Late Pliocene Time Research Articles

The role of salt weathering in the origin of the Qattara Depression, Western Desert, Egypt

Field studies and petrographic examinations of core samples and of the bedrock of the floor of the Qattara Depression, Egypt, indicate that salt weathering predominates in its western part in marked contrast to its eastern part. The eastern part of the depression is covered with more than 120-cm-thick, moist sands with sporadic occurrence of halite and gypsum due to the low salinity of the groundwater table. At the western part of the depression, the strongly saline, sodium chloride nature of the groundwater table favors crystallization of halite (and sometimes gypsum) at or near the surface of the outcropping bedrock of the Moghra clastics and/or Dabaa shale. Crystallization of halite and/or gypsum generates increased pressure that leads to mechanical disintegration of the bedrock into fine-grained debris. Features related to disintegration include blistering of the rock surface, splitting, spalling and/or granular disintegration. Alternation of dry and wet cycles favor halite crystallization, mechanical disintegration of the outcropping bedrock and dissolution of the halite cement, which exposes fine-grained debris to wind deflation. Removal of the debris from the floor of the depression leads to the accumulation of lunettes and other dunes in the downwind direction. Therefore, salt weathering provides fine-grained debris that are easily removed by deflation, which accounts for the topographically lower level of the western part of the depression (134 m below sea level (b.s.l.)). In contrast, the presence of moist sediments at the eastern part of the depression inhibits deflation and encourages sedimentation by adhesion of wind-blown sand to the damp surface of the sabkha at an elevation of 45 m below sea level. The disintegration of the bedrock of the Qattara Depression by salt weathering has been in effect since the onset of aridity in northern Egypt in Quaternary time. Whereas the initial excavation of the depression started in Late Miocene or Pliocene time by fluvial erosion, karstic process, mass-wasting and wind deflation.

Miocene–Pleistocene tectono-sedimentary evolution of Bahı́a Concepción region, Baja California Sur (México)

Bahı́a Concepción is one of the largest fault-bound bays in the Gulf of California. It is one of the area's best examples of an extensional basin, and an accommodation zone related to the Late Miocene extension in the Gulf of California region. Extensional tectonics in the Gulf region initiated from middle to early Late Miocene, in a simple east–west manner. The units within the Comondú Group are tilted between 14 and 45° in opposite directions (E/W), as a direct result of a single main extensional episode. This event produced subsidence that created the depocenters for nearshore marine basins. The oldest sedimentary units present in the region are assigned to the Late Miocene–early Pliocene Tirabuzón Formation. Up-faulted granodiorite basement occurs on the Peninsula Concepción, and at Punta San Antonio as a direct result of the Late Miocene extensional episode. Extension on the Bahı́a Concepción zone was responsible for development of a divided half-graben structure first flooded in Late Pliocene time. The tectono-sedimentary evolution of Bahı́a Concepción is recorded by three stratigraphic stages: (1) pre-rift strata represented by the Comondú Group, (2) a syn-rift unconformity, and (3) a post-rift strata represented by the Late Miocene to Pliocene flat laying sedimentary units. This triad of stratigraphic stages clearly varies from other basins along the margin of the Gulf of California. Upper Pleistocene terrace deposits generally conform to the 6–12 m elevation regionally associated with substage 5e. Their uniformity in elevation inside and outside Bahı́a Concepción indicates that tectonic uplift was locked in step throughout the immediate region at least since that time.

Late Pliocene sedimentation in Lake Baikal: implications for climatic and tectonic change in SE Siberia

Within the framework of the Baikal Drilling Project (BDP), a 192 m long sediment core (BDP-96-1) was recovered from the Academician Ridge, a submerged topographic high between the North and Central Basins of Lake Baikal. Sedimentological, clay mineralogical and geochemical investigations were carried out on the core interval between 90 and 124 m depth, corresponding to ca. 2.4–3.4 Ma. The aim was to reconstruct the climatic and tectonic history of the continental region during the intensification of Northern Hemisphere glaciation in Late Pliocene time. A major climate change occurred in the Lake Baikal area at about 2.65 Ma. Enhanced physical weathering in the catchment, mirrored in the illite to smectite ratio, and temporarily reduced bioproduction in the lake, reflected by the diatom abundance, evidence a change towards a colder and more arid climate, probably associated with an intensification of the Siberian High. In addition, the coincident onset of distinct fluctuations in these parameters and in the Zr/Al ratio suggests the beginning of the Late Cenozoic high amplitude climate cycles at about 2.65 Ma. Fluctuations in the Zr/Al ratio are traced back to changes in the aeolian input, with high values in warmer, more humid phases due to a weaker Siberian High. Assuming that the sand content in the sediment reflects tectonic pulses, the Lake Baikal area was tectonically active during the entire investigated period, but in particular around 2.65 Ma. Tectonic movements have likely led to a gradual catchment change since about 3.15 Ma from the western towards the eastern lake surroundings, as indicated in the geochemistry and clay mineralogy of the sediments. The strong coincidence between tectonic and climatic changes in the Baikal area hints at the Himalayan uplift being one of the triggers for the Northern Hemisphere Glaciation.

Evolution of the Sardinia Channel (Western Mediterranean): new constraints from a diving survey on Cornacya seamount off SE Sardinia

Sarcya 1 dive explored a previously unknown 12 My old submerged volcano, labelled Cornacya. A well developed fracturation is characterised by the following directions: N 170 to N–S, N 20 to N 40, N 90 to N 120, N 50 to N 70, which corresponds to the fracturation pattern of the Sardinian margin. The sampled lavas exhibit features of shoshonitic suites of intermediate composition and include amphibole-and mica-bearing lamprophyric xenoliths which are geochemically similar to Ti-poor lamproites. Mica compositions reflect chemical exchanges between the lamprophyre and its shoshonitic host rock suggesting their simultaneous emplacement. Nd compositions of the Cornacya K-rich suite indicate that continental crust was largely involved in the genesis of these rocks. The spatial association of the lamprophyre with the shoshonitic rocks is geochemically similar to K-rich and TiO 2-poor igneous suites, emplaced in post-collisional settings. Among shoshonitic rocks, sample SAR 1-01 has been dated at 12.6±0.3 My using the 40Ar/ 39Ar method with a laser microprobe on single grains. The age of the Cornacya shoshonitic suite is similar to that of the Sisco lamprophyre from Corsica, which similarly is located on the western margin of the Tyrrhenian Sea. Thus, the Cornacya shoshonitic rocks and their lamprophyric xenolith and the Sisco lamprophyre could represent post-collisional suites emplaced during the lithospheric extension of the Corsica–Sardinia block, just after its rotation and before the Tyrrhenian sea opening. Drilling on the Sardinia margin (ODP Leg 107) shows that the upper levels of the present day margin (Hole 654) suffered tectonic subsidence before the lower part (Hole 652). The structure of this lower part is interpreted as the result of an eastward migration of the extension during Late Miocene and Early Pliocene times. Data of Cornacya volcano are in good agreement with this model and provide good chronological constraints for the beginning of the phenomenon.

Late Miocene to Pliocene stratigraphic evolution of northeast Carmen Island, Gulf of California: implications for oblique-rifting tectonics

Abstract This paper describes a thick section of upper Miocene(?) to middle Pliocene marine sedimentary rocks exposed at Punta Perico, northeastern Carmen Island, in the southern Gulf of California. These strata overlie Miocene volcanic rocks along a low-angle unconformity and have a total thickness of ∼1100 m. The section contains the following units: (1) lower conglomerate (∼750 m thick) representing submarine debris flows and grain flows; (2) conglomerate and sandstone (∼90–160 m) deposited by gravelly grain flows and sandy turbidity currents; (3) marlstone and mudstone (∼120 m) with benthic forams that record bathyal water depths (400–500 m) and an age of ∼3.5–3.1 Ma; (4) dacite breccia and boulder beds (∼20 m) emplaced by submarine avalanches and debris flows and (5) stratified conglomerate and bioclastic limestone (≧80 m) deposited by traction currents in a shallow shelf environment. Conjugate syn-sedimentary faults, deformation bands, and growth structures are recognized within a 250-m-wide belt adjacent to a large N-striking, W-dipping normal fault that bounds the eastern margin of the Pliocene section, indicating that the eastern normal fault was active during deposition of at least the upper ∼300 m of the dipping section. Considering the thickness of the two units below the marlstone (∼900 m) and assuming a range of possible sediment-accumulation rates (0.2–1.0 m/ka), we postulate that deposition of the lower conglomerate was initiated in late Miocene or early Pliocene time (∼8–4 Ma), possibly coincident with initial opening of the Gulf of California. Deposition of the marlstone unit above a probable unconformity represents a major change in basinal tectonics at ∼3.5–3.1 Ma, which is about the time when seafloor spreading and transform faulting were initiated in the Gulf of California. These tentative correlations suggest that the Baja California peninsula was structurally and mechanically linked to the deep Gulf during late Miocene to middle Pliocene time.

Neogene to Quaternary sedimentary basins in the south Adriatic (Central Mediterranean): Foredeeps and lithospheric buckling

Up to several kilometers deep sedimentary basins of Neogene to Quaternary age are found in the south Adriatic between the Apennines and the Dinarides/Albanides. They are the Apennines foredeep, the Central Adriatic Basin, and the South Adriatic Basin. Two regional seismic lines, 260 and 170 km long, across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development. The Apennine foredeep imaged along the lines, formed in middle to late Pliocene times through a rapid westward tilting of the basin floor. A paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations. The Central and South Adriatic Basins formed in Neogene to Quaternary times and are both characterized by strong subsidence in their central parts, gradually diminishing toward the edges in the SW and NE. Depocenters did not shift laterally through time. Subsidence rates increase through time, and subsidence continued also following the end of main shortening episodes in the Dinarides/Albanides. The Central and South Adriatic Basins form two crustal‐scale synclines with subsidence concentrated in their central parts. Basins' geometries and subsidence patterns indicate that the Adriatic crust has undergone (episodes of) buckling since Miocene times. Wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium.

Palaeo-oceanographical implications of Early–Middle Miocene subtropical ostracod faunas from the continental shelf of the SE Atlantic Ocean

Early (Aquitanian and Burdigalian) and Middle (Langhian) Miocene marine Ostracoda were studied from the continental shelf off the Orange River, SW Africa. Eighty-one species belonging to 44 genera were recognised. Comparison with contemporary East African faunas indicate strong similarities (Simpson coefficient of generic affinity, SC=38%). This suggests that the shelf off the Orange River at that time experienced sub-tropical conditions, with water temperatures >20°C. In contrast, there were barriers to faunal exchange with areas farther north along the west African shelf (SC for Gabon=24%). Previously published ODP data suggest that by Late Miocene time, significant upwelling of cool water had begun over the northern Benguela region of the Walvis Ridge Abutment, and by Late Pliocene time intense frontal turbulence was established in the southern Benguela region. It is postulated that these phenomena isolated the Orange shelf ostracod faunas from further influence by the east coast Agulhas Current. A comparison of the Orange shelf ostracods with those from adjacent SE Atlantic deep-water regimes, indicates no simultaneous faunal changes in response to major Neogene palaeo-oceanographic events.

Sedimentologic and geomorphic evidence for seesaw subsidence of the Santo Domingo accommodation-zone basin, Rio Grande rift, New Mexico

Basin analysis of facies patterns and basin geomorphology reveals a complex subsidence pattern for part of the Rio Grande rift in north-central New Mexico, United States. The Santo Domingo basin study site is located in the accommodation zone between the east-tilted northern Albuquerque basin and the west-tilted Espanola basin half-graben. Upper Miocene through lower Pleistocene basin-fill sediment records a longitudinal, south-flowing, ancestral Rio Grande and flanking piedmont stream systems. Chronology of deposition is provided by 40Ar/39Ar geochronological study of lava flows and pyroclastic deposits interbedded with the sediment. Down-to-the-east faults concentrated in the western basin illustrate increasing displacement toward the north and merge with structures forming the western margin of the Espanola basin. Down-to-the-west faults in the central and eastern basin exhibit southward-increasing displacement and become the principal structures along the eastern margin of the northern Albuquerque basin. The latitudinal overlap of these fault systems in the Santo Domingo basin gives the appearance of a symmetrical graben with anticlinal bedding attitudes. Analysis of the distribution of sedimentary facies, high-level geomorphic surfaces, and Pleistocene terraces indicates, however, that the basin subsided in a seesaw fashion rather than as a symmetrical graben. During the late Miocene and early Pliocene, the course of the ancestral Rio Grande was deflected to the west, suggesting strong westward tilting of the basin. In late Pliocene and Pleistocene time, however, eastward tilting brought the river into the eastern basin. At that time, an east- sloping pediment was eroded across west- dipping strata in the western basin. Pediment gravel and tuff present as unconformity-bounded strata in the western basin correlate with continuously aggraded conformable basin-fill strata to the east. A return to westward tilting since middle Pleistocene time is suggested by unpaired terraces consistent with net westward migration of the Rio Grande, lack of post–middle Pleistocene motion on faults in the eastern basin, and numerous fault displacements of the pediment gravel in the western basin.

Ordovician erratic sponges from Gotland, Sweden

Erratic Ordovician sponges (Porifera) from Gotland in the collections of the Swedish Museum of Natural History in Stockholm and the Natural Museum in Visby were subject of an inventory, the results of which are presented in this paper. The sponges are part of an extensive and diverse Upper Ordovician sponge fauna that lived partly in tropical shelf areas and partly in a continental basin of the palaeocontinent Baltica. As a result of their transportation most of these sponges are isolated silicified bodies without adhering sediment. Since no major Ordovician sponge fauna has been found in solid rocks of Baltoscandia, the source area of these erratics is unknown. The sponges from Gotland were deposited during the Weichselian glaciation. They have been compared with erratic Ordovician sponges from Germany, The Netherlands, and Poland by a quantitative method of research. Generic composition of the sponge association from Gotland is identical to that from Sadewitz/Sawidowice (Poland), which was deposited during the Saalian glaciation. There is also a similarity to the majority of sponges in the Dutch/German border region that were deposited in glaciofluvial sediments during the Menapian (Early Pleistocene). The characteristics of the sponges from the Lausitz area (Germany) and from the Isle of Sylt (Germany), which were deposited in Middle Miocene and Late Pliocene time, respectively, are different. A supposed bipartition of these associations is discussed and related to the palaeogeography and palaeoecology in the Late Ordovician. Extinction of the Baltic sponge fauna is possibly related to the glaciations during the Hirnantian (Late Ordovician). The importance of this fossil sponge fauna is emphasized.

Palaeomagnetism of Late Miocene to Quaternary volcanics from the eastern segment of the Trans-Mexican Volcanic Belt

A systematic palaeomagnetic study in the eastern part of the Trans-Mexican Volcanic Belt includes 39 Miocene, Pliocene and Quaternary volcanic rocks in the southeastern Mexico Basin (Sierra Nevada and Sierra de Rı́o Frı́o), the Altiplano area, and the Palma Sola Massif. A total of 430 samples have been selectively demagnetized using mostly alternating field demagnetizing methods, supplemented by thermal analyses. Most characteristic remanences are carried by low-Ti titanomagnetites, with occasional titanohematites or slightly maghemitized low-Ti titanomagnetites, of similar direction. Seven sites were discarded because they presented intermediate directions, hydrothermal alteration or were remagnetized by lightning strikes. The mean directions of 32 sites, together with 24 sites from Sierra de las Cruces in the western Mexico basin, indicate rocks older than 2 Ma are rotated some 10° counterclockwise with respect to Quaternary rocks, whereas there is no rotational difference between Miocene and Pliocene rocks. Statistical analyses between different regrouped populations confirm that the rotational pattern is due to the age of the volcanics rocks but not to their spatial distribution. The Quaternary mean direction from the three Mexico Basin ranges is consistent with the geographical reference pole. In contrast, the Pliocene mean direction from volcanic rocks of the Altiplano area and the Sierra de Las Cruces is slightly rotated some 10° westwards with respect to the reference direction from North America. No significant rotations have been observed in the eastern TMVB (from the western Mexico Basin to the border of the Altiplano), between late Miocene and late Pliocene time. It suggests that a very small, counterclockwise vertical-axis rotation may have been taken place in this segment of the TMVB between late Pliocene and Quaternary times. Comparisons of these results with a summary of the available palaeomagnetic data in the area indicate that the previously reported Quaternary rotations are of questionable reliability, and that the large counterclockwise rotations, reported in Cretaceous to Miocene rocks, probably took place before the late Miocene. These new palaeomagnetic data support the idea that the eastern TMVB since the late Miocene, has been a zone of extension with a little, left-lateral shear component.

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.

When Did the Western Anatolian Grabens Begin to Develop?

Abstract To solve a long-lasting controversy on the timing and mechanism of generation of the western Anatolian graben system, new data have been collected from a mapping project in western Anatolia, which reveal that initially north-south trending graben basins were formed under an east-west extensional regime during Early Miocene times. The extensional openings associated with approximately north-south trending oblique slip faults provided access for calc-alkaline, hybrid magmas to reach the surface. A north-south extensional regime began during Late Miocene time. During this period a major breakaway fault was formed. Part of the lower plate was uplifted and cropped out later in the Bozdağ, Horst, and above the upper plate approximately north-south trending cross-grabens were developed. Along these fault systems, alkaline basalt lavas were extruded. The north-south extension was interrupted at the end of Late Miocene or Early Pliocene times, as evidenced by a regional horizontal erosional surface which developed across Neogene rocks, including Upper Miocene-Lower Pliocene strata. This erosion nearly obliterated the previously formed topographic irregularities, including the Bozdağ elevation. Later, the erosional surface was disrupted and the structures which controlled development of the Lower-Upper Miocene rocks were cut by approximately east-west trending normal faults formed by rejuvenated north-south extension. This has led to development of the present-day east-west trending grabens during Plio-Quaternary time.

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.

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.

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.

Palynology and paleoenvironments of a Pliocene carbonate platform: the Clino core, Bahamas

Neritic dinoflagellates from periplatform (slope) carbonates of the Clino borehole, located on the western, leeward margin of the Great Bahama Bank, record environmental fluctuations on the platform top. A lower Pliocene interval (3.6–4.2 Ma) contains platform-top sediments shed onto the lower slope when the platform was open and ramplike. Despite this open topography, abundantPolysphaeridium zoharyiindicate the presence of restricted marine environments on the platform top. Terrestrial palynomorphs are rare throughout this interval and imply a mostly or fully submergent platform top.By late Pliocene times (about 2.1–2.3 Ma) the platform had become flat-topped and steep-sided, with the Clino site located on its upper slope. Samples characteristic of sea-level highstands and lowstands were selected for analysis.Polysphaeridium zoharyiis abundant only in lowstand samples and may have thrived in proximity to terrestrial vegetation. In highstand samplesLingulodinium machaerophorumreplacesP. zoharyi, perhaps in response to less restricted marine environments on the platform top. This change in assemblages, along with apparent variations in cyst influx, reflects a fluctuating history of currents and salinities over the platform top in the late Pliocene. Upper Pliocene lowstand samples contain anomalously high proportions of terrestrial palynomorphs, allowing the identification of two phases of emergence and vegetation of the platform top. Palynology therefore appears to be a sensitive indicator of short-term (4th-order) sea-level change on carbonate platforms.Dinoflagellate concentrations correlate positively with carbonate compaction, and infer that compacted layers have undergone dissolution of their metastable constituents. Dinoflagellate concentrations therefore can be useful in the often difficult task of assessing compaction and dissolution in fine-grained limestones where other indicators are absent.The following dinoflagellate species are formally proposed:Operculodinium bahamenseHead new species,Operculodinium?megagranumHead new species, andSpiniferites rhizophorusHead new species.

Tephrochronology of late Cenozoic loess at Fairbanks, central Alaska

Nineteen distinctive, distal tephra beds from the Gold Hill Loess in the Fairbanks region, central Alaska, are divided into two groups based on their color, mineralogy, glass-shard morphology, and the major- and trace-element composition of their glass shards. This dichotomy in tephra composition is believed to reflect the two source regions, namely, the eastern Aleutian arc–Alaska Peninsula region and the Wrangell volcanic field. Despite the fragmentary nature of the preserved loess record, which contains many local unconformities, these tephra beds can be used to link the numerous loess exposures in the Fairbanks region in their proper time sequence, establishing thereby a comprehensive, reliable, time-stratigraphic framework. Because these distal tephra beds are related to large-magnitude volcanic eruptions, given the long distance to the nearest possible source vent, they will also enable correlation of the late Cenozoic sedimentary sequence at Fairbanks to those of adjacent regions of Alaska and the Yukon. Tephra beds with bubble-wall or chunky glass shards have been dated by the isothermal plateau fission-track method. Results demonstrate that the Gold Hill Loess spans a long interval of time from late Pliocene time to the last interglacial, about 125 ka. However, the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds. Paleomagnetic studies suggest that loess deposition in the Fairbanks region began about 3 Ma.

Palaeomagnetic study of the Karaman and Karapinar volcanic complexes, central Turkey: neotectonic rotation in the south-central sector of the Anatolian Block

In the Anatolian sector of the Afro–Eurasian collision zone a palaeotectonic collisional phase (Paleocene to Miocene) responsible for emplacement of the Pontide and Tauride orogens has been replaced by a neotectonic phase of continental deformation (Late Miocene/Early Pliocene to Recent). The latter phase appears to have been accommodated mainly by crustal thickening during Late Miocene and Pliocene times, but was succeeded by complex differential rotations of fault blocks during crustal extrusion in Late Pliocene and Quaternary times. In this study we have investigated palaeomagnetism of Miocene–Recent volcanic rocks comprising the western extension of the Central Anatolian Volcanic Province located in the south-central part of the Anatolian Block with the aim of resolving deformations near to the border with the Tauride orogen. Rock magnetic investigations identify low-Ti magnetite assemblages of primary cooling-related origin. These have predominant multidomain structures but significant fractions of single domains are always present; low-temperature alteration is largely absent. The Karaman Volcanic Complex (Late Pliocene) shows a net rotation of −5.7±6.9° not significantly different from the regional field axis during Recent times. The Karapinar Volcanic Field (Brunhes epoch) identifies a larger net rotation of −23.1±12.0° in a restricted sample. The adjoining Karacadağ Volcanic Complex (Late Miocene–Pliocene) and Middle Miocene lavas beneath the Hasandağ Complex define net rotations of −8.1±5.9° and −16.4±8.9° respectively. Analysis of palaeomagnetic results from Late Cretaceous–Recent rock units emplaced in Anatolia during the palaeotectonic and neotectonic regimes shows that rates of rotation have accelerated in post-Pliocene times as crustal thickening has given way to tectonic escape. A near-uniform anticlockwise rotation of 25–35° has characterised much of this block during the most recent phase of deformation and appears to have occurred in common with the Eurasian Plate to the north of the North Anatolian Fault Zone. Whilst this rotation appears to extend south eastwards across the Ecemiş Fault Zone towards the East Anatolian Fault, the present study shows that smaller differential anticlockwise rotations have characterised the south-central region of the block where it has interacted at its southwestern margin with oroclinal bending focussed on the Isparta angle.