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1.
Río Fardes剖面位于西班牙南部Granada东北,构造上属于深水环境的Subbetic中带。该剖面主要由白垩纪Fardes组第Ⅱ段和第Ⅲ段(半)远洋沉积构成,并出现浊流沉积和混杂沉积。本次研究在Fardes组浊流层序内首次发现两段红色沉积。钙质超微化石表明红层的时间从Turonian早期(UC7 带)到Coniacian中期—晚期界线(UC10/?UC11带)。红层由mm级红色泥岩夹灰色、杂色、偶尔黑色泥岩和钙质泥岩组成。沉积学研究表明新发现的Turonian Coniacian远洋红色泥岩沉积形成于CCD面之下深水盆地环境,浊流和碎屑流沉积强烈地影响着(半)远洋环境的背景泥岩相,并成为红色沉积结束的原因。  相似文献   

2.
Abstract

The Upper Prealpine nappe of the Swiss and French Prealps consists of a composite stack of various tectonic slivers (Gets, Simme, Dranse and Sarine sub-nappes, from top to bottom). The structural superposition and stratigraphic content of the individual sub-nappes suggests a successive stacking at the South Penninic/Adriatic transition zone during the Late Cretaceous and Early Paleogene. The present paper deals with two aspects. (1) new data obtained from the Complexe de base Series of the Dranse sub-nappe which underlies the Helminthoid Sandstone Formation, and (2) the development of a geodynamic accretionary model for the Upper Prealpine nappe stacking.

The Complexe de base Series reveals a succession of black shales at the base, grading upward into variegated red/green and red shales which were deposited in an abyssal plain environment starved of clastic input. It is overlain by the Helminthoid Sandstone Formation. The combined analysis of planktic and agglutinated benthic foraminifera and comparisons with other Tethyan series suggest an Albian to Campanian age of the Complexe de base succession. Tectonic transport of the abyssal plain segment into a trench environment allowed for the stratigraphic superposition by the Helminthoid sandstone sequence. The present findings combine well with the general scheme of the Upper Prealpine nappe stack and several single results on parts of the nappe stack. We take that opportunity to present a comprehensive model for the tectono-sedimentary evolution of the Upper Prealpine nappe.

We suggest that Late Jurassic-Early Cretaceous asymmetric (?) extension at the South Penninic-Adriatic margin created an extensional alloehthon. Later during the mid-Cretaceous, the start of convergence drove the obduction of oceanic crust on the northern margin of the extensional allochthon. The resulting ophiolitic/continental source supplied clasts to the trench basin in front (Manche turbidite series), and the backarc basin (Mocausa Formation) and abyssal plain (Perrières turbidite series) to the South. During Middle to Late Coniacian the main Adriatic margin was thrusted over the obductionrelated mixed belt and established an incipient accretionary prism containing the former trench, backarc and abyssal plain basin fill series. During this stage the Gueyraz (melange) Complex formed, which separates the trench series from the retroarc and abyssal plain formations. On top of the incipient accretionary prism a forearc basin developed hosting the Hundsrück Formation. The frontal abyssal plain formation (Complexe de base) still received few turbiditic intercalations. From Campanian time on, the forearc basin was bypassed and deposition of the Helminthoid Sandstone Formation occurred on the Complexe de base succession. During the Maastrichtian the abyssal plain and trench fill succession (Dranse nappe) was accreted to the incipient wedge, and in front of a newly active buttress, the Gurnigel trench basin was established. Another accretionary event during latest Paleocene/earliest Eocene added parts of that trench series to the base of the wedge (Sarine nappe). During the Late Eocene the accretionary wedge and remaining trench fill series (Gurnigel nappe) were thrusted en-bloc over the Middle Penninic limestone nappes and partly overtook the latter. Continued shortening of the resulting nappe pile and out-of-sequence thrusting accomplished the overriding of the Middle Penninic units over the former South Penninic Gurnigel trench series (inversion of palaeogeographic domains).  相似文献   

3.
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   

4.
Recognition of the occurrence and extent of hemipelagic and pelagic deposits in turbidite sequences is of considerable importance for environmental analysis (palaeodepth, circulation, distance from land, hemipelagic or pelagic versus turbidite sedimentation rates) of ancient basins. Differentiation between the finegrained parts (E-division) of turbidites and the (hemi-) pelagic layers (F-division of turbidite-pelagite alternations) is facilitated in basins where carbonate turbidites were deposited below the carbonate compensation depth (CCD) such as the Flysch Zone of the East Alps but may be difficult in other basins where less compositional contrast is developed between the fine-grained turbidites and hemipelagites. This difficulty pertains particularly in Palaeozoic and older basins. For Late Mesozoic-Cenozoic oceans with a relatively deep calcite compensation level three other types of turbidite basins may be distinguished for which differentiation becomes increasingly more difficult in the sequence from (1) to (3): (1) terrigenous turbidite basins above the CCD; (2) carbonate turbidite basins above the CCD; (3) terrigenous turbidite basins below the CCD. Criteria and methods useful for the differentiation between turbiditic and hemipelagic mudstone in the Upper Cretaceous of the Flysch Zone of the East Alps include calcium carbonate content, colour, sequential analysis, distribution of bioturbation, and microfaunal content. In modern turbidite basins clay mineral content, organic matter content, plant fragments, and grain-size (graded bedding, maximum grain diameter) have reportedly also been used as criteria (see Table 3). Deposition of muddy sediment by turbidity currents on weakly sloping sea bottoms such as the distal parts of deep-sea fans or abyssal plains is not only feasible but may lead to the accumulation of thick layers. Contrary to earlier speculation it can be explained by the hydrodynamic theory of turbidity currents, if temperature differences between the turbidity current and the ambient deep water as well as relatively high current velocities for the deposition of turbiditic muds (an order of magnitude higher on mud surfaces than commonly assumed) are taken into consideration. The former add to the capacity of turbidity currents to carry muddy sediment without creating a driving force on a low slope.  相似文献   

5.
In northern Euboea (Eastern Greece), Late Cretaceous platform carbonates of the Pelagonian Zone pass depositionally upwards into Maastrichtian hemipelagic limestones, possibly reflecting a rifting event in the adjacent Neotethys. This is followed by a c. 1 km-thick unit of siliciclastic turbidites, debris flows and detached limestone blocks. Thrust intercalations of ophiolitic rocks comprise altered pillow basalts and ultramafic rocks with ophicalcite. Calcite veins in sheared serpentinite contain planktonic foraminifera and the ophicalcite is directly overlain, with a depositional contact, by Globotruncana-bearing pelagic limestones and calciturbidites of Maastrichtian age. The ophiolitic rocks are interpreted as Late Cretaceous oceanic crust and mantle, that formed at a fracture zone, or rifted spreading axis within a Neotethyan, Vardar basin to the east. During the Early Tertiary (Palaeocene–Eocene), the Neotethyan basin began to close, with development of a subduction-accretion complex, mainly comprising sheared, trench-type sandstones, associated with ophiolitic slices. In response to trench/margin collision, the Pelagonian carbonate platform foundered and limestone debris flows and olistoliths were shed into a siliciclastic foreland basin. Suturing of the Neotethyan ocean basin then resulted in westwards thrusting of oceanic units over the foreland basin, thrusting of slices of inferred Late Cretaceous Pelagonian carbonate platform slope and large-scale recumbent folding.  相似文献   

6.
Lithological and micropaleontological studies of sediments were carried out along the meridional profile across the Brazil Basin. Based on nannoplankton and diatom assemblages, the sediments represented by oxidized miopelagic clays, differently reduced hemipelagic clays, and clayey-siliceous (Ethmodiscus) and calcareous (coccolith-foraminiferal) oozes are attributed to the Pleistocene-Holocene. Specific features of sedimentary material indicate its redeposition by Antarctic bottom waters, mudflows, slumps, and rockslides. It is shown that sedimentation in the Brazil Basin corresponds to the incomplete pelagic (miopelagic) type of oceanic lithogenesis transitional to the near-continental one.  相似文献   

7.
The scientific borehole Baden-Sooss penetrates a succession of Badenian (Langhian, Middle Miocene) sediments at the type locality of the Badenian, the old brickyard Baden-Sooss in the Vienna Basin. The sedimentary succession of the 102-m-cored interval consists of more than 95% bioturbated, medium-to-dark gray marly shales with carbonate contents between 11 and 25% and organic carbon contents between 0.35 and 0.65%. Biostratigraphic investigations on foraminifera (mainly lower part of Upper Lagenid Zone) and calcareous nannoplankton (standard zone NN5) indicate an early Badenian (Langhian) age. Cycles in carbonate content, organic carbon content, and magnetic susceptibility have been identified by power spectra analysis. Correlations between the three variables are extremely significant. Using cross-correlation, periods around 40 m correlate significantly with the 100 kyr−1 eccentricity cycle, the ∼20 m periods with the obliquity cycle, and the 15 to 11-m periods with both precession cycles. Wavelet transformation and decomposition of composite periodic functions were used to obtain the position of the cycle peaks in the profile. Cross-correlation with orbital cycles (La2004) dates the Baden-Sooss core between −14.379 ± 1 and −14.142 my ± 9 kyr.  相似文献   

8.
In this study, we describe a new stratigraphy of three exposed sections in central Tunisia, integrating Coniacian and Santonian planktic foraminifera and calcareous nannoplankton, supported by ammonite and inoceramid bioevents. In the three sections, the Coniacian/Santonian (C/S) boundary lies slightly above the lowest occurrence (LO) of the calcareous nannofossil Lucianorhabdus cayeuxii, which marks nannofossil Zone CC16 and matches well with the LO of the planktic foraminifera Dicarinella asymetrica. It also lies ∼4–7 m below the LO of the inoceramid Platyceramus cycloides and the ammonite Texanites (Texanites) sp. Comparing these marker C/S bioevents with the global stratotype section, the Olazagutia section (Spain) shows that the stratigraphic range of the bioevents are variable. This observation must be taken into consideration when making regional chronostratigraphic correlations.  相似文献   

9.
The Armutlu Peninsula and adjacent areas in NW Turkey play a critical role in tectonic reconstructions of the southern margin of Eurasia in NW Turkey. This region includes an inferred Intra-Pontide oceanic basin that rifted from Eurasia in Early Mesozoic time and closed by Late Cretaceous time. The Armutlu Peninsula is divisible into two metamorphic units. The first, the Armutlu Metamorphics, comprises a ?Precambrian high-grade metamorphic basement, unconformably overlain by a ?Palaeozoic low-grade, mixed siliciclastic/carbonate/volcanogenic succession, including bimodal volcanics of inferred extensional origin, with a possibly inherited subduction signature. The second unit, the low-grade znik Metamorphics, is interpreted as a Triassic rift infilled with terrigenous, calcareous and volcanogenic lithologies, including basalts of within-plate type. The Triassic rift was unconformably overlain by a subsiding Jurassic–Late Cretaceous (Cenomanian) passive margin including siliciclastic/carbonate turbidites, radiolarian cherts and manganese deposits. The margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in Turonian time. Geochemical evidence from meta-basalt blocks within ophiolite-derived melange suggests a supra-subduction zone origin for the ophiolite. The above major tectonic units of the Armutlu Peninsula were sealed by a Maastrichtian unconformity. Comparative evidence comes from the separate Almacık Flake further east.Considering alternatives, it is concluded that a Mesozoic Intra-Pontide oceanic basin separated Eurasia from a Sakarya microcontinent, with a wider Northern Neotethys to the south. Lateral displacement of exotic terranes along the south-Eurasian continental margin probably also played a role, e.g. during Late Cretaceous suturing, in addition to overthrusting.  相似文献   

10.
An integrated sequence stratigraphic study based on outcrop, core and wireline log data documents the combined impact of Cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern Gulf of Mexico. The diverse facies and abundant data of the Comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting Cretaceous platform development. Regional cross‐sections across the shoreline to shelf‐margin profile provide a detailed record of mixed carbonate–siliciclastic strata for the Hauterivian to lower Campanian stages (ca 136 to 80 Ma). The study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes. Three second‐order supersequences comprised of eight composite sequences are recognized in the Valanginian–Barremian, the Aptian–Albian and the Cenomanian–Campanian. The Valanginian–Barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting, as well as variable rates of mid‐ocean ridge volcanism. The Aptian–Albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b. The Cenomanian–Campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d, after which the platform evolved to a deep‐subtidal system consisting of anoxic/dysoxic shale and chalk in the time surrounding oceanic anoxic event 2. Each period of oceanic anoxia is associated with composite sequence maximum flooding, termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles. Composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain‐dominated facies and shallow‐subtidal to intertidal environments. Because they are products of eustacy and global oceanographic processes, the three supersequences and most composite sequences defined in the south Texas passive margin are recognizable in other carbonate platforms and published eustatic sea‐level curves.  相似文献   

11.
北美西部内陆海盆上白垩统Niobrara组中的钙质超微化石十分丰富,且多保存良好,呈现典型的晚白垩世远洋钙质超微化石组合面貌,经系统鉴定,计有60属100余种和亚种。为适应不同的环境,Kansas西部和South Dakota东部的钙质超微化石组合面貌稍有不同。经与白垩纪颗石藻化石带对比,可将Kansas西部的Niobrara组划分为6个化石带(CC13～CC18)和8个亚带,其中,根据本文研究地区的化石序列,CC15和CC16带被进一步划分。根据与同一剖面所建立的无脊椎动物化石带对比,钙质超微化石CC17带的时代被重新厘定,即该带应始于中Santonian的晚期,结束于晚Santonian的早期,并据此将Santoniatr／Campanian的界线划在CC18带之内。  相似文献   

12.
For the first time, the calcareous nannofossils of marly deposits near Kerman (Bardsir area) have been studied. This study presents the integrated (calcareous nannofossils) biostratigraphy of the Bardsir section in the Kerman basin, Central Iran. In most parts of Central Iran, the Upper Cretaceous sequence is complete and continuous and is divided into two groups: Cenomanian–Touronian flysch and Campanian–Maastrichtian flysch. Flyschs composed of sets of green marl sequences (Coniacian–Santonian) have been separated to reduce the basin depth and refer to the relative calm. Bardsir is located 57.6 km from Kerman (Central Iran). The lithology of this area includes light green marl with layers of calcareous siltstone, limestone, and flysch rocks. In this study, 24 samples were taken and prepared with smear slide. Most species were photographed with a light microscope. As a result of this study, 30 genera and 42 species of nannofossils have been identified. A high-resolution calcareous nannofossil biostratigraphic study has been carried out, allowing the division of the studied section into eight biozones of Late Santonian to Early Maastrichtian age (CC17–CC24).  相似文献   

13.
The East Sakhalin accretionary wedge is a part of the Cretaceous-Paleogene accretionary system, which developed on the eastern Asian margin in response to subduction of the Pacific oceanic plates. Its formation was related to the evolution of the Early Cretaceous Kem-Samarga island volcanic arc and Late Cretaceous-Paleogene East Sikhote Alin continental-margin volcanic belt. The structure, litho-, and biostratigraphy of the accretionary wedge were investigated in the central part of the East Sakhalin Mountains along two profiles approximately 40 km long crossing the Nabil and Rymnik zones. The general structure of the examined part of the accretionary wedge represents a system of numerous east-vergent tectonic slices. These tectonic slices. tens to hundreds of meters thick. are composed of various siliciclastic rocks, which were formed at the convergent plate boundary, and subordinate oceanic pelagic cherts and basalts, and hemipelagic siliceous and tuffaceous-siliceous mudstones. The siliciclastic deposits include trench-fill mudstones and turbidites and draping sediments. The structure of the accretionary wedge was presumably formed owing to off-scraping and tectonic underplating. The off-scraped and tectonically underplated fragments were probably tectonically juxtaposed along out-of-sequence thrusts with draping deposits. The radiolarian fauna was used to constrain the ages of rocks and time of the accretion episodes in different parts of the accretionary wedge. The defined radiolarian assemblages were correlated with the radiolarian scale for the Tethyan region using the method of unitary associations. In the Nabil zone, the age of pelagic sediments is estimated to have lasted from the Late Jurassic to Early Cretaceous (Barremian); that of hemipelagic sediments, from the early Aptian to middle Albian; and trench-fill and draping deposits of the accretionary complex date back to the middle-late Albian. In the Rymnik zone, the respective ages of cherts, hemipelagic sediments, and trench facies with draping deposits have been determined as Late Jurassic to Early Cretaceous (middle Albian), middle Aptian-middle Cenomanian, and middle-late Cenomanian. East of the rear toward the frontal parts of the accretionary wedge, stratigraphic boundaries between sediments of different lithology become successively younger. Timing of accretion episodes is based on the age of trench-fill and draping sediments of the accretionary wedge. The accretion occurred in a period lasting from the terminal Aptian to the middle Albian in the western part of the Nabil zone and in the middle Cenomanian in the eastern part of the Rymnik zone. The western part of the Nabil zone accreted synchronously with the Kiselevka-Manoma accretionary wedge located westerward on the continent. These accretionary wedges presumably formed along a single convergent plate margin, with the Sakhalin accretionary system located to the south of the Kiselevka-Manoma terrane in the Albian.  相似文献   

14.
Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.  相似文献   

15.
The first detailed biostratigraphic analyses of the Coniacian-middle Campanian shallow-marine carbonate successions exposed in the Mitla Pass, west central Sinai, Egypt have revealed the stratigraphic distribution of diverse calcareous nannofossil and planktonic foraminiferal species. Thirty-six calcareous nannofossils and thirty-two planktonic foraminifera are identified, indicating a Coniacian to middle Campanian age and four Tethyan planktonic foraminiferal and five calcareous nannofossil zones. A comparison of these bioevents from different palaeolatitudes shows considerable variation in age.Three sequence boundaries coincident with the Turonian/Coniacian, Coniacian/Santonian and Santonian/Campanian stage boundaries are recognized. A fourth sequence boundary is marked by a major upper Campanian to early Ypresian (early Eocene) unconformity. These sequence boundaries are primarily related to regional tectonism associated with the Syrian Arc Fold System and secondarily to eustatic sea-level fluctuations.  相似文献   

16.
The palaeogeographic setting of the studied Ain Medheker section represents an Early Campanian to Early Maastrichtian moderately deep carbonate shelf to distal ramp position with high rates of hemipelagic carbonate production, periodically triggered by mass-flow processes. Syndepositional extensional tectonic processes are confirmed to the Early Campanian. Planktonic foraminifera identified in thin sections and calcareous nannofossils allow the identification of the following biozones: Globotruncanita elevata, Contusotruncana plummerae (replacing former Globotruncana ventricosa Zone), Radotruncana calcarata, Globotruncana falsostuarti, and Gansserina gansseri. The following stable C-isotope events were identified: the Santonian/Campanian boundary Event, the Mid-Campanian Event, and the Late Campanian Event. Together with further four minor isotopic events, they allow for correlation between the western and eastern realms of Tunisia. Frequently occurring turbidites were studied in detail and discussed in comparison with contourites.  相似文献   

17.
The Amur and Kiselevka–Manoma accretionary complexes belong to the Cretaceous Khingan–Okhotsk active continental margin, which was formed in the east of Eurasia as a result of the subduction of the Pacific oceanic plates. The Kiselevka–Manoma complex is composed of oceanic pelagic and hemipelagic sedimentary rocks and intraplate oceanic basalts. It is located to the southeast, along the ocean-faced front of the Amur complex, which is predominantly composed of turbidites of the convergent boundary of lithospheric plates. The biostratigraphic study of radiolarians from rocks of the frontal part of the Amur complex allowed us to correlate them with rocks of the Kiselevka–Manoma complex and to define the period of accretion to be from the Late Aptian to the Middle Albian. The tectonostratigraphic interrelations of these two contrasting lithotectonic complexes are established and two possible models of their common emplacement are suggested. Both models suppose a continuous spatiotemporal relation of complexes with the primary paleolocation of the Kiselevka–Manoma complex in front of (on the ocean side) the Amur complex. The frontal part of the Amur complex and the Kiselevka–Manoma complex were emplaced synchronously with the western part of the East Sakhalin accretionary complex. This scenario defines the Early Cretaceous tectonic zonation of the region and the choice of the appropriate paleotectonic model. At the end of the Early Cretaceous, a single convergent boundary of the lithospheric plates is suggested with the position of the Sakhalin island arc system south of the Khingan–Okhotsk active continental margin.  相似文献   

18.
The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 (Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 (Aspidolithus parcus zone), CC19 (Calculites ovalis zone), CC20 (Ceratolithoides aculeus zone), CC21 (Quadrum sissinghii zone), and CC22 (Quadrum trifidum zone) represent the Campanian. Biozone CC23 (Tranolithus phacelosus zone) indicate the Late Campanian–Early Maastrichtian. Biozones CC24 (Reinhardtites levis zone) and CC25 (Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi–Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent.  相似文献   

19.
Mirrol Trough of the northeast Atlantic contains five NNE-SSW trending, en echelon, turbidite-filled basins deeper than 5500 m, each ranging from 4 to 10 km in width and 19 to 65 km in length. Trough deposition has consisted mainly of turbidites from adjacent hills and ridges as indicated by the physiography of the region, sediment isopach map, the nature of the sediments in the trough, and benthic foraminiferal depth indicator species. The sedimentation rate on abyssal hills and ridges, as deduced from palaeomagnetic evidence, is 1.36 cm/103 years. Using this sedimentation rate, it is estimated that Mirrol Trough subsided relative to the surrounding area and began receiving sediments between 8.3 and 11.5 m.y. ago; and the deposition of the most recent turbidite has occurred sometime between 29,000 and 44,000 years b.p. Tilting of the base of the most recent turbidite with respect to the basin floor is observed, and this is attributed to relative sinking of the eastern margin of the trough after the deposition of the most recent turbidite.  相似文献   

20.
New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.  相似文献   

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