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1.
Two regionally significant microbial-foraminiferal episodes (∼150 kyr each) occur within the Early Aptian shallow marine platform in Oman and throughout eastern Arabia. The stratigraphically lower of these two intervals is characterized by isolated or coalescent domes that share similarities with modern, open-marine stromatolites from the Exuma Cays, Bahamas. The upper interval is predominantly built by a problematic Lithocodium/Bacinella consortium in buildup and massive boundstone facies. Based on high-resolution chemostratigraphy, these shoalwater intervals are coeval with oceanic anoxic event 1a (OAE1a; Livello Selli). Field evidence demonstrates that the buildup episodes alternate with stratigraphic intervals dominated by rudist bivalves. This biotic pattern is also recognized in other coeval Tethyan sections and is perhaps a characteristic shoalwater expression of the OAE1a. The short-lived regional expansions of this microbial-foraminiferal out-of-balance facies cannot be explained by local environmental factors (salinity and oxygen level) alone and the buildup consortia do not occupy stressed refugia in the absence of grazing metazoans. Judging from recent analogues, the main fossil groups, i.e. microbial assemblages, macroalgae, larger sessile foraminifera, and rudist bivalves, all favoured elevated trophic levels but with different tolerance limits. The implication of this is that the influence of palaeofertility events, possibly related to OAE1a, on carbonate platform community structures must be investigated. The observations made in these coastal sections are a significant first step for the improved understanding of the Early Aptian period of biotic, oceanic and climatic change. 相似文献
2.
NIELS RAMEIL ADRIAN IMMENHAUSER GEORG WARRLICH HEIKO HILLGÄRTNER HENK J. DROSTE 《Sedimentology》2010,57(3):883-911
Lithocodium aggregatum and Bacinella irregularis are now extinct, shallow marine life forms of unknown taxonomic origin. Forming part of the tropical platform biota during much of the Mesozoic, these organisms experienced bloom periods and temporarily replaced rudist–coral assemblages during parts of the Early Aptian. Within the limitations of time resolution, this ‘out‐of‐balance’ facies is coeval with the Oceanic Anoxic Event 1a‐related black shale deposition in oceanic basins but the triggering factors remain poorly understood. Here, a platform‐wide comparison of Lithocodium–Bacinella geobodies and morphotypes from the Sultanate of Oman is presented and placed in its environmental, bathymetric and physiographic context. Lithocodium–Bacinella geobodies reach from kilometre‐scale ‘superstructures’ to delicate centimetre‐sized growth forms. Clearly, scale matters and care must be taken when drawing conclusions based on spatially limited observational data. Whilst the factors that cause Lithocodium–Bacinella expansion should probably be considered in a global context, regional to local factors affected growth patterns in a more predictable manner. Here, the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of Lithocodium–Bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment. Acknowledging these limitations, the following tentative patterns are observed: (i) Lithocodium–Bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings (margin, intrashelf basin, inner platform) by obtaining characteristic growth forms. (ii) Lithocodium–Bacinella favoured low‐sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth; a feature perhaps pointing to a phototrophic metabolism. Circumstantial evidence for continuous growth within the upper‐sediment column is debated. (iii) The availability of accommodation space had a direct influence on the maximum size of geobodies formed. (iv) Fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of Lithocodium–Bacinella. Understanding the relationship between Lithocodium–Bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments. This study might represent a useful first step in this direction. 相似文献
3.
Impact of dynamic sedimentation on facies heterogeneities in Lower Cretaceous peritidal deposits of central east Oman 总被引：1，自引：0，他引：1
This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m2 butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi‐Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre‐scale depositional sequences, from subtidal dominated sequences to supratidal‐capped sequences, which are bounded by regional discontinuity surfaces. At subaerial exposure and submarine erosion surfaces associated with a base level shift, sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events. Chemostratigraphy allows correlation between the Haushi‐Huqf and the age‐equivalent sections logged in the interior of the platform in Oman. The correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf. This study is the first to discuss the controls on Lower Cretaceous peritidal carbonate cyclicity of the Arabian epeiric platform. The results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context. 相似文献
4.
Jens Lehmann Matthias Heldt Martina Bachmann Mohamed E. Hedi Negra 《Cretaceous Research》2009,30(4):895-910
Thick Aptian deposits in north central Tunisia comprise hemipelagic lower Aptian, reflecting the sea-level rise of OAE 1a, and an upper Aptian shallow marine environment characterized by the establishment of a carbonate platform facies. Carbon stable isotope data permit recognition of the OAE 1a event in the Djebel Serdj section. Cephalopods are rare throughout these successions, but occurrences are sufficient to date the facies changes and the position of the OAE1a event. Ammonite genera include lower Aptian Deshayesites, Dufrenoyia, Pseudohaploceras, Toxoceratoides and ?Ancyloceras; and upper Aptian Zuercherella, Riedelites and Parahoplites. Correlation of carbon isotope data with those of other Tethyan sections is undertaken together with the integration of planktonic foraminiferal data. 相似文献
5.
During Aptian times the northeastern corner of the African plate, the Arabian craton, was in the tropics. Two-thirds of it was covered by a broad epeiric sea opening eastward into the Tethys Ocean. Carbonate sedimentation recorded several environmental perturbations caused by changes in relative sea-level and by interconnected coeval global events. A well in offshore Abu Dhabi was used as the reference because it was drilled through the whole of the interval of interest and cored strata dated Gargasian (middle Aptian sensu gallico, early late Aptian sensu anglico) downward to beds of Late Barremian age. The holostratigraphic approach employing biostratigraphy, lithostratigraphy and sequence stratigraphy, along with basic well log interpretation and δ13C-based chemostratigraphy, facilitated correlation with outcrops in Iran and Oman, and with other wells in Iraq, Qatar and the United Arab Emirates, over distances of several hundreds of kilometers. This approach made possible refinement of our regional model for this interval and the identification of a set of events that included several forced regressions, transgressions of varying importance (by extension in the literature those floodings of greatest magnitude have been called “drownings”), the Oceanic Anoxic Sub-Event 1a and a microbial Bacinella “bloom”. 相似文献
6.
Ryan M. Phelps Charles Kerans Robert G. Loucks Rui O.B.P. Da Gama Jason Jeremiah David Hull 《Sedimentology》2014,61(2):461-496
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
7.
The Adriatic-Dinaridic carbonate platform (ADCP) was one of the largest and relatively well preserved Mesozoic platforms in the Mediterranean region (central Tethys). The peninsula Istria, in the northwestern part of the ADCP, is built up predominantly of shallow-water carbonates of the Middle Jurassic (Dogger) to Eocene age and, to a lesser extent, of Paleogene clastic deposits (flysch and calcareous breccia). This study focuses on a Lower Cretaceous (Barremian to Albian) succession of strata at five localities in western Istria. Stratigraphic determinations are based on identification of nine microfossil assemblages (benthic foraminifera and calcareous algae Dasycladales) and on using their taxa as index fossils. The age of strata with these microfossil assemblages, however, is questionable. Most of the age uncertainties are associated with a regional emersion, which occurred on the ADCP during the Aptian or close to the Aptian-Albian transition. It is unclear what portions of the Upper Aptian and/or Lower Albian are missing along this unconformity. A stable isotope study was conducted on homogenous micritic matrix samples in an attempt to resolve some of these uncertainties. Variations in carbon isotope compositions proved useful for stratigraphic correlation between the examined successions of strata, for improving their age determination, and for relating them to other coeval successions that span an important time interval of major oceanographic changes and carbon-cycle perturbations associated with the Early Aptian oceanic anoxic event (OAE 1a). 相似文献
8.
Bernard Pittet Frans S. P. Van Buchem Heiko Hillgärtner Philippe Razin† Jürgen Grötsch‡ Henk Droste§ 《Sedimentology》2002,49(3):555-581
Abstract Barremian and Aptian shallow‐water carbonate facies (uppermost Lekhwair, Kharaib and Shuaiba Formations) are described from outcrops in northern Oman. Based on facies analysis and bedding pattern, three orders of depositional sequences are defined (third to fifth order) and correlated between sections. Over the course of three third‐order sequences, covering the Barremian to Lower Aptian, a third‐order depositional pattern is documented that consists of a succession of three distinct faunal assemblages: discoidal orbitolinids and calcareous algae were deposited during early transgression; microbialites and microencrusters dominate the late transgressive to early highstand facies; and a rudist‐ and miliolid‐dominated facies is typical of the highstand. This ecological succession was controlled largely by palaeoenvironmental changes, such as trophic level and clay influx, rather than sedimentological factors controlled by variations in accommodation space. Orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow‐water carbonate response to global changes affecting Late Barremian to Aptian palaeoclimate and palaeoceanography. 相似文献
9.
RICHARD G. WOODFINE HUGH C. JENKYNS MASSIMO SARTI† FRANCESCO BARONCINI† CRESCENZO VIOLANTE‡ 《Sedimentology》2008,55(4):1011-1028
Chemostratigraphic analyses (87Sr/86Sr, δ13Ccarb) of limestones from two Jurassic platform‐carbonate sequences in Italy (Trento and Campania–Lucania Platforms) illustrate previously established trends found in pelagic sediments and skeletal carbonates from biostratigraphically well‐calibrated sections elsewhere in Europe. Chemostratigraphic correlations between the platform‐carbonate successions and appropriate intervals from well‐dated reference sections allow the application of high‐resolution stratigraphy to these shallow‐water peritidal carbonates and, furthermore, elucidate the facies response to the Early Toarcian Oceanic Anoxic Event (OAE). Lower Jurassic (Toarcian) levels of the western Trento Platform (Southern Alps, Northern Italy) contain spiculitic cherts that appear where rising carbon‐isotope values characterize the onset of the OAE: a palaeoceanographic phenomenon interpreted as driven by increased nutrient levels in near‐surface waters. There is a facies change to more clay‐rich facies at the level of the abrupt negative carbon‐isotope excursion, also characteristic of the OAE, higher in the section. The Campania–Lucania Platform (Southern Apennines, Southern Italy) records a change to more clay‐rich facies where carbon‐isotope values begin to rise at the beginning of the OAE but the negative excursion, higher in the section, occurs within oolitic facies. Although, in both examples, the Early Toarcian OAE can be recognized by a change to more clay‐rich lithologies, this facies development is diachronous and in neither case did the platform drown. Although the Trento Platform, in the south‐west sector studied here, was adversely affected by the OAE, it did not drown definitively until Late Aalenian time; the Campania–Lucania Platform persisted throughout the Jurassic and Cretaceous. Differential subsidence rates, which can be calculated using comparative chemostratigraphy, are identified as a crucial factor in the divergent behaviour of these two carbonate platforms: relatively fast in the case of the Trento Platform; relatively slow in the case of the Campania–Lucania Platform. It is proposed that where water depths remained as shallow as a few metres during the OAE (Campania–Lucania Platform), dissolved oxygen levels remained high, nutrient levels relatively low and conditions for carbonate secretion and precipitation remained relatively favourable, whereas more poorly ventilated and/or more nutrient‐rich waters (Trento Platform) adversely influenced platform growth where depths were in the tens of metres range. The stage was thus set for drowning on the more rapidly subsiding western margin of the Trento Plateau and a pulse of oolite deposition post‐dating the OAE was insufficient to revitalize the carbonate factory. 相似文献
10.
A. Immenhauser B. Van Der Kooij A. Van Vliet W. Schlager & R. W. Scott† 《Sedimentology》2001,48(6):1187-1207
A high-energy Aptian–Albian platform margin in northern Oman fronted onto an open oceanic basin, making the area a valuable analogue for coeval guyot margins. Most similar aged carbonate margins described in the literature faced either intracratonic or minor oceanic basins. The studied margin is characterized by a stabilized outer rim, which, although it did not rise discernibly above the adjacent lagoonal deposits, flanked a steep upper slope (32–40°) basinwards with a relief of at least 30 m. Two main facies provided the rigidity of the outer margin: Lithocodium boundstones that constituted up to 50% of the rock volume; and marine fibrous cements that occluded up to 35% of primary pore space. In contrast, coral–rudist patches and other shelly sessile benthos were distributed irregularly, and the rudist bioherms of the outer margin were often disrupted, with shells being transported and redeposited. The inner margin is characterized by wedge-shaped storm layers that radiate from the platform top lagoonwards, where they interdigitate with carbonate sands and small rudist bioherms. Polygenetic discontinuity surfaces that bear evidence of both marine hardground and subaerial exposure stages are prominent features of the margin. Throughout the latest Aptian to Middle Albian, the platform succession recorded some 30 relative sea-level falls, of which seven reached amplitudes of many tens of metres. These seven high-amplitude falls in sea level are recorded across the entire south-eastern portion of the Arabian craton and are probably of eustatic origin. 相似文献
11.
Late Aptian–early Albian limestones from the eastern Brazilian continental margin record the early evolution of the South Atlantic Ocean. In Tethyan and North Atlantic domains, a planktic foraminiferal turnover and organic-rich deposits related to Oceanic Anoxic Event 1b (OAE 1b) point to major ocean-climate changes through this interval. Coeval organic-rich deposits of the South Atlantic Ocean have been interpreted as the product of restricted circulation rather than attributed to a global event. However, previous investigations of the early marine phase of South Atlantic lack data from more distal facies, making correlations to global events difficult. Here, we present C, O, and Sr isotopes, elemental geochemistry, TOC and pyrolysis data, as well as a microfacies analysis of an upper Aptian–lower Albian distal section from the Campos Basin (southeastern Brazil). Our focus is on the paleoenvironmental characterization of and the possible association between organic-rich deposits and major perturbations related to Aptian–Albian transition. Five microfacies associations (MA) were identified in the informal units I and III, which were deposited in the neritic region on a carbonate ramp. Organic-rich deposits were described in unit III, composed of planktic-dominated wackestones interbedded with black shales, in a distal dysoxic to anoxic environment. The carbonates 87Sr/86Sr ratios showed a drastic increase (0.7072–0.7074), interpreted as enhanced chemical weathering, supported by the increase of continental input to the top of section. This trend was accompanied by a long-term δ13Ccarb negative excursion, which were assigned to the latest late Aptian–early Albian interval of the isotope reference curves, in accordance with the described occurrence of Colomiella recta. This scenario matches those proposed for the late Aptian–early Albian transition and OAE 1b set, as an enhanced greenhouse stage, pointing to the influence of the referred ocean-climate changes on the deposition of organic-rich deposits of the early South Atlantic Ocean. This investigation gives more evidences that these perturbations were a widespread event, as a product of broad-scale disturbances in the global carbon cycle which also controlled organic deposition and preservation on restricted settings. 相似文献
12.
13.
Z. M. ZHANG G. C. ZHAO M. SANTOSH J. L. WANG X. DONG J. G. LIOU 《Journal of Metamorphic Geology》2010,28(7):719-733
The eastern Himalayan syntaxis in southeastern Tibet consists of the Lhasa terrane, High Himalayan rocks and Indus‐Tsangpo suture zone. The Lhasa terrane constitutes the hangingwall of a subduction zone, whereas the High Himalayan rocks represent the subducted Indian continent. Our petrological and geochronological data reveal that the Lhasa terrane has undergone two stages of medium‐P metamorphism: an early granulite facies event at c. 90 Ma and a late amphibolite facies event at 36–33 Ma. However, the High Himalayan rocks experienced only a single high‐P granulite facies metamorphic event at 37–32 Ma. It is inferred that the Late Cretaceous (c. 90 Ma) medium‐P metamorphism of the southern Lhasa terrane resulted from a northward subduction of the Neo‐Tethyan ocean, and that the Oligocene (37–32 Ma) high‐P (1.8–1.4 GPa) rocks of the High Himalayan and coeval medium‐P (0.8–1.1 GPa) rocks of the Lhasa terrane represent paired metamorphic belts that resulted from the northward subduction of the Indian continent beneath Asia. Our results provide robust constraints on the Mesozoic and Cenozoic tectonic evolution of south Tibet. 相似文献
14.
Dominik Hennhoefer Aisha Al Suwaidi Cinzia Bottini Emina Helja Thomas Steuber 《Sedimentology》2019,66(2):536-555
The sedimentary record of the Arabian Shelf offers a unique opportunity to study the Cretaceous (Albian–Turonian) greenhouse climate from a palaeoequatorial perspective. In particular, hemipelagic to pelagic carbonate successions from the extensive Shilaif intra‐shelf basin have the potential to produce an excellent record of carbon cycle perturbations during this interval. This study presents a 269 m thick chemostratigraphic (carbonate δ13C and δ18O) record from the Middle Albian to Early Turonian of central Abu Dhabi (United Arab Emirates), representing over 14 Myr of uninterrupted carbonate sedimentation. The Mauddud to Shilaif formations represent outer ramp to basinal intra‐shelf carbonates with variations from laminated organic‐rich to clean bioturbated intervals. Isotopic evidence of the latest Albian Anoxic Event (Oceanic Anoxic Event 1d), Middle Cenomanian Event I and the Cenomanian–Turonian Anoxic Event (Oceanic Anoxic Event 2) are confirmed and biostratigraphically calibrated by means of calcareous nannofossils. The carbon isotope record allows correlation with other regional records and well‐calibrated records across the Tethyan Ocean and represents a significant improvement of the chronostratigraphic framework of the United Arab Emirates (Shilaif) and Oman (Natih) intra‐shelf basins. The study further confirms that low carbon isotope values corresponding to the two source rock intervals in the Shilaif Formation clearly precede the isotopic expressions of Oceanic Anoxic Event 1d and Oceanic Anoxic Event 2. 相似文献
15.
In Provence and Languedoc, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age. Their recognition is based on sedimentological and stratigraphical evidence, and their timing, referred to ammonite zones or subzones, is as follows:
(1)
Late Barremian, at the G. sartousiana–Imerites giraudi transition, or merely the lowermost part of the I. giraudi zone, (2)
Middle Bedoulian, at the Deshayesitesweissi–Deshayesites deshayesi transition, (3)
Mid late Bedoulian in correspondence with the “Roloboceras hambrovi subzone”, (4)
Late Bedoulian at the Deshayesites grandis–Deshayesites furcata transition.
16.
B. Pomerol 《Cretaceous Research》1983,4(1):85-93
In the North Atlantic DSDP/IPOD cores, carbon isotope data on the bulk carbonates show significant fluctuations. In sediments now exposed on land coeval fluctuations in the carbon isotope concentrations are also recorded in pelagic and epeiric facies. For instance, in the Upper Cretaceous chalks of the Paris Basin, there is a major break at the Cenomanian-Turonian boundary. At this time, the manganese content of the chalks was also at a maximum and consequently a positive relation can be demonstrated between δ13C and manganese concentrations. The same positive correlation is also recorded in many pelagic limestones.In the North Atlantic cores, carbon isotope events are related to the black shale facies and to global oceanic anoxic events and one can suppose that in sediments deposited on the continental margins they are also related to mildly anoxic conditions. Considering the manganese geochemistry in carbonate rocks, a high manganese content in such a reducing environment can be found in the sediments only if the Mn concentration of the interstitial solutions are abnormally high. As a high Mn content in marine pore waters is believed to originate from hydrothermal process, Mn and δ13C positive excursions are ultimately related to mid-oceanic ridge activity and to a closely connected phenomenon, the great transgressive pulses during which mid-depth waters may have been anoxic. Consequently, major Mn and carbon isotope events would seem to be useful tools in paleooceanographic reconstructions. 相似文献
17.
Palaeotemperatures during the late Barremian–early Aptian (Early Cretaceous) on the Russian Platform have been determined on the basis of oxygen isotope analysis of aragonitic bivalve molluscan and ammonoid shells and belemnite rostra with well-preserved microstructure from the Ulyanovsk area. Those obtained from the planispiral and heteromorph ammonoid shells from the lower Aptian Volgensis–Schilovkensis, Deshayesi–Tuberculatum, and Deshayesi–Renauxianum zones range from 26.7 to 33.2 °C, from 29.2 to 33.1 °C, and from 27.0 to 29.5 °C, respectively. A heteromorph Helicancylus? cf. philadelphius shell from the uppermost lower Aptian Bowerbanki Zone was secreted in highest temperature conditions (32.8–35.2 °C). In contrast, upper Barremian molluscs (bivalve Cyprina sp. and belemnite Oxyteuthis sp.) of the Ulyanovsk area show significantly lower palaeotemperatures: 16.9–18.5 °C and 7.9–17.8 °C, respectively, which is in accordance with known palaeogeographic and palaeobotanical evidences, showing that a distinct climatic optimum seems to have occurred during the late early Aptian, when warm Tethyan water penetrated into the basin. Marked changes in calculated growth temperatures for investigated molluscs from the Russian Platform were most likely connected with both the general warming trend during the late Barremian–early Aptian and local palaeonvironmental conditions. New data from the Bowerbanki Zone of the Russian Platform provide evidence on existence of the positive carbon isotope anomaly (2.4–6‰) at the end of the lower Aptian. There were apparently the three positive C-isotope anomalies during the late Barremian–early Aptian. The onset of mid early Aptian Oceanic Anoxic Event (OAE) 1a seems to coincide with both the beginning of significant warm conditions (followed by short-term cooling) and the abrupt decline in heavy carbon isotope concentrations in marine carbonates, which partly were the likely consequences of the intensive release of CO2 (biased by volcanic activity) and/or dissociation of methane gas hydrate. 相似文献
18.
MELODY STEIN ANNIE ARNAUD‐VANNEAU THIERRY ADATTE DOMINIK FLEITMANN JORGE E. SPANGENBERG KARL B. FÖLLMI 《Sedimentology》2012,59(3):939-963
A major shift from Urgonian oligotrophic carbonate accumulation to orbitolinid‐rich mixed siliciclastic–carbonate deposition is observed near the Barremian–Aptian boundary in many sections both within and outside the shallow‐marine Tethyan Realm. This important facies change in the Swiss Helvetic Alps is documented here and interpreted in the context of general palaeoenvironmental change. To achieve this, a detailed micropalaeontological, sedimentological, mineralogical and geochemical study has been carried out on six sections across the upper part of the lower Schrattenkalk Member (Late Barremian), the Rawil Member (formerly ‘Lower Orbitolina Beds’, earliest Aptian) and the lowermost part of the upper Schrattenkalk Member (Early Aptian). The sediments of the Rawil Member exhibit inner‐platform facies with rudists, miliolids, orbitolinids and dasycladals to outer‐platform facies characterized by small benthic foraminifera, orbitolinids, crinoids and bryozoans. Stratigraphic trends in microfacies environments and the composition of microfossil assemblages, indicate that the Rawil Member includes a transgressive systems tract and the base of a highstand systems tract which are composed of an increasing number of parasequences in distal directions (five to nine in the sections studied here). The sea‐level rise discerned in the Rawil Member is coeval with increased detrital input and phosphorus burial, with maximum values up to 80 times and 21 times the background values in the subjacent part of the lower Schrattenkalk Member, respectively. Furthermore, the Rawil Member records the appearance of kaolinite, indicating a change towards tropical and more humid climate conditions. This change may have led to an increase in continental weathering rates and an associated increase in detrital and nutrient fluxes towards the ocean. The phase of climate change observed near the Barremian–Aptian boundary may have been triggered by a phase of intensified volcanic activity linked with the onset of the Ontong Java large igneous province and the Rawil Member may be the expression of a precursor episode to Oceanic Anoxic Event 1a in the shallow‐marine environment. 相似文献
19.
Strontium and carbon isotope stratigraphy was applied to a 202 m-thick shallow marine carbonate section within the Late Jurassic Bau Limestone at the SSF quarry in northwest Borneo, Malaysia, which was deposited in the western Palaeo-Pacific. Strontium isotopic ratios of rudist specimens suggest that the SSF section was formed between the latest Oxfordian (155.95 Ma) and the Late Kimmeridgian (152.70 Ma), which is consistent with previous biostratigraphy. The δ13Ccarb values of bulk carbonate range from −0.10 to +2.28‰ and generally show an increasing upward trend in the lower part of the section and a decreasing upward trend in the upper part of the section. A comparable pattern is preserved in the δ13Corg isotope record. Limestone samples of the SSF section mainly preserve the initial δ13Ccarb values, except for the interval 84–92 m, where an apparent negative anomaly likely developed as a result of meteoric diagenesis. Comparing with the Tethyan δ13Ccarb profile, a negative anomaly in the lower SSF section can be correlated with the lowered δ13C values around the Oxfordian/Kimmeridgian boundary. In addition, δ13Ccarb values of the Bau Limestone are generally ∼1‰ lower than the Tethyan values, but comparable with the values reported from Scotland and Russia, located in Boreal realm during the Late Jurassic. This suggests that either the Tethyan record or the other records have been affected by the δ13C values of regionally variable dissolved inorganic carbon (DIC). The Late Jurassic δ13CDIC values are thought to have been regionally variable as a result of their palaeoceanographic settings. This study shows that δ13C chemostratigraphy of the Palaeo-Pacific region contributes to an improved understanding of global carbon cycling and oceanography during this time period. 相似文献
20.
In the southern Tethyan margin, the Essaouira-Agadir Basin (EAB), south of Morocco, exhibits well-exposed and fossiliferous sections of Aptian–Albian age. Biostratigraphy by ammonoids and sedimentological analysis have been realized for five sections located along an E-W transect in the EAB. The studied successions were dated from the latest Early Aptian to the Early Albian and are characterized by five major sedimentary discontinuities defining at least four main sedimentary sequences. The Late Aptian–Early Albian succession can be considered a gently westward-dipping ramp, marked by a deepening upward evolution. A quantitative study of calcareous nannofossils and calcium carbonate content has been performed on three of these sections. At this time, the EAB was located in the tropical-equatorial hot arid belt. The decrease in both calcium carbonate content and Nannoconus abundances at the Aptian–Albian transition could be the result of cooler climatic conditions recognized in the EAB, and/or of the associated increasing terrigenous input and nutrients, which hindered carbonate production. In the EAB, the nannofossil productivity is higher below the deposition of dark levels, which are coeval with the Niveau Paquier, recognized as the expression in southern France of the OAE 1b (Early Albian). During the Early Albian, the EAB was characterized by nannofossil fluxes two times lower than the upwelling-influenced Mazagan Plateau (southern Tethyan margin) and eight times lower than the Vocontian Basin (northern Tethyan margin). These results show that, with respect to the northern Tethyan margin, trophic conditions in sea surface waters of the pelagic realm of the southern Tethyan margin were lower. Comparable results obtained by Heldt et al. in the neritic realm of the southern Tethyan margin have been ascribed to more arid climatic conditions. 相似文献