Pliocene Time Research Articles

The tectonic evolution of the Norwegian Sea Continental Margin with emphasis on the Vøring and Møre Basins

Abstract The Norwegian Sea continental margin is dominated by two major basins with a very thick Cretaceous basin fill: the Vøring and Møre Basins. The basins are flanked by the uplifted mainland and the Cretaceous Trøndelag Platform to the east and by the Møre and Vøring Marginal Highs capped by Eocene lavas to the west. The tectonic development of the area is controlled by two structural trends: NE-SW and NW-SE. The area has been tectonically active from Carboniferous to Late Pliocene time with the main tectonic phases in Late Palaeozoic, late Mid-Jurassic-Early Cretaceous and Late Cretaceous-Early Tertiary time. The general tectonic development comprised a long period of extension and rifting that ended in Early Eocene time by continental separation, major volcanism and subsequent sea-floor spreading in the Norwegian-Greenland Sea. In Carboniferous to Early Cretaceous time the extensional tectonics were related to within-plate continental rifting. The tectonics of the Late Cretaceous and the Tertiary periods were controlled by the relative movements along plate boundaries. The overall NE-SW structural grain is constituted by faults and basin axes that probably originated in Late Palaeozoic time and were active during all subsequent tectonic phases. The transverse NW-SE trend is expressed as major lineaments that probably reflect the old, Precambrian grain of the basement. These lineaments, two of which are the continuation into the continental crust of major oceanic fracture zones, controlled the tectonic activity throughout Cretaceous and Tertiary time and constitute the boundaries between the major structural provinces of the area. The differentiation into the Cretaceous basins and the bounding platforms and marginal highs started by the late Mid-Jurassic-Early Cretaceous extensional phase. The subsequent Cretaceous subsidence history, where the basin flanks formed by flexuring rather than faulting, resulted in an exceptionally thick basin fill. In the Vøring Basin the Cretaceous development comprised an early thermal subsidence phase and a post-Cenomanian phase of tectonically driven subsidence involving intermittent phases of normal faulting and compression and folding. The Vøring Basin was tectonically active also during Tertiary time with the main phases of strike-slip-compression coinciding with the Alpine orogenies in Late Eocene and Mid-Miocene time. Within the Vøring Basin there is evidence of the formation of a fossil opal A-opal-CT transition and extensive regional marine erosion in Mid-Miocene and Late Pliocene times. In contrast, the Møre Basin was generally tectonically quiet throughout the Cretaceous and Tertiary periods, experiencing mainly continuous subsidence.

Cenozoic Extension in Bulgaria and Northern Greece: the Northern Part of the Aegean Extensional Regime

Abstract The well-known Cenozoic Aegean extensional regime, initiated at c. 25 Ma, thinned the crust so that most of it now lies submerged. North of the western continuation of the North Anatolian Fault the Aegean extensional regime is present in central and southern Bulgaria, northern Greece, Former Yugoslavian Republic (FYR) of Macedonia and eastern Albania. Here the system is exposed on land and offers an opportunity to reconstruct the extensional evolution of the system. The southern Balkan peninsula forms the northern part of the Aegean extensional system; deformation is not as great as in the Aegean, but reconstruction of this part of the extensional regime will provide important constraints on its dynamics. Following a period of arc-normal extension associated with Late Eocene-Late Oligocene magmatism, major lithospheric extension appears have begun between 26 and 21 Ma in northern Greece, involving east-northeast-west-southwest extension east of Mount Olympos, on the Island of Thasos and near Kavala. This period of extension may have been accompanied by a short period of coeval compression north of the arc during Early Miocene time or perhaps a little earlier in the Thrace Basin of northwestern Turkey. Northeast-southwest directed Middle-Late Miocene extension appears to have developed obliquely to the older magmatic arc and migrated northward into southwestern Bulgaria in the Sandanski Graben (and perhaps also into the Mesta and Padesh Grabens) by 16.3–13.6 Ma, and in the Blagoevgrad and Djerman Grabens by c. 9 Ma. Extension in south-western Bulgaria was reorganized by c. 5 Ma and in northern Greece extension on the Strymon Valley detachment fault ended by c. 3.5 Ma, but extension continued on new fault systems. From limited structural and stratigraphic data, it is speculated here that related extension may have also occurred during this time in FYR Macedonia and eastern Albania. This northeast-southwest extension is interpreted to be related to trench roll-back along the northern part of the subduction boundary in the western Hellenides. North-south extension along east-west striking faults in central Bulgaria began only after extension was well underway in northern Greece and the Sandanski Graben of south-western Bulgaria. Within the Sofia Graben, the Sub-Balkan grabens, and grabens to their east, north-south extension began at c. 9 Ma, and may have begun about the same time in the Plovdiv, Zagore and Tundja Grabens of the northern Thracian Basin: north-south extension has continued to the present in these grabens. The cause of the north-south extension is unclear and may be related to trench roll-back along the central part of the subduction zone in the Hellenides, or more local causes of clockwise and counterclockwise rotation of the western Hellenides and western Turkey, respectively. By Late Pliocene time a major erosion surface, the sub-Quaternary surface, was developed over a large area of central Bulgaria creating a major unconformity that marks the beginning of Quaternary deposition in the basinal areas. Many large and small graben-bounding faults in west-central Bulgaria displace this erosion surface and demonstrate the widespread extent of Quaternary north-south extension. North-south extension extended westward, with probably decreasing magnitude, across the older northwest trending graben of southwest Bulgaria (the Simitli and Djerman Grabens) and into eastern FYR Macedonia. During latest Pliocene(?) and Quaternary time, northern Greece developed a complex pattern of northeast-southwest extension associated with northeast to east-west striking right-lateral faults forming transfer faults between more local extensional areas. This system of faults overprinted the older northwest trending extensional faults, such as the Strymon Detachment, and may be related to the propagation of the right-lateral North Anatolian Fault into the north Aegean Sea and formation of parallel faults to its north. These two different tectonic regimes extend into FYR Macedonia, where a third regime of east-west extension in western FYR Macedonia and eastern Albania is present, and where extension may represent the continuation of the east-west extensional regime initiated in Middle-Late Miocene time. Active deformation determined from seismicity and Global Positioning System studies suggest northern Greece, and perhaps southwest Bulgaria and FYR Macedonia, is dominated by north-south extension. This pattern of deformation must have developed as recently as perhaps Late Quaternary time. Except for mountains near the Adriatic Sea all of the mountainous topography in the southern Balkan region may be the result of Miocene-Recent extension.

Detachments and normal faulting in the Marche fold-and-thrust belt (central Apennines, Italy): inferences on fluid migration paths

In the outermost domains of the central Apennines fold-and-thrust belt, the structural architecture of the late Miocene–early Pliocene contractional edifice was controlled by competence contrasts in the Calcareous–Marly sequences of Mesozoic–Tertiary age, and by a different state of lithification of the rock units at the onset of deformation. Field data on relative chronology of outcrop-scale structures (cleavage, veins, faults, folds) are presented for the three largest thrust-ramp anticlines of the Marche fold-and-thrust belt: Monte Gorzano, Acquasanta and Montagna dei Fiori-Montagnone. The data show that the timing and geometry of deformation structures differ for: (1) the lower Calcareous interval of late Triassic–early Cretaceous age (LCI) bounded on top by the intermediate detachment (ID) of the Fucoidi Marls; (2) the upper Calcareous–Marly interval (UCMI) of late Cretaceous–Oligocene age; (3) the uppermost detachment zone (UDZ) of lower–middle Miocene age; (4) the topmost Messinian Flysch sequence (FS). In the UDZ early episodes of deformation are manifested by compaction of a poorly lithified sequence followed by pervasive development of layer-parallel pressure-solution cleavage. Reverse faults ramp obliquely across the stratigraphic sequence, and are coated by multiple overgrowths of calcite fibers. These structures are deformed by large, eastward-verging asymmetric folds with N–S axial trends, and are cut by late generations of reverse faults. Normal faults started to develop in the fold backlimbs during the final stages of shortening, in middle–late Pliocene times. These early normal faults were reactivated during episodes of late Pliocene–Pleistocene extensional downfaulting, and are now superposed on the compressional edifice. The UDZ is interpreted to have temporarily sealed the upward escape of fluids during the initial episodes of shortening. Pervasive interlayer flow in the poorly lithified sequence was responsible for development of broken beds and scaly fabrics, similar to those observed in accretionary prisms. Only in the latest stages of deformation did propagation of discrete faults provide an interconnected pathway for fluid migration, until the final offset of the UDZ. The structural relationships suggest that fluids trapped within the fold cores and sealed by the UDZ were finally driven upwards due to progressive disruption of the thrust belt by late normal faults of late Pliocene to Pleistocene and Holocene age. Large-scale fluid migration along structurally-controlled pathways was enhanced by the strong components of uplift consequent to the final stages of deformation in the Marche fold-and-thrust belt, and was eventually associated with episodes of normal seismic faulting.

Cenozoic evolution of the northern Vøring margin

The northern Voring volcanic margin was initiated by late Campanian–Paleocene rifting, culminating with massive breakup-related igneous activity near the Paleocene-Eocene transition. Paleocene uplift of the central rift zone led to subaerial erosion and deposition in a restricted basin west of the Fles fault complex. The western source area was active toward the end of Eocene time. In the east, the low-relief land surface underwent modest relative uplift, which led to the construction of an early Oligocene delta system on the Trondelag platform. This event was followed by a period of margin subsidence and modest sedimentation until late Pliocene time. Although Miocene and early Pliocene biosiliceous hemipelagic sediments dominate on the outer margin, the influx of ice-rafted detritus records the climatic deterioration and the establishment of glaciers in late Miocene and early Pliocene time. Since ca. 2.6 Ma, ongoing epeirogenic uplift of Fennoscandia and the onset of Northern Hemisphere glaciation increased the erosion potential. A huge prograding wedge of glacial sediments was constructed from ca. 2.6 to 1.0 Ma, when the glacial mode changed from moderate, relatively stable icecaps to distinct glacial-interglacial cycles. The wedge overlies the base of the late Pliocene horizon, which marks pronounced changes in lithology and physical sediment properties, and corresponds to a distinct, regional velocity inversion. The differential glacial sediment load over unconsolidated and mobile biosiliceous oozes may have caused abundant small-offset faulting and diapirism in the western Voring basin.

Seismic stratigraphy of the Miocene–Pleistocene sedimentary basins of the Northern Tyrrhenian Sea and western Tuscany (Italy)

Seismic and stratigraphic data of the inland Volterra Basin and of the Tuscan Shelf (Northern Tyrrhenian Sea) have been analysed to determine the tectono‐sedimentary evolution of this part of the Northern Apennines from the early Miocene (about 20 Ma) to the present. The area is a good example for better understanding the evolution of postcollisional related basins.The study area is characterized by a series of sedimentary basins separated by tectonic ridges. Similar environmental conditions existed both onshore and offshore as indicated by the occurrence of similar seismic units. The units are separated by major unconformities. The cross‐sectional geometries of the deposits of these basins, as defined through seismic reflection profiles, change in a quasi‐regular manner through time and space.Early stages (late Burdigalian to early Tortonian) of evolution of the basins are marked by either flat‐lying deposits, quasi‐uniform in thickness, probably remnants of originally wider and shallow settings, or, in places, by relatively small bowl‐shaped basins. The latter may have been strongly affected by the pre‐existing topography and tectonics, as they developed at or near the leading edges of pre‐Neogene substrate thrusts. These early deposits represent sedimentation during a transitional period from the end of compressional tectonics to the start of an extensional phase and represent a pre‐narrow rift stage of evolution of the region. The subsequent stage of tectonic evolution (late Tortonian to early Messinian), where preserved, is recorded by fault‐bounded triangular‐shaped basins interpreted as half‐grabens. This is one of the periods of major development of narrow rifts in the area. The following stage (late Messinian to Early Pliocene) is marked by variable types of basins, showing wide and deep bowl‐shaped geometries persistent in the offshore, whereas inshore (Volterra Basin) they alternate with half‐graben, synrift deposits. This period thus represents a transitional stage where part of the system is still affected by synrift sedimentation and part is developing into incipient post‐rift conditions. This stage was followed in early to middle Pliocene times by wide bowl‐shaped to blanket‐type deposits both in offshore and in inshore areas, indicating regional post‐rifting conditions. The pre‐, syn‐ and post‐rift stages have followed each other through time and space, starting first in the westernmost offshore area and shifting later toward the east, inshore.

Neogene sedimentary evolution of Baja California in relation to regional tectonics

During the Neogene, the tectonic and sedimentary evolution of the Baja California Peninsula followed four stages: (1) during the early Miocene (22 Ma), the initiation of transform motion between Pacific and North American plates, caused a rapid subsidence in the Continental Borderland Province and in some adjacent areas.This subsidence coincided in time with with a global rise in sea level. At this time, the eastern and southern parts of the peninsula did not show any evidence of subsidence. (2) During the middle Miocene (12 Ma), normal and strike slip faulting migrated eastward, causing subsidence in the northern part of the Gulf of California, where the oldest Tertiary marine sedimentary rocks were deposited. The areas in central Baja California Sur and the central part of the Gulf itself received abundant volcanic deposits related to continental extension. (3) During the late Miocene (8 Ma), the western margin of the Peninsula changed to a slightly compressive regime, while the northern part of the Gulf contained a marine basin with upper bathyal environments. The central area of the Gulf continued receiving abundant volcanic deposits, while the Los Cabos block received marine sedimentation, correlatable with sedimentary units reported from the continental margins in Nayarit, Jalisco and Michoacán. (4) Beginning in the early Pliocene (5 Ma), the present configuration of the Gulf of California developed through right-lateral strike slip and extension in the Gulf itself. Since Pliocene times, the Gulf presents widespread marine sedimentation with deep basins reaching lower bathyal depths.

RESPONSE OF BEETLES TO GLOBAL CHANGE: THE PAST IS A CLUE TO THE FUTURE

Fossils of beetles preserved as heads, pronota, and elytra in Pliocene, Pleistocene, and Holocene sediments are an important resource from which the historical effects of climate change and human activities on insect faunas can be examined. During the Plio-Pleistocene transition ∼2 million years ago, a diverse beetle fauna inhabited Kap Kobenhavn, northernmost Greenland. The beetle fauna inhabited a forested landscape in contrast to the polar desert of today. A significantly warmer climate also may have existed in the interior of Antarctica until Pliocene time, based on a fossil assemblage that includes fossils of beetles. During the last 2 million years of the Quaternary Period, both the northern and southern hemispheres have undergone repeated glaciations in both polar and temperate latitudes. Beetle species have responded by tracking the changing climates. Even though populations were isolated and the conditions theoretically conducive to speciation and extinction, only a few new species have been described and only a few species became extinct. Regional extinctions have been detected but these did not lead to species extinctions. Human activities during the Holocene and within historical times have produced effects in the fossil record as striking as those of climate changes. In the British Isles and Europe, clearance of old growth forests, starting in Neolithic times ∼5000 years ago, led to the reduction in habitat and the extinction or restriction of several species of beetles. Much later in the midnineteenth century, the arrival of Europeans and their cultivation practices modified the insect fauna of the American Midwest so profoundly that the event is as detectable in the fossil record as any ice age climate change. The lesson from the fossil record of insects is that with increasing human disturbance there will be more extinction of insect species.

Lake-level and salinity reconstruction from diatom analyses in Quillagua formation (late Neogene, Central Andean forearc, northern Chile)

A sedimentary and micropaleontological study of the Quillagua Formation provides a detailed paleohydrological reconstruction of the lacustrine system which occupied the present-day hyperarid Quillagua–Llamara fore-arc Basin (Northern Chile) from lattermost Miocene (5.8±0.4 Ma) to Early Pliocene times. Diatom and lithofacies analyses were carried out in two correlated stratigraphic sections of the lacustrine system. The Quebrada Temblor section is located at the southern margin of the ancient lake and is directly influenced by the freshwater inputs of a northward flowing fluvial system draining the Precordillera and Calama regions. The Cerro Mogote section occupies a western marginal location in the northern zone sheltered from direct fluvial inputs from the south but subjected to the activity of the alluvial fan systems of the Coastal Range. A mostly shallow oligosaline waterbody occupied the basin during the interval studied, though with fluctuations in salinity and the extent of the inner, open waters. The southern margin sector — represented by Quebrada Temblor — had, in general terms, a palustrine oligosaline character with almost freshwater conditions during certain periods, which favoured the establishment of semi-permanent to permanent freshwater plumes overlying a saline waterbody. Development of shoreline facies subjected to desiccation events was also characteristic at the top of this section. The innermost shallow lacustrine areas — represented by Cerro Mogote — maintained more homogeneous oligosaline characteristics and more persistent open waters. They were also subjected to freshwater pulses mediated in this case by the activity of the terminal alluvial fan zones. Paleohydrological evolution of the basin was strongly conditioned not only by shifts in the climatic–tectonic system but by variations in the local hydrological parameters. Four hierarchical orders of variability in the lake level of the basin were distinguished both by stratigraphic analysis of lithofacies and from changes undergone by the diatom record. Strong intrasample mixing of diatoms of incompatible salinity spectra and the presence of fine laminated lacustrine facies in some terms define the highest order short-term intra- or inter-annual pulses experienced by the lacustrine system (higher than 6th order). Diatom-based punctuated interruptions of the minor order bathymetrical trends highlight the high frequency variability in the basin (probably 6th order, 0.001–0.01 Ma), while the deepening/shallowing facies defined by the arrangement of the decimetre thick lithological sequences revealed a lower order of variability (5th order, 0.01–0.1 Ma). Combined lithofacies and diatom analyses delineate the lowest order of variability (4th order, 0.1–1 Ma) allowing the reconstruction of two well-established highstand and lowstand situations which implied the existence of a regressive trend between two transgressive trends. This order of variability is related to the interplay of tectonic events in the Calama Basin, and the regional climatic evolution during late Neogene to Pliocene times.

The Gargano Promontory: a Neogene contractional belt within the Adriatic plate

The Gargano Promontory lies on the Adriatic plate between the Dinaride and Apennine fold‐and‐thrust belts and associated foredeeps. Neogene sediments and structures in the Gargano Promontory demonstrate the existence of significant contrac‐tional structures which have not been reported previously. Beginning in early Miocene times, the future Gargano Promontory experienced shortening along NW‐trending, mainly SW‐vergent folds and thrusts. Deformation persisted until the Tortonian, and, most likely, until the Messinian. Limited NW‐directed contraction affected the Promontory probably during Pliocene times. Morphological relief was minimal until the Messinian but from the middle Pliocene onwards, it was substantially similar to the present‐day one partly as a consequence of extension along NE–SW‐trending normal faults. The along‐strike projection of kinematic relationships and quantities observed in the Gargano might call for a re‐interpretation of previously underestimated structures NW and SE of the Promontory.

Post-Gondwana drainage and the development of diamond placers in western South Africa

The post-Gondwana history of the major rivers in the western part of South Africa is important because these rivers were instrumental in the development of diamond placers along the west coast of southern Africa. The evolution of the drainage systems that developed after breakup of west Gondwana can be viewed in three time-slots: the middle to Late Cretaceous, the early to middle Cenozoic, and the late Cenozoic periods. During the middle to Late Cretaceous there were two main river systems draining the interior. The one in the south, also referred to as the Karoo River, had its source in the present upper Orange/Vaal drainage basin and its outlet was at the present Olifants River mouth. The second and more northerly system, also known as the Kalahari River, drained southern Botswana and Namibia and entered the Atlantic Ocean via the lower Orange River. Erosion dominated the period immediately after breakup of west Gondwana and most of the diamonds released during erosion of Cretaceous kimberlites in central South Africa were transported by the Karoo River to the coast. By early Cenozoic times, the lower Kalahari River had captured the upper part of the Karoo River and the broad configuration of the present Orange River network was established. This capture and northerly shift of the Orange River, on the newly exhumed pre-Karoo surface, was the result of an accelerated uplift of the southern and eastern subcontinental margins ca. 100 to 80 Ma. During the early and middle Cenozoic, the climate was arid to semiarid. This resulted in a substantial reduction in erosion rates and hence few diamonds were released from the primary bodies during that time. Late Cenozoic fluvial gravels, however, dated as either middle Miocene or Plio-Pleistocene, contain diamonds that were reworked out of older Tertiary fluvial deposits. Sediments at the base of the Koa Valley and in the upper terraces in the Sak Valley formed the Koa River, a major tributary of the Orange River during the Miocene, and drained most of the area previously occupied by the lower Karoo River. The Koa River thus reworked diamonds trapped in the Cretaceous Karoo River deposits or terraces. Younger sediments of the Carnarvon Leegte were never part of the Koa system. In fact, the Sak River captured the upper Koa River by late Pliocene times and the Plio-Pleistocene lower terraces in the Sak Valley and the paleo-Carnarvon Leegte joined as the paleo-Hartbees River--another major tributary of the Orange in the Plio-Pleistocene. Although climatic changes were the major controls that initiated the alluvial pulses during the Cenozoic, asymmetric uplift of the subcontinent was ultimately responsible for the northwesterly shift of the Orange River.

Evolution and geochemical signatures in a Neogene forearc evaporitic basin: the Salar Grande (Central Andes of Chile)

The Salar Grande is a 45-km-long (N–S axis), 4–5-km-wide, fault-bounded (pull-apart) Neogene forearc evaporitic basin, located in the Cordillera de la Costa of northern Chile whose sedimentary record is composed almost exclusively of a massive halite salt body. Underground waters coming from the east (now the Precordillera and Altiplano) were progressively enriched in solutes by interaction with volcanic rocks. These fluids drained into a lacustrine system located in the Depresión Central (in the Llamara–Quillagua area) and thick sequences of diatomites, carbonates, evaporites and clastic sediments were deposited. These lacustrine areas eventually dried out and became a salar with anhydrite and halite. During this stage (Late Miocene–Pliocene), evolved brines of the Llamara–Quillagua area migrated eastwards through structural paths, reaching the Salar Grande basin which acted as a final sink. A proof of this connection is the anhydrite level that links the western Llamara and southeastern Salar Grande areas. The accessory minerals and geochemical signatures in the rock salt are a record of the inputs arriving to the former lake and reflect variations in climate, and in tectonic and volcanic activity. The arrangement of halite textures along the sequence shows an evolution from a very shallow ephemeral saline lake (some cm–dm deep on average) to a salar where interstitial processes controlled by phreatic brines dominate. This evolution is coherent with a slight increase in the terrigenous content of the rock salt, and documents the increasing aridity of the climate as a response to the tectonic uplift of the Andean Ranges. In Pliocene times pore brines were definitively lost as a response to the downfall of the water table generated by the beginning of the exorheism due to the opening of the Loa River canyon towards the sea. The aim of this paper is to describe the Salar Grande through the study of its geological setting and its salt record. A detailed description of the salar will enable us to reach valuable conclusions about environmental conditions in the area during the Neogene, prior to the opening of the hydrologic system to the Pacific Ocean.

Evidence from the Gediz graben for episodic two-stage extension in western Turkey

Western Turkey falls within a wide belt of NNE–SSW-directed, active continental extension, generally similar to the Basin and Range Province of the USA. It comprises a zone of WNW–ESE-trending major grabens. Detailed study of the Gediz graben reveals two contrasting infills that represent two distinct extensional stages, separated by a short phase of compression. The older infill consists of an 800 m thick, folded and exhumed continental sedimentary sequence with intercalated calc-alkaline volcanics. It accumulated in a basin formed in the northern hanging wall of a detachment fault during Miocene–early Pliocene times. The younger infill rests on the older infill with angular unconformity and consists of about 170 m of undeformed, terraced continental sediments and basaltic lavas. It accumulated during Plio-Quaternary times in an asymmetric graben bounded by step-like normal faults. This later extension was probably triggered by the commencement of sea-floor spreading along the Red Sea in early Pliocene times and has persisted to the present. Almost all the grabens in western Turkey are best explained by this episodic, two-stage graben model with an intervening phase of short-term compression, which differs from the progressive evolution inferred for the Basin and Range Province of the USA.

Depth and modes of Pliocene–Pleistocene crustal extension of the Apennines (Italy)

Since early Pliocene times the Apenninic chain has been dissected by normal faults propagating towards the Adriatic foreland. In the Tyrrhenian Sea extension involved deep crustal sections, whereas in the ‘Central Apennines Downfaulted Area’ it affected the shallow crust. The Tyrrhenian back‐arc domain is connected to the overall flexural retreat of the Adriatic–Apulia plate in front of the Apenninic collisional wedge. In the outer Apenninic belt thin‐skinned delamination and gravitational collapse occurred in the hanging wall of a thickened wedge, overthrusting the uplifted, buoyant crust of the Apulia foreland. Differential sinking velocity of the foreland plate results from the inherited competence contrast between the rigid Gargano–Apulia carbonate platform to the south, and the low‐competence lithology of the pelagic sequence of the Adriatic basin to the north. During late Messinian–early Pliocene times this palaeogeographical boundary acted as a lithospheric tear, separating segments of the Apulia plate subjected to different subduction modes.

X chromosome evidence for ancient human histories.

Diverse African and non-African samples of the X-linked PDHA1 (pyruvate dehydrogenase E1 alpha subunit) locus revealed a fixed DNA sequence difference between the two sample groups. The age of onset of population subdivision appears to be about 200 thousand years ago. This predates the earliest modern human fossils, suggesting the transformation to modern humans occurred in a subdivided population. The base of the PDHA1 gene tree is relatively ancient, with an estimated age of 1.86 million years, a late Pliocene time associated with early species of Homo. PDHA1 revealed very low variation among non-Africans, but in other respects the data are consistent with reports from other X-linked and autosomal haplotype data sets. Like these other genes, but in conflict with microsatellite and mitochondrial data, PDHA1 does not show evidence of human population expansion.

The Sinai subplate and tectonic evolution of the northern Red Sea region

Although the precise boundaries and kinematics of the Sinai subplate are still doubtful, it has a significant role in the tectonic evolution of the northern Red Sea region. On the basis of earthquake distribution, the Sinai region can be considered as a subplate partially separated from the African plate by the Suez rift. The relative motion between Africa, Sinai and Arabia is the main source generating the present-day earthquake activity in the Gulf of Suez and the Gulf of Aqaba regions. According to geological observations, the southern segment of the Dead Sea fault system can be characterized by a left-lateral displacement of about 107km since the Middle Miocene, in contrast to the northern segment where only 25 to 35km offset can be inferred. We think that along the southern segment the total displacement was 72km until the late Miocene (10Ma). The earthquake activity is strongly reduced along the northern segment of the Dead Sea fault segment. Therefore, we suggest that the northern part (Yammouneh fault) evolves through initial cracking of the crust due to build-up of stress since the Pliocene time (5Ma) and propagates northward into Lebanon and Syria. This last 5 million years is the period when the southern and northern segments became linked and formed a single fault system with a new displacement of 35km. According to the proposed model the predicted opening pole of the Red Sea is near 34.0̊N, 22.0̊E with an angle of total rotation of 3.4̊ since the early miocene, providing a 0.82cm/a opening rate in the northern Red Sea. We suggest that the Dead Sea strike-slip fault was active since Middle Miocene time (15Ma) with a slip rate of 0.72cm/a to provide a total displacement of about 107km. This strike slip motion occured about an Euler pole near 33.0̊N, 21.0̊E with a rotation angle of about 3.0̊. It can be inferred from the proximity of the pole and angle of rotations for the Red Sea and Dead Sea fault that more than 85% of the motion has been accommodated on the Gulf of Aqaba and the Dead Sea fault and less than 15% in the Gulf of Suez. This model predicts a normal extensional motion in the Gulf of Suez with a minor left-lateral strike-slip component. We expect the pole of this motion to be at 31.0̊N, 29.0̊E, offshore of Alamein city about 320 km west of the Nile Delta. The rate of motion through the last 15Ma (Middle Miocene) is about 0.1 cm/a and the angle of rotation is 0.9̊. During this period the total opening of the Suez rift is 15 km while the rest of the motion (45 km) occured mainly through the first phase of the development before the Middle Miocene.

Neogene development of the onland part of the forearc in northern Wairarapa, North Island, New Zealand: A synthesis

Northern Wairarapa, North Island, New Zealand, lies in the onland part of the forearc of the Hikurangi margin, which formed since early Neogene time when the Pacific plate commenced westward subduction beneath the Australian plate. The onland part of the forearc is now 75 km wide, and there are two dextral fault zones: the Wellington Fault and the Alfredton‐Pleckville Faults. However, in early Miocene time, a zone of dextral faulting lay adjacent to the inboard part of the trench slope break. At various times during its development, the onland part of the forearc comprised the following units: (1) Coastal Block (outboard); (2) Tawhero Basin; (3) Forearc Platform; (4) Mt Bowen Basin; (5) Mauriceville Ridge; (6) Eketahuna Basin, a successor basin with two subunits; and (7) Axial Ranges (Tararua Range) (inboard). However, currently only the Coastal Block, the widespread Eketahuna Basin (comprising units 2, 3, 4, 5 and 6), and the Axial Range units are developed. At various times the following NNE‐ and NE‐trending faults bounded the units: Tinui (outboard), Waihoki, Mauriceville, Pleckville‐Hastwells, and Wellington (inboard). The Coastal Block developed in early Miocene time in an area where there is now a gradient change in the subduction zone. In post‐Waitakian time, c. 22.4 Ma, the Coastal Block and the Forearc Platform (which lies inboard of the Coastal unit) were commonly uplifted and shed sediment into the c. 8 km wide Tawhero Basin which lay between them. Oblique subduction probably commenced at c. 16.7 Ma, causing dextral transpression in the Coastal Block and the Tawhero Basin. At c. 11.3 Ma, the Forearc Platform of the mapped area was submerged by the sea. Part of the inboard part of the forearc, destined to become the Mt Bowen Basin, was hilly or mountainous before c. 8 Ma, when it represented a late Miocene axial range, but it was then downwarped, thus increasing the width of the forearc in North Wairarapa. At c. 7 Ma the Wellington Fault was active whereas the Waihoki Fault became inactive at c. 6.6 Ma. During early Pliocene time, the largely bathyal Eketahuna Group (max. 1.5 km thick) was deposited in the 30 km wide NNE‐trending Eketahuna Basin. Subsequently, probable underplating of the onland part of the forearc occurred at c. 3.7 Ma and c. 1.6 Ma, causing widespread uplift. Tectonics similar to that of the present commenced at c. 3.7 Ma or somewhat earlier. The Tawhero Basin was shortened at least 9% in the period from early Tongaporutuan (11.3 Ma) to latest Kapitean (5.2 Ma) time, due to increasing compression at that time. In the Forearc Platform there was at least 10% crustal shortening (shown by the development of the Spring Hill Anticline) during the same period. However, crustal shortening was greatest (>33%) in the 8 km wide belt adjoining the eastern side of the Wellington Fault (since c. 7 Ma).

Late Cenozoic emergence of the islands of the northern Lau-Colville Ridge, southwest Pacific

Abstract The Lau-Colville Ridge is part of an island arc abandoned during Pliocene time as a result of development of the back-arc Lau Basin. Throughout much of Plio-Pleistocene time, the ridge subsided, and its volcanic peaks were submerged and cloaked with (reef) limestone. Uplift, mostly during Pleistocene time, caused the northern part of the ridge to emerge by at least 315m. Islands along the northern Lau-Colville Ridge exhibit ten well-defined terraces above c. 10m whose ages are constrained by those of anomalously young lavas and avian phosphates. Low-level emerged shorelines may be all of Holocene age and exhibit a recurrence interval of coseismic uplift events of 1500 years.

Magnetostratigraphic correlation of Miocene regression-and-transgression boundaries in central Honshu, Japan.

Regression-and-transgression boundaries (RTBs) were defined in Miocene strata of the Yatsuo area (RTBs Y1, Y2, and Y3) in a backarc basin, the Mizunami area (RTBs M1, M2, and M3) in an intra-arc basin, and the Kakegawa area (RTBs K1 and K2) in a forearc basin, across central Honshu, Japan. The sedimentary successions of the Yatsuo and Mizunami areas consist of coastal-shelf deposits, and the RTBs are recorded as unconformities or ravinement surfaces. In the Kakegawa area, the middle of a turbidite section (RTB K1) and an erosional surface (RTB K2) in thick mudstone might represent maximum regressions.The recognized RTBs were formed in Miocene time, except for RTB M3 in Pliocene time. The Miocene RTBs can be correlated within four time zones by means of magnetostratigraphy ; Zone Jmi1 (RTB K1) in Chron C5Dn (17.62-17.28 Ma), Zone Jmi2 (RTBs Y1, M1, and K2) in Chron C5Br (16.01-15.16 Ma), Zone Jmi3 (RTBs Y2 and M2) in Subchron C5Bn1r (15.03-14.89 Ma), and Zone Jmi4 (RTB Y3) between 14.89 and 12.3±1.9 Ma. The synchronicities of the RTBs in Zones Jmi2 and Jmi3 in the different tectonic settings suggest that the RTBs were formed by regional sea-level changes.

新潟・長野県境富倉地域における中新～鮮新統の堆積過程

The turbidite of the Kamikozawa Formation in the Tomikura region was deposited in a NE-SSW trending trough-basin at the west flank of the Tomikura Anticline and in a channel-like trough basin at the east flank differentiated by tectonic movement from latest Miocene to Pliocene time. In the eastern channel-like trough basin, andesite clasts were supplied laterally from the Kato Mountains, south of the Tomikura area, by tectonic uplift of asement rocks, and channel-fill deposits were developed. In the trough-like basin at the west flank, turbidite deposits were formed by sheet flow turbidity currents supplied longitudinally from the Minochi region southwest of the Tomikura region. The Tomikura region was a junction of a NNE-SSW trending trough continuous from the Minochi region to the Higashikubiki region and a channel-like trough connected from the Kato Mountains to the south.

Origin of overpressures on the Halten Terrace, offshore mid-Norway: the potential role of mechanical compaction, pressure transfer and stress

Abstract The Halten Terrace, a structural element on the mid-Norwegian margin, is characterized by distinct spatial variations in subsurface fluid pressure. Jurassic formations on the western part of the Halten Terrace are highly overpressured (> 30 MPa), whereas the same formations have fluid pressures close to hydrostatic in the central and eastern parts of the terrace. The cretaceous formations are moderately overpressured in the whole area. The porosities in the overpressured middle Jurassic formations and lower Cretaceous shales are only slightly influenced by the present-day overpressures, suggesting that most of the overpressure development was recent. Overpressure generation as a result of mechanical compaction, induced by the weight of the Plio-Pleistocene sediments, is not sufficient to explain the overpressure magnitudes in the Jurassic and Cretaceous formations. Results from forward modelling of mechanical compaction suggest that the deep Rås Basin adjacent to the Halten Terrace has been highly overpressured since Cretaceous time. Pressure transfer from this basin to the western part of the Halten Terrace is therefore a possible explanation for the observed overpressures. Migration of the overpressured fluids may have occurred through the Klakk Fault Complex separating the basin from the terrace, during an event related to a basinal stress reorientation in early Pliocene time.