Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 31
Filtrar
1.
Coral Reefs ; 38(5): 1023-1037, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31632191

RESUMO

The present centre of coral diversity in the Western Indian Ocean is defined by the northern Mozambique Channel with an extension northward to Mafia Island in Tanzania (Eastern Africa). The geological and evolutionary history of this hotspot of marine biodiversity remains so far completely obscure, because Cenozoic fossil reef communities of this area are not well known. This study presents a new fossil scleractinian fauna from the Mikindani Formation in southern Tanzania. It comprises 16 symbiotic coral taxa of which nine could be identified to the species and five to the genus level. Coral habitat consisted of low-relief biostromes that developed in shallow water at the front of the Rovuma Delta under conditions of variable sediment input. The biostromes are dated to be Messinian based on associated calcareous nannoplankton and planktic foraminifers. The studied coral assemblage shows close affinities with the Recent Western Indian Ocean biogeographic province and Central Indo-West Pacific biogeographic region as well as with the Miocene of Indonesia. Faunistic relations with the Oligocene-early Miocene of Somalia and Iran do not exist. The patterns of species distribution document a major palaeobiogeographic change in the Indian Ocean that correlates with the onset of the Miocene Indian Ocean Equatorial Jet during the middle Miocene. The clear Indonesian affinity of the Messinian coral fauna from southern Tanzania implies that this westerly oceanic surface current provided high biogeographic connectivity across the Indian Ocean during the late Miocene. Today, the coastal waters of Indonesia are located in the Coral Triangle. Diversification of this global epicentre of marine biodiversity started in the early Miocene and it was established already during the middle Miocene. Our results indicate that the East African hotspot of coral biodiversity originated as an offshoot of the Coral Triangle in the middle to late Miocene.

2.
Paleoceanography ; 30(4): 332-352, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27546980

RESUMO

During the Miocene prominent oxygen isotope events (Mi-events) reflect major changes in glaciation, while carbonate isotope maxima (CM-events) reflect changes in organic carbon burial, particularly during the Monterey carbon isotope excursion. However, despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions. The Decontra section on the Maiella Platform (central Apennines, Italy), however, allows to resolve them for the first time in such a setting during the early to middle Miocene. The present study improves the stratigraphic resolution of parts of the Decontra section via orbital tuning of high-resolution gamma ray (GR) and magnetic susceptibility data to the 405 kyr eccentricity metronome. The tuning allows, within the established biostratigraphic, sequence stratigraphic, and isotope stratigraphic frameworks, a precise correlation of the Decontra section with pelagic records of the Mediterranean region, as well as the global paleoclimatic record and the global sea level curve. Spectral series analyses of GR data further indicate that the 405 kyr orbital cycle is particularly well preserved during the Monterey Event. Since GR is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the Decontra section, it follows the same long-term orbital pacing as observed in the carbon isotope records. The 405 kyr GR beat is thus correlated with the carbon isotope maxima observed during the Monterey Event. Finally, the Mi-events can now be recognized in the δ18O record and coincide with plankton-rich, siliceous, or phosphatic horizons in the lithology of the section.

3.
Glob Planet Change ; 123: 36-43, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25844022

RESUMO

The Early Ottnangian Cooling (EOC), a distinct cold-spell in European climate at ~ 18 Ma preceding the Miocene Climate Optimum, is frequently reported in Paratethys records; however, the duration, magnitude, and underlying causes are poorly understood. A new palaeoclimatic data-set provides unexpected insights into this event. UK'37-based sea-surface temperatures > 24 °C between ~ 18.1 and 17.7 Myrs substantially exceed existing estimates, and indicate a significantly warmer European climate than previously assumed for this usually poorly recovered time interval. The EOC is expressed as an average drop of 2-3 °C in Paratethyan water temperatures between ~ 18.1 and 17.8 Myrs with two distinct cold snaps at ~ 17.86 Ma and ~ 17.81 Ma. The short duration of the EOC excludes Tethyan Seaway closure as its underlying cause, although the enhanced palaeoclimatic sensitivity of the Paratethys due to this palaeogeographic configuration potentially contributed to the magnitude of SST deterioration during the EOC. The revealed palaeoclimatic pattern shows a strong correlation with isotope event Mi-1b in deep-sea δ18O records, and we propose a tight palaeoclimatic link between the Southern Ocean and the Paratethys/Mediterranean realm as an alternative hypothesis. The interplay of modulations in the long-term (~ 400 kyrs) and short-term (~ 100 kyrs) eccentricity cycles most likely acted as pacemaker of this palaeoclimatic interaction.

4.
Mar Micropaleontol ; 111: 53-65, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26089589

RESUMO

Within a 5.5-m-thick succession of upper Burdigalian (CNP-zone NN4) shallow neritic sediments from the North Alpine Foreland Basin in Lower Austria a high-resolution section of finely laminated sediment with a thickness of 940.5 mm was logged. The section was continuously sampled, resulting in 100 samples, covering a thickness of ~ 10 mm each. An integrated approach was applied to these samples in order to study proxy records including calcareous nannoplankton, geochemical and geophysical data. Multivariate statistics on the autochthonous assemblage were used to evaluate the ecological preferences of each taxon and to rule out possible contamination of the signal by taphonomic processes. In order to assess changes in the assemblage composition throughout the section, three taphogroups were defined using both the autochthonous and allochthonous nannofossils. Based on the distribution of these taphogroups five distinct intervals were defined that are indicative of centennial to decadal changes in palaeoenvironmental conditions. Combining these results with other proxies (geochemistry, geophysics) we were able to reconstruct short-term, small-scale variations in terms of temperature, primary productivity, bottom water oxygenation, organic matter flux, freshwater influx and changes in relative sea level in a highly dynamic shallow marine setting. This study represents the first such high-resolution analysis performed on a marine succession of late Burdigalian age. It is also a first attempt to analyse outcrop data on such a high-resolution, sub-Milankovitch scale, with respect to calcareous nannoplankton in conjunction with geochemical and sedimentological data.

5.
Crustaceana ; 87(8-9): 1043-1071, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-28090120

RESUMO

Quantitative approaches dealing with soft- and hard-part morphological variability of ostracods are very rare for most species. Here we present intraspecific limb and shell variability of the Neotropical freshwater ostracod species assumed as Cytheridella ilosvayi. For the first time such an analysis considered adult females and males, as well as juveniles. Variability of the appendages included the antennule, second antenna as well as the first and second thoracopod and was analysed in terms of ratios of podomeres, setae and limbs. Limb variability of adult and juvenile individuals (down to A-3) is generally low. The highest variation is shown in podomere proportions of the antennas, while thoracopods and setae provide minor and/or non-significant influence on the variability. Based on discrimination analyses shell parameters (i.e., shell length, position of the transversal sulcus) emerge to be more important for differentiation of groups than limb ratios. Adult females exhibit a large size range in which two clearly separated morphotypes exist. Although differences in limbs are small their existence can be proven also on the basis of proportions between podomeres of the antennas. Males and juveniles, however, do not display a separation into corresponding subgroups or morphotypes. The presence of two morphologically similar females and only one type of males indicates the coexistence of female morphotypes which may represent either two (cryptic) species or a mixed reproduction population in which parthenogenetic and sexual reproduction coexists.

6.
Geobiology ; 22(2): e12590, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38468508

RESUMO

Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen-Zollhaus, Vienna-Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia-coralline algal boundstone, stromatolitic/thrombolitic boundstone and serpulid-nubeculariid-microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross-bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbonates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia-coralline algal to stromatolitic/thrombolitic boundstone. The serpulid-nubeculariid-microbial boundstone reflects an internal succession with a decrease of the same parameters. Water depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline. The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic!


Assuntos
Carbonatos , Plantas , Fácies , Água
7.
Palaeogeogr Palaeoclimatol Palaeoecol ; 370(C): 167-83, 2013 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-23407808

RESUMO

A high-resolution multi-proxy analysis was conducted on a 1.5-m-long core of Tortonian age (~ 10.5 Ma; Late Miocene) from Austria (Europe). The lake sediments were studied with a 1-cm resolution to detect all small-scale variations based on palynomorphs (pollen and dinoflagellate cysts), ostracod abundance, geochemistry (carbon and sulfur) and geophysics (magnetic susceptibility and natural gamma radiation). Based on an already established age model for a longer interval of the same core, this sequence can be limited to approx. two millennia of Late Miocene time with a resolution of ~ 13.7 years per sample. The previous study documented the presence of solar forcing, which was verified within various proxies on this 1.5-m core by a combination of REDFIT spectra and Gaussian filters. Significant repetitive signals ranged in two discrete intervals corresponding roughly to 55-82 and 110-123 years, fitting well within the lower and upper Gleissberg cycle ranges.Based on these results, the environmental changes along the 2000-year Late Miocene sequence are discussed. No major ecological turnovers are expected in this very short interval. Nonetheless, even within this brief time span, dinoflagellates document rapid changes between oligotrophic and eutrophic conditions, which are frequently coupled with lake stratification and dysoxic bottom waters. These phases prevented ostracods and molluscs from settling and promoted the activity of sulfur bacteria. The pollen record indicates rather stable wetland vegetation with a forested hinterland. Shifts in the pollen spectra can be mainly attributed to variations in transport mechanisms. These are represented by a few phases of fluvial input but mainly by changes in wind intensity and probably also wind direction. Such influence is most likely caused by solar cycles, leading to a change in source area for the input into the lake.Furthermore, these solar-induced variations seem to be modulated by longer solar cycles. The filtered data display comparable patterns and modulations, which seem to be forced by the 1000-year and 1500-year cycles. The 1000-year cycle modulated especially the lake surface proxies, whereas the 1500-year cycle is mainly reflected in hinterland proxies, indicating strong influence on transport mechanisms.

8.
Glob Planet Change ; 111: 226-236, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25844021

RESUMO

Shallow-marine sediment records have the strong potential to display sensitive environmental changes in sedimentary geometries and skeletal content. However, the time resolution of most neritic carbonate records is not high enough to be compared with climatic events as recorded in the deep-sea sediment archives. In order to resolve the paleoceanographic and paleoclimatic changes during the Oligocene-Miocene transition in the Mediterranean shallow water carbonate systems with the best possible time resolution, we re-evaluated the Decontra section on the Maiella Platform (central Apennines, Italy), which acts as a reference for the correlation of Oligocene-Miocene shallow water deposits in the Mediterranean region. The 120-m-thick late Oligocene-late Miocene carbonate succession is composed of larger foraminiferal, bryozoan and corallinacean limestones interlayered with distinct planktonic foraminiferal carbonates representing a mostly outer neritic setting. Integrated multi-proxy and facies analyses indicate that CaCO3 and total organic carbon contents as well as gamma-ray display only local to regional processes on the carbonate platform and are not suited for stratigraphic correlation on a wider scale. In contrast, new biostratigraphic data correlate the Decontra stable carbon isotope record to the global deep-sea carbon isotope record. This links relative sea level fluctuations, which are reflected by facies and magnetic susceptibility changes, to third-order eustatic cycles. The new integrated bio-, chemo-, and sequence stratigraphic framework enables a more precise timing of environmental changes within the studied time interval and identifies Decontra as an important locality for correlating not only shallow and deep water sediments of the Mediterranean region but also on a global scale.

9.
Gondwana Res ; 23(3): 1172-1177, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27087778

RESUMO

Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3-4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall.

10.
J South Am Earth Sci ; 42: 216-241, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26523090

RESUMO

Western Amazonia's landscape and biota were shaped by an enormous wetland during the Miocene epoch. Among the most discussed topics of this ecosystem range the question on the transitory influx of marine waters. Inter alia the occurrence of typically brackish water associated ostracods is repeatedly consulted to infer elevated salinities or even marine ingressions. The taxonomical investigation of ostracod faunas derived from the upper part of the Solimões Formation (Eirunepé; W-Brazil) documents a moderately diverse assemblage (19 species). A wealth of freshwater ostracods (mainly Cytheridella, Penthesilenula) was found co-occurring with taxa (chiefly Cyprideis) usually related to marginal marine settings today. The observed faunal compositions as well as constantly very light δ18O- and δ13C-values obtained by measuring both, the freshwater and brackish water ostracod group, refer to entirely freshwater conditions. These results corroborate with previous sedimentological and palaeontological observations, which proposed a fluvial depositional system for this part of western Amazonia during the Late Miocene. We demonstrate that some endemic, "brackish" water ostracods (i.e., Cyprideis) have been effectively adapted to freshwater conditions. Thus, their occurrence is no univocal evidence for the influence of brackish or marine waters in western Amazonia during the Miocene.

11.
Facies ; 69(2): 5, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-36876224

RESUMO

Bryozoan-serpulid-algal-thrombolite bioherms of up to 50 cm size are described from the Sarmatian (upper Middle Miocene) of the Central Paratethys. They occur on top of lower Sarmatian carbonate sediments of high-energy conditions and the individual bioherms settle on crests of ripples. The buildups are overlain and partly truncated by cross-bedded oolites of late Sarmatian age. Buildup growth starts with a Cryptosula/Hydroides (bryozoan/serpulid) pioneer community, followed by nodular Schizoporella (bryozoan) colonies overgrown by coralline algae/microbial mats and a thrombolite with calcareous algal filaments. All these constituents form a framestone fabric which is overall dominated by bryozoans labeling them as bryoherms. Inside the bioherms ecological successions of higher frequencies occur which are interpreted to reflect short-time environmental fluctuations such as nutrient availability, oxygenation (possible anoxia), salinity (possible brackish water), temperature and water level. The internal succession in individual bioherms is related to long-term environmental changes including general shallowing, increasing nutrient supply and decreasing water circulation and oxygenation. The described bioherms are most similar to modern bryostromatolites of the Coorong lagoon in S Australia and also similar to structures in the Netherlands. The widespread occurrence of bryoherms/bryostromatolites in the Central Paratethys suggests a phase of considerable eutrophication during the early Sarmatian.

12.
J Quat Sci ; 38(7): 1103-1127, 2023 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-38505380

RESUMO

The Mariana forearc system, in the northwestern Pacific, is known as the only convergent margin setting with currently active serpentine mud volcanism. The Fantangisña serpentinite mud volcano lies 62 km west of the Mariana trench, within the influence of the North Equatorial Current (NEC). Cores recovered by International Ocean Discovery Program (IODP) Expedition 366 contain pelagic sediments overlying layered serpentinite mud deposits. At the bottom of the sequence, nannofossil-rich forearc deposits were recovered from under the seamount edifice. In this study, we investigated 47 samples from Site U1498A on the southern flank of the seamount for benthic and planktonic foraminifera assemblages. Statistical analyses on planktonic assemblages differentiated two sample groups related to the ratio between thermocline/mixed layer taxa, which indicate fluctuations in the depth of the thermocline (DOT) during the Pleistocene. Variations in the DOT reflect changes in the intensity of the NEC associated with El Niño/La Niña conditions. Mudflows do not influence the ecology of planktonic foraminifera but possibly enhance their preservation against dissolution, which was instead detected in the pelagic deposit as suggested by common Globigerinoides conglobatus. Benthic foraminifers were rare in serpentinite mud deposits as they are severely affected by mudflows. Conversely, they showed high diversity pre-/post-mud-volcanism, and indicate oligotrophic bottom-water conditions.

13.
Palaeogeogr Palaeoclimatol Palaeoecol ; 317-318(1-2): 1-12, 2012 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-23576820

RESUMO

High resolution pollen and dinoflagellate analyses were performed on a continuous 98-cm-long core from Tortonian deposits of Lake Pannon in the Styrian Basin in Austria. The sample distance of 1-cm corresponds to a resolution of roughly one decade, allowing insights into environmental and climatic changes over a millennium of Late Miocene time. Shifts in lake level, surface water productivity on a decadal- to centennial-scale can be explained by variations of rainfall during the Tortonian climatic optimum. Related to negative fine scale shifts of mean annual precipitation, shoreline vegetation belts reacted in an immediate replacement of Poaceae by Cyperaceae as dominant grasses in the marshes fringing the lake. In contrast to such near-synchronous ecosystem-responses to precipitation, a delayed lake level rise of 4-6 decades is evident in the hydrological budget of Lake Pannon. This transgression, caused by a precipitation increase up to > 1200 mm/yr, resulted in a complete dieback of marshes. Simultaneously, "open-water" dinoflagellates, such as Impagidinium, took over in the brackish lagoon and fresh water dinoflagellates disappeared. As soon as the rainfall switched back to moderate levels of ~ 1100-1200 mm/yr, the rise of the lake level slowed down, the marsh plants could keep up again and the former vegetation belts became re-established. Thus, mean annual precipitation, more than temperature, was the main driving force for high-frequency fluctuations in the Tortonian wetlands and surface water conditions of Lake Pannon. Such high resolution studies focusing on Tortonian decadal to centennial climate change will be crucial to test climate models which try to compare the Tortonian models with predictions for future climate change.

14.
Biogeochemistry ; 159(1): 103-138, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35535298

RESUMO

Calcitic valves of non-marine ostracodes are important geochemical archives. Investigations of the relationship between the ranges of oxygen and carbon isotope values of modern ostracode populations and their host water provide important information on local or regional conditions and influences. Here we present the first δ18Oostracode and δ13C of the freshwater ostracode species Cytheridella ilosvayi along with the isotopic composition of the waters in which the ostracodes calcified, δDwater, δ18Owater, δ13CDIC values-covering a large geographical range (Florida to Brazil). With this data we extended a newly developed approach based on the estimation of δ18O values of monthly equilibrium calcites as references for the interpretation of δ18Oostracode values. The expected apparent oxygen isotope fractionation between CaCO3 and H2O is correlated with temperature with smaller values occurring at higher temperatures as valid at isotope equilibrium (δ18Ocalcite_eq). Uncertainties about the expected equilibrium calcites derive from incomplete knowledge of high-frequency variations of the water bodies caused by interplay of mixing, evaporation, and temperature. Coincidence between δ18Oostracode and δ18Ocalcite_eq is restricted to few months indicating a seasonal calcification of Cytheridella. There is a characteristic pattern in its difference between mean δ18Oostracode and δ18Ocalcite_eq which implies that Cytheridella provides a synchronous life cycle in its geographical range with two calcification periods in spring (May, June) and autumn (October). This ubiquitous life cycle of Cytheridella in the entire study area is considered to be phylogenetically inherited. It might have originally been adapted to environmental conditions but has been conserved during the migration and radiation of the group over the Neotropical realm. Supplementary Information: The online version contains supplementary material available at 10.1007/s10533-022-00917-9.

15.
Swiss J Geosci ; 115(1): 25, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36524048

RESUMO

In the area of Bad Deutsch-Altenburg (Hainburg Mountains, Lower Austria) a Middle Miocene transgression over Mesozoic basement was explored in the course of the Danube power plant project "Hainburg". The Mesozoic basement forms a narrow ridge dipping to the northeast towards the Vienna Basin, covered by various Miocene sediments. The ridge represents a specific paleotopography that required a detailed study with 78 shallow, fully cored drill holes in an area of c. 0.5 km2. Ten drillings were selected for this study based on sedimentary composition and position relative to the Mesozoic ridge. These 10 cores, ranging in drilling depth from 26.5 to 96.4 m, were studied in respect to sedimentology, corallinacean algae, calcareous nannoplankton, foraminifers and ostracodes to reconstruct sediment distribution and paleoenvironment. Sediment distribution clearly shows that the Mesozoic ridge formed a physical barrier with siliciclastics dominating in the SW of the ridge and carbonate sediments prevailing in the NE. Based on biostratigraphy (calcareous nannoplankton, foraminifera, ostracodes, dinoflagellates) the majority of the sediments can be dated to the late Badenian (early Serravallian) only in some drillholes lower Sarmatian (upper Serravallian) sediments were detected. In terms of sequence stratigraphy, the Badenian sediments represent the transgressive and highstand systems tract of 3rd order sequence TB 2.5 (bound by the lowstands Ser 2 and Ser 3), the lower Sarmatian sediments can be correlated to sequence TB 2.6. Carbonate sediments show a wide spectrum of 13 facies which are mostly dominated by coralline algae. According to the relative positions of the drill holes a water depth between 0 and about 50 m can be reconstructed what is supported by the occurrence of the benthic biota. This biota indicates that the sedimentary succession started from the very beginning under full marine conditions. Except of basal conglomerates/breccias water energy conditions were low and turbidity high. Close to the Sarmatian boundary a reduction in salinity and depth may have occurred which is also observed in the Sarmatian sediments. Carbonate sediments and, in particular, larger benthic foraminifers indicate tropical to warm-temperate conditions for the late Badenian of the studied sections. The siliciclastic sediments NW of the Mesozoic ridge reflect riverine input indicated by the occurrence of freshwater ostracodes and characean oogonias. Calcareous nannoplankton and dinoflagellates show a high share of reworking from Upper Cretaceaous and Paleogene sediments. Supplementary Information: The online version contains supplementary material available at 10.1186/s00015-022-00425-w.

16.
Palaeogeogr Palaeoclimatol Palaeoecol ; 312(1-2): 181-193, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22319221

RESUMO

A multidisciplinary study was performed on a c. 30 m thick, limnic-deltaic sequence in the Styrian Basin (Austria). Geophysical (gamma ray activity, rock magnetism), geochemical (organic carbon, sulphur) and sedimentological observations were combined with palaeontological information (mainly ostracods). On this base, several ecological factors were deduced (terrigenous influx, salinity, water depth and oxygenation). Based on integrated stratigraphy as well as on palaeomagnetic results the whole section is set to Chron C5r.2r-1n (11.308-11.263 Ma) and covers a period of less than 45 kyr. In addition to the long-term record, we analysed short-term changes by high-resolution sampling (5 mm sample interval; ostracods, magnetic susceptibility). This ~ 2.3 m-thick interval spans in total < 3500 yr with an individual sample resolution of a few years only. The combination of these data permit the description of the palaeoenvironmental evolution of the section in detail: at the base of the section, the development of a conifer swamp on the lakeside of Lake Pannon is documented. This almost freshwater swamp existed for some centuries before it became extinct within a few decades due to a rise of the water-table. The drowning is related to a transgression of Lake Pannon, which triggered the establishment of a brackish-water fauna as well as greigite formation in the lake sediments. In general, the ongoing transgression favoured benthic life due to increased salinity (up to mesohaline conditions). The high-resolution ostracod and magnetic susceptibility record reflect short-term fluctuations in bottom-water ventilation. These oscillations probably range in the order of centuries and decades and are possibly related to climatic shifts. Later, the successive deepening of the lake resulted in a significant faunal turnover. A meromictic system with a well-established, oxygen-depleted hypolimnion developed. Finally, the limnic phase was replaced by a prograding deltaic system, where the amplified input of coarse-grained material and freshwater also affected benthic life. Periodic changes in clay (illite) content were detected by the gamma ray-log throughout the entire section. The observed cycles (5-12 kyr) of the gamma ray-log may reflect a super-ordinate modulation of the sedimentary record by climatically forced changes in precipitation or run-off.

17.
J South Am Earth Sci ; 32(2): 169-181, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26523089

RESUMO

In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake ("Lake Pebas") or any influx of marine waters can be excluded for that region during the Late Miocene.

18.
Sci Adv ; 6(7): eaay2126, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32095524

RESUMO

Coralline red algae (CRA) are important ecosystem engineers in the world's oceans. They play key roles as primary food source and carbonate producers in marine habitats. CRA are also vital for modern reef systems where they act as substrate for coral growth and stabilizers of reef frameworks. However, morphotaxonomic identification of these important marine organisms is hampered by the fact that morphological concepts used for their classification do not correspond to molecular data. We present the first analysis of nanoscale features in calcified cell walls of CRA in a globally distributed sample set. We use new morphological traits based on these cell wall ultrastructures to construct an independent morphological phyletic tree that shows a promising congruency with existing CRA molecular phylogenies. Our results highlight cellular ultrastructures as a tool to define the phenotypic expression of genotypic information showing their potential to unify morphology with molecular phylogeny.


Assuntos
Antozoários/genética , Nanopartículas/química , Rodófitas/genética , Animais , Antozoários/anatomia & histologia , Calcificação Fisiológica , Parede Celular/ultraestrutura , Genótipo , Nanopartículas/ultraestrutura , Fenótipo , Filogenia , Rodófitas/anatomia & histologia
19.
Palaeogeogr Palaeoclimatol Palaeoecol ; 270(1-2): 102-115, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21179376

RESUMO

A detailed ultra-high-resolution analysis of a 37-cm-long core of Upper Miocene lake sediments of the long-lived Lake Pannon has been performed. Despite a general stable climate at c. 11-9 Ma, several high-frequency oscillations of the paleoenvironments and depositional environments are revealed by the analysis over a short time span of less than 1000 years. Shifts of the lake level, associated with one major 3rd order flooding are reflected by all organisms by a cascade of environmental changes on a decadal scale. Within a few decades, the pollen record documents shifting vegetation zones due to the landward migration of the coast; the dinoflagellate assemblages switch towards "offshore-type" due to the increasing distance to the shore; the benthos is affected by low oxygen conditions due to the deepening. This general trend is interrupted by smaller scale cycles, which lack this tight interconnection. Especially, the pollen data document a clear cyclicity that is expressed by iterative low pollen concentration events. These "negative" cycles are partly reflected by dinoflagellate blooms suggesting a common trigger-mechanism and a connection between terrestrial environments and surface waters of Lake Pannon. The benthic fauna of the core, however, does not reflect these surface water cycles. This forcing mechanism is not understood yet but periodic climatic fluctuations are favoured as hypothesis instead of further lake level changes. Short phases of low precipitation, reducing pollen production and suppressing effective transport by local streams, might be a plausible mechanism. This study is the first hint towards solar activity related high-frequency climate changes during the Vallesian (Late Miocene) around Lake Pannon and should encourage further ultra-high-resolution analyses in the area.

20.
Zootaxa ; 4495(1): 1-64, 2018 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-30313727

RESUMO

Examination of normal pore canals, especially sieve-type pore canals, in living and fossil representatives of ten genera of the family Limnocytheridae, subfamily Timiriaseviinae, has revealed important diversity of structure. These complex pore canals have been studied via high-resolution scanning electron microscopy (the Cartographic Method) and analysed via the application of newly devised indices to assess patterns of consistency and variation in both detailed structure of individual pores and of their distribution on the calcified valve. The timiriaseviine taxa are compared with species of the genera Limnocythere, sub-family Limnocytherinae and Cyprideis (family Cytherideidae). The relationship between the living animal and its aquatic environment is discussed in the light of previous studies and of new evidence herein. The importance of normal pore canals for systematics is highlighted by the recognition and definition of the new tribe Gomphodellini Danielopol, Cabral Lord nov. tribe, subfamily Timiriaseviinae, family Limnocytheridae.


Assuntos
Crustáceos , Fósseis , Animais , Microscopia Eletrônica de Varredura
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA