Late Cretaceous-Paleocene extension on the Vøring Volcanic Margin

High-quality seismic data document a Maastrichtian-Paleocene rift episode on the Vøring margin lasting for 20 m.y. prior to continental breakup. The rift structures are well imaged in the Fenris Graben and Gjallar Ridge region in the western Vøring Basin, and are characterized by low-angle detachment faults with variable fault geometries from south to north. The structural restoration has facilitated the division of pre- and syn-rift sediments across the extensional terrain, which is subsequently used to evaluate mode and mechanism for the lithospheric deformation. Extension estimates based on the structural restoration, subsidence analysis and crustal thickness evaluations yield stretching factors ranging between 1.5 to 2.3 across the main fault zone just landward of the early Tertiary flood basalts. The structural restoration also shows that a middle crustal dome structure, observed beneath the low-angle faults, can be explained by extensional unroofing. Thus, the dome structure may represent a possible metamorphic core complex. Calculations of the effects on vertical motion, assuming uniform and two-layer differential stretching models combined with the arrival of the Iceland mantle plume during rifting, indicate that the uniform extension model may account for both observed early rift subsidence and subsequent late rift uplift and erosion. Although the differential model can not be excluded, it implies early rift uplift which is not compatible with our seismic interpretation. The direct and indirect effects of the Iceland mantle plume may have caused as much as 1.2 km of late rift uplift. Comparison of the volcanic Vøring margin and the non-volcanic West Iberian margin shows similarities in terms of structural style as well as in mode and distribution of extension.     

Structural development and tectonic evolution of Gunsan Basin (Cretaceous–Tertiary) in the central Yellow Sea

This study analyzes the structural development of the Gunsan Basin in the central Yellow Sea, based on multi-channel seismic reflection profiles and exploratory well data. The basin comprises three depressions (the western, central, and eastern subbasins) filled with a thick (ca. 6000 m) Cretaceous to Paleogene nonmarine succession. It was initiated in the early Cretaceous due to intracontinental extension caused by oblique subduction of the Izanagi plate under the Eurasian plate and sinistral movement of the Tan-Lu fault. The basin appears to have undergone transtension in the late Cretaceous–Eocene, caused by dextral movement of the Tan-Lu and its branching faults. The transtension was accommodated by oblique intra-basinal normal faults and strike-slip (or oblique-slip) movement of a NE-trending bounding fault in the northern margin of the central subbasin. The entire basin was deformed (NE–SW contraction) in the Oligocene when tectonic inversion occurred, possibly due to the changes in strike-slip motion, from right- to left-lateral, of the Tan-Lu fault. During the early Miocene, extension resumed by reactivation of the pre-existing normal and transpressional faults. A combination of extension, uplift, and erosion resulted in differential preservation of the early Miocene succession. At the end of the early Miocene, extension ceased with mild contraction and then the basin thermally subsided with ensued rise in sea level.     

Regional constraints of the Sørkapp Basin: A Carboniferous relic or a Cretaceous depression?

The Sørkapp Basin (NW Barents Shelf) contains a comprehensive sedimentary succession that provides insight into regional tectonics and depositional development of the shelf from the Devonian to the Cretaceous. With its location east of the mid-Atlantic spreading ridge and south of Svalbard, the Basin serves as an important link between the offshore and onshore realms.This study subdivides this sparsely studied basin into six main seismic units (three Paleozoic and three Mesozoic). A metamorphic basement together with assumed Devonian sedimentary deposits form the foundation for a chiefly Carboniferous basin. The Basin forms a syncline with infill showing limited fault-influence. Overlying the early infill are Late Carboniferous deposits which show less lateral variation in thickness but also active growth on the few faults showing significant displacement. The overlying platform deposits of the latest Carboniferous and Permian show a change in depositional geometry, with onlapping deposits towards the east probably resulting from uplift of the Stappen High and regional flooding. Subsequent, particularly Late, Triassic sedimentation shows a more distinctly progradational pattern with a dominantly southeastern source for sediments. During this shallow shelf-filling stage, the Sørkapp Basin is sheltered by the Gardarbanken High, blocking the Early Triassic clinoform development. The High was transgressed in the Middle Triassic and the platform-edge progressively approached the present Svalbard coastline.The youngest Mesozoic unit forms a separate saucer-shaped depocenter west of the Sørkapp Basin, where deposits are truncated by the seafloor in a mid-basin position and across the Gardarbanken High. The depositional pattern for this succession correlates with the outcrop pattern of the Adventdalen Group implying a post Middle Jurassic to Cretaceous age. The Sørkapp Basin has been referred to as a Cretaceous feature based in this depocenter. However, the foundations are much older and the Cretaceous depression is located west of the deeper basin. Accordingly, we propose the informal term Sørkapp Depression for the Cretaceous basin.     

Seep carbonate formation controlled by hydrothermal vent complexes: a case study from the Vøring Basin, the Norwegian Sea

Several hundred hydrothermal vent complexes were formed in the Vøring Basin as a consequence of magmatic sill emplacement in the late Palaeocene. The 6607/12-1 exploration well was drilled through a 220-m-thick sequence of Eocene–Miocene diatomites with carbonate nodules above the apex of one of these vent complexes. Analysed calcites and dolomites from this interval have isotopic signatures typical for methane seep carbonates, with low ¹³C signatures of –28 to –54 PDB. The data suggest that the vent complex acted as a fluid migration pathway for about 50×10⁶ years after its formation, leading to near-surface microbial activity and seep carbonate formation.     

Sedimentary environment and glacial history during the last 40 ka of the Vøring continental margin,mid-Norway

This study is based on detailed investigation of sediment cores and high resolution seismics. We identified and describe five lithofacies on the Vøring Plateau and eight on the mid-Norwegian continental slope. The various lithofacies are mainly related to the fluctuations of the Fennoscandian Ice Sheet and the varying intensity of bottom currents and inflow of Atlantic water masses. Ocean circulation was highly variable between 40 and 22 ¹⁴C ka BP, being vigorous during interstadials and sluggish during stadials. Between ca 22 and 15 ¹⁴C ka BP the sedimentary environment was significantly influenced by fluctuations of the Fennoscandian Ice Sheet, repeatedly reaching the outermost shelf. These fluctuations are reflected in the sedimentary record as ice-rafted debris (IRD) accumulation peaks, deposition of stratified diamicton, and glacigenic debris flows on the continental slope. During this period the sediment accumulation rate increased, bottom currents influenced the sedimentary pattern, and surface waters were seasonally ice-free, indicating inflow of Atlantic waters. Subsequent to ca 15 ¹⁴C ka BP the glacier influence decreased as the margin of the Fennoscandian Ice Sheet retreated to reach the coast before 12.5 ¹⁴C ka BP. The modern sedimentary environment is characterised by relatively strong bottom current action, causing winnowing or non-deposition down to approximately 1000 m water depth.     

Organic geochemical identification of reservoir oil–gas–water layers in the Junggar Basin,NW China

The identification of reservoir oil–gas–water layers is a fundamental task in petroleum exploration and exploitation, but is difficult, especially in cases of complex hydrocarbon migration and accumulation. In such cases, hydrocarbon remigration and dysmigration take place very commonly, leading to the presence of residual or paleo-oil accumulations and layers, which cannot be easily identified or misinterpreted as oil layers by conventional logging and geophysical data. In this paper, based on a case study in the Luxi area of the central Junggar Basin, NW China, we seek to characterize such layers in terms of organic geochemistry. We suggest specific indicator parameters of organic geochemistry such as the chloroform bitumen content of reservoir extracts, which is usually >1.0% in oil layers. We explore the application of grains containing oil inclusions (GOI) (the ratio of mineral grains containing oil inclusions to the total number of mineral grains) for the identification of oil–gas–water layers in the Junggar Basin for the first time; this method has been used elsewhere. The maximum GOI values for the oil layers, oil–water layers, water layers and dry layers are >11%, 7%–11%, 6%–7% and <6%, respectively. In addition, gas layers and heavy-oil layers that are difficult to identify by conventional organic geochemical parameters were identified using biomarkers. The typical characteristics of the soluble reservoir bitumen in the gas layers include a much greater abundance of tricyclic terpanes (two times in general) relative to pentacyclic terpanes and a tricyclic terpane distribution of C₂₀ > C₂₁ > C₂₃. In contrast, the typical characteristic of the heavy-oil layers is the presence of 25-norhopanes in reservoir bitumen extracts. These specific indicators can be applied in the Junggar Basin and in similar settings elsewhere.     

Tectonostratigraphic evolution of the northern Porcupine Basin,Irish Atlantic margin,during the Late Jurassic–Early Cretaceous,implication for a regional compressional event

The conventional interpretation of the Jurassic–Lower Cretaceous succession in the Porcupine Basin suggests an extensional setting with progressive deepening of the basin. However, well data show a prominent gap of several million years between the Upper Jurassic and Lower Cretaceous. A data base of 15 key wells and approximately 5,000 km of seismic reflection data were examined in the northern Porcupine Basin, in order to understand the nature, controls and mechanisms of this unconformity. Seven seismic markers, constrained by well data, are mapped. It is shown that during the Late Jurassic (possibly the Oxfordian–Kimmeridgian), the basin experienced extension and synrift deposition. During the latest Jurassic–earliest Cretaceous (possibly the Tithonian–early Berriasian), a series of north-trending structural highs and lows developed and extensive areas in the northern Porcupine Basin experienced folding, uplift and erosion. Evidence from the study suggests that compression, uplift and erosion played an important role in the shaping of the depositional and structural architecture of the basin and caused formation of the regional Base Cretaceous Unconformity in the northern basin. It is suggested that the deformation in the northern Porcupine Basin during the latest Jurassic–earliest Cretaceous may be related to the initial closure of the Alpine Tethys during the late Tithonian. This tectonic event may also have resulted in compressional deformation and formation of the Base Cretaceous Unconformity elsewhere in Western Europe.     

Linear magnetic anomalies and tectonic development of the middle Okinawa Trough

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Morpho-tectonic evolution of the ?anakkale Basin (NW Anatolia): evidence for a recent tectonic inversion from transpression to transtension

Onshore and offshore seismic and geologic-morphologic evidence from the wider region of the ?anakkale Basin indicates that this area has been widely exposed to transpressional tectonism, which already commenced in the Pliocene. During this transpressional tectonism, the Gelibolu Fault and the Anafartalar Shear Zone on the Gelibolu Peninsula, as well as the Bozcaada-Biga Shear Zone on the Biga Peninsula were activated. As a consequence, the northern part of the Gelibolu Peninsula, and a broad zone between Bozcaada Island and the Karaburun Peninsula were uplifted to form the northern and southern boundaries of the ?anakkale Basin, respectively. This remained a low-elevation intermontane basin between these two highlands. The original morphology of the ?anakkale Basin may have developed as a coastal and shelf section of the large extensional Marmara Sea Basin at the end of the Late Miocene. This tectonic phase was followed in the Pliocene by the transpressional tectonism of the North Anatolian Fault Zone, which destroyed the initial morphology and formed the present V-shaped basin. The activity of the Gelibolu Fault and the Anafartalar Shear Zone along the northern boundary of the ?anakkale Basin ended in the late Pleistocene with the initiation of the northern segment of the North Anatolian Fault Zone. The tectonism along the northern boundary of the ?anakkale Basin thus shifted from a transpressional to a transtensional regime. Seismic data indicate that the Bozcaada-Biga Shear Zone continues to be active to the present day.     

Diagenetic evolution of the upper Cretaceous limestone and sandstone exhumed reservoirs in the western Basque–Cantabrian Basin,North Spain

The Basque–Cantabrian Basin (NE Spain) has been considered one of the most interesting areas for hydrocarbon exploration in the Iberian Peninsula since the 60th to 70th of last century. This basin is characterized by the presence of numerous outcrops of tar sands closely associated with fractures and Triassic diapirs. The aims of this work is to establish the diagenetic evolution of the Upper Cretaceous reservoir rocks with special emphasis in the emplacement of oil and their impact on reservoir quality. The studied rocks are constituted of carbonates and sandstones that contain massive quantities of bitumen filling vugs and fractures.Petrographic results indicate that the carbonate rocks from Maestu outcrops are bioclastic grainstones and wackestones, whereas the tar sandstones from Atauri and Loza outcrops are dominated by quartzarenites and subordinated subarkoses. The paragenetic sequence of the main diagenetic phases and processes include, pyrite, bladed and drusy calcite cement, calcite overgrowths, silicification of bioclasts and microcrystalline rhombic dolomite cement, and first stage of oil emplacement, blocky calcite cement, coarse crystalline calcite cement, calcitized dolomite, calcite veins, saddle dolomite and stylolites filled by the second phase of oil entrance. Together with the above mentioned diagenetic alterations, the arenites are affected by early kaolinitization of feldspars and the scarce formation of clay rim and epimatrix of illite. All sandstones and dolomitized carbonate rocks show high intercrystalline and intergranular porosity which is full by biodegraded hydrocarbons (solid bitumen). The biodegradation affects alkanes, isoprenoids and partially hopanes and steranes saturated hydrocarbons. Aromatics hydrocarbons, like naphthalenes, phenanthrenes, dibenzothiophenes and triaromatics are also affected by biodegradation. Results indicate that the first HC emplacement corresponds to early stage of calcite and dolomite cementation, and the second and more important emplacement is related to fracturation processes resulting in the formation of excellent reservoirs.     

Transgressions of Late Cretaceous to Early Tertiary in Eastern China

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Late Neogene evolution of the Taza–Guercif Basin (Rifian Corridor,Morocco) and implications for the Messinian salinity crisis

Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza–Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza–Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Rifian Corridor. (1) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza–Guercif area, marked by deposition of precession-controlled turbidite–marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza–Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean.     

Peculiarities of the Rock–Fluid System of the Subduction Zone in the South Caspian Basin

Izvestiya, Atmospheric and Oceanic Physics - The goal of this study is to identify the properties of the rock–fluid system in the subduction zone of lithospheric plates using the example of...     

Rift–shear architecture and tectonic development of the Ghana margin deduced from multichannel seismic reflection and potential field data

The Ghana margin displays one of the best-known transform margins. Studies of the margin have provided the framework for a number of conceptual models aimed at understanding transform margin development worldwide. However, the deep structure of the margin is poorly known as knowledge is based only on wide-angle refraction measurements obtained from two separate localities on the margin. Consequently, complexities in the rift–shear margin architecture have been overlooked by current interpretations of margin development. Based on combined analysis of a detailed grid of ∼2710 km multichannel (MCS) lines and potential field data, we provide new insights into the structural architecture and tectonic development of the Ghana margin. In particular, we outline the deep structure of the entire margin using a series of 2D gravity modelled transects constrained by MCS and published wide-angle data. Our study reveals more complex rift–shear margin architecture than previously envisaged. We demonstrate that the main transform boundary representing the continental extension of the Romanche Fracture Zone, is actually composed of two distinct margin segments, i.e., the ENE–WSW trending sheared margin segment of the Cote d’Ivoire-Ghana Ridge and the NE–SW trending rift-influenced sheared margin segment of the Ghana Platform. These segments evolved under varying stress regimes, and during different time intervals. West of the transform margin, divergent rifting during the Early Cretaceous initiated the development of the Deep Ivorian Basin, essentially, as a single major pull-apart structure. However, east of the shear zone, oblique rifting resulted in the development of the Eastern Ghana Slope Basin as a composite of at least two coalescing pull-apart basins displaced along strike-slip faults. Our structural interpretation of the transform boundary geometry shows that the ridge and platform margin segments were each subjected to separate thermal influences from two different migrating spreading centres. Tectonic uplift of the ridge began through transpression during mid-Albian time following a change in relative direction of plate motion from NE–SW to ENE–WSW. However, the ridge uplift was amplified by thermal heating from a previously undocumented spreading centre whose progressive westward migration along the ridge followed closely after the Albian transpressional phase. The structural architecture of the Ghana margin resulted from a combination of factors, notably, pre-existing basement structure, plate boundary geometry, the relative direction of plate motion and thermal heating.     

Two Modes of Atmosphere–Ocean Interaction in the Atlantic Sector of the Arctic Basin

Oceanology - The paper examines the influence of the main mode of interannual variability of the North Atlantic climate system—the North Atlantic Oscillation (NAO)—on the hydrophysical...     

Response of Landscapes of the Sikhote-Alin Western Slopes to the Middle–Late Holocene Climatic Changes

The response of landscape biotic components of the western slope of the Sikhote-Alin Mountains (Bikin River middle flow) to the Middle–Late Holocene climate changes is discussed. The paleoreconstruction object was the Krasny Yar mari, which developed under the control of multidirectional short-term climatic changes. The last millennium was marked by particularly rapid and frequent changes in the local landscapes. The closely spaced orographic barrier strongly affected the development of biotic components and changes in the swamp hydrological regime. The moisture dynamics within the river catchment considerably controlled the development and change of the peat-forming plants. Several stages of the mari development were reconstructed; each began from the accumulation of eutrophic peat. It was followed by the transitional eutrophic–mesotrophic stage, with a higher role of atmospheric supply. The larch forests appeared in this part of the valley within the Atlantic–Subboreal cooling period. Korean pine developed in the forest vegetation in the low mountain relief at the beginning of the Subboreal and became one of the leading trees ~2.6–2.3 ka BP. The lower role of the Korean pine and birch forest expansion in the first half of the Subatlantic could be related to the fires. The broadleaf–Korean pine forests became widespread in the Medieval Warm Period. Local swamp landscapes changed dramatically in the Little Ice Age, while the slope vegetation was not subject to any major changes. The landscapes were also affected by the fires, which became more frequent. The derivative communities with birch appeared on the mari. Moreover, this part of the valley was occasionally subject to heavy flooding.     

New insights into the tectono-stratigraphic evolution of the southern Stappen High and its transition to Bjørnøya Basin,SW Barents Sea

Within the context of the southwestern Barents Sea, the southern Stappen High and its transition to the Bjørnøya Basin are still underexplored. Improved quality seismic reflection data are utilised to describe new insights into the Paleozoic to early Cenozoic tectono-stratigraphic evolution of the area, as well as to discuss the structural inheritance and the rift development. Well-defined syn-rift wedges and better resolution images for both the deep Carboniferous and Permian successions are revealed. In particular, both the mid-Carboniferous and Late Permian-earliest Triassic extensional phases are characterized by widespread NE-SW oriented normal faults that are mostly westward dipping. Although Triassic is mostly considered as a tectonically stable period in the Barents Sea, in the southern Stappen High there is clear identification of a localised depocentre (named herein “Intra Stappen Basin”) where syn-tectonic geometries characterize the upper Paleozoic and Triassic deposits. Regional correlation to Middle and Upper Triassic outcrops in southwestern Svalbard reveals possible progradation from a west-northwest Northeast Greenland provenance as a western sediment source area during the Triassic, in addition to the well-known eastern sediment source area. Thin but distinct Jurassic sequences are expected to be present on Stappen High associated with prominent regional NW-SE extension throughout Late Jurassic that culminated during the earliest Cretaceous. Furthermore, structural and stratigraphic relations are observed within the study area that clearly indicate a distinct early Aptian rift phase with increasing evidence for its occurrence in the southwestern Barents Sea. Upper Cretaceous sequences bounded by major low-angle west-dipping detachment faults are observed in southwest Stappen High. During early Cenozoic, the study area was located at the proximity of the paleo-coastline and paleo-shelf edge for both Paleocene and Eocene gravity mass-waste deposits. These are most probably related to a progressively evolving steep bathymetric gradient between the developing margin, mainly towards the west and to the south, and the uplifted Stappen High.     

Late Pleistocene–Holocene history of the Golden Horn Estuary,Istanbul

The historical Golden Horn Estuary (GHE), near the confluence of the Istanbul Strait (Bosphorus) and the Sea of Marmara in the European part of Istanbul, has been used as a natural harbor since 330 a.d. The sedimentary infill of the GHE is 15–46 m thick, deposited unconformably above the turbiditic sandstones of the Carboniferous Trakya Formation. Chronostratigraphic and paleontological analyses of the infill sequence indicate that the GHE was a fluvial channel prior to 13,500 cal. a (calibrated to calendar years) B.P. It subsequently became gradually influenced by marine waters, and was a brackish-water environment until 9,500 cal. a B.P. Normal marine salinities prevailed at ca. 9,500−5,600 cal. a B.P., with suboxic/dysoxic bottom-water conditions. The increase in salinity at 9,500 cal. a B.P. was most likely caused by Mediterranean water outflow into the Black Sea through the Istanbul Strait. The estuary was influenced by large fluvial inputs between 5,600 and 1,000 cal. a B.P., possibly during a distinct pluvial period, as shown by coarse siliciclastic sediments deposited on the flanks. It has become a highly polluted environment with marked anthropogenic inputs during the last millennium. The finding that the sediment infill sequence above the Carboniferous basement is not older than about 20 ka strongly suggests that the Golden Horn Estuary acquired its present-day morphology during the late glacial–Holocene period.     

Variation of freshwater components in the Canada Basin during 1967–2010

As a conservative tracer, oxygen isotopes in seawater are widely used for water mass analysis, along with temperature and salinity. In this study, seawater oxygen-18 datasets in the Canada Basin during 1967–2010 were obtained from the four cruises of the Chinese National Arctic Research Expedition(1999, 2003, 2008, and 2010) and the NASA database. Fractions of sea ice meltwater and river runoff were determined from the salinity-18O system. Our results showed that the river runoff decreased from the south to the north in the Canada Basin. The enhanced amount of river runoff observed in the southern Canada Basin may originate from the Mackenzie River, transported by the Beaufort Gyre. The river runoff component showed maximum fractions during 1967–1969, 1978–1979, 1984–1985, 1993–1994, and 2008–2010, indicating the refresh time of the river runoff was 5.0–16.0 a in the Canada Basin. The temporal variation of the river runoff was related to the change of the Arctic Oscillation(AO) index, suggesting the freshwater stored in the Canada Basin was affected by surface sea ice drift and water mass movement driven by atmospheric circulation.