigmoids can be correlated to the ten 4 th order units of Hernández-Molina et al. (2002) (Fig. 68).

The same can be done for unit 2A, although this is more speculative, due to several reasons:

1) Clearly expressed sigmoidal units are absent 2) The difference in amplitude of the reflectors between the alternating units is smaller and therefore more difficult to distinguish 3) The time span to cover is much larger (2.4 Ma (UPR) - 0.9 Ma (MPR)) 4) Sea-level amplitudes were less (about 50 meters instead of 100 meters after the MPR), which can lead to a minor expression.

101

Table 8: The sigmoids in unit 2B and their associated MIS and assumed age.

Number of sigmoide MIS Approximate age (ka) 11 -12 2 50 10 4 175 9 6 220 8 8 320 7 10 400 6 12 500 5 14 600 4 16 680 2-3 18 780 1 20 860

All of these reasons make it more difficult to correlate a small unit to a more precise age. In profile 34_out, 6 divergent to sigmoid-like alternations are found and in other profiles, 4 to 6 alternations are found in the draping part of the unit (when a paleo-depression is filled, more units can be recognized). The six divergent units in profile 34_out are correlated to the largest drops δ 18 O-values of the period between the UPR and MPR. The correlations and estimated ages are given in Table 9.

The assumed correlation shows deposition of the units in pairs. Each pair is deposited within 100-150 ka (in two sea-level lowstands) and 350-400 ka of net zero deposition exists between the three pairs. The 200 ka cyclicity in the deposits of the Alboran Sea, observed by Hernández-Molina et al. (2002) is not observed here, indicating towards different settings between the UPR and MPR in the two regions.

Table 9: The small units in unit 2A, their associated MIS and estimated age.

unit MIS Age (ka) 6’ 82 2150 5’ 78 2050 4’ 58 1700 3’ 52 1550 2’ 34 1150 1’ 30 1050

Unit 1A and 1B are correlated to the Pliocene deposits of Hernández-Molina et al. (2002) ( respectively unit M/P1 and P2 in the Alboran sequence) on the base of the same transparent seismic characteristics, which have been recognized all over the Mediterranean area. Further refinement of the stratigraphy cannot be done in this sequence, as no clear alternating layers of lower and higher amplitudes are found in these units.

102

Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain The The Lisiecki and curves. Lisiecki and - O 18 δ

s s of sequence 2 to the Fig. 60. The upper curve is from is is the average of its 25 surrounding points. , , each point and the lower curve is made after the data from Correlation of the small unit : 69

103Fig. seismic profile itself can be seen in Raymo (2005) Raymo (2005) be can Explanation found the textin above.

5.4 Sedimentation rates The thickness of each sequence and unit is known (through conversion of milliseconds TWT into meters using the approximate velocity values for seismic waves in water (1450 m/s) and sediment (1650 m/s), the last on being the average of values obtained from cores in the Mediterranean during ODP leg 161, site 975 (Comas et al., 1996)). The place where the depths of the upper boundaries have been measured is indicated by the dotted black line in Fig. 50. This profile was chosen as all four sedimentary units occur there and from each and every unit, large thicknesses are observed. The individual thicknesses are given in Table 10.

Table 10: Depth of the upper boundary and thickness of every unit occurring in the area.

Unit Depth upper boundary Depth upper boundary Thickness (meter) (ms TWT) (meter) 2B 255 185 66 Sequence 2: 2A 335 253 24.75 90.75 1B 365 275.75 74.25 Sequence 1: 1A 455 350 53.625 127.875 Reef 520 403.625 - -

These individual thicknesses can now be used together with the derived ages to infer a sedimentation rate for each unit. This is done by dividing each thickness by its appropriate age. The results of this can be seen in Table 11.

Table 11: Thickness, age and sedimentation rates of every unit occurring in the area.

Unit Thickness (meter) Age (ka) Sedimentation rates (cm/ka) 2B 66 920 -0 7.174 Sequence 2: 2A 24.75 2400 -920 1.672 3.781 1B 74.25 4200 -2400 4.125 Sequence 1: 1A 53.625 5332 (*) -4200 4.737 4.361 (*): An exact age for the lower boundary of unit 1A has never been determined. It has been set at the Lower- Pliocene. Here, the Mio-Pliocene boundary has been used.

Table 11 tells that in the Pliocene, the sedimentation rates were more or less constant (4.7 cm/ka and 4.1 cm/ka respectively for unit 1A and 1B). The smallest sedimentation rates in the area occurred between the UPR and MPR (1.7 cm/ka) and the largest after the MPR (7.1 cm/ka). Refinement of the sedimentation rates after the UPR can be done by using the divergent (unit 2A) and sigmoidal (unit 2B) units and their associated MIS (and thus ages). The results of this can be seen in Table 12.

This table tells us that sedimentation rates were way larger after the MPR (8.6 cm/ka) then before (5 cm/ka). This is consistent with Table 11. However, the obtained rates in Table 12 are way larger than those of Table 11 for the same units (8.6 cm/ka compared to 7.1 cm/ka for unit 2B and 5 cm/ka compared to 1.7 cm/ka for unit 2A). This might be explained due to the lower position of the divergent and sigmoidal units in the channel of the canyon with regard to the position of the sediment used for Table 11, which is in the draping part of the unit. The deeper, protecting channel might have preserved

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain the sediment of unit 2B better than the draping part, which was prone to erosion due to the prevailing contour current. Also note that the boundary between unit 2A and 2B is here positioned at 860 ka (MIS 20), instead of 920 ka (derived from the literature, e.g. Hernández-Molina et al. (2002)).

Table 12: Thickness, MIS, age and sedimentation rate of the divergent and sigmoidal units of sequence 2.

Unit Thickness Thickness (meters) MIS Age (ka) Sedimentation rate (cm/ka) (ms TWT) 12/11 11 9.35 2 175 -50 7.48 10 6 5.1 4 220 -175 11.333 9 7 5.95 6 320 -220 5.95 8 15 12.75 8 400 -320 15.938 7 8 6.8 10 500 -400 6.8 Unit 2B: 6 8 6.8 12 600 -500 6.8 8.581 5 10 8.5 14 680 -600 10.625 4 7 5.95 16 780 -680 5.95 3/2 22 18.7 18 860 -780 15.583 1 12 10.2 20 1050 -860 5.368 6’ 15 12.75 30 1150 -1050 12.75 5’ 12 10.2 34 1550 -1150 2.55 4’ 7 5.95 52 1700 -1550 3.967 Unit 2A: 3’ 13 11.05 58 2050 -1700 3.157 4.974 2’ 12 10.2 78 2150 -2050 10.2 1’ 20 17 82 2400 -2150 6.8

The evolution of the sedimentation rate in the area can be seen in Fig. 70.

Fig. 70: Evolution of the sedimentation rate during the Plio-Pleistocene. Data before the UPR are scarce, after, they are more abundant.

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6 Conclusions

6.1 Summary The seismic data (obtained on the southeastern shelf and shelf break of Mallorca) display a great variety of depositional features. The goal of this study was to find out the origin of these deposits and put them in a stratigraphic and hydrographic perspective.

The data can be divided into two parts: one where a reef prevails and another where sediments of Plio- Pleistocene age are abundant. They are separated by a NE-SW-orientated reef edge, with a maximum height difference of about 250 meters. The area north of this edge contains a thick package of sediments on top of the reef and shows a weak shelf break with mass transport deposits and gentle slopes. The area south of the edge has a high position of the reef and is characterized by steep slopes and a sharp shelf break, this due to the hard nature of the carbonate reef. The boundary between the two areas runs across the southern grid and can be traced in the seismic profiles.

The reef in the area is of Miocene age and belongs to the platform margin of the Llucmajor reef deposits (southwestern Mallorca). The northern grid (and most likely also the southern grid) belongs to the open platform and slope facies described by Pomar (1991). Subaerial erosion after the Messinian salintiny crisis left many U- to V-shaped wedges in the reef which have been filled by post-reef sediments.

The entire Plio-Pleistocene sequence has been divided into two sequences (1 and 2) and each sequence subdivided into two major units (A and B). Unit 1A drapes the reef and is of Lower Pliocene age, the upper boundary is formed by the Lower Pliocene discontinuity (LPR, 4.2 Ma). Unit 1B has a Lower- Pliocene to lower Upper-Pliocene age and has been correlated to transparent seismic facies observed all over the Mediterranean during the Pliocene. Its upper boundary is the Upper Pliocene Revolution (UPR, 2.4 Ma). Based on internal characteristics, the unit has been subdivided into two major (and one minor) parts. One part has an elongate mounded contourite drift or turbiditic origin and the second part (which cuts the first one) probably has a channel-related drift origin. Both are associated to NW-SE-orientated currents. These probably originating from the permanent deviatory current of the Balearic Current, running through the Mallorca Channel southwards, or from the semi-permanent wind-driven storm currents inferred by Werner et al. (1993). The third part, in the most eastern parts of the southern grid displays very transparent facies.

Sequence two consists of higher amplitude reflector deposits and can be divided into three parts. The first part occurs in the northwestern part of the southern grid and displays cut-and-fill structures. These have a northwestern sediment infill. The second part displays aggradational (sub) parallel continuous strata and both first two parts are associated to elongate mounded drift deposits. The causing currents, probably coming from the northwest, can again be the semi-permanent wind-driven currents inferred by Werner et al. (1993) or the permanent offshoot current from the Balearic Current, going from north to south trough the Mallorca Channel. The cut-and-fill structures indicate towards an intensifying and diminishing strength of this current. The third part occurs just northwest of the steep reef edge and contains mainly deposits of unit 2B. The layers dip towards a channel and in this channel, divergent (unit 2A) to sigmoidal (unit 2B) small units are observed. The current causing the elongate mounded drift

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain deposits probably deflected against the reef edge, flowing parallel to it after deflection, intensifying and eroding sediment of unit 2A. When currents slowed down, sediment was deposited again on steep slopes in the canyon, occasionally failing and causing the sigmoidal deposits.

The alternating units of lower and higher amplitude reflectors of sequence 2 have been correlated to sea-level variations throughout the Pleistocene. Unit 2A has been deposited from the UPR (2.4 Ma) to Middle Pleistocene Revolution (MPR, 0.92 Ma) and was subject to sea-level variations in the order of 50 meters. Maximum six smaller units were recognized and correlated to Marine Isotopic Stages. Unit 2B has been deposited from the MPR to present and was subject to sea-level variations in the order of 100 meters. Ten small units have been recognized in this unit and can be associated to Marine Isotopic Stages as well.

Sedimentation rates have been calculated based on the observed thicknesses and calculated ages. Rates before the UPR are about 4.5 cm/ka, but have to interpreted with caution, as few data are obtained from this period. After the UPR, rates vary greatly, but tend to be higher on average (Fig. 70). Especially after the MPR, they are way higher with rates reaching 15 cm/ka.

6.2 Recommended future reearch As no groundthruthing is known in the area, deep cores, just next to the reef edge, in the western parts of the southern grid, of a minimum of 500 meters would be extremely helpful to find out the nature of the sediments and refine the stratigraphy (as all four units occur there and are the thickest). Also, drilling at least 500 meters at that place, will allow you to collect the upper reef deposits and comparison can then be made with onshore rocks. If possible, dating of the sediment could aid in refining the age-estimation of the different boundaries and units, refining the sedimentation rate estimates. Especially sequence 1 can use a refinement of the stratigraphy, as no correlation to isotopic stages could be done in this sequence.

Expansion of the seismic data to the west, following the canyon system, would be extremely helpful in understanding the dynamics of the region even better (1 in Fig. 71). An expansion to the north- northwest is also advisable, to find out the area of origin of the contourite deposits found in the southern grid (2 in Fig. 71).

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Fig. 71: Proposed grids for future research

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

6.3 Dutch summary/Nederlandse samenvatting

6.3.1 Doelstelling De Vrije Universiteit Amsterdam heeft een lopend onderzoek waarbij de anatomie van sequenties en grenzen vergeleken worden met acoustische eigenschappen van ontsluitingen en offshore seismische data. In het kader van dat onderzoek zijn de data van dit onderzoek bekomen door een samenwerking van de Vrije Universiteit Amsterdam en het RCMG (Renard Centre of Marine Geology) van de Universiteit Gent. Doel was deze data te vergelijken met landsecties (reflecties van een carbonaat platform) en de relatie met geofysische parameters te verduidelijken. De data op zich bleken een rijke variëteit aan seismische facies te vertonen, waarbij besloten werd deze verder te onderzoeken. Reconstructie van paleoceanografische en sedimentologische condities en het opstellen van een stratigrafie op de shelf en shelfrand ter hoogte van zuidwest Mallorca zijn de doelstellingen van dit onderzoek.

6.3.2 Materiaal en methode Dit onderzoek werd verwezenlijkt door seismische en multibeam bathymetrische data te onderzoeken. De seismische data werden vergaard in 2003 met een seismische sparker en zijn verdeeld over twee grids: een noordelijk en zuidelijk. Sommige profielen werden bewerkt (oa multiples verwijderen en filters toepassen). Bestudering van deze data werd met “The Kingdom Suite” gedaan, waarmee isochronen en isopachen kaarten werden gemaakt op basis van aangeduide reflectors.

De multibeam bathymetrische data zijn dezelfde als deze onderzocht door Acosta et al. (2004). De multibeam bathymetrische data bevatten de Balearische eilanden en hun omgeving, maar enkel het gebied relevant voor deze studie (het Mallorca Kanaal en de westelijke en zuidwestelijke shelf van Mallorca) werd onderzocht. Verwerking van deze data gebeurde met “Global Mapper” en “Surfer”.

Figuren werden bewerkt met “Corel Draw”.

6.3.3 Situering Het onderzochte gebied bevindt zich op de westelijke en zuidwestelijke shelf en shelfrand van Mallorca, in het oostelijke gedeelte van het Mallorca Kanaal, net ten westen van het eiland Cabrera. Het gebied behoort tot het Balearisch Promontorium, een structurele hoogte, bestaande uit vier eilanden: Ibiza, Formentera, Mallorca en Menorca. Het zuiden van dit Promontorium wordt begrensd door de Emile Baudot Escarpment, een steile rand met een hoogteverschil van ongeveer 1500 meter. De aangrenzende zeeën van het Promontorium bestaan uit de Valencia Trough (in het noorden), de Alerijnse Zee (in het zuiden) en de Balearische-Provencaalse Zee (in het oosten). Deze laatste zijn, samen met het Balearisch Promontorium een onderdeel van de Westelijke Middellandse Zee (MZ).

6.3.4 Evolutie De Cenozoïsche evolutie van het gebied is gecontroleerd door de convergentie tussen de Afrikaanse en de Euraziatische plaat, de back-arc extentie die ermee gepaard ging en de gerelateerde slab detachment processen (drie volgens Carminati et al. (1998b)). Het Balearisch Promontorium is ontstaan door een compressionele fase tijdens het Vroeg-Langhiaan, waarbij het Betisch gebergte onstond, een gebergteketen in het Zuiden van het Iberisch Schiereiland (het Balearisch Promontorium is deel van het

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Betisch gebergte). Dit was tijdens de laatste fase van de opening van de Westerse MZ, erna verschoof deze naar de Centrale MZ. Het is toen (Langhiaan) dat de Balearische eilanden voor het eerst boven zeeniveau kwamen te liggen.

De Messiaanse saliniteitscrisis (MSC) zorgde voor een zeer laag zeeniveau tijdens een deel van deze periode. Het zeeniveau daalde op sommige plaatsen meer dan 1000 meter, waardoor grote delen van de MZ droog kwamen te liggen en bedekt werden met dikke evaporietafzettingen Fauquette et al. (2006). Op de plaats van het noordelijk en zuiderlijk grid zijn er echter geen evaporieten te vinden door hun ondiepe positie, in de nabije omgeving (oa het Mallorca Kanaal) vinden we deze wel. De oorzaak van de MSC dient gezocht te worden in het sluiten van de mariene connecties van de MZ met de Atlantische Oceaan (dit gebeurde in het Mioceen via de Betische en Rif passages).

Tijdens het Plioceen “zonk” een deel van het Balearisch Promontorium, waardoor ondermeer het Mallorca Kanaal ontstond. Tijdens het Pleistoceen vond tragere subsidentie plaats, waardoor de zeebodem niet meer zo snel daalde als voorheen. Dit alles gebeurde langs twee breukrichtingen: NW-ZO en NO-ZW (Stanley et al., 1976). Tijdens het Plio- en Pleistoceen was de Mallorca shelf onderhevig aan glacio-eustatische zeespiegelschommelingen (Acosta et al., 2002). Een samenvatting van de geologische evolutie van het gebied is te vinden in Tabel 1.

6.3.5 Hydrografie De MZ wordt gekenmerkt door een anti-estuariene circulatie met een ondiepe (0 tot 200 meter diep), oostwaartse instroom van Atlantisch water en een “diepe” (200 tot 260 meter diep in de Straat van Gibraltar) uistroom van gemodifieerd Mediterraan water. De hydrografie van de Westerse MZ bestaat globaal gezien uit drie lagen: oppervlakkige water massas (tussen 0 en 200 meter diepte), intermediaire water massas (tussen 200 en 2000 meter water diepte) en diepe water massas (beneden 2000 meter water diepte). Elke water massa heeft zijn eigen stromingen (bijvoorbeeld de Algerijnse ondiepe stroom, de Levantijnse midden stroom en de westerse Middellandse diepe stroom).

Het onderzochte gebied is een gebied waar een belangrijke uitwisseling plaatsvind tussen warm water van de MZ met koud water van de Atlantische Oceaan. De oppervlakkige en intermediaire water massas en stromingen in het gebied zijn: de Noordelijke Stroom (langs de Catalaanse kust), de Balearische Stroom (langs de noordkant van de Balearen), gyres van de Algerijnse Stroom (langs de zuidkant van de Balearische ijslanden) en WIW (in de Valencia Trough , bij het Ibiza Kanaal). Deze laatste is aanwezig in een eddie tijdens de lente en zomer na een relatief koude winter en blokkeert dan de Noordelijke Stroom, waardoor hij niet door het Ibiza Kanaal zuidwaarts stroomt, maar wordt afgebogen richting het oosten in de Balearische Stroom (Fig. 27).

Het Mallorca Kanaal ondervind een permanente oppervlakkige zuidwaarts gerichte aftakking van de Balearische stroom richting Algerijns bekken en occasioneel een noordwaartse gerichte stroom van een aftakking van een gyre van de Algerijnse stroom richting Balearische stroom.

Tijdens storm omstandigheden wordt er op de zuidwestelijke shelf van Mallorca een zuidoostwaartse stroom van ongeveer 40 cm/s geacht te stromen volgens, terwijl tijdens wind-stille condities er bijna

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain geen stroming is waargenomen (Werner et al., 1993). Kanaaltjes met levees , geobserveerd op de zeebodem (vooral in het noordelijk grid) in de seismische data lijken een NW-ZO stroom te bevestigen.

6.3.6 Rif Het rif is van Miocene oorsprong (veel riffen van Miocene oorsprong zijn gekend in de Westelijke MZ) en kan op land bestudeerd worden op het Llucmajor platvorm (Pomar, 1991). Hoogst waarschijnlijk behoort het rif in onze grids tot het open platvorm en hellings-facies (Pomar, 1991). De grens van dit platvorm loopt door ons zuidelijk grid. De bovengrens van het rif heeft vele scherpe insnijdingen. Deze zijn waarschijnlijk ontstaan tijdens de Messiniaanse saliniteitscrisis, toen de zeespiegel meer dan 1000 meter gedaald was (Fauquette et al., 2006) en er dus subaerische erosie mogelijk was.

6.3.7 Multibeam Ten noorden van de steile rifrand vinden we op de multibeam data (Fig. 40) meerdere massa transport afzettingen en geen duidelijke shelfrand, terwijl we zuidelijk van deze rand een scherpe shelfrand en een steile helling waarnemen. Deze steile rand is de plaats waar het Mioceen rif dieper voorkomt ten noorden ervan en waarlangs een canyon loopt die draineert richt de Centrale Depressie (een depressie in het middelste deel van het Mallorca Kanaal). Het rif ten noorden van deze rand is bedekt door een dikke laag Plio-Pleistocene sedimenten, terwijl ten zuiden deze nauwelijks voorkomen. Dit laat ons besluiten dat de ondergrond (rif-sediment) de shelfrand structuur bepaalt: zwakke sedimenten zorgen voor massatransport afzettingen en onduidelijke shelfranden, terwijl harde rif-carbonaten zorgen voor een duidelijke shelfrand en steile randen zonder veel hellingsinstabiliteiten.

6.3.8 sedimenten Uit vroegere seismische profielen uit de regio blijkt dat in het gebied een Mioceen rif voorkomt, met daarboven een Plio-Pleistocene sequentie. De onderzochte seismische profielen bevestigen dit. Aangezien geen boringen op het onderzochte gebied zelf bekend zijn, kan geen exacte samenstelling van de voorkomende sedimenten achterhaald worden. Acosta et al. (2001) beweert dat de sedimenten uit het gebied bestaan uit Pliocene mergels en Pleistocene kalkarenieten en mergels die eventueel turbidieten vormen in regio’s met steile hellingen. Hoe dieper de sedimenten voorkomen, hoe fijnkorreliger ze zijn.

De zeebodem in alle profielen (zowel bewerkte als niet-bewerkte) vertonen meerdere “lijnen” (oranje en blauwe), dit tengevolge van de eigenschappen van de seismische sparker golf en het grote verschil in akoestische impedantie (Fig. 32). Het noordelijk grid (dicht bij de kust) bevat een zeer ondiep positie van het rif met slecht op enkele plaatsen sedimenten erboven. Deze sedimenten zijn waarschijnlijk dezelfde als deze uit de bovenste unit van het zuiderlijk grid (unit 2B), omdat dit de enige unit is die boven het rif is waargenomen in het zuiderlijke grid. Een connectieprofiel is geschoten, maar bevat foute data (Fig. 45), dus correlatie van sedimenten uit het zuiden en noorden kan niet worden gemaakt.

De sedimenten van het zuidelijk grid zijn opgedeeld in twee sequenties (1 en 2), elke met twee units A en B). De twee sequenties worden gescheiden door een sterke discontinuiteit (D2) die een erosief karakter heeft en afzettingen van lage amplitudes van die van hoge amplitudes scheidt.

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De onderste unit (1A) is enkel aanwezig in de diepere delen van het grid (het westen) en is over het algemeen zeer dun. Hij drapeert het onderliggende rif. De tweede unit (1B) is de meest transparante unit van de gehele sequentie en bestaat uit drie delen. Het eerste deel bevindt zich net ten noordwesten van de rifrand en heeft (sub) parallelle, golvende strata. Deze zijn ofwel van een turbidiet (levees) ofwel van een contouriet ( elongate mounded drift ), dit valt op seismische data alleen niet te onderscheiden. Deel 2 bevindt zich ten noordwesten van deel 1 en vertoont kanaal-gerelateerde afzettingen. Deze zijn waarschijnlijk terug door een contouriet stroom (kanaal-gerelateerde drift) ontstaan. Deel 3 komt enkel voor in het uiterste noordoosten van het zuidelijke grid en heeft een vrij transparant facies, dat gelijkenissen vertoont met het rif-facies. Het is aanwezig boven een stijgende rifgrens.

Correlatie van sequentie 1 met afzettingen uit de Zee van Albora en de Golf van Cadiz is mogelijk waardoor unit 1A een Laat-Mioceen tot Vroeg-Plioceen en 1B een Vroeg-Plioceen tot vroeg Laat- Plioceen ouderdom heeft. De twee units worden gescheiden door een discontinuiteit van het Vroeg- Pleistoceen (LPR, Lower Pleistocene discontinuity ) (Hernández-Molina et al., 2002).

De bovenste sequentie (bestaande uit afzettingen van hogere amplitude reflectoren) vertoont eveneens contouriet eigenschappen. In het noordwesten van het zuiderste grid zijn twee tot drie kleinere kanaaltjes per unit geobserveerd die een sediment-opvulling hebben die NW-ZO-geörienteerde stromingen doen vermoeden. Ten zuidoosten van deze kanaaltjes vinden we parallelle, continue afzettingen, ontstaan door een contourstroom (opnieuw een elongate mounded drift ).De stroom die deze afzettingen vormde is terug NW-ZO geörienteerd. Tegen de rifrand vinden we een diepe insnijding die met afzettingen van unit 2B gevuld is. De contourstroom (reeds besproken) werd waarschijnlijk afgebogen door de steile rifrand, versnelde en veroorzaakte erosie tegen de rifrand. Het daardoor ontstane kanaal werd opgevuld met afzettingen van unit 2B eens de stroming verzwakte. De steile helling in het kanaal zorgde voor occassionele sediment failures en de sigmoidale vorm van de geobserveerde afzettingen.

6.3.9 Seismische stratigrafie Sequentie 2 vertoont een afwisseling van units met hogere en lagere amplitude reflectoren. Vooral in unit 2B is dit zeer duidelijk. In de canyon vertonen deze zelfs een divergente (unit 2A) tot sigmoidale (unit 2B) vorm. Deze afwisseling werd veroorzaakt door 4 e orde eustatische zeespiegelschommelingen. Sedimenten worden voornamelijk afgezet tijdens laagstanden (Hernández-Molina et al., 2002). Deze periodes worden gekenmerkt door een hoger pecentage aan stormen (Einsele, 1993). Stormen in deze regio hebben NW-ZO geörienteerde stromingen (Werner et al., 1993) die de contouriet afzettingen kunnen verklaren. De verschillende kleine units kunnen bijgevolg gecorreleerd worden aan eustatische laagstanden, Marine Isotopic Stages , bekomen uit δ 18 O- curves. De bekomen stratigrafie wijst uit dat unit 2A werd afgezet tussen de UPR en MPR (Laat Pleistocene Revolutie en Midden Pleistocene Revolutie respectievelijk) en unit 2B tussen de MPR en het heden. De sterkere amplitude-afwisselingen in unit 2B zijn hoogstwaarschijnlijk het gevolg van de grotere zeespiegelschommelingen tijdens deze periode (100 meter in plaats van 50 meter) in vergelijking met de voorgaande.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

6.3.10 Afzettingssnelheid De gemeten dikte in milliseconden Two Way Travel Time (TWT) uit de seismische profielen werden omgezet naar meter. De dikte van elke sequentie en unit werd dan gedeeld door de duur van de overeenkomstige tijdsperiode. Hierdoor werd de sedimentatiesnelheid van elke periode bekomen. Buiten de canyon was de sedimentatiesnelheid tijdens het Plioceen hoger dan tijdens het Pleistoceen, in de canyon werd het omgekeerde geobserveerd. Dit komt waarschijnlijk door de betere preservatie in deze laagte. Over het algemeen gezien lag de sedimentatiesnelheid in de regio tijdens het Plio- en Pleistoceen rond de 4 centimeter per 1000 jaar (Fig. 70, Table 11 and Table 12).

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Appendix A: Paleogeographic evolution

The maps from the Paleo- and Mesozoicum are from Stampfli and Borel (2002). They give the evolution of the Paleo- and Neo-Tethys Ocean up till the end of the Cretaceous. See the accompanying text in Geological evolution for further information.

The maps from the Cenozoicum are from Meulenkamp and Sissingh (2003).They show the evolution of the Peri-Tethys region from the Eocene onwards. The figures are ordered in order of descending age. Explanation is given in the text in geological evolution.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A1: Paleogeographic maps of the Tremadoc, Lower Ordovican (below); Llandovery, Lower Silurian (middle) and Ludlow, Upper Silurian (top).

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Fig. A2: Paleogeographic maps from the Early Emsian, Lower Devonian (below); Early Givetian, Middle Devonian (middle) and Famennian, Upper Devonian (top).

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A3: Paleogeographic maps from the Early Visean, lower Carboniferous (below); Bashkirian, middle Carboniferous (middle) and Kasimovian, upper Carboniferous (top).

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Fig. A4: Paleogeographic maps from the Sakmarian, lower Permian (below), Late Wordian, middle Permian (middle) and the Permian-Triassic boundary (top)

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A5: Paleogeographic maps from the Anisian, Middle Triassic (below); Ladinian, Middle Triassic (middle) and Early Norian, Upper Triassic (top)

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Fig. A6: Paleogeographic maps from the Sinemurian, Lower Jurassic (below); Aalenian, Middle Jurassic (middle) and Oxfordian, Upper Jurassic (top)

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A7: Paleogeographic maps from the Valangian, Lower Cretaceous (below); Aptian, middle Cretaceous (middle) and Santonian, Upper Cretaceous (top)

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Fig. A8: Paleogeographic maps from the Late Lutetian, Eocene.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A9: Paleogeographic maps from the Late Rupelian, Oligocene.

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Fig. A10: Paleogeographic maps from the Early Burdigalian, Upper Miocene.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A11: Paleogeographic maps from the Early Langhian, Middle Miocene.

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Fig. A12: Paleogeographic maps from the Late Tortonian, Late Miocene.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

Fig. A13: Paleogeographic maps from the Piacenzian/Gelasian, Pliocene.

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Appendix B. Profiles

In this appendix, profiles which have not been inserted in between the text are displayed. All the information needed is within the text and/or captions.

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

the northern the grid. northern rebox.indicated bythewhite in the This east of Profile 03. The few deposits present in this grid a gridpresent few this deposits 03. TheProfile in : : 1 Fig. B

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ern side of theside profile. ern is situated within the situated is the within white box.eastthis is 2: Profile 22_out. The "textbook" channel structurechannel "textbook" 2: 22_out. Profile The Fig. B

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

nel. In this profile, the eviously eviously mentioned chan this this profile almost at the exact location of the pr hite box. hite : : Profile 23_out. Perpendicular to 22_out and cuts 3 Fig. B leveecanchannel seen,w of be this

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ofile of theofile southern grid.visible.The is canyon 4: Profile 27_out. This is the is 4: 27_out. Profile This outermost western pr Fig. B

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Seismic stratigraphy of Plio-Pleistocene deposits on the shelf edge SW off Mallorca, Spain

channel. Unit 1A 1A channel.reef. drapes Unit the

s s visible justwith 1 : Profile 43_out, : 45_out.just 43_out, Profile east canyonof The i 5 Fig. B

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