Balearic Basin Research Articles

Valencia Fan (northwestern Mediterranean): Distal deposition fan variant

The Valencia Fan, one of the larger deep-sea depositional systems in the western Mediterranean Sea, developed in the large depression between the Valencia Trough and the Balearic Basin Plain. Six main lithoseismic units are identified and sedimentary processes inferred from 6000 km of sparker profiles. This fan is largely formed by channelized and irregularly stratified units. The sedimentary processes controlling the development of these units include channelized sediment flows that evolve downfan into sheet flows. Three fan depositional provinces are differentiated on the basis of the relative proportions of lithoseismic units and the inferred sedimentary processes. Regularly stratified seismic units predominate in the non-fan environments. These units are dominated by fine-grained deposits resulting from hemipelagic settling and overbank flows from turbid currents. Distal flows from the continental slopes of the Iberian Peninsula and Balearic Islands also contribute materials for the development of these environments. The wavy units flanking the upper fan may have resulted from migrating sediment waves or limited mass-displacement of the stratified units, while the transparent units are attributed to extensive mass-flow. The Valencia Valley is largely an erosional feature across which sediments from several source areas bypassed to the distal, deep-sea depositional system of the Valencia Fan. Deposition begins at the mouth of the valley beyond which there is a break in slope. The fan migrated upslope and filled the Valencia Valley from the distal sectors. This evolution has been controlled by the interplay between sedimentary processes active in the fan growth and large-scale geological factors related to the structural framework of the study area.

Valencia Fan (Northwestern Mediterranean): Channelized Distal Deposition Fan Variant: ABSTRACT

The Valencia Fan, a large deep-sea depositional system in the western Mediterranean Sea, developed in the structural depression between the Valencia Trough and the Balearic Basin Plain. Six main lithoseismic units are identified from 6,000 km of sparker profiles. Channelized and irregularly stratified units predominate. It is inferred that the sedimentary processes controlling the development of these units include channelized sediment flows that evolve downfan into sheet flows. Three fan depositional provinces are differentiated on the basis of the relative proportions of lithoseismic units and the inferred sedimentary processes. Regularly stratified seismic units predominate in the non-fan environments. These units are dominated by fine-grained deposits resulting from hemipelagic settling and overbank flows from turbidity currents. Distal flows from the continental slopes of the Iberian Peninsula and Balearic Islands also contribute sediment for the development of these environments. The wavy units flanking the upper fan probably resulted from migrating sediment waves, whereas transparent units are attributed to extensive mass flow. The Valencia Valley is largely an erosional feature across which sediments from several source areas bypassed to the distal, deep-sea depositional system of the Valencia Fan. Deposition begins at the mouth of the valley where it is constricted by a volcano and beyond which there i a break in slope. End_of_Article - Last_Page 282------------

The Western Mediterranean Basin geological evolution

The Western Mediterranean Sea is explained as a marginal basin, generated by a N-NW subduction of the African—Apulian plates beneath the European plate. Following an Oligocene rifting phase, oceanic accretion occurred between −21 and −18 m.y., along three main spreading axis trending NE-SW in the Liguro—Provençal Basin, NW-SE in the southern Sardo—Balearic Basin and E-W in the North Algerian Basin. Such kinematics and chronology are consistent with: (a) paleomagnetic data supporting the Sardinian rotation; (b) basin and margin structure; (c) subsidence since 21 m.y., especially during Messinian time; and (d) heat-flow measurements.

Deep Seismic Sounding in Europe: ABSTRACT

During the past 3 decades, several seismological techniques have been used to explore the deep structure of Europe. Profound lateral variations in the lithosphere-asthenosphere system became immediately apparent from the observed delay of teleseismic P-waves. On the basis of a uniform dispersion analysis of all the presently available long-period Rayleigh wave observations and applying a new method of regionalization, a map outlining the thickness of the elastic lithosphere in Europe could be constructed. Regions of markedly thinned lithosphere are the Tyrrhenian and Balearic basins of the western Mediterranean Sea. Another extensional structure of particular interest is the Central European rift which extends from the western Alps to the North Sea. In contrast, an increased lithospheric thickness has been found beneath the Betic Cordillera and the Alps which must be ascribed to underthrusting and subfluence leading to the formation of a pronounced lithospheric root reaching to a depth of about 200 km. Long-range seismic refraction profiles have permitted insight into details of upper mantle structure to depths of nearly 400 km in a few tectonic provinces. Travel-time and amplitude data obtained in crustal seismic refraction experiments, supplemented by wide-angle and near-vertical reflection observations, have made it possible to study the major features within the continental crust of Europe. Regions selected for detailed studies include the southern part of the Iberian Peninsula, the Pannonian basin, the Rhine graben rift system, the northern Alpine foreland, and the Alps. End_of_Article - Last_Page 797------------

Orleansville Turbidite: ABSTRACT

The Orleansville earthquake in 1954 produced a turbidity current on the Algerian Mediterranean margin and adjacent South Balearic basin sea floor which broke five telephone cables. The report of this event represented a cornerstone in the evolution of turbidity current theory. The resulting turbidite has been mapped on the Balearic abyssal plain for the purpose of relating flow paths and turbidite size, and areal extent to cable break locations. This study is based on 50 gravity cores. Figure The Orleansville turbidity current actually consisted of two currents which arrived simultaneously on the basin plain via two canyon mouths separated by 30 km. The merged turbidity currents flowed 170 km out on the basin-plain floor and covered an area of 8,000 km2. The turbidite is a tongue-shaped sediment body, 50 km wide, oriented northeast-southwest. It consists of a central band of 5-cm thick sand with a fringing 2 to 3-cm thick band of coarse to fine silt. Two of the cable breaks occurred on the abyssal plain at the extreme edge of the turbidite where the sediment is only 2 cm thick. An underlying turbidite of very similar dimensions to the Orleansville turbidite is separated from it by a 10 to 15-cm pelagic sequence. The consistent spacing between these two events in icates that although the Orleansville turbidity current broke telephone cables at its extreme margins, it caused no detectable erosion on the basin-plain floor. End_of_Article - Last_Page 641------------

Models of Mediterranean back-arc basin formation

During and mainly after the Tertiary continental collisions, regions of extension and subsidence developed within the Alpine-Mediterranean orogenic belt in the rear part of the contemporaneously active arcs. Mediterranean back-arc basins are characterized by a hot upper mantle, overlain by crust transitional from continental to oceanic, which reflects their different stages of maturation. The four basins considered here are, in order of increasing maturity, the Pannonian Basin, the Aegean Basin, the Alboransouth Balearic Basin and the Tyrrhenian Basin. Back-arc extension is not a rigid plate opening but rather an areal expansion associated with progressive bending of the arc. The most successful models suggested for the evolution of Mediterranean back-arc basins imply updoming of the asthenosphere accompanied by lithospheric attenuation, stretching and dyke intrusion. The force behind asthenospheric updoming is under debate; active and passive mechanisms have been suggested. It seems, however, certain that gravity plays an important role in initiating and maintaining back-arc extension. Basin subsidence is an isostatic response to structural changes of the lithosphere and to conductive decay of the associated heat anomaly. A quantitative model for basin formation can be obtained only if the subsidence history is well documented.

Plate tectonic model for the oligo-miocene evolution of the western Mediterranean

This paper outlines a plate tectonic model for the Oligo-Miocene evolution of the western Mediterranean which incorporates recent data from several tectonic domains (Corsica, Sardinia, the Kabylies, Balearic promontory, Iberia, Algero-Provençal Basin and Tunisian Atlas). Following late Mesozoic anticlockwise rotation of the Iberian peninsula (including the Balearic promontory and Sardinia), late Eocene collision occurred between the Kabylies and Balearic promontory forming a NE-trending suture with NW-tectonic polarity. As a result of continued convergence between the African and European plates, a polarity flip occurred and a southward-facing trench formed south of the Kabylie—Balearic promontory suture. During late Oligocene time an E-W-trending arc and marginal basin developed behind the southward-facing trench in the area of the present-day Gulf of Lion. Opening of this basin moved the Corsica—Sardinia—Calabria—Petit Kabylie—Menorca plate southward, relative to the African plate. Early Miocene back-arc spreading in the area between the Balearic promontory and Grand Kabylie emplaced the latter in northern Algeria and formed the South Balearic Basin. Coeval with early Miocene back-arc basin development, the N-S-extension in the Gulf of Lion marginal basin changed to a more NW-SE direction causing short-lived extension in the area of the present-day Valencia trough and a 30° anticlockwise rotation of the Corsica-Sardinia-Calabria—Petit Kabylie plate away from the European plate. Early—middle Miocene deformation along the western Italian and northeastern African continental margins resulted from this rotation. During the early late Miocene (Tortonian), spreading within a sphenochasm to the southwest of Sardinia resulted in the emplacement of Petit Kabylie in northeastern Algeria.

Le canyon messinien de la Durance (Provence, France): Une preuve paléogéographique du bassin profond de dessiccation

Beginning in 1950, oil drilling in Camargue disclosed the existence of the Rhône palaeovalley, filled with 700 m of Pliocene sediments. Data from later drilling, in the Gulf of Lion and up the Durance River valley, permitted a satisfactory reconstruction of the former Messinian valley of the Durance River. This valley shows up as a 300 km long canyon linking the abyssal plains of the Balearic Basin to the Alpine domain. Such a reconstruction requires the cancelling of the tectonic deformations (contemporary or subsequent) which have affected that palaeotopography, nam ely: down-stream subsidence resulting from the sedimentary load and the collapse of the continental shelf, and by up-stream compression warpings, which are very perceptible at the crest of the anticlines (Eyguières and Mirabeau). Keeping in mind these observations, it is possible to produce a satisfactory reconstruction of the longitudinal profile of the canyon. The depth increases from up-stream to down-stream where its value is over 1000 m. Such an extraordinary deepening, as well as the Pliocene filling that has followed, cannot be tectonically controlled because: (1) the excavation is maximum down-stream; and (2) there is evidence for typical oscillatory movement. A eustatic interpretation integrates these two facts because during the Messinian salinity crisis, the Mediterranean Sea was affected by the strongest eustatic oscillation of its history. One knows that in the case of rejuvenation provoked by the subsidence of the base level, erosion proceeds from down-stream to up-stream. The magnitude of the Messinian channel across the continental shelf suggests a depth of about 2000 m before the basin dried up. These observations confirm the evidence that only the desiccated deep basin model is able to explain coherently the whole of the phenomena linked to the salinity crisis.

Contribution de l'aeromagnetisme a l'etude du golfe de Valence (Mediterranee occidentale)

We present an aeromagnetic survey of the Gulf of Valencia and the Balearic Islands (western Mediterranean). A total field anomaly map and a map of the anomalies reduced to the pole have been obtained. From these maps, it is apparent that there are two regions of opposing magnetic style: the Balearic archipelago which is magnetically very smooth, and the north Balearic basin (or Gulf of Valencia) where anomalies are in places very intense. From a comparison of these two domains, we conclude that the Valencian basin was created during an extensional tectonic phase.

Quantitative evaluation of the depth of the western Mediterranean before, during and after the Late Miocene salinity crisis

ABSTRACTQuantitative geophysical calculations which take into consideration the isostatic loading of sediment overburden, the overlying water cover, and the thermal cooling history of the continental edge, and its adjacent oceanic lithosphere, demonstrate the foundering of the margins of the western Mediterranean had already commenced in the Aquitanian stage of the early Miocene. The calculations are based on magnitudes and rates of sediment accumulation observed along a profile of three commercial boreholes into the subsurface of the continental shelf of southern France. By the time of the late Miocene (Messinian) salinity crisis, the depth of the seafloor within the Balearic basin exceeded 2.5 km.Sea‐level fluctuations induced by evaporitic draw‐down permitted the exposure of large tracts of the former submerged continental margins to subaerial processes. The measured magnitude of sediment removal by erosion and channel incision near the outer shelf of the modern Gulf of Lion surpasses 1 km.The subsidence history of this shelf platform south of France provides new evidence that the continental lithosphere behaves as if it is rigidly coupled to its oceanic counterpart commencing with the initial phase of the pull‐apart. No major vertical fault displacements have subsequently offset their overlying crustal layers.The sedimentary shaping and construction of the margin seaward of the Rhône delta resulted in a pronounced shelf edge migration and slope progradation during the pre‐salinity crisis Miocene. It has taken 5 million years of predominant upbuilding to establish a new equilibrium profile similar in cross‐section to the precrisis depositional surfaces created by outbuilding.

Changes in the ostracodes of the Mediterranean with the Messinian salinity crisis

The likelihood of an environmental “crisis” in the evolution of the Tethys Ocean-Sea to the Mediterranean Ocean-Sea during Late Miocene is examined and tested against the present knowledge of the ostracode fossil record in Italy, Sicily, Crete, northern Tunisia, southern Spain and from some of the DSDP cores of the deep regions of the Mediterranean, especially in the Balearic Basin. It is concluded that there has been a substantial evolutionary and ecological change in the ostracode fauna that occurred at the time of the crisis. At the present time the best explanation available is that of isolation of deep basins from the World Ocean accompanied by extreme environmental change. The sudden oceanic “normalization” th that followed the “crisis” was perhaps just as extreme, but because of the buffering effects of the re-establishment of marine conditions in the newly formed Mediterranean, the shallower ostracode faunas coming from the Atlantic were not greatly different from those of westernmost Tethys.

Miocene deep-sea ostracodes of the Iberian Portal and the Balearic Basin

Discovery of deep-sea (psychrospheric) ostracodes in the Middle Miocene (Serravallian and Tortonian) of Andalusia, Spain, and in the cores of Site 372 of DSDP Leg 42a in the Balearic Basin east of Menorca indicates the presence of an opening (the Iberian Portal) between the Atlantic and the western Tethys basin complex at a depth estimated at more than 2000 m. Because of the concurrence of the ostracodes along a structural line marking the Prebetic and Subbetic boundary with the Meseta Massif, it is inferred and the rapidly shallowing ostracode faunas suggest, that this opening represents a structural trough closed by Alpine-type lateral movements during the Late Miocene (Messinian). During the Messinian “salinity crisis” the ostracodes to the east were nonmarine, while those on the western end of the line previously occupied by the trough remained marine.

Evidence of Migrating Liquid Hydrocarbons in Deep Sea Drilling Project Cores

Cores from the Deep Sea Drilling Project contain evidence that liquid hydrocarbons are migrating in or into near-bottom sediments at three widely separate locations. The first occurrence noted was the highly publicized, visually observed accumulation of immature petroleum in sediments on the Challenger Knoll in the Gulf of Mexico. Later, systematic chemical analyses revealed two more possible examples of migrated hydrocarbons. The first of these was a low-grade bitumen enrichment in a thin porous zone in Pleistocene sediments on the Shatsky Rise in the western Pacific Ocean. The second was a small but geochemically significant quantity of gasoline-range hydrocarbon and wet gas that apparently has seeped upward into Miocene sediments in the Balearic basin of the western Me iterranean Sea. These migrated hydrocarbons, in addition to the methane gas frequently found in the deep-ocean cores, reveal that hydrocarbon source rocks must be present, at least locally, in deep-ocean sediments, because liquid as well as gaseous hydrocarbons have begun to migrate.

Crustal structure of the Balearic sea

Within the frame of the German-French project ANNA-1970, two long refraction profiles were investigated north and south of the island of Majorca. For the southern Balearic Basin an oceanic crust can be derived from the travel-time curves consisting of a 4.0 km thick Cenozoic sedimentary layer with: V p = 2.35 (km/sec) + 0.35 (sec −1) × Z (km) and a 5 km thick layer with: V p = 4.0 (km/sec) + 0.28 (sec −1) × Z (km) The transition to the upper mantle takes place at a depth of 12 km. Directly south of Majorca a crustal thickening was measured which may be caused by the process of crustal shortening. P]In the northern Balearic Basin a faulted transitional type of crust has been observed indicating probably an embryonic and juvenile ocean expansion.

Magnetic anomaly pattern in the western mediterranean

A survey of the southern part of the Balearic Basin was flown in 1971 at a height of 600 m. The results of a survey of the northern part, flown at a height of 3000 m, which was previously published, have been downward continued to a height of 600 m. The resulting composite map shows well defined low amplitude (100 gammas) magnetic lineations of the Vine et Matthews' type offset by fracture zones. The lineated zones are bounded by large quasi-circular anomalies on the edge of possibly “continental” non magnetic zones. The results define a complex kinematic pattern of the opening of the Balearic Basin, in terms of plate tectonics.

Une structure compressive au nord de l'Algérie?

From the study of continuous seismic reflection profiles (Flexotir) we have revealed a marked morphological contrast between the Northern Algerian margin and the other margins of the Balearic basin. Such a difference is made particularly clear by a downwarping of the sedimentary layers at the limit of the Algerian margin. This downwarping could be explained by the existence of a trench being formed by compression.

Evidence of Migrating Hydrocarbons in Deep Sea Drilling Project Cores: ABSTRACT

To date the Deep Sea Drilling Project has revealed migrated liquid hydrocarbons in 3 widely separate areas of the globe. The first occurrence was the highly publicized, visually observed accumulation of immature petroleum in sediments on the Challenger Knoll in the Gulf of Mexico. Subsequent to the discovery of this obvious saturation, chemical analyses revealed 2 more possible examples of migration. The first was a low-grade bitumen saturation in a thin porous zone in Pleistocene sediments on the Shatsky Rise in the western Pacific Ocean. The second and latest was a small but geochemically significant quantity of wet gas and gasoline-range hydrocarbon that apparently seeped upward into Miocene rocks in the Balearic basin of the western Mediterranean Sea. These migrated h drocarbons--in addition to the methane gas commonly encountered in deep ocean cores--reveal that hydrocarbon source beds are present, and that liquids as well as gases have begun to migrate, at least locally, in deep-ocean sediments. End_of_Article - Last_Page 639------------