The Klippfisk Formation—a new lithostratigraphic unit of Lower Cretaceous platform carbonates on the Western Barents Shelf

A new Lower Cretceous lithostratigraphic unit of the Western Barents Shelf, named the Klippfisk Formation, is formally introduced. The formation represents a condensed carbonate succession deposited on platform areas and structural highs, where it consists of limestones and marls, often glauconitic. The limestones may have a nodular appearance, and fossil debris, which are dominated by Inoceramus prisms, may be abundant. The Klippfisk Formation is composed of two members: the Kutling Member defined herein from cores drilled on the Bjarmeland Platform, and the coeval Tordenskjoldberget Member described on Kong Karls Land. The base of the formation is defined by the abrupt decrease in gamma-ray intensity, where the dark shales of the underlying Hekkingen or Agardhfjellet formations are replaced by marls. It is often unconformable. The Klippfisk Formation is of Berriasian to Early Barremian age and appears to be time-transgressive over parts of the Western Barents Shelf (including Kong Karls Land). It passes laterally into the basinal Knurr Formation. On Kongsøya (Kong Karls Land) a thin shale unit, bounded by unconformities, earlier included in the Tordenskjoldberget Member, represents the northernmost extension of the overlying Kolje Formation in the Barents Shelf.     

Quantifying multiple Permian–Recent exhumation events during the break‐up of eastern Gondwana: sonic transit time analysis of the central and southern Perth Basin

The central and southern Perth Basin in southwestern Australia has a geological history involving multiple regional unconformity‐forming events from the Permian to Recent. This study uses sonic transit time analysis to quantify the magnitudes of net and gross exhumation for four stratigraphic periods from 43 wells. Most importantly, we quantify gross exhumation of the Permian–Triassic, Triassic–Jurassic, Valanginian break‐up and post‐Early Cretaceous events. Post‐Early Cretaceous gross exhumation averages 900‐m offshore and 600‐m onshore. Up to 200 m of this exhumation may be attributed to localized fault block rotation during extension in the Late Cretaceous and/or reverse fault re‐activation due to the compressive stresses in Australia in the last 50 Ma. The remainder is attributed to regional exhumation caused by epeirogenic processes either during the Cenozoic or at the Aptian–Albian boundary. Maximum burial depths prior to the Valanginian unconformity‐forming event were less than those reached subsequently, so that the magnitude of Valanginian break‐up exhumation cannot be accurately quantified. Gross exhumation prior to the break‐up of Gondwana was defined by large magnitude differences (up to 2500 m) between adjoining sub‐basins. At the end of Triassic, exhumation is primarily attributed to reverse re‐activation of faults that were driven by short‐wavelength inversion and exhumation at the end Permian is likely caused by uplift of rotated fault blocks during extension. The evidence from quantitative exhumation analysis indicates a switch in regime, from locally heterogeneous before break‐up to more regionally homogeneous after break‐up.     

Subsidence and thermal history of an inverted Late Jurassic‐Early Cretaceous extensional basin (Cameros,North‐central Spain) affected by very low‐ to low‐grade metamorphism

The Cameros Basin (North Spain) is a Late Jurassic‐Early Cretaceous extensional basin, which was inverted during the Cenozoic. It underwent a remarkable thermal evolution, as indicated by the record of anomalous high temperatures in its deposits. In this study, the subsidence and thermal history of the basin is reconstructed, using subsidence analysis and 2D thermal modelling. Tectonic subsidence curves provide evidence of the occurrence of two rapid subsidence phases during the syn‐extensional stage. In the first phase (Tithonian‐Early Berriasian), the largest accommodation space was formed in the central sector of the basin, whereas in the second (Early Barremian‐Early Albian), it was formed in the northern sector. These rapid subsidence phases could correspond to relevant tectonic events affecting the Iberian Plate at that time. By distinguishing between the initial and thermal subsidence and defining their relative magnitudes, Royden's (1986) method was used to estimate the heat flow at the end of the extensional stage. A maximum heat flow of 60–65 mW/m² is estimated, implying only a minor thermal disturbance associated with extension. In contrast with these data, very high vitrinite reflectance, anomalously distributed in some case with respect to the typical depth‐vitrinite reflectance relation, was measured in the central‐northern sector of the basin. Burial and thermal data are used to construct a 2D thermal basin model, to elucidate the role of the processes involved in sediment heating. Calibration of the thermal model with the vitrinite reflectance (%Ro) and fluid inclusion (FI) data indicates that in the central and northern sectors of the basin, an extra heat source, other than a typical rift, is required to explain the observed thermal anomalies. The distribution of the %Ro and FI values in these sectors suggests that the high temperatures and their distribution are related to the circulation of hot fluids. Hot fluids were attributed to the hydrothermal metamorphic events affecting the area during the early post‐extensional and inversion stages of the basin.     

Lower Jurassic magnetostratigraphy at the Breggia Gorge (Ticino, Switzerland) and Alpe Turati (Como, Italy)

Summary. The Breggia gorge (Ticino, Switzerland) provides a continuous outcrop of Mesozoic limestones covering the time between the Lower Jurassic and Upper Cretaceous. The Jurassic section from the Lower Pliens-bachian to Aalenian is well dated by ammonites. The limestones of these stages are a good quality recorder of the polarity of the geomagnetic field during this time interval. More than 500 cores have been drilled along a 120 m thick section with a median distance between cores of about 20 cm. Detailed thermal and af demagnetization and further rock magnetic studies were used to determine the characteristic NRM direction for each sample. Initial NRM intensities and low field susceptibilities reflect variations in oxidation potential and sedimentation rate during carbonate deposition. The Breggia section covers an estimated 12Myr of Lower to Middle Jurassic time during which more than 60 distinct reversals of the geomagnetic field are recorded. This corresponds to a comparatively high mean reversal frequency of about 5 reversals Myr⁻¹. The Breggia polarity zonation can be correlated with the nearby section at Alpe Turati (Como, Italy) and comparable polarity patterns are recognized in other biostratigraphically well-dated magnetostratigraphic profiles from Hungary and Umbria (Italy).     

对珠江三角洲第四纪断裂运动的再认识

编制了珠江三角洲番禺台地东缘第四纪堆积阶地、陆域钻孔及海域地震探测等一系列联合剖面,分析了抬升区、下沉区和海陆之间的沉积差异和控制因素,剖析了地动型和水动型海平面变化对三角洲形成演化的影响,厘清了各组断裂的活动及其对三角洲沉积发育的影响,结果发现北东东向和北北西向2组断裂为珠江三角洲地区的主要活动断裂,它们共轭联动,控制着珠江三角洲沉积的格局和水道的变迁,尤其是北东东向断裂,可能是南海北部大陆架滨海断裂系的组成部分。相比而言,陆域断裂活动性较弱,以缓慢蠕动和断块的差异升降和掀斜为主,海域断裂活动性较强,滨海断裂带是危险性很高的活动大断裂。三角洲其他方向的断裂更新世以来无明显活动。     

Triassic to Early Jurassic climatic trends recorded in the Jameson Land Basin,East Greenland: clay mineralogy,petrography and heavy mineralogy

During the Early Triassic the Jameson Land Basin (Central East Greenland) was located around 30° N, in the Northern arid belt, but by the Early Jurassic was positioned at a latitude of approximately 50° N. This study examines the record of this transition through a largely continental succession using clay mineralogy, sedimentology, petrography and heavy mineralogy. The Jameson Land Basin is aligned north–south and is 280 km long and 80 km wide. Following an Early Triassic marine phase the basin was filled by predominantly continental sediments. The Early‐to‐Late Triassic succession comprises coarse alluvial clastics (Pingo Dal Formation) overlain by a succession of fine‐grained evaporite‐rich playa/lacustrine sediments (Gipsdalen Formation), indicative of arid climatic conditions. The overlying buff, dolomitic and then red lacustrine mudstones with subordinate sandstones (Fleming Fjord Formation) record reduced aridity. The uppermost Triassic grades into dark organic‐rich, and in places coaly, mudstones and buff coarse‐grained sandstones of lacustrine origin that belong to the Kap Stewart Group, which spans the Triassic–Jurassic boundary, and appear to record more humid climatic conditions. Clay mineralogy analyses highlight significant variations in the kaolinite/illite ratio, from both mudstone and sandstone samples, through the Triassic and into the earliest Jurassic. Complementary heavy mineral analyses demonstrate that the variations recognised in clay mineralogy and sandstone maturity through the Triassic–Early Jurassic succession are not a product of major provenance change or the effect of significant diagenetic alteration. The observed variations are consistent with sedimentological evidence for a long‐term trend towards more humid conditions through the Late Triassic to Early Jurassic, and the suggestion of a significant pluvial episode in the mid‐Carnian.     

Lower Cretaceous magnetic stratigraphy in Umbrian pelagic carbonate rocks

Summary. A record of geomagnetic field polarity for the Barremian, Aptian and Albian stages of the Early Cretaceous has been derived in three over-lapping sections of pelagic carbonate rocks in the Umbrian Apennines of northern Italy. The remanence carrier in the greyish-white Majolica limestone and Fucoid Marls is magnetite, with haematite also an important constituent in a zone of 'couches rouges' within the Fucoid Marls. The weak remanent magnetizations were measured with a cryogenic magnetometer. Alternating field or thermal demagnetization was used to isolate the characteristic remanent magnetization (ChRM) in 655 specimens from 248 stratigraphic levels. The samples respond positively to a tectonic fold test, indicating that the ChRM predates the Late Tertiary folding of the Umbrian sequence. The magnetic stratigraphy derived from variations of virtual geomagnetic pole latitude clearly defines the recognizable reversal pattern associated with Mesozoic marine magnetic anomalies M0 to M4. The sections have been zones palaeontologically on the basis of planktonic foraminifera and calcareous nannofossil assemblages. The ages of magnetic anomalies M0 to M4 determined in this way are somewhat older than those in the reversal time scale of Larson & Hilde (1975). Anomaly M0 is located in the Early Aptian, close to the Aptian/Barremian boundary. A long period of normal polarity in the Aptian and Albian corresponds to the early part of the Cretaceous magnetic quiet zone. It is interrupted in the Late Aptian by a reversal which we find in only one of the Fucoid Marl sections, and which has not been reported in oceanic magnetic anomaly investigations.     

Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of Adria

The Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.     

Exploring the reservoir potential of Lower Cretaceous Clinoforms in the Fingerdjupet Subbasin,Norwegian Barents Sea

Sandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high-resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7-1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post-rift tectonic quiescence, shelf-edge clinoforms (foreset height > 150 m) prograded into an under-filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north-western FSB and mass wasting towards the SE were followed by deposition of delta-scale (<80 m high), high-angle (c. 8°) clinoform sets seaward of older shelf-edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high-angle (10–12°), low-relief, delta-scale (25–80 m) clinoform sets occurs between shelf-edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7-1, positioned on a direct hydrocarbon indicator, <1 km NNW of the high-angle, low-relief, delta-scale clinoforms, found upward coarsening siltstone-cycles linked to relative sea-level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high-angle, low-relief foresets of the delta-scale clinothems (which are typical geometries elsewhere interpreted as ‘delta-scale, sand-prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud-dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.     

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.     

Influence of oblique basement strike–slip faults on the Mesozoic evolution of the south-eastern segment of the Mid-Polish Trough

A series of analogue models are used to demonstrate how the multistage development of the Mid‐Polish Trough (MPT) could have been influenced by oblique basement strike–slip faults. Based on reinterpretation of palaeothickness, facies maps and published syntheses of the basin development, the following successive stages in the Mesozoic history of the south eastern part of the MPT were simulated in the models: (1) Oblique extension of the NW segment of the MPT connected with sinistral movement along the Holy Cross Fault (HCF, Early Triassic–latest Early Jurassic). (2) Oblique extension of both NW and SE segment of the MPT, parallel to the HCF (latest Early and Middle Jurassic). (3) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the HCF (Early Oxfordian–latest Early Kimmeridgian). (4) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the Zawiercie Fault (ZF, latest Early Kimmeridgian–Early Albian). (5) Oblique inversion of the NW segment of the MPT connected with dextral movement along the HCF (Early Albian–latest Cretaceous). (6) Oblique inversion of the SE segment of the MPT along the W–E direction (latest Cretaceous–Palaeogene). The different sense of movements of these two basement strike–slip faults (HCF and ZF) resulted in distinct segmentation of the basin and its SW margin by successive systems of extensional en‐echelon faults. The overall structure of this margin is controlled by the interference of the border normal faults with the en‐echelon fault systems related to successive stages of movement along the oblique strike–slip faults. This type of en‐echelon fault system is absent in the opposite NE‐margin of the basin, which was not affected by oblique strike–slip faults. The NE‐margin of the basin is outlined by a typical, steep and distinctly marked rift margin fault zone, dominated by normal and dip–slip/strike–slip faults parallel to its axis. Within the more extended segment of the basin, extensive intra‐rift faults and relay ramps develop, which produce topographic highs running across the basin. The change in the extension direction to less oblique relative to the basin axis resulted in restructuring of the fault systems. This change caused shifting of the basin depocentre to this margin. Diachronous inversion of the different segments of the basin in connection with movement along one of the oblique basement strike–slip faults resulted in formation of a pull‐apart sub‐basin in the uninverted SE‐segment of the basin. The results of the analogue models presented here inspire an overall kinematic model for the southeastern segment of the MPT as they provide a good explanation of the observed structures and the changes in the facies and palaeothickness patterns.     

An Early Proterozoic U-Pb zircon age from an Eskolabreen Formation gneiss in southern Ny Friesland, Spitsbergen

A preliminary U/Pb zircon age determination has been carried out on a grey gneiss of the Eskolabreen Formation, the lowest observable lithostratigraphic unit of Precambrian metamorphic rocks in southern Ny Friesland, NE Spitsbergen. The obtained age, ca. 2, 400 Ma, is considered to be a metamorphic age and suggests an Early Proterozoic tectonothermal event.     

Tectono-sedimentary evolution of Jurassic–Cretaceous diapiric structures: Miravete anticline,Maestrat Basin,Spain

Integration of extensive fieldwork, remote sensing mapping and 3D models from high-quality drone photographs relates tectonics and sedimentation to define the Jurassic–early Albian diapiric evolution of the N–S Miravete anticline, the NW-SE Castel de Cabra anticline and the NW-SE Cañada Vellida ridge in the Maestrat Basin (Iberian Ranges, Spain). The pre shortening diapiric structures are defined by well-exposed and unambiguous halokinetic geometries such as hooks and flaps, salt walls and collapse normal faults. These were developed on Triassic salt-bearing deposits, previously misinterpreted because they were hidden and overprinted by the Alpine shortening. The Miravete anticline grew during the Jurassic and Early Cretaceous and was rejuvenated during Cenozoic shortening. Its evolution is separated into four halokinetic stages, including the latest Alpine compression. Regionally, the well-exposed Castel de Cabra salt anticline and Cañada Vellida salt wall confirm the widespread Jurassic and Early Cretaceous diapiric evolution of the Maestrat Basin. The NE flank of the Cañada Vellida salt wall is characterized by hook patterns and by a 500-m-long thin Upper Jurassic carbonates defining an upturned flap, inferred as the roof of the salt wall before NE-directed salt extrusion. A regional E-W cross section through the Ababuj, Miravete and Cañada-Benatanduz anticlines shows typical geometries of salt-related rift basins, partly decoupled from basement faults. These structures could form a broader diapiric region still to be investigated. In this section, the Camarillas and Fortanete minibasins displayed well-developed bowl geometries at the onset of shortening. The most active period of diapiric growth in the Maestrat Basin occurred during the Early Cretaceous, which is also recorded in the Eastern Betics, Asturias and Basque-Cantabrian basins. This period coincides with the peak of eastward drift of the Iberian microplate, with speeds of 20 mm/year. The transtensional regime is interpreted to have played a role in diapiric development.     

Relief development of a Mesozoic carbonate platform margin (Southern Alps, northern Italy)

The effect of various erosional processes on the relief development of a carbonate platform margin is documented from outcrops of the Southern Alps, northern Italy, by the occurrence of truncation surfaces and redistribution of remobilized sediments. The periplatform depositional history, with periods of intensive submarine erosion along the north-western Trento plateau margin, is recorded by various carbonate deposits ranging in age from the Early Jurassic to Late Cretaceous with numerous gaps. The first Early Jurassic period of submarine erosion is marked by truncation and extensive tectonic fracturing of lower Liassic oolitic skeletal periplatform deposits. These are overlain by pelmicritic sediments of late Hettangian to Toarcian age. The second period of submarine erosion during the late Early Jurassic resulted in almost complete truncation of the pelmicritic unit. Crinoidal to oolitic periplatform carbonate sands were subsequently deposited along the carbonate margin until the Aalenian/Bajocian. The third truncation surface was produced by partial current erosion of the crinoidal to oolitic periplatform deposits during the late Bajocian to Callovian. The fourth, and most prominent, truncation surface was produced by erosion during the Early Cretaceous cutting down from Aptian/Albian pelagic units to Toarcian periplatform deposits. The resulting submarine relief was completely buried during the late Maastrichtian by onlapping pelagic sediments. The documentation of the depositional history during the Late Mesozoic of the north-western Trento plateau pinpoints the main mechanisms responsible for the relief of the drowned carbonate platform margin. Extensional tectonic activity during differential subsidence and current-induced erosional truncation, followed by gravitational downslope mass transport and rapid pelagic burial mainly determined the morphology of the drowned carbonate platform margin.     

Late Quaternary palaeohydrology of the Konya Basin, Turkey, based on isotope studies of modern hydrology and lacustrine carbonates

The Konya plain in south central Anatolia, Turkey, which is now largely dry, was occupied around the time of the Last Glacial Maximum by a fresh-oligosaline lake covering more than 4000 km². Sediment cores from three residual water bodies (Pinarbai, Akgöl and Süleymanhaci) within the larger Pleistocene lake basin, have been analysed using a multidisciplinary approach. The sediment sequences are dated as spanning the last 50 Ka years, although breaks in sedimentation mean that there is only partial chronological overlap between them. Carbon and oxygen isotope analyses on lacustrine carbonate from the three cores give contrasting isotope profiles which reflect the different ages and independent hydrological behaviour of different sub-basins through the late Quaternary. Distinguishing changes that are regional from local effects is aided by modern isotope hydrology studies and by comparing the carbonate ¹³C and ¹⁸O values to diatom and other analyses undertaken on the same cores.     

The late Pleistocene ostracod record of the crater lake sediments from Lago di Albano (Central Italy): changes in trophic status, water level and climate

Four cores (ranging between ca. 9 and ca. 14 m in length) from Lago di Albano in Central Italy were studied for their ostracod content, as well as algal and bacterial pigments, CaCO3 and concentration of organic matter. Cores PALB 94 1E and PALB 94 1C from Site 1, located at the bottom of a steep slope at 70 m water depth, where oxygen concentration is below 6 mg l-1, spans the Holocene and the late Pleistocene until 28 kyr B.P. (calibrated age). The other cores, PALB 94 6A and PALB 94 6B taken at a depth of 30 m, where oxygen is 7--11 mg l-1, represent mainly Pleistocene deposits.Ostracod valves were found in the lowermost ca. 3 m of the sequence at Site 1, dated to ca. 28--24 kyr B.P., and throughout the sequence from Site 6 which represents the interval 23--17 kyr B.P.Candona neglecta is the dominant species in most of the levels at Site 1, whereas both C. neglecta and Cyclocypris sp. dominate during different biostratigraphic zones at Site 6. The influx of springs entering the lake at Site 1 was inferred on the basis of species of the genus Potamocypris and Ilyocypris bradyi present in the record. Wide fluctuations in species abundance and assemblages in both coring sites indicate lake-water level oscillations between 28 to 17 kyr B.P. In particular, a strong rise in water level of the order of 40 m occurred between 24 and 23 kyr B.P. Fluctuations in productivity, oxygen availability and water temperature at both sites were also reconstructed on the basis of the ostracod assemblages and the algal and bacterial pigment concentrations. The environmental reconstruction reached using ostracod remains and pigments was verified with other proxy records published elsewhere such as invertebrate remains, diatoms, magnetic properties, etc. A synthesis of climatic reconstructions for Central and Southern Italy for the late Full Glacial is attempted on the basis of previous studies on hydrology, lithostratigraphy and palynology. Sharp fluctuations in lake palaeoproductivity/palaeoclimate recorded by invertebrate and pigment remains at both sites from Lago di Albano might be related to similar events reported in North Atlantic Full-Glacial records from marine and ice cores.     

Palaeomagnetism of the Lower Ordovician Orthoceras Limestone, St. Petersburg, and a revised drift history for Baltica in the early Palaeozoic

Palaeomagnetic investigation of Lower Ordovician limestone in the vicinity of St. Petersburg yields a pole position at latitude 34.7°N, longitude 59.1°E ( dp / dm =5.7°/6.4°). A probable primary remanence origin is supported by the presence of a field reversal. The limestone carries one other remanent magnetization component associated with a Mesozoic remagnetization event.
An apparent polar wander path is compiled for Baltica including the new result, ranging in age from Vendian to Cretaceous. Ages of the published Lower to mid-Palaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of Tucker & McKerrow (1995). The new Arenig result is the oldest of a series of Ordovician and Silurian palaeomagnetic pole positions from limestones in the Baltic region. There are no data to constrain apparent polar wander for the Tremadoc, Cambrian and latest Vendian. If the Fen Complex results, previously taken to be Vendian in age ( c . 565 Ma), are reinterpreted as Permian remagnetizations, an Early Ordovician–Cambrian–Vendian cusp in the polar wander path for Baltica is eliminated. The apparent polar wander curve might then traverse directly from poles for Vendian dykes on the Kola peninsula ( c . 580 Ma) towards our new Arenig pole ( c . 480 Ma). The consequence of this change in terms of the motion of Baltica in Cambrian times is to reduce significantly a rotational component of movement.
The new Arenig pole extends knowledge of Ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of Baltica in some published palaeogeographies. Exclusion of the Fen Complex result places Baltica in mid- to high southerly latitudes at the dawn of the Palaeozoic, consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions.     

Age of Tertiary formations on Spitsbergen

Biostratigraphic evidence for the age of Tertiary formations on Spitsbergen is critically reviewed and new evidence from dinoflagellates is presented. The shift in basin geometry and sediment source area observed in the Gilsonryggen Formation is dated as latest Palaeocene, coinciding with the initial opening of the Norwegian Sea at anomaly 24–25 time. An Upper Eocene age is proposed for sediments from Forlandsundet (Sarsbukta), indicating that the Forlandsundet graben was created during the phase of shear movement between Greenland and Spitsbergen before anomaly 13 time.     

Controls on Late Jurassic seismic sequences, Inner Moray Firth, UK North Sea: a critical test of a key segment of Exxon's original global cycle chart

A new interpretation of a comprehensive seismic- and well-database has resulted in the subdivision of the Mesozoic into four, basin-wide, seismo-stratigraphic depositional megasequences in the Inner Moray Firth (IMF) basin. Regional mapping of the megasequences has led to the construction of a new model for Mesozoic-Recent basin development in the IMF. It now appears that extensional tectonics was the main control on the basin's evolution during the Mesozoic. Structural geometries suggest that both the Triassic (Tr) and Rhaetian-mid Oxfordian (Jl) megasequences were controlled by regional broad-based subsidence associated with local extensional fault activity prior to the onset of renewed rifting in the IMF. In contrast, the late Oxfordian-Ryazanian (Berriasian; J2) megasequence developed in response to active extension characterised by half-graben development. Subsequent Early Cretaceous (Kl) deposition appears to have occurred during a further period of broad regional (thermal) subsidence. It is evident that strike-slip movement on the Great Glen Fault played a negligible role in Mesozoic basin development and it appears only to have had a local control on structural styles during its reactivation in the Tertiary as it accommodated regional uplift and basin inversion. Further subdivision of the J2 megasequence was possible using biostratigraphically-controlled seismic reflector terminations and led to the definition of five regional seismo-stratigraphic sequences (J2.1–2.5). Their geometric, thickness and sedimentary facies variations imply that the onlap-defined sequence boundaries within the late Oxfordian-Ryazanian (Berriasian; J2) megasequence were caused by syn-sedimentary extensional tectonism in a fully marine domain, rather than by fluctuations in global sea-level in a basin that was relatively quiescent tectonically. The new interpretation has particular significance in view of the fact that the Late Jurassic of the IMF was used by Exxon workers to construct part of their chart demonstrating relative changes of coastal onlap and global eustatic sea levels. As they considered that data from the area showed ‘no evidence that tectonics caused the unconformities’, the new interpretation casts doubt on the global applicability of the Late Jurassic section of Exxon's original sea-level chart. Furthermore, the study demonstrates that reflector terminations within both tectonically active and/or fully marine sequences should be treated with extreme caution and not be used to define either periods of apparent low-stand or coastal onlap. Indeed, their appearance may sometimes only represent relatively local, auto- and allo-cyclic sedimentary processes such as submarine fan avulsion or channel switching, unrelated to changes in sea-level. Finally, the work shows that care must be taken in the selection of seismic lines used to establish and illustrate the nature of depositional sequences and their geometries if pitfalls are to be avoided.     

Structural evolution and the partitioning of deformation during basin growth and inversion: A case study from the Mizen Basin Celtic Sea,offshore Ireland

The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW-trending half-grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S-oriented extension gave rise to E–W-striking minor normal faults and reactivation of the pre-existing basin bounding faults that propagated upwards as left-stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression-causing basin inversion is dated as Middle Eocene to Miocene by a well-preserved syn-inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near-orthogonal NW–SE dextral strike-slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn-inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.