| 5041. |
- Sinnl, Giulia, et al.
(författare)
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Synchronizing ice-core and U/Th timescales in the Last Glacial Maximum using Hulu Cave 14C and new 10Be measurements from Greenland and Antarctica
- 2023
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Ingår i: Climate of the Past. - 1814-9324. ; 19:6, s. 1153-1175
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Tidskriftsartikel (refereegranskat)abstract
- Between 15 and 27kyrb2k (thousands of years before 2000CE) during the last glacial, Greenland experienced a prolonged cold stadial phase, interrupted by two short-lived warm interstadials. Greenland ice-core calcium data show two periods, preceding the interstadials, of anomalously high atmospheric dust loading, the origin of which is not well understood. At approximately the same time as the Greenland dust peaks, the Chinese Hulu Cave speleothems exhibit a climatic signal suggested to be a response to Heinrich Event 2, a period of enhanced ice-rafted debris deposition in the North Atlantic. In the climatic signal of Antarctic ice cores, moreover, a relative warming occurs between 23 and 24.5kyrb2k that is generally interpreted as a counterpart to a cool climate phase in the Northern Hemisphere. Proposed centennial-scale offsets between the polar ice-core timescales and the speleothem timescale hamper the precise reconstruction of the global sequence of these climatic events. Here, we examine two new 10Be datasets from Greenland and Antarctic ice cores to test the agreement between different timescales, by taking advantage of the globally synchronous cosmogenic radionuclide production rates. Evidence of an event similar to the Maunder Solar Minimum is found in the new 10Be datasets, supported by lower-resolution radionuclide data from Greenland and 14C in the Hulu Cave speleothem, representing a good synchronization candidate at around 22kyrb2k. By matching the respective 10Be data, we determine the offset between the Greenland ice-core chronology, GICC05, and the Antarctic chronology for the West Antarctic Ice Sheet Divide ice core (WDC), WD2014, to be 125±40 years. Furthermore, via radionuclide wiggle-matching, we determine the offset between the Hulu speleothem and ice-core timescales to be 375 years for GICC05 (75-625 years at 68% confidence) and 225 years for WD2014 (-25-425 years at 68% confidence). The rather wide uncertainties are intrinsic to the wiggle-matching algorithm and the limitations set by data resolution. The undercounting of annual layers in GICC05 inferred from the offset is hypothesized to have been caused by a combination of underdetected annual layers, especially during periods with low winter precipitation, and misinterpreted unusual patterns in the annual signal during the extremely cold period often referred to as Heinrich Stadial 1.
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| 5042. |
- Sippo, J. Z., et al.
(författare)
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Reconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on record
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17:18, s. 4707-4726
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Tidskriftsartikel (refereegranskat)abstract
- A massive mangrove dieback event occurred in 2015-2016 along similar to 1000km of pristine coastline in the Gulf of Carpentaria, Australia. Here, we use sediment and wood chronologies to gain insights into geochemical and climatic changes related to this dieback. The unique combination of low rainfall and low sea level observed during the dieback event had been unprecedented in the preceding 3 decades. A combination of iron (Fe) chronologies in wood and sediment, wood density and estimates of mangrove water use efficiency all imply lower water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid, large mobilization of sedimentary Fe, which is consistent with redox transitions promoted by changes in soil moisture content. Elemental analysis of wood cross sections revealed a 30- to 90-fold increase in Fe concentrations in dead mangroves just prior to their mortality. Mangrove wood uptake of Fe during the dieback is consistent with large apparent losses of Fe from sediments, which potentially caused an outwelling of Fe to the ocean. Although Fe toxicity may also have played a role in the dieback, this possibility requires further study. We suggest that differences in wood and sedimentary Fe between living and dead forest areas reflect sediment redox transitions that are, in turn, associated with regional variability in groundwater flows. Overall, our observations provide multiple lines of evidence that the forest dieback was driven by low water availability coinciding with a strong El Nino-Southern Oscillation (ENSO) event and was associated with climate change.
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| 5043. |
- Sissakian, Varoujan K., et al.
(författare)
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Safeen anticline: a complicated structure and its negative impact on oil exploration, Iraqi Kurdistan Region
- 2022
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Ingår i: Arabian Journal of Geosciences. - : Springer Nature. - 1866-7511 .- 1866-7538. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Safeen anticline is one of the most complicated anticlines in Iraqi Kurdistan Region (IKR), with NW–SE trend. Structurally, the anticline is truncated by different types of faults; some of them are deep-seated faults, which have complicated the subsurface form of the anticline. The anticline includes two domes with two parasitic anticlines and synclines along both limbs. Moreover, two hanging synclines exist northeastwards and one southwestwards. Six possible deep seated transversal faults may occur along the anticline, dissecting the anticline in NE–SW trend and extending northeastwards and southwestwards. Moreover, the deep-seated faults dissect many anticlines on both sides of the Safeen anticline. The deep-seated faults have contributed to the complexity of the anticline, as compared to other anticlines in the Zagros Fold–Thrust Belt, especially inside IKR, and have negative impact to the oil exploration activities in the anticline. Therefore, the drilled Safeen Oil well 01 has missed the target. We have used satellite images from land viewer website + Terraincognita app to study the structural style of the anticline, and to recognize different structural features. Field investigation was carried out to check the interpreted data.
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| 5044. |
- Sivalneva, Olga, et al.
(författare)
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Structure and Composition of Basement and Sedimentary Cover in the Southwestern Part of the Siljan Ring, Central Sweden : New Data from the C-C-1 Drill Core
- 2021
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- The results from the geological and geophysical investigations of the Siljan Ring impact structure (central Sweden) have shown that the Paleozoic sedimentary succession and the Precambrian basement were strongly affected by complex deformational processes. Studies of a new drill core from the C-C-1 well provide valuable additional information necessary for the reconstruction of the geological setting in the southwestern part of the Siljan Ring. It was found that the contact between the basement and the sedimentary cover is tectonic, not normal sedimentary, in origin. The basement interval comprises Precambrian metavolcanic and metasedimentary rocks with a single mafic intrusion (gabbro-dolerite) in the upper part. The rocks have only been partially metamorphosed. The intercalation of calcareous mudstones, skeletal wackstones, and black shales in the sedimentary cover interval is not consistent with the regional lithostratigraphy scheme. Thus, more likely that the sedimentary sequence is not complete as a result of tectonic displacements, and a significant part of the Lower and Middle Ordovician succession is missing. The Post-Proterozoic tectonic reactivation and impact event also caused the formation of four types of fracture. The third type of fracture is accompanied by cataclastic zones and probably have an impact-related nature. In the highly fractured basement rocks, a dissolution along the second type of fracture has resulted in the development of open vugs. Open vugs and microporosity in cataclastic zones have been considered to be an effective storage space for hydrocarbons.
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| 5045. |
- Siverson, Mikael, et al.
(författare)
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Anacoracid sharks from the Albian (lower cretaceous) Pawpaw shale of Texas
- 2007
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 50:4, s. 939-950
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Tidskriftsartikel (refereegranskat)abstract
- Recent collecting from the Pawpaw Shale in northeast Texas has yielded several hundred teeth of anacoracid sharks. The material allows for a much-needed revision of the Late Albian anacoracids from North America. The previously recognized Squalicorax sp., also referred to as S. volgensis in more recent publications, is a mix of two different species: S. priscoserratus sp. nov. and S. pawpawensis sp. nov. In addition to these two new species, a single tooth is assigned to S. aff. S. baharijensis. Our data indicate that anacoracids were considerably more diverse group in the North American Cretaceous than previously thought. We attribute much of the underestimation of diversity to vague species concepts, poor preparation techniques and the associated lack of attention to certain dental features, in particular neck morphology, root surface porosity and the root's vascularization.
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| 5046. |
- Siverson, Mikael, et al.
(författare)
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Late cretaceous sharks Cretoxyrhina and Cardabiodon from Montana, USA
- 2005
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Ingår i: Acta Palaeontologica Polonica. - 0567-7920. ; 50:2, s. 301-314
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Tidskriftsartikel (refereegranskat)abstract
- The middle part of the Cretaceous represents a time of high diversity and rapid rates of dental evolution in lamniform sharks. Several species had a very wide spatial distribution with recorded occurrences in both hemispheres. We have examined isolated teeth of Cretoxyrhina and Cardabiodon from eastern Russia, Mangyshlak in Kazakhstan, and the Western Interior of the USA. The material indicates that samples of isolated teeth of the two genera have high potential in intercontinental correlation of the upper Albian to mid-Turonian interval in mid-palaeolatitude deposits, poor in other age-diagnostic fossil groups. The utilization of these lamniforms in mid-Cretaceous biostratigraphy is currently hampered by the nearly total absence in the literature of well illustrated, well dated and sufficiently large samples of isolated teeth of the two genera. As a first Step towards the establishment of an intercontinental elasmobranch zonation for mid-Cretaceous strata in temperate palaeo-regions, we describe and illustrate samples of teeth of Cardabiodon venator SP. nov. and Cretoxyrhina mantelli from the lower middle Turonian Collignoniceras woollgari regulare Zone in the Fairport Member of the Carlile Shale in east-central Montana, USA. These samples could serve as reference points for future biostratigraphic studies of Cretoxyrhina and Cardabiodon. The extinction of Cretoxryhina may be diachronous, as regional last appearance data range from the upper Santonian (Marsupites testudinarius Zone) in Western Australia to the uppermost lower Campanian (informal Belemnellocamax maminillatus zone; a lateral equivalent to the German Gonioteuthis quadrata gracilislBelemnitella inucronata Zone) in southern Sweden.
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| 5047. |
- Siverson, Mikael, et al.
(författare)
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Mid-Cretaceous Cretoxyrhina (Elasmobranchii) from Mangyshlak, Kazakhstan and Texas, USA
- 2013
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Ingår i: Alcheringa. - : Informa UK Limited. - 0311-5518. ; 37:1, s. 87-104
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Tidskriftsartikel (refereegranskat)abstract
- SIVERSON, M., WARD, D.J., LINDGREN, J. & KELLEY, L.S., iFirst article. Mid-Cretaceous Cretoxyrhina (Elasmobranchii) from Mangyshlak, Kazakhstan and Texas, USA. Alcheringa, 118. ISSN 0311-5518. The holotype of the nominal lamniform shark Pseudoisurus' vraconensis comprises an isolated tooth from a late Albian stratum at Besakty, Mangyshlak, Kazakhstan. Its stratigraphical provenance indicates that it is of Mortoniceras perinflatum Zone-age or somewhat older. It is indistinguishable at the species level from isolated teeth from the Mortoniceras rostratum Zone of the Pawpaw Shale in northeast Texas. Abundant teeth of P'. vraconensis-type from slightly younger strata close to the AlbianCenomanian boundary at Kolbay, eastern Mangyshlak, Kazakhstan, enabled the reconstruction of a dentition adhering to the dental blueprint of Cretoxyrhina, clarifying the generic identity of P'. vraconensis. In the Kolbay population, the distal lobe of the root on the three probable third upper anterior teeth at hand is not labiolingually compressed relative to the mesial lobe. Labiolingual flattening of the root lobe facing the mesial side of the intermediate bar is a characteristic feature of modern lamnids and may reflect limited accommodation space for a thick root lobe to form at the distal margin of the anterior hollow. An intermediate bar adds structural strength to the anterior part of the palatoquadrate while isolating the upper anterior teeth, facilitating deep penetration by their enlarged cusps. Individuals of Cretoxyrhina from the late Coniacian to earliest Campanian Smoky Hill Chalk in Kansas display a strongly disjunct heterodonty in the anterior half of the upper jaw dentition. This so-called lamnoid tooth pattern' is regarded by some researchers as a synapomorphy of the Lamniformes. The dwarfed teeth creating the lamnoid tooth pattern' in Smoky Hill Chalk individuals are seemingly matched by relatively larger, corresponding teeth in the 15 million years older C. vraconensis. The probable weakening of the disjunct upper jaw heterodonty in Cretoxyrhina with increasing geological age indicates that the lamnoid tooth pattern' might have evolved independently in two or more lamniform clades. ?????Pseudoisurus'vraconensis???????????, ?????Mangyshlak??Besakty??Albian????????????????Mortoniceras perinflatum????????????, ???????????Pawpaw??Mortoniceras rostratum??????????????Mangyshlak???Kolbay, ??Albian-Cenomanian??????????????? P'. vraconensis-???, ????Cretoxyrhina?????? 'P'. vraconensis ???????????Kolbay???, ????????????????????????????????????????????????????????????????????????????, ???????????????????????????????, ???????, ???????????????????Coniacian??Campanian?????Smoky Hill ????Cretoxyrhina???????????????????????lamnoid??????????????????????????????Smoky Hill ?????lamnoid?????, ???????15??????C. vraconensis ????????Cretoxyrhina???????????????????, ??lamnoid?????????????????????
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| 5048. |
- Siversson, Mikael, et al.
(författare)
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Cenomanian-Campanian (Late Cretaceous) mid-palaeolatitude sharks of Cretalamna appendiculata type
- 2015
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Ingår i: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920. ; 60:2, s. 339-384
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Tidskriftsartikel (refereegranskat)abstract
- The type species of the extinct lamniform genus Cretalamna, C. appendiculata, has been assigned a 50 Ma range (Albian-Ypresian) by a majority of previous authors. Analysis of a partly articulated dentition of a Cretalamna from the Smoky Hill Chalk, Kansas, USA (LACM 128126) and isolated teeth of the genus from Cenomanian to Campanian strata of Western Australia, France, Sweden, and the Western Interior of North America, indicates that the name of the type species, as applied to fossil material over the last 50 years, represents a large species complex. The middle Cenomanian part of the Gearle Siltstone, Western Australia, yielded C. catoxodon sp. nov. and "Cretalamna" gunsoni. The latter, reassigned to the new genus Kenolamna, shares several dental features with the Paleocene Palaeocarcharodon. Early Turonian strata in France produced the type species C. appendiculata, C. deschutteri sp. nov., and C. gertericorum sp. nov. Cretalamna teeth from the late Coniacian part of the Smoky Hill Chalk in Kansas are assigned to C. ewelli sp. nov., whereas LACM 128126, of latest Santonian or earliest Campanian age, is designated as holotype of C. hattini sp. nov. Early Campanian deposits in Sweden yielded C. borealis and C. sarcoportheta sp. nov. A previous reconstruction of the dentition of LACM 128126 includes a posteriorly situated upper lateroposterior tooth, with a distally curved cusp, demonstrably misplaced as a reduced upper "intermediate" tooth. As originally reconstructed, the dentition resembled that of cretoxyrhinids (sensu stricto) and lamnids. Tooth morphology, however, indicates an otodontid affinity for Cretalamna. The root is typically the most diagnostic feature on an isolated Cretalamna tooth. This porous structure is commonly abraded and/or corroded and, consequently, many collected Cretalamna teeth are indeterminable at species level.
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| 5049. |
- Sivhed, U, et al.
(författare)
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Upper Ordovician carbonate mounds on Gotland, central Baltic Sea: Distribution, composition and reservoir characteristics
- 2004
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Ingår i: Journal of Petroleum Geology. - : Wiley. - 0141-6421 .- 1747-5457. ; 27:2, s. 115-140
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Tidskriftsartikel (refereegranskat)abstract
- We present a multidisciplinary description of the Upper Ordovician carbonate mounds which are found throughout the central Baltic Sea and which were studied in detail on the island of Gotland. These mounds were the subject of intense exploration between 1974 and 1992 and a total of 323 shallow wells were completed in more than 100 mounds on Gotland. Many of these were put into production and a total of 100, 000 cu. m of high quality oil was produced. In this paper, we discuss the mounds' occurrence, lithological characteristics, age, faunal composition, petroleum chemistry and reservoir properties. The study is based on analyses of core material from wells in the northern part of Gotland. Upper Ordovician mound reservoirs here contain oil which has a similar geochemical signature to that in Lithuania and in the Kaliningrad district (Russia). The oil was probably derived from marine anoxic shales and migrated up-dip from more central parts of the Baltic Syneclise where oil-prone shales are known to occur. An intraformational origin for the oil is unlikely. The mounds contain large numbers of vugs and moulds which communicate mainly through dissolution fractures and surfaces and probably reflect a marine regression. Various lithofacies were recognized from petrographic studies including sub-mound, intra-mound, cap and flank, and supra-mound facies. Algae and stromatolites dominate the intra-mound facies, providing an organic framework for the entire structure. Consequently, the mounds are not merely poorly defined build-ups of mud and micrite, as has previously been assumed. Biostratigraphic data indicates a late Caradoc to Ashgill age for the mounds and their associated lithologies.
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| 5050. |
- Sjoberg, Lars E., et al.
(författare)
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Quasigeoid-to-geoid determination by EGM08
- 2012
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Ingår i: Earth Science Informatics. - : Springer Science and Business Media LLC. - 1865-0473 .- 1865-0481. ; 5:2, s. 87-91
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to estimate the difference between quasigeoid and geoid heights globally from the Earth Gravitational Model EGM08 and a related topographic model. The numerical computations with the standard topographic density of 2.67 g/cm(3) show that the maximum and minimum of the separations are estimated to 5.47 m and -0.11 m on the Tibet plateau and in the Indian Ocean, respectively. These estimates do not consider possible topographic density variations, which result in topographic bias changes proportional to the topographic elevation squared. Assuming such density changes of 10% from the standard value, the separation may change up to 5 dm.
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