See discussions, stats, and author profiles for this publication at: https://ww

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/255884005 Evolution of the Paleocene-Early Eocene larger benthic foraminifera in the Tethyan Himalaya of Tibet, China Article in International Journal of Earth Sciences · July 2013 DOI: 10.1007/s00531-012-0856-2 CITATIONS 12 READS 385 3 authors: Qinghai Zhang Universität Bremen 9 PUBLICATIONS 186 CITATIONS SEE PROFILE Helmut Willems Universität Bremen 124 PUBLICATIONS 2,041 CITATIONS SEE PROFILE Lin Ding Chinese Academy of Sciences 186 PUBLICATIONS 6,335 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately. Available from: Qinghai Zhang Retrieved on: 05 September 2016 ORIGINAL PAPER Evolution of the Paleocene-Early Eocene larger benthic foraminifera in the Tethyan Himalaya of Tibet, China Qinghai Zhang • Helmut Willems • Lin Ding Received: 11 April 2012 / Accepted: 30 November 2012  Springer-Verlag Berlin Heidelberg 2013 Abstract The Paleocene-Early Eocene larger benthic foraminifera (LBF) in the far eastern Neo-Tethyan Ocean of Tibet still remain poorly known. Here, we present a novel, high-resolution larger foraminiferal biozonation from the shallow-water limestones in Tibet, which will improve our current understanding of the larger forami- niferal evolution in the eastern Neo-Tethyan Ocean. Based on one continuous section at Tingri and three separate sections at Gamba, ten Shallow Benthic Zones (SBZ 1–10) have been designated in Tibet by following the principle of Oppel Zone. In contrast to those in Europe, the Paleocene LBFs in Tibet are characterized by high diversification of Lockhartia, Kathina, Daviesina, Mis- cellanea, Ranikothalia, and Operculina and show pro- gressively increasing diversity of genera and species during SBZ 2–5. Adult dimorphism and large shell size of some LBFs as well as differentiation of the diversity between genera and species initiated as early as SBZ 3. It suggests that the occurrence of the Larger Foraminifera Turnover (LFT) was probably not synchronous in the entire Neo-Tethyan Ocean, because in Europe, the LFT was generally thought to occur at the beginning of SBZ 5. During the Early Eocene, the LBFs in Tibet decreased markedly on the generic level and increased on the spe- cies level, and some new genera (Alveolina, Orbitolites, Nummulites, Assilina, Discocyclina) have gained pre- dominance in Tibet. It is nearly identical to the evolution of the LBFs in Europe and indicates a high-degree homogenization of the LBFs in the entire Neo-Tethyan Ocean. Furthermore, the Paleocene-Eocene (P-E) bound- ary in shallow-water environments has been clearly identified by us, and it is situated in the upper part of SBZ 5 and associated with no evident biotic turnover of shal- low benthic foraminiferal communities. The possible di- achroneity of the LFT in the Neo-Tethyan Ocean and the evident lagging of the Paleocene-Eocene Thermal Maxi- mum (PETM) behind the LFT imply that the LFT could only be the result of a natural evolutionary process and has no linkage with the PETM. Notably, a transient but distinct larger foraminiferal extinction and origination (LFEO) event has been found in Tibet, which is charac- terized by a sudden disappearance of all Paleocene lamellar-perforate LBFs, such as Lockhartia, Kathina, Daviesina, Miscellanea, Ranikothalia, and Operculina, and the initial dominance of the Early Eocene porcella- neous-walled Alveolina. The LFEO marks the boundary between SBZ 5 and 6, and might only occur in the low- latitude areas of the Neo-Tethyan Ocean. Surprisingly, the LFEO coincides with the initial recovery of the Carbon Isotope Excursion (CIE), and their synchronicity implies that some possible mechanisms causing the rapid recovery of the CIE probably had also led to the LFEO in the shallow-water environments. Keywords Tibet  SBZ  Larger foraminiferal turnover  PETM  CIE  P-E boundary  Larger foraminiferal extinction and origination Q. Zhang (&)  H. Willems Department of Geosciences, University of Bremen, 28359 Bremen, Germany e-mail: zhang@uni-bremen.de Q. Zhang  L. Ding Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China H. Willems Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China 123 Int J Earth Sci (Geol Rundsch) DOI 10.1007/s00531-012-0856-2 Introduction Based mainly on the detailed studies of the Early Paleo- gene alveolinids and nummulitids by Hottinger (1960) and Schaub (1981), 20 Shallow Benthic Zones (SBZs) (Serra- Kiel et al. 1998) have been recognized for the Paleocene and Eocene interval in the Neo-Tethyan realm. These SBZs have been used successfully to construct high-resolution biostratigraphy in shallow-water environments, where the Larger Benthic Foraminifera (LBF) once dominated in the Paleocene and Eocene (Scheibner et al. 2005; Drobne et al. 2011). However, the work by Hottinger (1960) and Schaub (1981) was mainly conducted in the western Neo-Tethyan Ocean of Europe and the Mediterranean area. Direct application of the SBZs in the eastern Neo-Tethyan Ocean and regionally stratigraphic correlations between Europe and Asia still remain, to some extent, ambiguous in the shallow-water environments. Owing to high diversity of the Paleocene Lockhartia from the Ranikot and Lockhart formations in the Indus basin, the eastern Neo-Tethyan Ocean was once named ‘‘Ranikot Sea’’ (Davies 1938) or ‘‘Lockhartia Sea’’ (Hott- inger 1998). Geographically, the Lockhartia Sea covers a huge area at least from Tibet in the east to the Persian Gulf in the west (Davies 1938). After a preliminary investigation on Alveolina from Pakistan, Hottinger (1971) came to the conclusion that ‘‘the larger foraminifera contained in these Far Eastern shallow-water formations are similar to but not identical with Mediterranean assemblages.’’ In the last 20 years, progresses on larger foraminiferal biostratigraphy have been achieved in India and Pakistan by Butt (1991), Weiss (1993), Jauhri (1996, 1998), Ferra `ndez-Can ˜adell (2002), and Sameeni and Butt (2004), and rough SBZs following the ones in Europe have been tentatively built in the Indus Basin (Afzal et al. 2010). Compared with India and Pakistan, Tibet was paleo- geographically located in the easternmost Neo-Tethyan Ocean and consequently provides a unique chance to study the Early Paleogene LBFs in the east. Although systematic descriptions of the LBFs in Tibet have been reported in the last four decades (He et al. 1976; Zhang 1988; Wan 1990, 1991), a detailed biostratigraphic work following the concept of the SBZs is still missing. Therefore, further investigations on the Paleocene and Eocene LBFs in Tibet can not only improve our understanding of the larger foraminiferal evolution in the east, but also extend the SBZs in the entire Neo-Tethyan Ocean. This paper presents a first-hand, detailed study of the Paleocene to Early Eocene LBFs in Tibet and shows their high genera and species diversity in the eastern Neo- Tethyan Ocean. Our results indicate that the Paleocene LBFs might evolve earlier in the east than those in the west, and the occurrence of the Larger Foraminifera Turnover (LFT) was probably not synchronous in the entire Neo-Tethyan Ocean. Besides, a larger foraminiferal extinc- tion and origination (LFEO) event is firstly found by us, which occurred at the boundary of SBZ 5 and 6 and coincided with the initial recovery of the carbon isotope excursion (CIE). More importantly, based on high-resolution carbon isotopic variations, the Paleocene-Eocene (P-E) boundary in Tibet is placed in the upper part of SBZ 5 by us, which conflicts with the opinion that the P-E boundary was located at the boundary between SBZ 4 and 5 (Orue-Etxebarria et al. 2001; Scheibner et al. 2005; Pujalte et al. 2009a, b; Scheibner and Speijer 2009), but is in agreement with time intervals for the P-E boundary recommended by Serra-Kiel et al. (1998) and Hottinger (2001). Geologic setting and lithostratigraphy The Tethyan Himalaya of Tibet is bounded to the Lhasa terrane by the Indus-Yarlung Zangbo Suture (IYS) to the north, and neighbors on the High Himalaya Crystalline sequences by the South Tibet Detachment System (STDS) to the south (Yin and Harrison 2000) (Fig. 1). After the Lhasa terrane rifted from Gondwana supercontinent at the Triassic (Liu and Einsele 1994), the Tethyan Himalaya persisted at the northernmost Indian continent, representing a passive continental margin environment until the end of the Paleocene (Zhang et al. 2012). Paleozoic to Cretaceous marine sedimentary strata are widely exposed within the Tethyan Himalaya, whereas the Paleocene-Lower Eocene shallow-water limestones crop out mainly in the Gamba and Tingri areas of the southern Tethyan Himalaya. At Gamba and Tingri, the Paleocene limestones are rich in LBFs andhave been interpreted torepresenta carbonateramp on the Indian passive continental margin (Willems 1993, 1996). At the P-E boundary, the India–Asia continental col- lision caused the flexure of the northern Indian continental marginandformed theinitial development ofa forelandbasin on the Tethyan Himalaya (Zhang et al. 2012). Subsequently, owing to the maintenance of a tectonic-induced uplift at Gamba and Tingri, the LBFs still highly thrived in these areas until the end of the Ilerdian (i.e., Early Ypresian). At the beginning of the Cuisian (i.e., Late Ypresian), southward migration of the foreland basin and arrival of a foredeep de- pozone to Gamba and Tingri resulted in a deepening of depositional environments, which drowned the Early Eocene carbonate ramp and terminated the Paleocene-Early Eocene largerforaminiferalevolution in the areas (Zhanget al.2012). Lithologically, the Paleocene-Lower Eocene foraminif- era-bearing limestones are uploads/Geographie/ zhang-et-al-2013.pdf

• Détails
• Publié le Dec 19, 2021
• Catégorie Geography / Geogra...
• Langue French
• Taille du fichier 3.5425MB