| 1. |
- Babcock, Loren, et al.
(författare)
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Global climate, sea level cycles, and biotic events in the Cambrian Period
- 2015
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Ingår i: Palaeoworld. - : Elsevier BV. - 1875-5887 .- 1871-174X. ; 24:1-2, s. 5-15
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Tidskriftsartikel (refereegranskat)abstract
- The developing high-resolution chronostratigraphy of the Cambrian provides an updated age model for various geologic and biotic events that occurred during this critical period of Earth history. Broad, time-specific patterns of lithofacies, such as organic-rich deposits, and biofacies appear to be consistent across all Cambrian paleocontinents. Records of important evolutionary events including first appearances of certain metazoan taxa, migrations, and extinctions, tend to coincide with changes in eustatic sea level, as do the positions of many Konservat-Lagerstatten, concretion horizons, agnostoid-rich beds, and other sedimentary features. Most of these events or horizons also show a relationship to perturbations in the global carbon cycle. The positions of organic-rich deposits bear strong relationship to both paleogeographic position and sea level history. Cambrian strata show evidence of cyclicity at multiple scales. Synchronous or near-synchronous global cyclicity is inferred to be associated with oceanographic and climatic cycles characteristic of glacial expansion and deglaciation. (C) 2015 Published by Elsevier B.V. on behalf of Nanjing Institute of Geology and Palaeontology, CAS.
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| 2. |
- Coney, Louise, et al.
(författare)
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Geochemical and mineralogical investigation of the Permian-Triassic boundary in the Continental Realm of the Southern Karoo Basin, South Africa
- 2007
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Ingår i: Palaeoworld. - : Elsevier BV. - 1875-5887 .- 1871-174X. ; 16, s. 67-104
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Tidskriftsartikel (refereegranskat)abstract
- Mineralogical and geochemical studies of the non-marine Permian–Triassic (P–Tr) boundary across two stratigraphically wellconstrained sections (Commando Drift Dam and Wapadsberg, Eastern Cape Province) in the southern Karoo Basin, South Africa, have been undertaken to provide further input on the cause of this mass extinction event, and so has a sedimentological and geochemical evaluation of a third P–Tr boundary section at Injusiti (Kwazulu-Natal) in the eastern Karoo Basin, South Africa. The Commando Drift Dam section has been constrained by previous palaeontological and palaeomagnetic work, with a palaeomagnetic reversal positioned 5.3m above the palaeontological P–Tr boundary. The Wapadsberg section has been constrained palaeontologically. All these P–Tr sections studied here mostly comprise mudstones, together with siltstones, sandstones, and in the southern Karoo Basin, carbonate nodular horizons. A change in colour of the mudstones from green-grey to red-brown takes place at the palaeontologically defined boundary. Variations in the major and trace element abundance profiles are usually limited to the carbonate nodular horizons, besides the overall effects of weathering. Bulk carbon isotopic studies of the Commando Drift Dam section revealed a negative δ13Cbulk excursion (background values of −15 to −20‰, with total extent of excursion to −24.9‰) 2 cm below the palaeontological boundary, followed by a gradual recovery and then another decrease in values leading towards the palaeomagnetic boundary. Above this boundary recovery to less negative δ13Cbulk values (ca. −18‰) occurs. The organic carbon record from the Commando Drift Dam (southern Karoo Basin) and Injusiti (eastern Karoo Basin) oscillates between −26.1 and −28.9‰, which is comparable to previous studies of different sections in the southern Karoo Basin. The magnitude of both the bulk and organic carbon isotopic variation can be interpreted to indicate a number of inputs (due to the fluctuating values) of organic carbon. The carbon isotope data for carbonates in the Injusiti section are different from the results on carbonates from other studies, but more work to expand this dataset is necessary. The palynological studies on the Commando Drift Dam section reveal the presence of a low diversity flora composed principally of bryophytes, lycophytes, and gymnosperms. These forms, including several Late Permian key-species, are traces of the surviving plants enduring after the major extinction-pulse. The presence of fungal palynomorphs and dearth of pollen/spores related to photosynthetic plants some metres above the palaeontological P–Tr boundary demonstrate similarities to the pattern of floral extinction at the Cretaceous–Palaeogene (K–Pg) boundary. The timing of vertebrate extinctions in the Karoo Basin has so far not been determined, but the 252.5 Ma age for a single zircon crystal from Commando Drift Dam dated here gives a maximum constraint on the age of the event bed, which is in agreement with the accepted age of the boundary. No evidence for impact-produced microdeformation features were found in quartz grains from either the Wapadsberg or Commando Drift Dam sections. Also, siderophile element data (including platinum group element (PGE)concentrations) do not support the possible presence of a meteoritic component at the boundary. Thus, a link between impact and P–Tr extinction is not indicated by the results of this study.
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| 3. |
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| 4. |
- Harper, David A.T., et al.
(författare)
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The Furongian (late Cambrian) Biodiversity Gap : Real or apparent?
- 2019
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Ingår i: Palaeoworld. - Amsterdam : Elsevier BV. - 1871-174X .- 1875-5887. ; 28:1-2, s. 4-12
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Tidskriftsartikel (refereegranskat)abstract
- Two major, extended diversifications punctuated the evolution of marine life during the Early Palaeozoic. The interregnum, however, between the Cambrian Explosion and the Great Ordovician Biodiversification Event, is exemplified by the Furongian Gap when there was a marked drop in biodiversity. It is unclear whether the gap is apparent, due to sampling failure or lack of rock, or real — associated with unique and fluctuating environments, a distinctive palaeogeography and extreme climates during the late Cambrian. Indications suggest that there has been little attention paid to this interval compared with those below and above, while some of the classical areas for Cambrian research, such as Bohemia, have poor coverage through the Furongian. Moreover, based on information available in databases and the literature, together with the ghost ranges of many higher taxa through the Furongian, data suggest that biodiversity in this stage has been significantly underestimated. Emphasis, to date, has been placed on widespread, deeper-water dark shale facies of the interval, with generally low diversity faunas, whereas shallow-water communities have often been neglected.
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| 5. |
- Hu, Yu-Zhi, et al.
(författare)
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High resolution XCT scanning reveals complex morphology of gnathal elements in an Early Devonian arthrodire
- 2019
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Ingår i: Palaeoworld. - : ELSEVIER. - 1871-174X .- 1875-5887. ; 28:4, s. 525-534
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Tidskriftsartikel (refereegranskat)abstract
- Arthodire placoderms, as a possible sister group of Chinese 'maxillate' placoderms plus crown gnathostomes, provide important information regarding early evolution of jaws and teeth. High-resolution computed tomography and digital dissection on a unique articulated 400 million-year-old buchanosteid arthrodire permitsa detailed description of the three types of gnathal elements in basal arthrodires for the first time, giving insights into their morphology and the organization of the associated dentition. In displaying numerous denticle rows (dental fields), the gnathal element morphology is very different from the much-reduced denticulation of higher brachythoracid arthrodires, even though the latter have been used recently to interpret origin and early evolution of teeth. Ossification centres are anterolateral on the anterior supragnathal (attached to the braincase), anteromesial on the posterior supragnathal (attached to the palatoquadrate), and in the central part of the biting portion of the infragnathal (attached to the meckelian cartilage). The latter bone shows no evidence of two ossification centres as has been interpreted for more advanced arthrodires. Denticle rows radiating from the ossification centre form dental fields in all three elements, and are more similar to the gnathal elements of phlyctaeniid and actinolepid arthrodires than to advanced brachythoracids. The new evidence gives insights into the primitive arthrodire condition for comparison with the dermal jaw bones of Chinese 'maxillate' placoderms that have been homologised with the premaxilla, maxilla, and dentary of osteichthyans. The new details will help clarify the sequence of character acquisition in the evolution of marginal jaw bones in basal gnathostome groups.
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| 6. |
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| 7. |
- Li, Li-Qin, et al.
(författare)
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Palynofacies analysis for interpreting paleoenvironment and hydrocarbon potential of Triassic–Jurassic strata in the Sichuan Basin, China
- 2021
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Ingår i: Palaeoworld. - Nanjing : Elsevier. - 1871-174X .- 1875-5887. ; 30:1, s. 126-137
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Tidskriftsartikel (refereegranskat)abstract
- The Sichuan Basin is one of the largest petroliferous basins in China. The continental fluvial‒lacustrine sediments of the Upper Triassic Xujiahe Formation and the Lower Jurassic Zhenzhuchong Formation yield diverse fossil organisms and host one of the most important gas reservoirs in thebasin. However, paleontological implication for the paleoenvironment and hydrocarbon source is less documented. Here, we report, for the first time for this basin, results from palynofacies analyses combined with thermal alteration data in the Early Mesozoic deposit of the Qilixia section, northeastern Sichuan Basin. The results show that, organic matters in sediments are dominated by phytoclasts, with less abundant palynomorphs and a few amorphous organic matters (AOMs). Four palynofacies assemblages were identified, reflecting depositional settings in a general proximal and oxicfluvial‒deltaic environment, with two distal-proximal sedimentary cycles. The prominent dominance of opaque phytoclasts within the lower Zhenzhuchong Formation may be related to frequent wildfires across the Triassic-Jurassic transition. Palynofacies data (especially the relative abundanceof opaque phytoclasts) may reflect 405 kyr eccentricity cyclicity pattern. The palynofacies and thermal alteration index (TAI), combined with geochemical data indicate the presence of type III kerogen in mature to post-mature phases, suggesting gas potential of the Xujiahe and Zhenzhuchong formations in the northeastern Sichuan Basin. This study provides significant implications for better understanding the paleoenvironment variationsduring the Triassic-Jurassic transition and the future gas exploration in this area.
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| 8. |
- Maas, Andreas, et al.
(författare)
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The ‘Orsten’—More than a Cambrian Konservat-Lagerstätte
- 2006
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Ingår i: Palaeoworld. - 1871-174X .- 1875-5887. ; 15, s. 266-282
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- In several areas of southern Sweden, limestone nodules, locally called Orsten occur within bituminous alum shales. Theseshales and nodules were deposited under dysoxic conditions at the bottom of what was most likely a shallow sea during the lateMiddle to Upper Cambrian (ca. 500 million years ago). Subsequently, the name ‘Orsten’ has been referred to particular, mainlyarthropod, fossils from such nodules, and, in a wider sense, to the specific type of preservation of minute fossil through secondarilyphosphatization. This preservation is exceptional in yielding uncompacted and diagenetically undeformed three-dimensional fossils.‘Orsten’-type preservation resulted from incrustation of a thin external layer and also by impregnation by calcium phosphate and,therefore, mineralization of the surface of the former animals during early diagenesis. Primarily, this type of preservation seems tohave affected only cuticle-bearing metazoans such as cycloneuralian nemathelminths and arthropods. ‘Orsten’ preservation in thissense seems to be limited by size, in having yielded no partial or complete animals larger than 2 mm. On the other end of the scale,even larvae 100
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| 9. |
- Miller, J.F., et al.
(författare)
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Proposed stratotype for the base of the highest Cambrian stage at the first appearance datum of Cordylodus andresi, Lawson Cove section, Utah, USA
- 2006
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Ingår i: Palaeoworld. - : Elsevier BV. - 1871-174X .- 1875-5887. ; :15, s. 384-405
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Tidskriftsartikel (refereegranskat)abstract
- We propose a candidate for the Global Standard Stratotype-section and Point (GSSP) for the base of the highest stage of the Furongian Series of the Cambrian System. The section is at Lawson Cove in the Ibex area of Millard County, Utah, USA. The marker horizon is the first appearance datum (FAD) of the conodont Cordylodus andresi Viira et Sergeyeva in Kaljo et al. [Kaljo, D., Borovko, N., Heinsalu, H., Khazanovich, K., Mens, K., Popov, L., Sergeyeva, S., Sobolevskaya, R., Viira, V., 1986. The Cambrian-Ordovician boundary in the Baltic-Ladoga clint area (North Estonia and Leningrad Region, USSR). Eesti NSV Teaduste Akadeemia Toimetised. Geologia 35, 97-108]. At this section and elsewhere this horizon also is the FAD of the trilobite Eurekia apopsis (Winston et Nicholls, 1967). This conodont characterizes the base of the Cordylodus proavus Zone, which has been recognized in many parts of the world. This trilobite characterizes the base of the Eurekia apopsis Zone, which has been recognized in many parts of North America. The proposed boundary is 46.7 m above the base of the Lava Dam Member of the Notch Peak Formation at the Lawson Cove section. Brachiopods, sequence stratigraphy, and carbon-isotope geochemistry are other tools that characterize this horizon and allow it to be recognized in other areas. ?? 2006 Nanjing Institute of Geology and Palaeontology, CAS.
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