塔里木盆地晚奥陶世生物礁中钙质微生物古生态对比研究

Calcimicrobes include calcified cyanobacteria fossils and associated calcareous microfossils. A dramatic event occurs during Late Mid-Ordovician with the changeover from microbial-dominated to metazoan and algal-dominated reefs. It is widely suggested that the abundance of reefal calcimicrobes and their roles in reef building significantly declined. However, the current preliminary researches show that the diversity of calcimicrobes in metazoan and algal-dominated reefs is abundant. The Late Ordovician Lianglitag Formation developed many kinds of metazoan and algal-dominated reefs, which contains abundant calcimicrobes. Basing on high research degree of systematic paleontology of these calcimicrobes, comparative study on paleoecology of calcimicrobes in metazoan and algal-dominated reefs of the Late Ordovician Lianglitag Formation will be carried on. Study materials are from reefs in the standard section of the Lianglitag Formation in Bachu area and reef limestones in drilling cores of 18 wells scattered in margin of the Bachu-Tazhong and inner Tabei platforms. Basing on comprehensive researches on paleontology, sedimentology and paleoecology, the diversity, roles in reef building, and paleoecology characteristics of calcimicrobes in metazoan and algal-dominated reefs will be analyzed and compared. This study will greatly improve our recognition on diversity, roles in reef building of calcimicrobes in metazoan and algal-dominated reefs and ecosystem structure of different metazoan and algal-dominated reefs.

钙质微生物包括钙化蓝细菌化石和与其相关的疑问钙质微体化石。晚中奥陶世之后生物礁由微生物为主转变为后生动物和藻类为主导。一般认为之后礁相的钙质微生物丰度大量减少，造礁作用显著降低。然而目前初步研究揭示出后生动物礁和藻礁中钙质微生物类型很丰富，只是研究不充分。塔里木盆地晚奥陶世良里塔格组发育多种后生动物礁和藻礁，并且含有丰富的钙质微生物化石。这些钙质微生物化石已有较高的系统古生物学研究的基础，故拟开展良里塔格组不同后生动物礁和藻礁中钙质微生物的古生态对比研究。将结合巴楚地区良里塔格组标准剖面生物礁, 巴楚-塔中台地边缘及塔北内部18口井下良里塔格组生物礁岩心，运用古生物学、沉积学和古生态学综合研究对各种类型生物礁群落中的钙质微生物进行多样性、造礁作用及钙质微生物组合对比研究。有望极大地提高晚奥陶世后生动物礁和藻礁中钙质微生物的多样性、造礁作用及不同后生动物礁和藻礁生态系统结构的认识。

晚中奥陶世之后生物礁由微生物为主导转变为以后生动物和藻类为主导。一般认为钙质微生物在后生动物和藻礁中丰度大量减少，在生态系统中处于次要地位。本项目通过巴楚地区晚奥陶世良里塔格组标准剖面生物礁, 巴楚-塔中台地边缘及塔北内部18口井下良里塔格组生物礁岩心，运用古生物学、沉积学和古生态学综合研究，对各种类型生物礁群落中的钙质微生物多样性、造礁作用及生态作用进行了对比研究。. 研究揭示出良里塔格组共发育四种生物礁类型，分别为钙质红藻礁、层孔虫礁、珊瑚礁和微生物-钙质绿藻礁。红藻礁、层孔虫礁中发育Wetheredella-Rothpletzella组合；珊瑚礁中发育 Acuasiphonoria-Proaulopora组合；钙质微生物-钙质绿藻礁中发育Renalcis–Phacelophyton 组合。红藻礁和层孔礁中只含有很少的非固氮颤菌目蓝细菌Girvanella，几乎未见固氮蓝细菌。这很可能表明层孔虫礁是发育在贫营养的环境中，而蓝细菌在与红藻对N、P营养盐吸收竞争中处于劣势地位。珊瑚礁中不仅含有一些非固氮蓝细菌Girvanella、Acuasiphonoria而且含有较多种类的固氮蓝细菌Proaulopora、 Gomphosiphon、 Apophoretella、 Bija，说明是N、P营养盐水平中等的环境，进一步表明蓝细菌在珊瑚礁的发育中起着重要的生态作用。绿藻礁中包含大量的非固氮蓝细菌Girvanella、Acuasiphonoria和Razumovskia，和固氮蓝细菌Phacelophyton和Gomphosiphon，说明是高N、P营养盐水平的环境，此推断得到了其中富含的泥质的支持。这很可能说明钙质绿藻礁的形成需要高N、P营养盐的支持。. 本研究首次揭示出了塔里木盆地晚奥陶世不同类型后生动物礁和藻礁的营养盐水平，尤其揭示出蓝细菌在晚奥陶世珊瑚礁和绿藻礁中扮演着重要的造礁作用和生态作用。这一研究成果对奥陶纪及其他时代生物礁生态系统演化都具有重要的科学意义。