Tertiary Time Research Articles

Palynology and sequence stratigraphy of the Cretaceous of eastern Venezuela

From Jurassic to Tertiary times, northeastern Venezuela represented the continental shelf of a tectonically passive margin. A dominantly marine Cretaceous sedimentary section, within an overthrusted allochthonous block and with a maximum thickness of 3658 m, is found in the subsurface in this area. Palynomorph recovery from these strata, together with planktonic foraminifera and calcareous nannofossils, indicate an age-range from at least Aptian to Maastrichtian. The palynological assemblages observed exhibit changes with time and environments, which are here related to the sedimentary evolution. Integrated analyses of palynology, lithology, and well logs are the basis for the reconstruction of the sedimentary evolution in the area. The oldest marine sediments in this section correspond to the uppermost part of the Lower Zuni Megacycle and contain a maximum flooding surface correlative with that dated at 111Ma. The rest of the sequence represents a major transgressive-regressive cycle (Upper Zuni) and contains seven sequences correlative with global eustatic cycles. The Turonian transgression dated at 91.5Ma is the most important marine transgression in the entire section and is recognizable in all sections studied, while the Maastrichtian-Paleocene boundary dated at 68Ma is not always clearly recognizable.

Development of Evaporites and the Counterclockwise Rotation of Anatolia, Turkey

In western and central Anatolia, numerous basins developed during Tertiary time. The major basins generally are not connected to one another, and cover large areas containing substantial sedimentary deposits. These basins include the following: Thrace, Gediz, Büyük Menderes, Beypazari, Tuz Gölü, Ulukisla, Sivas, Erzincan, Mus, and Adana, as well as others. Two significant differences can clearly be seen in the basin sequences: (1) the age of evaporites—in central Anatolia, evaporites developed during the Oligocene, whereas in western Anatolia they formed during the late Miocene; and (2) the character of the deposition—in central Anatolia, Oligocene redbed molasse deposits are abundant, whereas in western Anatolia they developed in the late Miocene and the beds are thin and not very abundant. Climate is one of the governing factors of deposition, controlled by elevation and latitude. Therefore, the difference in sequences between central and western Anatolia depends on these two parameters. In this study, paleogeographic latitudes of central and western Anatolia during the Oligocene and post-Oligocene are investigated in light of paleomagnetic data and GPS measurements. These studies reveal that the Anatolian block was subjected to considerable displacement along different latitudes by counterclockwise rotation. The change in climate by rotational displacement of central and western Anatolia over time is the main reason for differences in depositional characteristics and ages of the evaporites.

THE IRISH SEA REGION: WHY THE GENERAL LACK OF EXPLORATION SUCCESS?

With the exception of the prolific East Irish Sea Basin, there have been no hydrocarbon discoveries to date in the other basins in the Irish Sea region. Excellent reservoirs, viable seals and structural traps have been identified in all the basins, suggesting that other factors have prevented the accumulation or preservation of oil and gas. The lack of exploration success in the Larne ‐ Lough Neagh, Solway and Peel, Kish Bank and Central Irish Sea Basins is attributed to a combination of poor preservation of regional source rocks, unfavourable timing of hydrocarbon migration and trap formation and, locally, a lack of seal integrity. Inversion episodes during latest Carboniferous, Late Jurassic‐Early Cretaceous and Early Tertiary times were critical in preventing the optimum conditions necessary for the generation and preservation of oil and gas in these basins.

High thermal maturity in the Lower Saxony Basin: intrusion or deep burial?

The Lower Saxony Basin (LSB) is situated at the southern rim of the Northern Permian Basin, the most important hydrocarbon-bearing province in Europe. In its southern part, areas of high thermal maturation (up to 6% R r) occur which were previously explained as being caused by magmatic intrusions of Turonian to Santonian age that affected Carboniferous to Lower Cretaceous rocks. In this area, 2D numerical basin modelling was carried out in order to reconstruct the temperature histories along two parallel, N–S-trending seismic sections. Along these sections, new data about maturity distribution and temperature history were obtained by vitrinite reflectance measurements and apatite fission track analysis. For the areas with highest maturity values, low coalification gradients were established which agree well with earlier published data on wells further towards the west. This new information does not support previous hypotheses on high heat flows from magmatic intrusions, even if lateral heat transport is taken into account. Instead, comparisons with a recently published map of the subsurface structure of the LSB indicate that maturity distribution may be closely related to major tectonic structures. Deep burial of individual structures of the LSB, which are bordered by deep E–W- to ESE–WNW-trending faults is further suggested by (a) rapidly increasing thicknesses of preserved Cretaceous strata towards the south and (b) structural restoration of one of the seismic sections. To achieve a fit between measured and calculated palaeo-temperature and vitrinite reflectance data, deep burial of Carboniferous source rocks during Cretaceous time has to be assumed. Due to an inversion phase in the early and middle Upper Cretaceous, major amounts of sediment were removed and further uplift occurred in Tertiary times. In contrast, the northern part of the LSB experienced maximum burial and temperatures during Tertiary times.

Taphocoenoses of Arthropods on Saltpan Floodplains of the Oshana Region / Namibia (Arthropoda: Solifugae, Scorpiones, Chilopoda, Diplopoda, Insecta)

A taphocoenosis was found (Steffan 1991) in the saltcrust of the floodplain of a saltpan (Okandeka Pan) north of the Etosha Pan. From the resulting collection, 3 species of Solifugae (3 individuals), 3 spp of Scorpiones (10 ind), 1 sp of Chilopoda (6 ind), 1 sp of Diplopoda (2 ind), and 85 spp of Insecta (580 ind) were identified (A Mursch). All of them were of non-aquatic origin, i.e: allochthonous. The possible ways of active or passive introduction onto the floodplain are discussed for the various groups as well as the probable manner of their selection from the neighbouring biocoenosis. The overrepresentation of reproductives of eusocial insect species (Isoptera: Termitidae, Hodotermitidae; Hymenoptera: Formicidae: Dorylinae) which are on the wing during distinct seasons only, suggests that their embedding in the saltcrust happened soon after this seasonal event. Most of the other subfossilized arthropods might have invaded the floodplain at the same time, either actively or unvoluntarily by air, or they have been washed by rainfloods from the surrounding shoulders of the saltpan onto the floodplain, dead or still alive. There are two embedding zones, an outer one where mainly larger arthropods (Arachnida, Myriapoda, Coleoptera) with strong and heavy exoskeletons are to be found in spots, and an inner embedding zone, where small insects, insect and plant particles are assembled in larger layers. Most of the large and middle-size insects were embedded in the 0,3-1,0 cm thick saltcrust, with their bodies in parallel, and almost parallel to the northern shore-line. This means, that before conservation in the salt-crust they must have floated at the surface of shallow water, must have been drifted by wind and waves towards the northern shore, and with this movement must have been sorted out as by size and weight. With the gradual water decline, they were left on the muddy ground earlier or later, and with further drying and crystallising of the surface layer, became tightly embedded into the salt-crust. A consideration of the actual initial phases of fossilisation reported here, i.e: the manner of selection of species and specimens from the nearby biocoenotic resource, as well as of their various ways of active invasion or passive transportation into the taphotope, and their being sorted out by water movements, might contribute to the understanding of fossilisation processes in terrestrial habitats of the past. To evaluate possible similarities, this actuo-taphocoenosis was partly compared with palaeo-taphocoenoses primarily described from Tertiary times.

The influence of Deccan volcanism on climate: insights from lacustrine intertrappean deposits, Anjar, western India

A sedimentary succession from Anjar sandwiched between basaltic flows records what transpired as continental India passed from Cretaceous to Tertiary times in the immediate vicinity of the Deccan Trap Province. The deposits consist of interlayered peloidal cherty limestones and shales. The shales are dominated by the mineral sepiolite. Chert occurs as three varieties. These include an amorphous cement, microcrystalline quartz and chalcedony. The last two usually fill gastropodal chambers and peloids. These sediments are interpreted as being deposited in an alkaline closed-basin lake that periodically received silica-saturated hydrothermal solutions. The lake in spite of having fluctuating shorelines was perennial. This wave-dominated lake was highly productive biogenically which is evident in the abundance of molluscan shell debris. Based on the sedimentological characteristics the site appears to be located proximal to the palaeo-shoreline. The palaeolatitude position of India during the Maastrichtian would suggest a sub-humid to humid, seasonal climate in Kachchh. A semi-arid climate is inferred on the basis of the lake deposits for Anjar. This apparent contradiction is believed to be due to `mock aridity'. This term is used to explain volcanically influenced climates that mimic characters of xeric semi-arid climates. Similar signatures of semi-aridity in the Indian Peninsula are observed in calcic palaeosols of the contemporaneous Lameta Formation sediments around Jabalpur.

Association of oil source algae in some Tertiary basins, northern Thailand

A coal petrographic study of sediments, including coals, oil shale, and oil source rocks, in the fossil fuel deposits of northern Thailand revealed changes in alginite associations. In the Lower part of these Tertiary deposits, especially in the Fang oilfield, alginite A (a Botryococcus sp.) was the only type of alga found. Later, the association of Botryococcus braunii, Pila algae, thick-walled alginite B, and temperate palynomorphs were recognized in many coalfields, as well as in the middle part of the deposits in the Fang Basin. Their ages were Late Oligocene (?) to Early Miocene. In the upper part of the fossil fuel deposits, alginite B is dominant in many basins, together with Botryococcus-related taxa such as Pila algae, Reinschia and fresh-water-dwelling ferns. In the Mae Sod Basins Reinschia was found to be dominant in the northern part, whereas lamaginite dominated in the south, showing different environmental conditions in different parts of the basin during deposition. These different associations indicate changes in depositional environments in northern Thailand, resulting from climatic and/or sea level changes during Tertiary time.

The petroleum systems of the Southeast Basin and Gulf of Lion (France)

Abstract The Southeast Basin is the thickest onshore French sedimentary basin where up to 10 km of Mesozoic-Cenozoic sediments can locally be found. This basin is surrounded to the east and to the south by two segments of the Alpine Thrust Belt, the Western Alps and the Pyrenees-Provence respectively, and to the west by recently uplifted elements of the Palaeozoic Basement (Massif Central). The development of the basin was related to several stages of subsidence between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two Alpine compressive events in early Tertiary and late Tertiary times. They were separated by an intervening stretching event of Oligocene age which further south led to the opening of the western Mediterranean oceanic basin in Burdigalian times and, as a result, to the formation of the Gulf of Lion passive continental margin. In Neogene times the Palaeozoic basement of the Massif Central was uplifted to approximately 2000 m as the result of an ascending athenospheric plume. A large oil seep near the city of Gabian has been exploited since the beginning of the seventeenth century. Most of the exploration undertaken from 1945 (onshore) and 1965 (offshore) to the present time has, however, been disappointing as no significant oil or gas accumulations have been discovered, despite drilling of about 150 wells. A recent re-assessment of the potential remaining prospectivity of the Southeast Basin and Gulf of Lion basin has been undertaken by IFP. This study has benefited from scientific researches developed within the Integrated Basin Studies programme. This paper focuses on the source rocks and the petroleum system aspects. The review of all potential source rocks indicates that, from a qualitative and quantitative point of view, the best source rocks are located within three specific stratigraphic intervals (Stephanian-Autunian, late Lias and late Eocene-Oligocene). This analytical work allowed the reconstruction of the history of the different petroleum systems from the Jurassic to the present day. Because of the severe tectonic disturbances that these areas have experienced in Tertiary times, we can conclude that the best potential for economical discoveries are within the Gulf of Lion and some sub-basins of the Southeast Basin where subsidence has been active in Neogene times, or, in other words, where the processes of hydrocarbon generation, expulsion and migration can still be active today.

Gondwana: Its shape, size and position from Cambrian toTriassic times

Gondwana and the associated peri-Gondwana fragments cover an area which isabout two-thirds of the area of all continents above the 2000 m bathymetric contour. The Gondwana continents formed by break-up during a geologically short period (Jurassic to Tertiary times), coinciding with the eruption of flood basalts. The uplift caused by associated plumes probably provided the extra stresses necessary for continental separation. It is unclear whether plumes alone were able to fragment Gondwana. By contrast, the smaller, more numerous, peri-Gondwana fragments are generally elongate and their period of formation spans the whole of the Phanerozoic. Their shapes are tentatively attributed to trench suction and associated effects caused by south dipping slabs acting mostly on the northern margin of Gondwana; their migration to retreat of the hinge lines of the subduction zones generally northwards. Gondwana's position during the Cambrian to Triassic interval is uncertain. The most recent apparent polar wander paths (APWPs), based on high quality palaeomagnetic data, are incompatible with the distributions of corals, tillites and the Clarkeia shelly fauna of Silurian age. Somewhat surprisingly, a new APWP based on all available pal˦omagnetic poles is in much better agreement with the fossil and sediment distributions even though many poles have not been magnetically tested. A solution to the ‘Pang˦a problem’ is proposed, in which it is suggested that many of the Gondwana poles for the period 340-200 Ma have been remagnetised. However, all the APWPs give improbable polar positions for some Early Cambrian Moroccan archaeocyathids. Rates of change of pole position for the new modified APWP (‘apparent drift rates’) are similar to post-Triassic rates, implying that plate driving forces have not changed much during the Phanerozoic.

Hydrocarbon-bearing fluid inclusions in the Drau Range (Eastern Alps, Austria): implications for the genesis of Bleiberg-type Pb-Zn deposits

Hydrocarbons in ore minerals of Bleiberg-type Pb-Zn deposits and in authigenic quartz of the Drau Range (Eastern Alps) have been analysed by bulk-sample gas chromatography and fluorescence microscopy. Microthermometric data and the molecular composition of the hydrocarbons indicate a hot (120° to 130°C) pulse of migrating condensate-like hydrocarbons within Late Triassic sediments during Middle Cretaceous to Early Tertiary times. The molecular composition of hydrocarbons enclosed in authigenic quartz corresponds to the composition of hydrocarbons trapped in Bleiberg-type ore minerals, therefore a common fluid source is assumed. The hydrocarbons possibly played an important role as reducing agents in the late stage of sulfide precipitation.

Cu, Mn, and Ag mineralization in the Quebrada Marquesa Quadrangle, Chile: the Talcuna and Arqueros districts

The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper deposits of Lower Cretaceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese mineralization (Mn1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the second one (Mn2) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag) and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bornite, with variable amounts of galena, tetrahedrite (vein-related), chalcocite, sphalerite, pyrite, hematite, digenite and covellite. Alteration processes at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native silver, polybasite, cerargyrite and pyrargyrite-proustite; associated alteration includes strong chloritization of the country rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between 120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result of the complex interplay of two different processes: boiling and fluid mixing; the former is considered to control the major mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization (manto-type stage) developed in response to widespread hydrothermal activity (geothermal field-type) involving basinal brines.

Postorogenic denudation along the late Paleozoic Ouachita trend, south central United States of America: Magnitude and timing constraints from apatite fission track data

The magnitude and timing of synorogenic and postorogenic denudation along fold and thrust belts and their associated foreland basins, of interest because of both tectonic and economic implications, is generally poorly constrained. Along the late Paleozoic Ouachita trend, a thin veneer of Cretaceous strata is preserved above a low‐relief erosional surface that beveled the Ouachita orogen and adjacent foreland areas. This regional erosion surface provides a valuable constraint for interpreting new and previously published apatite fission track (AFT) data obtained from exposed structural highs along the Ouachita trend (Marathon, Llano, Arbuckle, and Benton uplifts). AFT data from sampled localities within the deformation belt (Marathon and Benton uplifts) exhibit younger ages and, generally, longer mean lengths than data from localities on the foreland side of the deformation front (Llano and Arbuckle uplifts). This observation suggests that erosion of the orogen, rather than its extensional collapse, was the primary mechanism responsible for flexural isostatic unloading of the foreland crust. In addition, all samples show evidence for mild reheating following their pre‐Cretaceous cooling history. Specifically, the lack of a significant population of >14.5‐μm tracks in all samples appears to require residence at temperatures of ≥55°±5°C after development of the sub‐Cretaceous erosional surface. This implies that ∼1000 m of Cretaceous‐Paleogene (?) strata were deposited across the entire Ouachita frontal trend and subsequently removed during later Tertiary time. This Tertiary denudation is interpreted to reflect the interplay between regional denudation and isostatic compensation in response to slow (∼10 m/m.y.) epeirogenic uplift of the southern midcontinent and a long‐term drop (∼200 m) in eustatic sealevel during this time.

Southwestern Barents Sea margin: late Mesozoic sedimentary basins and crustal extension

The deep sedimentary basins of the southwestern Barents Sea were formed in response to several late Mesozoic–early Cenozoic tectonic events within the North Atlantic rift zone, which culminated with continental breakup and formation of a mainly sheared margin in early Tertiary times. Due to deteriorating data quality, the development of the margin-bordering Sørvestsnaget Basin is not well known. To improve on this, we use both seismic interpretation and gravity modelling to estimate the depth to the Middle Jurassic (MJ) sequence boundary, which marks the onset of Mesozoic rifting. The horizon represents a first-order contrast in seismic velocity and density, and the gravity field correlates well with its depth of burial. Only one seismic line enables tracing of the MJ from surrounding areas into the Sørvestsnaget Basin, down to a depth of at least 17 km in the northeastern part of the basin. The deep basin is reflected in a general thinning of the crust from 30–36 km within the Barents Sea to 20–24 km in the margin area. The gravity modelling show that the Middle Jurassic–Lower Cretaceous sequences are of comparable thicknesses in the Tromsø and Sørvestsnaget Basins. However, adjacent to the rifted margin segment the deep northern part of the Sørvestsnaget Basin is affected by additional large Late Cretaceous normal faulting and subsidence. These faults also caused additional structuring of the intrabasinal Veslemøy High. Post-Middle Jurassic crustal thinning in the southwestern Barents Sea shows maximum cumulative β-values exceeding 4 within the Tromsø and the northern Sørvestsnaget Basins. The corresponding crustal extension is estimated to 70–85 km in a west to northwest direction. There is no uniform increase in crustal thinning toward the continent–ocean boundary, which we attribute to the transform origin of the margin. However, there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached.

Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution

Mafic dykes of the Antarctic Peninsula continental-margin arc are compositionally diverse, comprising calc-alkaline (dominant), shoshonite, tholeiite, and OIB-like varieties. Their compositions give information about different mafic magma sources tapped during arc evolution. The compositional groups represent partial melts of at least five distinct mantle sources: a low-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (older calc-alkaline); a high-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (shoshonites); a high-ɛNd subduction-modified, spinel-bearing, asthenospheric mantle (younger calc-alkaline); E-MORB-like spinel-bearing asthenosphere depleted by a previous melting event (tholeiites); and within-plate non-subduction modified, garnet- and spinel-bearing, asthenosphere (OIB-like). Slab-derived fluids, subducted sediment, and arc crust also contributed to the magmas. Consideration of previous work in the light of our new compositional and geochronological data enables presentation of a summary of arc evolution. For most of the Cretaceous and Tertiary, the tectonic regime of the Antarctic Peninsula arc was transtensional, and calc-alkaline magmas intruded. An oceanic spreading centre collided with the trench during the Late Cretaceous and induced tectonic changes which caused tapping of different magma sources. A pulse of shoshonitic, tholeiitic, and OIB-like mafic magmatism resulted. Three ridge-trench collisions are now recognized during the history of the arc, in Mid–Late Jurassic, Late Cretaceous, and Early–Mid Tertiary times.

New constraints on plate tectonic puzzle of the SW Pacific

A long‐standing problem in the tectonics of the southwest Pacific has been the lack of closure of the plate circuit linking the Antarctic, Australia, Lord Howe Rise, and Pacific plates in late Cretaceous and early Tertiary time [Molnar et al., 1975]. Avoiding unacceptable overlaps and underlaps in reconstructions of these plates requires invoking relative motion on one or more nebulous plate boundaries somewhere along the plate circuit, such as between East and West Antarctica, within West Antarctica [Stock and Molnar, 1987], or perhaps between the Lord Howe Rise and Challenger Plateau in the Tasman Sea [Lawverand Gahagan, 1994]. This problem is of more than mere local interestsince the motion of the Pacific plate relative to the rest of the globe is constrained through its connection with West Antarctica.

Deformation history of a Mesozoic forearc basin sequence on Alexander Island, Antarctic Peninsula

The Mesozoic Fossil Bluff Group of Alexander Island contains trench-slope and forearc basin deposits that formed during the eastward subduction of oceanic crust beneath the Antarctic Peninsula region. The oldest rocks of the group were deposited in the Early to Middle Jurassic on the upper trench slope, with the forearc basin (sensu stricto) forming in Late Jurassic times. Deposition continued until at least Early Cretaceous (Albian) times. The Fossil Bluff Group was affected by three phases of deformation, as follows: 1. D1 — Movement on a major fault (the LeMay Range Fault) in the accretionary complex during the Middle Jurassic. Structural evidence suggests that the fault had a strike-slip component, and that the dip-slip component varied along strike from normal to reverse. 2. D2 — Basin inversion in the late Early Cretaceous, whilst deposition was still occurring. Fold patterns and fault movement directions indicate that inversion occurred in a dextral transpressional setting. 3. D3 — Late Cretaceous or Tertiary post-inversion extension. This caused the opening of a linear graben, George VI Sound, in a dextral transtensional setting. Phases (1) and (3) can be most easily explained by an oblique subduction model, with SE-directed subduction causing strike-slip motion on large-scale N-S trending structures in both arc and forearc. Dextral transtensional structures, such as those resulting from D3, formed when the forearc was in extension; whereas in a compressional forearc setting, sinistral transpressional structures would have resulted. As basin inversion (D2) occurred by dextral transpression, it cannot be explained by the above geometric model. It is likely, therefore, that the subduction direction was different during the D2 inversion event and that it corresponded to a Pacific-wide mid-Cretaceous compressional event. The D3 transtensional event corresponded with a dramatic decrease in spreading and subduction rates in early Tertiary times.

The subsidence history of the northern Hyblean plateau margin, southeastern Sicily

The southeastern corner of Sicily is dominated by the Hyblean plateau which is composed of carbonate rocks of Triassic to Miocene age. The plateau forms part of the African foreland which collided during Tertiary times with the Calabrian Arc giving rise to the Maghrebian thrust belt. The present study attempts to reconstruct the subsidence history of the northern Hyblean plateau. During the Neogene climax of the plate collision this area has been a centre for widespread basaltic volcanic activity (8-1 Ma) and uplift. At the close of the collisional events (Pliocene-Early Pleistocene) the area under consideration has been affected by subsidence and the progressive consumption of the northern margin of the Hyblean plateau led to the development of the modern foredeep. A quantitative analysis was done by one-dimensional Airy backstripping of seven deep wells located on this crucial part of the Hyblean plateau. The results of the analysis show that the subsidence history of the northern Hyblean plateau area is characterized by four main phases, similar to other domains in the central and eastern Mediterranean basins. These phases are: (a) Neotethyan rifting during Late Triassic-Early Jurassic time; (b) a slow thermal subsidence from Early Jurassic until Late Cretaceous time, leading to the formation of a widespread Mesozoic carbonate platform; (c) compressional phase during Late Cretaceous-Palaeogene time, which resulted in the formation of fold systems; and (d) uplift and subsidence events during the middle Tertiary which are probably the result of the continued collision of the European-African plates. After the Early Pleistocene, unlike other terranes within the Mediterranean, an uplift occurred in the northern Hyblean plateau following the Upper Miocene-Lower Pleistocene massive volcanic activity. This uplift is probably associated with the latest stages of thrusting along the frontal part of the Maghrebian thrust belt.

Structure et mise en place d'une ride océanique dans un contexte de limite de plaques convergentes: le banc de Gorringe (SW Ibérie)

Interpretation of a deep seismic reflection profile (IAM GB2) extending through the SW termination of the Gorringe Bank provides new structural and timing constraints regarding the emplacement of the ridge. Using lateral variations of sedimentary sequences as indicators for vertical movements leads to the conclusion that the ridge initiated during Barremo-Aptian times, in a general extensional setting. During Tertiary times, the northerly wedging-out of the Tortonian nappe along the southern flank of the oceanic ridge is a sign of progressive uplift of the Bank, as a response to the compressional stress induced further south, close to the Africa-Europe converging plate boundary. In the kinematic model proposed here, both the extensional and compressional stages of the Gorringe Bank culmination are thought to be controlled by steep N70 °-oriented crustal-scale discontinuities.

Paleoceanography of coral reefs in the Hawaiian-Emperor Chain – revisited

This paper is a review of the present knowledge of coral reef ecology and paleoecology in the Hawaiian-Emperor Chain during the last 70 Ma. Research on fossil coral deposits throughout the H-E Chain has played a major role in producing information concerning the subsidence, uplift and drowning of individual islands, as well as the paleocirculation of the North Pacific Ocean during Tertiary time. The origin of the Hawaiian Islands and seamounts over the Hawaiian hotspot and their subsequent subsidence and transport by plate motion to the north and northwest are reviewed and new data concerning uplift of the central high Hawaiian Islands caused by lithospheric flexure and the effect of sea level change on the geological evolution of individual islands are presented. The Darwin Point, where atolls drown to form guyots, is redefined in dynamic terms as a function of climate and sea level history. The absence of coral reefs during the first half of Hawaiian history is evidence for a major change in ocean circulation in the north Pacific about 35 million years ago during the Middle Tertiary.

Paleomagnetic evidence for motion of the Hawaiian hotspot during formation of the Emperor seamounts

The bend in the Hawaiian-Emperor chain is the best example of a change in plate motion recorded in a fixed-hotspot frame of reference. Alternatively, the bend might record primarily differences in motion of the Hawaiian hotspot relative to the Pacific lithosphere. New paleomagnetic data from the Emperor chain support the latter view. Althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain, the best available paleomagnetic data suggest Pacific hotspots may have moved at rates comparable to those of lithospheric plates (> 30 mm yr −1) in late Cretaceous to early Tertiary times (81-43 Ma). If correct, this requires a major change in how we view mantle dynamics and the history of plate motions. In the early to mid-Cretaceous (128-95 Ma), hotspots in the Atlantic moved at similar rates. These episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion, such as the past 5 m.y.