Cyclic sedimentation patterns in Lower Lias mudstones of Yorkshire (GB)

Distinct stratification patterns in Lower Liassic mudstones are due to the regular occurrence of shell beds, silty/sandy layers and concretionary horizons. The mudstones formed in four depositional environments: (1) a storm dominated shallow marine system; (2) a hemipelagic system; (3) a shallow marine system influenced by climatic changes at astronomical frequencies; and (4) a pro-deltaic offshore transition/shallow marine system. The tectonic setting played an important role in determining the facies sequence, whereas eustatic sea-level changes were of lesser influence.     

Normal faulting as a control on the stratigraphic development of shallow marine syn-rift sequences: the Nukhul and Lower Rudeis Formations, Hammam Faraun fault block, Suez Rift, Egypt

Tectono-stratigraphic analysis of the East Tanka fault zone (ETFZ), Suez Rift, indicates that the evolution of normal fault segments was an important control on syn-rift depositional patterns and sequence stratigraphy. Sedimentological and stratigraphic analysis of the Nukhul Formation indicates that it was deposited in a narrow (ca 1–2 km), elongate (ca 5 km), fault-bounded, tidally influenced embayment during the low subsidence rift-initiation phase. The Nukhul Formation is composed of transgressive (TST) and highstand (HST) systems tract couplets interpreted as reflecting fault-driven subsidence and the continuous creation of accommodation in the hangingwall to the ETFZ. The overlying Lower Rudeis Formation was deposited during the high subsidence rift-climax phase, and is composed of forced regressive systems tract (FRST) shallow marine sandbodies, and TST to HST offshore mudstones. Activity on the ETFZ led to marked spatial variability in stratal stacking patterns, systems tracts and key stratal surfaces, as footwall uplift, coupled with regressive marine erosion during deposition of FRST sandbodies, led to the removal of intervening TST–HST mudstone-dominated units, and the amalgamation of FRST sandbodies and the stratal surfaces bounding these units in the footwall. This study indicates that the evolution of normal fault segments over relatively short (i.e. <1 km) length-scales has the potential to enhance or suppress a eustatic sea-level signal, leading to marked spatial variations in stratal stacking patterns, systems tracts and key stratal surfaces. Crucially, these variations in sequence stratigraphic evolution may occur within time-equivalent stratal units, thus caution must be exercised when attempting to correlate syn-rift depositional units based solely on stratal stacking patterns. Furthermore, local, tectonically controlled variations in relative sea level can give rise to syn-rift stacking patterns which are counterintuitive in the context of the structural setting and perceived regional subsidence rates.     

安徽宿松上石炭统碳酸盐岩台地沉积物定量分析与海平面变化

安徽宿松地区上石炭统碳酸盐岩发育,厚约100m,化石丰富,属于比较典型的浅海碳酸盐岩台地沉积。定量分析显示,研究区岩石类型主要为颗粒灰岩和泥粒灰岩,颗粒平均含量分别为81.2％和69.6％,以浅海生物碎屑为主;其次为粒泥灰岩和泥晶灰岩,颗粒平均含量分别为26.4％和4.1％。依据岩石学特征,研究区主要发育开阔台地相和潮坪相,并可进一步划分出5种沉积亚相,分别是台内滩、台内盆、台内坪、潮间坪和潮上坪。在研究区上石炭统中共识别出3个长期的海进—海退旋回,其表现出在海平面变化总体呈下降趋势的背景之上叠加了短期的高频海平面波动的特征。这3个旋回与扬子板块其他地区及欧美板块同时代地层中的长期海进—海退旋回相当,表明海平面的变化可能受到晚古生代冈瓦纳大陆冰川的冰期和间冰期交替活动的影响。     

Sedimentology of middle ordovician carbonates in the Argentine precordillera: evidence of regional relative sea-level changes

The Las Aguaditas Formation in the Argentine Precordillera of San Juan is the only Ordovician carbonate sequence deposited on a slope. Spiculites, mudstones and calcisiltites represent the autochthonous sediments, characterized by a fine lamination, rare fossils and their dark colour. The pelagic fauna consists of rare radiolarians/calcispheres, trinucleid trilobites, graptolites and conodonts. The latter are typical of an open marine environment and proved a Llanvirn—Llandeilo age for the Las Aguaditas Formation.In the upper part of the succession there are several intercalations of megabreccias. Their thickness decreases from about 20 to 4 m towards the top of the formation, accompanied by an increasing amount of carbonate turbidites. The clasts of the breccias are derived from the slope as well as the platform. Each of the megabreccia horizons represents a system of channels, lobes and interchannel deposits, which together form a slope apron. On top of the lower breccia a small biostrome developed, where bryozoans and crinoids are preserved in an autochthonous position.Sedimentation of the Las Aguaditas Formation started with the drowning of the underlying carbonate platform (San Juan limestones). Near the Arenig-Llanvirn boundary, a rapid ecstatic sea-level rise led to the deposition of graptolitic black shales and mudstones. Upwards, allochthonous carbonates become increasingly abundant. The onset of megabreccia deposition coincides with a major relative sea-level fall, caused by block movements in connection with rifting. The subsequent transition from breccia formation towards turbiditic sedimentation corresponds to an environmental shift from the slope towards the toe of slope and basin and marks a renewed moderate sea-level rise. Correspondence to: M. Keller     

Diagenesis of Barremian-Aptian platform carbonates (the Urgonian Limestone Formation of SE France): near-surface and shallow-burial diagenesis

The diagenesis of carbonate platform sediments is controlled by the original facies and mineralogy, climate, sea-level changes and burial history; these controls are clearly seen in the diagenesis of the Urgonian platform carbonates of SE France. Early diagenesis in the Urgonian platform included the precipitation of marine cements, dissolution of rudist shells and minor karstification. Diagenetic features produced during this phase were controlled by several falls in relative sea-level during the Barremian to mid-Aptian punctuating platform sedimentation, the original mineralogy of the sediment and the prevailing semi-arid/arid climate in the region at this time. Following a relative sea-level rise and further sedimentation, progressive burial of the platform led to minor compaction, followed by precipitation of coarse, equant, zoned to non-luminescent, calcite cement. This cement was cut by later stylolites, suggesting a relatively shallow-burial origin. Stable isotope (mean values - 7.94%δ¹⁸O and 0.36%δ¹³C) and trace element (mean values of Fe 334 ppm, Mn 92 ppm and Sr 213 ppm) data suggest that these cements precipitated from meteoric fluids at temperatures slightly elevated relative to depositional temperatures. A variable thickness of replacive dolomite which occurs preferentially within the shelf-margin facies of the lower part of the Urgonian post-dates mechanical fracturing and chemical compaction, but pre-dates the main phase of stylolitization. It is probable that the dolomitizing fluid was sourced by the early compaction-driven release of connate fluids held within the underlying muddy units. The burial history of these rocks suggests that calcite cementation and dolomitization took place at relatively shallow burial depths (1–1.5 km). The overall diagenetic history of the Urgonian Limestone Formation is a reflection of the pre-conditioning of the platform limestones by climate, sea level, tectonics and the shallow burial depths experienced by the platform during the later Mesozoic.     

贵州瓮安陡山沱组含磷岩系沉积序列及磷块岩的形成

贵州瓮安陡山沱组磷块岩为碳酸盐岩型含磷岩系,属于浅海碳酸盐岩台地沉积区。对瓮安磷矿大塘剖面进行沉积环境研究,将Marinoan冰期后沉积的陡山沱组地层分为6个向上变浅的沉积序列。瓮安含磷岩系大部分为多旋回的叠置体,其常见的交错层理、波状层理、透镜状层理等表明了磷块岩形成于水体较浅的高能环境。南沱冰期后,陡山沱期剧烈的海侵作用引发上升洋流,携带富磷海水涌入浅水区,在海平面间歇性波动的条件下,为磷块岩的形成提供了物源与动力条件。     

Facies analysis and sequence stratigraphy of neoproterozoic Platform deposits in Adrar of Mauritania, Taoudeni basin, West Africa

The Neoproterozoic and Palaeozoic Taoudeni basin forms the flat-lying and unmetamorphosed sedimentary cover of the West African Craton. In the western part of this basin, the Char Group and the lower part of the Atar Group make up a 400-m-thick Neoproterozoic siliciclastic succession which rests on the Palaeoproterozoic metamorphic and granitic basement. Five erosional bounding surfaces of regional extent have been identified in this succession. These surfaces separate five stratigraphic units with lithofacies associations ranging from fluvial to coastal and fluvial-, tide-, or wave-dominated shallow marine deposits. Owing to their regional extent and their position within the succession, the erosive bounding surfaces correspond to relative sea-level falls, and accordingly the five stratigraphic units they bound represent allocyclic transgressive–regressive depositional sequences (S₁–S₅). Changes in the nature of the deposits forming the transgressive–regressive cycles reflect landward or seaward shifts of the stacked sequences. These successive relative sea-level changes are related to the reactivation of basement faults and tilting during rifting of the Pan-Afro-Brasiliano supercontinent 1000 m.y. ago. The stromatolite bearing carbonate-shale sequences which form the rest of the Atar Group mark the onset of a quiet period of homogeneous subsidence contemporaneous with the Pan-African I oceanization 800–700 m.y. ago.     

C30-steranes,novel markers for marine petroleums and sedimentary rocks

A series of C₃₀-steranes has been identified in petroleum through the application of metastable scanning gas chromatography-mass spectrometry. Their Chromatographic pattern in crude oil resembles an epimerized distribution of steranes. It is proposed that the biological precursors for the C₃₀-steranes are marine sterols which contain 30 carbon atoms, hence C₃₀-steranes are markers for input to sedimentary lipids from marine organisms.     

Carbonate platform depositional sequences, Upper Cretaceous, south-central Pyrenees (Spain)

The Upper Cretaceous (Cenomanian-Maastrichtian) of the south-central Pyrenees shows five carbonate platform sequences where the major parameters are tectonism, relative sea-level fluctuations and inherited depositional profile. Depositional geometries and basin analysis permit an understanding of the depositional history.Five depositional sequences have been recognized: (1) The Santa Fe sequence (Middle-Upper Cenomanian), a ramp to a skeletal rimmed shelf with an escarpment bypass margin. The lower boundary is an angular unconformity and the upper one records a sea-level drop. The platform location of the margin was determined by a listric normal fault. (2) An abrupt sea-level rise drowned the former platform. The Congost sequence (Turonian-Lower Coniacian), a distally steepened ramp with erosional distal deep slope. The depositional model was largely controlled by pre-existing basin morphology. Cessation of platform development was due to a relative sea-level drop. (3) The Sant Corneli sequence (Upper Coniacian-Lower Santonian), a mixed terrigenous-skeletal homoclinal ramp with upright margin, deep slope and dysaerobic basin. The slope results from the backstepping by 24 km of the previous margin and gentle basin tilting. The platform margin remained more or less at the same position, and relief between platform and slope increased indicating continuous relative sea-level rise. The upper boundary is an angular unconformity at the platform margin produced by an abrupt sea-level rise and platform drowning, and by listric normal faulting. (4) The Vallcarga sequence (Upper Santonian-Campanian), a distal-steepened skeletal homoclinal ramp, erosional escarpment and turbidite basin, which corresponds to the Mesozoic maximum marine expansion. A listric normal fault created two depositional areas: a more or less flat footwall block with a north-northwest prograding carbonate ramp.     

Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes,Las Negras and Nijar areas,southeastern Spain

During Serravallian through Messinian time, marine carbonates flanked topographic highs that rimmed Neogene basins in the Western Mediterranean. Middle to upper Miocene carbonate strata in the Las Negras and Nijar areas (southeastern Spain) are 50-150 m thick and display 50-200 m of shelf-to-basin relief over 1-2 km. Detailed studies in those areas document the effects of relative sea-level change on sedimentation, biotic composition, and reef development. We identify three previously unrecognized, regionally correlatable depositional sequences (DS1, DS2, DS3) that occur between the underlying basement and the overlying Terminal Carbonate Complex. The lower depositional sequences (DS1, DS2) are mostly normal marine shelf (ramp) carbonates deposited on the flanks of basement highs. The basal part of DS2 locally contains some megabreccia reef blocks composed of Tarbellastraea and Porites. These blocks are the first evidence of reef growth in the area and represent a previously unrecognized period of reef development prior to the fringing reef development. The reef blocks probably formed as upslope patch reefs that were eroded and transported to distal slope locations. The upper sequence (DS3) is characterized by clinoform strata of a Porites-dominated fringing reef complex that prograded basinward in a downstepping style with successively younger reefs forming in a topographically lower and more basinward position as a result of a net sea-level drop. Regional correlation of Miocene shallow-marine strata between basins in Spain and elsewhere in the western Mediterranean is complicated because basins were semi-isolated from adjacent basins making physical correlation impossible. In addition, age-definitive biostratigraphic markers are poorly preserved in most of the Miocene shallow-water strata; basinal sediments that are more easily dated by microfossils do not typically interfinger with the shallow-marine strata in outcrop. Even where datable microfossils are found, resolution of dating is poor. Our studies in the Las Negras and Nijar areas illustrate the usefulness of integrating sedimentological, geometric and biotic data with locally derived relative sea-level (accommodation space) curves for correlation. The relative sea-level curves for each area show remarkable similarities in shape and magnitude of sea-level changes. These curves indicate several relative sea-level fluctuations during Miocene carbonate deposition prior to the major sea-level drop at the end of DS3 deposition that culminated in the exposure of the basin margin deposits and the deposition of evaporites in basinal areas during the Messinian. The depositional sequences in the Las Negras and Nijar areas may correlate with depositional sequences of similar age throughout the southern Cabo de Gata area, in Mallorca some 600 km to the northeast, and possibly in other Mediterranean locations. The widespread occurrence and possible correlation of the depositional sequences suggest regional processes such as eustacy or tectonism for their formation. The integration of sedimentological, palaeontological and sequence stratigraphic studies, and the construction of relative sea-level (accommodation space) curves may help in the interpretation of depositional histories of shallow-marine carbonate complexes and correlation of these strata between isolated areas. Other dating methods, in addition to microfossil dating, may allow for better age determination of the sequences and aid in identifying the importance of eustacy and tectonism in sequence development.     

鄂尔多斯盆地侏罗纪煤中古野火事件及其对古气候的影响

[研究目的]野火是陆地生态系统的一个重要组成部分,燃烧产生的温室气体会对气候环境产生影响.对地史时期古野火的研究可以获得野火对生态系统的潜在长期影响.[研究方法]采集了鄂尔多斯盆地侏罗纪延安组5个主采煤层的56个样品,并对其进行了宏观煤岩观察、煤岩显微组分定量、惰质组反射率测定、微观形貌观察.[研究结果]结果显示在煤层...     

Interstadial coral reef terraces and relative sea-level changes during marine oxygen isotope stages 3–4, Kikai Island, central Ryukyus, Japan

Coral reef terraces are one of the best recorders of relative sea-level changes during the last glacial cycle. Thus far, knowledge of relative sea-level record based on coral reefs during the marine Oxygen Isotope Stage (OIS) 3 has been limited to studies of the Huon Peninsula, Papua New Guinea. High-precision a α-spectrometric ²³⁰Th/²³⁴U dating demonstrated an offlapping sequence of five coral reef complexes, ages of which are 66, 64, 62, 55 and 52 ka, in the northern part of Kikai Island, central Ryukyus of Japan. Interstadial reefs, characterized by deepening-upward sequences of coral assemblages, recorded three hemicycles from transgression to highstand at 52, 62, and 66 ka, during which these reefs were drowned. These highstands in the relative sea-level record can be correlated with the eustatic record reconstructed from the Huon reef terraces and with the interstadials 14, 18, and 19 of the GISP 2 oxygen isotope record. This consistency confirms the Huon sea-level record of OIS 3 and implies that the eustatic sea level responded to the millennial-scale climate changes even during the glacial period of OIS 4.     

Braarudosphaera -rich sediments in the Turonian of the Bohemian Cretaceous Basin, Czech Republic

Braarudosphaera -rich sediments occur in the Turonian (nannofossil zones CC13 and UC9a) epicontinental marine sediments of the Bohemian Cretaceous Basin. This phenomenon is linked to the input of terrigenous material during deceleration of sea-level rise, or stillstand in sea level, which possibly both triggered the Braarudosphaera bigelowii bloom and reduced the diversity of the nannoplankton assemblages. The occurrence of Marthasterites furcatus and Lithastrinus septenarius probably reflects depositional conditions that were suitable for their preservation. Hence, the resultant limitations to their use as local zonal markers in the Bohemian Cretaceous Basin are discussed. The influence of the Tethyan Bioprovince is documented by the coincident first occurrences of L. septenarius and M. furcatus. The presence of the high-latitude species Thiersteinia ecclesiastica indicates penetration of Boreal biota into this depositional area within the Turonian.     

Evolution of an organic‐rich lake basin – stratigraphy,climate and tectonics: Piceance Creek basin,Eocene Green River Formation

The Piceance Creek basin formed as a continental foreland basin ca 53 to 48 Ma in the early to middle Eocene. On a global basis, the basin contains one of the richest oil shale resources known, where the profundal oil shale deposits, kerogen‐rich mudstones (clay and carbonate), exist over most of the basin. Despite its economic importance, the evolution of the Piceance Creek basin is still somewhat unclear. Based on facies association analysis, depositional trends, and gamma ray and Fischer assay data, six evolutionary lake stages are recognized: (i) fresh lake; (ii) transitional lake; (iii) highly fluctuating lake; (iv) rising lake; (v) high lake; and (vi) closing lake. Lake stages are composed of depositional units and characterize large‐scale changes in sedimentological patterns, depositional trends and fluctuations in the oil shale richness related to changes in climate and tectonics. Lake stage evolution is also consistent with the global Eocene climate trend. Stage 1 formed prior to the Eocene climate optimum. At the beginning of the Eocene climate optimum, a saline‐restricted lake formed (Stage 2) and evolved into the highly fluctuating lake (Stage 3) indicating rapid climate changes during the peak of the Eocene climate optimum. This stage was followed by the rising and high lakes (Stages 4 and 5) after the climate optimum and during a change to a more humid climate. The closing of the lake (Stage 6) was caused by increased sand input from the north, indicating the influence of both tectonics and climate. Based on depositional trends and climate evolution, it is suggested that, during the arid climate, laterally heterogeneous highly cyclic depositional units dominate, whereas, during the humid climate, depositional units form laterally continuous sediments that can be traced over long distances.     

Organic geochemistry in a sequence stratigraphic framework. The siliciclastic shelf environment of Cretaceous series, SE France

For a better understanding of siliciclastic shelf environments, correlation between sequence stratigraphy and organic geochemistry is used. Our study is focused on the Cretaceous deposits of Marcoule (Gard, France), particularly on a close-packed siltites layer (200–400 m thick), which is well characterized as a marine flooding facies of a single trangressive–regressive cycle. During the Uppermost Albian and the Lower Cenomanian, the stratigraphic data indicate a change in the depositional environment from offshore to shoreface. Organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data. The study is carried out on core samples from 2 drill holes (MAR 203 and MAR 501). Analyses of the aliphatic and aromatic hydrocarbons were performed using GC–MS and focused on biomarker distributions. The biomarkers indicate a contribution of mixed terrestrial and marine organic matter. The changes in molecular signatures are related to variations in the source of organic matter (marine versus terrestrial), preservation conditions (largely influenced by clay and early diagenesis), environmental oxidation-reduction and acidic conditions as well as bioturbation. Various environmental zones, characterized by different molecular signatures, can be distinguished. Resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of Gymnospermae versus Angiospermae during the transgressive/regressive cycle. The relative sea-level variations are clearly correlated with the nature and the preservation of the organic matter. For example, the Pr/Ph and Pr/n-C₁₇ ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies. We observe a good correlation between the organic data and sequence stratigraphy: changes in geochemical signatures reflect the 3rd order depositional cycles.     

Vegetation, Climate, and Sea Level in the Past 55,000 Years, Hanjiang Delta, Southeastern China

Pollen in Quaternary deposits from the subtropical Hanjiang Delta records three major phases in the local vegetation and climate history during the last 55,000 yr: (1) a prevalent cool-to-temperate and humid climate at ca. 24,000 ¹⁴C yr B.P. is indicated by abundant pollen of temperate trees including conifers; (2) between 20,000 and 15,000 ¹⁴C yr B.P., a cold, dry environment was associated with low sea level during the last glaciation, leading to subaerial exposure, weathering, and interruption of sedimentation, as well as departure from the region of Dacrydium and Sonneratia; (3) a short-term expansion of grassland at ca. 10,300 ¹⁴C yr B.P. reduced the predominant Lauraceae-Fagaceae evergreen forest, possibly corresponding to the Younger Dryas cooling. The combined data indicate a maximum sea-level rise in the mid-Holocene (7500–4000 ¹⁴C yr B.P.) and a marine influence in the late Pleistocene at 45,000–20,000 ¹⁴C yr B.P. The Holocene warming, however, did not bring back moisture-sensitive taxa, indicating high seasonal aridity probably caused by renewed monsoon conditions.     

Depositional facies,environments and sequence stratigraphic interpretation of the Middle Triassic–Lower Cretaceous (pre-Late Albian) succession in Arif El-Naga anticline,northeast Sinai,Egypt

The Middle Triassic–Lower Cretaceous (pre-Late Albian) succession of Arif El-Naga anticline comprises various distinctive facies and environments that are connected with eustatic relative sea-level changes, local/regional tectonism, variable sediment influx and base-level changes. It displays six unconformity-bounded depositional sequences. The Triassic deposits are divided into a lower clastic facies (early Middle Triassic sequence) and an upper carbonate unit (late Middle- and latest Middle/early Late Triassic sequences). The early Middle Triassic sequence consists of sandstone with shale/mudstone interbeds that formed under variable regimes, ranging from braided fluvial, lower shoreface to beach foreshore. The marine part of this sequence marks retrogradational and progradational parasequences of transgressive- and highstand systems tract deposits respectively. Deposition has taken place under warm semi-arid climate and a steady supply of clastics. The late Middle- and latest Middle/early Late Triassic sequences are carbonate facies developed on an extensive shallow marine shelf under dry-warm climate. The late Middle Triassic sequence includes retrogradational shallow subtidal oyster rudstone and progradational lower intertidal lime-mudstone parasequences that define the transgressive- and highstand systems tracts respectively. It terminates with upper intertidal oncolitic packstone with bored upper surface. The next latest Middle/early Late Triassic sequence is marked by lime-mudstone, packstone/grainstone and algal stromatolitic bindstone with minor shale/mudstone. These lower intertidal/shallow subtidal deposits of a transgressive-systems tract are followed upward by progradational highstand lower intertidal lime-mudstone deposits. The overlying Jurassic deposits encompass two different sequences. The Lower Jurassic sequence is made up of intercalating lower intertidal lime-mudstone and wave-dominated beach foreshore sandstone which formed during a short period of rising sea-level with a relative increase in clastic supply. The Middle-Upper Jurassic sequence is represented by cycles of cross-bedded sandstone topped with thin mudstone that accumulated by northerly flowing braided-streams accompanying regional uplift of the Arabo–Nubian shield. It is succeeded by another regressive fluvial sequence of Early Cretaceous age due to a major eustatic sea-level fall. The Lower Cretaceous sequence is dominated by sandy braided-river deposits with minor overbank fines and basal debris flow conglomerate.     

Lacustrine source rock deposition in response to co-evolution of environments and organisms controlled by tectonic subsidence and climate, Bohai Bay Basin, China

Three Paleogene syn-rift intervals from the Bohai Bay Basin, the most petroliferous basin in China, were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities, to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions. The third (Es₃) and first (Es₁) members of the Eocene Shahejie Formation and the Oligocene Dongying Formation (Ed) display widely variable total organic carbon contents, hydrogen indices and visual kerogen compositions, suggesting changes in organic facies from deep to marginal sediments. Carefully selected deep-lake facies samples from any interval, however, display fairly uniform biomarker composition. These three intervals have distinctly different biomarker assemblages, which indicate weakly alkaline, freshwater lakes with a moderately deep thermocline during Es₃ deposition, alkaline-saline lakes with shallow chemocline during Es₁ deposition and acidic, freshwater lakes with deep, unstable thermocline during the deposition of the Dongying Formation. Such environmental changes corresponded to changes in subsidence rate and paleoclimate, from rapid subsidence and wet climate during Es₃ deposition, through slow subsidence and arid climate during Es₁ deposition to rapid subsidence and wet climate during Ed deposition and resulted in synchronous changes in terrigenous organic matter input, phytoplankton community and primary productivity. The co-evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics. Most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn-rift evolutions. The models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins.     

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, as reflected by marine palynology

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, has been analysed palynologically by high resolution sampling to reconstruct changes in relative sea-level and water mass character within photic zone waters. Based on changes in the ratio of terrigenous sporomorphs to marine palynomorphs (t/m index), the distribution of the organic-walled algal taxa as well as of selected dinocyst taxa and groups the section can largely be subdivided into pre-“plenus-bed” and post-“plenus-bed” intervals, reflecting different stages of third-order relative sea-level cycles and/or changes in water mass influence in the photic zone. Accordingly, the pre-“plenus-bed” interval is placed in a transgressive systems tract starting at the “facies change” event (C. guerangeri/M. geslinianum ammonite Zone boundary) with the maximum flooding surface at the top of the “Chondrites II” bed (top of R. cushmani Biozone). A highstand systems tract is suggested from the base of the “plenus-bed” up the base of the “fish-shale” event. Within the “fish-shale” event interval, a transgressive systems tract is suggested to start at the base of the thin, grey-green marly interbed. The Cenomanian/Turonian boundary proper, as defined by the first occurrence of Mytiloides spp., as well as the lowermost Turonian are located within the initial phase of a transgressive systems tract. With respect to water mass characteristics within photic-zone waters, the pre-“plenus-bed” interval is predominantly characterized by warm water masses that changed gradually towards the deposition of the “Chondrites II” bed, where a strong influence of cool and/or salinity-reduced waters is indicated by various palynological proxies. Within the post-“plenus-bed” interval a mixture and/or alternation of warmer and cooler waters is indicated, with the warmer water influence increasing gradually towards and within the Lower Turonian stage. The increased proportions of prasinophytes within the “Chondrites II” bed and parts of the “fish-shale” interval may indicate availability of reduced nitrogen chemospecies, especially ammonium, within photic-zone waters as a function of a vertical expansion of the oceanic O₂-minimum zone.     

海平面相对上升与生物礁相沉积——以中国西南地区晚二叠世海绵礁为例

晚二叠世是我国西南地区地史上的第二次造礁高峰期,礁体发育良好,分布广泛,类型齐全,且有较好的找矿前景,已先后在建南、石宝寨等潜伏礁体中打出了工业性气流。前人已对本区晚二叠世生物礁作了大量的研究,但主要侧重于古生物生态和礁体沉积相方面,而对海平面相对变化与礁体的关系以及礁控构造等方面的研究还很少。本文为《中国南方晚二叠世生物礁研究》课题成果中的一部份,主要探讨晚二叠世海平面相对上升与生物礁相沉积之间的关系。西南地区晚二叠世生物礁主要分布在南盘江地区(滇黔桂交界区)和川东鄂西地区,礁