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1.
《Journal of African Earth Sciences》2005,41(1-2):41-59
This article outlines geomorphological and tectonic elements of the Afar Depression, and discusses its evolution. A combination of far-field stress, due to the convergence of the Eurasian and Arabian plates along the Zagros Orogenic Front, and uplift of the Afar Dome due to a rising mantle plume reinforced each other to break the lithosphere of the Arabian–Nubian Shield. Thermal anomalies beneath the Arabian–Nubian Shield in the range of 150 °C–200 °C, induced by a rising plume that mechanically and thermally eroded the base of the mantle lithosphere and generated pulses of prodigious flood basalt since ∼30 Ma. Subsequent to the stretching and thinning the Afar Dome subsided to form the Afar Depression. The fragmentation of the Arabian–Nubian Shield led to the separation of the Nubian, Arabian and Somalian Plates along the Gulf of Aden, the Red Sea and the Main Ethiopian Rift. The rotation of the intervening Danakil, East-Central, and Ali-Sabieh Blocks defined major structural trends in the Afar Depression. The Danakil Block severed from the Nubian plate at ∼20 Ma, rotated anti-clockwise, translated from lower latitude and successively moved north, left-laterally with respect to Nubia. The westward propagating Gulf of Aden rift breached the Danakil Block from the Ali-Sabieh Block at ∼2 Ma and proceeded along the Gulf of Tajura into the Afar Depression. The propagation and overlap of the Red Sea and the Gulf of Aden along the Manda Hararo–Gobaad and Asal–Manda Inakir rifts caused clockwise rotation of the East-Central Block. Faulting and rifting in the southern Red Sea, western Gulf of Aden and northern Main Ethiopian Rift superimposed on Afar. The Afar Depression initiated as diffused extension due to far-field stress and area increase over a dome elevated by a rising plume. With time, the lithospheric extension intensified, nucleated in weak zones, and developed into incipient spreading centers. 相似文献
2.
《Earth》2006,77(3-4):191-233
A Cenozoic tectonic reconstruction is presented for the Southwest Pacific region located east of Australia. The reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for Pacific–Australia and Lord Howe Rise–Pacific relative plate motion. The reconstruction is based on a conceptual tectonic model in which the large-scale structures of the region are manifestations of slab rollback and backarc extension processes. The current paradigm proclaims that the southwestern Pacific plate boundary was a west-dipping subduction boundary only since the Middle Eocene. The new reconstruction provides kinematic evidence that this configuration was already established in the Late Cretaceous and Early Paleogene. From ∼ 82 to ∼ 52 Ma, subduction was primarily accomplished by east and northeast-directed rollback of the Pacific slab, accommodating opening of the New Caledonia, South Loyalty, Coral Sea and Pocklington backarc basins and partly accommodating spreading in the Tasman Sea. The total amount of east-directed rollback of the Pacific slab that took place from ∼ 82 Ma to ∼ 52 Ma is estimated to be at least 1200 km. A large percentage of this rollback accommodated opening of the South Loyalty Basin, a north–south trending backarc basin. It is estimated from kinematic and geological constraints that the east–west width of the basin was at least ∼ 750 km. The South Loyalty and Pocklington backarc basins were subducted in the Eocene to earliest Miocene along the newly formed New Caledonia and Pocklington subduction zones. This culminated in southwestward and southward obduction of ophiolites in New Caledonia, Northland and New Guinea in the latest Eocene to earliest Miocene. It is suggested that the formation of these new subduction zones was triggered by a change in Pacific–Australia relative motion at ∼ 50 Ma. Two additional phases of eastward rollback of the Pacific slab followed, one during opening of the South Fiji Basin and Norfolk Basin in the Oligocene to Early Miocene (up to ∼ 650 km of rollback), and one during opening of the Lau Basin in the latest Miocene to Present (up to ∼ 400 km of rollback). Two new subduction zones formed in the Miocene, the south-dipping Trobriand subduction zone along which the Solomon Sea backarc Basin subducted and the north-dipping New Britain–San Cristobal–New Hebrides subduction zone, along which the Solomon Sea backarc Basin subducted in the west and the North Loyalty–South Fiji backarc Basin and remnants of the South Loyalty–Santa Cruz backarc Basin subducted in the east. Clockwise rollback of the New Hebrides section resulted in formation of the North Fiji Basin. The reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere, a change in plate kinematics or slab–mantle interaction. 相似文献
3.
New 40Ar/39Ar ages, based on incremental heating techniques for groundmass separates of 25 samples, are presented for the Harrat Al-Madinah volcanic field, part of Harrat Rahat in the north western part of the Arabian plate. This area is an active volcanic field characterized by the occurrence of two historical eruptions approximately in 641 and 1256 AD. Field investigations of the main volcanic landforms indicate dominantly monogenetic strombolian eruptions, in addition to local more explosive eruptions. The lavas consist mainly of olivine basalt and hawaiite flows with minor evolved rocks of mugearite, benmoreite, and trachyte that occur mainly as domes, tuff cones and occasionally as lava flows. Previous K/Ar dating shows that the Harrat Al-Madinah lava flows and associated domes comprise seven units spanning an age range of ca. 1.7 Ma–Recent. The new 40Ar/39Ar age determinations confirm, to a great extent, the previously obtained K/Ar ages in the sense that no major systematic biases were found in the general stratigraphy of the different flow units. However, the 40Ar/39Ar plateau ages show that volcanism in this area began in the Neogene (∼10 Ma) and continued to Recent, with the most voluminous eruptions occurring in the Quaternary. Neogene volcanism occurred in at least three pulses around 10, 5 and 2 Ma, whereas Quaternary volcanism produced at least seven units reflecting lava flow emplacement in the time period of 1.90 Ma–Recent. Thus, the whole duration of volcanic activity in the Harrat Al-Madinah (10 Ma–Recent) appears much longer than that previously identified. The longevity of volcanism in the same part of the moving Arabian plate and absence of evidence for uni-directional migration of volcanic activity indicate that there is no fixed plume beneath this region. The NNW-trending distribution of the volcanic vents is parallel to the Red Sea, and suggests their origin is related to periodic extensional episodes along the reactivated Red Sea fault system. 相似文献
4.
《Comptes Rendus Geoscience》2015,347(4):161-169
The Dead Sea Fault is a major strike-slip fault bounding the Arabia plate and the Sinai subplate. On the basis of three GPS campaign measurements, 12 years apart, at 19 sites distributed in Israel and Jordan, complemented by Israeli permanent stations, we compute the present-day deformation across the Wadi Arava fault, the southern segment of the Dead Sea Fault. Elastic locked-fault modelling of fault-parallel velocities provides a slip rate of 4.7 ± 0.7 mm/yr and a locking depth of 11.6 ± 5.3 km in its central part. Along its northern part, south of the Dead Sea, the simple model proposed for the central profile does not fit the velocity field well. To fit the data, two faults have to be taken into account, on both sides of the sedimentary basin of the Dead Sea, each fault accommodating ∼ 2 mm/yr. Locking depths are small (less than 2 km on the western branch, ∼ 6 km on the eastern branch). Along the southern profile, we are once again unable to fit the data using the simple model, similar to the central profile. It is very difficult to propose a velocity greater than 4 mm/yr, i.e. smaller than that along the central profile. This leads us to propose that a part of the relative movement from Sinai to Arabia is accommodated along faults located west of our profiles. 相似文献
5.
Whole-rock geochemical and Sr, Nd and Pb isotope data are presented for the Harrat Al-Madinah volcanic field, in the north western part of the Arabian plate, aiming to understand their origin and the composition of their mantle source. This area is an active volcanic field characterized by the occurrence of two historic eruptions approximately in 641 and 1256 A.D. Field investigation of the main volcanic landforms indicates dominantly monogenetic strombolian eruptions, in addition to local phreatomagmatic eruption style. The lavas consist mainly of alkali olivine basalt, olivine transitional basalt, and hawaiite with ocean island basalt (OIB)-like characteristics. Evolved rocks, represented by mugearites, benmoreites, and trachytes, occur mainly as domes, tuff cones and occasionally as lava flows. Chemical variations in the evolved rocks indicated their evolution by low pressure crystal fractionation of olivine, plagioclase, clinopyroxene, and Fe–Ti oxides from the relatively primitive basalts. The isotopic compositions of 143Nd/144Nd (0.512954–0.512995), 87Sr/86Sr (0.702899 to–0.702977) and Pb (206Pb/204Pb = 18.5515–18.7446, 207Pb/204Pb = 15.5120–15.5222, 208Pb/204Pb = 38.1347–38.4468), show restricted variations suggesting only minor crustal contamination. They defined an array consistent with mixing of two geochemically distinct components of depleted MORB-mantle (DMM) and high 238U/204Pb ratio (HIMU). The variations in Tb/Yb, La/Yb and Sm/Yb ratios in the relatively primitive basalts (MgO > 6 wt.%) indicated garnet peridotite source. However, the positive Nb, Sr, Ba and Ti anomalies in the primitive mantle-normalized incompatible element patterns and the significant variation between Zr/Nb vs. Ce/Y and La/Yb vs. Yb suggest contribution of an amphibole-bearing spinel lherzolite source. Moreover, the negative correlations between SiO2 vs. 87Sr/86Sr and Th vs. 143Nd/144Nd are interpreted as an indication of mixing melts derived from two end-members; one is garnet bearing asthenospheric source with OIB characteristic and the other is amphibole-bearing spinel lherzolite. The Harrat Al-Madinah volcanic field occurs near the Red Sea Rift System and its origin reflects a strong lithospheric control on the loci of partial melting. The dominantly NNW alignment patterns of the volcanoes, which is similar to the regional Red Sea trend, may suggest that the magmas were produced by decompression partial melting triggered by lithospheric extension related to the Red Rift. 相似文献
6.
《Quaternary Science Reviews》2007,26(19-21):2586-2597
Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ18O of seawater (δ18Osw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ18Osw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ18Osw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon. 相似文献
7.
《Gondwana Research》2011,19(4):583-595
Ophiolites are key components of the Neoproterozoic Arabian–Nubian Shield (ANS). Understanding when they formed and were emplaced is crucial for understanding the evolution of the ANS because their ages tell when seafloor spreading and terrane accretion occurred. The Yanbu–Onib–Sol Hamed–Gerf–Allaqi–Heiani (YOSHGAH) suture and ophiolite belt can be traced ∼ 600 km across the Nubian and Arabian shields. We report five new SHRIMP U–Pb zircon ages from igneous rocks along the Allaqi segment of the YOSHGAH suture in southernmost Egypt and use these data in conjunction with other age constraints to evaluate YOSHGAH suture evolution. Ophiolitic layered gabbro gave a concordia age of 730 ± 6 Ma, and a metadacite from overlying arc-type metavolcanic rocks yielded a weighted mean 206Pb/238U age of 733 ± 7 Ma, indicating ophiolite formation at ∼ 730 Ma. Ophiolite emplacement is also constrained by intrusive bodies: a gabbro yielded a concordia age of 697 ± 5 Ma, and a quartz-diorite yielded a concordia age of 709 ± 4 Ma. Cessation of deformation is constrained by syn- to post-tectonic granite with a concordia age of 629 ± 5 Ma. These new data, combined with published zircon ages for ophiolites and stitching plutons from the YOSHGAH suture zone, suggest a 2-stage evolution for the YOSHGAH ophiolite belt (∼ 810–780 Ma and ∼ 730–750 Ma) and indicate that accretion between the Gabgaba–Gebeit–Hijaz terranes to the south and the SE Desert–Midyan terranes to the north occurred as early as 730 Ma and no later than 709 ± 4 Ma. 相似文献
8.
The study of a 300-cm-thick exposed lacustrine sediment section in the Hedong village in Zhaoqing area which is located in sub-tropical west Guangdong Province in South China, demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of Asian monsoon climate. Multi-proxy records, including the humification intensity, total organic carbon, and grain size fractions, reveal a general trend towards dry and cold conditions in the late Holocene that this is because of a decrease in solar insolation on an orbital scale. Three intensified Asian summer monsoon (ASM) intervals (∼3300–3000 cal yr BP, ∼2600–1600 cal yr BP, and ∼900–600 cal yr BP), and three weakened ASM intervals (∼4000–3300 cal yr BP, ∼3000–2600 cal yr BP, and ∼1600–900 cal yr BP) are identified. Our humification record (HDcal) shows a good correlation on multi-centennial scale with the tree ring Δ14C record, a proxy of solar activity. A spectral analysis of HDcal reveals four significant cycles, i.e., ∼1250 yr, 300 yr, 110 yr, and 70 yr, and most of these cycles are related to the solar activity. Our findings indicate that solar output and oceanic–atmospheric circulation probably have influenced the late Holocene climate variability in the study region. 相似文献
9.
《Journal of African Earth Sciences》2005,41(1-2):103-117
Over 35,000 onshore and offshore gravity stations have been compiled in order to test isostatic models against geologic structures over a part of the Afro–Arabian shield. The area of Ethiopia covers an important part of this system because it contains the major section of the ≈5000 km Afro–Arabian rift and includes the transition between the Arabo-Nubian-Shield (ANS) and the Mozambique Belt (MB).Isostatic residual anomalies have been calculated using both Airy and Vening-Meinesz (flexural rigidity D = 1022 Nm) models. The isostatic residual anomalies outline the major Precambrian belts, the Cenozoic rifts and associated major structures. Positive residual anomalies associated with the main Ethiopian Rift (MER) and Kenyan rift systems could be the expressions of an axial intrusive body and swarms of local faults and fractures. The residual anomalies indicate relative stability in the MER and increased tectonic activity in the areas of the Red Sea, Gulf of Aden and Afar. Near-zero isostatic residuals flank the MER and Kenya rifts and are found within the Danakil Alps and some plateau regions.The small mean isostatic residual anomaly (about 8 mGal) and the isostatic analysis show a slight positive bias indicating under compensation. The undercompensation may imply that there are upper crustal features that are not compensated regionally (probably supported by the rigidity of the lithosphere) and isostatic disequilibrium in the region. Therefore, the high topography of Ethiopia and East African plateau is partly compensated by thicker crust (broad negative isostatic regional anomaly) and partly by dynamic forces.The results of the qualitative interpretation form the basis of continuing three-dimensional gravity modelling and quantitative analysis that also integrates data from eastern Sudan. 相似文献
10.
《Quaternary Science Reviews》2007,26(5-6):627-643
Buried submarine landforms mapped on 3D reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central North Sea by two palaeo-ice-streams, between 58–59°N and 0–1°E. Streamlined subglacial bedforms (mega-scale glacial lineations) and iceberg plough marks, within the top 80 m of the Quaternary sequence, record the presence and subsequent break-up of fast-flowing grounded ice sheets in the region during the late Pleistocene. The lengths of individual mega-scale glacial lineations vary from ∼5 to ∼20 km and the distance between lineations typically ranges from 100 to 1000 m. The lineations incise to a depth of 10–12 m, with trough widths of ∼100 m. The most extensive and best-preserved set of lineations, is attributed to the action of a late Weichselian ice stream which either drained the NE sector of the British–Irish ice sheet or was sourced from the SW within the Fennoscandian ice sheet. The 30–50 km wide palaeo ice-stream is imaged along its flow direction for 90 km, trending NW–SE. An older set of less well-preserved lineations is interpreted as an earlier Weichselian or Saalian ice-stream, and records ice flow in an SW–NE orientation. Cored sedimentary records, tied to 3D seismic observations, support grounded ice sheet coverage in the central North Sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till. The identification of a late Weichselian ice stream in the Witch Ground area of the North Sea basin provides independent geomorphic evidence in support of ice-sheet reconstructions that favour complete ice coverage of the North Sea between Scotland and Norway during the Last Glacial Maximum. 相似文献
11.
《Quaternary Science Reviews》2005,24(10-11):1217-1222
Tide gauge data at seven sites of the Permanent Service for Mean Sea Level (PSMSL), with information for relative sea-level during the past 140–200 yr, were analyzed to examine the rates and causes of the global sea-level rise (GSLR) during the twentieth century. By subtracting linear trends for relative sea-level rise during the past 100 yr from the observed data, we get the apparent GSLRs of ∼1 mm yr−1 for five sites around the Baltic Sea and Brest. The rate for San Francisco is significantly larger than this, with an optimum value ∼2 mm yr−1. The spatial difference of ∼1 mm yr−1 between these sites is reasonably explained by the recent melting of the Greenland ice sheet with an equivalent sea-level rise of ∼1 mm yr−1. The predicted relative sea-level change for this melting scenario is 0.5 mm yr−1 at sites around the Baltic Sea and Brest, and 1.5 mm yr−1 for San Francisco. The residuals between observations and predictions, ∼0.5 mm yr−1 at all sites, may be contributed by thermal expansion of seawater and/or other melting sources. These results suggest the rate of twentieth-century GSLR to be 1.5 mm yr−1. 相似文献
12.
Sedimentological, geomorphic, and ground penetrating radar (GPR) data are combined with optically stimulated luminescence data to define the Holocene evolution of a coastal system in peninsular Malaysia. The Setiu coastal region of northeast Malaysia comprises five geological and geomorphic units representing distinct evolutionary phases of this coastline. Estimated marine limiting point elevations indicate deposition of an early aggradational shoreline associated with a sea-level elevation of −0.1 to +1.7 m (MSLPMVGD datum) between ∼6.8 ka and 5.7 ka, in agreement with previous sea-level studies from the Malay–Thai peninsula. A hiatus occurs in the record between ∼5.7 ka and 3.0 ka, possibly due to a relative sea-level oscillation and shoreline erosion. Long-term relative sea-level fall and possible still-stands created strandplains that are interrupted by aggradational to transgressive paleo-barrier and estuary formation corresponding with brief episodes of RSL rise. Analyses of GPR facies and OSL ages suggest annual clinoform deposition, with geometries dictated by variations in ENSO. These data demonstrate the utility of high resolution studies of coastal facies as useful proxy indicators for paleoclimate studies at subdecadal to millennial time-scales. 相似文献
13.
《Quaternary Science Reviews》2007,26(22-24):2844-2863
We present the first overall synthesis of the terrace deposits of the River Euphrates in SE Turkey, northern Syria, and western Iraq, combining new observations with summaries of data sets from different reaches that had previously been independently studied on a piecemeal basis. The largest number of terraces observed in any reach of the Euphrates is 11, in western Iraq, where this river leaves the uplands of the Arabian Platform. In many other localities not more than 5 or 6 terraces have previously been identified, although we infer that some of these are resolvable into multiple terraces. These terraces are typically formed of gravel, principally consisting of Neotethyan ophiolite and metamorphic lithologies transported from Anatolia. Although older gravels are also evident, most of the Euphrates terrace deposits appear, given the chronologies that have been established for different parts of the study region, to date from the late Early Pleistocene onwards, the cold stages most often represented being interpreted as marine Oxygen Isotope Stages 22, 16, 12, 8, 6 and/or 4, and 2. The formation of this terrace staircase reflects regional uplift of the Arabian Platform. Estimated amounts of uplift since the Middle Pliocene decrease southeastward from almost 300 m in SE Turkey to ∼150 m in western Iraq. Uplift rates increased in the late Early Pleistocene, the uplift estimated since then decreasing from ∼110 m in SE Turkey to a minimum of ∼50 m in the Syria–Iraq border region, then increasing further downstream across western Iraq to ∼70 m. Numerical modelling of this uplift indicates a relatively thin mobile lower-crustal layer, consistent with the low surface heat flow in the Arabian Platform. 相似文献
14.
The collision of the Iranian microcontinent with the Afro-Arabian continent resulted in the deformation of the Zagros orogenic belt. The foreland of this belt in the Persian Gulf and Arabian platform has been investigated for its petroleum and gas resource potentials, but the Zagros hinterland is poorly investigated and our knowledge about its deformation is much less than other parts of this orogen. Therefore, this work presents a new geological map, stratigraphic column and two detailed geological cross sections. This study indicates the presence of a hinterland fold-and-thrust belt on northeastern side of the Zagros orogenic core that consists of in-sequence thrusting and basement involvement in this important part of the Zagros hinterland. The in-sequence thrusting resulted in first- and second-order duplex systems, Mode I fault-bend folding, fault-propagation folding and asymmetric detachment folding which indicate close relationships between folding and thrusting. Study of fault-bend folds shows that layer-parallel simple shear has the same role in the southeastern and northwestern parts of the study area (αe = 23.4 ± 9.1°). A major lateral ramp in the basement beneath the Talaee plain with about one kilometer of vertical offset formed parallel to the SW movement direction and perpendicular to the major folding and thrusting. 相似文献
15.
Geochemical, isotopic, and geochronologic data for exhumed rocks in the Woodlark Rift of Papua New Guinea (PNG) allow a tectonic link to be established with the Late Cretaceous Whitsunday Volcanic Province (WVP) of northeastern Australia. Most of the metamorphic rocks in the Woodlark Rift have Nd isotopic compositions (εNd = + 1.7 to + 6.2) similar to the Nd isotopic compositions of rocks in the WVP (εNd = + 1.3 to + 6.6; Ewart et al., 1992), and contain inherited zircons with 90 to 100 Ma U–Pb ages that overlap the timing of magmatism in the WVP. None of the metamorphic rocks in the Woodlark Rift have the highly evolved Hf and Nd isotopic compositions expected of ancient continental crust. Magmas were erupted in the WVP during the middle Cretaceous as eastern Gondwana was rifted apart. The protoliths of felsic and intermediate metamorphic rocks in the Woodlark Rift are interpreted to be related to the magmatic products produced during this Cretaceous rifting event. Some mafic metamorphic rocks exposed in the western Woodlark Rift (eclogites and amphibolites) are not related to the WVP and instead could have originated as basaltic lavas crystallized from mantle melts at (U)HP depths in the Late Cenozoic, or as fragments of Mesozoic aged oceanic lithosphere.Isotopic and elemental comparisons between basement gneisses and Quaternary felsic volcanic rocks demonstrate that felsic lavas in the D'Entrecasteaux Islands did not form solely from partial melting of metamorphic rocks during exhumation. Instead, the isotopic compositions and geochemistry of Quaternary felsic volcanic rocks indicate a significant contribution from the partial melting of the mantle in this region. When combined with geophysical data for the western Woodlark Rift, this suggests that future seafloor spreading will commence south of Fergusson Island, and west of the present-day active seafloor spreading rift tip. 相似文献
16.
《Quaternary Science Reviews》2007,26(17-18):2201-2218
Late Holocene vegetation and geomorphological history is reconstructed from a 800 cm long high-resolution palynological and sedimentological record sampled from Bereket, a 6.3 km2 semi-arid to sub-humid intramontane basin in the Western Taurus Mountains (southwest Turkey). The well-dated Bereket record provides from cal. 360 BC to cal. AD ∼400 a unique record of biennial-to-decadal landscape changes caused primarily by intensive human impacts against a background of global climate variations. During this period, land clearance with multiple fire episodes, intensive agricultural practices and grazing pressure profoundly altered the pre-existing warm mixed forest. Increasing moisture availability since cal. ∼280 BC has acted as a trigger to crop cultivation and mountain-adapted arboriculture starting with Juglans regia during the Beyşehir Occupation Phase. Pollen from olive groves have been recorded above 1400 m a.s.l. only at cal. ∼23 BC and have disappeared definitively at cal. AD ∼294. During this phase, the sediment accumulation rate was extremely high, reflecting landscape instability. From cal. AD 450 to recent times, the area has mainly recorded pasture and minor cultivation activities reflected in stable soils and thin colluvial depths. 相似文献
17.
Kurt Lambeck Anthony Purcell Nicholas. C. Flemming Claudio Vita-Finzi Abdullah M. Alsharekh Geoffrey N. Bailey 《Quaternary Science Reviews》2011,30(25-26):3542-3574
The history of sea level within the Red Sea basin impinges on several areas of research. For archaeology and prehistory, past sea levels of the southern sector define possible pathways of human dispersal out of Africa. For tectonics, the interglacial sea levels provide estimates of rates for vertical tectonics. For global sea level studies, the Red Sea sediments contain a significant record of changing water chemistry with implications on the mass exchange between oceans and ice sheets during glacial cycles. And, because of its geometry and location, the Red Sea provides a test laboratory for models of glacio-hydro-isostasy. The Red Sea margins contain incomplete records of sea level for the Late Holocene, for the Last Glacial Maximum, for the Last Interglacial and for earlier interglacials. These are usually interpreted in terms of tectonics and ocean volume changes but it is shown here that the glacio-hydro-isostatic process is an additional important component with characteristic spatial variability. Through an iterative analysis of the Holocene and interglacial evidence a separation of the tectonic, isostatic and eustatic contributions is possible and we present a predictive model for palaeo-shorelines and water depths for a time interval encompassing the period proposed for migrations of modern humans out of Africa. Principal conclusions include the following. (i) Late Holocene sea level signals evolve along the length of the Red Sea, with characteristic mid-Holocene highstands not developing in the central part. (ii) Last Interglacial sea level signals are also location dependent and, in the absence of tectonics, are not predicted to occur more than 1–2 m above present sea level. (iii) For both periods, Red Sea levels at ‘expected far-field’ elevations are not necessarily indicative of tectonic stability and the evidence points to a long-wavelength tectonic uplift component along both the African and Arabian northern and central sides of the Red Sea. (iv) The observational evidence is consistent with tectonic and isostatic processes both operating over the past 300,000 years without requiring changes in the time averaged (over a few thousand years) tectonic rates. (v) Recent bathymetric data for the Bab al Mandab region have been compiled to confirm the location and depth of the sill controlling flow in and out of the Red Sea. Throughout the last 400,000 years the Red Sea has remained open to the Gulf of Aden with cross sectional areas at times of glacial maxima about 2% of that today. (vi) The minimum channel widths connecting the Red Sea to the Gulf of Aden at times of lowstand occur south of the Hanish Sill. The channels are less than 4 km wide and remain narrow for as long as local sea levels are below ?50 m. This occurs for a number of sustained periods during the last two glacial cycles and earlier. (vii) Periods suitable for crossing between Africa and Arabia without requiring seaworthy boats or seafaring skills occurred periodically throughout the Pleistocene, particularly at times of favourable environmental climatic conditions that occurred during times of sea level lowstand. 相似文献
18.
《Quaternary Science Reviews》2007,26(17-18):2128-2151
After the first emergence following deglaciation, relative sea level rose by 10 m in western Norway and culminated late in the Younger Dryas (YD). The relative sea-level history, reconstructed by dating deposits in isolation basins, shows a sea-level low-stand between ∼13 640 and 13 080 cal yr BP, a 10 m sea-level rise between ∼13 080 and 11 790 cal yr BP and a sea-level high-stand between ∼11 790 and 11 550 cal yr BP. Shortly after the YD/Holocene boundary, sea level fell abruptly by ∼37 m. The shorelines formed during the sea-level low-stand in the mid-Allerød and during the sea-level high-stand in the YD have almost parallel tilts with a gradient of ∼1.3 m km−1, indicating that hardly any isostatic movement has taken place during this period of sea-level rise. We conclude that the transgression was caused by the major re-advance of the Scandinavian Ice Sheet that took place in western Norway during the Lateglacial. The extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea. Our results show that the crust responded to the increased load well before the YD (starting ∼12 900 cal yr BP), with a sea-level low-stand at 13 640 cal yr BP and the subsequent YD transgression starting at 13 080 cal yr BP. Thus, we conclude that the so-called YD ice-sheet advance in western Norway started during the Allerød, possibly more than 600 years before the Allerød/YD transition. 相似文献
19.
The Reed Bank Basin in the southern margin of the South China Sea is considered to be a Cenozoic rifted basin. Tectono-thermal history is widely thought to be important to understand tectonics as well as oil and gas potential of basin. In order to investigate the Cenozoic tectono-thermal history of the Reed Bank Basin, we carried out thermal modeling on one drill well and 22 pseudo-wells using the multi-stage finite stretching model. Two stages of rifting during the time periods of ∼65.5–40.4 Ma and ∼40.4–28.4 Ma can be recognized from the tectonic subsidence rates, and there are two phases of heating corresponding to the rifting. The reconstructed average basal paleo-heat flow values at the end of the rifting events are ∼60 and ∼66.3 mW/m2, respectively. Following the heating periods, this basin has undergone a persistent thermal attenuation phase since ∼28.4 Ma and the basal heat flow cooled down to ∼57.8–63.5 mW/m2 at present. In combination with the radiogenic heat production of the sedimentary sequences, the surface heat flow of the Reed Bank Basin ranges from ∼60.4 to ∼69.9 mW/m2. 相似文献
20.
The eastern Coral Sea is a poorly explored area at the north-eastern corner of the Australian Tectonic Plate, where interaction between the Pacific and Australian plate boundaries, and accretion of the world's largest submarine plateau – the Ontong Java Plateau – has resulted in a complex assemblage of back-arc basins, island arcs, continental plateaus and volcanic products. This study combines new and existing magnetic anomaly profiles, seafloor fabric from swath bathymetry data, Ar–Ar dating of E-MORB basalts, palaeontological dating of carbonate sediments, and plate modelling from the eastern Coral Sea. Our results constrain commencement of the opening of the Santa Cruz Basin and South Rennell Trough to c. 48 Ma and termination at 25–28 Ma. Simultaneous opening of the Melanesian Basin/Solomon Sea further north suggests that a single > 2000 km long back-arc basin, with at least one triple junction existed landward of the Melanesian subduction zone from Eocene–Oligocene times. The cessation of spreading corresponds with a reorganisation of the plate boundaries in the area and the proposed initial soft collision of the Ontong Java Plateau. The correlation between back-arc basin cessation and a widespread plate reorganisation event suggests that back-arc basins may be used as markers for both local and global plate boundary changes. 相似文献