Holocene shorelines and tectonic movements in eastern Saudi Arabia

Although Quaternary marine terraces have been reported from eastern Saudi Arabia at heights of up to 150 m, unambiguous shoreline deposits could be identified only within 3 m of present-day High Water and close to the modern shoreline. Unaltered aragonitic mollusc shells from five such deposits yielded ¹⁴C ages of 3700–6000 yr B.P. Comparison of their elevations with those of coeval deposits on the Zagros coast of Iran demonstrates the relative stability of the Saudi shore of the Gulf during the late Holocene.     

Late Holocene tephrochronology of the northern Antarctic Peninsula

Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct ¹⁴C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.     

Late Holocene beetle assemblages and environmental change in Gammelhemmet,northern Sweden

Analysis of insect fossil remains retrieved from a bog close to the abandoned farm at Gammelhemmet, near Lycksele in Swedish Lapland, enabled the reconstruction of environmental changes at the site over the last 2500 years. These results represent the first late Holocene palaeoentomological succession studied for insect remains in the Västerbotten interior, and they provide new evidence for landscape change in the area. Around 2000 years ago, at the end of the early Iron Age, disappearance of the tree and leaf litter fauna and an increase in aquatic species indicate the expansion of wetlands in the area. Patches of a multi‐aged mixed woodland with a diverse assemblage of forest‐dwelling beetles succeeded the wetland ～1500 years ago, at the beginning of the late Iron Age. A marked change to open and drier conditions, and the presence of species often found in grassland and cultivated ground took place during the post‐Medieval period. Our evidence indicates drainage of the area prior to the 18th century, placing the initiation of agricultural activities in Gammelhemmet earlier than the documentary record. Our research shows the potential of the use of fossil insects for understanding environmental change and also human impact on the landscape, even of limited scale, from natural contexts.     

Geodetic control on recent tectonic movements in the central Mediterranean area

During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models.Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy.The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations.In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.     

Late Holocene sea-level changes and isostatic crustal movements in Atlantic Canada

It has long been recognised that sea levels along the shores of Atlantic Canada have been rising rapidly during the Holocene in response to isostatic crustal movements. New sea-level data for the Bay of Fundy coast of southern New Brunswick (Little Dipper Harbour) and the Atlantic coast of Nova Scotia (Chezzetcook Inlet) show that late Holocene average rates of sea-level rise in these areas have been 1.0 and 2.5 m per 1000 yr, respectively. Numerical model calculations suggest that the high rates of sea-level rise are due to crustal subsidence produced by the combined effects of Laurentide ice loading (forebulge collapse) and ocean loading of the Scotian shelf. Although ice loading is the dominant contributor to the regional sea-level pattern, ocean loading is also important, contributing up to 40% of the total crustal subsidence in some areas. Tide gauges record rates of sea-level rise during the 20^th century that are 0.7–1.9 mm/yr higher than late Holocene trends, with the highest residuals occurring in the Bay of Fundy.     

Late Holocene climatic history of northern Germany and Denmark: peat macrofossil investigations at Dosenmoor, Schleswig-Holstein, and Svanemose, Jutland

Plant macrofossil remains have been analysed from two raised peat bogs in northern Germany and Denmark. The quantified vegetation reconstructions of each profile were subjected to multivariate analyses to extract records of changing bog surface wetness (BSW), which are interpreted in these rain-fed bogs as being proxy climate signals. Age/depth models were constructed using radiocarbon dates and a number of drier and wetter phases were defined. The records both register cooler/wetter conditions around 2700, 1800 and 1400 cal. yr BP, and at the beginning of the Little Ice Age around AD 1250–1350. These rising bog water tables must have been reflected in poorer conditions for agriculture, and in particular near Dosenmoor where the profile records a catastrophic change to such conditions culminating at 2750–2600 cal. yr BP.     

Late Pleistocene–Holocene rise and collapse of Lake Suguta,northern Kenya Rift

The Late Pleistocene to Middle Holocene African Humid Period (AHP) was characterized by dramatic hydrologic fluctuations in the tropics. A better knowledge of the timing, spatial extent, and magnitude of these hydrological fluctuations is essential to decipher the climate-forcing mechanisms that controlled them. The Suguta Valley (2°N, northern Kenya Rift) has recorded extreme environmental changes during the AHP. Extensive outcrops of lacustrine sediments, ubiquitous wave-cut notches, shorelines, and broad terrace treads along the valley margins are the vestiges of Lake Suguta, which once filled an 80 km long and 20 km wide volcano–tectonic depression. Lake Suguta was deep between 16.5 and 8.5 cal ka BP. During its maximum highstand, it attained a water depth of ca 300 m, a surface area of ca 2150 km², and a volume of ca 390 km³. The spatial distribution of lake sediments, the elevation of palaeo-shorelines, and other geomorphic evidences suggest that palaeo-Lake Suguta had an overflow towards the Turkana basin to the north. After 8.5 cal ka BP, Lake Suguta abruptly disappeared. A comparison of the Lake Suguta water-level curve with other reconstructed water levels from the northern part of the East African Rift System shows that local insolation, which is dominated by precessional cycles, may have controlled the timing of lake highstands in this region. Our data show that changes of lake levels close to the Equator seem to be driven by fluctuations of spring insolation, while fluctuations north of the Equator are apparently related to variations in summer insolation. However, since these inferred timings of lake-level changes are mostly based on the radiocarbon dating of carbonate shells, which may have been affected by a local age reservoir, alternative dating methods are needed to support this regional synthesis. Between 12.7 and 11.8 cal ka BP, approximately during the Northern Hemisphere high-latitude Younger Dryas, the water level of Lake Suguta fell by ca 50 m, suggesting that remote influences also affected local hydrology.     

Late Pleistocene stratigraphy at Boliden, northern Sweden

Till-covered sand and silt sediments with organic material from Boliden, northern Sweden, have been resampled and reinvestigated. Texture and petrographic analyses demonstrated one till bed overlying, and one underlying the sandy sediments. Low frequencies of diatoms were noted, representing freshwater, halophilous and brackish water taxa. The diatoms may be allochthonous or autochthonous, or redeposited from older deposits. Pollen analysis revealed a new picture of the composition of the vegetation, as compared with earlier investigations. The flora consisted of an arctic-subarctic treeless shrub and herb vegetation dominated by Salix, Betula nana , Gramineae and Cyperaceae. Artemisia and several arctic-alpine herbs were important elements. The identification of Salix wood as well as fruits and fruit scales of Betula nana and Betula cf. humilis is in agreement with the pollen-analytical results, as is the occurrence of Nordicboreal species of Coleoptera. Two radiocarbon datings resulted in an age of c. 45,000 B. P. and >40,000 B.P. The Boliden till-covered sediments were most probably deposited during an Early or Middle Weichselian interstadial, but the initial or final stage of an interglacial (Eemian) is also possible.     

藏北南羌塘陆块北缘晚三叠世弄佰组火山岩的特征及构造环境

藏北南羌塘陆块北缘发育一套晚三叠世火山岩,命名为弄佰组。该组火山岩以玄武岩为主。岩石化学成分以低TiO_2、FeO Fe_2O_3、K_2O为特征。∑REE介于162.91×10~(-6)383.4×10~(-6)之间,∑Ce／∑Y介于1.83～3.00之间,δEu介于0.47～0.97之间,平均为0.73,负Eu异常较明显。微量元素Sr、K、Rb、Ba、Th、Ce、Sm强烈富集,Ta、Nb、P、Ti、Cr相对亏损。岩石学和岩石地球化学特征表明弄佰组火山岩形成于消减带岛弧区。弄佰组火山岩出露于龙木错-双湖结合带的南侧,K-Ar同位素年龄值为223Ma±5Ma.与双湖带中蓝片岩和绿片岩相变质岩系的形成年龄(220～235Ma)基本一致,时空关系的紧密相连,说明其形成可能与晚三叠世龙木错-双湖古特提斯洋的南向俯冲消减事件有关。     

西藏羌塘盆地中生代晚期构造事件与油气的关系

羌塘盆地在中生代晚期发生一次重要的构造运动,导致盆地结束海相沉积历史并形成区域性不整合。对该期构造事件发生的时代以及其对盆地油气成藏与保存的影响一直存在争议。本文根据近年来对羌塘盆地地层时代的新认识,结合盆地沉积埋藏和油气生成过程分析,认为该构造事件主要发生于早-晚白垩世之间(~100Ma),为班公湖-怒江洋盆最终闭合和拉萨-羌塘地块碰撞的结果。构造事件与盆地主要烃源岩该的生烃同时,盆地内与构造事件有关的圈闭构造为油气成藏提供了良好的场所,是盆地的主要评价和勘探目标。     

Late Pleistocene and Holocene History at Mubwindi Swamp, Southwest Uganda

Deposits beneath Mubwindi Swamp provide a partial record of vegetation history since at least 43,000 yr ago. We studied pollen from two cores and obtained nine radiocarbon ages from one of these cores and three radiocarbon ages from the other. Pollen deposited before and soon after the last glacial maximum represents vegetation very different from the modern vegetation of the Mubwindi Swamp catchment. Although species now associated with higher altitudes were dominant some elements of moist lower montane forest persisted, possibly because of favorable soils or topography. The pollen data provides evidence for a late glacial montane forest refuge near Mubwindi Swamp. Moist lower montane forest became much more widespread soon after the glacial maximum. The only irrefutably Holocene sediments from Mubwindi Swamp date to the past 2500 yr. During this time a combination of climatic and human-induced changes in vegetation can be seen in the pollen records.     

Late Holocene vegetational history,human impact and pollen representativity variations in northern Cumbria,England

The comparison of pollen diagrams and their inferred vegetational histories are an important component of palaeoecological research. Radiocarbon-dated pollen profiles from three cores taken from two adjacent mires located in northern Cumbria, Bolton Fell Moss and Walton Moss, have been used to reconstruct the Late Holocene vegetation history between the Bronze Age and the present day. The profiles have been interpreted in the light of available archaeological and historical records and, although the pollen records are broadly similar, there are some notable differences between them, particularly during Iron Age and medieval times. Dissimilarities between the diagrams are explored numerically, and the statistical and palynological results are discussed in relation to pollen representativity. The results suggest that it may be advantageous to construct more than one pollen diagram from a mire, or even adjacent mires, as extra-local pollen may be a more important part of the pollen rain than previously envisaged. © 1998 John Wiley & Sons, Ltd.     

Late Jurassic-Neocomian volcanism of the northern Okhotsk region: Geology,tectonic settings,and mineralization

The paper deals with new data on the geology, geochronometry, and petrogeochemistry of the Upper Jurassic-Neocomian basaltic andesites constituting the base of the Cretaceous volcanogenic section in the northern Okhotsk region. The geochronometric data confirm the Late Jurassic-Neocomian age of these rocks (147–138 Ma, K-Ar method). Their characteristic features provide grounds for considering these rocks as fragments of the Uda volcanic belt. The comparison of the petrogeochemical characteristics with similar parameters of other different-age tectonic structures of the region under consideration that were formed in different geodynamic environments (intracontiental and continental marginal volcanogenic belts, island arcs) revealed similarity between the conditions of the formation of the Late Jurassic-Neocomian (Uda belt) and Albian-Cenomanian (Okhotsk-Chukotka belt) volcanics: both characterize continental marginal environments. It is assumed that the Late Jurassic-Neocomian volcanism associates with Au-Ag mineralization, which is also expected in other similar although poorly known volcanic structures.     

Late Pleistocene and Holocene vegetation and climate on the northern Taymyr Peninsula, Arctic Russia

Pollen data from a Levinson-Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32 000 [Formula: See Text]C years. The continuous records confirm that a scarce steppe-like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000-10 300 [Formula: See Text]C yr BP, while tundra-like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18 000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10 500 [Formula: See Text]C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10 300-10 000 [Formula: See Text]C yr BP, is characterized by a change from the herb-dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000-8500 [Formula: See Text]C yr BP and disappeared c. 4000-3500 [Formula: See Text]C yr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10 000-3500 [Formula: See Text]C yr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500-3000 [Formula: See Text]C yr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 [Formula: See Text]C yr BP) temperature 2-4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 [Formula: See Text]C yr BP; later summers were similar to present or slightly warmer.     

晚新生代天山北缘构造变形定量研究

晚新生代以来,由于印藏板块陆—陆碰撞,天山山脉重新活动并隆升剥蚀。确定天山隆升变形时间和规模对研究大陆岩石圈变形以及构造活动、气候和剥蚀关系具有重要意义。本文通过生长地层和磁性地层研究,结合天山北缘地震剖面的构造解析,确定了天山北缘三排平行于天山山脉的褶皱带形成时间,并对三排褶皱带的变形量进行平衡恢复,其中三排褶皱中第一排的构造缩短量约为2.9 km(缩短率为15.1％),构造形成时间约为6 Ma,其缩短速率为0.4 mm/a;第二排构造缩短量约为5.9km(缩短率为23.7％),构造形成时间约为2 Ma,缩短速率为2.9mm/a;第三排构造缩短量约为4.3 km(缩短率为15.7％),构造形成时间约为1Ma,缩短速率为4.3mm/a;结果表明晚新生代以来天山构造活动强度可能在加大。     

晚新生代天山北缘构造变形定量研究

晚新生代以来,由于印藏板块陆—陆碰撞,天山山脉重新活动并隆升剥蚀。确定天山隆升变形时间和规模对研究大陆岩石圈变形以及构造活动、气候和剥蚀关系具有重要意义。本文通过生长地层和磁性地层研究,结合天山北缘地震剖面的构造解析,确定了天山北缘三排平行于天山山脉的褶皱带形成时间,并对三排褶皱带的变形量进行平衡恢复,其中三排褶皱中第一排的构造缩短量约为2.9 km(缩短率为15.1％),构造形成时间约为6 Ma,其缩短速率为0.4 mm/a;第二排构造缩短量约为5.9km(缩短率为23.7％),构造形成时间约为2 Ma,缩短速率为2.9mm/a;第三排构造缩短量约为4.3 km(缩短率为15.7％),构造形成时间约为1Ma,缩短速率为4.3mm/a;结果表明晚新生代以来天山构造活动强度可能在加大。     

Development of calcrete of the Late Cretaceous carbonate platform,northern Jordan,and its tectonic implications

A calcrete horizon, 3–10 m thick, is found exposed in northern Jordan in three localities, Rumman, Marsa’, and Wasfi At Tal forest (WTF). It is situated at the base of the dominantly limestone, Late Cenomanian Hummar Formation, separating it from the underlying marly Fuheis Formation. The calcrete horizon exhibits all the diagnostic features characteristic of calcrete, such as diagenetic pisoids; a mottled or clotted texture; circumgranular cracks around grains in a nodular texture; pendant or microstalactitic cement; meniscus cement; plant roots or rhizogenic structures, both longitudinal and transverse; exfoliation on boulder and cobbles; alagally laminated hard pans; and abundant dissolution of cracks and vugs. Consequently, it represents a subaerial erosional unconformity and type 1 sequence boundary (SB) that was not previously noticed. The Hummar Formation is considered as a third-order sequence with the SB at the base of the calcrete horizon, while the calcrete horizon itself forms the lowstand system tracts (LST). The transgressive systems tracts (TST) involve the lower two third of the Hummar Formation ending with peloidal grainstone representing the maximum flooding surface (MFSs). The rest of the formation is the falling highstand systems tracts (HST). The next SB is not seen due to a thick soil-covered gap. The calcrete horizon formed due to the formation of a paleohigh, in the study area, associated with the compression produced by the initial subduction of the Afro-Arabian Plate under the Eurasian Plate during the Late Cenomanian, slightly earlier than the previously known Turonian subduction and compression.     

Late Holocene paleoenvironment in northern New Caledonia, southwestern Pacific, from a multiproxy analysis of lake sediments

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 ¹⁴C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070-960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 ¹⁴C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.