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| 2. |
- Aljinović, Dunja, et al.
(författare)
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Western Tethyan Epeiric Ramp Setting in the Early Triassic : An Example from the Central Dinarides (Croatia)
- 2018
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Ingår i: Journal of Earth Science. - : Springer Science and Business Media LLC. - 1674-487X .- 1867-111X. ; 29:4, s. 806-823
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Tidskriftsartikel (refereegranskat)abstract
- In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick (927.5 m) Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The δ13C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the +8‰ amplitude around the Dienerian-Smithian boundary (DSB), followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary (SSB) a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary (SAB). Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated: 1) the dolostone member (Early Griesbachian); 2) the siliciclastic member (red-coloured shale, siltstone, sandstone with oolitic/bioclastic grainstone intercalations), which can be further divided into lower, middle and upper intervals (Late Griesbachian, Dienerian and Smithian); and 3) the mudstone member (grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods-Spathian). The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.
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| 3. |
- Baldermann, Andre, et al.
(författare)
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Palaeo-environmental evolution of Central Asia during the Cenozoic : New insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)
- 2021
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 17:5, s. 1955-1972
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Tidskriftsartikel (refereegranskat)abstract
- The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical, and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning from ~ 34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or opensteppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K-Ar ages of detrital muscovite (~ 798-728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite-smectite and "hairy"illite (K-Ar ages of ~ 34-25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (~32-29 and ~ 29-25 Ma). Changes in hydroclimate are recorded in δ18 O and δ13 C profiles of soil carbonates and in silicate mineral weathering patterns, indicating that comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ~ 34-33, ~ 31, ~ 28 and ~ 23 Ma and coincide with some episodes of high-latitude ice-sheet expansion inferred from marine deep-sea sedimentary records. This suggests that long-term variations in the ocean-atmosphere circulation patterns due to pCO2 fall, reconfiguration of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai Mountains and modulated by global climate events.
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| 4. |
- Baud, Aymon, et al.
(författare)
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Sponge Takeover from End-Permian Mass Extinction to Early Induan Time : Records in Central Iran Microbial Buildups
- 2021
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The end-Permian mass extinction was the most severe biotic crisis in Earth’s history. In its direct aftermath, microbial communities were abundant on shallow-marine shelves around the Tethys. They colonized the space left vacant after the dramatic decline of skeletal metazoans. The presence of sponges and sponge microbial bioherms has largely gone unnoticed due to the sponges’ size and the cryptic method of preservation. In addition to sponge dominated facies recently described in South Armenia and Northwestern Iran, we describe here sponge-microbial bioherms cropping out in two well-known Permian-Triassic boundary localities: the Kuh-e Hambast section, south-east of Abadeh city and the more distal Shahreza section, near Isfahan. In both sections, the extinction horizon is located at the top of an upper Changhsingian ammonoid-rich nodular limestone, called Paratirolites limestone. At Kuh-e Hambast, the overlying decimetric thick shale deposit called “boundary clay,” the latest Permian in age, is conformably overlain by well-dated transgressive basal Triassic platy limestone containing four successive levels of decimeter to meter scale, elongated to form cup-shaped mounds made of branching columnar stromatolites. Sponge fibers from possibly keratose demosponge, are widely present in the lime mudstone matrix. At the Shahreza section, above the extinction level, the boundary clay is much thicker (3 m), with thin platy limestone intervals, and contains two main levels of decimeter to meter scale mounds of digitate microbialite crossing the Permian-Triassic boundary with similar sponge fibers. Three levels rich in thrombolite domes can be seen in the overlying 20 m platy limestone of earliest Triassic age. Sponge fibers and rare spicules are present in their micritic matrix. These sponge fibers and spicules which are abundant in the latest Permian post-extinction boundary clay, followed microbial buildups during the Griesbachian time.
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| 5. |
- Brandstätter, Jennifer, et al.
(författare)
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The Origin of Carbonate Veins Within the Sedimentary Cover and Igneous Rocks of the Cocos Ridge : Results From IODP Hole U1414A
- 2018
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 19:10, s. 3721-3738
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Tidskriftsartikel (refereegranskat)abstract
- Carbonate veins in the igneous basement and in the lithified sedimentary cover of the Cocos Ridge at International Ocean Discovery Program (IODP) Hole 344-U1414A reveal the hydrologic system and fluid-rock interactions. IODP Hole 344-U1414A was drilled on the northern flank of the Cocos Ridge and is situated 1 km seaward from the Middle America Trench offshore Costa Rica. Isotopic and elemental compositions were analyzed to constrain the fluid source of the carbonate veins and to reveal the thermal history of Hole 344-U1414A. The formation temperatures (oxygen isotope thermometer) of the carbonate veins in the lithified sedimentary rocks range from 70 to 92 °C and in the basalt from 32 to 82 °C. 87Sr/86Sr ratios of the veins in the altered Cocos Ridge basalt range between 0.707307 and 0.708729. The higher ratios are similar to seawater strontium ratios in the Neogene. 87Sr/86Sr ratios lower 0.7084 indicate exchange of Sr with the igneous host rock. The calcite veins hosted by the sedimentary rocks are showing more primitive 87Sr/86Sr ratios <0.706396. The isotopic compositions indicate seawater, modified into a hydrothermal fluid by subsequent heating, as the main fluid source. Low-temperature alteration and the presence of a high-temperature fluid resulted in different carbonate precipitates forming up to several cm thick veins. The geochemical data combined with age data of the sedimentary rocks suggest intraplate seamount volcanism in the area between the Galapagos hot spot and the Cocos Island as an additional heating source, after the formation of the Cocos Ridge at the Galapagos hot spot.
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| 6. |
- Brylka, Karolina, et al.
(författare)
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Looking for the oldest diatoms
- 2024
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Ingår i: Marine Micropaleontology. - 0377-8398. ; :190
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Tidskriftsartikel (refereegranskat)abstract
- Paleontological observations of ancient flora and fauna provide powerful insights into past diversity and relationshipdynamics between organisms and their environments. Diatoms are globally distributed protists thatinfluence major biogeochemical cycles and sustain oceanic food webs. The fossil diatom record extends 120million years back to the Early Cretaceous where rare deposits were discovered worldwide and are occasionallyrepresented by diverse communities. However scarce, the taxonomic richness and geographical spread of thesediatom communities suggest prior evolutionary events and therefore earlier deposits. To complement the existingfossil information and to discover diatom deposits predating 120 Ma, we examined 33 study sites from cores andoutcrops across oceans and continents. These efforts did not generate new fossil discoveries, however. Ourassessment suggests biogenic silica that comprises the cell wall of diatoms was likely dissolved from Mesozoicsediments through diagenetic processes. Altogether, the search for the oldest diatoms must continue but shouldtarget sediments that experienced shallow burial and concretions.
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| 7. |
- Brylka, Karolina, et al.
(författare)
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Uncertainties surrounding the oldest fossil record of diatoms
- 2023
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Ingår i: Scientific Reports. - 2045-2322. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Molecular clocks estimate that diatom microalgae, one of Earth’s foremost primary producers, originated near the Triassic–Jurassic boundary (200 Ma), which is close in age to the earliest, generally accepted diatom fossils of the genus Pyxidicula. During an extensive search for Jurassic diatoms from twenty-five sites worldwide, three sites yielded microfossils initially recognized as diatoms. After applying stringent safeguards and evaluation criteria, however, the fossils found at each of the three sites were rejected as new diatom records. This led us to systematically reexamine published evidence in support of Lower- and Middle-Jurassic Pyxidicula fossils. Although Pyxidicula resembles some extant radial centric diatoms and has character states that may have been similar to those of ancestral diatoms, we describe numerous sources of uncertainty regarding the reliability of these records. We conclude that the Lower Jurassic Pyxidicula fossils were most likely calcareous nannofossils, whereas the Middle Jurassic Pyxidicula species has been reassigned to the Lower Cretaceous and is likely a testate amoeba, not a diatom. Excluding the Pyxidicula fossils widens the gap between the estimated time of origin and the oldest abundant fossil diatom record to 75 million years. This study underscores the difficulties in discovering and validating ancient microfossils.
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| 8. |
- Chen, Yanlong, et al.
(författare)
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Middle Triassic conodont assemblages from the Germanic Basin: implications for multi-element taxonomy and biogeography
- 2018
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Ingår i: Journal of Systematic Palaeontology. - : Informa UK Limited. - 1477-2019 .- 1478-0941. ; , s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Conodonts have been a key tool for biostratigraphical, evolutionary and palaeobiogeographical studies, and the GermanicBasin has been one of the most important regions for these studies. However, few modern studies provide systematic data onthe mainly endemic conodonts of the Middle Triassic Germanic Basin. Here we document conodonts from two sections inGermany, one Bithynian in age and the other late Anisian to early Ladinian in age. The two sections captured two episodesof marine fauna invasion in the Germanic epicontinental basin during the Middle Triassic. The conodont Neogondolellamombergensis, elsewhere reported as appearing globally, is reviewed and revised, confirming previous suggestions that thisspecies only occurs in the Germanic Basin. Apparatuses of Neogondolella haslachensis and Nicoraella germanica from theGermanic Basin are proposed. It was generally expected that S and M elements within clades have a very high morphologicalstability compared to P elements. However, the apparatus of Nicoraella germanica differs significantly from that of southChina, indicating that the morphology of S elements within a genus can be unstable, and thus promotes our understanding ofconodont evolution. The rarely documented genus Gondolatus, which was suggested as representing pathological specimens,is confirmed as a valid genus in the Germanic Basin. Our data suggest that endemic conodonts evolved twice, not only in theUpper Muschelkalk Subgroup, but also in the Lower Muschelkalk Subgroup.
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| 9. |
- Chen, Yanlong, et al.
(författare)
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Quantitative stratigraphic correlation of Tethyan conodonts across the Smithian-Spathian (Early Triassic) extinction event
- 2019
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 195, s. 37-51
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Forskningsöversikt (refereegranskat)abstract
- Three small-scale extinctions occurred in the Early Triassic with one of them recognized close to the Smithian-Spathian boundary. In the last two decades, the end-Permian mass extinction as well as the subsequent recovery have been intensively studied throughout the Tethys region, but correlations within the Lower Triassic are difficult due to conodonts endemism. Here we use paleontological and geochemical methods to document a high-resolution biostratigraphy of the Smithian-Spathian boundary interval from two sections of Oman. In combination with previously published data from both South-Central Europe and South China, a quantitative stratigraphic correlation has been achieved with 7 conodont UA Zones recognized using the unitary association method. Based on conodonts and carbonate carbon isotope data, the Smithian-Spathian boundary is identified in the interval from UAZ4 to UAZ5 close to the last occurrence of Nv. pingdingshanensis in Oman and South China, and within the range of P. inclinata, Ns. planus, Pl. regularis, and Pl. corniger in South-Central Europe. UAZ7 fauna displays a clear diachronism as it starts from South China, arrives a bit later in Oman and even later in western Tethys. Foliella gardenae and Icriospathodus zaksi are reported from Oman for the first time and thus expand the geographical distribution of these rarely reported species.
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| 10. |
- Chen, Yanlong, et al.
(författare)
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Smithian and Spathian (Early Triassic) conodonts from Oman and Croatia and their depth habitat revealed
- 2021
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181. ; 196
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Tidskriftsartikel (refereegranskat)abstract
- Conodont ecology of the Early Triassic Smithian–Spathian transition is still poorly understood. Here we use oxygen isotope ratios of monogeneric conodonts from Omani samples to reveal the differences of oxygen isotopic composition between different taxa. Oxygen isotope analyses from Oman reveal that Neogondolella inhabited a deeper part of the water column relative to neospathodids and Icriospathodus. This indicates that species of Neogondolella lived in an environment ca. 1.7 °C cooler than where neospathodids lived. The investigation of conodonts from these Smithian and Spathian sections has also enabled the first recovery of some rarely reported species (e.g., Icriospathodus zaksi, Paullella omanensis sp. nov. Chen and Gladigondolella laii sp. nov. Chen) from Oman. Paullella omanensis sp. nov. was further recovered from Plavno, Croatia, indicating a large geographic distribution, and its value for biostratigraphic correlations. The discovery of these species in both Oman and Croatia expands their geographical distribution.
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