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1.
This work depends on integrated high-resolution calcareous plankton nannofossil and foraminiferal biostratigraphic analyses for three Upper Cretaceous-Lower Paleogene successions at Farafra-Abu Minqar area, Western Desert, Egypt. These sections are distributed in a north-south geologic profile as follows: El Aqabat, North Gunna, and Abu Minqar. Lithostratigraphically, four formations are recorded in the study area, namely, Khoman (at base), Dakhla, Tarawan, and Esna (at top). In the north at El Aqabat section, Khoman Formation (carbonate facies) is only represented which changes partially toward the south to Dakhla Formation (siliciclastic facies). In the extreme south at Abu Minqar section, it changes completely into siliciclastic facies of Dakhla Formation. Biostratigraphically, seven calcareous nannofossil and eleven planktonic foraminiferal zones represent the Late Cretaceous-Early Paleogene are identified. Based on the occurrence or missing of these zones accompanied with the field criteria resulted in detecting four tectonic events. These tectonic events took place at the Cretaceous/Paleogene (K/Pg), the Danian/Selandian (D/S), the Selandian/Thanetian (S/T), and the Paleocene/Eocene (P/E) boundaries. These tectonic events are related to the impact of the Syrian Arc System. Four sequence boundaries (SB1, SB2, SB3, and SB4) are defined in the Late Cretaceous-Early Paleogene sequence in the Farafra-Abu Minqar area.  相似文献   

2.
The stratigraphy, sedimentology and syn-depositional tectonic events (SdTEs) of the Upper Cretaceous/Paleogene (K–P) succession at four localities in north Eastern Desert (NED) of Egypt have been studied. These localities are distributed from south-southwest to north-northeast at Gebel Millaha, at North Wadi Qena, at Wadi El Dakhal, and at Saint Paul Monastery. Lithostratigraphically, four rock units have been recorded: Sudr Formation (Campanian–Maastrichtian); Dakhla Formation (Danian–Selandian); Tarawan Formation (Selandian–Thanetian) and Esna Formation (Thanetian–Ypresian). These rock units are not completely represented all over the study area because some of them are absent at certain sites and others have variable thicknesses. Biostratigrapgically, 18 planktonic foraminiferal zones have been recorded. These are in stratigraphic order: Globotruncana ventricosa Zone (Campanian); Gansserina gansseri, Contusotruncana contusa, Recimguembelina fructicosa, Pseudohastigerina hariaensis, Pseudohastigerina palpebra and Plummerita hantkenenoides zones (Maastrichtian); Praemurica incostans, Praemurica uncinata, Morozovella angulata and Praemurica carinata/Igorina albeari zones (Danian); Igorina albeari, Globanomanlina pseudomenradii/Parasubbotina variospira, Acarinina subsphaerica, Acarinina soldadoensis/Globanomanlina pseudomenardii and Morozovella velascoensis zones (Selandian/Thantian); and Acarinina sibaiyaensis, Pseudohastigerina wilcoxensis/Morozovella velascoensis zones (earliest Ypresian). Sedimentologically, four sedimentary facies belts forming southwest gently-dipping slope to basin transect have been detected. They include tidal flats, outer shelf, slumped continental slope and open marine hemipelagic facies. This transect can be subdivided into a stable basin plain plus outer shelf in the extreme southwestern parts; and an unstable slope shelf platform in the northeastern parts. The unstable slope shelf platform is characterized by open marine hemipelagic, fine-grained limestones and fine siliciclastic shales (Sudr, Dakhla, Tarawan and Esna formations). The northeastern parts are marked by little contents of planktonic foraminifera and dolomitized, slumped carbonates, intercalated with basinal facies. Tectonically, four remarkable syn-depositional tectonic events (SdTEs) controlled the evolution of the studied succession. These events took place strongly within the Campanian–Ypresian time interval and were still active till Late Eocene. These events took place at: the Santonian/Campanian (S/C) boundary; the Campanian/Maastrichtian (C/M) boundary; the Cretaceous/Paleogene (K/P) boundary; and the Middle Paleocene–Early Eocene interval. These tectonic events are four pronounced phases in the tectonic history of the Syrian Arc System (SAS), the collision of the Afro-Arabian and Eurasian plates as well as the closure of the Tethys Sea.  相似文献   

3.
The Late Cretaceous (Maastrichtian) to early Paleocene (Thanetian) shallow water (<100 m) agglutinated foraminifera from a section at Dakhla Oasis (Western Desert, Egypt) were analyzed for their assemblage, species and genera distribution, diversity, depositional environment, community structure and palaeobathymetry with respect to regional tectonics, climate and global eustasy. Data suggest an equitable benthic environment with low species dominance deposited in a brackish littoral and/or marsh setting. Sea level curves using characteristic benthic foraminiferal species, genera and assemblages corroborate quantitatively generated estimate and statistical analysis. Data suggests that in the absence of or of an impoverished benthic foraminiferal fauna, a high resolution agglutinated foraminiferal dataset can be as good a predictor of the benthic community structure and environment, as its calcareous counterpart, at least for shallow settings (<100 m). Present data also provides a good window in better understanding the distribution and interrelationship between the three dominant genera, Haplophragmoides, Trochammina and Ammobaculites. Faunal changes at boundaries (Cretaceous/Paleogene, Danian/Selandian and Selandian/Thanetian) are also evaluated.  相似文献   

4.
《Gondwana Research》2014,25(1):257-269
The well-known Maastrichtian–Ypresian vertebrate-bearing phosphate series, in the Ouled Abdoun Basin, Morocco, is classically dated using regional selachian biostratigraphic zonation. These marine sediments yielded Paleocene and Eocene mammals comprising the earliest known placentals from Africa. This study provides the first insight into the organic carbon isotope chemostratigraphy (δ13Corg) of the Moroccan phosphate series and a refined dating of its vertebrate-bearing levels. Four Paleocene–Eocene sections in the NE Ouled Abdoun quarries show consistent δ13Corg long term evolutions, from the base to the top: 1) positive trend in phosphorite Bed IIa, beginning with the lower Bone Bed yielding mammals such as Eritherium, Ocepeia, Abdounodus, Lahimia, of early Thanetian and Selandian age; 2) transitional negative trend in the Intercalary phosphorite Beds II/I that includes the Otodus obliquus and Phosphatherium escuilliei Bone Bed of earliest Ypresian age; 3) negative trend to the lowermost δ13Corg values that are correlative to the early–middle Ypresian interval including ETM 2 and ETM 3 hyperthermal events in the global record; 4) positive trend in chert-enriched facies containing the middle Ypresian EECO global climatic event. Our chemostratigraphic study of the Ouled Abdoun phosphate series provides a new chronostratigraphic framework for calibrating the beginning of the evolution of placental mammals in Africa. The lower Bone Bed level from the Paleocene phosphorite Bed IIa yielding Eritherium is not younger than early Thanetian, and is most likely Selandian. The Phosphatherium Bone Bed in the Intercalary Beds II/I is earliest Ypresian. The phosphorite Bed 0, from which Daouitherium probably came, is early–middle Ypresian, just below the EECO. This suggests that the first large proboscideans evolved after the PETM, during mid-Ypresian warming events. The δ13Corg study does not support the presence of Lutetian in the NE Ouled Abdoun phosphate series and suggests that a noticeable part of the upper Thanetian is absent.  相似文献   

5.
The Zumaya section, northern Spain, is a suitable candidate to define the Global Stratotype Section and Point for the base of the Selandian Stage (Palaeocene) because of its excellent accessibility, exposure and stratigraphic continuity. Uncertainties exist, however, with regard to the stratigraphic horizon where to place the Danian/Selandian (D/S) boundary. Five potential stratigraphic horizons (HDS1 to HDS5) to define the D/S boundary have been identified at Zumaya, based on integrated stratigraphic studies that include quantitative planktic and benthic foraminiferal results, as well as δ13C isotopic and lithological data. Two of these horizons (HDS2 and HDS4) placed in Zone C26r appear to have particularly good potential for serving as the D/S boundary marker, because they may represent significant global palaeoceanographic, palaeoclimatic and eustatic events.  相似文献   

6.
Twelve calcareous nannofossil biozones of Late Oligocene-Late Miocene in Northern Egypt were defined and correlated with their corresponding biozones in Egypt and other parts of the world. These are arranged from the top to base as Zone NN12, Zone NN11, Zone NN10, Zone NN8, Zone NN7, Zone NN6 Zone NN5, NN4, Zone NN3, Zone NN2 Zone NP25 and Zone NP24. In the present study (Boughaz-1 Well), the Late Miocene unconformably overlies the Middle Miocene. This unconformity surface is recognized by the missing of calcareous nannofossil zones NN7 to NN9. While, in North Sinai (Malha-1 Well), the Early/Middle Miocene boundary cannot be recognized, where the Middle Miocene unconformably overlies the topmost Oligocene, and it is defined by the missing calcareous nannofossil zones NN1 to NN4.  相似文献   

7.
Calcareous nannoplankton biostratigraphy has been performed on five sedimentary sections through the marine Akveren Formation from the Bartin region of northern Turkey, on the southern Black Sea coast. This new biostratigraphy provides an age for the formation of the Early Campanian (nannofossil zone UC15aTP) to Early Selandian (nannofossil zone NP5), and highlights the presence of the Campanian/Maastrichtian, Cretaceous/Tertiary (K/T), and Danian/Selandian boundaries in this intermediate palaeolatitude location. Micula murus was identified below the K/T boundary, but Micula prinsii and Nephrolithus frequens were not, which implies that the K/T boundary interval is not complete in the study area. These dates are in agreement with previous micropaleontological studies.  相似文献   

8.
Integrated sedimentology, mineralogy, geochemistry, and microfossil and macrofossil biostratigraphies of the Maastrichtian–early Paleocene Dakhla Formation of the Western Desert, Egypt, provide improved age resolution, information on the cyclic nature of sediment deposition, and the reconstruction of depositional environments. Age control based on integrated biostratigraphies of planktic foraminifera, calcareous nannofossils and macrofossils yields the following ages for stratigraphic and lithologic sequences. The contact between the Duwi and Dakhla formations marks the Campanian/Maastrichtian boundary (zone CF8a/b boundary) and is dated at about 71 Ma. The age of the Dakhla Formation is estimated to span from 71 Ma at the base to about 63 Ma at the top (zones CF8a–Plc). The Cretaceous/Tertiary (K/T) boundary is within the upper unit of the Kharga Shale Member and marked by a hiatus that spans from 64.5 Ma in the lower Paleocene (base Plc) to at least 65.5 Ma (base CF2, base M. prinsii zones) in the upper Maastrichtian at Gebel Gifata, the type locality of the Dakhla Formation. As a result, the Bir Abu Minqar horizon, deposited between about 64.2 and 64.5 Ma (Plc(l) zone), directly overlies the K/T boundary hiatus. Major hiatuses also span the late Maastrichtian–early Paleocene in sections to the northwest (c. 61.2–65.5 Ma at North El Qasr, c. 61.2–69 Ma at Bir Abu Minqar and c. 61.2–65.5 Ma at Farafra), and reflect increased tectonic activity.During the Maastrichtian–early Paleocene a shallow sea covered the Western Desert of Egypt and the clastic sediment source was derived primarily from tectonic activity of the Gilf El Kebir spur to the southwest of Dakhla and the Bahariya arch. Uplift in the region resulted in major hiatuses in the late Maastrichtian–early Paleocene with increased erosion to the southwest. The area was located near the palaeoequator and experienced warm, wet, tropical to subtropical conditions characterized by low seasonality contrasts and predominantly chemical weathering (high kaolinite and smectite). A change towards perennially more humid conditions with enhanced runoff (increased kaolinite) occurred towards the end of the Maastrichtian and in the early Paleocene with shallow seas fringed by Nypa palm mangroves. Sediment deposition was predominantly cyclic, consisting of alternating sandstone/shale cycles with unfossiliferous shales deposited during sea-level highstands in inner neritic to lagoonal environments characterized by euryhaline, dysaerobic or low oxygen conditions. Fossiliferous calcareous sandstone layers were deposited in well-oxygenated shallow waters during sea-level lowstand periods.  相似文献   

9.
Eight zonal dinocyst assemblages and three bio stratigraphic units ranked as “beds with flora” are first distinguished in the Danian—lower Lutetian interval of the Paleogene succession, penetrated by the reference borehole Novousensk no. 1, where eight standard and one local nannoplankton zones are simultaneously recognized. The direct correlation of nannoplankton and dinocyst zones is used to refine the paleon-tological substantiation and stratigraphic position of regional lithostratigraphic units, ranges of hiatuses, and the correlation with the general stratigraphie scale. The nannoplankton of the Danian NP2 Cruciplacolithus tenuis and NP3 Chiasmolithus danicus zones is characteristic of the Algai Formation (Fm). The nannoplankton of the NP4 Coccolithus robustus Zone and dinocysts of the D3a Alterbidinium circulum Zone from the Tsyganovo Fm characterizes the Danian top. The Lower Syzran Subformation (Subfm) corresponds to the upper part of the NP4 Coccolithus robustus Zone (Neochiastizygus junctus local zone) and to the D3b (part) Cerodinium depressum Zone of the Selandian dinocysts. The latter spans part of the Upper Syzran Subformation, whose characteristic nannofossils are the nannoplankton of the NP5 Fasciculithus tympaniformis Zone and the dinocysts of the D3b (part) Isabelidinium? viborgense Zone of the Selandian. The Novouzensk Fm is represented by a succession of the dinocyst Cerodinium markovae Beds and the standard D4c Apectodinium hyperacanthum Zone of the upper Thanetian. The coccolitophorids of the lower Thanetian NP6 Heliolithus kleinpelli Zone occur at the formation base. The Bostandyk Fm includes successive bio stratigraphie units of the Ypresian. In the dinocyst scale, these are the D5a Apectodinium augustum Zone, the Pterospermella Beds (DEla Zone of the North Sea scale), and zones DBlb-c Deflandrea oebisfeldensis, D7c Dracodinium varielon-gitudum, and D8 Dracodinium politum—Charlesdowniea coleothrypta, while units of the nannoplankton scale correspond to the NP12 Martasterites tribrachiatus and NP13 Discoaster lodoensis zones. The Kopterek Fm yields Lutetian nannofossils: the nannoplankton of the NP14 Discoaster sublodoensis Zone and the dinocysts of the Wetzeliella coronata—Areosphaeridium diktyoplokum Beds. Three meaningful hiatuses are established at the Danian base, Selandian top, and in the lower Ypresian.  相似文献   

10.
High-resolution carbon isotope stratigraphy of the upper Campanian-Maastrichtian is recorded in the Boreal Realm from a total of 1968 bulk chalk samples of the Stevns-1 core, eastern Denmark. Isotopic trends are calibrated by calcareous nannofossil bio-events and are correlated with a lower-resolution δ13C profile from Rørdal, northwestern Denmark. A quantitative approach is used to test the reliability of Upper Cretaceous nannofossil bio-events and provides accurate biohorizons for the correlation of δ13C profiles. The Campanian-Maastrichtian boundary (CMB) is identified through the correlation of dinoflagellate biostratigraphy and δ13C stratigraphy between Stevns-1 and the Global boundary Standard Stratotype-section and Point at Tercis les Bains (SW France), allowing the identification of new chemical and biostratigraphic markers that provide a precise placement of the stage boundary on a regional scale. The boundary interval corresponds to the third phase of a stepwise 0.8‰ negative δ13C excursion, lies in calcareous nannofossil subzone UC16dBP, and encompasses the last occurrence of nannofossil Tranolithus stemmerikii and first occurrence of nannofossil Prediscosphaera mgayae. Fifteen δ13C events are defined and correlated to sixteen reliable nannofossil biohorizons, thus providing a well-calibrated standard high-resolution δ13C curve for the Boreal Realm.  相似文献   

11.
In the past15 years,the Cenozoic calcareous nannofossilsin the East China Sea were biostratigraphically studied duringthe extensive offshore petroleum exploration in a number ofbasins on the shelf of the East China Sea.A number of Pale-ocene to Quaternary nannofossil zones were recognized basedon the nannofossils from m any offshore wells (SBMGS,1989,1985 ) .These previous studies indicated a lot of biostratigraphicproblems,resulting in difficulties in the understanding of afurther detail…  相似文献   

12.
Seven planktic foraminiferal zones are distinguished in the Maastrichtian-Paleocene succession at the north Farafra Oasis. These are the Rugoglobigerina hexacamerata (CF8b), Gansserina gansseri, and Contusotruncana contusa zones in the Maastrichtian topped by a well-known unconformity across the Cretaceous/Paleogene (K/Pg) boundary. The Danian is subdivided into two biozones: Globanomalina compressa/Praemurica inconstans-Praemurica uncinata Subzone (P1c) and Praemurica uncinata–Morozovella angulata (P2) Zone. The Late Paleocene is divided into two zones: Morozovella angulata-Globanomalina pseudomenardii (P3) and Globanomalina pseudomenardii (P4). A minor hiatus between the Danian/Selandian and Selandian/Thanetian boundaries are also recorded. These time gaps across the stage boundaries may be related to the tectonic events that affected the sedimentation regime throughout the Upper Cretaceous–Lower Paleogene interval in the Farafra Oasis.  相似文献   

13.
This study is based on calcerous nannofossil assemblages changes and fluctutions of stable carbon and oxygen isotopes was collected clayey limestones, limestones, and marls in the Maastrichtian to Selandian from Akveren Formation (Western Black Sea). As the relative abundances of species of Micula spp, Watznauera barnesiae, and Arkhangelskiella cymbiformis, which tolerated changes of temperature and nutrition, carbon and oxygen isotopes compositions, and low species richness imply strong diagenesis effect at the Maastrichtian, there is no important diagenesis effect at Paleocene. Just after the Cretaceous/Tertiary (K-Pg) boundary, Thoracosphaera spp. and Braarudosphaera bigelowi were dominant species; Danian is characterized by Thoracosphaera, Ericsonia ovalis, Cruciplacolithus spp., Coccolithus pelagicus, and Ericsonia subpertusa. Generally, the nutrition productivity is good–moderate in Lower Maastrichtian, and decreasing carbon isotope values during the Uppermost Maastrichtian shows the presence of oligotrophic environmental conditions suitable with global nutrition crises before the K-Pg boundary and diagenesis in study area. Throughout the Danian, mesotrophic–oligotrophic environmental conditions dominate; however, the decrease in nutrition before Selandian represents oligotrophic environmental conditions. The increasing nutrition at Selandian is related to the change in the environmental conditions.  相似文献   

14.
The widely exposed siliciclastic/carbonate succession exposed at Gebel El-Qurn, west Luxor, has been investigated from the mineralogical, petrographical and biostratigraphical points of view. The succession belongs to the lower Eocene, including the upper Esna Shale and the Thebes Formations that have been deposited under varied marine conditions and during alternating periods of abundant and ceased clastic influx. They contain abundant and well-diversified planktonic foraminifera and calcareous nannoplankton, suggesting deposition in open marine inner to middle shelf environments. Mineralogical analysis carried out by XRD revealed the presence of smectite, illite, kaolinite, sepiolite, palygorskite, and smectite–illite-mixed layer as the principal clay minerals, and calcite, dolomite, quartz, anhydrite, gypsum, hematite, and goethite as non-clay minerals. The clay mineral distributions in the sediments reflect the climatic conditions and the weathering processes at the source area as well as the differential hydraulic sorting during transportation. Calcite is the most abundant non-clay mineral, and this is consistent with high calcareous fossil content of the sediments. Petrographic examination of the carbonate lithologies within the succession enables to identify eight microfacies associations. These microfacies were affected by several diagenetic processes including; micritization, compaction, cementation, neomorphism, dissolution, dolomitization, and silicification. Dissolution of original test wall and replacement and infilling by iron oxides and recrystallized calcite were commonly observed. Calcareous nannofossils are generally common to frequent, highly diversified, and moderately to well preserved. Two calcareous nannofossil biozones; Tribrachiatus contortus Zone (NP10) and Discoaster binodosus (NP11) are recorded in the studied sediments suggesting lower Eocene age. Their associated nannofossil taxa are characterized by the predominance of warm water species. Sea-level fluctuations, basin physiography, climate, paleogeography, and sediment supply were the major controls on the deposition of the lower Eocene sediments at Gebel El-Qurn.  相似文献   

15.
An integrated biostratigraphic (foraminifera, calcareous nannofossils, crinoids), chemostratigraphic (stable carbon isotopes) and magnetostratigraphic study of the Bocieniec section (southern Poland) is presented here. The section presents a continuous and lithologically monotonous sedimentary record across the Santonian–Campanian boundary transition. A large number of macrofossil, foraminiferal and calcareous nannofossil bioevents along with several well-identified carbon-isotope excursions of the upper Santonian and lowermost Campanian are documented. The base of the Campanian is well-constrained by the last occurrence (LO) of the crinoid Marsupites testudinarius, and correlates to the onset of the first δ13C positive peak of the Santonian–Campanian Boundary Event (SCBE peak a). A presumable primary Cretaceous paleomagnetic signal highlights the potential presence of the C34N/C33R magnetic reversal although its exact position remains uncertain between peaks a and b of the SCBE. The planktic foraminifer Dicarinella asymetrica is very rare at Bocieniec but a potential LO of this important marker may be recorded in coincidence with peak b of the SCBE. The first occurrence (FO) of calcareous nannofossil Broinsonia parca parca coincides with the lower part of chron C33R and with the early Campanian pilula zone event. A large set of additional nannofossil events and benthic foraminifer events further constrain the stratigraphy of the section and along with the carbon isotopes, allows for correlation with other important sections of the Boreal realm. Although the Bocieniec section is relatively thin and condensed (5.5 m), the successive order of events and presence of all past proposed stratigraphic criteria for the Santonian-Campanian boundary makes it the most complete reference section for this interval at the European and at the global scale. Moreover, this section allows for a precise correlation of the Tethyan and Boreal domains. The Bocieniec section fulfils the geological criteria to be a potential boundary stratotype candidate for the base of the Campanian Stage.  相似文献   

16.
The Lockhart Formation from a major carbonate unit of the Paleocene Charrat Group in Upper Indus Basin, Pakistan represents a larger foraminiferal–algal build up deposited in a cyclic sequence of the carbonate ramp. The foraminiferal–algal assemblages of the Lockhart Formation are correlated here to larger foraminiferal biostratigraphic zone, i.e. Shallow Benthic Zone (SBZ3) of the Thanetian Age. Inner ramp lagoon, shoal and fore shoal open marine are three main facies associations represented by wackstone and packstone foraminiferal–algal deposits. These facies are present in a cyclic order and displayed a retrograding carbonate ramp indicating the Thanetian transgressive deposits associated with eustatic sea level rise. The correlation of the microfacies of the Lockhart Formation (Upper Indus Basin) and facies of the Dungan Formation (Lower Indus Basin) provide detailed configuration of the depositional setting of the Indus Basin during the time interval represented by the Thanetian Zone SBZ3.  相似文献   

17.
In this study, progradation and the subsequent retrogradation of a late Paleocene isolated carbonate platform (Galala Mountains, Eastern Desert, Egypt) is demonstrated by variations of distinct facies associations from the platform margin in the north to the hemipelagic basin in the south. A combination of a sea-level drop and tectonic uplift at around 59 Ma (calcareous nannofossil biozone NP5) favored the initiation of the carbonate platform. From this time onwards, the facies distribution along the platform–basin transect can be subdivided into five facies belts comprising nine different facies associations. Their internal relationships and specific depositional settings are strongly coupled with the Maastrichtian–Paleocene seafloor topography, which resulted from local tectonic movements. Patch reefs and reef debris were deposited at the platform margin and the horizontally bedded limestones on the upper slope. Slumps and debris flows were stored on the lower slope. In the subhorizontal toe-of-slope facies belt, mass-flow deposits pass into calciturbidites. Further southwards in the basin, only hemipelagic marls were deposited. Between 59 and 56.2 Ma (NP5–NP8), the overall carbonate platform system prograded in several pulses. Distinct changes in facies associations from 56.2 to 55.5 Ma (NP9) resulted from rotational block movements. They led to increased subsidence at the platform margin and a coeval uplift in the toe-of-slope areas. This resulted in the retrogradation of the carbonate platform. Furthermore the patch-reef and reef-debris facies associations were substituted by the larger foraminifera shoal association. The retrogradation is also documented by a significant decrease in slump and debris-flow deposits on the slope and calciturbidites at the toe of slope.  相似文献   

18.
The Lower Cretaceous sediments of the Ceahl?u Nappe (from the bend region of the Romanian Carpathians) were investigated from lithological and micropaleontological (calcareous nannoplankton) points of view. Our investigations revealed that the studied deposits were sedimented within the latest Tithonian-Albian interval. The calcareous nannofossil assemblages of the turbidite calcareous successions (the Sinaia Formation) were assigned to the NJK-?NC5 calcareous nannofossil zones, which cover the Late Tithonian-Early Barremian interval. The sandy-shaly turbidites, which followed the calcareous turbidites of the Sinaia Formation, are Early Barremian-Early Albian in age (interval covered by the ?NC5-NC8 calcareous nannofossil zones). Because the studied deposited are mainly turbidites, many reworked nannofossils from older deposits are present in the calcareous nannofloras. Thus, some biozones (i.e., NC5), defined based on the last occurrences of nannofossils, could not be identified. The calcareous nannofossil assemblages are composed of Tethyan taxa (which dominate the nannofloras) and cosmopolitan taxa. During two intervals (the Late Valanginian and across the Barremian/Aptian boundary), Tethyan and cosmopolitan nannofossils, together with Boreal ones, were observed. This type of mixed calcareous nannoplankton assemblage is indicative for sea-level high-stand, which allows the nannofloral exchange between the Tethyan and Boreal realms, within the two-above mentioned intervals.  相似文献   

19.
The Gurpi section in western Shiraz, faulted Zagros range of southwestern Iran, contains one of the most complete Early Santonian to Late Maastrichtian sequences. The lack of a good fundamental paleontological study is a strong motivation for investigating calcareous nannofossils in southwestern Iran. The Gurpi Formation is mainly made up of grey shale. As a result of this study, 23 genera and 47 species of nannofossils have been identified for the first time. This confirms the existence of biozones CC14–CC26, which suggests the age of Early Santonian to Late Maastrichtian. All Early Santonian to Late Maastrichtian calcareous nannofossil biozones from CC14 (equivalent to the Micula decussate Zone) to CC26 (equivalent to the Nephrolithus frequens Zone) are discussed. Additionally, the zonal subdivision of this section based on calcareous nannofossils, is correlated with planktonic foraminiferal zones (Dicarinella asymetrica Zone to Abathomphalus mayaroensis Zone). We can also learn about the predominant conditions of the studied sedimentary basin that was in fact a part of the Neotethys basin with the existence of index species of calcareous nannofossils indicating a warm climate and high depths of the basin in low latitudes.  相似文献   

20.
《Cretaceous Research》2008,29(1):40-64
The proposed definition of the Turonian/Coniacian boundary, at the first occurrence of the inoceramid bivalve Cremnoceramus deformis erectus (Meek) (= Cremnoceramus rotundatus (sensu Tröger non Fiege)), prompted a rigorous study of the calcareous nannofossil events through this interval, both for calibration of the calcareous nannofossil biostratigraphy, and to provide an assessment of the suitability, in calcareous nannofossil terms, of the proposed stratotype section. New calcareous nannofossil data are presented here, detailing the biostratigraphy of the boundary interval from four locations. These include the candidate boundary-stratotype, the Salzgitter-Salder Quarry section (northern Germany), as well as the Slupia Nadbrzezna outcrop (central Poland), a potential secondary reference section. Also included is the Brezno Pd-1 Borehole and outcrops in the Brezno Formation (= Priesener Schichten) type-area (north-western Czech Republic), which represents an original boundary candidate (Copenhagen Stage Boundaries Meeting, 1983), and the Langdon Stairs coastal section (south-eastern England), part of the British Chalk succession. The calcareous nannofossil events derived from each section provide a sequence across the boundary of (in stratigraphical order): below the boundary, the first occurrence of Lithastrinus septenarius followed by that of Broinsonia parca expansa; above the boundary, the last occurrence of Helicolithus turonicus followed by the first occurrence of Micula staurophora (= Micula decussata of some authors). This places the boundary within Nannofossil Subzone UC9c. A similar sequence of events has previously been determined from sections in north-eastern England and in the south-eastern Indian Ocean. The presented data and correlations suggest that either the Salzgitter-Salder Quarry section or the Slupia Nadbrzezna outcrop section would make a suitable Global Stratotype Section for the Turonian/Coniacian boundary, as far as calcareous nannofossils are concerned. The use of the calcareous nannofossil Marthasterites furcatus, widely quoted as an indicator of this boundary, is discussed and proved to be untenable.  相似文献   

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