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

During 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.     

Messinian stromatolite-thrombolite associations,Santa Pola,SE Spain: an analogue for the Palaeozoic?

Stromatolite-thrombolite associations are the dominant facies forming large portions of the Santa Pola carbonate platform (SE Spain) during deposition of the Terminal Carbonate Complex (TCC). The TCC, the last period of marine sedimentation in the Western Mediterranean associated with the Messinian Salinity Crisis, comprises a NE-SW trending thrombolite reef with occasionally interlayered stromatolite horizons and a predominantply stromatolite and oolite facies in the back-reef area. The stromatolites are mainly dome shaped, but fine-columnar or wavy-undulose forms can occur. The stromatolites form huge bioherms, extending tens to hundreds of metres. They are finely laminated with alternating layers of dolomicrite and dolomicrospar. The dolomicrite layers appear to be a primary dolomite precipitate, whereas the dolomite crystals in the dolomicrospar layers apparently formed around a meta-stable nuclei which was subsequently dissolved or degraded. The low content of sand-sized particles in the stromatolitic layers indicates formation under low-energy conditions, possibly on a tidal flat. As reported from other areas in the Western Mediterranean, deposition of the TCC at Santa Pola was apparently cyclic, whereby stromatolites generally terminate each depositional cycle. Subtidal Conophyton stromatolites, possibly the only known occurrence younger than Palaeozoic, are, however, found on the reef slope at the base of the first TCC depositional cycle. The dolomitic nature of the unadulterated stromatolitic laminations and the association of stromatolites and thrombolites as platform builders were a common feature in the Early Palaeozoic but are unusual in post-Ordovician carbonate facies. We propose that the conditions during TCC deposition were very restricted, possibly reflecting an environment similar to that of the Early Palaeozoic.     

The onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin

Astronomical tuning of the Messinian pre‐salt succession in the Levant Basin allows for the first time the reconstruction of a detailed chronology of the Messinian salinity crisis (MSC) events in deep setting and their correlation with marginal records that supports the CIESM ( 2008 ) 3‐stage model. Our main conclusions are (1) MSC events were synchronous across marginal and deep basins, (2) MSC onset in deep basins occurred at 5.97 Ma, (3) only foraminifera‐barren, evaporite‐free shales accumulated in deep settings between 5.97 and 5.60 Ma, (4) deep evaporites (anhydrite and halite) deposition started later, at 5.60 Ma and (5) new and published ⁸⁷Sr/⁸⁶Sr data indicate that during all stages, evaporites precipitated from the same water body in all the Mediterranean sub‐basins. The wide synchrony of events and ⁸⁷Sr/⁸⁶Sr homogeneity implies inter‐sub‐basin connection during the whole MSC and is not compatible with large sea‐level fall and desiccation of the Mediterranean.     

Messinian sea level fall in the Dacic Basin (Eastern Paratethys): palaeogeographical implications from seismic sequence stratigraphy

The signature of the Mediterranean Messinian Salinity Crisis (MSC) in the Paratethys has received wide attention because of the inferred changes in connectivity and base level. In this article, we present sequence stratigraphic interpretations on a seismic transect across the western part of the semi-isolated Late Miocene–Pliocene Dacic Basin (Eastern Paratethys, Romania), chronologically constrained by biostratigraphic field observations and well data. They reveal significant sea level changes during the middle Pontian that are coeval with the MSC. These changes were most likely transmitted to the western Dacic Basin from the downstream Black Sea and controlled by the sill height of the interconnecting gateway. During the middle Pontian lowstand of the western Dacian Basin, sedimentation continued in a remnant ∼300 m deep lake with a positive water balance. Our observations show that the evolution of semi-isolated sedimentary basins is strongly dependent on the communication with other depositional realms through its control on base level and sediment supply.     

The opening of the Plio-Quaternary Gibraltar Strait: assessing the size of a cataclysm

Abstract

The widespread Lago-Mare facies show that the Mediterranean was fully isolated from the World Ocean at the end of the Messinian salinity crisis (MSC): the Plio-Quaternary Gibraltar Strait has no geographical feature in common with the Miocene Portals, which were continentalised before the end of the MSC. A copy of a budget model has been modified to study the infilling of the Mediterranean. The yearly Atlantic water supply follows an exponential increase law. The level of the basins does not change significantly during the 26 early years, but the refill of the Mediterranean basins is completed within the next 10–11 years. The high velocity of the flow of Atlantic water can be reconfirmed by hydraulic calculations. The morphological study of the area suggests that the Gibraltar Strait originates from an eastwards flowing stream, which drained the eastern slope of an emergent Gibraltar Isthmus to the Mediterranean Basins at the end of the Messinian. Similar canyons are still found in the marine topography towards the Alboran Sea. The present Spartel and Camarinal Sills both originate from the coeval mass sliding of the northern bank of the strait. The strait of Gibraltar results from the work of a stream, which managed water-piracy from an Ocean. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

The Messinian Sicilian stratigraphy revisited: new insights for the Messinian salinity crisis

Controversies around the Messinian salinity crisis (MSC) are because of the difficulties in establishing genetic and stratigraphic relationships between its deep and shallow‐water record. Actually, the Sicilian foreland basin shows both shallow and deep‐water Messinian records, thus offering the chance to reconstruct comprehensive MSC scenarios. The Lower Gypsum of Sicily comprises primary and resedimented evaporites separated in space and time by the intra‐Messinian unconformity. A composite unit including halite, resedimented gypsum and Calcare di Base accumulated between 5.6 and 5.55 Ma in the main depocentres; it records the acme of the Messinian Salinity Crisis during a tectonic phase coupled with sea‐level falls at glacials TG14‐TG12. These deposits fully post‐date primary gypsum, which precipitated in shallow‐water wedge‐top and foreland ramp basins between 5.96 and 5.6 Ma. This new stratigraphic framework results in a three‐stage MSC scenario characterized by different primary evaporite associations: selenite in the first and third stages, carbonate, halite and potash salt in the second one associated with hybrid resedimented evaporites.     

3D and 4D controls on carbonate depositional systems: sedimentological and sequence stratigraphic analysis of an attached carbonate platform and atoll (Miocene, Níjar Basin, SE Spain)

This study investigates the controls on three-dimensional stratigraphic geometries and facies of shallow-water carbonate depositional sequences. A 15 km² area of well-exposed Mid to Late Miocene carbonates on the margin of the Níjar Basin of SE Spain was mapped in detail. An attached carbonate platform and atoll developed from a steeply sloping basin margin over a basal topographic unconformity and an offshore dacite dome (Late Miocene). The older strata comprise prograding bioclastic (mollusc and coralline algae) dominated sediments and later Messinian Porites reefs form prograding and downstepping geometries (falling stage systems tract). Seven depositional sequences, their systems tracts and facies have been mapped and dated (using Sr isotopes) to define their morphology, stratigraphic geometries, and palaeo-environments. A relative sea-level curve and isochore maps were constructed for the three Messinian depositional sequences that precede the late Messinian evaporative drawdown of the Mediterranean. The main 3D controls on these depositional sequences are interpreted as being: (i) local, tectonically driven relative sea-level changes; (ii) the morphology of the underlying sequence boundary; (iii) the type of carbonate producers [bioclastic coralline algal and mollusc-dominated sequences accumulated in lows and on slopes of < 14° whereas the Porites reef-dominated sequence accumulated on steep slopes (up to 25°) and shallow-water highs]. Further controls were: (iv) the inherited palaeo-valleys and point-sourced clastics; (v) the amount of clastic sediments; and (vi) erosion during the following sequence boundary development. The stratigraphy is compared with that of adjacent Miocene basins in the western Mediterranean to differentiate local (tectonics, clastic supply, erosion history, carbonate-producing communities) versus regional (climatic, tectonic, palaeogeographic, sea-level) controls.     

Record of climatic change in neritic carbonates: turnover in biogenic associations and depositional modes (Late Miocene,southern Spain)

In order to evaluate the geological record of climatic change in neritic carbonates, we studied Late Miocene rock outcrops in southern Spain. Six episodes of reef growth are documented (Burdigalian to Messinian) in Neogene basins of the Betic Cordillera, which were located close to the margin of the global reef belt. The reefs are characterized by various zooxanthellate corals which decrease in diversity with time, andHalimeda; the youngest reefs of the latest Messinian are characterized by the dominance of the genusPorites. Late Miocene coral reefs and reef-rimmed platforms alternate over time with non-reefal carbonate ramps characterized by skeletal calcirudites or with gypsum such as that formed during the Messinian salinity crisis. The calcirudites lack reef corals, calcified green algae and extensive marine cement, but exhibit skeletal components described from both modern and fossil nontropical carbonates. These include bryozoans, mollusks, foraminifers, echinoderms and minor balanids, as well as coralline algae of a bryomol association. The presence of some larger foraminifers indicates high temperatures, close to the lower temperature threshold of the reef assemblage. Sea level lowstands and highstands are documented by wedges of bryomol carbonate and chlorozoan patch reefs or prograding platforms. Thus, temperate climate depositional modes correspond to relatively low sea levels, and warm-water modes to high sea levels. The Neogene infill of the Agua Amarga and Sorbas basins documents two of these cycles. Other climate/sea-level cycles (including Messinian gypsum in the cool water depositional mode) are well established in adjacent Neogene basins in southern Spain. This type of composite sequence seems to occur only along the margin of the global reef belt and indicates an oscillatory latitudinal movement of the margin, which is associated with global climatic change. The analysis of turnover in neritic depositional carbonate systems may therefore be considered a sensitive tool for reconstructing climatic change from the fossil record. However, warm-water modes and temperate-water modes of carbonate sedimentation and diagenesis differ significantly. For this reason the interpretation of composite system sequences by sequence stratigraphy requires an extended concept. The particular type of mixed bryomolchlorozoan depositional sequence also bears some potential for drowning, because sea level rise may be faster than the net production rate of temperate carbonate systems.     

Messinian events in the Black Sea

Past hydrological interactions between the Mediterranean Sea and Black Sea are poorly resolved due to complications in establishing a high‐resolution time frame for the Black Sea. We present a new greigite‐based magnetostratigraphic age model for the Mio‐Pliocene deposits of DSDP Hole 380/380A, drilled in the southwestern Black Sea. This age model is complemented by ⁴⁰Ar/³⁹Ar dating of a volcanic ash layer, allowing a direct correlation of Black Sea deposits to the Messinian salinity crisis (MSC) interval of the Mediterranean Sea. Proxy records divide these DSDP deposits into four intervals: (i) Pre‐MSC marine conditions (6.1–6.0 Ma); (ii) highstand, fresh to brackish water conditions (~6.0–5.6 Ma); (iii) lowstand, fresh‐water environment (5.6–5.4 Ma) and (iv) highstand, fresh‐water conditions (5.4–post 5.0 Ma). Our results indicate the Black Sea was a major fresh‐water source during gypsum precipitation in the Mediterranean Sea. The introduction of Lago Mare fauna during the final stage of the MSC coincides with a sea‐level rise in the Black Sea. Across the Mio‐Pliocene boundary, sea‐level and salinity in the Black Sea did not change significantly.     

Sedimentology and paleoenvironmental evolution of Messinian evaporites in the Iskenderun-Hatay basin complex, Southern Turkey

Messinian evaporites, which resulted from the salinity crisis during the final closure of the Mediterranean Sea, are exposed in SE Turkey. These evaporites formed in two isolated sub-basins, Iskenderun-Arsuz (IA) and Hatay-Samanda? (HS), which belong to different depositional configurations and tectonic structures. The Neogene fill of these sub-basins consists of a thick sedimentary succession that started with Early Miocene terrestrial clastics, followed by reefs (Middle Miocene) and shallow water siliciclastics (Tortonian - Early to Late Miocene) and finally Messinian evaporates. These sub-basins accumulated in a diverse range of depositional environments from very shallow to deeper water. Evaporite facies in the IA sub-basin consist of sabkhas, saline lagoons and ponds. They are mainly represented by chemical deposits such as scattered gypsum nodules and balls, nodular bedded gypsum, laminated gypsum (Type-A) and selenites (Type-S1). Evaporites in the HS sub-basin mainly consist of detrital gypsum composed of gypsum laminae (Type-B, C), gypsum arenite-rudites and deeper water selenites (≤ 20 m), and resedimented selenites (Type-S2), which were deposited on a sulfate platform with a slope-basin transitional zone. Secondary gypsum with alabastrine and porphyroblastic textures as well as satin spar veins is commonly associated with the sabkha-type evaporites of the IA sub-basin. Deeper-water clastic evaporites of the HS sub-basin have generally remained as primary gypsum or have only been slightly affected by diagenetic alterations. The isotope values (^87/86Sr; δ¹⁸O SMOW; and δ³⁴S CDT) from the different kinds of gypsum lithofacies of the sub-basin are similar to those of the Messinian evaporites in other peri-Mediterranean basins, indicating an origin from marine water without external or basinal contributions.The Messinian evaporites examined in this paper are overlain by Early Pliocene (Zanclean) deposits composed of shallow- and deep-water siliciclastics and carbonates with local intercalations of Lago-Mare-type strata. Throughout the Messinian evaporitic stage, the IA sub-basin was mainly comprised of shallow water evaporites, while the HS sub-basin underwent deepening related to regional tectonics induced by the Dead Sea Fault during the construction of the Hatay Graben.     

Structure and evolution of a Messinian mixed carbonate‐siliciclastic platform: the role of evaporites (Sorbas Basin,South‐east Spain)

The Sorbas Member is a late Messinian complex sedimentary system that formed immediately following deposition of the Messinian evaporites in the Sorbas Basin (South‐east Spain). This work describes the sequence architecture and facies organization of a continuous kilometre long, alluvial fan to open platform transect near the village of Cariatiz in the north‐east of the basin. The post‐evaporitic Cariatiz platform was a mixed carbonate‐siliciclastic system composed of four intermediate‐frequency, fifth‐order depositional sequences (Depositional Sequences 1 to 4) arranged in an overall prograding trend. The intense fracturing and brecciation of these deposits is attributed to the deformation and dissolution of an evaporite body measuring several tens of metres in thickness. The four sequences display significant spatial–temporal variability in both architecture and facies distribution, with two main phases: (i) Depositional Sequences 1 and 2 are ooid and oobioclastic dominated, and show normal marine faunas; and (ii) Depositional Sequences 3 and 4 show a higher siliciclastic contribution and are microbialite dominated. These important changes are interpreted as modifications of the primary controlling factors. Following an initial 70 m drowning, possibly linked to increased oceanic input, Depositional Sequences 1 to 3 were controlled mainly by eustatic variations and inherited topography; their progradation destabilized the evaporite body near the end of the Depositional Sequence 2 period. During the second phase, Depositional Sequences 3 and 4 recorded a progressive restriction of the Sorbas Basin related to a 30 to 40 m fall in water level that was driven mainly by regional factors. These regional factors were dissolution and gravity‐induced deformation of the evaporites and correlative evaporative fluid circulation associated with the contrasted arid/humid regional climate that, respectively, controlled sequence geometry and fluctuating water salinity which caused a microbialite bloom.     

Messinian events in the Sorbas Basin in southeastern Spain and their implications in the recent history of the Mediterranean

The Messinian (Late Miocene) marine stratigraphic record of the Sorbas Basin (S.E. Spain) is well preserved and can be considered as being representative of the entire western Mediterranean. It exhibits a series of features relating to: (1) the composition, characteristics and evolution of coral reefs; (2) changes between temperate and subtropical climates; and (3) the extensive development of microbial carbonates (stromatolites and thrombolites) at the end of the Messinian. Each of these features has global significance.

Porites, which is the major and almost only coral component in reefs, is heavily encrusted with stromatolites. These reefs grew at the edge of the subtropical belt and were totally eliminated at the end of the Messinian because of global cooling.

Lowermost-Messinian carbonate sediments in the Sorbas Basin reflect a temperate climate, whereas those immediately above, which contain bioherms and coastal reefs, are subtropical. The shift from temperate to subtropical conditions during the early Messinian was accompanied by an important change in water circulation within the western Mediterranean. Temperate times were marked by cold surface Atlantic waters entering the Mediterranean, whereas subtropical times coincided with warm surface waters entering the western Mediterranean from the east. The subtropical waters were thermally stratified, which favoured the deposition of euxinic marls and diatomites at the centre of the basin. The upwelling of nutrient-rich water promoted stromatolite development within reefs and Halimeda growth on adjacent slopes.

Lastly, microbial carbonates (stromatolites and thrombolites) attained giant dimensions during the late Messinian, which can be regarded as a measure of their success in occupying a variety of ecological niches. This abundance of available habitats is believed to have resulted from the Messinian “salinity crisis”, which was followed by a re-colonization of the western Mediterranean. In this context stromatolite proliferation was due to opportunism of microbial communities in colonizing the new environments, rather than to a complete absence of other competitive biota. We do not believe that hypersaline conditions were a causal factor in stromatolite development because of the normal-marine biota associated with them.     

The Messinian Guadalhorce corridor: the last northern, Atlantic–Mediterranean gateway

Messinian marine deposits of the Guadalhorce River valley in southern Spain record evidence of the last northern gateway that existed between the Mediterranean and the Atlantic. They comprise sandstones and conglomerates with unidirectional cross-bed sets up to nearly 1 km long in their down-sedimentary-dip direction. These cross-bed sets relate to extremely fast (1.0–1.5 m s⁻¹) bottom currents flowing from the Mediterranean into the Atlantic. The Guadalhorce gateway (which had a maximum width of 5 km and a maximum water depth of 120 m) was an important element controlling the Messinian pre-evaporitic oceanic circulation in the Mediterranean Sea, as it acted as a major outflow channel. Its closure limited the exchange of water between the Atlantic and the Mediterranean to the Rifian corridors of Morocco, inducing water-mass restriction and stratification in the western Mediterranean immediately prior to the `Messinian Salinity Crisis'.     

Deep-water clastic evaporites deposition in the Messinian Adriatic foredeep (northern Apennines,Italy): did the Mediterranean ever dry out?

A new genetic facies model for deep-water clastic evaporites is presented, based on work carried out on the Messinian Gessoso-solfifera Formation of the northern Apennines during the last 15 years. This model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts. The model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites, representing the most common evaporite facies of the northern Apennines, and the definition of the genetic and stratigraphic relationship with primary shallow-water evaporites formed and preserved in marginal settings. Due to the severe recrystallization processes usually affecting these deposits, petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity-driven deposits ranging from debrisflow to low-density turbidites. Almost all the laminar ‘balatino’ gypsum, previously considered a deep-water primary deposit, is here reinterpreted as the fine-grained product of high to low-density gravity flows. Facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the Apennine foredeep basin. The Messinian Salinity Crisis occurred during an intense phase of geodynamic reorganization of the Mediterranean area that also produced the fragmentation of the former Miocene Apennine foredeep basin. In this area, primary shallow-water evaporites equivalent to the Mediterranean Lower Evaporites, apparently only formed in semi-closed thrust-top basins like the Vena del Gesso Basin. The subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins. Vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the Messinian tectonic evolution of the Apennine thrust belt and related exhumation–erosional processes. The facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts; the importance of clastic evaporites deposits has been overlooked in the study of other Mediterranean areas. Based on the Apennine basins experience, it is suggested here that evaporites diffused into the deeper portions of the Mediterranean basin may consist mainly of deep-water resedimented deposits rather than shallow-water to supratidal primary evaporites indicative of a complete basin desiccation.     

Precise 40Ar/39Ar dating of volcanic tuffs within the upper Messinian sequences in the Melilla carbonate complex (NE Morocco): implications for the Messinian Salinity Crisis

The Melilla carbonate complex (NE Morocco) is the only area of the Paleo-Mediterranean Sea where volcanic activity was present throughout most of the Messinian. ⁴⁰Ar/³⁹Ar dating of volcanic tuffs interbedded within the upper Messinian sedimentary deposits, known as the Terminal Carbonate Complex (TCC), yields accurate ages of paleoenvironmental and sea-level changes related to the Messinian Salinity Crisis. The new chronologic data (1) provide an average of 5.95–5.99 Ma for the base of the TCC, thus being synchronous with the onset of the Messinian Salinity Crisis, (2) demonstrate for the first time that the basal unconformity of the TCC does not represent a hiatus of long duration, (3) define a precise time line at 5.87±0.02 Ma (2σ) corresponding to sedimentary rocks exhibiting a lateral transition between continental and marine deposits typical of the TCC and (4) yield evidence that emersion of the Melilla platform during deposition of the TCC is partly related to tectono-magmatic activity. An erosional surface, capping the TCC deposits in the Melilla basin, is related to the major Messinian Mediterranean drawdown. The duration of the hiatus, associated with this surface, is estimated to be at most 450 kyr, but is probably shorter.     

Study of a Neogene basin dynamics: The “Bizerte basin”, northeastern Tunisia: relevance to the global Messinian Salinity Crisis

The Messinian sediments of northeastern Tunisia were deposited under an active tectonic setting. They are organized in sequences indicating a transitional deposit from margin – littoral to lacustrine – continental facies. These series unconformably overlie the Serravallian–Tortonian silty clays packages, and are overlain by the transgressive Early Pliocene marl (Zanclean). The presence of evaporitic strata points out to the Messinian Salinity Crisis described in the peripheral basins of the western Mediterranean. The Messinian sedimentation was found to have been closely controlled by transtensive tectonics and differential subsidence at a large spatio-temporal scale. It is organized in sequences typical of a depositional environment controlled by eustatism, tectonic and maybe by climate changes. Despite the existence of some local specific sedimentological characteristics, our results corroborate previous findings that pointed out to the Messinian times as a singular period all around the Mediterranean Basin. Field and subsurface seismic profile data helped reconstructing either the sedimentary or tectonic unconformities existing between the studied Messinian series and older Neogene successions.     

中国西部三大盆地海相碳酸盐岩台地边缘类型及特征

在回顾经典的碳酸盐沉积模式类型研究和我国学者对碳酸盐岩台地边缘特征研究的基础上,以构造控盆、盆地控相、相控生储盖组合为指导思想,依据中国西部三大海相盆地碳酸盐岩发育的特殊性,从中国西部三大盆地海相碳酸盐岩发育特征和地质实际情况出发,系统建立了5种碳酸盐岩台地边缘类型及沉积模式和12种亚类类型。以中国西部三大盆地不同时期发育的碳酸盐沉积特征为主线,从盆地构造演化、岩性特征、相带变化以及模式演化等方面详细分析了各个碳酸盐岩台地边缘类型及沉积模式特征。不同类型台地边缘及其沉积模式演化特征研究对分析生烃、储烃和盖烃物质等油气要素的时间和空间匹配关系具有重要的指导意义。     

Age refinement of the Messinian salinity crisis onset in the Mediterranean

We propose a revised age calibration of the Messinian salinity crisis onset in the Mediterranean at 5.971 Ma based on the recognition of an extra gypsum cycle in the transitional interval of the Perales section (Sorbas basin, Spain) and the revision of the magnetostratigraphy of the Monticino section (Vena del Gesso basin, Italy). This age re‐calibration allows to state more accurately that: (i) the interval encompassing the MSC‐onset is continuous, thus ruling out any erosional feature or stratigraphic hiatus related to a major sea‐level fall affecting the Mediterranean; (ii) the first gypsum was deposited during the summer insolation peak at 5.969 Ma associated with an eccentricity minimum and roughly coincident with glacial stage TG32; (iii) the MSC‐onset was preconditioned by the tectonically‐driven reduction of the hydrological exchanges with the Atlantic Ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa.     

Restricted shallow-water sedimentation of Early Archean stromatolitic and evaporitic strata of the Strelley Pool Chert,Pilbara Block,Western Australia

The 3.4 Ga-old Strelley Pool Chert is a 25-m thick sedimentary unit near the top of the predominantly volcanic Warrawoona Group in greenstone belts of the eastern Pilbara Block, Western Australia. It is here subdivided into 5 members containing 13 lithofacies. The basal Member, I, is composed of quartzose sandstone deposited in a high-energy wave- or tide-dominated shallow-water system. Overlying this are Members II and III, which make up the bulk of the formation and were deposited in a low-energy, partially restricted hypersaline basin. They record a predominantly regressive succesion of deposits including subaqueous laminite, stromatolite and evaporite; stromatolite, carbonaceous laminite, black-and-white banded chert, evaporite and intraformational detrital units deposited under intermittently to predominantly exposed conditions; and subaerially deposited windblown sand, evaporite and evaporite-solution layers. Members IV and V record the progradation of a volcaniclastic alluvial fringe.The Strelley Pool Chert represents an association of sedimentary environments directly comparable to that observed in modern, low-energy, shallow-marine carbonate-evaporite systems, such as along the Trucial Coast of the Persian Gulf, and abundantly developed in Phanerozoic carbonate platform deposits. There is no evidence, however, that uniquely identifies the environment as having been marine. Deposition may have taken place in either a large hypersaline lake or a restricted marine basin. Evidence of predominantly low energy depositional conditions and a paucity of terrigenous detritus indicate that sedimentation was dominated by orthochemical and biological processes. Silicified evaporites, including coarsely crystalline layers resembling Messinian selenite, are widespread and similar to younger evaporite deposits. They clearly indicate that evaporites were common within shallow-water Archean sequences. The presence of an assemblage of biogenic deposits, including organic laminite, stromatolites, encrusting carbonaceous mats, carbonaceous granules and oncolites, deposited under conditions ranging from fully subaqueous to nearly subaerial and locally evaporitic, points to the existence of an ecologically and probably biologically diverse microbial community 3.4 Ga ago.     

Multiepisodic evaporite sedimentation as an indicator of palaeogeographical evolution in foreland basins (South‐eastern Pyrenean basin,Early–Middle Eocene)

Extensive deposition of marine evaporites occurred during the Early–Middle Eocene in the South‐eastern Pyrenean basin (north‐east Spain). This study integrates stratigraphic and geochemical analyses of subsurface data (oil wells, seismic profiles and gravity data) together with field surveys to characterize this sedimentation in the foredeep and adjacent platform. Four major evaporite units were identified. The oldest was the Serrat Evaporites unit, with a platform‐slope‐basin configuration. Thick salina and sabkha sulphates accumulated on the platform, whereas resedimented and gravity‐derived sulphates were deposited on the slope, and salt and sulphates were deposited in the deep basin. In the subsequent unit (Vallfogona evaporites), thin sulphates formed on the platform, whereas very thick siliciclastic turbidites accumulated in the foredeep. However, some clastic gypsum coming from the platform (gypsarenites and gypsum olistoliths) was intercalated in these turbidites. The following unit, the Beuda Gypsum Formation developed in a sulphate platform‐basin configuration, where the topography of the depositional surface had become smooth. The youngest unit, the Besalú Gypsum, formed in a shallow setting. This small unit provides the last evidence of marine influence in a residual basin. Sulphur and oxygen isotope compositions are consistent with a marine origin for all evaporites. However, δ³⁴S and δ¹⁸O values also suggest that, except for the oldest unit (Serrat Evaporites), there was some sulphate recycling from the older into the younger units. The South‐eastern Pyrenean basin constitutes a fine example of a foreland basin that underwent multiepisodic evaporitic sedimentation. In the basin, depositional factors evolved with time under a structural control. Decreasing complexity is observed in the lithofacies, as well as in the depositional models, together with a diminishing thickness of the evaporite units.