How did the Messinian Salinity Crisis end?

The cause of the desiccation of the Mediterranean Sea during the Messinian Salinity Crisis has been widely debated, but its re-flooding remains poorly investigated. Interpretations generally involve tectonic collapse of the Strait of Gibraltar or global sea-level rise, or even a combination of both. The dramatic sea-level fall in the Mediterranean has induced deep fluvial incision all around the desiccated basin. We investigate erosion dynamics related to this base level drop by using the numerical simulator EROS. We show that intense regressive erosion develops inevitably in the Gibraltar area eventually inducing the piracy of the Atlantic waters by an eastward-flowing stream and the subsequent re-flooding of the Mediterranean.     

Messinian deposits and erosion in northern Tunisia: inferences on Strait of Sicily during the Messinian Salinity Crisis

Outcrops, offshore wells, electric logs and seismic profiles from northern Tunisia provide an opportunity to decipher the Messinian Salinity Crisis in the Strait of Sicily. Messinian deposits (including gypsum beds) near the Tellian Range reveal two successive subaerial erosional surfaces overlain by breccias and marine Zanclean clays, respectively. In the Gulf of Tunis, Messinian thick evaporites (mostly halite) are strongly eroded by a fluvial canyon infilled with Zanclean clays. The first erosional phase is referred to the intra-Messinian tectonic phase and is analogous to that found in Sicily. The second phase corresponds to the Messinian Erosional Surface that postdates the marginal evaporites, to which the entire Sicilian evaporitic series must refer. The Western and Eastern Mediterranean basins were separated during deposition of the central evaporites.     

Mantle resistance against Gibraltar slab dragging as a key cause of the Messinian Salinity Crisis

The Messinian Salinity Crisis (5.97–5.33 Ma) was caused by the closure of the Atlantic‐Mediterranean gateways that cut through the Gibraltar orogenic system. The geodynamic drivers underlying gateway closure and re‐opening are still debated. Here, we interrogate the gateway successions to find the imprints of surface deformation, infer the timing and nature of associated geodynamic drivers, and test such inferences against numerical simulations of slab dynamics. We find that since the latest Miocene, a tectonic framework was established in the gateway region dominated simultaneously by (a) relative plate convergence, (b) slab tearing under the eastern Betic Cordillera and (c) mantle resistance against north‐northeastward dragging of the Gibraltar slab by the African plate's absolute motion. We propose that mantle‐resisted slab dragging and slab tearing operated in concert closing the gateways that caused the Messinian Salinity Crisis, whereas sinking of heavy oceanic lithosphere located between buoyant continental plates re‐opened the Strait of Gibraltar at 5.33 Ma.     

Late Miocene sedimentary architecture of the Ebro Continental Margin (Western Mediterranean): implications to the Messinian Salinity Crisis

The Messinian Salinity Crisis (MSC) resulted from a significant multi-phase drop and subsequent reflooding of the Mediterranean Sea from 5.96 to 5.33 Ma. Well-developed drainage networks, characterized by step-like profiles and abrasion platforms, are associated to this event. The Ebro Continental Margin (Western Mediterranean) presents an additional complexity since the capture of the drainage of the adjacent subaerial Ebro Basin took place sometime prior to the Messinian stage. Using 3D seismic reflection data, this work provides new insights into the origin of the step-like profile of the Messinian erosional surface (MES) and timing of the capture of the subaerial Ebro Basin. The results obtained indicate a sedimentary-active continental slope and delta progradation during Middle-Late Miocene, in a normal regressive context associated to a pre-Messinian proto-Ebro River. The mature development attained by the Messinian Ebro River network during the MSC corroborates that the capture of the Ebro Basin occurred prior to the MSC. The configuration of the clinoforms below the MES suggests that deltaic sediments of the Messinian Paleo-Ebro River deposited during the Tortonian and initial Messinian sea-level drawdown. The MES formed at the top of the Tortonian Highstand, where a fluvial network was deeply carved, and in the topset region of the Messinian Falling Stage Systems Tract, where minor erosion occurred. Fluvial deposits are outstandingly preserved on the main valleys of the MES. Therefore, the step-like profile of the MES was not created during Zanclean inundation, but during the latest stages of the main Messinian sea-level fall and lowstand.     

Messinian events in the Black Sea

Past hydrological interactions between the Mediterranean Sea and Black Sea are poorly resolved due to complications in establishing a high‐resolution time frame for the Black Sea. We present a new greigite‐based magnetostratigraphic age model for the Mio‐Pliocene deposits of DSDP Hole 380/380A, drilled in the southwestern Black Sea. This age model is complemented by ⁴⁰Ar/³⁹Ar dating of a volcanic ash layer, allowing a direct correlation of Black Sea deposits to the Messinian salinity crisis (MSC) interval of the Mediterranean Sea. Proxy records divide these DSDP deposits into four intervals: (i) Pre‐MSC marine conditions (6.1–6.0 Ma); (ii) highstand, fresh to brackish water conditions (~6.0–5.6 Ma); (iii) lowstand, fresh‐water environment (5.6–5.4 Ma) and (iv) highstand, fresh‐water conditions (5.4–post 5.0 Ma). Our results indicate the Black Sea was a major fresh‐water source during gypsum precipitation in the Mediterranean Sea. The introduction of Lago Mare fauna during the final stage of the MSC coincides with a sea‐level rise in the Black Sea. Across the Mio‐Pliocene boundary, sea‐level and salinity in the Black Sea did not change significantly.     

The end of the Messinian Salinity Crisis in the western Mediterranean: Insights from the carbonate platforms of south-eastern Spain

How the Messinian Salinity Crisis (MSC) ended is still a matter of intense debate. The Terminal Carbonate Complex (TCC) is a late Messinian carbonate platform system that recorded western Mediterranean hydrological changes from the final stages of evaporite deposition till the advent of Lago-Mare fresh- to brackish water conditions at the very end of Messinian times. A multidisciplinary study has been carried out in three localities in south-eastern Spain to reconstruct the history of TCC platforms and elucidate their significance in the MSC. Overall, this study provides evidence that the TCC formed following a regional 4th order water level rise and fall concomitant with an opening-restriction trend. It can be subdivided into four 5th order depositional sequences (DS1 to DS4) recording two phases: (1) from DS1 to DS3, a tide-dominated ooidic to oobioclastic system with stenohaline faunas developed as a result of a 70 m water level rise. During this period, the TCC developed in a shallow sea with close to normal marine salinity; (2) in depositional sequence 4, a microbialite-dominated platform system developed. This is indicative of a significant environmental change and is attributed to a 30 to 40 m water level fall in the basins under study. These restricted conditions were coeval with intense evaporite deformation and brine recycling. The syn-sedimentary deformation of evaporites had a major impact on platform architecture and carbonate production, affecting the Messinian series throughout south-eastern Spain at the end of the TCC history. At that time, the TCC developed in a lake with fluctuating, brackish- to hypersaline water. These findings suggest a temporary restoration of marine conditions in the western Mediterranean marginal basins due to Atlantic water influxes prompted by a global sea level rise around 5.6 Ma. Whether marine conditions extended to the entire western Mediterranean still needs to be investigated.     

Precise 40Ar/39Ar dating of volcanic tuffs within the upper Messinian sequences in the Melilla carbonate complex (NE Morocco): implications for the Messinian Salinity Crisis

The Melilla carbonate complex (NE Morocco) is the only area of the Paleo-Mediterranean Sea where volcanic activity was present throughout most of the Messinian. ⁴⁰Ar/³⁹Ar dating of volcanic tuffs interbedded within the upper Messinian sedimentary deposits, known as the Terminal Carbonate Complex (TCC), yields accurate ages of paleoenvironmental and sea-level changes related to the Messinian Salinity Crisis. The new chronologic data (1) provide an average of 5.95–5.99 Ma for the base of the TCC, thus being synchronous with the onset of the Messinian Salinity Crisis, (2) demonstrate for the first time that the basal unconformity of the TCC does not represent a hiatus of long duration, (3) define a precise time line at 5.87±0.02 Ma (2σ) corresponding to sedimentary rocks exhibiting a lateral transition between continental and marine deposits typical of the TCC and (4) yield evidence that emersion of the Melilla platform during deposition of the TCC is partly related to tectono-magmatic activity. An erosional surface, capping the TCC deposits in the Melilla basin, is related to the major Messinian Mediterranean drawdown. The duration of the hiatus, associated with this surface, is estimated to be at most 450 kyr, but is probably shorter.     

Flexural isostatic response of the Alps to increased Quaternary erosion recorded by foreland basin remnants,SE France

We test the hypothesis that flexural isostatic compensation of the mass removed by enhanced Quaternary erosion is responsible for uplift of the Western European Alps and their forelands. We use two well‐preserved and well‐dated (1.8 Ma) abandonment surfaces of foreland basin remnants in SE France (the Chambaran and Valensole plateaux) as passive benchmarks for tilting of the foreland. Estimating their initial slope from morphometric scaling relationships, we determine bulk post‐depositional tilting of 0.5–0.8% for these surfaces. The calculated isostatic response of the Alpine lithosphere to erosional unloading, using the method recently proposed by Champagnac et al. [Geology 35 (2007) 195–198] , yields a predicted tilting of 0.3–0.4% in the considered areas, explaining approximately half of the determined post‐depositional tilting. Such long‐term deformation being insensitive to cyclic loading/unloading because of glaciations, we suspect the other half to be related to as yet undetermined long‐wavelength and long‐lived tectonic process(es).     

Messinian events in the Sorbas Basin in southeastern Spain and their implications in the recent history of the Mediterranean

The Messinian (Late Miocene) marine stratigraphic record of the Sorbas Basin (S.E. Spain) is well preserved and can be considered as being representative of the entire western Mediterranean. It exhibits a series of features relating to: (1) the composition, characteristics and evolution of coral reefs; (2) changes between temperate and subtropical climates; and (3) the extensive development of microbial carbonates (stromatolites and thrombolites) at the end of the Messinian. Each of these features has global significance.

Porites, which is the major and almost only coral component in reefs, is heavily encrusted with stromatolites. These reefs grew at the edge of the subtropical belt and were totally eliminated at the end of the Messinian because of global cooling.

Lowermost-Messinian carbonate sediments in the Sorbas Basin reflect a temperate climate, whereas those immediately above, which contain bioherms and coastal reefs, are subtropical. The shift from temperate to subtropical conditions during the early Messinian was accompanied by an important change in water circulation within the western Mediterranean. Temperate times were marked by cold surface Atlantic waters entering the Mediterranean, whereas subtropical times coincided with warm surface waters entering the western Mediterranean from the east. The subtropical waters were thermally stratified, which favoured the deposition of euxinic marls and diatomites at the centre of the basin. The upwelling of nutrient-rich water promoted stromatolite development within reefs and Halimeda growth on adjacent slopes.

Lastly, microbial carbonates (stromatolites and thrombolites) attained giant dimensions during the late Messinian, which can be regarded as a measure of their success in occupying a variety of ecological niches. This abundance of available habitats is believed to have resulted from the Messinian “salinity crisis”, which was followed by a re-colonization of the western Mediterranean. In this context stromatolite proliferation was due to opportunism of microbial communities in colonizing the new environments, rather than to a complete absence of other competitive biota. We do not believe that hypersaline conditions were a causal factor in stromatolite development because of the normal-marine biota associated with them.     

North-south asymmetry in response of geomagnetic activity to different solar events

Study of the response of geomagnetic activity to five different kinds of solar events reveals that an average north-south asymmetry of about 15% exists which diminishes with enhanced geomagnetic activity. The response of the geomagnetic field is quite significant only when high speed solar wind stream in association with sector boundary of interplanetary magnetic field (IMF) or solar proton streams near sector boundary sweeps past the earth. When the frequency of occurrence of indices of geomagnetic activity is considered, the index zero shows a marked difference in its response characteristics for the southern hemisphere. This appears to be a real feature and not attributable to any artefact of the index or its derivation.     

Regional frequency analysis of extreme rainfall events in Jakarta

Natural Hazards - Jakarta is vulnerable to flooding and extreme rainfall events are always the main cause of the occurrence of heavy flood events with loss of life and property. The flood in...     

Messinian carbonate and alluvial fan sedimentation in Alonnisos Island,Greece: sedimentary response to basement controls,inversion tectonics and climatic fluctuations

A marginal marine carbonate environment, giving away to an alluvial one, was established during Messinian time on Alonnisos Island, the footwall upland of the Southern Marginal Fault of the Sporades Basin (SMFS). Analysis of the evolving depositional systems, with emphasis on their sedimentation processes, faulting patterns and palaeopedological factors, has permitted an interpretation of the simultaneous controls of tectonism and climate. The carbonate sediments were deposited in a shallow marine environment formed along a faulted continental margin under warm and semi-arid climatic conditions. Faulting consisted of NE-trending dextral reverse faults and NW-trending strike slip faults, produced by WNW-directed compression. The basement structural elements affected the spatial distribution of the offshore and shoreface facies, whereas fifth-order cycles of sea-level change were responsible for the development of metre-scale, shallowing-up cycles. The compressional structures were subsequently reactivated by NNE extension. This tectonic inversion, together with a global sea-level fall, triggered alluvial fan sedimentation. Fan sedimentation was disrupted by long periods of non-deposition and soil formation under warm climatic conditions. Three distinct units are recognized in the fan: a lower unit consisting of clast-poor debris flows, attributed to semi-arid–humid periods; an intermediate unit of clast-rich sheetfloods and channel flows, deposited during arid periods; and an upper unit consisting of matrix-rich sheetfloods related to a return to semi-arid–humid conditions. We interpret that the water-flow processes responsible for deposition were most prevalent on fans of arid and semi-arid climates, whereas debris-flow processes were more typical of climates with higher rainfall. As the extension proceeded during the Plio-Quaternary time, the main tectonic activity of the Sporades Basin was taken up by the SMFS causing significant footwall uplift. Due to this process, Alonnisos Island was elevated above the Pliocene highstand and became an area starved of Quaternary sedimentation. Copyright © 1998 John Wiley & Sons, Ltd.     

Barrier island response to late Holocene climate events, North Carolina, USA

The Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence (OSL) dating (26 samples) of inlet-fill and flood tide delta deposits, recognized in cores and geophysical data, provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data. OSL ages of historical inlet fill compare favorably to historical documentation of inlet activity, providing confidence in the technique. Comparison suggests that the Medieval Warm Period (MWP) and Little Ice Age (LIA) were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today. Given present understanding of atmospheric circulation patterns and sea-surface temperatures during the MWP and LIA, we suggest that increased inlet activity during the MWP responded to intensified hurricane impacts, while elevated inlet activity during the LIA was in response to increased nor'easter activity. A general decrease in storminess at mid-latitudes in the North Atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets.     

全新世岱海流域化学风化及其对气候事件的响应

通过对岱海 12.08 m沉积岩芯 210Pb和 AMS- 14C精确定年及地球化学、物理指标的综合分析,重建了包括 8.2 ka冷期、中世纪暖期 (MWP)和小冰期 (LIA)等典型气候事件在内的全新世以来所经历的化学风化及其环境演化过程.全新世早-中期 (9.0～ 3.5 ka),岱海流域处于温暖湿润气候环境,主要环境特征表现为流域化学风化显著增强、生物生产力逐步提高、湖泊水位大幅度抬升.在 7.90～ 8.25 ka期间存在一次冷气候事件,其发生时间与来自湖沼、海洋、生物组合和极地冰芯等在内的全球环境记录基本一致,具体表现为流域化学风化减弱、湖泊生产力降低以及湖泊水位下降. 2.5 ka以来,岱海沉积物中环境指标的显著变化,表明进入气候波动更频繁的新冰期.岱海沉积物中的指标变化也展示了本世纪以来的气候增暖过程,但其化学风化强度还没有达到 MWP的程度.     

红岩煤矿岩溶水对暴雨响应特征研究

岩溶地下水系统由于管道流和扩散流同时存在而非常复杂。岩溶区暴雨过程中矿井突水造成了生命与财产的重大损失，因此在这些地区掌握矿井突水对暴雨响应特征是极其关键的。本文在大量监测资料基础上研究了红岩煤矿岩溶地下水系统，利用时间序列频谱分析建立了突水与暴雨之间的响应模型，并利用该模型预测了矿井突水趋势。     

云南高海拔湖泊对末次冰消期气候突变的响应

气象观测资料表明,在当前全球暖化背景下高海拔地区的增温速率更快,其气候对全球气候变化的响应更为敏感。但是,高海拔地区如何响应快速气候事件,由于古气候古环境重建资料在高海拔地区较少,这一问题还没有很好的回答。为此选择云南省高山湖泊错恰湖为研究对象（海拔约3960 m）,分析了湖泊沉积岩芯（深度范围90~244 cm）中正构烷烃的分布特征,重建了末次冰消期（19000~9500 a B.P.）沉积物有机质来源的变化,进而推断古气候演变。在17800~17000 a B.P.,错恰湖有机质以陆源输入为主,水生贡献相对减少,气候以暖湿为主;在17000~15100 a B.P.,水生有机质的贡献的比例增加,气候以冷干为主;在15100~12700 a B.P.,湖泊沉积有机质的陆源贡献增加,水生贡献相对减少,气候相对暖湿;在12700~11400 a B.P.时段,湖泊沉积水生有机质来源相对增多,气候相对冷干。与其他区域和全球气候记录对比发现,错恰湖的沉积记录指示的气候变化事件,受高纬冰量以及北大西洋驱动的西南季风突变所影响,在末次冰消期记录的4个明显的千年尺度气候事件,在时间上与First warmth、H1、B-A和YD事件相对应。与云南地区其他湖泊记录对比发现,小型湖泊或高海拔湖泊对这些全球快速气候事件的响应更加敏感。

     

晚中生代地球表层重大地质事件的陆地环境剧变与生物群演替响应

晚中生代时期华北东北部发育燕辽生物群、热河生物群和阜新生物群陆地生物群。它们的快速演变过程和华北克拉通上同时期发育的岩石圈减薄、大面积强烈岩浆活动、变质核杂岩及伴随的伸展盆地等地球表层重大地质事件并行发生,表现着地壳表层系统圈层间的相互作用和响应。生物群的繁盛与灭绝与地球表层大规模岩浆-火山活动(髫髻山组—张家口组和大北沟组—义县组)发育时代高度协同一致。地球表层重大地质事件直接或间接地控制或改造着地球表层古地理和古生态环境,生物群只得调整自身去适应环境和生态背景的改变。火山-岩浆活动改变着地质-生态环境,生物群都紧密联系多期次火山-岩浆活动,化石也都被埋葬在沉积-火山碎屑岩中。华北克拉通破坏重大地质事件发生响应于全球变化和统一地球表层系统。盆地沉积充填序列、特殊陆相环境沉积建造、特殊环境沉积物等记录了响应的古地理、古环境变化与响应。陆地生物群分布、演化、更替与精确定年,脊椎-无脊椎生物(化石)埋葬特征,生物演化速率、消长关系和生物群(组合)更替的形式和性质,以及脊椎动物骨骼、牙齿的常量、微量元素、H-B-C-N-O-S和C-O-Sr等地球化学特征的研究可以恢复和重建古地理、古生态环境和古生态系统。     

Rapid mapping in support of emergency response after earthquake events

Earthquakes and other sudden onset natural disasters require quick and efficient emergency response. Earth observation (EO) data can make a valuable contribution to emergency response efforts if provided within hours and at the most days after the event. Mechanisms like the International Charter Space and Major Disasters and the European GMES Emergency Response Service provide the necessary basis for an efficient and rapid provision of EO data and damage mapping. This paper provides an overview of earthquake damage assessment methodologies, their potential and their limitations in a rapid mapping context and outlines a methodology for casualty estimation. Two case studies—the 2010 Haiti earthquake and the 2011 Van (Turkey) earthquake—are presented, where DLR’s Center for satellite-based crisis information (ZKI) provided rapid damage maps using a team-based visual interpretation approach. Additionally, the application of a casualty estimation method in the immediate aftermath of an earthquake is outlined.