Paleoenvironmental reconstruction of a Late Quaternary lagoon system in southern Brazil (Jaguaruna region,Santa Catarina state) based on multi‐proxy analysis

This paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (δ¹³C, δ¹⁵N and C/N), microfossil (pollen and diatom) and grain‐size analysis from three shallow cores (～2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid‐Holocene than today, with a gradual and continuous lagoon–sea disconnection until the present. We add to the debate regarding relative sea‐level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi‐proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright © 2011 John Wiley & Sons, Ltd.     

晚第四纪长江源区水系演化对断裂活动和气候变化的响应

河流沉积/侵蚀过程和水系演化对构造活动、气候变化和侵蚀基准面的响应过程与机制是流域地貌的重要科学问题。长江源地区河流受高寒气候和走滑断层引起的局部多种构造活动样式的影响, 是河流地貌过程对气候变化和构造活动响应的典型案例。文章通过野外考察、地貌指数(陡峭指数(k_sn)、Chi(χ)、Gilbert指数、河谷宽高比(Vf))的计算、沉积学和地形分析, 探讨了长江源水系演化对构造活动和气候变化的响应过程。通天河和澜沧江支流从上游相对年老的谷地(北西-南东向低k_sn值、高Vf值的宽谷)转变为下游相对年轻的谷地(南西-北东向高k_sn值、低Vf值的陡峭峡谷), 表明南西-北东向河流对北西-南东向河流的袭夺。通天河和澜沧江支流上游地区显示的高χ值、低起伏地形向下游方向快速转变为低χ值、高起伏地形, 也指示澜沧江和通天河向上游溯源侵蚀、袭夺分水岭地区原有老年期水系。局部分布的北西-南东向河谷(风口)、一系列间隔分布低洼地内河流沉积物和初步光释光年测年结果(13.3ka和>115ka)表明该地区在晚第四纪(可能在暖期)发育一条南东流向的古河流。随后断层走滑运动导致的局部构造抬升将河流分割成相互独立的内流湖。后期通天河和澜沧江干流(局部侵蚀基准面)侵蚀下降导致南西-北东向支流溯源侵蚀, 袭夺内流湖; 水系由树枝状演化为倒勾状。区域构造活动和局部侵蚀基准面变化是控制该地区水系演化的主要因素。晚第四纪气候变化引起河流堆积/侵蚀过程的改变也对水系的连通/中断有一定的影响, 后期需要进一步的研究。

     

Late Quaternary environmental phases in the Eastern Cape and adjacent Plettenberg Bay-Knysna region and Little Karoo, South Africa

Four major climato-environmental phases have been identified in the Eastern Cape, Plettenberg Bay-Knysna region and Little Karoo between somewhat before ∼40 000 cal. a BP and the present: the Birnam Interstadial from before 40 000 cal. a BP until ∼24 000 cal. a BP; the Bottelnek Stadial (apparently equating with the Last Glacial Maximum) from ∼24 000 cal. a BP until before ∼18 350 cal. a BP; the Aliwal North (apparently equating with the Late Glacial) from before ∼18 350 cal. a BP until ∼11 000 cal. a BP; the Dinorben (apparently equating with the Holocene) from ∼11 000 cal. a BP until the present. The evidence for, and the characteristics of, these phases is briefly described.     

青藏高原南部第四纪花粉植物群及古气候

本文选择了青藏高原南部具有代表性的６个花粉剖面，应用主成分分析处理这些剖面的花粉数据，重建了这些地区的古植被和古气候。研究表明，在青藏高原南部，早、中更新世的植被类型主要是松林、云杉林、铁杉林、桦林、桤木林和栎林，晚更新世和全新世的植被类型主要是高山灌丛草原、小半灌木草原、杂类草草甸、亚高山灌丛和落叶阔叶灌丛；在早、中更新世气候条件良好，有森林生长，晚更新世以后气候明显恶化，基本无森林生长。     

Late Quaternary fluvial activity in the dry valleys (mekgacha) of the Middle and Southern Kalahari,southern Africa

Kalahari dry ‘fossil’ valleys (mekgacha) have been little used in palaeoenvironmental reconstruction, partly because the origins and functions of the valleys are a subject of debate, and partly because they contain few datable sediments. In the Middle Kalahari the valleys are endoreic, and, following a decline in ground-water tables owing to human interference over the past 150 years, rarely contain water. Evidence from three sites suggests that the valleys contained standing water between 15000 and 12000 yr BP, and that the main Okwa-Mmone system flowed into palaeolake Makgadikgadi at 920 m a.s.l. during this period. The Southern Kalahari contains the exoreic Molopo network which is hydrologically more active, being prone to surface flows in response to extreme rainfall events. The spring—fed Kuruman valley has two terraces, the lower composed of a series of flood deposits of late Holocene age. The flood of February 1988 provides a useful analogue for the conditions under which these deposits were formed, and of the temporal regime of the Kuruman River. Comparison with adjacent sites suggests that evidence put forward to indicate cycles of climatic amelioration in the last 4000 yr may, in part, represents the effect of extreme precipitation events. Historical floods show a strong correlation to Southern Oscillation high-phase (cold event) episodes, suggesting possibilities for extension of the Southern Oscillation record through palaeoflood studies.     

Late Glacial and Holocene vegetation history in the southern part of Transylvania (Romania): pollen analysis of two sequences from Avrig

We present here the results of pollen analysis of two sequences of about 8.06 m and 11.90 m length, originating from two adjacent peat bogs in the southern part of Transylvania province, Romania (155 and 122 pollen spectra). The vegetation record, which is supported by 17 ¹⁴C dates, begins in the Late Glacial interstadial when forest recolonisation began with the development of Pinus, without a pioneer Betula phase. Picea began to expand from regional refuges. After a well‐defined Younger Dryas, the Holocene opens with the expansion of Betula, Ulmus and Picea, followed, at about 10 400 cal. yr BP, by Fraxinus, Quercus and Tilia. The Corylus optimum is correlated with the Atlantic chronozone (after 8600 cal. yr BP). The local establishment of Carpinus occurred at about 6500 cal. yr BP, with a maximum at about 5700 cal. yr BP. Fagus pollen is regularly recorded after 8200 cal. yr BP. This taxon became dominant at about 3700 cal. yr BP. The first indications of human activities appear at around 7200 cal. yr BP. Copyright © 2005 John Wiley & Sons, Ltd.     

Response of chironomids to Late Quaternary environmental change in the Taitao Peninsula,southern Chile

An Erratum has been published for this article in Journal of Quaternary Science 17(7) 2002, 721. There is conflicting evidence concerning the extent and timing of late Quaternary climate variability in southern South America and how this may be linked to climate change in the Northern Hemisphere. Critical unresolved questions include whether or not a cool period occurred in southern South America during the Younger Dryas Chronozone (YDC) (11 000–10 000 ¹⁴C yr BP; 13 000–11 200 yr BP), and the timing of wet and dry phases during the Holocene. To date most evidence is from glacial, pollen and beetle records but, in an attempt to resolve these questions, we have used chironomid midges as an independent proxy in one of the first studies of its kind in Patagonia. We investigated the dynamics of midge assemblages during the Late‐glacial and Holocene at Lago Stibnite on the Taitao Peninsula, southern Chile (46°S). Changes in the midge assemblage suggest that the climate may have become cooler and drier during the YDC. During the Holocene there were cyclical changes in the midge assemblage that may have been in response to trophic change and/or to changes in precipitation when conditions appear to have been drier than today at 9400–6300 ¹⁴C yr BP and 2400–1600 ¹⁴C yr BP. Copyright © 2002 John Wiley & Sons, Ltd.     

Tropical chemical weathering of hillslope deposits and bedrock source in the Aburrá Valley, northern Colombian Andes

Tropical chemical weathering produces extensive lateritization and formation of deep weathering profiles. Both processes are fundamental to landscape evolution and slope instability. The Aburrá Valley of the northern Colombian Andes is characterized by tropical conditions. The valley slopes are mostly covered by hillslope deposits originating from four basement rock suites which comprise contrasting granitoid, volcanic–sedimentary, ophiolitic, and metamorphic sources, respectively. Tropical chemical weathering of the Aburrá hillslope deposits and their respective bedrock were examined using X-ray fluorescence and X-ray diffraction analysis, to document and quantify their chemical weathering profiles, compositions, and mineralogical properties. The Chemical Index of Alteration (CIA), loss on ignition (LOI), and the Mobiles index (Imob) were used to quantify the degree of weathering of hillslope deposits and bedrock source. Weathering trends were analyzed using A–CN–K and A–CNK–FM diagrams. The material mantling the slopes in the Aburrá Valley records an intense weathering history. Chemical weathering is characterized by increased development of clay minerals (kaolinite, halloysite) and iron and aluminum sesquioxides. Lateritization characterizes the final stage of the weathering profiles. Concentrations of CaO, Na₂O, K₂O decrease markedly in the weathering products compared to the fresh bedrock source, whereas concentrations of Al₂O₃, Fe₂O₃, and MgO increase significantly. CIA ratios of matrix slope deposits derived from all four sources near 100, whereas those of boulder slope deposits and saprolites are lower, but exceed source rock values. Different A–CN–K weathering paths are evident for each lithotype, validating the correlation established between the hillslope deposits and their various parents. Chemical weathering indices in some samples are strongly influenced by the presence of sesquioxides, as reflected by high LOI, anomalously low CIA, and varying enrichment trends on the A–CNK–FM diagrams. Consequently, different chemical indices based on different criteria need to be combined to obtain best results, as illustrated here by the combination of LOI, CIA, and Imob. The overall results suggest that tropical conditions have dominated for a long time in the northern Colombian Andes, leading to uniformly high weathering indices in matrix slope deposits irrespective of parent lithotype. Prolonged warm and humid conditions could thus be responsible for the weathering and remobilization of extensive old hillslope deposits during the Quaternary. However, in addition to the influence of climatic factors, tectonism has also undoubtedly influenced slope evolution in the Aburrá Valley.     

Late Quaternary vegetation and fire history in the northernmost Nothofagus forest region: Mallín Vaca Lauquen,Neuquén Province,Argentina

The last 16 000 cal. a of vegetation, fire and limnological history are described from the steppe‐forest ecotone in the northernmost Nothofagus forest region east of the Andes (Mallín Vaca Lauquen, Neuquén Province, Argentina, latitude 36° 51.336′ S, longitude 71° 02.538′ W). Between 16 000 and 14 800 cal. a BP, scrub steppe with substantial open ground expanded in formerly glaciated valleys, whereas Nothofagus–Prumnopitys andina woodland covered mountain slopes. The site was a relatively deep and unproductive small lake at this time. After 14 800 cal. a BP, both steppe and woodland vegetation became denser, indicating increased moisture and temperatures, although not to present levels. The lake was still relatively deep and dystrophic, but became more alkaline by 10 000 cal. a BP. Between 8900 and 5500 cal. a BP, conditions were markedly drier than before; a Cyperaceae marsh developed and disturbance taxa increased. After 5500 cal. a BP, moisture increased but varied greatly, as evidenced by fluctuating water levels and high fire activity from 5500 to 4400 cal. a BP and from 2300 to 1000 cal. a BP. Human activity, in terms of forest clearance and livestock grazing, is documented in the uppermost levels. The evidence of high environmental variability in the middle and late Holocene is consistent with the onset or strengthening of the El Niño–Southern Oscillation, but differences in the timing of fire activity among sites on the west and east sides of the Andes suggest that fuel conditions were important in determining the local occurrence of fire. Copyright © 2008 John Wiley & Sons, Ltd.     

甘肃武威盆地南缘断裂带晚第四纪活动特征及变形分析

武威盆地南缘断裂带位于青藏高原东北缘的前锋地带,关于该构造带的空间展布和晚第四纪活动习性等科学问题尚不清楚。此外,1927年8.0级古浪地震也造成断裂带上的一些地表破裂。运用构造地质学与地貌学原理及年代学测试方法, 展开了相关调查和研究。结果表明,①武威盆地南缘断裂带为NWW—SEE走向、呈右阶斜列式展布。②自西向东, 断裂带的晚第四纪活动方式整体表现为以逆冲为主,逐步过渡为逆冲兼走滑运动或走滑活动为主;垂向上的活动强度整体上西弱东强,且中间增加的幅度最大, 而断裂带的水平左旋滑移分量中-东段较大。③断裂活动具有明显的分段性,即西段的最新活动一般早于区域性T1阶地的形成时间,中-东段切割了T1阶地面,反映了断裂最新活动具有东向迁移的变化趋势。④结合露头揭示的1927年8.0级古浪地震地表破裂遗迹,该断裂中-东段的最新活动发生于全新世末期。⑤依据武威盆地南缘断裂带的晚第四纪活动方式、断面擦痕、晚新生代地层内发育的剪切节理运动学特征及共轭张性节理等,该区域的第四纪晚期最大主压应力水平方向表现为NNE—SSW向,且自西向东应力场方位略有变化。上述认识,对探索武威盆地三维变形的晚新生代构造演化、青藏高原东北缘地层生长和构造地貌变形过程,以及古浪地震的破裂机制与气候环境变迁等,提供了重要依据。     

贵州西部晚全新世植被演替、气候变化与火灾历史

贵州西部位于北亚热带云贵高原山地湿润-半湿润气候区,西南季风是该区域水汽来源的主要气候系统。贵州六盘水娘娘山有连片分布的垫状泥炭沼泽沉积,较完整记录了过去的植被和气候历史,是研究气候-植被-火灾-人类活动变化的理想场所。本研究以六盘水娘娘山1999 m海拔的一处泥炭湿地钻孔上部52 cm岩芯为研究材料,通过AMS ¹⁴C测年获得年代框架,采用孢粉和炭屑分析,重建了该地区晚全新世气候变化和人类活动叠加影响下的植被演替及火灾活动历史。结果表明：3500~3100 cal.a B.P. 期间,当地亚热带常绿阔叶林繁盛,火灾活动为气候控制为主的森林火灾,但火灾活动并未改变阔叶林的总体面貌;3100~600 cal.a B.P. 期间,气候呈变干趋势,阔叶类木本植物显著减少,当地植被从亚热带常绿阔叶林转变为疏林草地和针叶类疏林,极可能是趋于冷干的气候环境的结果;大约600 cal.a B.P. 之后,当地植被演变为开阔林,同时,出现大颗粒炭屑(>125 μm)以及伴人花粉的明显增加,表明人类农业活动高强度的刀耕火种已经扩张到较高海拔山区。区域对比显示,西南地区在3500 cal.a B.P. 以来,主要以区域性火灾为主,而3100 cal.a B.P. 以后的火灾活动受到气候变干和人类活动的双重影响,特别是600 cal.a B.P. 以来,人类活动(刀耕火种)成为局地火灾和植被更替的主要因素。

     

Spatial distribution of climatic conditions from the Middle Eocene to Late Miocene based on palynoflora in Central,Eastern and Western Anatolia

The continental climatic evolution of Anatolia has been reconstructed quantitatively for the last 45 million years using the coexistence approach. Although there were some regional effects, the Anatolian Cenozoic continental climate record correlated with the European climatic condition and the global oxygen isotope record from marine environments. From middle Eocene to late Miocene, continental warming in Anatolia was pronounced for inferred winter temperature and mean annual temperature as in Europe. Generally, the palaeoclimatic property of Anatolia resembles the European climatic changing and marine temperature changing based on the oxygen isotope record; however, climatic values of the terrestrial area in Anatolia are higher from Lutetian to Aquitanian and these values are lower than European values from Aquitanian to Tortonian. Correspondingly, Cenozoic climatic cooling in Anatolia is directly associated with an increase of seasonality, palaeogeographic position and terrestrial condition. Furthermore, mean annual precipitation values of Anatolia remained relatively stable during the Eocene–Oligocene; however, these values indicated changing throughout middle–late Miocene. Moreover, in this study, decline of abundance and variables for the mangrove and back mangrove palaeocommunities during the last 45 million years is recorded because of the decreasing of humidity, temperature and increasing of terrestrial condition.     

Late Quaternary stratigraphic development in the lower Luni,Mahi and Sabarmati river basins,western India

This study reviews the Quaternary alluvial stratigraphy in three semi-arid river basins of western India i.e., lower Luni (Rajasthan), and Mahi and Sabarmati (Gujarat alluvial plains). On the basis of OSL chronologies, it is shown that the existing intra-valley lithostratigraphic correlations require a revision. The sand, gravel and mud facies are present during various times in the three basins, however, the fluvial response to climate change, and the resulting facies associations, was different in the Thar desert as compared to that at the desert margin; this makes purely lithostratigraphic correlations unviable. It is further shown that the rivers in the Thar desert were more sensitive to climate change and had small response times and geomorphic thresholds as compared to the desert-margin rivers. This is illustrated during the early OIS 1, when the Luni river in the Thar desert was dynamic and showed frequent variations in fluvial styles such as gravel bedload braided streams, sand-bed ephemeral streams and meandering streams, all followed by incision during the early Holocene. The coeval deposits in Sabarmati, however, only show a meandering, floodplain-dominated river. Late Quaternary alluvial deposits in these basins unconformably overlie some older deposits that lack any absolute chronology. Based on the facies types and their associations, and the composition and architecture of the multistoried gravel sheets in the studied sections, it is suggested that older deposits are of pre-Quaternary age. This hypothesis implies the presence of a large hiatus incorporating much of the Quaternary period in the exposed sections     

Late Quaternary vegetation,climate and fire dynamics inferred from the El Tiro record in the southeastern Ecuadorian Andes

In order to study the stability and dynamics of mountain rainforest and paramo ecosystems, including the biodiversity of these ecosystems, the Holocene and late Pleistocene climate and fire variability, and human impact in the southeastern Ecuadorian Andes, we present a high‐resolution pollen record from El Tiro Pass (2810 m elevation), Podocarpus National Park. Palaeoenvironmental changes, investigated by pollen, spores and charcoal analysis, inferred from a 127 cm long core spanning the last ca. 21 000 cal. yr BP, indicate that grass‐paramo was the main vegetation type at the El Tiro Pass during the late Pleistocene period. The grass‐paramo was rich in Poaceae, Plantago rigida and Plantago australis, reflecting cold and moist climatic conditions. During the early Holocene, from 11 200 to 8900 cal. yr BP, subparamo and upper mountain rainforest vegetation expanded slightly, indicating a slow warming of climatic conditions during this period. From 8900 to 3300 cal. yr BP an upper mountain rainforest developed at the study site, indicated by an increase in Hedyosmun, Podocarpaceae, Myrsine and Ilex. This suggests a warmer climate than the present day at this elevation. The modern subparamo vegetation became established since 3300 cal. yr BP at El Tiro Pass. Fires, probably anthropogenic origin, were very rare during the late Pleistocene but became frequent after 8000 cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd.     

Extensional Late Paleozoic deformation on the western margin of Pangea, Patlanoaya area, Acatlán Complex, southern Mexico

New mapping in the northern part of the Paleozoic Acatlán Complex (Patlanoaya area) records several ductile shear zones and brittle faults with normal kinematics (previously thought to be thrusts). These movement zones separate a variety of units that pass structurally upwards from: (i) blueschist-eclogitic metamorphic rocks (Piaxtla Suite) and mylonitic megacrystic granites (Columpio del Diablo granite ≡ Ordovician granites elsewhere in the complex); (ii) a gently E-dipping, listric, normal shear zone with top to the east kinematic indicators that formed under upper greenschist to lower amphibolite conditions; (iii) the Middle–Late Ordovician Las Minas quartzite (upper greenschist facies psammites with minor interbedded pelites intruded by mafic dikes and a leucogranite dike from the Columpio del Diablo granite) unconformably overlain by the Otate meta-arenite (lower greenschist facies psammites and pelites): roughly temporal equivalents are the Middle–Late Ordovician Mal Paso and Ojo de Agua units (interbedded metasandstone and slate, and metapelite and mafic minor intrusions, respectively) — some of these units are intruded by the massive, 461 ± 2 Ma, Palo Liso megacrystic granite: decussate, contact metamorphic muscovite yielded a ⁴⁰Ar/³⁹Ar plateau age of 440 ± 4 Ma; (iv) a steeply-moderately, E-dipping normal fault; (v) latest Devonian–Middle Permian sedimentary rocks (Patlanoaya Group: here elevated from formation status). The upward decrease in metamorphic grade is paralleled by a decrease in the number of penetrative fabrics, which varies from (i) three in the Piaxtla Suite, through (ii) two in the Las Minas unit (E-trending sheath folds deformed by NE-trending, subhorizontal folds with top to the southeast asymmetry, both associated with a solution cleavage), (iii) one in the Otate, Mal Paso, and Ojo de Agua units (steeply SE-dipping, NE–SW plunging, open-close folds), to (iv) none in the Patlanoaya Group. ⁴⁰Ar/³⁹Ar analyses of muscovite from the earliest cleavage in the Las Minas unit yielded a plateau age of 347 ± 3 Ma and show low temperature ages of  260 Ma. Post-dating all of these structures and the Patlanoaya Group are NE-plunging, subvertical folds and kink bands. An E–W, vertical normal fault juxtaposes the low-grade rocks against the Anacahuite amphibolite that is cut by megacrystic granite sheets, both of which were deformed by two penetrative fabrics. Amphibole from this unit has yielded a ⁴⁰Ar/³⁹Ar plateau age of 299 ± 6 Ma, which records cooling through  490 °C and is probably related to a Permo-Carboniferous reheating event during exhumation. The extensional deformation is inferred to have started in the latest Devonian ( 360 Ma) during deposition of the basal Patlanoaya Group, lasting through the rapid exhumation of the Piaxtla Suite at  350–340 Ma synchronous with cleavage development in the Las Minas unit, deposition of the Patlanoaya Group with active fault-related exhumation suggested by Mississippian and Early Permian conglomerates ( 340 and 300 Ma, respectively), and continuing at least into the Middle Permian (≡ 260 Ma muscovite ages). The continuity of Mid-Continent Mississippian fauna from the USA to southern Mexico suggests that this extensional deformation occurred on the western margin of Pangea after closure of the Rheic Ocean.     

Late Quaternary palaeoecological and palaeoclimatological reconstruction in the Gutaiului Mountains,northwest Romania

Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss‐on‐ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus–Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13 400 and 13 200 cal. yr BP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13 400 cal. yr BP. A distinct decrease in temperature and humidity between 12 900 and 11 500 cal. yr BP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11 800 cal. yr BP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11 500 cal. yr BP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11 250 cal. yr BP. Larix pollen was not found, but macrofossil evidence indicates that Larix was an important forest constituent at the onset of the Holocene. Moister conditions were followed by a dry period starting about 10 600 cal. yr BP, which was more pronounced between 8600 and 8200 cal. yr BP, as inferred from aquatic macrofossils. The maximum expansion of Tilia, Quercus, Fraxinus and Acer between 10 700 and 8600 cal. yr BP may reflect a more continental climate. A drier and/or cooler climate could have been responsible for the late expansion (10 300 cal. yr BP) and late maximum (9300 cal. yr BP) of Corylus. Increased water stress, and possibly cooler conditions around 8600 cal. yr BP, may have caused a reduction of Ulmus, Tilia, Quercus and Fraxinus. After 8200 cal. yr BP moisture increased and the forests included Picea, Tilia, Quercus and Fraxinus. Copyright © 2004 John Wiley & Sons, Ltd.     

渤海莱州湾晚第四纪底栖有孔虫分布特征及其地质意义

通过对渤海莱州湾GK138、GK111及GK95孔的255个沉积物样品中的有孔虫定量统计分析,共鉴定出底栖有孔虫15属32种。根据底栖有孔虫的丰度和分异度等分布特征和AMS14C和光释光（OSL）测年结果,揭示晚第四纪以来研究区共发育3套海相地层,分别是中更新世晚期的第三海相层、晚更新世的第二海相层和全新世的第一海相层,通过与全球海面变化曲线对比,发现其与MIS7、MIS5和MIS1阶段的高海面有良好的对应关系。样品的Q型聚类及主成分分析划分出3组代表不同沉积环境的有孔虫化石组合,第III化石组合带为中更新世晚期海侵的产物,为河口-滨岸浅海环境。第Ⅱ化石组合为晚更新世海侵的产物,为潮间带-潮下带沉积环境,第I化石组合带为潮上带-潮间带沉积环境。海相地层顶、底板高程和厚度的分析结果显示中更新世晚期至晚更新世期间发生过不同期次、不同强度的构造活动,而进入全新世以后构造活动相对减弱。     

Depositional system and palaeoclimatic interpretations of Middle to Late Pleistocene travertines: Kocabaş, Denizli,south‐west Turkey

Travertine deposits in western Turkey are very well‐exposed in the area of Kocaba?, in the eastern part of the Denizli Basin. The palaeoclimatic significance of these travertines is discussed using U/Th dates, stable isotope data and palynological evidence. The Kocaba? travertine occurrences are characterized by successions of depositional terraces associated with palaeosols and karstic features. The travertines have been classified into eight lithotypes and one erosional horizon, namely: laminated, coated bubble, reed, paper‐thin raft, intraclasts, micritic travertine with gastropods, extra‐formational pebbles and a palaeosol layer. The analysed travertines mostly formed between 181 ka and 80 ka (Middle to Late Pleistocene) during a series of climatic changes including glacial and interglacial intervals; their δ¹³C and δ¹⁸O values indicate that the depositional waters were mainly of basinal thermal origin, occasionally mixed with surficial meteoric water. Palynological results obtained from the palaeosols showed an abundance of non‐arboreal percentage and xerophytic plants (Oleaceae and Quercus evergreen type) indicating that a drought occurred. Marine Isotope Stage 6 is represented by grassland species but Marine Isotope Stage 5 is represented by Pinaceae–Pinus and Abies, Quercus and Oleaceae. Uranium/thorium analyses of the Kocaba? travertines show that deposition began in Marine Isotope Stage 6 (glacial) and continued to Marine Isotope Stage 4 (glacial), but mostly occurred in Marine Isotope Stage 5 (interglacial). The travertine deposition continued to ca 80 ka in the south‐west of the study area, in one particular depression depositional system. Palaeoenvironmental indicators suggest that the travertine depositional evolution was probably controlled by fault‐related movements that influenced groundwater flow. Good correlation of the stable isotope values and dates of deposition of the travertines and palynological data of palaeosols in the Kocaba? travertines serve as a starting point for further palaeoclimate studies in south‐west Turkey. Additionally, the study can be compared with other regional palaeoclimate archives.     

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr^− 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr^− 1.

Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr^− 1. Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr^− 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the ²¹⁰Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr^− 1) exceeds the maximum sedimentation rate by 1.8 m kyr^− 1, which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.