Jurassic magmatic bodies of mountainous Crimea in the Bodrak River catchment (Southwestern Crimea)

The synthetic (geological and petrochemical) study of Jurassic magmatic bodies in the catchment of the Bodrak River (mountainous Crimea) is conducted. Their structural position and a Middle Jurassic age were determined. The magmatic bodies of mountainous Crimea were compared to those of the Lozovskaya zone. The study considers the geodynamic settings of the Middle Jurassic magmatism in mountainous Crimea.     

Berriasian (Lower Cretaceous) brachiopods from the Crimea

Four successive assemblages of Berriasian brachiopods distinguished for the first time in the Crimea are correlated with concurrent subdivisions of the ammonoid scale. Berriasian brachiopods are represented by 44 species of 27 genera and 14 families, which are most complete in terms of taxonomic composition as compared to other concurrent brachiopod faunas known elsewhere. The assemblages are dominated by local species. As is proved, the Berriasian brachiopods studied are appropriate for age determination, subdivision and correlation of their host deposits. Their geographic distribution that has been analyzed elucidates connections of the Berriasian sea basins within the Mediterranean paleozoogeographic region.     

下扬子区早三叠世风暴沉积及其特征

<正> 早三叠世,下扬子区为位于华北古陆与华夏古陆之间的陆表海,其中发育一套以碳酸盐岩为主的海相沉积物。近年来,笔者在该区(图1)工作期间,发现在早三叠世时,沿皖南到苏南的广大区域内,风暴沉积作用产生的特征十分显著,风暴岩广为发育。     

Upper Triassic (Norian) cephalopod limestones of the Hallstatt-type, Oman

Norian crinoidal/brachiopod limestones and cephalopod limestones of the Hallstatt-type occur as blocks in a Hettangian(?) calcareous breccia of the Haliw Formation in the Oman Mountains. Crinoidal and brachiopod packstones, up to 12 m thick, prevail in the lower part of the sequence and were deposited on a substrate of Norian forereef breccia. The overlying cephalopod wackestones, up to 4.9 m thick, have a basal white bed followed by red limestones with abundant planar and scalloped, corroded surfaces and local stromatolites. Upward, red, nodular wackestones and, finally, slumped grey wackestones follow. The analysis of geopetal fabrics in orientated samples shows that bedding of these facies is, in fact, inclined bedding. Inclinations varied between 15 and 29°. In addition, the restored dip directions demonstrate rotation, indicating deposition on a gliding block. The preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics. Such features, generally interpreted as current-induced, are here interpreted as gravity-induced. The overall mud-supported rock fabric thus indicates deposition under very low-energy conditions. The common mud-supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags, particularly in the crinoidal/brachiopod facies and the lower, stratigraphically condensed, cephalopod limestones. This indicates that deposition of lime mud alternated with periods of elevated current strength. A comparison of the Hallstatt-type limestones and current-influenced sediments on the northern slope of the Little Bahama Bank suggests that condensed sequences of the Hallstatt-type are restricted to relatively shallow depths with strong fluctuation of contour-following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean. On steep slopes, sediment bypassing may be an additional factor for stratigraphic condensation.     

Flora from the Induan stage (Lower Triassic) of Middle Siberia

The first data on the taxonomic composition of the Induan flora of Siberia are presented. The investigation of Triassic reference sections in northern Siberia (eastern Taimyr, Lena–Anabar Trough, Verkhoyansk region) and correlation with volcano-sedimentary complexes of the Tungus and Kuznetsk basins made it possible to establish for the first time the taxonomic composition of the flora from the Induan Stage of Siberia. Its composition is heterogeneous, forming two large plant formations, which occupied different ecological niches. On the eastern coastal-marine margins of Siberia (eastern Taimyr, Olenek coast, Verkhoyansk region), the Induan flora was largely characterized by lepidophytic (Tomiostrobus) plants, while in the intracontinental areas (Tungus and Kuznetsk basins, partly Verkhoyansk region), it was characterized by Equisetales–Filicales communities.     

The First Upper Triassic Vertebrate Locality in Antarctica

In December 1999 we collected bones of two small reptiles from Upper Triassic mudstone on Mount Dearborn in southern Victoria Land, Antarctica. One specimen includes indeterminate limb fragments of a small reptile and the other is a tusk of a small dicynodont. We found both specimens in loose clasts on a slope of fine-grained strata above the second major channel-form sandstone above the base of member C in the Lashly Formation. The fossils occur in medium gray mudstone of the same lithology as the surrounding bedrock. Lashly member C at Mount Dearborn and in southern Victoria Land is composed of fining-upward cycles. At Mount Dearborn the cycles begin with channel-form, medium- to fine-grained sandstone. Quartz pebbles and cobbles occur at the base and in lenses with mudstone clasts. Lenses of coal occur along bedding planes and scours. The cycles fine upward gradually from sandstone to siltstone and carbonaceous mudstone with coal at the top. The Dicroidium flora is better preserved in the upper part of the cycles. A palynomorph assemblage from one of the bone-bearing samples suggests a Late Triassic (Carnian) age for the locality.This is the first report of Upper Triassic vertebrates in Antarctica and also of terrestrial vertebrates in Victoria Land. All previous vertebrate localities have been in non-carbonaceous beds in the central Transantarctic Mountains. The discovery expands the sequence of tetrapod occurrences in Lower, Middle and Upper Triassic and Lower Jurassic rocks in the Transantarctic Mountains. It appears that reptilian faunas managed to inhabit high latitudes (>60°), at least intermittently, for a period of 50 million years, suggesting a relatively warm climate for parts of Antarctica during those times.     

Significance of stromatolites for the environmental interpretation of the Buntsandstein (Lower Triassic) rocks

When interpreting the depositional environment of the Buntsandstein sequence, thin stromatolite layers, if present, were often overlooked or given short shrift. The present paper provides evidence of value of stromatolites for the environmental interpretation of the Buntsandstein rocks. Algal stromatolites found in western Poland occur in form of thrombolites, LLH-type structures, SH-type structures, and rarely as oncolites. Stromatolites are usually associated with oolites. Very often stromatolites show important traces of scouring and channelling action of water. Since stromatolites occurred in the zone of clastic-carbonate deposition they were covered up by continuous sheet of detrital grains. Periodic catastrophic erosion and deposition was produced by hurricanes and severe storms in the peritidal and shallow subtidal zone. It is possible to distinguish the peritidal and subtidal stromatolites. In the vicinity of stromatolites are of frequent occurrence spirorbids, conchostracs, gastropods, and rare foraminifers. Besides, spirorbids are associated with stromatolites — they constituted the initial hard substratum for the stromatolitic structures and sometimes they also occur inside stromatolites. The not-hypersaline sedimentary environment of the Buntsandstein rocks can be compared with modern environments of the Persian Gulf and the Gulf of Aqaba.     

四川盆地泸州古隆起嘉陵江组储层特征研究

对研究区嘉陵江组沉积背景认识的基础上,通过岩心观察、岩石薄片确定了不同类型的储集岩和储集空间,得出本地区储层岩石类型和储渗空间类型均多样化的特点。从成因角度识别出来了溶蚀孔隙型储层、膏溶孔洞型储层、裂缝型储层等三类储层。研究不同类型储层的孔、渗特征及关系表明,溶蚀孔隙型储层物性要优于膏溶孔洞型储层,而溶蚀孔隙型储层中的颗粒云岩溶蚀孔隙型储层物性最好、颗粒灰岩溶蚀孔隙型物性其次、粉晶云岩溶蚀孔隙型储层物性最差,其原因是不同储层受沉积环境和成岩作用控制和影响。     

First record of stereospondyls (Tetrapoda,Temnospondyli) in the Upper Triassic of Southern Brazil

Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic.     

The petrology of the Upper Albian tuffites from the Bakhchysarai district,southwestern Crimea

We present the first data on the composition of plagioclase and quartz-hosted melt inclusions, plagioclase primary magmatic zoning and mineral compositions for the Upper Albian tuffites from the Bakhchysarai district. The estimated composition of the magmatic melts corresponds to the high potassium rhyolites. The measured water content in the melt inclusions reaches 4 wt %. The phenocrysts crystallized at the temperature within the range 820–860°C and under the pressure not less than 0.1 GPa. The Upper Albian tuffites from the Bakhchysarai district were formed in the active continental margin environment.     

The MARID (mica-amphibole-rutile-ilmenite-diopside) suite of xenoliths in kimberlite

Within the ‘glimmerite’ nodules occurring within kimberlite pipes we recognize the MARID suite consisting of varying proportions of mica, amphibole, rutile, ilmenite and diopside. Banding of some specimens is interpreted as cumulate layering. All specimens were deformed either before incorporation into the host kimberlite or during intrusion. Compared with minerals in peridotite xenoliths, the MARID ones are lower in Al₂O₃ and Cr₂O₃, but richer in total iron. The MARID micas, amphiboles, diopsides, ilmenites and probably rutiles contain substantial Fe₂O₃ indicative of oxidizing conditions. The amphibole is potassic richterite. Micas of the megacryst suite in kimberlite have less total iron and Fe₂O₃ than micas of the MARID suite. We suggest that the rocks of the MARID suite crystallized under oxidizing conditions from a magma, chemically similar to kimberlite, within the higher parts of the upper mantle: the presence of amphibole restricts the depth to less than ~ 100 km. A xenolith containing olivine and orthopyroxene as well as minerals similar to but not the same compositionally as MARID-types is interpreted as a metasomite, possibly representing wall-rock of a magma body from which MARID-suite rocks crystallized.     

Lower Triassic alkaline granites of Central Chile (30‡S) in the high-Andean Cordillera

The Na₂O + K₂O/Al₂O₃ molar ratio (agpaitic index) of Lower Triassic leucogranites samples from the Rios Elqui-Lamarí batholith is close to one which is typical of alkaline granites. Loss of alkalis due to groundwater interaction should have occur causing a depletion of the original peralkalinity.It is assumed that this alkaline magmatism has been generated, during crustal extension period, by partial melting of water undersaturated deep crustal rocks.

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Zusammenfassung Das Mol-VerhÄltnis von Na₂O + K₂/Al₂O₃ (agpaitischer Index) der untertriassischen Leukogranit-Proben des Batholithen vom Rios Elqui-Limari liegt in der NÄhe von 1. Dieses ist typisch für Alkaligranite. Der Verlust von Alkali könnte durch Grundwassereinwirkung zustandegekommen sein, was eine Verringerung der ursprünglichen HyperalkalinitÄt verursacht hat.Es wird angenommen, da\ dieser alkalische Magmatismus in einer Phase der Krustenausdehnung entstanden ist durch partielles Aufschmelzen von wasseruntersÄttigten Gesteinen der Tiefenkruste.

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Resumen Leucogranitos de edad triásica inferior pernecientes al batolito compuesto Ríos Elqui-Limarí están caracterizados por presentar una razón molecular Na₂O + K₂O/Al₂O₃ (índice agpaítico) cercano a uno, propio de los granitos alcalinos. Una probable pérdida de álcalis de estos granitos, provocada por el agua infiltrada, sería causante de una disminución de la peralcalinidad original.Se infiere un mecanismo de fusión parcial de rocas corticales profundas subsaturadas en agua, para la génesis de este magmatismo alcalino en un ambiente tectónico de extensión cortical.

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Na₂O + K₂/l₂₃ - - -- 1. . , . , .

     

Planktonic foraminiferal biostratigraphy of the Upper Barremian and Aptian of Crimea

Reexamination of the Barremian–Aptian planktonic foraminifers from three sections (Verkhoirechie, mountain Krasnaya, and Marino) allowed the biostratigraphic scheme for Southwest and Central Crimea to be refined and updated. The following standard zones are recognized in the studied sections: Blowiella blowi (upper Barremian), Hedbergella excelsa (upper Barremian–lower Aptian), Leupoldina cabri (lower Aptian), H. luterbacheri, Globigerinelloides ferreolensis, Gl. barri, Gl. algerianus, Hedbergella trocoidea, Paraticinella rohri (upper Aptian). Beds with Hedbergella ruka are recognized in the B. blowi Zone. Foraminifers from the Partizanskoe section, representing the lower Aptian L. cabri and H. luterbacheri zones, are studied. The recognized strata are correlated with ammonite and nannoplankton zones and paleomagnetic data.     

Synrift sedimentation on the northern Tethys margin: an example from the Ligurian Alps (Upper Triassic to Lower Cretaceous,Prepiedmont domain,Italy)

The Prepiedmont domain succession of the Ligurian Alps is formed by a thick Mesozoic sedimentary cover tectonically detached from its substratum. The Arnasco–Castelbianco unit preserves the most complete record of the Ligurian Prepiedmont, although completely overturned and deformed due to Alpine tectonics. It is composed of carbonate and clastic rocks deposited during the Upper Triassic to Lower Cretaceous interval. This paper is focused on the stratigraphy of the Jurassic series and its relationships to the Tethyan rifting. Each term of the sedimentary record is seen as a witness of the several phases through which the rifting took place. An early rifting phase (Late Hettangian to Early Sinemurian) brought to the formation of a normal fault system affecting the carbonate platform and favoured the development of condensed sedimentation on pelagic highs. The rapid transition from open-platform carbonates to slope-basin cherty limestones testifies the increased subsidence of the margin in the Late Sinemurian, during which moderate fault activity is recorded (intraformational breccia horizons). Until the Early Pliensbachian, a tectonic pause brought to the sedimentation of a succession of pelagic carbonates, occasionally interrupted by clastic flows. During the Late Pliensbachian (?) to Toarcian, the rifting phase followed, evidenced by the large amount of clastics and generated by renewed fault activity. Clastics flowed down into the basin as fluxoturbidites first, and then passed to breccias during the maximum tectonic pulse. In the Late Toarcian to Aalenian (?), the thermal uplift of the Briançonnais shoulder generated a basin fill of fine clastics. The following thermal subsidence (Aalenian to Tithonian) favoured the restoration of quiet basinal conditions evidenced by the deposition of radiolarites.     

Geochemistry of Cenomanian/Turonian boundary sediments in the mountainous part of Crimea and the northwestern Caucasus

Detailed data obtained on the chemistry of sedimentary rocks from the mountainous part of Crimea and the northwestern Caucasus that were dated at the Cenomanian/Turonian boundary and were formed during Oceanic Anoxic Event 2 (OAE 2) make it possible to calculate the dissolved oxygen concentration in the bottom waters of the sedimentation basin. The enrichment coefficients of trace elements in the black shales are revised and an explanation is suggested for the genesis of the rocks with regard for unusual climatic changes.     

鄂尔多斯盆地上三叠统延长组浊沸石的形成机理、分布规律与油气关系

鄂尔多斯盆地延长组长 6储层中广泛分布浊沸石胶结物,包体测温结果表明其形成温度在 6 0～ 70℃之间,主要形成于早成岩阶段B期。浊沸石形成以后,有机质脱羧作用形成的有机酸对其溶蚀,并形成大量次生孔隙。勘探结果证实延长统找到的油藏大部分都聚集在这些浊沸石次生孔隙中。因此,关于浊沸石胶结物的形成机理及分布规律研究对延长组油气藏的成藏机理,以及油气富集规律研究非常重要。本文从沉积微相研究入手,通过野外露头、岩心及铸体薄片、包裹体测温、扫描电镜、电子探针等分析,研究浊沸石的形成机理、分布规律以及与沉积微相的关系,从而达到通过沉积微相的展布特征来预测浊沸石分布规律。最后通过研究浊沸石次生孔隙的发育特征,预测油气藏的分布。     

The start‐up of the Dolomia Principale/Hauptdolomit carbonate platform (Upper Triassic) in the eastern Southern Alps

Wide carbonate platform environments developed on the western passive margin of the Tethys during the Late Triassic, after a major climate change (Carnian Pluvial Episode) that produced a crisis of high‐relief microbial carbonate platforms. The peritidal succession of this epicontinental platform (Dolomia Principale/Hauptdolomit, Dachstein Limestone) is widespread in the Mediterranean region. However, the start‐up stage is not fully understood. The original platform to basin depositional geometries of the system have been studied in the north‐eastern Southern Alps, close to the Italian/Slovenian boundary where they are exceptionally preserved. Sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile. The analysis of the facies architecture allowed reconstruction of the palaeoenvironments of the Dolomia Principale platform during its start‐up and early growth stages in the late Carnian. The carbonate platform was characterized by an outer platform area, connected northward to steep slopes facing a relatively deep basin. Southward, the outer platform was connected to inner sheltered environments by a narrow, often emerged shelf crest. Behind this zone, carbonate sedimentation occurred in shallow lagoons and tidal flats, passing inward to a siliciclastic mudflat. The Dolomia Principale platform was initially aggrading and able to keep pace with a concomitant sea‐level rise, and then prograding during the late Carnian. This stratigraphic interval was correlated with the Tuvalian succession of the Dolomites, allowing depiction of the depositional system on a wide scale of hundreds of kilometres. This large‐scale depositional system presents features in common with some Palaeozoic and Mesozoic carbonate build‐ups (for example, the Permian Capitan Reef complex, Anisian Latemar platform), both in terms of architecture and prevailing carbonate producers. A microbial‐dominated carbonate factory is found in the outer platform and upper slope. The recovery of high‐relief microbial carbonate platforms marks the end of the Carnian Pluvial Episode in the Tuvalian of Tethys.