Messinian Times Research Articles

The significance of Messinian occurrences of Globorotalia margaritae and Globorotalia puncticulata in Sicily

ABSTRACT Globorotalia puncticulata and Globorotalia margaritae are critical species that define internationally recognized planktonic foraminiferal biozones in the Pliocene. These biozones are defined from stratotype sections on Sicily and their fauna are commonly considered to have been introduced to the Mediterranean after an influx of Atlantic water that terminated the late Miocene desiccation of the basin. Herein new discoveries of these species in rocks that predate the late Miocene desiccation are described. These data are supported by magneto‐ and lithostratigraphy that have been integrated at a single continuous section. Not only do these discoveries question the existing foraminiferal biozone stratigraphy, they also suggest new models for the dispersal of planktonic species. It is proposed that Globorotalia puncticulata and perhaps even Globorotalia margaritae evolved in the Mediterranean during earliest Messinian times (during or before chron C3Bn1n) and dispersed into the Atlantic. This suggests that a marine connection remained between the two sea areas until at least chron C3An.1n. Using the existing geomagnetic polarity time scale, these occurrences are some 2 Myr earlier than previously recorded in the Mediterranean. The distribution of G. margaritae and G. puncticulata in Mediterranean sections is likely to reflect palaeoenvironment or the preservation of deposits rather than the absolute age of the sediments.

The buried Afiq Canyon (eastern Mediterranean, Israel): a case study of a Tertiary submarine canyon exposed in Late Messinian times

The Afiq submarine canyon was one of a series of canyons initially incised in a drowned shelf edge and slope of the eastern Mediterranean margins in early Oligocene times (P19 zone). During most of the Early Miocene submarine erosion or non-deposition prevailed. This was followed by deposition of pelagic marls and debris flows in early Middle Miocene (N8) times. Large-scale sliding in late Middle Miocene times (N14) resulted in the collapse of the slope, the removal of most of the middle Miocene sequence and the formation of a box-shaped scar. Back-cutting incision ultimately resulted in the incision of the shelf in Late Miocene times. A sea-level fall ranging between 50 and 800 m below the canyon's rim resulted in the deposition of the Messinian Lower Evaporites (Mavqiim Formation) within the canyon. A subsequent rise of a similar extent led to the deposition of the Upper Evaporites (Be'eri Gypsum) which are found on the canyon's southern shoulder. The final Messinian sea-level drop, below the canyon's floor resulted in a subaerial environment in the canyon, the erosion of the upper evaporites and the subsequent deposition of fluvial and brackish sediments (Afiq Formation). The latter correspond to the Lago-Mare sediments known throughout the Mediterranean. The rapidly rising sea level during the Pliocene along with the high rate of Nilotic clastic sedimentation resulted in the final burial of the Afiq Canyon, and a pronounced seaward progradation (20–30 km) of the shelf edge.

Hemiasterid echinoids (Echinodermata: Spatangoida) from the Cretaceous Tethys to the present-day Mediterranean

Hemiasterid echinoids form one of the oldest and most varied spatangoid groups. Current data on stratigraphical and geographical distribution pattern show that their biogeographical history is closely related to Mediterranean-Tethyan structural and climatic changes. The group first appeared in the Aptian in the central Tethys (southwestern Europe) and developed and diversified remarkably in the Late Cretaceous through the subgenera Hemiaster (Hemiaster), H. (Bolbaster) and H. (Leymeriaster). Marked morphological changes arose in the early Paleogene when new Tertiary forms H. (Trachyaster), Opissaster and Ditremaster, originating in the Caribbean and Madagascan regions, respectively, replaced H. (Bolbaster) which partly survived and H. (Hemiaster) and H. (Leymeriaster) which disappeared entirely. These new forms achieved their greatest diversity during the Eocenee and thrived in the Mediterranean basin until it was sealed off from the Indo-Pacific in the Middle Miocene. Then Late Neogene climatic and structural events reduced hemiasterids to only a few Mediterranean species. The survivors of modern groups persisted in refuge areas of the western Mediterranean until middle Messinian times before being reduced to only one species, the last fossil one, during the Pliocene. Then, the Cenozoic groups H. (Trachyaster) and Opissaster definitively disappeared. Outside the Mediterranean basin primitive H. (Bolbaster) and modern Ditremaster, which colonized deep-water Atlantic environments from the Late Cretaceous and Middle Miocene respectively, survived the Messinian and Plio-Pleistocene climatic crises. They flourished in the northern Atlantic where their present-day descendants Ditremaster (Sarsiaster) griegii and H. (Bolbaster) expergitus still survive. H. (Bolbaster) expergitus spread worldwide and colonized the western Mediterranean in the Plio-Pleistocene via the Straits of Gibraltar.

On late miocene to recent vertical motions in the Cretan segment of the Hellenic arc

High-resolution foraminiferal and calcareous nannoplankton biostratigraphy and reliable paleobathymetry estimates based on plankton-benthos ratios in foraminifera make it possible to reconstruct in detail Late Neogene vertical motions along the Central Cretan segment of the Hellenic arc. These motions are considered to express the surficial effect of the roll-back process of the Hellenic subduction zone, which started about 12 Ma ago. In contrast to earlier views there is no sustained uplift since the late Middle Miocene. Successive paleotopographic profiles for central Crete show a predominance of subsidence, coupled with an increase of differential reliefs, from the latest Serravallian until the Messinian. Subsidence was most pronounced between the Tortonian-Messinian boundary interval and the early part of the Early Pliocene, locally up to a magnitude of more than 1000 m. A two-phased uplift history, coupled with tilting to the north or northeast, can be inferred from the late Early Pliocene-Recent record separated by a short, early Late Pliocene episode of subsidence. Rates of uplift were highest in the Early Pliocene up to about 125 cm/ka. The Central Cretan Late Neogene to Recent paleotopographic profiles are compared with those reconstructed from seismic interpretations and drilling data from the Cretan Sea. The combined results show that paleotopographic configurations between the Cyclades and Crete were fairly similar to those on central Crete until Messinian time. Foundering of the Cretan Basin started in the course of the Early Pliocene, but subsidence rates were less than the contemporaneous uplift rates of Crete. The timing and magnitude of the vertical motions along the Cretan Sea-Central Cretan transect put detailed geological constraints on tectonophysical modelling of the surficial effects of the roll-back process. These vertical motions are discussed in view of the model of southward translation of a large supracrustal slab, resulting in the origin of the Cretan Sea and in thrusting and uplift in the frontal parts of the slab, where it thrusted over the northern limb of the subducted Ionian Plate.

Bathymetric reconstructions of the Miocene-age ?calcari aLucina? (northern Apennines, Italy) from oxygen isotopes and benthic Foraminifera

Two independent methods of paleobathymetry, applicable to hydrocarbon-derived carbonates, are explored in this study. The oxygen isotope method exploits the temperature decline with depth that leaves a measurable imprint on theδ18O composition of pristine products of venting comprised of aragonites and dolomites. The other method makes use of the bathymetric preferences of benthic foraminiferal taxa entrapped in the carbonate buildups. These two methods were tested on the “calcari aLucina” limestones hosted in turbidites and mudstones infilling the Miocene-age Marnoso-arenacea basin. The limestone blocks, rich in fossils of chemosymbiotic-like fauna, preserve a 10-Ma record of hydrocarbon venting from Langhian to lower Messinian times. Our results indicate that carbonate accretion and lithification occurred at upper bathyal depths in waters not shallower than 200–250 m. Theδ18O of venting products contains the imprints of profound hydrographic changes that occurred in the ancient Mediterranean basin from the lower Serravallian to the lower Messinian.

A stratigraphic and tectonofacies framework of the ?calcari aLucina? in the Apennine Chain, Italy

The Apennine Chain provides the first example of stratigraphic (time) and synsedimentary tectonic (space) distribution of the “calcari aLucina” Miocene equivalents of modern cold-vent carbonates. Chemosynthetic faunal assemblages and related carbonate deposits are found at different stratigraphic levels, with peaks during Langhian-Serravallian and late Tortonian-early Messinian times. A general increase in frequency and volume occurs with time. A “genetic link” between venting and the Messinian Evaporite event is difficult to demonstrate. However,Lucina limestones are limited to preevaporitic times, and their maximum abundance is reached just before the onset of the Messinian Evaporite accumulation.Lucina limestones occur in almost all tectofacies of the orogen, from backland to foreland.

Tectonic controls on base‐level variations and depositional sequences within thrust‐top and foredeep basins: examples from the Neogene thrust belt of central Sicily

AbstractTectonic subsidence and uplift may be recorded by concomitant sedimentation, not only from decompacted accumulation curves but also from the evolving depositional environment relative to sea level at the time. In thrust belts there are two types of processes capable of generating vertical movements, each with different wavelengths and amplitudes. Regional subsidence is driven by flexural loading by the orogenic hinterland, the thrust belt and accumulated sediments of the underlying foreland lithosphere. Within this flexure, the foreland thrust belt will generate areas of local uplift, notably at the crests of thrust anticlines. In this contribution we examine how these processes have interacted to influence relative sea level as recorded by late Neogene sediments in an array of basins developed above and adjacent to the Maghrebian thrust belt of central Sicily. Two particular periods are addressed, the late Tortonian to early Messinian (Terravecchia Formation) and early to early late Pliocene. The earlier of these is characterized by a deltaic complex that formed prograding depositional geometries, migrating into perched basins. Collectively, however, these units are transgressive and migrate back towards the orogen. A depositional model is presented that links the migration of facies belts to subsidence caused by accentuated tectonic loading in the hinterland and break‐back thrust sequences across the basins. We infer that a palaeobathymetric profile of underfilled sub‐basins resulted and that this influenced the pattern of evaporite accumulation during Mediterranean desiccation in Messinian times. The Pliocene sediments, accumulated under renewed global sea levels, prograded towards the foreland. A waning tectonic load in the hinterland driving isostatic rebound, uplift and coastal offlap is the proposed explanation. This contribution is a case history for the depositional evolution of dominantly submarine thrust systems and their record of relative sea‐level changes.

Sea-level events in the South Pacific linked with the Messinian salinity crisis

Cores drilled through the carbonate cap of Niue, a mid-oceanic carbonate platform in the South Pacific, contain an unusually well resolved stratigraphic section of the latest Miocene at 35 to 140 m depth below sea level. Intensely leached and chalky intervals associated with pronounced 18 O and 13 C depletions mark the position of dissolution unconformities representing eight episodes of eustatic falls that outstripped the local rate of subsidence. We demonstrate, on the basis of Sr isotope chronostratigraphy, that these eustatic changes are correlative with the Messinian salinity crisis events in the Mediterranean. Sea-level changes of about 10 m amplitude commenced at 6.14 Ma and culminated in a large sea-level fall that reached at least 30 m at 5.26 Ma, corresponding to the Miocene-Pliocene boundary. Evaluation of the sea-level history reported here and the contemporaneous Mediterranean events supports the model of coupling between tectonic and eustatic factors that caused the onset and demise of the salinity crisis. The available evidence suggests that during Messinian time, glacio-eustatic falls and rises are likely to have modulated the connection between the Atlantic and the Mediterranean and influenced the evaporite deposition, and may have contributed significantly to the final phase of isolation and desiccation of the Mediterranean and its subsequent refilling during the Zan-clean deluge.

Origin and deformation of the Neogene–Recent Maghrebian foredeep at the Gela Nappe, SE Sicily

SE Sicily contains one of the few exposures of orogenic foreland to the Maghrebian-Apennine orogenic system in the central Mediterranean. Here the African foreland is represented by the Hyblean plateau, adjacent to the frontal thrust structures of the Maghrebian chain. These structures include the disrupted foredeeps to earlier parts of the thrust system. One of these, the Gela nappe, is a major structure composed of late Oligocene to early Pliocene sediments emplaced onto Pliocene–Pleistocene rocks of the buried foreland. This paper presents a correlation of late Miocene stratigraphic units between the foreland and the foredeep basin. Abrupt lithological and thickness variations of these units suggest that the foredeep basin was limited towards the foreland by normal faults. In the hinterland these foredeep sediments lap back onto previously emplaced thrust sheets, including the far-travelled units of ‘Numidian flysch’. The precursor Oligocene–Serravallian foredeep may also have been controlled by normal faulting. Compressional tectonics are reflected in folding and thrusting which post-dates deposition of lower Pliocene chalks (Trubi Formation), although minor folding and erosion preceded this unit. Larger thrusts repeat the basin stratigraphy and carry it out onto the adjacent foreland. A minimum of 8 km shortening since Messinian times can be demonstrated although a more realistic figure is c. 25 km, at a time-averaged rate off. 0.5cm/a −1 . The stratigraphic relationships on the foredeep sedimentary sequences may provide analogues for offshore areas of the thrust belt.

Miocene syntectonic sedimentation along the western margins of the Hyblean-Malta platform: A guide to plate margin processes in the central Mediterranean

The central Mediterranean Hyblean-Maltese Platform is part of the Pelagian Block of the African Plate and occupies a critical site between two neotectonically active structural zones. To the south in the Sicily Channel lies the Malta Graben, part of the larger Pantelleria Rift System. To the north lies a broad, foreland verging thrust-belt generated by Africa-Europe plate convergence during the Tertiary. Miocene sedimentation patterns within the NW Hyblean syntectonic successions record the initiation of tectonic deformation associated with African intraplate tectonic processes. Initially, in the Early Miocene, local NE-SW orientated highs developed on the seafloor but later, in the Middle Miocene, these irregularities were levelled by prolonged marl sedimentation. These structures became active again in the Late Tortonian, in association with volcanicity. By Early Messinian times the sea floor irregularities had developed into NE-SW oriented grabens associated with evaporite deposition. A similar, time related syntectonic sedimentary history can be deduced for the Maltese region to the south. The common tectonic behaviour pattern of the two regions results from both being controlled by a common N-S to the NE-SW orientated transform fault zone, the full effects of which are documented for the first time. This dextral wrench system became active during the Late Miocene in order to accomodate continuing intraplate divergence (especially associated with the Malta Graben) and differential rates of African Foreland underthrusting.

Palaeogeographic implications of the Messinian surface in the Valencia trough, northwestern Mediterranean Sea

Sparker (3000 J and 8000 J) and multichannel seismic reflection profiles across the Valencia trough show a Messinian unconformity incised by numerous valleys. The main feature of this surface is a large valley that generally underlies the present Valencia valley and is deeply entrenched into the Miocene deposits. The size of this palaeo-valley ranges from 0.5 km wide and 15–100 m deep at its western end, to 1.6–2.8 km wide and 200–250 m deep downstream. An important tributary system is observed, with a main canyon (6–8 km wide and 150–200 m deep) draining the Ebro margin, as well as many other smaller valleys draining the Catalan and Balearic margins. Downstream, other tributaries underlie the present canyons of the Catalan margin. The location of the tributary system is controlled by the Early Miocene rift structures. The relief of the Messinian surface is affected by post-Miocene deformation that results from salt diapirism, extensional faulting and related volcanism. Late Neogene to Quaternary volcanic edifices cut the Messinian surface and coincide with large residual magnetic anomalies. Lower Pliocene to Quaternary salt diapirism in the abyssal plain north of Menorca has created a series of structural highs. Between these highs are deep interdiapiric troughs or basins that have become sediment depocentres during the Plio-Quaternary. The complex network of erosional valleys from the Valencia trough continental margin demonstrates that the valley system in the basin was not related to the refilling of the Mediterranean, but to the Iberian and Balearic margin palaeodrainage that developed during the Messinian desiccation. The presence of at least three erosional unconformities suggests that there were alternating periods of flooding and retreat of Atlantic water during Messinian time. The Messinian subaerial margin with erosional valleys contrasts sharply with the Pliocene-Quaternary marine margin with progradational turbidite systems.

Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras and Nijar areas, southeastern Spain

ABSTRACTDuring Serravallian through Messinian time, marine carbonates flanked topographic highs that rimmed Neogene basins in the Western Mediterranean. Middle to upper Miocene carbonate strata in the Las Negras and Nijar areas (southeastern Spain) are 50‐150 m thick and display 50‐200 m of shelf‐to‐basin relief over 1‐2 km. Detailed studies in those areas document the effects of relative sea‐level change on sedimentation, biotic composition, and reef development. We identify three previously unrecognized, regionally correlatable depositional sequences (DS1, DS2, DS3) that occur between the underlying basement and the overlying Terminal Carbonate Complex. The lower depositional sequences (DS1, DS2) are mostly normal marine shelf (ramp) carbonates deposited on the flanks of basement highs. The basal part of DS2 locally contains some megabreccia reef blocks composed of Tarbellastraea and Porites. These blocks are the first evidence of reef growth in the area and represent a previously unrecognized period of reef development prior to the fringing reef development. The reef blocks probably formed as upslope patch reefs that were eroded and transported to distal slope locations. The upper sequence (DS3) is characterized by clinoform strata of a Porites‐dominated fringing reef complex that prograded basinward in a downstepping style with successively younger reefs forming in a topographically lower and more basinward position as a result of a net sea‐level drop.Regional correlation of Miocene shallow‐marine strata between basins in Spain and elsewhere in the western Mediterranean is complicated because basins were semi‐isolated from adjacent basins making physical correlation impossible. In addition, age‐definitive biostratigraphic markers are poorly preserved in most of the Miocene shallow‐water strata; basinal sediments that are more easily dated by microfossils do not typically interfinger with the shallow‐marine strata in outcrop. Even where datable microfossils are found, resolution of dating is poor.Our studies in the Las Negras and Nijar areas illustrate the usefulness of integrating sedimentological, geometric and biotic data with locally derived relative sea‐level (accommodation space) curves for correlation. The relative sea‐level curves for each area show remarkable similarities in shape and magnitude of sea‐level changes. These curves indicate several relative sea‐level fluctuations during Miocene carbonate deposition prior to the major sea‐level drop at the end of DS3 deposition that culminated in the exposure of the basin margin deposits and the deposition of evaporites in basinal areas during the Messinian.The depositional sequences in the Las Negras and Nijar areas may correlate with depositional sequences of similar age throughout the southern Cabo de Gata area, in Mallorca some 600 km to the northeast, and possibly in other Mediterranean locations. The widespread occurrence and possible correlation of the depositional sequences suggest regional processes such as eustacy or tectonism for their formation.The integration of sedimentological, palaeontological and sequence stratigraphic studies, and the construction of relative sea‐level (accommodation space) curves may help in the interpretation of depositional histories of shallow‐marine carbonate complexes and correlation of these strata between isolated areas. Other dating methods, in addition to microfossil dating, may allow for better age determination of the sequences and aid in identifying the importance of eustacy and tectonism in sequence development.

Late cenozoic identation/escape tectonics in the eastern Betic Cordilleras and its consequences on the Iberian foreland

The structuration of the southeastern quarter of the Iberian Peninsula (eastern Betics and Iberian foreland), since Messinian time, was the result of a series of complex deformational events, as related to a major NNE-SSW sinistral shear zone disrupting the southeasternmost part of the Betic cordilleras (Trans-Alboran-Palomares shear zone; TAPSZ). Deformation along this shear zone was characterized by two differentiated and sequential scenarios: 1) periods of stress-build-up associated to momentary slip-obstruction along the TAPSZ, involving NW-directed indentation of the southeastern Iberian domain, and 2) periods of stress-release resulting from the lateral escape of wedge-shaped blocks, thus allowing full-scale strike-slip displacements along the TAPSZ. These events imposed compressional stress fields on the Iberian foreland, with a series of consequences such as alkaline volcanism in Calatrava and Cofrentes, protorift zones, changes in previous structural trends, localized uplift/doming processes, and changes in the sedimentary records of sorne basins.

Valencia gorge: Possible Messinian refill channel for the western Mediterranean Sea

A deeply incised gorge is buried nearly 800 m beneath the floor of the Valencia Trough in the western Mediterranean Sea. The gorge is steeply cut more than 200m into Messinian evaporite deposits and has been mapped for more than 40 km. Published and unpublished seismic profiles show the total length to be nearly 300 km. The gorge is not aligned with any known large fluvial systems, and its orientation indicates that it may have been connected near Valencia with the Betic Strait, the portal in southern Spain proposed to link the Atlantic and the western Mediterranean. The Betic Strait was probably open at least through early Messinian time. Conservative estimates show that sea water flowing through the Valencia gorge at rates of 0.5 to 2 m/s could have refilled the western Mediterranean basins below 2000 m in less than 50 yr.

Stratigraphy and palaeogeography of the Capo Milazzo area (NE Sicili, Italy): clues to the evolution of the southern margin of the Tyrrhenian Basin during the Neogene

The Neogene sedimentary sequence of Capo Milazzo (NE Sicily, Italy), with particular reference to the Niocene interval, is described in detail and a paleoenvironmental evolution for the Late Miocene/Pliocene time is proposed. The sequence represents a portion of the northern side of the Calabrian Arc and documents the response of the coastal environment to the complex events (salinity crisis, opening of the Tyrrhenian Basin) which affected the Mediterranean Basin during the Neogene. The beginning of rifting and increased subsidence of the northern sectors along NE-SW faults are recorded in the Late Tortonian, together with a southbound marine transgression, documented by clastic littoral facies. The transgressive trend continued during the Early Messinian, though the moderate subsidence maintained a neritic environment in which a small reef complex adjacent to a lagoon developed. Emersion, and karstic erosion of the Early Messinian limestones is recorded in the Late Messinian time equivalent of the Lower Evaporite. Reactivation of NE-SW faults at this time favoured the formation of large breccias, collapsed from the peripheral portions of the reef complex. Subsequent lowering of the NW sector allowed the area to ne reached by a limited marine episode during the Intra-Messinian Transgression. High-energy stream deposits, coeval with the deposition of the “Lago-Mare” facies in the Mediterranean, end the Messinian sequence. The Pliocene sequence fossilizes a complex palaeotopography with submerged highs and narrow depressions. A rapid marine transgression is recorded at the Miocene/Pliocene boundary, with the development of circalittoral/epibathyal environments. Tensional movements during the latest Messinian/earliest Pliocene and Late Pliocene are recorded by a system of fractures and respective fillings that affect the upper portion of the Early Messinian limestones. The erosion and reworking of most Early Pliocene sediments into Late Pliocene bathyal deposits, together with the local presence of clastic foreset deposits and large blocks of Messinian limestones collapsed into the lower part of Late Pliocene deep water sediments, document a Mid-Pliocene event, likely referable to the Middle-Pliocene Tectonic Phase.

The sedimentary expression of regional tectonic events during the Miocene-Pliocene transition in the southern Cyprus basins

AbstractA well-known tectonic event affecting the East Mediterranean region, generally referred to as ‘the’ Miocene–Pliocene phase, occurs at, or near the Miocene–Pliocene boundary. Recent sedimentological studies in Cyprus indicate that this ‘event’, in fact, is complex. The Tortonian–Lower Pliocene period is marked by a stress involving an N20 extension in the Polemi and Pissouri basins and by an N100 extension in the Psematismenos basin. Sedimentological studies have demonstrated three tectonic pulsations during Messinian time, prior to the Pliocene transgression. These are expressed by two episodes of seismic brecciation, and a palaeo-emersion is indicated by palaeosols and detrital discharges. These phenomena suggest brief tectonic instability during Messinian time. Microtectonic studies in the South Troodos basins of Cyprus reveal that the main change in tectonic stress does not coincide with the Miocene–Pliocene contact but occurs at the end of Lower Pliocene time. The authors conclude that the so-called Miocene–Pliocene ‘event’, in reality, is a series of subtle tectonic pulsations recorded clearly by sedimentary parameters.

Le magmatisme neogene betico-rifain et le couloir de decrochement trans-Alboran

Abstract The Miocene basin evolution of southeastern Spain and eastern Morocco is linked to a "shear zone" elongated from SW across the Alboran Sea. In Spain the magmatism is mostly calc-alkaline (or K-rich calc-alkaline). Most of the products are locatred on strike-slip faults (Almeria-Cabo de Gata). Lavas of dacitic compositions are interpreted as products of crustal anatexis. During Messinian time, lamproites are erupted over an extended area. Later (Plio-Quaternary), alkali basalts are located near Cartagena. In Morocco, calc-alkaline magmatism is not as developed as in Spain; late Tortonian-Messinian volcanoes (Gourougou, Guilliz) have erupted of shoshonitic lavas. Alkali basalts are abundant and appear from the end of Messinian to Quaternary all over northwestern Africa. In the studied area, there are no chronological nor geochemical polarity of the magmatism according to the existence of a Miocene subduction. The association of the magmatism with tectonics and basin evolution shows that it is linked with their aperture. The structure of the lithosphere, as it appears from the geophysical data, shows the existence of two different crusts, separated by the western part of the "shear zone". Trans-Alboran calc-alkaline magmatism is clearly correlated with the activity of this "shear zone", from Miocene to present time.

Genesis and evolution of strontium deposits of the granada basin (Southeastern Spain): Evidence of diagenetic replacement of a stromatolite belt

There are important strontium deposits in the Granada Basin, the most noteable of which (Montevives) has an annual production of approximately 50,000 tons of almost pure celestite. Two types of mineralization can be recognized: a primary variety consisting of stromatolitic carbonate that has been partially replaced by celestite, and a secondary variety consisting of celestite-pebble karst deposits. Both are included in an evaporitic Messinian succession. The primary variety of mineralization is within carbonates that interfinger with, and prograde across, gypsum deposits. The development of these deposits can be interpreted in the context of the general evolution of the Granada Basin during Late Tortonian and Messinian times. Open marine conditions prevailed during the late Tortonian. During the transition from Tortonian to Messinian a restriction of the basin resulted in evaporite sedimentation, with stromatolites thriving at the basin's margin. The stromatolites were distributed along a coastal belt that was limited on the east by the tectonically active Sierra Nevada with its local alluvial fans. Runoff from the Sierra Nevada produced a freshwater lens and surface salinities that permitted the development of stromatolites, rather than the accumulation of gypsum. The replacement of stromatolitic carbonate by celestite occurred within the mixing zone of the coastal aquifers during sedimentation and/or early diagenesis. An essentially marine origin is considered for the strontium. Supplementary influxes from continental weathering are also thought to have been produced. Further restriction of the Granada Basin led to complete desiccation and the deposition of a 20 m thick halite layer. Later, gypsum deposits were exposed, and resulting cavities (“dolinas”) were filled with celestite pebbles. The return of sediment accumulation within lakes buried and preserved these deposits.

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.

Neogene to Quaternary geodynamics of the area of the Ionian Sea and surrounding land masses

Summary Investigations in the north-eastern and central Ionian Sea document important palaeogeographic and palaeoceanographic changes since Neogene time. These findings support the model of shallow basinal evaporation during Messinian time. On this basis the rate of subsidence of the Ionian Sea is calculated for the last 6 Ma, at about 1 m per 1000 years for basinal settings and half this for marginal settings. Elevated terraces corresponding to high glacio-eustatic stages in the Quaternary are frequent on Mediterranean coasts at heights up to more than 150 m above present sea level. Together with elevated marine deposits of Pliocene age, they testify to general coastal uplift. These epeirogenic tectonics are interpreted as compensation for the subsidence of Mediterranean basins. In its present general form the Mediterranean Sea has existed since Pliocene time. The first indications of the foundering of the Ionian basin are Messinian evaporites. The formation of such huge basins is interpreted as the result of the transformation of former continental crust to ‘intermediate’ or ‘oceanized’ crust. The important fast vertical tectonics of the margins of ‘Mediterranean type’ differ considerably from those of the Atlantic or Pacific type.