Correlation of Aptian-Albian sediments in the central part of North Caucasus and Ciscaucasia. Paper 1. Composition and rock distribution features

The lithology change patterns between sections on the northern slope of Caucasus and in Ciscaucasia wells must be taken into account in addition to geophysical and biostratigraphic characteristics during detailed correlation of Aptian and Albian sediments. This paper discusses rock lithologic types (LT), rock distribution patterns in the covered territories, and their formation conditions. It includes a facies profile showing these patterns.     

Small-scaled environmental changes: indications from stable isotopes of gastropods (Early Miocene, Korneuburg Basin, Austria)

The Korneuburg Basin, with mainly upper Lower Miocene (Karpatian) sediment filling, is divided by the Mollmannsdorf–Obergänserndorf Swell into two sub-basins characterised by different environmental settings. Paleoecological data indicate a marine northern part and a mainly estuarine southern part. Nevertheless, short-termed marine ingressions from the north allowed marine faunas (ostracods, molluscs, and echinoids) to temporarily settle the southern part of the basin. The carbon and oxygen isotopic composition of gastropod shells from these different environmental settings were investigated. Highest δ¹⁸O and δ¹³C values are found in Turritella shells from the northern part of the basin, and in Turritella shells from layers interpreted as a marine ingression in the south. Generally, components of the mudflat fauna (Tympanotonos cinctus, Granulolabium bicinctum, Terebralia bidendata, and Ocenebra crassilabiata) have slightly lower isotope values. Considerable freshwater influx in the southern part is documented by abundant freshwater genera such as Melanopsis, which show low carbon and oxygen isotope values. Data of identical taxa, especially Turritella and Granulolabium, reflect a trend from higher isotope values at the marine northern part to slightly lower values in the mainly estuarine southern part of the basin. Differences in δ¹⁸O between the marine and the estuarine assemblages are interpreted to be caused by changes in salinity and isotopic composition of ambient water rather than by temperature. Paleotemperature estimates derived from oxygen isotope data are in good agreement with existing paleoclimatic proxies for the Korneuburg Basin. Hence, an annual range of the sea-surface temperature from 13 to 26°C can be predicted within that protected basin.     

晚第三纪以前形成古土壤的鉴别、分类及其在古环境研究中的应用

晚第三纪以前形成的古土壤可以揭示地质时期的古环境。辨识古土壤的主要标志包括野外形态特征、微形态特征、地球化学特征等。当前古土壤分类一般基于现代土壤的系统分类体系,即采用诊断层和诊断特征,辅之以古土壤总体的化学性质等指标划分古土壤类型。形成于晚第三纪以前的古土壤可以重建全球范围的古气候变化历史,同时揭示前寒武纪时期古大气O2分压以及后寒武纪时期古大气CO2浓度水平的演化过程;古土壤具有空间和时间等多重信息,能反映流域或区域的古景观、古地貌、古水文特征。但目前缺乏一个广为接受的古土壤分类系统,成岩作用对古土壤特征的影响以及古土壤记录的古环境信息机制与解译等方面也还需要深入探讨。今后必须加强成岩作用对古土壤特性的影响以及现代土壤与其环境的对应关系的研究。     

Stable isotopic insights into paleoclimatic conditions and alluvial depositional processes in the Kaiparowits Formation (Campanian,south-central Utah,U.S.A.)

The Kaiparowits Formation contains an exceptionally rich history of tectonic, climatic, and biologic conditions within the Western Interior of North America during the Campanian. Here we reconstruct aspects of the southern Cordilleran foreland basin's paleohydrology using δ¹⁸O and δ¹³C values determined from unionoid bivalve shells and pedogenic carbonate nodules derived from a suite of lithofacies associations. Unionoid shells derived from fluvial deposits display average water δ¹⁸O estimates of −13.7‰ ± 2.1 (1σ) (VSMOW) and shell δ¹³C values of −4.0‰ ± 1.5 (VPDB), whereas pedogenic carbonate nodules display average values of −6.0‰ ± 0.5 and −8.7‰ ± 0.8, respectively. Unionoid shells derived from pond deposits fall in between the two other environments with average values of −9.5‰ ± 1.8 and −5.7‰ ± 2.1, in δ¹⁸O and δ¹³C values respectively. Water δ¹⁸O estimates are interpreted to represent high altitude runoff within river systems, low elevation precipitation within the basin onto floodplain soils, and varying degrees of mixing between these two components within floodplain ponds. δ¹³C values track the isotopic composition of dissolved inorganic carbon within river, soil, and pond waters with high values likely reflecting greater contribution from chemically weathered marine carbonates exposed in the hinterland and lower values reflecting greater contributions from the in situ degradation of plant matter. Up-section there is a shift to lower δ¹⁸O values and higher δ¹³C values in fluvially-derived unionoid shells that post-dates an incursion of the Western Interior Seaway, but coincides with a shift in sediment provenance, an increase in basin sedimentation rates, and a change to a more anastomosed-style channel morphology within the basin foredeep depocentre. By combining the isotopic patterns with previously published sedimentologic, climate model, and paleofloral records we find: 1) additional evidence for humid, wet, and potentially monsoonal conditions within the region, 2) support for a tectonic uplift event, potentially related to Laramide deformation, and 3) greater aggradation and overbank flooding within the alluvial system in response to the uplift event.     

Stable isotope study of cave percolation waters in subtropical Brazil: Implications for paleoclimate inferences from speleothems

We analyze the interannual monthly variability of oxygen isotope ratios in data from IAEA stations along the Atlantic coast of South America between 23° and 34° S to evaluate the influence of parameters such as temperature, rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical Brazil. In addition, a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the Santana Cave System (24°31′ S; 48°43′ W), is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water δ¹⁸O.

Interannual monthly variations in δ¹⁸O of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer (negative values of δ¹⁸O) to a more extratropical regime in winter (positive values of δ¹⁸O). Variations in groundwater δ¹⁸O indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters, regardless of location of collection in the cave. In addition, the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs. Significant perturbations in the groundwater composition, characterized by more positive values of δ¹⁸O, are probably connected to an increased Atlantic moisture contribution associated with extratropical precipitation. This implies that the δ¹⁸O of speleothems from caves in this region may be a suitable proxy for studying tropical–extratropical interactions over South America, a feature that is intrinsically related to the global atmospheric circulation.     

Evidence for multiple, episodic, mid-Holocene Hypsithermal recorded in two soil profiles along an alluvial floodplain catena, southeastern Tennessee, USA

Floodplain soil-paleosol successions are valuable archives for reconstructing Pleistocene-Holocene climate changes but have been relatively unstudied in the southern Appalachian region. Two soil profiles on a small floodplain in southeastern Tennessee, USA were described and sampled in detail using both pedological and geological approaches, including stable carbon isotope analysis of soil organic matter (SOM). Correlation between the 2 profiles was constrained by uncalibrated AMS ¹⁴C ages of bulk humates, and using SOM δ¹³C values, both mobile and immobile elements. Four distinct 2.5-4‰ shifts towards less negative δ¹³C values for SOM suggest ∼ 300-yr cyclicity and transient warmer and drier climate events, with either water-stressed C₃ vegetation or as much as 35% C₄ plants present during the mid-Holocene. These postulated multi-episodic drier climate conditions have never before been documented in the southern Appalachian region and are tentatively correlated with mid-Holocene warming and drying in the eastern US, the nearly time-equivalent mid-Holocene events documented in Texas, the US High Plains and in the Gulf of Mexico. High rates of floodplain sediment accumulation (0.5-3 mm/yr), high clay content and maintenance of poorly drained soil conditions favor preservation of high-resolution climate archives in floodplain deposits by inhibiting oxidation and translocation of organic C.     

Restricted utility of δC of bulk organic matter as a record of paleovegetation in some loess-paleosol sequences in the Chinese Loess Plateau

Molecular stratigraphic analyses using gas chromatograph-mass spectrometry have been performed in the upper section (S₀, L₁, S₁) of the Yuanbo loess-paleosol sequences in northwest China, with a record extending from the last interglaciation through the present interglaciation. The CPI (Carbon Preference Index) values of both n-alkanols and n-alkan-2-ones display variations between loess deposits and paleosols, showing a correlation with the magnetic susceptibility record, an indicator of the East Asian summer monsoon. The observed variations in the indexes in relation to changes in lithology/paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols. The CPI values of n-alkanes, n-alkanols, and n-alkan-2-ones are negatively correlated with δ¹³C of bulk organic matter. The correlations suggest that the observed glacial-interglacial variations of δ¹³C data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms (including both the degradation and the addition of organic matter) and allochthonous loess/soil parent materials. It is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the δ¹³C analysis of bulk organic matter in some loess-paleosol sequences of the Chinese Loess Plateau.     

The Aptian-Cenomanian flora of primor’e, part 2: Correlation of floral assemblages

Taxonomic composition of plant fossils from the Aptian-Cenomanian sediments of the Alchan, Razdol’naya, and Partizanskaya depressions of Primor’e is studied in detail. Each of the established floral assemblages characterizes a particular stage of flora stabilization. Correlation of the assemblages is performed. Floral assemblages of the Alchan depression, which occur in association with macrofauna, are suggested to be the standard ones for the southern Far East. New species are described.     

Palynomorph and palynofacies indications of age, depositional environments and source potential for hydrocarbons: Lower Cretaceous Zubair Formation, southern Iraq

Assemblages of miospores and dinoflagellate cysts encounterd in core samples three boreholes drilled in southern Iraq an Aptian-mid Albian age-range for the Zubair Formation, the largest oil reservoir in southern Iraq and neighbouring Kuwait. Four types of palynofacies have been identified, and are interpreted to indicate delta top swamp and marsh, delta front, prodelta and marine platform environments respectively. Amorphous matter comprises more than 50% of the organic component of some of the palynofacies in the upper part of the Zubair Formation. The rocks with which they are associated are highly rated as a potential source of liquid hydrocarbons. Those deposits yielding less than this (down to 12%) are considered to have moderate potential.     

Mid-Holocene stable isotope record of corals from the northern Red Sea

We present a study based on X-ray chronologies and the stable isotopic composition of fossil Porites spp. corals from the northern Gulf of Aqaba (Red Sea) covering the mid-Holocene period from 5750 to 4450 ¹⁴C years BP (before present). The stable oxygen and carbon isotopic compositions of five specimens reveal regular annual periodicities. Compared with modern Porites spp. from the same environment, the average seasonal δ ¹⁸O amplitude of the fossil corals is higher (by ca. 0.35–0.60‰), whereas annual growth rates are lower (by ca. 3.5 to 2 mm/year). This suggests stronger seasonality of sea surface temperatures and increased variability of the oxygen isotopic composition of the sea water due to changes in the precipitation and evaporation regime during the mid-Holocene. Most likely, summer monsoon rains reached the northern end of the Red Sea at that time. Average annual coral growth rates are diminished probably due to an increased input and resuspension of terrestrial debris to the shallow marine environment during more humid conditions. Our results corroborate published reports of paleodata and model simulations suggesting a northward migration of the African monsoon giving rise to increased seasonalities during the mid-Holocene over northeastern Africa and Arabia. Received: 4 January 1999 / Accepted: 13 September 1999     

Isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland Pacific Northwest of the USA

Large-scale atmospheric circulation patterns determine the quantity and seasonality of precipitation, the major source of water in most terrestrial ecosystems. Oxygen isotope (δ¹⁸O) dynamics of the present-day hydrologic system in the Palouse region of the northwestern U.S.A. indicate a seasonal correlation between the δ¹⁸O values of precipitation and temperature, but no seasonal trends of δ¹⁸O records in soil water and shallow groundwater. Their isotope values are close to those of winter precipitation because the Palouse receives  75% of its precipitation during winter. Palouse Loess deposits contain late Pleistocene pedogenic carbonate having ca. 2 to 3‰ higher δ¹⁸O values and up to 5‰ higher carbon isotope (δ¹³C) values than Holocene and modern carbonates. The late Pleistocene δ¹⁸O values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter-dominated infiltration. The δ¹³C values are attributed to a proportional increase of atmospheric CO₂ in soil CO₂ due to a decrease in soil respiration rate and ¹³C discrimination in plants under much drier paleoclimate conditions than today. The regional climate difference was likely related to anticyclonic circulation over the Pleistocene Laurentide and Ice Sheet.     

Controls, variation, and a record of climate change in detailed stable isotope record in a single bryozoan skeleton

The long-lived (about 20 yr) bryozoan Adeonellopsis sp. from Doubtful Sound, New Zealand, precipitates aragonite in isotopic equilibrium with seawater, exerting no metabolic or kinetic effects. Oxygen isotope ratios (δ¹⁸O) in 61 subsamples (along three branches of a single unaltered colony) range from −0.09 to +0.68‰ PDB (mean = +0.36‰ PDB). Carbon isotope ratios (δ¹³C) range from +0.84 to +2.18‰ PDB (mean = +1.69‰ PDB). Typical of cool-water carbonates, δ¹⁸O-derived water temperatures range from 14.2 to 17.5 °C. Adeonellopsis has a minimum temperature growth threshold of 14 °C, recording only a partial record of environmental variation. By correlating seawater temperatures derived from δ¹⁸O with the Southern Oscillation Index, however, we were able to detect major events such as the 1983 El Niño. Interannual climatic variation can be recorded in skeletal carbonate isotopes. The range of within-colony isotopic variability found in this study (0.77‰ in δ¹⁸O and 1.34 in δ¹³C) means that among-colony variation must be treated cautiously. Temperate bryozoan isotopes have been tested in less than 2% of described extant species — this highly variable phylum is not yet fully understood.     

High-frequency cycles in the upper Aptian carbonates of the Organyà basin,NE spain

High-frequency cycles in Upper Aptian carbonates have been studied on the carbonate ramp of Organyà (southeastern Pyrenees). The depositional area comprises a shallow marine to deeper marine transect. A detailed facies model is developed subdividing the transect into an inner ramp area (above fairweather wave base), a mid-ramp area (between fairweather wave base and storm wave base) and an outer ramp area (below storm wave base). Based on microfacies analysis a cyclostratigraphic and sequence stratigraphic interpretation is established. Variations of the sedimentary patterns within different sections of the homoclinal ramp are due mainly to sea level changes. Sea level changes of third and fourth order are reflected by the shifting of the shallow subtidal facies belts up and down the ramp. The study of fifth-order sea level changes is based on statistical methods (quantitative facies analysis and principal component analysis). The ratio of the fourth- and fifth-order cycles is very similar to the well-known ratio of the eccentricity (100 ka) and the precession (18.6/22.5 ka). The absolute age values derived from the cyclostratigraphy fit into the biostratigraphic framework. Thus, a global eustatic control is assumed to be responsible for the cycles of higher frequency. The lower frequency third-order sequences, however, were considerably influenced by local tectonic processes.     

Oxygen isotope records of goethite from ferricrete deposits indicate regionally varying Holocene climate change in the Rocky Mountain region, U.S.A.

Oxygen isotopes of goethite from ferricrete deposits were measured from both northern and southern Rocky Mountain localities to assess geographic variability in regional Holocene paleoclimate change. A ∼3.7‰ increase in oxygen isotope values of ¹⁴C-dated goethites in the northern Rocky Mountains suggests a regional-scale relative increase in amounts of isotopically heavy summer precipitation since the early Holocene. In contrast, oxygen isotope values from the southern Rocky Mountains increase abruptly ∼2.1‰ at ∼6200 ¹⁴C yr B.P., then decrease ∼2.4‰ between ∼2000 ¹⁴C yr B.P. and the present. We interpret this period of relatively high δ¹⁸O values as evidence for a middle Holocene warm period combined with a relatively strong summer monsoon. These variable climate records suggest that the Rocky Mountains of the western United States have had a spatially heterogeneous Holocene climate history.     

Palaeoecology and biostratigraphy of early Cretaceous (Aptian) calcareous nannofossils and the δCcarb isotope record from NE Iran

Upper Barremian-Lower Aptian sediments of the Sarcheshmeh and Sanganeh formations in the Kopet Dagh area, northeast Iran were studied with regard to their calcareous nannofossil content and their δ¹³C_carb signal. The sediments are composed mainly of marlstones, argillaceous limestones and limestones. Based on the occurrence of biostratigraphic index taxa, the calcareous nannofossil zones NC5, NC6 and the NC7A Subzone were recognised. The calcareous nannofossils and the δ¹³C_carb data enable recognition of the early Aptian Oceanic Anoxic Event 1a (OAE 1a). The deposits of the OAE 1a interval are characterised by the rarity of nannoconids and a sharp negative δ¹³C_carb excursion (1.36‰), followed by an abrupt positive δ¹³C_carb excursion of 4-5‰; both events have been recognised elsewhere in OAE 1a deposits in the Tethys. In the OAE 1a interval, the relative abundance of Watznaueria barnesiae/Watznaueria fossacincta is higher (more than 40%) than that of Biscutum spp., Discorhabdus spp. and Zeugrhabdotus spp., which indicates dissolution. In the upper part of the section, the higher relative abundance of mesotrophic and oligotrophic taxa (Watznaueria spp. and nannoconids respectively) and the enhanced relative abundance of eutrophic taxa (Biscutum spp., Discorhabdus spp., Zeugrhabdotus spp.) is indicative of an environment with slightly increased nutrient content. The presence of warm water taxa (Rhagodiscus asper and nannoconids) and the absence of cool water taxa (Repagulum and Crucibiscutum) suggest warm surface-water conditions.     

洞穴石笋代用指标的古气候意义初探

现代全球气候变化是当前人类社会普遍关注的一个热门问题。全球气候变化研究的热点问题是获得十年到百年甚至年月分辨的气候变化规律。洞穴石笋作为恢复古气候、研究古环境演变的一把钥匙,因其诸多优点,将在古环境研究中发挥越来越重要的作用。从当前研究现状出发,对石笋中微层年层对比、微层形成机制、稳定同位素记录、微量元素记录、生长速率及微层发光等方面进行一个简单的回顾。     

The earliest record of Asian Eusuchia from the Lower Cretaceous Khok Kruat Formation of northeastern Thailand

We describe remains of a new crocodyliform found from the Lower Cretaceous (Aptian) Khok Kruat Formation, northeastern Thailand. Remains consist of two caudal ends of mandibles, two rostral symphyseal parts of right rami of mandibles, a dorsal part of postorbital, a cranial end of squamosal and one osteoderm. Phylogenetic analyses supported inclusion of this crocodyliform into the Eusuchia as it shares several morphological characters with other eusuchians, such as a dorsocaudally oriented retroarticular process, smooth lateral surface of the caudoventral region of mandible, and a craniocaudally oriented ridge on the dorsal surface of retroarticular process. The shape of symphyseal region showed this crocodyliform had a longirostrine snout shape, which is uncommon in early eusuchians. Finding of this crocodyliform draws back the oldest record of Asian eusuchians, which was Tadzhikosuchus, approximately 30 million years and it is the only Mesozoic eusuchian found in East and Southeast Asia.     

First sauropod bones from Italy offer new insights on the radiation of Titanosauria between Africa and Europe

Here we describe the first sauropod skeletal remains from the Italian peninsula that also represent the earliest record of titanosaurs in Southern Europe. Scattered bones, including an almost complete anterior caudal vertebra, were found in Cretaceous (Aptian–Albian) marine deposits, some 50 km East of Rome. The vertebra shows a bizarre and perhaps unique orientation of the zygapophyseal articular facets that renders their interpretation problematic. Phylogenetic retrofitting tests support the placement of the Italian titanosaur among basal lithostrotians. Palaeobiogeographic analysis based on the resulting phyletic relationships suggests an Afro-Eurasian route for the ancestors of the Italian titanosaur, a scenario compatible with the palaeogeographic evolution of the Italian microplates during the Cretaceous. Together with previously recorded titanosaurian-like ichnites from a Cenomanian locality in Latium, this new find suggests a quite long emersion for the Apenninic carbonate platform. We suggest that the Italian titanosaur was member of a population that crossed the western Tethys Sea through a “filtering bridge” composed of a chain of ephemeral islands and peninsulae, known as Periadriatic (Adria) carbonate platforms, that connected sporadically Africa and Europe since the Early Cretaceous.