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- Volume 22, Issue 4, 2016
Petroleum Geoscience - Volume 22, Issue 4, 2016
Volume 22, Issue 4, 2016
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Introduction to the thematic set: Exploring the Mediterranean – new concepts related to the Messinian salt
Authors Juan I. Soto and Gabor TariThis thematic set of papers is derived from a workshop, dedicated to the Messinian sequence, which was convened during the 77th EAGE Conference and Exhibition in Madrid in 2015. The main goal of the workshop was to introduce a geological exploration topic to the EAGE meeting. With this objective, and in collaboration with Héctor González of REPSOL and Jean-Loup Rubino of TOTAL, we co-ordinated a dedicated meeting to bring together people studying the Mediterranean region, particularly those dealing with the Messinian sequence, from both academic and exploration viewpoints.
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The Messinian salinity crisis: open problems and possible implications for Mediterranean petroleum systems
A general agreement on what actually happened during the Messinian salinity crisis (MSC) has been reached in the minds of most geologists but, in the deepest settings of the Mediterranean Basin, the picture is still far from being finalized and several different scenarios for the crisis have been proposed, with different significant implications for hydrocarbon exploration. The currently accepted MSC paradigm of the ‘shallow-water deep-basin’ model, which implies high-amplitude sea-level oscillations (> 1500 m) of the Mediterranean up to its desiccation, is usually considered as fact. As a consequence, it is on this model that the implications of the MSC events on the Mediterranean petroleum systems are commonly based.
In fact, an alternative, deep-water, non-desiccated scenario of the MSC is possible: it (i) implies the permanence of a large water body in the Mediterranean throughout the entire Messinian salinity crisis, but with strongly reduced Atlantic connections; and (ii) envisages a genetic link between Messinian erosion of the Mediterranean margins and deep brine development.
In this work, we focus on the strong implications of an assessment of the petroleum systems of the Mediterranean and adjoining areas (e.g. the Black Sea Basin) that can be based on such a non-desiccated MSC scenario. In particular, the near-full basin model delivers a more realistic definition of Messinian source-rock generation and distribution, as well as of the magnitude of water-unloading processes and their effects on hydrocarbon accumulation.
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The Messinian record of Spanish onshore and offshore data (Atlantic Ocean and Western Mediterranean Sea)
Authors W. Martínez del Olmo and D. MartínSpanish territory offers a remarkable location to study the Messinian salinity crisis (MSC). So much so, that sub-basins and open margins to the Mediterranean Sea and the Atlantic Ocean can be studied from outcrop data, 2D and 3D seismic surveys, and well logs. From the analysed data, it can be determined that the Messinian sediments are involved in three third-order depositional sequences: (1) Late Tortonian–Messinian, with temperate carbonates, coral reefs and sandy turbidities; (2) Messinian, with on- and offshore deposition of shallow-marine evaporate and isotopic freshwater facies; and (3) Messinian–Early Pliocene, comprising deposits of sandy (Atlantic) and gypsum-sandy turbidites (Mediterranean) that filled incised valleys. From seismic images, the best exploration opportunities involve the lowstand systems tracts (LST), the carbonates and different facies under deep-water evaporates. For these, however, the problem is to establish the source rock, by: (a) the presence of Messinian deep-water paper shales; (b) the gas having to be biogenic in the absence of paper shales; and (c) reaching the maturity level in areas with limestone and coral reef prospects. The above possibilities come from our conception of the Messinian crisis, which was caused by two different episodes: climatic change in a restricted, but not desiccated, Mediterranean Sea, following by multiple sea-level falls and the deposition of their correlative LST turbiditic systems.
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Seismic imaging of Late Miocene (Messinian) evaporites from Western Mediterranean back-arc basins
Authors M. Dal Cin, A. Del Ben, A. Mocnik, F. Accaino, R. Geletti, N. Wardell, F. Zgur and A. CamerlenghiAn analysis of multichannel seismic reflection data was conducted focusing on the comparison between the Messinian Salinity Crisis (MSC) and Plio-Quaternary (PQ) evolution of the eastern Sardo-Provençal and northern Algero-Balearic basins and related margins in the West Mediterranean Sea. Both basins were completely opened during the MSC and their well-defined seismic stratigraphy is very similar in the deep parts. The primary difference between these two basins is due to their different pre-MSC extensional history, including the opening age and the stretching factors. These factors influenced the occurrence of post-MSC salt tectonics on these margins.
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Geodynamical framework and hydrocarbon plays of a salt giant: the NW Mediterranean Basin
The NW Mediterranean Basin developed during the Oligocene–Miocene rifting of the Eastern Iberian–European magma-poor continental margin. The margin developed as a result of back-arc extension associated with the rollback of the retreating Calabrian–Tethys subduction zone. Reinterpretation of 2D regional seismic reflection data suggests that rifting took place by hyperextension of the Iberian–European lithosphere. This process led to the seawards arrangement of distinct crustal domains: namely, proximal, necking and distal. The late post-rift Messinian salinity crisis (MSC) gave rise to significant margin erosion and canyon incision, the lowstand sedimentary by-products of which were largely deposited prior to the Messinian evaporitic sequences. Mesozoic–Cenozoic and Messinian–Recent salt tectonics events have been recognized. A regional hydrocarbon play concept is proposed here for shelf–deep-water settings, including pre-salt, Messinian and post-salt plays.
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The barren Messinian Tripoli in Sicily and its palaeoenvironmental evolution: suggestions on the exploration potential
Authors Raimondo Catalano, Enrico Di Stefano, Rodolfo Sprovieri, Gabriele Lena and Vera ValentiNew observations on the Sicily Messinian Tripoli have yielded a variably thick diatomitic, calcareous and shaly rock interval marked by an upwards disappearance of calcareous and siliceous plankton (barren lithosome), coexisting with a variability in vegetal remains and significant amounts of amorphous organic matter (AOM). Facies analysis associated with biostratigraphy and palaeoecology of the several field and borehole sections has been framed in a well-accepted chronological scheme that points to this barren interval coinciding with the stratigraphic upper and younger part of some Tripoli sections (bituminous Tripoli) located in the northern part of the study area.
Biostratigraphically, the barren lithosome falls within the Non-Distinctive Zone (NDZ) and is generally younger than the First Common Occurrence (FCO) of T. multiloba. The age of its diachronous base appears older than the Messinian salinity crisis (MSC) deposits, because is well constrained by the calcareous plankton biostratigraphic markers along the underlying portions of the Tripoli. The top boundary of the barren rock interval, that is not always identifiable, could be age dated, following the proposed stratigraphic criteria. We infer that the Tripoli initial open-marine environment became, in more inner areas, progressively confined, with freshwater floodings alternating with short marine-water incursions in a shallow-water to continental domain. The collected information appears useful in addressing further exploration.
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The Eastern Mediterranean Messinian salt-depth imaging and velocity analysis considerations
Authors Ye E. Feng and Moshe ReshefNewly acquired 3D seismic datasets over the Eastern Mediterranean Basin are used to image the massive Messinian salt body. Accurate imaging of this salt body is critical to the precise definition of the prospective pre-salt geological section. The availability of recent well logs, which are the only ones to date to have penetrated the entire Messinian salt sequence, enables a clear definition of the highly deformed clastic units within the salt. This study shows that these highly reflective clay units cause a significant reduction in the overall seismic velocity of the salt. It also demonstrates why 3D pre-stack depth migration, including a tomographical velocity update inside the salt body, is recommended as the preferred imaging technique.
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Gravity-driven deformation of a youthful saline giant: the interplay between gliding and spreading in the Messinian basins of the Eastern Mediterranean
Authors Hayley Allen, Christopher A.-L. Jackson and Alastair J. FraserThe triggers and drivers for salt-related deformation on continental margins are intensely debated, reflecting uncertainties regarding the diagnostic value of certain structural styles, in addition to the fundamental mechanics associated with the two principal mechanisms (gliding and spreading). Determining the triggers and drivers for salt-related deformation is important because they provide insights into continent-scale geodynamic processes, the regional kinematics of gravity-driven deformation, and sediment dispersal and hydrocarbon prospectivity. The processes associated with and the timing of deformation of Messinian salt in the offshore Eastern Mediterranean are uncertain, and thus so is our understanding of the geodynamic evolution of this tectonically complex region. We here use an extensive 2D and 3D seismic reflection dataset to test models for the salt-tectonic development of Messinian salt. We contend that gliding and spreading were not mutually exclusive, but were likely to have overlapped in time and space, being associated with local and far-field tectonics (gliding), as well as differential overburden loading (spreading). We also argue that intrasalt strain and seismic-stratigraphic patterns can be explained by a model invoking a single, post-Messinian period of salt-related deformation, rather than a more complex model involving two separate deformation events that occurred during and after salt deposition.
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The impact of the Messinian salinity crisis on the petroleum system of the Eastern Mediterranean: a critical assessment using 2D petroleum system modelling
The offshore Levant Basin demonstrates one of the most phenomenal natural examples of a working petroleum system associated with a relatively rapid unloading and loading cycle caused by the Messinian salinity crisis (MSC). In this study, 2D basin and petroleum systems modelling suggests that the geologically instantaneous water unloading of approximately 2070 m, and subsequent rapid salt deposition and refill, impact the subsurface pore pressure and temperature in the underlying sediments. The pressure drop is modelled to be instantaneous, whereas the impact on temperature is more of a transient response. This has important consequences for the shallow sub-Messinian biogenic petroleum system, which is assumed to have experienced fluid brecciation associated with massive fluid escape events. Deeper Oligo-Miocene sediments are far less affected, thus indicating a ‘preservation window’ for biogenic gas accumulations, which host the recent discoveries (Tamar, Leviathan, Aphrodite). Hydrocarbon accumulations of a ‘bubblepoint oil’ composition are modelled to have experienced cap expansion during the drawdown, with the pressure drop being the primary control. This study suggests that seal-limited traps are expected to have undergone a catastrophic seal failure, whereas the impact of the MSC is modelled to be less destructive for size-limited and, particularly, charge-limited traps.
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Why are there no Messinian evaporites in the Black Sea?
Authors G. Tari, M. Fallah, C. Schell, W. Kosi, Z. Bati, N. Ö. Sipahioğlu, Cs. Krezsek, Zs. Schleder, E. Kozhuharov and A. KitchkaAn unconformity has been observed along the Black Sea shelf on seismic reflection profiles and wells which is broadly similar to the one associated with that formed during the Messinian salinity crisis (MSC) in the Mediterranean. Therefore, this intra- (or Middle) Pontian unconformity has been traditionally interpreted as the manifestation of the MSC in the Black Sea Basin. However, the magnitude of the sea-level fall associated with this erosive surface does not appear to be nearly as significant as was assumed previously. Also, the inferred MSC surface itself cannot be easily followed into the palaeo-deep-water basin as a regional unconformity in the same manner as in the Mediterranean. Moreover, around the Black Sea, there is no evidence of major river incisions during the MSC, unlike the well-documented cases in the Mediterranean region. If the MSC evaporites in the Mediterranean indeed deposited in a subaerial setting at the basin floor, the lack of a major drawdown in the Black Sea explains why there are no Messinian evaporites in the Black Sea. Owing to the approximately 500 m MSC sea-level drop the Black Sea basin system, this basin did not even get close to the conditions required for the formation of evaporites in the basin centre. As the magnitude of the sea-level drop and the overall impact of the MSC in the Black Sea is interpreted to be less significant than in the Mediterranean, the risk of breaching pre-existing hydrocarbon traps during the MSC is less than has been suggested before.
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The Messinian sea-level fall in the western Black Sea: small or large? Insights from offshore Romania
Authors C. Krezsek, Z. Schleder, Z. Bega, G. Ionescu and G. TariThe Messinian sea-level fall in the western Black Sea is poorly understood and often debated. We provide evidence for the sea-level fall, offshore Romania. There, the Messinian sedimentation is closely related to the gravitational collapse of the basin margin above the Maykop shales. This thin-skinned system controlled the Messinian lowstand depocentres. We estimated about 500–600 m of sea-level drop based on the erosional valleys cut into the formed lower Pontian slope and the Messinian erosional surface (MES).
The Messinian lowstand sediments are delimited by the basal erosional surface (BES) formed at the onset of the sea-level fall and by the MES related to transgressive wave erosion during the initial slow rise in sea level. Subsequent rapid sea-level rise drowned the remaining erosional topography on the lower Pontian palaeo-shelf. Similar features have been described in the Mediterranean Basin.
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Structural style in a Messinian (intra-Pontian) gravity-driven deformation system, western Black Sea, offshore Romania
Authors Z. Schleder, C. Krezsek, A. Lapadat, Z. Bega, G. Ionescu and G. TariMiocene sediments of the western Black Sea failed gravitationally during the intra-Pontian (Messinian) sea-level fall. In the region of the Histria Trough, this generated two independent collapse systems detaching on the upper part of Oligocene–Lower Miocene shale. This contribution focuses on the eastern system. The eastern linked system is approximately 60 km long in the dip direction, containing about 10 major extensional faults in the updip domain, with a cumulative extension (heave) of 11.4 km. This extension is accommodated downdip partially by 6 – 7 km of lateral compaction and on a single toe thrust with 4.8 km of shortening.
The thin-skinned extension generated both basinwards-dipping faults and counter-regional faults (dip towards the basin margin), with associated rollovers, tilted fault blocks and keystone graben. Broad shale pillow (3 km across) and cuspate shale upwelling developed due to reactive shale diapirism. The collapse of the rollover anticlines into the half-graben suggests a high deformation rate. Downdip, the thrust follows the top of the Oligocene–Lower Miocene unit and steps up into the top of Sarmatian. The thrust hanging-wall anticline collapsed and triggered a mass transport complex (MTC). The top of the MTC is a rugose surface, and we suggest that it remained under water during the Messinian event due to its lack of visible erosion.
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Volumes & issues
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Volume 30 (2024)
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Volume 29 (2023)
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Volume 28 (2022)
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Volume 27 (2021)
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Volume 26 (2020)
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Volume 25 (2019)
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Volume 24 (2018)
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Volume 23 (2017)
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Volume 22 (2016)
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Volume 21 (2015)
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Volume 20 (2014)
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Volume 19 (2013)
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Volume 18 (2012)
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Volume 17 (2011)
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Volume 16 (2010)
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Volume 15 (2009)
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Volume 14 (2008)
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Volume 13 (2007)
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Volume 12 (2006)
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Volume 11 (2005)
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Volume 10 (2004)
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Volume 9 (2003)
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Volume 8 (2002)
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Volume 7 (2001)
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Volume 6 (2000)
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Volume 5 (1999)
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Volume 4 (1998)
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Volume 3 (1997)
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Volume 2 (1996)
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Volume 1 (1995)