Basin Dynamics

The methodological and practical issues in respect of assessment of the flood-plain and stream-way complex of<br> the Berezhnytsya river are presented in the article. Researched river is one of the Ukrainian Carpathians minor rivers and<br> constituted the right-bank tributary of the Dniester river. The presented study typify the stream-way segments. Furthermore<br> were shown identification of the reasons of decreasing the qualitative characteristics of the Berezhnytsya flood-plain<br> and stream-way complex. The set of works to stop processes that are destructive for the river and its ecosystem should be<br> made.

In contrast to Eocene Himalayan foreland basin sedimentary deposits in India and Pakistan, coeval sedimentary rocks of the Bhainskati Formation in Nepal contain scant petrographic evidence of orogenic input. Such data have been used as evidence to promote models of diachroneity of India-Asia collision. In this paper we document orogenic input into the Eocene foreland basin rocks of Nepal, from fission-track analyses of detrital zircons. Our data provide evidence that significantly reduces the possible duration of any diachroneity of collision, and brings the interpretation of the sedimentary record into better agreement with ages of early thrusting and metamorphism in the orogen. We also use our detrital fission-track data to bolster previous age determinations of the overlying Dumri Formation, confirming the basin-wide occurrence of a major unconformity. Comparison of our data set with that from coeval along-strike rocks in India suggests that there is no evidence of diachroneity in early stages of the orogen's exhumation.

The study of the deep structure and evolution of passive continental margins is important for the understanding of rifting processes and the formation of associated sedimentary basins. Since the classical models of McKenzie (1978) and Wernicke (1985), understanding how passive continental margins form, that is to say mainly the way that continental lithosphere is thinned leading to subsidence, remains one of the main challenges in the Earth sciences. Many recent observations and discoveries have modified our basic views of margin formation. The conservational models paradigm (i.e., simple shear, pure shear, or polyphase models), which exclude exchanges between lower continental crust and upper mantle and which are usually proposed to explain lithospheric stretching and consequent crustal thinning of passive continental margins, fail to completely explain all these observations. Furthermore, these models imply a large amount of horizontal movement, movements not observed in the field...

The Orphan Basin, offshore Newfoundland, Canada, is approximately conjugate to the rifted margin basins on the Irish Atlantic margin. At the onset of seafloor spreading, plate reconstructions, based solely on oceanic magnetic anomalies, show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin. Here, the nature of this potentially continuous basin is examined through the development of a Newfoundland-Ireland conjugate basins model. 2D and 3D reconstructions of the West Orphan and Rockall basins yielded the thickness of the post-rift and syn-rift sedimentary packages, as well as the pre-rift crust. A discrepancy inspired additional analysis of the East Orphan Basin to aid in the reconstruction of the continuous Mesozoic basins. Based on the results of the reconstruction of the East Orphan Basin, it is possible that the Rockall Basin was originally conjugate to, and continuous with, the East Orphan Basin.

The East Orphan, Porcupine, and Galicia Interior basins are several of the most promising basins for hydrocarbon exploration along the rifted continental margins of the southern North Atlantic Ocean. Despite having formed at similar geological times, the basins exhibit fundamental differences in symmetry, crustal thickness, sedimentary cover thickness, and amount of extension. Interpretation of seismic reflection and well data was integrated with published 3D grids of depth-to-basement and Moho proxy depth to interpret and restore select seismic reflection lines. Publicly available kinematic evolution models were also integrated to evaluate and compare the restored seismic reflection lines in a more global regional context. Interpretation of five seismo-stratigraphic units and three tectonostratigraphic megasequences along the East Orphan, Porcupine, and Galicia Interior basins reveals similar seismic character for each unit and comparable tectonic history. The structural restoration of the selected lines indicates that evolution, sedimentary cover thickness, faulting style, crustal structure, and kinematic evolution of the East Orphan and Porcupine basins differ significantly. A variable and asymmetrical crustal structure is found in the East Orphan Basin contrasting with the elongated and symmetric Porcupine and Galicia Interior basins. Rift domain maps of the three basins reveal that they are each underlain by hyperextended crust, with possible exhumed mantle in the centre of the Porcupine Basin. Based on a holistic analysis of the results obtained, the linkage between the East Orphan and the Porcupine basins seems implausible, but rather a contemporaneous relationship is interpreted. Moreover, a potential connection between the Galicia Interior Basin and the Porcupine Basin during the Early to Late Jurassic is proposed. Such scenarios imply an oblique and synchronous rifting evolution around the Bay of Biscay triple junction of the southern North Atlantic.

Reconstructions of the opening of the North Atlantic Ocean generally result in the Orphan Basin, offshore Newfoundland, Canada, lying approximately conjugate to the rift basins on the Irish Atlantic margin at the onset of seafloor spreading toward the end of the Early Cretaceous. Most of these plate reconstructions have involved rigid plates with plate motions based solely on the interpretation of oceanic magnetic anomalies. In particular, these reconstructions often show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin, offshore Newfoundland. However, more recent plate reconstructions involving deformable plates have called this conjugate relationship into question. The goal of this study is to investigate the validity of this potentially continuous basin system by reconstructing and restoring present-day seismically-constrained geological models both spatially and temporally back to their original configurations pre-rift. By compar...

In recent years the Gulf of Lion within the Occidental Mediterranean Sea has become a unique natural laboratory for the study both the evolution and interaction of deep processes (geodynamics, tectonics, subsidence, isostasy) and surficial processes (river behavior, ...

Scientific drilling provides extended records of continental environmental conditions during the Neogene in Asia and northern Australia. Spectral data allows reconstruction of the environment using abundances of hematite and goethite. Hematite formation is favoured by dry or seasonal conditions. Hemipelagic sites show the most regular records. Monsoon strengthening started in the Early Miocene and peaked at 17–20 Ma in the Bay of Bengal and at 10–15 Ma in southern China before weakening after ~12 Ma and ~10 Ma respectively. The Indus dried after ~8 Ma and again after 3 Ma, while eolian sediment sources to the Sea of Japan show increased aridity after 5 Ma and 3 Ma. The Mekong indicates increasing aridity after 6 Ma, similar to Eastern Australia. In contrast, NW Australia shows a trend towards wetter conditions after 8 Ma, a humid period at 4–6 Ma, followed by drying. There is a link between drying and vegetation in the Mekong and Pearl River basins, as well as Eastern Australia. Monsoon strengthening is linked to topographic uplift in the Himalaya, together with Tethyan gateway closure. Long term drying is likely driven by global cooling since the Middle Miocene.

The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re-visited onshore data from Italy and Turkey that lead to a new concept of a twostep reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at 500 m for the first rise and 600-900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic

More than 40 yr after the discovery of salt giants buried below the Mediterranean deep basin floor, debate on the Messinian Salinity Crisis (MSC) is still continuing about whether there was a large or only moderate drawdown in base level related to the deposition of deep evaporites during its peak. In this paper, we constrain the magnitude of this sea-level drawdown during the MSC. An analysis of the late Neogene faunas of the Balearic Islands, combined with the available geostructural data, shows that a minimum of 800-1200 m drawdown would be required to allow the colonization of the Balearic Islands by new continentalterrestrial fauna during the MSC peak, which provides solid new evidence in favor of a deep desiccated basin in the Mediterranean during the MSC.

The combined effects of post-rift magma emplacement and tectonic inversion on the hyper-extended West Iberian Margin are unravelled in detail using multichannel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first-order transfer zones, shows evidence of four post-rift tectonic

This thesis describes the collection, processing, and interpretation of marine geophysical data from southern Rockall Trough, Porcupine Abyssal Plain and Porcupine Bank. 4,200 km of gravity, magnetic, bathymetric and single channel seismic data were collected on two cruises. Time to basement and free air gravity anomaly maps are produced. A new feature, the Clare Lineament, is mapped. The Lineament lies at the southern end of Rockall Trough, trends WNW-ESE, and links the Charlie Gibbs Fracture Zone with Porcupine Bank. A colinear magnetic feature, the Clare Trend, crosses Porcupine Bank. The Clare Lineament and Clare Trend are interpreted as the probable offshore continuation of the Iapetus Suture. A 500 gamma magnetic anomaly to the south of the Clare Trend is correlated with anomalies of the Avalon Platform of Newfoundland. Modelling of the crustal thickness beneath southern Porcupine Seabight indicates that the crust may be as thin as 2 km. The mapped continuity of structure across the mouth of the Seabight, from Porcupine Bank to Goban Spur, shows that the Seabight must be floored by continental crust. It is thought that the southern Porcupine Seabight was initiated as a Devonian wrench fault basin, with further Permo-Triassic and Mesozoic stretching episodes. The continent-ocean boundary is mapped in Porcupine Abyssal Plain, approximately 55 km west of Porcupine Bank. The continent-ocean boundary lies about 10 km to the east of anomaly 32(34). Initial spreading is therefore of Campanian or Santonian age. Porcupine Bank to the north of the Clare Trend is characterised by NNE-SSW Caledonide trends. A graben within the Bank and probable igneous centres are described. Within southern Rockall Trough, magnetic modelling and interpretation of the seismic profiles show that magnetic lineations in the centre of the Trough are caused by shallow igneous intrusions within continental crust, and not by sea-floor spreading reversals. In southern Rockall Trough massive fracturing and intrusion occurred in the Upper Cretaceous when the Charlie Gibbs Fracture Zone was initiated as a leaky transform fault. Crustal thicknesses in southern Rockall Trough are approximately 7 km, giving a stretching factor of 4. The sedimentary section, which is up to 4 seconds (TWT) thick, is described in a separate paper by Dingle, Megson, and Scrutton (1982). Probable Late Cretaceous/Palaeocene sills are present within the section. Southern Rockall Trough is probably the site of Permo-Triassic, Jurassic, and Cretaceous rifting episodes. A maturation study suggests that deeply buried sediments within the Rockall Trough are within the oil window of hydrocarbon generation.

Analysis was carried out of part of the northern North Sea to test what the presence and style of gas chimneys indicate about fluid pressure (P f) within hydrocarbon reservoirs. Previous results suggest that broad chimneys above a trap and thin chimneys on the flanks indicate the presence of hydrocarbons, whilst thin chimneys in the crest suggest the hydrocarbons have escaped. Each type of gas chimney is usually associated with overpressure within Mesozoic reservoirs, but the water leg is hydrostatically-pressured in most Cenozoic reservoirs. This indicates: (a) gas leaking from a trap does not necessarily cause P f to become hydrostatic; (b) overpressure may not be necessary for the expulsion of gasses through seal units to create the chimneys; (c) although gas chimneys indicate the existence of an active hydrocarbon system, their presence does not appear to indicate anything significant about present-day P f .

Passive margins are characterised by an important tectonic and thermal subsidence, which favours a good preservation of sedimentary sequences. This sedimentation in turn enhances the subsidence because of loading effects. We present here a direct method based on sedimentary markers seen on seismic data, to evaluate total subsidence rates from the coast to the outer shelf and to the deep basin in the Gulf of Lion, from the beginning of massive salt deposition up to present day (the last circa 6 Ma) with minimal theoretical assumptions. On the shelf, the Pliocene-Quaternary subsidence shows a seaward tilt reaching a rate of 240 m/Ma (±15 m/Ma) at the shelf break (70 km from the present day coastline) (i.e. a total angle of rotation of 0.88° (0.16°/Ma)). We were also able to measure and quantify for the first time the isostatic rebound of the outer shelf due to the Messinian salinity crisis (MSC). This value is very high and reaches up to 1.3 km of uplift during the crisis around the Herault-Sète canyon heads (around 1.8 km/Ma). On the slope, we also find a seaward tilting subsidence from Km 90 to Km 180 with a measured angle of 1.41°. From 180 km to the deepest part of the basin, the total subsidence is then almost vertical and reaches 960 m/Ma (±40 m/Ma) during the last 5.7 Ma (±0.25 Ma) in the deepest part of the basin. The subsidence is organised in three compartments that seem related to the very deep structure of the margin during the opening of the Liguro-provencal basin. These very high total subsidence rates enable high sedimentation rates along the margin with sediments provided by the Rhône river flowing from the Alps, which in turn enable the detailed record of climate evolution during Pliocene-Quaternary that make of the Gulf of Lion a unique archive. Highlights ►Quantifying subsidence using sedimentary markers and minimal assumptions. ►Quantifying isostatic rebound related to the MSC using sedimentary markers. ►Subsidence is organised in three compartments separated by hinge points.

Within the French 'Margins' Programme (Groupement de Recherches 'Marges', or 'GDR Marges'), The Gulf of Lions was selected as a key area where scientists specialized in complementary aspects of geosciences (structural geology, tectonics, stratigraphy, sedimentology, various aspects of modeling) work together in order to better understand the processes that control the formation and evolution of continental margins. A key objective was to link offshore data (that mainly consist of seismic data and few wells) and onshore studies (mainly based on well and field data). This special edition of Marine and Petroleum Geology on the Gulf of Lions presents some of the main results obtained during three years of research by the group 'GDR Marges-Golfe du Lion'.

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Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97-5.33 Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSC base-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place <2600 cal. years BP; (ii) deposition by bottom currents across the entire depth range of the Malta Escarpment; (iii) tectonic deformation in the southern Malta Escarpment in association with a wrench zone; (iv) widespread, small-scale sedimentary slope failures preconditioned by oversteepening and loss of support due to canyon erosion, and triggered by earthquakes. 3 We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800-2000 m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation predominantly occurred before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes.

he Gibraltar Strait-Alboran Sea connection is a key area to understand the zanclean reflooding of the Mediterranean basin, at the end of the messinian salinity crisis. In spite of this importance, suggested by many authors, little is known about the submarine geological record of this area where the large magnitude of the Earliest Zanclaean reflooding had to produce a

The so-called S reflector is a group of bright, continuous reflections underlying the landward-tilted fault blocks of the west Galicia rifted margin. S has been interpreted as the brittle-ductile transition, the top of an intrusion, a detachment fault, and the crust-mantle boundary. To constrain the internal structure of the reflector, we have carried out detailed analyses of these reflections. We compare the waveforms of the seafloor reflection and its first multiple, both to determine the amplitude of the seafloor reflection and to show that the seafloor is in effect a spike in the reflectivity series SO that the seafloor reflection can be used as the far-field wavelet, including both source and receiver ghosts. We compare the waveform of the seafloor and S and show that, within the resolution of our data, S is a reflection from a step increase in acoustic impedance. This result is confirmed through complex trace analysis, and in particular the determination of the apparent polarity of S, and the examination of the instantaneous frequency function: S is consistently positive polarity, and shows no significant frequency anomaly. Simple modelling shows that S is very unlikely to be a reflection from a thin layer. We thus conclude that S is probably a single steplike interface. From the varying frequency content of the data, we determine a value for the effective Q between S and the seafloor, and use this to assess the amplitude loss due to attenuation and scattering. We use a comparison between the seafloor and the S reflection to constrain the amplitude of S, and estimate a reflection coefficient for S of at least 0.2 in places, decreasing landwards. By analogy with structures developed in the highly extended regions of the western United States, we consider that the most likely interpretation of S is as a sharp west-dipping detachment fault separating a 'granitic' upper plate from a higher-velocity lower plate, locally probably serpentinized mantle.

Correlation of new multichannel seismic profiles across the upper Indus Fan and Murray Ridge with a dated industrial well on the Pakistan shelf demonstrates that ;40% of the Indus Fan predates the middle Miocene, and ;35% predates uplift of the Murray Ridge (early Miocene, ;22 Ma). The Arabian Sea, in addition to the Makran accretionary complex, was therefore an important repository of sediment from the Indus River system during the Paleogene. Channel and levee complexes are most pronounced after the early Miocene, coincident with an increase in sedimentation rates. Middle Eocene sandstones from Deep Sea Drilling Project Site 224 on the Owen Ridge yield K-feldspars whose Pb isotopic composition, measured by in situ ion microprobe methods, indicates an origin in, or north of, the Indus suture zone. This observation requires that India-Asia collision had occurred by this time and that an Indus River system, feeding material from the suture zone into the basin, was active soon after collision. Pleistocene provenance was similar to that during the Eocene, albeit with greater contribution from

Sedimentary archives in the Himalayan foreland basin and Indus submarine fan provide the most detailed records of how changing monsoon strength may have affected erosion and the development of tectonic structures in the western Himalaya during the Neogene. Muscovite Ar-Ar ages show that fast exhumation of the Greater Himalaya was earlier in the west (20-35 Ma) than in the central Himalaya (10-25 Ma), probably driven by progressive lithospheric slab tearing that caused both rock uplift and an intensified summer monsoon to start earlier in the western Himalaya. Rates of exhumation reduced after~17 Ma as uplift also slowed, apparently unrelated to climate change. However, further reduction at 6-8 Ma coincided with a time of weakening summer rains, as shown by carbon isotope data from the foreland and hematite-goethite records from ODP Site 730 on the Oman margin. Coming at a time of stronger winds, this drying was linked to global climatic cooling. Weakening of Late Miocene monsoon rains coincided with a southward migration of the ITCZ and faster erosion of the Lesser rather than Greater Himalaya. Unroofing of the Inner Lesser Himalaya, starting after 9 Ma, followed as a consequence of duplex formation enabled by focused erosion, although widespread exposure of that range was delayed until after 6 Ma. Inner Lesser Himalayan exposure, combined with unroofing of the Nanga Parbat Massif, caused a decrease in average ε Nd values of Indus River sediment after 5 Ma, rather than large-scale drainage capture.

Offshore frontier sedimentary basins are characterised by a lack of constraining geological and geophysical data. This lack of data is generally the result of deep water (>500 m), difficult geology (volcanics and salt), remoteness and harsh met-ocean conditions. These characteristics present significant challenges to marine surveying, which means that frontier basins tend to be underexplored. With continuing interest in exploration for energy resources in frontier regions, many frontier basins around the world have been the focus of increasingly-sophisticated geophysical studies that integrate a range of methodologies, including those based on potential-field (gravity and magnetic) data. Underexplored frontier basins around Australia's continental margin have received increased attention during the last decade, largely as a result of government-funded programs of precompetitive data acquisition and analysis. The components of this work that have relied heavily on potential-field data include: first-pass depth-to-basement estimation using spectral techniques applied to magnetic data; enhancement of gravity and magnetic images to aid the identification of basin depocentres and to facilitate onshore-offshore geological interpretation of basement structure; multi-scale edge-detection applied to gravity and magnetic data to aid the interpretation of basement structure; 3D forward and stochastic inverse modelling of gravity data to guide seismic interpretation of sediment thickness and basement structure; and using supercomputers for high-resolution, regional-scale 3D inverse modelling of magnetic and gravity data to constrain the physical properties of the crust. Despite the additional insight offered by this work, efforts to understand frontier basins are not without challenges, one of the most fundamental of which is to ensure that non-specialists are not misinterpreting data (e.g. wrongly interpreting artefacts arising from specific processing). The other main challenge in Australian frontier basins arises from a lack of constraints on crustal structure. This leads to significant ambiguity when using gravity data to infer sediment thickness or to understand the nature of basement. This ambiguity could be vastly reduced through the acquisition of seismic refraction data that focuses on imaging crustal structure.

Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97-5.33 Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSC base-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place <2600 cal. years BP; (ii) deposition by bottom currents across the entire depth range of the Malta Escarpment; (iii) tectonic deformation in the southern Malta Escarpment in association with a wrench zone; (iv) widespread, small-scale sedimentary slope failures preconditioned by oversteepening and loss of support due to canyon erosion, and triggered by earthquakes. 3 We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800-2000 m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation predominantly occurred before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes.

The level of anthropogenization of the natural processes and the geocomponents of the basin geosystems of small rivers in Western Podillya has been estimated and rated as ecologically dangerous from the viewpoint of sustainable and conflict free functioning. The scales of the transformation of the components of natural environment by economic activities since 1774 were revealed using the method of comparative-geographic analysis of cartographic sources. The scales of deforestation were determined, as well as the scales of the influences of drainage meliorations on wetlands, river floodplains and riverbed complexes. It has been established that such transformations of the state of the components of landscape systems have caused the manifestation of a set of unfavorable processes and phenomena (lowering of ground water level, promoting desiccation, soil erosion and deflation, soil dehumification, decreasing landscape and biological diversity, etc.). Calculated indices of the anthropog...

We processed and interpreted a newly acquired geophysical dataset (WS10 project) integrated with vintage seismic profiles to study the evolution of the Sardinian passive margin of the Sardo-Provençal basin. The most prominent features of the area of study are a consequence of the Messinian Salinity Crisis (MSC) which produced a thick salt layer in the deep basin. Complex halokinetic tectonics deformed the overlying Messinian Upper Unit (UU) and the Pliocene-Quaternary (PQ) sediments, sometimes also bending the sea bottom. A thinner autochthonous salt in the UU suggests at least one further low stand during the late MSC. The Messinian Erosional Surface (MES) separates the erosional truncation of the pre-Messinian sedimentary sequence from the overlaying Plio-Pleistocene sequence with a clear angular discordance, which almost completely masks possible earlier erosional events. The MES is present across the middle and upper slopes of the Sardinian margin and can be easily recognized down to the lower slope, where it interfingers with the Messinian evaporites which gradually thicken basinward. We propose a correlation between the main erosional surface of the lower slope and the salt layer recognized in the UU as a consequence of a falling stage during the last part of the MSC. The seismic profiles now available along the West Sardinian margin provide novel and crucial information to correlate the Messinian depositional units in the deep basin with those present in the lower continental slope and with the erosional surface of the middle and upper slopes. Our data and interpretation highlight the main units of the Messinian trilogy and further internal sequences that are probable related to cyclic fluctuations during their deposition.

Crisis: Isostatic response to desiccation and evaporite deposition. Hanneke Heida (hheida@ictja.csic.es) Institute of Earth Science Jaume Almera (ICTJA-CSIC)  Daniel García-Castellanos Institute of Earth Science Jaume Almera (ICTJA-CSIC)  Ivone Jiménez-Munt Institute of Earth Science Jaume Almera (ICTJA-CSIC)  Agnès Maillard Université Toulouse III Paul Sabatier  Johanna Lofi Université de Montpellier  Fadl Raad Université de Montpellier

Himalayan orogenesis remains enigmatic in terms of Tibetan Plateau geodynamics originating from the Cenozoic India–Eurasian continental collision. India underthrusts below Tibet to the Yarlung–Tsangpo suture, which has been identified as the northernmost boundary for underplating. However, the way in which the historical evolution of continental subduction induces plateau uplift and the way it controls the variation in uplift between outboard and inboard areas is still unclear. To interpret the evolutionary mechanisms involved in the Himalayan growth history, we constructed different 3-D dynamic models at important stages to address these questions related to the formation of the Himalayas on the basis of paleoenthalpy evidence encoded in fossil leaves from recently documented assemblages in southern Tibet. The results show that (1) the effect of crustal thickening was the predominant factor in the early evolution from the Paleocene to the early Eocene, which resulted in a moderate ...

Carbonates are mostly produced in shallow-marine environments and their deposition is sensitive to water depth changes on carbonate platforms. The water depth in depositional environments of a particular carbonate platform is controlled by the interplay of eustatic sea-level change, tectonic subsidence, platform morphology, and depositional rate. Due to the morphological variations of carbonate platforms in different tectonic settings, facies distribution across carbonate platforms varies significantly even during a single eustatic sea-level cycle. Carbonate platforms developed on passive continental margins are thought to be the most stable platforms and their facies distribution is commonly taken as examples in textbook depositional models. Some studies, however, have documented significant variations in facies and cycles across the passive-margin carbonate platforms, implying that the existing depositional models are overly simplified. To better understand the facies and geochemical change across passive-margin carbonate platforms, this dissertation applies three-dimensional (3D) modeling techniques to visualize the internal facies and isotope change of the Darriwilian (Middle Ordovician; ca. 467-458 Ma) carbonate platform in the southern Great Basin. Lithological, sedimentological, and carbon and oxygen isotope (δ 13 Ccarb and δ 18 Ocarb) data used for modeling were collected from nine sections including the Nopah Range (NR), Arrow Canyon Range (AC), Meiklejohn (MJ), Pahranagat Range (PR), Shingle Pass (SP), Lone Mountain (LM), Monitor Valley (MV) and Hot Creek Range (HC). Among these, the isotope data from the Ibex Hills (IH) were analyzed in this study and those from the AC, PR, LM, MV, and HC sections were unpublished data from previous students of Dr. Jiang's Group. Isotope data from the MJ and SP sections were from literature. In all these sections, the Darriwilian carbonate rocks are unconformably overlain by the Eureka Quartzite, the base of which serves as a datum for iv stratigraphic correlation across the platform. The stratigraphic units belong to the upper Pogonip Group and the age of these units is constrained by biostratigraphy of conodonts, brachiopod, bivalves, gastropods, trilobites and calcareous algae. The 3D modeling proceeded with data preparation, grid creation, data interpolation, and quality check on modeling outputs. Data preparation involved extracting data from literature and fieldwork examination in some of the sections. Grid creation was conducted using the Petrel software with grids of 170 cells in the x-direction, 120 cells in the y-direction and 251 cells in the z direction. The interpolation was conducted on all lithological, sedimentological, and δ 13 Ccarb and δ 18 Ocarb data using the moving average geostatistical method. The modeling outputs were visually checked with input data in each section to test the validity of the 3D modeling procedure. Chemostratigraphic modeling used the global Darriwilian δ 13 Ccarb and δ 18 Ocarb curves documented from Baltoscandia (BC) and summarized from well-preserved brachiopods, respectively. The δ 13 Ccarb curve of the Darriwilian strata is divided into five isotope intervals in Baltoscandia (BC1, BC2, BC3, BC4 and BC5; BC = Baltoscandia carbon isotope interval) that are roughly correlatable across the Darriwilian platform in the southern Great Basin. In general, both δ 13 Ccarb and δ 18 Ocarb values in the southern Great Basin are lower than those of the standardized Darriwilian curves and the modeling results show large variations in both δ 13 Ccarb and δ 18 Ocarb across the carbonate platform. The lower values in δ 13 Ccarb and δ 18 Ocarb in the Great Basin may have been exerted by intensive bioturbation and organic matter respiration, along with potential diagenetic alterations beneath the basal Eureka Quartzite unconformity. The spatial variations in δ 13 Ccarb and δ 18 Ocarb may record isotope changes in locally restricted depositional environments on the Darriwilian carbonate platform. v Within the chemostratigraphic framework, facies modeling results show significant variations in facies association and cyclicity across the Darriwilian carbonate platform. In general, the northern and eastern areas are dominated by shallow-water facies (mostly intertidal to supratidal), while the southern regions show frequent facies changes from BC1 to BC5. During BC1 and BC2, facies show a general pattern that deepened from the north-northeast towards the southern region. During BC3 and BC4, however, the southern area was dominated by shallowwater facies (supratidal and intertidal). During BC5, facies changed back to the southwarddeepening trend similar to that of BC1 and BC2 but had more inter-platform facies variations. The modeled results also show temporal and spatial variations in meter-scale cycles. The thicknesses of cycles in BC3 to BC4 intervals (10-15 m) are larger than those of BC1, BC2, and BC5 (6-10 m). In the north and northwest regions, meter-scale cycles are absent (most likely amalgamated) and only large-scale cycles (sequences) with a thickness of 20-50 m are recorded. Based on the thickness of the Darriwilian strata and duration of this interval, the 20-50-m-thick cycles recorded in the northern areas are most likely third-order cycles (sequences) correspondent with major eustatic sea-level changes (>1-million-year duration) during the Darriwilian. The temporal and spatial changes in facies and cyclicity suggest that even in a carbonate platform that was developed in a passive continental margin, sedimentary facies distribution and platform morphology may not have been as stable as previously thought. The morphological change of the Darriwilian carbonate platform may record a local tectonic event or fast growth of a shelf margin shoal complex in the southern part of the platform, which needs to be tested in future studies. vi

Magnetic and gravity anomalies in the vicinity of the continent-ocean transition at Goban Spur have been modeled to give crustal structure and magnetization. If the location of the transition identified from seismic reflection profiles (see Masson et al., this volume) is accepted, then the magnetic anomalies together with drilling results, suggest widespread basaltic igneous activity in the continental rift zone just before and just after the onset of seafloor spreading. This spreading took place at a rate of about 5 mm/yr. for approximately the first 25 m.y., during the long Cretaceous interval of normal polarity. Gravity modeling suggests that a continental crust 6 to 14 km thick occurs between Pendragon Escarpment and the transition, and that relatively less crustal thinning has occurred adjacent to the continentocean transition in the region of 48-48.5°N than has occurred farther north. In the same region, both magnetic and gravity data could be interpreted in terms of a contine...

Basin and petroleum system modeling (BPSM) has had increasing impact on industry decisions related to exploration and new venture opportunities over the last decade. Basin and petroleum system modeling technology, usability, and user group size have grown as a result of its capacity to reduce exploration risk. Based on current statistics, improvements in BPSM have significant potential to reduce future well failures, particularly when caused by lack of petroleum charge. To bring BPSM practitioners from academia and industry together, an AAPG Hedberg Research Conference was organized to discuss the latest developments and issues in this field. A survey was conducted during the conference in Santa Barbara, California (April 2016), and this paper summarizes the results. A key takeaway was an overarching consensus throughout the BPSM community that improved understanding of hydrocarbon migration and more flexible workflows are necessary to better assess charge and migration risk in exploration and new ventures. In addition, BPSM is increasingly used to predict pore pressure and porosity at field scales, which opens new opportunities to integrate BPSM workflows with other technologies, such as seismic rock property analysis and reservoir quality modeling. In this paper, we discuss these and other issues that arose from in-depth discussion and an online survey.

The connection of the Ebro basin via the Ebro River to the Mediterranean Sea is supposed to have played a major role in the rejuvenation of relief of northern Spain and especially of the South Pyrenees from the Neogene by lowering the initial base level of the Ebro internal drainage area down to sea level. However, the timing and causes of this connection are still debated. A fundamental issue is whether the Ebro basin became connected to the Mediterranean before or after the Messinian salinity crisis? Morphological analysis and numerical modeling of landscape evolution show that this connection did not exist before the Messinian salinity crisis but is effective from the Pliocene because of progressive regressive erosion.

Deep seismic profiles and subsidence history of the Gulf of Lion margin reveal an intense stretching of the distal margin and strong postrift subsidence, despite weak extension of the onshore and shallow offshore portions of the margin. We revisit this evolution from the geological interpretation of an unpublished multichannel seismic profile and other published geophysical data. We show that an 80 km wide domain of thin lower continental crust, the "Gulf of Lion metamorphic core complex," is present in the ocean-continent transition zone and exhumed mantle makes the transition with oceanic crust. The exhumed lower continental crust is bounded upward and downward by shallow north dipping detachments. The presence of exhumed lower crust in the deep margin explains the discrepancy between the amount of extension deduced from normal faults in the upper crust and total extension. We discuss the mechanism responsible for exhumation and present two scenarios: the first one involving a simple coupling between mantle extension due to slab retreat and crustal extension and the second one involving extraction of the lower crust and mantle from below the margin by the southeastward flow of hot asthenosphere in the back-arc region during slab rollback. In both scenarios, the combination of Eocene crustal thickening related to the Pyrenees, the nearby volcanic arc, and a shallow lithosphere-asthenosphere boundary weakened the upper mantle and lower crust enough to make them flow southeastward. The overall hot geodynamic environment also explains the subaerial conditions during most of the rifting stage and the delayed subsidence after breakup. The Gulf of Lion margin shows many of those features typical of Atlantic-type passive margins [Aslanian et al., 2009; Bache et al., 2010], but it evolved in an entirely different tectonic setting associated with back-arc JOLIVET ET AL.

We processed and interpreted a newly acquired geophysical dataset (WS10 project) integrated with vintage seismic profiles to study the evolution of the Sardinian passive margin of the Sardo-Provençal basin. The most prominent features of the area of study are a consequence of the Messinian Salinity Crisis (MSC) which produced a thick salt layer in the deep basin. Complex halokinetic tectonics deformed the overlying Messinian Upper Unit (UU) and the Pliocene-Quaternary (PQ) sediments, sometimes also bending the sea bottom. A thinner autochthonous salt in the UU suggests at least one further low stand during the late MSC. The Messinian Erosional Surface (MES) separates the erosional truncation of the pre-Messinian sedimentary sequence from the overlaying Plio-Pleistocene sequence with a clear angular discordance, which almost completely masks possible earlier erosional events. The MES is present across the middle and upper slopes of the Sardinian margin and can be easily recognized down to the lower slope, where it interfingers with the Messinian evaporites which gradually thicken basinward. We propose a correlation between the main erosional surface of the lower slope and the salt layer recognized in the UU as a consequence of a falling stage during the last part of the MSC. The seismic profiles now available along the West Sardinian margin provide novel and crucial information to correlate the Messinian depositional units in the deep basin with those present in the lower continental slope and with the erosional surface of the middle and upper slopes. Our data and interpretation highlight the main units of the Messinian trilogy and further internal sequences that are probable related to cyclic fluctuations during their deposition.

Though the late Miocene "Messinian Salinity Crisis" has been intensely researched along the circum-Mediterranean basins, few studies have focused on the central part of the Mediterranean Basin and, especially, the pre-salt deposits. To improve our knowledge of the Messinian events, it is imperative to better understand this domain. In this study, we provide a more complete understanding of this central domain in the Provence Basin. We were able to recognize: a) thick marine detrital series (up to 1000 m) derived from the Messinian subaerial erosion which is partly prolongated in the distal part by b) a thick unit of deep marine deposits (up to 800 m) prior to the evaporites; c) a thick presumed alternation of detritals and evaporites (1500 m) below the mobile halite; and d) a two-step transgression at the end of the Messinian. Spatially, we document the eroded shelf to the deep basin (and from the western to the eastern parts of the Gulf of Lions), and temporally, we extend the interpretations from the early deposition of detritic sediments to the final sea-level rise. The results provide a new basis for discussion not only for the development of the Messinian Salinity Crisis but also for the reconstruction of the subsidence history of the Provence Basin.

Key Points: 1. High-quality seismic data image the internal structure of the 85°E Ridge 2. Volcanic conduit and series of lava deltas identified within the 85°E Ridge reveal nature of the ridge 3. Tectonic model proposed for the emplacement of the 85°E Ridge and its growth through time

The sediment succession in the Bay of Bengal (BoB) records the signatures corresponding to India-Asia collision, regional climate change, and erosional processes of both the Himalayan orogen and Indian subcontinent. The Bengal Fan-the world's largest submarine fan-has long been studied to understand the link between the Himalayan tectonics and Asian monsoon. But, lack of detailed information on corresponding signals hampered the understanding of related processes of tectonics, climate and erosion. The present study of long-streamer seismic reflection profile data and information from deep drill well logs in the western BoB has revealed two different phases of sediment deposition. In the first phase, until Oligocene-Miocene (~23 Ma), Indian peninsular rivers discharged sediments to the BoB which accumulated at a rate ~20 m/m.y. with an aberration of two fairly enhanced sediment pulses during the periods from 65 to 54 Ma and 34 to 23 Ma. In the second phase, since 23 Ma, the Ganges and Brahmaputra rivers added huge volumes of sediments to the bay at variable rates ranging from 40 to >1000 m/m.y. A distinct increase in sediment discharge (~140 m/m.y.) during the Oligocene-Miocene (~23 Ma) together with the development of regional onlap unconformity and the start of turbidity system provide an important age marker corresponding to rapid exhumation of the Himalaya, which intensified the erosional process and commencement of Bengal Fan sedimentation. Further rise in the rate of sedimentation during the period 6.8-0.8 Ma is coincident with the change in monsoon intensity, but surprisingly not in agreement with the decrease in sediment rate reported at ODP Leg 116 sites in the distal Bengal Fan. Here we provide wellconstrained ages for the commencement and growth of the Bengal Fan, which can serve as benchmark information for understanding the interaction between the Himalayan exhumation and Asian climate.

Mass-transport complexes (MTCs) dominate the stratigraphic record of many salt-influenced sedimentary basins. Commonly in such settings, halokinesis is invoked as a primary trigger for MTC emplacement, although the link between specific phases of salt movement, and related minibasin dynamics, remains unclear. Here, we use high-quality 3D seismic reflection and well data to constrain the composition, geometry, and distribution (in time and space) of six MTCs preserved in a salt-confined, supra-canopy minibasin in the northern Gulf of Mexico, and to assess how their emplacement relate to regional and local controls. We define three main tectono-sedimentary phases in the development of the minibasin: (1) initial minibasin subsidence and passive diapirism, during which time deposition was dominated by relatively large-volume MTCs (c. 25 km 3) derived from the shelf-edge or upper slope; (2) minibasin margin uplift and steepening, during which time small-volume MTCs (c. 20 km 3) derived from the shelf-edge or upper slope were emplaced; and (3) active diapirism, during which time very small volume MTCs (c. 1 km 3) were emplaced, locally derived from the diapir flanks or roofs. We present a generic model that emphasises the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. Although based on a single data-rich case study, our model may be applicable to other MTC-rich, salt-influenced sedimentary basins.