Late Quaternary climatic events and sea-level changes recorded by turbidite activity, Dakar Canyon, NW Africa

The relationship of sea-level changes and short-term climatic changes with turbidite deposition is poorly documented, although the mechanisms of gravity-driven sediment transport in submarine canyons during sea-level changes have been reported from many regions. This study focuses on the activity of the Dakar Canyon off southern Senegal in response to major glacial/interglacial sea-level shifts and variability in the NW-African continental climate. The sedimentary record from the canyon allows us to determine the timing of turbidite events and, on the basis of XRF-scanning element data, we have identified the climate signal at a sub-millennial time scale from the surrounding hemipelagic sediments. Over the late Quaternary the highest frequency in turbidite activity in the Dakar Canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea-level rise. However, episodic turbidite events coincide with the timing of Heinrich events in the North Atlantic. During these times continental climate has changed rapidly, with evidence for higher dust supply over NW Africa which has fed turbidity currents. Increased aridity and enhanced wind strength in the southern Saharan-Sahelian zone may have provided a source for this dust.     

North Atlantic control on precipitation pattern in the eastern Mediterranean/Black Sea region during the last glacial

Based on proxy records from western Black Sea cores, we provide a comprehensive study of climate change during the last glacial maximum and late-glacial period in the Black Sea region. For the first time we present a record of relative changes in precipitation for NW Anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration. The good correspondence between reconstructed rainfall intensity in NW Anatolia and past western Mediterranean sea surface temperatures (SSTs) implies that during the glacial period the precipitation variability was controlled, like today, by Mediterranean cyclonic disturbances. Periods of reduced precipitation correlate well with low SSTs in the Mediterranean related to Heinrich events H1 and H2. Stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater/sediment source concomitant to the meltwater inflow after 16.4 cal ka BP. This change implies intensification of the northern sediment source and, with other records from the Mediterranean region, consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the European continent. The early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the Mediterranean region, leading simultaneously to more humid conditions in central and northern Europe.     

Organic matter characterisation of the Selli Level (Umbria-Marche Basin, central Italy)

The Selli Level is a marker-bed in the Umbria-Marche Apennines that represents the regional sedimentary expression of the Lower Aptain Oceanic Anoxic Event 1a. This one to three-metre-thick interval shows a remarkable uniformity on a regional scale, with a green to grey marly lower part overlain by black shales. Bulk geochemical studies and an examination of palynofacies were carried out on three sections in order to characterise the distribution and nature of the organic matter in the Selli Level which has been poorly known hitherto. The organic content is medium (0.5 to 2.9% TOC) in the basal part and higher (4.5% on average, and up to 18% TOC) in the black shales. Pyrolysis and palynological data indicate that the organic matter is mainly of marine origin. The geochemical characteristics of the Selli Level are compared to other, more or less organic-rich marker-beds in the Cretaceous succession of the Umbria-Marche Apennines.

Abstract

Le Niveau Selli est un niveau-repère des Apennins d'Ombrie-Marches qui correspond à l'enregistrement régional de l'événement anoxique océanique 1a. Ce niveau, épais de un à trois mètres, présente une remarquable uniformité à l'échelle régionale avec une partie inférieure argileuse, verdâtre à grise, surmontée par des black shales. Des analyses géochimiques et l'examen des palynofacies ont été entreprises sur trois coupes afin de caractériser le contenu en matière organique du niveau Selli, jusqu'à présent mal connu. Les teneurs en carbone organique sont moyennes (0,5 à 2,9% COT) dans la partie basale et élevées (4,5% en moyenne et jusque 18% COT) dans les black shales. Les résultats de pyrolyse et des observations palynologiques indiquent que la matière organique est essentiellement d'origine marine. Les caractéristiques géochimiques du niveau Selli sont comparées aux autres niveaux repères, plus ou moins riches en carbone organique, qui émaillent la série du Crétacé du basin d'Ombrie-Marches.     

Late Pleistocene sea-level oscillations (MIS 10–2) recorded in shallow marine and coastal plain sediments of the southern Wanganui Basin, New Zealand

The northern Wanganui Basin, New Zealand, is one of the key global sites for understanding marine cyclic sedimentation during the Quaternary. This paper presents the first evidence of marine cyclic sedimentation from its central-southern parts. Sedimentological, micropalaeontological and palynological analyses on a 280-m-deep borehole encountered units dating back to MIS 10. The sequence includes four marine cycles spanning MIS 9–5, which are overlain by terrestrial fluvial aggradation surfaces dating from MIS 4–2. Each marine unit represents a progressively shallowing depositional environment from the mid-shelf to coastal plain. This is overlain by a terrestrial sequence of lowstand fluvial terraces. Localized fault movements appear to have influenced the sedimentary character of the sequence during MIS 7a and 5e producing basement highs which provided protection to the shoreline. The cyclothems described in this paper now extend the already extensive, previously described record from MIS 17–10 to produce a combined eustatic record of Quaternary sea level change within the basin to MIS 5. They also provide an excellent example of the sedimentary response of a coastal basin to a progressive loss of sedimentation accommodation space.     

北淮阳晓天盆地早白垩世玄武岩地球化学:富集地幔的证据

产出于北淮阳地区晓天盆地的早白垩世玄武岩的主量元素具有碱性系列和亚碱性系列过渡的特征。其微量元素特征表现为Rh、Ba、Th、K、Pb的显富集和Nb、Ti的亏损。锶和钕同位素的初始比值分别为0．7076，0.7080和—13．9，—12．7。这些特征表明所研究玄武岩来自富集的源区，很可能是古老的扬子型岩石圈地馒。与长江中下游和大别造山带中同时代幔源岩石相比表明，虽然总体上都表现为富集特征，但具有明显的不均一性。长江中下游地幔源区最亏损，可能反映来自亏损的软流圈地慢和富集的岩石圈地幔的物质的混合。大别造山带的源区最富集，代表古老岩石圈的贡献。北准阳地区玄武岩的源区特征与大别造山带的非常相似，但富集程度略低。     

The relative utility of foraminifera and diatoms for reconstructing late Holocene sea-level change in North Carolina, USA

Foraminifera and diatoms preserved in salt-marsh sediments have been used to produce high-resolution records of Holocene relative sea-level (RSL) change. To determine which of these microfossil groups is most appropriate for this purpose we investigated their relative utility from salt marshes in North Carolina, USA. Regional-scale transfer functions were developed using foraminifera, diatoms and a combination of both (multi-proxy) from three salt marshes (Oregon Inlet, Currituck Barrier Island and Pea Island). We evaluated each approach on the basis of transfer-function performance. Foraminifera, diatoms and multi-proxy-based transfer functions all demonstrated a strong relationship between observed and predicted elevations (r²_jack > 0.74 and RMSEP < 0.05 m), suggesting that they have equal utility. Application of the transfer functions to a fossil core from Salvo to reconstruct former sea levels enabled us to consider relative utility in light of ‘paleo-performance’. Fossil foraminifera had strong modern analogues, whilst diatoms had poor modern analogues making them unreliable. This result reflects the high diversity and site-specific distribution of modern diatoms. Consequently, we used foraminifera to reconstruct RSL change for the period since ∼ AD 1800 using a ²¹⁰Pb- and ¹⁴C-based chronology, and we were able to reconcile this with tide-gauge records.     

北黄海盆地LV井侏罗系油砂抽提物地球化学特征

对北黄海盆地侏罗系两块含油砂岩的抽提物进行了常规的有机地球化学分析和碳同位素测试,结果表明它们具有不同的地球化学特征:埋藏较深的油砂抽提物属正常原油,饱和烃以正构烷烃为主,色谱图显示单峰型正态分布;而埋藏较浅的油砂抽提物,在饱和烃色谱图中有明显的UCM鼓包,同时含有完整的低碳数的正构烷烃、姥鲛烷和植烷,全油及族组成碳同位素分布范围广,为-24.7‰~-32.3‰,其中,全油及沥青质碳同位素偏重,饱和烃和芳烃碳同位素轻,反映出遭受了强烈的生物降解作用。与成熟度相关的生物标志物参数显示,原油已进入成熟—高成熟阶段。生物标志物和碳同位素组成表明,母质是在水体较浅的湖相环境下沉积的,受陆源高等植物和低等水生藻类的双源控制。综合判断,研究区存在两期油气充注。     

北羌塘盆地索瓦组上段的时代、古气候及石油地质特征

索瓦组上段是羌塘盆地演化晚期的一套潮坪—潟湖相沉积,分布于北羌塘盆地中部。通过对索瓦组上段区域地层对比,发现索瓦组上段在盆地东部、西部和南部的岩性变化较大,海相油页岩的出露地仅分布于北羌塘坳陷南部胜利河—长蛇山—托纳木一线的局限海湾—潟湖的边缘带,其形成明显受到了古地理条件的控制。根据索瓦组上段以及其下伏地层产出的生物化石组合,并结合油页岩的Re-Os同位素年龄,认为索瓦组上段的时代可能为早白垩世。对该组产出的孢粉化石组合和硅化木分析表明,索瓦组上段在沉积早期和晚期的古气候条件发生了明显的变化,早期为温暖和湿润气候,而晚期为半干旱—干旱气候,这种垂向上的古气候变化特征不仅仅局限于胜利河地区,可能在整个北羌塘盆地都普遍存在。索瓦组上段发育的油页岩及其上部膏岩沉积组合的发现,对于评价羌塘盆地演化晚期的石油地质条件具有重要的意义。     

勘探早—中期的沉积盆地有效烃源岩综合预测方法探讨——以北黄海某盆地为例

针对勘探程度较低的地区,提出了一套有效烃源岩的综合预测方法。其基本思路是,从钻井出发,井震结合,按由点到面、由剖面到平面的顺序分五步进行:确定有利沉积相带;确定烃源岩平面分布;划分区域沉积相分布;确定平面热演化分布;有效烃源岩分布预测。利用该方法,对北黄海某盆地侏罗系SQ1层序进行了有效烃源岩预测。