Tertiary Strata Research Articles

Variable post-Paleozoic deformation detected by seismic reflection profiling across the northwestern “prong” of New Madrid seismic zone

High-resolution shallow seismic reflection profiles across the northwesternmost part of the New Madrid seismic zone (NMSZ) and northwestern margin of the Reelfoot rift, near the confluence of the Ohio and Mississippi Rivers in the northern Mississippi embayment, reveal intense structural deformation that apparently took place during the late Paleozoic and/or Mesozoic up to near the end of the Cretaceous Period. The seismic profiles were sited on both sides of the northeast-trending Olmsted fault, defined by varying elevations of the top of Mississippian (locally base of Cretaceous) bedrock. The trend of this fault is close to and parallel with an unusually straight segment of the Ohio River and is approximately on trend with the westernmost of two groups of northeast-aligned epicenters (“prongs”) in the NMSZ. Initially suspected on the basis of pre-existing borehole data, the deformation along the fault has been confirmed by four seismic reflection profiles, combined with some new information from drilling. The new data reveal (1) many high-angle normal and reverse faults expressed as narrow grabens and anticlines (suggesting both extensional and compressional regimes) that involved the largest displacements during the late Cretaceous (McNairy); (2) a different style of deformation involving probably more horizontal displacements (i.e., thrusting) that occurred at the end of this phase near the end of McNairy deposition, with some fault offsets of Paleocene and younger units; (3) zones of steeply dipping faults that bound chaotic blocks similar to that observed previously from the nearby Commerce geophysical lineament (CGL); and (4) complex internal deformation stratigraphically restricted to the McNairy, suggestive of major sediment liquefaction or landsliding. Our results thus confirm the prevalence of complex Cretaceous deformations continuing up into Tertiary strata near the northern terminus of the NMSZ.

Spatial probabilistic modeling of slope failure using an integrated GIS Monte Carlo simulation approach

Spatial probabilistic modeling of slope failure using a combined Geographic Information System (GIS), infinite-slope stability model and Monte Carlo simulation approach is proposed and applied in the landslide-prone area of Sasebo city, southern Japan. A digital elevation model (DEM) for the study area has been created at a scale of 1/2500. Calculated results of slope angle and slope aspect derived from the DEM are discussed. Through the spatial interpolation of the identified stream network, the thickness distribution of the colluvium above Tertiary strata is determined with precision. Finally, by integrating an infinite-slope stability model and Monte Carlo simulation with GIS, and applying spatial processing, a slope failure probability distribution map is obtained for the case of both low and high water levels.

Palynology and paleoecology of strata associated with the Ohoopee river dune field, Emanuel county, Georgia

Fourteen auger holes were drilled through ancient dunes near the Ohoopee River in Emanuel County, Georgia. Driller's logs and sieve analyses show that the wind‐blown sands of the dune field overlie a layer of coarse sand and gravel, which in turn overlies clayey Late Tertiary strata. Clay‐rich sediment recovered from two of the holes contained diatoms, sponge spicules, and other siliceous marine microfossils, while clay analyses from seven other holes revealed the presence of the clay mineral attapulgite (a variety of palygorskite). Twenty‐two sediment samples collected from six of the drill holes contained sufficient organic material to warrant palynological analysis. Eighty‐one taxa of pollen, spores, and algal cysts were used along with the diatoms, clay analyses, and stratigraphy to indicate probable ages and environments of deposition of the sediments. Both the diatoms and the attapulgite indicate marine depositional conditions. Overlying the marine units, but below the eolian sands we found rare occurrences of the extinct or extirpated genera Casuarinidites, Sciadopitys, Pterocarya, and Momipites. We believe these support a Late Tertiary age interpretation for the clayey strata. The presence of taxa such as the Cyrillaceae, Nyssa, Sphagnum, Myriophyllum, and Pseudoschizaea in the uppermost Tertiary units indicates that these sediments accumulated in freshwater wetlands. Our interpretation of the depositional history is that Late Tertiary marine strata accumulated first, probably during the Miocene. As sea level dropped fluvial and paludal conditions led to the accumulation of freshwater swamp/marsh sediments and probable stream sands or gravels later in the Tertiary. Exposure of the Inner Coastal Plain during the Pleistocene resulted in the formation of dunes that migrated over the Tertiary strata at the site of deposition.

Occurrence and Paleoecology of Marsilea from the Eocene Wasatch Formation, Johnson County, Wyoming

Fossil Marsiliaceae , referable to Marsilea (also known as water clover or pepperwort), were found as impressions in baked claystone (clinker) of the Eocene Wasatch Formation near Buffalo, Wyoming. This is the first documented evidence of Marsilea foliage in Tertiary strata. The fossil is in the Bureau of Land Management9s Petrified Tree Environmental Education Area where strata are associated with the Healy and Walters coal beds. Previous palynological analyses, the presence of the ferns Salvinia preauriculata and Lygodium kaulfussi , and the stratigraphic position of the deposits indicate an Early Eocene age for the fossils. Leaf impressions of a variety of pteridophytes and spermatophytes, in conjunction with more than 100 pollen and spore taxa, indicate deposition on a tropical to subtropical fluvial floodplain. Leaf morphology, including leaf size, shape, and venation, are very similar to living species of Marsilea . The preservation in thermally altered sedimentary rock that was derived from claystone is consistent with the plants9 current preference for moist clay soils. The conservative morphology and environmental preferences of Marsilea indicate that it is an ecologically conservative genus that can be a reliable indicator of quiet freshwater habitats with clay substrata.

A Miocene collisional belt in north Borneo: uplift mechanism and isostatic adjustment quantified by thermochronology

Subduction followed by underthrusting of continental lithosphere, driven by Oligocene–Early Miocene spreading in the South China Sea marginal basin, account for the tectonic features of Sabah. Isostatic rebound then caused Late Miocene uplift of the Western Cordillera. The strata were buried under 4–8 km of overburden then rapidly exhumed and cooled at >10°C Ma −1 . A rate of exhumation of 0.5–0.7 mm a −1 is deduced from thermochronology. The same order of uplift in the Labuk Highlands has exposed metamorphic rocks of the epidote-glaucophane facies. Rapid erosion of the Western Cordillera supplied abundant clastic sediments to the Miocene–Pliocene Baram Delta oil-bearing basin and to the Eastern Lowlands and Sulu Sea. The Eastern Lowlands were affected by Miocene rifting of the Sulu Sea marginal basin. In contrast to the Western Cordillera, the strata contain apatite crystals whose fission track ages pre-date the containing rocks, indicating burial by only about 2–3 km of overburden. The terrain has been isostatically stable. Some apatite and all zircon crystals, extracted from Tertiary strata, yield Cretaceous fission track provenance ages.

R. M. Kleinpell's Zones And Stages: An Oppelian Biostratigraphic Solution To A Challenge In The Search For Petroleum In California

Robert M. Kleinpell (1905-1986) brought new concepts into oil exploration in California in the late 1920s that enhanced oil recovery. He used basic biostratigraphic principles developed by Albert Oppel (1831-1865) in a study of the ammonite-bearing Jurassic successions in Europe to solve a challenge that faced California's petroleum industry in the 1920s. That challenge was how to recognize a specific stratigraphic position in a sequence of unseen and seemingly unfossiliferous, homogenous California Tertiary strata being perforated by oil-well drilling equipment and how to identify oil-bearing strata from well to well. Kleinpell's insightful use of relevant biostratigraphic principles led to recovery of many millions of barrels of petroleum from California's Tertiary stratigraphic succession. Despite considerable economic success, rarely have geologists outside California's petroleum industry recognized the significance of Kleinpell's economically rewarding application of scientific principle. Furthermore, rarely have American geologists noted the similarity between biostratigraphic practice of most Europeans and that of Kleinpell.

Quaternary grabens in southernmost Illinois: deformation near an active intraplate seismic zone

Narrow grabens displace Quaternary sediments near the northern edge of the Mississippi Embayment in extreme southern Illinois, east-central United States. Grabens are part of the Fluorspar Area Fault Complex (FAFC), which has been recurrently active throughout Phanerozoic time. The FAFC strikes directly toward the New Madrid Seismic Zone (NMSZ), scene of some of the largest intra-plate earthquakes in history. The NMSZ and FAFC share origin in a failed Cambrian rift (Reelfoot Rift). Every major fault zone of the FAFC in Illinois exhibits Quaternary displacement. The structures appear to be strike-slip pull-apart grabens, but the magnitude and direction of horizontal slip and their relationship to the current stress field are unknown. Upper Tertiary strata are vertically displaced more than 100 m, Illinoian and older Pleistocene strata 10 to 30 m, and Wisconsinan deposits 1 m or less. No Holocene deformation has been observed. Average vertical slip rates are estimated at 0.01 to 0.03 mm/year, and recurrence intervals for earthquakes of magnitude 6 to 7 are on the order of 10,000s of years for any given fault. Previous authors remarked that the small amount of surface deformation in the New Madrid area implies that the NMSZ is a young feature. Our findings show that tectonic activity has shifted around throughout the Quaternary in the central Mississippi Valley. In addition to the NMSZ and southern Illinois, the Wabash Valley (Illinois–Indiana), Benton Hills (Missouri), Crowley's Ridge (Arkansas–Missouri), and possibly other sites have experienced Quaternary tectonism. The NMSZ may be only the latest manifestation of seismicity in an intensely fractured intra-plate region.

Abstract: Thermal Maturity of Cretaceous and Tertiary strata, Crazy Mountains Basin, South-Central Montana 

Abstract: Thermal Maturity of Cretaceous and Tertiary strata, Crazy Mountains Basin, South-Central Montana 

Deep burial of the footwall of the northern Snake Range decollement, Nevada

Metapelitic Eocambrian strata from eastern exposures of the footwall of the northern Snake Range decollement experienced Mesozoic amphibolite facies metamorphism and greenschist facies overprint accompanying extreme ductile thinning. Samples from the Hampton Creek area where the overprint is weakest contain the assemblage quartz + muscovite + biotite + garnet + plagioclase + opaque oxides + staurolite ± kyanite ± tourmaline ± apatite. Textural relations and consistency of rim analyses among multiple domains in each sample indicate equilibrium. Rim pressure-temperature estimates were obtained using the garnet-biotite Fe-Mg exchange thermometer and the garnet-muscovite-plagioclase-biotite and garnet-aluminosilicate-plagioclase barometers. The results suggest final equilibration at 610 ± 50 °C and 810 ± 70 MPa, or a depth of 30 ± 3 km, about a factor of 3 greater than the stratigraphic depth. To the west, in the Schell Creek Range, correlative strata are contiguous with unmetamorphosed upper Paleozoic and Tertiary strata. From west to east, exposures of Eocambrian rocks in the two ranges collectively show increasing intensity of crystal-plastic deformation, metamorphic recrystallization, and metamorphic grade from subgreenschist to amphibolite facies, and a monotonic decrease in ^(40)Ar/^(39)Ar muscovite ages from Mesozoic age to about 23 Ma. In light of these relations, the pressure-temperature data suggest that Eocambrian strata were inclined eastward during Mesozoic metamorphism with ∼15–20 km of structural relief. We interpret the eastward tilting and burial to be the result of west-directed thrusting, as expressed by folding to the north in the Deep Creek Range. Unroofing of the deeply buried strata may have occurred partly in Cretaceous or early Cenozoic time, with final unroofing in Oligocene and Miocene time along the northern Snake Range decollement. These results exclude the hypothesis that the northern Snake Range decollement initiated as a brittle-ductile transition zone within Cambrian strata of a little-deformed miogeoclinal section, and support the hypothesis that it is a major low-angle extensional shear zone.

Structural setting, geological development and basin modelling in the Rockall Trough

Evidence from wide-angle seismic data in the Irish sector of the Rockall Trough suggests that the basin is underlain by thinned continental crust which has undergone differential stretching. The upper crust has been thinned by a stretching factor of 8–10 while the middle and lower crust (and probably also the lithospheric mantle) was stretched by a factor of 2–3. The latter figure is suggested as being representative of the overall lithospheric stretching. Crustal modelling fails to demonstrate any significant effect of the Iceland plume on the development of the basin. The Rockall Trough contains up to 6 km of sedimentary strata. Well and seismic data from adjacent basins indicate that the succession in the basin is likely to be of Late Palaeozoic to Recent age. The pre-Cretaccous faeies are suggested to be broadly similar to other basins of the Atlantic borderlands. Cretaceous and Tertiary strata show progressive clastic starvation as thermal subsidence outstripped sedimentation in the basin, Sandy facies are likely to be concentrated towards the faulted basin margins and the re-entrant regions where the basin margin changes orientation. Basin modelling, based on normal incidence and wide-angle seismic profiles from a number of areas in the Irish sector of the basin, demonstrates that the observed seismic geometries and subsidence patterns cannot be explained by a single rift episode in the Cretaceous, The best fit of possible models suggests that the basin developed in response to discrete rift episodes in the Triassic, Late Jurassic and Early Cretaceous.

Petroleum systems of the Atlantic margin of northwest Europe

The Atlantic margin region of northwest Europe includes, on its inboard side, five basins which have been explored since the 1970s and contain proven, Jurassic-sourced petroleum systems: Halten Terrace, the Northern North Sea, the Faeroe-Shetland Basin, the Slyne-Erris troughs and Porcupine Basin. The hydrocarbons in most of these basins are in Jurassic sandstone reservoirs within late Jurassic fault traps. To the northwest, on the outboard side of the Atlantic margin, lie four frontier areas in which exploration is mostly only just beginning: the Vøring, Møre and Rockall basins and the Faeroes Shelf. The basins often have Cretaceous strata which are many kilometres thick, whilst Tertiary strata are thick in some places but thin (starved) in others. Cretaceous and Tertiary extensional faulting phases created fault traps in some parts of the basins and mid Tertiary compressional domes provide important traps elsewhere. The least known aspect of the petroleum geology of these basins is the presence and maturity history of any source rocks. The outboard basins are bordered to the northwest by a zone of Paleocene-Eocene volcanic rocks, which are over 5 km thick at the Faeroe Islands. The lava sheets were dominantly subaerial and may conceal eroded but prospective Paleocene and Mesozoic strata. The outboard frontier areas may contain extensive petroleum systems. In the Vøring Basin two major discoveries prove the existence of petroleum systems there but both their geographical extent and source are unknown. Petroleum systems may be present in the main Møre Basin, beneath some part of the Faeroes Shelf and along both margins of the Rockall Trough.

ESTABLISHMENT OF FOSSIL ENTOMOFAUNAS AND THEIR EVOLUTIONARY SUCCESSION IN NORTH CHINA*

Abstract According to a systematic study of large numbers of fossil insects collected from the Paleozoic, Mesozoic and Tertiary strata in North China, three evolutionary mega‐stages of fossil insects including 14 fossil entomofaunas and 29 entomassemblages have been established. These insect faunas reflect their order or law of evolution—the history of their rise and fall, and form their evolutionary succession in North China. Such a history provides an important reference not only for understanding fossil insects through time, but also showing for stratigraphical correlation.

Dewatering the Thanet Beds in SE London: three case histories

Abstract The construction of the Jubilee Line Extension in southeast London required the construction of a number of deep excavations extending into the Thanet Beds. These Lower Tertiary strata are predominantly silty fine sands, and in order for the excavations to be carried out in the dry, dewatering was necessary. Three examples of excavations in the Thanet Beds are described in this paper, in each of which dewatering was attempted by pumping from the underlying Chalk to induce drainage of the Thanets. Although the three sites were only approximately 1 km apart, the performance of the dewatering schemes was different at each site. One excavation proved impossible to dewater by this method, whilst the other two, although successfully completed, demonstrate very clearly the extreme variations in the permeability of the Chalk and the difficulties that may arise therefrom.

The structural development of the Central English Channel High — constraints from section restoration

Abstract The Central English Channel High is an east-west-trending asymmetric, southfacing, anticlinal structure which forms the southern boundary of the Central Channel Basin. Upper Jurassic rocks are exposed at seabed in the core of the structure, while Tertiary strata are preserved immediately to the south. Elsewhere in the Wessex-Channel basins structures of this overall form are interpreted as linear inversion structures formed during the mid-Tertiary by the reactivation of Mesozoic extensional faults, themselves formed by the partial reactivation of Variscan thrust ramps. Projection of the eroded sequence over the high using the geometry of the preserved section indicates the original presence of an approximately symmetrical Upper Jurassic-Lower Cretaceous sub-basin formed in the hanging wall of a north-dipping Mesozoic extensional structure, the Central Channel Fault. Seismic velocities from wells over the high are consistent with the implied post-Cretaceous relative uplift of up to 1500 m. The deeper geometry of the Central Channel Fault has been determined using the restored hanging wall geometry and the main aspects of the inversion structure have been recreated by forward modelling. The internal structure of the Central Channel High is consistent with a moderately steep fault near surface which passes relatively abruptly into a lower-angle fault. This is interpreted to indicate the presence of a Variscan backthrust at depth which has been partially reactivated during both Mesozoic extension and mid-Tertiary inversion.

Tectonic inheritance, crustal architecture, and contrasting structural styles in the Venezuela Andes

Surface and subsurface data image contrasting structural styles for the two flanks of the Venezuela Andes. In the north, a flexural basin developed in Neogene times between the Andes and the Lake Maracaibo. North verging thrusts are mainly detached in the pre‐Cretaceous substratum and form a deeply buried antiformal stack. Secondary décollement levels occur both in the Upper Cretaceous and Tertiary strata, accounting for the passive roof thrust of a conventional frontal triangle zone. In the south, the Barinas basin hardly compares with a flexural basin. It is largely dominated by both north and south verging basement‐involving structures. Paleogene normal faults are locally inverted, and Caribbean nappes are frequently reactivated or refolded by younger oblique Neogene Andean structures. Seismic profiles in this area also attest to the strong Neogene structural inversion of Upper Jurassic‐Lower Cretaceous grabens. Hercynian, or more likely Early Paleozoic structures account for local preexisting crustal heterogeneities, reactivated during both the Tethyan rifting and the Andean deformations. Two trans‐Andean regional profiles have been balanced and constrained by an inversion of the gravimetric data. They imply a progressive deepening of the northern Moho and a south dipping subduction of the infracontinental lithospheric mantle of the Maracaibo block. The shortening for both sections averages 60 km. Palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the Andes and minimize the possible effects of a progressive right‐lateral escape of the Maracaibo block with respect to stable South America along the Bocono Fault. Strain partitioning during Neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary, strike‐slip motion in the allochthon along the Bocono Fault, and an asymmetric subduction (wedging) at depth.

On phytogeographical affinities of the forest floras between east China and Japan

The flora of the eastern China is the main part of Sino-Japanese floristic region. It shows from the analysis and comparison that the floristic relation of East China with Japan is closer than that with northeast China and Korea. The similarity indices of genera and species of seed plants in the two regions are very high, being 72.6% and 43.3% respectively. The structure and species composition of broad-leaved evergreen forests in the two regions are also similar, and there exist many corresponding communities, such as the forests of Castanopsis carlesii and C. sieboldii. Many plants in East China are conspecific with those in Japan, such as Cercidiphyllum japonicum, Magnolia sieboldii, Nandina domestica etc. Though the genera of Ginkgo, Liriodendron, Sassafras etc. existing now in China are extinct from Japan, their fossils have been discovered from the Tertiary strata in Japan. It seems to indicate that the phytogeographical affinities between East China and Japan are closer in ancient time than it is now, and both of the forest floras originated from the same flora. The flora in Japan did not evolve independently until it separated from Chinese continent and drifted northeastwards in the late period of the Tertiary.

A new stratigraphy for the islands of the Sumatran Forearc, Indonesia

The Sumatran Forearc of western Indonesia contains a number of islands where extensive exposures of basement rocks and their sedimentary cover may be examined. The islands, such as Nias and the Batu Islands, are located along the outer-edge of the Sumatran Forearc, whilst others, including the Banyak Island Group and Pini Island, lie within the forearc basin. Detailed sedimentological, palaeontological and palaeobathymetric data from the Tertiary strata from the forearc region require a new stratigraphy, as previous stratigraphic schemes have not explained the variations across the region adequately. This stratigraphy, developed initially from detailed data collected on Nias and the Banyak Islands, can fully account for the successions of sedimentary rocks on the Banyak and Batu Islands and Siberut and explains many of the apparent inconsistencies between previous stratigraphies. A basement complex and six new formations are formally defined in this paper; important sedimentological differences between these formations represent key stages in the evolution of the outer part of the Sumatran Forearc. Studies of the basement rocks across the forearc area suggest the basement is inhomogeneous; large intact sections of ophiolitic material occur in some areas, whilst there is evidence for both oceanic and continental basement in others. Such heterogeneity is to be expected in a long lived obliquely convergent margin. In Oligocene-earliest Miocene times extension of the heterogeneous basement is inferred through indirect evidence. Palaeobathymetric data from the Oyo Formation indicates that the initial deposition in the newly formed extensional sub-basins on Nias was, in most areas, deep marine, in many cases below the CCD. Detailed biostratigraphic analyses and structural and geochronological studies indicate a major Early Miocene unconformity in the western (Lahewa Sub-basin) and parts of central Nias (Mujoi Sub-basin). This unconformity was developed as a direct result of a period of basin inversion that affected western parts of Nias. Whilst sub-aerial erosion occurred in parts of western Nias, conformable deposition of the Gawo and Olodano Formation continued in the Gomo and eastern parts of the Mujoi Sub-basins. The shallow marine sedimentary rocks of the Olodano Formation tended to accumulate on intra sub-basinal highs whose position was controlled by active faults that transected the sub-basins. The sedimentary record reveals that the Lower and Middle Miocene phases of differential uplift and subsidence had ceased by the Late Miocene. A massive influx of Himalayan derived Bengal Fan sediments reached the Sunda Trench in the Sumatra area in the late Middle Miocene. Continued addition of Bengal Fan material to the accretionary wedge south-west of Nias resulted in steady plate deflection and subsidence through flexural processes in forearc basin areas. The flexural consequence of increased load added to the prism, and associated subsidence history is documented by the sedimentary record on Nias where the shallow marine Olodano Formation passes up into the neritic to upper bathyal Lahomie Formation. The Pliocene unconformity which is observed over all areas studied in the forearc is well constrained by structural, biostratigraphic and sedimentological studies. The unconformity represents the initiation of a major phase of uplift and deformation that continues to the present day. Rapid uplift of the outer arc ridge and deformation of the prism during the Pliocene led to increased subsidence landward of the deformation. The rapid subsidence of the forearc basin landward of the outer-arc ridge has contributed greatly to the “apparent” differences between the forearc basin and the outer-arc ridge at the present day: two areas with remarkably similar pre-Pliocene histories now have remarkably different physiographies.

A new stratigraphy for the islands of the Sumatran Forearc, Indonesia

Abstract The Sumatran Forearc of western Indonesia contains a number of islands where extensive exposures of basement rocks and their sedimentary cover may be examined. The islands, such as Nias and the Batu Islands, are located along the outer-edge of the Sumatran Forearc, whilst others, including the Banyak Island Group and Pini Island, lie within the forearc basin. Detailed sedimentological, palaeontological and palaeobathymetric data from the Tertiary strata from the forearc region require a new stratigraphy, as previous stratigraphic schemes have not explained the variations across the region adequately. This stratigraphy, developed initially from detailed data collected on Nias and the Banyak Islands, can fully account for the successions of sedimentary rocks on the Banyak and Batu Islands and Siberut and explains many of the apparent inconsistencies between previous stratigraphies. A basement complex and six new formations are formally defined in this paper; important sedimentological differences between these formations represent key stages in the evolution of the outer part of the Sumatran Forearc. Studies of the basement rocks across the forearc area suggest the basement is inhomogeneous; large intact sections of ophiolitic material occur in some areas, whilst there is evidence for both oceanic and continental basement in others. Such heterogeneity is to be expected in a long lived obliquely convergent margin. In Oligocene-earliest Miocene times extension of the heterogeneous basement is inferred through indirect evidence. Palaeobathymetric data from the Oyo Formation indicates that the initial deposition in the newly formed extensional sub-basins on Nias was, in most areas, deep marine, in many cases below the CCD. Detailed biostratigraphic analyses and structural and geochronological studies indicate a major Early Miocene unconformity in the western (Lahewa Sub-basin) and parts of central Nias (Mujoi Sub-basin). This unconformity was developed as a direct result of a period of basin inversion that affected western parts of Nias. Whilst sub-aerial erosion occurred in parts of western Nias, conformable deposition of the Gawo and Olodano Formation continued in the Gomo and eastern parts of the Mujoi Sub-basins. The shallow marine sedimentary rocks of the Olodano Formation tended to accumulate on intra sub-basinal highs whose position was controlled by active faults that transected the sub-basins. The sedimentary record reveals that the Lower and Middle Miocene phases of differential uplift and subsidence had ceased by the Late Miocene. A massive influx of Himalayan derived Bengal Fan sediments reached the Sunda Trench in the Sumatra area in the late Middle Miocene. Continued addition of Bengal Fan material to the accretionary wedge south-west of Nias resulted in steady plate deflection and subsidence through flexural processes in forearc basin areas. The flexural consequence of increased load added to the prism, and associated subsidence history is documented by the sedimentary record on Nias where the shallow marine Olodano Formation passes up into the neritic to upper bathyal Lahomie Formation. The Pliocene unconformity which is observed over all areas studied in the forearc is well constrained by structural, biostratigraphic and sedimentological studies. The unconformity represents the initiation of a major phase of uplift and deformation that continues to the present day. Rapid uplift of the outer arc ridge and deformation of the prism during the Pliocene led to increased subsidence landward of the deformation. The rapid subsidence of the forearc basin landward of the outer-arc ridge has contributed greatly to the “apparent” differences between the forearc basin and the outer-arc ridge at the present day: two areas with remarkably similar pre-Pliocene histories now have remarkably different physiographies.

Phytogeographical affinities of forest floras between China and Japan

The flora of eastern China is the main part of Sino-Japanese floristic region. It shows by the analysis and comparison that the floristic relations of Eastern China with Japan are closer than that of northeast China with Korea. The similarity indices of genera and species of seed plants in the two regions are very high, being 72.6% and 43.3% respectively. The structure and species composition of broad-leaved evergreen forests in the two regions are also similar, in which there exist the corresponding communities, such as the forests of Castanopsis carlesii, C. Sieboldii.. Many plants in Easter China are nonspecific with those in Japan, e. g, Cercidiphyllum japonicum, Magolia sieboldii, Nandina domestica etc.. Though the genera Ginkgo, Liriodendron, Sassafras etc. existing now in China are extinct from Japan, their fossils have been discovered from the Tertiary Strata in Japan. It seems to indicate that the phytogeographical affinities between Japan and E. China was closer in ancient time than it is now; and both of the forest floras originated from one same flora, The flora in Japan did not evolve independently until it separated from Chinese continent and drifted to northeast in the late period of the Tertiary.

Pliocene-Holocene contourite deposition under the Antarctic Circumpolar Current, western Falkland Trough, south Atlantic Ocean

The eastward-flowing Antarctic Circumpolar Current (ACC) has influenced sedimentation on the slope and floor of the western Falkland Trough, where the axis of the current is topographically constrained. Deep-water flow (below 3000 m) has produced a symmetrical sediment drift on the trough floor, with non-depositional margins indicating higher current velocities at the base of slope. To the southeast of the Falkland Islands there is a gap in the North Scotia Ridge, north of which the floor of the trough is swept clean of sediment by the ACC. Both echo character mapping and GLORIA side-scan data indicate that currents follow the bathymetric contours along the slope, redistributing sediment and locally eroding furrows. From six cores on the drift and on the northern slope, two styles of contourite deposition have been identified. On the drift, Holocene biogenic sandy contourites overlie Last Glacial Maximum muddy contourites and fine-grained diatomaceous hemipelagites. Sedimentation rates here average 3–4 cm ka−1. The sandy contourites present in four of the cores from the sediment drift are sharply underlain by the finer-grained, diatomaceous hemipelagites. The lack of a coarsening upward sequence, commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer (negative) sequence. Pliocene and Mid-Pleistocene glaucony-rich sandy contourites containing radiolaria characterise the Falkland Plateau and the floor of the trough near the gap in the North Scotia Ridge. We suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping Cretaceous and Tertiary strata; this is supported by dinoflagellate analysis. Sedimentation rates in these current-swept areas average < 1 cm ka−1.