广西上泥盆统F-F界线碳同位素的变化特征

发生在晚泥盆世弗拉期(Frasnian)-法门期(Famennian)之交的生物灭绝事件(简称F-F事件)是古生代以来五大生物集群灭绝事件之一,其原因仍含糊不清。碳同位素研究显示,伴随F-F事件全球碳循环发生了显著的变化。但对中国南方F-F事件地层碳同位素变化特征的认识不够,缺乏系统的研究。对广西桂林杨堤上泥盆统灰岩剖面的碳同位素的分析结果表明,在上泥盆统存在两次碳同位素正偏移,分别出现在下rhenana带和F-F的界线,其中,出现在F-F界线的碳同位素正偏移与广西垌村以及欧美和非洲等地的上泥盆统F-F界线附近的碳同位素记录一致,且具有相近的变化幅度。进一步对广西桂林附近的杨堤和垌村剖面F-F界线的碳同位素组成变化模式的分析发现,这次正偏移可能是由多次次级变化组成,与F-F事件中生物的灭绝步骤相似。     

Phosphatic microspherules and their geobiological implications from the Frasnian-Famennian transition at the Yangdi section,Guilin, South China

Abundant perfectly-preserved phosphatic microspherules have been discovered across the Frasnian-Famennian(F-F)transition from the Yangdi section in Guilin,Guangxi,South China.They are mostly spherical or elliptical in shape and about 150μm in diameter with smooth exterior surfaces.Each microspherule consistently possesses a small dimple on the surface.The internal texture of microspherules consists of concentric light-colored apatite and dark-colored organic matter bands alternating around a central core.Conodonts have also been found preserved together with phosphatic microspherules in the same horizon,and the abundance of the former is obviously higher than that of the latter.Laser Raman spectral studies show close similarities in spectral patterns between the outer shells of phosphatic microspherules and the blade of the conodont genus Palmatolepis sp.,as well as between the microspherule nucleus and the platform of the same conodont genus.Furthermore,the statistical results and geochemical data demonstrate that the elevated abundance of phosphatic microspherules roughly coincides with the blooms of bacteria and algae,but is later than the sharp increase of oceanic nutrients.The phosphatic microspherules are interpreted here to be the‘otoliths’secreted by conodont animals based on the compositional similarities between phosphatic microspherules and conodonts and their interrelated abundances.In addition,an analogous study reveals morphological and textural similarities between fish otoliths and phosphatic microspherules.The formation of phosphatic microspherules is probably related to seawater eutrophication.We speculate that the explosive growth of bacteria and algae is probably caused by the enrichment of nutrients that is most likely associated with the increase of terrestrial inputs,submarine hydrothermal activities or the upwelling anoxic bottom waters in the late Devonian,which would stimulate the conodont animals to secrete phosphatic microspherules—the‘otoliths’of conodont animals.This study reveals the coupling relationship between organisms and environments from the perspective of phosphatic microspherules and provides new evidence for the cause of faunal crisis during the Late Devonian F-F transition.     

Coupling relationships between brachiopods and Girvanella during the Late Devonian F-F transition in Guilin, South China

The abundance curves derived from area proportions of brachiopods and Girvanella in the thin sections from the Yangdi section, South China, exhibits complex relationships during the Late Devonian Frasnian-Famennian transition. The living activity of brachiopods such as grazing and borrowing did great damage to the growth of Girvanella. However, there was more to just a mere a survival competing relationship between them, Girvanella actually improved marine environments by oxygenating the dysoxic ambient sea-water through photosynthesis in the lower Kellwasser Horizon. Profited from this improvement brachiopods’ abundance increased subsequently and suppressed Girvanella again. Nonetheless, without Girvanella’s photosynthesis, brachiopods were wiped out by the farther anoxic environments in the upper Kellwasser Horizon. The complex relationships between Girvanella and brachiopods may be a key to unlocking the relationships between geomicrobes and metazoans in the geological overturn periods. Supported by NSFC Innovation Research Group Program (Grant No. 40621002), MOE Innovative Research Team Program (Grant No. IRT0546), the National Natural Science Foundation of China (Grant Nos. 40472020, 40730209, 40802005 and 40872001) and SINOPEC Project (Grant No. G0800-06-ZS-319)     

Pioneer organisms after F-F mass extinction in Dushan region, Guizhou Province, and their significance in establishing new ecosystem

After bio-mass extinction, the ecosystems in most areas were damaged seriously and may become an “ecologically barren area” lacking or even without ecosystems. To know what the pioneer organisms would be and their development, and to trace the es- tablishment process of the ecosystems are of great importance for the study of the biological evolution and recovery in aftermath. As one of the “big five” mass extinctions in the geological history, the Late Devonian Frasnian-Famennian (F-F) e…     

Coupling relationships between brachiopods and Girvanella during the Late Devonian F-F transition in Guilin, South China

The abundance curves derived from area proportions of brachiopods and Girvanella in the thin sections from the Yangdi section, South China, exhibits complex relationships during the Late Devonian Frasnian-Famennian transition. The living activity of brachiopods such as grazing and borrowing did great damage to the growth of Girvanella. However, there was more to just a mere a survival competing relationship between them, Girvanella actually improved marine environments by oxygenating the dysoxic ambient sea-water through photosynthesis in the lower Kellwasser Horizon. Profited from this improvement brachiopods' abundance increased subsequently and suppressed Girvanella again. Nonetheless, without Girvanella's photosynthesis, brachiopods were wiped out by the farther anoxic environments in the upper Kellwasser Horizon. The complex relationships between Girvanella and brachiopods may be a key to unlocking the relationships between geomicrobes and metazoans in the geological overturn periods.