Age and depositional environment of the Draa Sfar massive sulfide deposit, Morocco     

C. Moreno  R. Sáez  F. González  G. Almodóvar  M. Toscano  G. Playford  A. Alansari  S. Rziki  A. Bajddi 《Mineralium Deposita》2008,43(8):891-911

The Draa Sfar mineralization consists of two main stratabound orebodies, Sidi M’Barek and Tazacourt, located north and south of the Tensift River (“Oued Tessift”), respectively. Each orebody is comprised by at least two massive sulfide lenses. The hosting rocks are predominantly black shales, although minor rhyolitic rocks are also present in the footwall to the southern orebody. Shales, rhyolitic volcanic rocks, and massive sulfides are all included into the Sarhlef Series, which is recognized as one of the main stratigraphic units of the Moroccan Variscan Meseta. Hydrothermal activity related with an anomalous thermal gradient, together with a high sedimentation rate in a tectonically driven pull-apart marine basin, favored the accumulation of organic-rich mud in the deepest parts of the basin and the sedimentary environment suitable for massive sulfide deposition and preservation. This took place by replacement of the hosting unlithified wet mud below the sediment–water interface. Geochemical data suggest a sedimentary environment characterized by oxic water column and anoxic sediment pile with the redox boundary below the sediment–water interface. The low oxygen availability within the sediment pile inhibited oxidation and pyritization of pyrrhotite. Biostratigraphic analysis, based on the palynological content of the hosting black shales, restricts the age of the sulfides to the Asbian substage (mid-Mississippian). This age is consistent with earlier geochronological constraints.  相似文献   

First U–Pb SHRIMP age of the Hauterivian stage, Neuquén Basin, Argentina     

M. Beatriz Aguirre-Urreta  Pablo J. Pazos  Darío G. Lazo  C. Mark Fanning  Vanesa D. Litvak   《Journal of South American Earth Sciences》2008,26(1):91-99

A high-resolution ion-microprobe (SHRIMP) U–Pb zircon age from a tuff layer intercalated in the ammonoid bearing sedimentary succession of the Neuquén Basin in Argentina provides a robust geochronologic date to add to the absolute ages and to improve the relative chronology of the Early Cretaceous Hauterivian stage. The tuff layer appears interbedded between shales of the upper member (Agua de la Mula) of the Agrio Formation within the Spitidiscus riccardii ammonoid zone (base of the Late Hauterivian) yielding a date of 132.5 ± 1.3 Ma. This date confirms and supports an accurate correlation between the ammonoid biostratigraphy of the Neuquén Basin with the Western Mediterranean Province of the Tethys during the Early Cretaceous and matches with the most recently published time scale. It also casts doubts on the validity of K–Ar ages on glauconite-grains recently reported from the Lower Cretaceous of the Vocontian Basin of France.  相似文献   

Confirmation of an Early Cretaceous age for the Qihulin Formation in eastern Heilongjiang Province, China: constraints from a new discovery of radiolarians   总被引：1，自引：0，他引：1  

Gang Li  Qun Yang 《Cretaceous Research》2003,24(6):691-696

The coal-bearing, alternating marine and non-marine Longzhaogou Group in eastern Heilongjiang, northeastern China, has long been considered as Jurassic, or mainly Jurassic, in age. However, recent studies have demonstrated that the ammonites and dinoflagellate cysts are of Early Cretaceous age. This has now been confirmed by new radiolarian evidence. The radiolarian fauna recovered from the upper Qihulin Formation of the Longzhaogou Group consists of nine poorly preserved species referable to nine genera. Novixitus is a Cretaceous genus, and the specimens of Archaeodictyomitra sp. and Xitus sp. recovered resemble A. vulgaris Pessagno and X. spicularius (Aliev), respectively.  相似文献   

中国东北区古生代生物地层学几个问题   总被引：3，自引：0，他引：3  

苏养正 《吉林地质》1996,(Z1)

作者对东北区古生代地层中，几个人们关注的生物地层学问题，诸如麻山动物群、清河镇动物群等，作了比较客观的评价，可供今后的研究工作参考。  相似文献   

Stratigraphy of the upper cretaceous and lower tertiary strata in the Tethyan Himalayas of Tibet (Tingri area,China)   总被引：26，自引：0，他引：26  

H. Willems  Z. Zhou  B. Zhang  K. -U. Gräfe 《International Journal of Earth Sciences》1996,85(4):723-754

The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outer-shelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression — regression cycle during the Paleocene and Eocene, documented in the Zhepure Shan formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian.  相似文献   

Middle Campanian–lowermost Maastrichtian nannofossil and foraminiferal biostratigraphy of the northwestern Australian margin     

Robert J. Campbell  Richard W. Howe  John P. Rexilius   《Cretaceous Research》2004,25(6):827-864

The middle–late Campanian was marked by an increase in the bioprovinciality of calcareous microfossil assemblages into distinct Tethyan, Transitional, and Austral Provinces that persisted to the end of the Maastrichtian. The northwestern Australian margin belonged to the Transitional Province and the absence of key Tethyan marker species such as Radotruncana calcarata and Gansserina gansseri has led petroleum companies operating in the area to use the locally developed KCCM integrated calcareous microfossil zonation scheme. The KCCM zonation is a composite scheme comprising calcareous nannofossil (KCN), planktonic foraminiferal (KPF) and benthonic foraminiferal (KBF) zones. This paper presents the definitions and revisions of Zones KCCM8–19, from the highest occurrence (HO) of Aspidolithus parcus constrictus to the lowest occurrence (LO) of Ceratolithoides aculeus, and builds on our previous early–late Maastrichtian study. The presence of a middle–upper Campanian disconformity is confirmed by microfossil evidence from the Vulcan Sub-basin, Exmouth and Wombat plateaus, and the Southern Carnarvon Platform. In the Vulcan Sub-basin and on the Exmouth Plateau (ODP Hole 762C) the hiatus extends from slightly above the LO of common Rugoglobigerina rugosa to above the LO of Quadrum gothicum. On the Wombat Plateau (ODP Hole 761B) it spans from above the LO of Heterohelix semicostata to above the LO of Quadrum gothicum; and in the Southern Carnarvon Platform the disconformity has its longest duration from above the HO of Heterohelix semicostata to above the LO of Quadrum sissinghii. A significant revision of the events which define Zones KCCM18 and 19 was necessary owing to the observation that the LO of Ceratolithoides aculeus occurs below the HOs of Archaeoglobigerina cretacea and Stensioeina granulata incondita and the LO of common Rugoglobigerina rugosa. In the original zonation these events were considered to be coincident.  相似文献   

元谋人时代研究评述——兼论我国早更新世古人类时代问题   总被引：1，自引：0，他引：1  

姚海涛  邓成龙  朱日祥 《地球科学进展》2005,20(11):1191-1198

我国早更新世古人类遗址时代的确定对于认识早期人类起源、扩散与演化具有重要意义。对元谋人化石的各种年龄测定结果和认识分歧进行了综合评述。综合分析认为，在翔实的岩石地层学和古生物地层学基础上，开展高分辨率磁性地层学研究是解决包括元谋人在内的这一时期哺乳动物时代科学问题的最有效的研究途径。  相似文献   

Le Viséen supérieur d'Azarhare (Maroc central) : environnements de dépôt,datation et évolution diagénétique     

Atika Karim  Mostafa Berkhli  Daniel Vachard  Nicolas Tribovillard  Beate Orberger 《Comptes Rendus Geoscience》2005,337(5):525-532

The unexplored area of Azarhare in central Morocco is studied thanks to three sections composed of five lithological facies Main biostratigraphical and sedimentological results concern (1) the identification of Late Visean biozones, with important presence of problematic algae Ungdarella, (2) the regional extension of deposit sequences SD5, SD6 and SD7 previously defined, (3) and an analysis of the diagenetic kaolinite. To cite this article: A. Karim et al., C. R. Geoscience 337 (2005).  相似文献   

Small sized charophyte gyrogonites in the Maastrichtian of Coll de Nargó, Eastern Pyrenees: An adaptation to temporary floodplain ponds     

《Cretaceous Research》2016

Charophytes bearing small sized fructifications dominated in fluviatile floodplain facies (red beds) from the Maastrichtian of Coll de Nargó and neighbouring basins in the southern Pyrenees (Catalonia, Spain). These charophytes mainly belong to the genus Microchara and are often disregarded in biostratigraphic studies, which focus their attention instead on facies from permanent lakes that are richer in species which usually bear fructifications with a larger size range. However, small sized gyrogonites are also significant for biostratigraphic purposes and even include some of the index species for Maastrichtian biozones in Europe. Indeed, the charophyte assemblages from the Maastrichtian of Coll de Nargó belong to the Microchara punctata biozone, recently calibrated to the middle-upper Maastrichtian.Floodplain ponds from the Maastrichtian red beds of Coll de Nargó (Lower Red Unit) were extremely shallow, received considerable terrigenous influx and were frequently exposed, probably resulting in turbid, warm waters with high light availability. These conditions could explain the almost exclusive occurrence of charophytes with small fructifications in the Lower Red Unit. The available data, mainly based on oospores from extant species, indicate that the small size observed in gyrogonites from temporary ponds may represent an adaptation to environmental stress. Fossil species with small gyrogonites of Microchara cristata, M. punctata and Microchara nana would thus develop massively in stressed shallow ponds on fluvial floodplains. To contrast these hypotheses, we compared our results to those of four well-known case studies with similar sedimentological contexts, ranging from the Lower Cretaceous to the upper Eocene–lower Oligocene. Gyrogonite size patterns were similar in all cases, possibly suggesting that characeans display a long history of adaptation to shallow, temporary and turbid floodplain ponds by means of producing a high number of small gyrogonites, probably representing short life cycles and opportunistic strategies.  相似文献   

Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean     

《Marine and Petroleum Geology》2016

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.  相似文献