| Foraminifera are unicellular protists and major micro-organisms in the marine and ocean environments, which derive from the early Cambrian and have been surviving so far. They have wide geological distribution and habitat from nearly all kinds of ocean niche, such as shallow water, estuaries, slope, and deep ocean, etc. A great amount of foraminiferal fossils had been found in the sediments during the geological history. Because faunal composition, ultrastructure of the wall, test shape, are very sensitive to the environmental factors, foraminifera have long been a useful tool for the reconstruction of paleoclimate and paleoenvironment. Especially, they have been widely used in the studies of mass extinctions and recoveries during the significant turnover interval in geological history. The Permo-Triassic mass extinction was the greatest mass extinction in the Phanerozoic and an important evolutionary stagefrom Paleozoic to Mesozoic. The foraminiferal fauna had a great transition during this crisis, and the learning on their taxon, evolution and paleoecology had implied many important clues declaring the extreme crisis on the earth. However, the Late Permian foraminiferal fauna in deep water were little known. This study will help to comprehensively understand the foraminiferal evolution during the significant geological interval.The present dissertation focussed on the deep water foraminiferal fauna of Late Permian in South China. Based on abundant free tests, well oriented thin section had been made for identification. The Micro-CT Scanning and 3D Model Rending technology are also used for the taxonomic study. A phylogenetic tree of the Family Genitzinidae was built based on the morphology characters of the test, and implied for the Geinitzinidae evolution. Finally, according to the test shape, life behaviour and feeding strategy analysis,10 foraminiferal morphogroups were defined, which were furtherly discussed for their relationship with paleoecology.There were seven deep water section of Late Permian in South China studied in this dissertation, including the Dongpan section, Liuqiao section, Xinmin section, Ma’anyin section in Qian-Gui basin, which located in the southwestern margin of the Yountze block; the Tianqiao section, Daxiakou section at the north of Middle Yangtze block, and the Pingdingshan section from Chaohu in the Lower Yangtze basin. The foraminiferal taxonomy was carried out as the preliminary work. In total, there are 37 genera and 78 species identified herein. Among them,23 species are new or revised, including Nodosaria quinquecostata sp. nov., Pseudolangella minuta sp. nov., Lingulonodosaria changxingensis sp. nov., Xintania minuta sp. nov., Pachyphloides acutus sp. nov., Tristx guizhouensis sp. nov., Pseudotristix elongata sp. nov., Geinitzinita strigata (Wang 1976), Geinitzinita kongdongshanensis (Zhang and Hong 2004), Geinitzinita bandongensis sp. nov., Geinitzinita elongata sp. nov., Lunucammina subtriangula sp. nov., Ichthyolaria ornata (Miklukho-Maklay 1954), Ichthyolaria guizhouensis sp. nov., Ichthyolaria xianxiensis sp. nov., Ichthyolaria celsa sp. nov., Ichthyolaria optima sp. nov., Howchinella chaohuensis sp. nov., Howchinella hubeiensis sp. nov., Howchinella inflata sp. nov., Howchinella complanata sp. nov., Ichthyofrondina latilimbata (Sellier de Civrieux and Dessauvagie 1965), Frondina paraovata sp. nov.The recognized foraminiferal fauna in late Permian of South China has its own unique identity in the generic and species diversity, the abundance distribution, and dominated assemblage:1. Lower diversity and abundance. The generic diversity in each single section is low, with about 10-20 genera in each in each section. However, the species diversity in each genus is extremely low, which is significantly different from the shallow water environment. And also, the abundance is much less than the contemporary shallow water faunas.2. Taxonomy composition of the deep water foraminifera is typically with high proportion of nodosariids. This study indicates that the dominated assemblages of deep water foraminifera fauna in Late Permian of South China is the Order Nodosariida, mainly including families Geinitzinidae and Nodosariidae. The Geinitzinidae is the most abundant forms with the most individuals in the fauna. For the studied section, the species proportion of nodosariids is 69.6% in Dongpan,71.4% in Liuqiao,75% in Xinming,81.8% in Ma’anying,78.9% in Daxiakou,75.9% in Pingdingshan, and 83.9% in Tianqiao. The non-nodosariid forms are mainly Glomospira, Glomospirella, Lasiodiscus, Ammodiscus, whose test is built by second tuber chamber spiraling with the proloculus. They are relatively low in species diversity and species abundance, and occurred in all the studied sections.3. The dominated test morphology is small size, thin test wall, simple internal structure and flattened. The representative nodosariid foraminifera in deep water are those forms of Geinitzinidae which have flattened tests. Colaniella, Langella, Pachyphloia, Robuloides, Globivalvulina, which have bigger and stronger test, are rare or absent here. In this study, Geinitzinita、Howchinella、Ichthyolaria、Pachyphloides、Frondina are the most dominant genera, which always show a peak in some beds. These typical deep water forms with flattened tests have high surface area/volume ratios, which enhance their capacity in oxygen uptake from lower-oxygen bottom-water. Smaller forms have been thought to consume less oxygen than larger ones, then would be more successful in the oxygen depleted environments.4. Similar forms such as Howchinella, Lunucammina, and Ichthvolaria are also commonly present in cold water of higher latitudes, such as northern and western Gondwana, north Caucasus, Siberia, so the present fauna may be also linked to a cold water environment.5. The present fauna has similar forms with respect to the early Mesozoic foraminifera, such as Ichthyolaria, Howchinella, Geinitzinita, Pachyphloia, Austrocolomia, most of them possess the same overall test shape and internal structure. However, more work is needed to determine whether they are convergent or not.As representatives of deep water foraminifera, Geinitzinidae are thriving in Permian. However, most of them have traditionally classified based on non-oriented thin sections, which have caused much controversy. This study builds a phylogenetic tree based on the morphology characters shown on well preserved free specimens. The phylogenetic analysis show that Geinitzinidae may be separated by four clades:Geinitzina clade, Howchinella clade, Frondina clade. and Pachyphloia clade. The four clades mainly differ in the chamber growth features. The Geinitzina clad has low and wide chamber, without or with slightly embracement; the Frondina clade has higher chamber and slight embracement; the Howchinella clade has low chamber with moderate embracement, and Pachyphloia clade has very low and wide chamber with strongly embracement. This separation also reflects the different types of foraminiferal ontogeny, and may suggest these clades maybe originated from a common ancestor, and adopted different strategies as the environment changed. It supports the cladistics analysis on the evolution of test growth mode.According to the tree, Frondina, Geinitzina postcarbonica gr., Lingulonodosaria have closed phylogenetic relationship, whoes chambers are relatively high and without embracement. And their fossil records are the first occurrence in Upper Carboniferous-Lower Permian, or more earlier. The other two clades gave their origin and thriving since late Early Permian. It could be a lineage that the chamber growth in the evolution to more lower, compressed and strong embracement. This chamber growth strategy also indicates that during Permian, Geinitzinidae minimizes the distance between proloculus and the last aperture and to obtain some advantages for intracellular transportation.Foraminiferal morphogoup studies indicate that the deep water environment of South China is characterized by the predonimace of morphogroup M2c, M5b, M5c, M6. Among them, M5c is the most dominant. These forms are mainly flattened and elongated represented by Geinitzinia, Genitzinita, Howchinella, Ichthyolaria, etc., which favor for shallow infaunal to deep infaunal habitats. Their tests are always flattenedand small in size, sometimes latitudinal costae or ribs develope. These characters make them adapted to a deep water with low dissolved oxygen environment. Cylindrical forms such as M2b, M2c are second abundant, which includs Nodosaria, Pseudolangella, Lingulonodosaria, etc. Compare to shallow water, the M1, M2a, M4 group such as Langella, Colaniella, Climacammina, are extremely rare in deep water environments. The M6 group, which is composed of proloculus succeeded by tubular secondary chamber, such as Glomospira, Glomospirella, Ammodiscus, and Hermigordius etc., are of low abundance and are commonly appeared in all studied sections.The M6 group’s abundance vary with the primary productivity. They could be in favor of feeding on the planktonic detritus falling into the sediment surface. |
PDF Full Text Request