南疆塔里木板块北部轮南油田在上奥陶统良里塔格组沉积期显示大致由东向西加深的陆表海缓坡地貌, 19口钻井岩芯灰岩中可鉴定出钙质微生物Renalcis、Girvanella、Wetheredella、Garwoodia、Phacelophyton yushanensis、Hedstroemia?和Halysis; 钙藻类Vermiporella、Dasyporella、Plexavaria和Solenopora; 后生动物类型含海绵、珊瑚、苔藓虫、三叶虫、腕足动物、棘皮动物、腹足类、介形类等。不同钻井之间的古生态地层单元对比显示生物礁和灰泥丘主要发育于轮南油田西部井区, 而东部井区则多为台内碎屑滩相沉积; 海底地貌差异, 特别是向西水深加大可视为控制轮南油田良里塔格组生态组合展布的主要因素。

Ordovician carbonate deposits in the Tarim Block are considered as key targets for oil-gas explorations. Limestones of the Upper Ordovician Lianglitag Formation in Lunnan Oil Field, Tabei Uplift of northern Tarim Block, are considered to be economically significant reservoirs. The present paper demonstrates biotic and taphonomic features of the limestones in drill cores of 19 wells from Lunnan Oil Field. Index profiles of grain size, sorting and rounding, as well as grain/matrix ratio, are comprehensively described for ecological unit divisions in individual wells; palaeoecological correlations between the wells are outlined. The limestone-dominated sequences of the Lianglitag Formation were deposited on a westward deepening ramp in an epicontinental sea setting, in which high-clarity water and warm and shallow marine-floor were favorable for the thriving of the benthic biota. Intraclasts with diverse components and fabrics were identified under a polarizing microscope; abundant non-skeletal grains and fossils were also examined. Biotic structures are composed of calcimicrobes of Renalcis, Girvanella, Wetheredella，Garwoodia，Phacelophyton yushanensis，Hedstroemia and Halysis; calcareous algae of Vermiporella, Dasyporella, Dimorphosiphon, Plexavaria, Solenopora; metazoans of sponges, corals, bryozoa, trilobites, brachiopods, echinodermata, gastropods, ostracoda and others. Bioclasts are the key components in these limestones. With respect to lithological categories, the limestones are grouped into three microfacies types:Type 1 represents reefal units distinguished by coarse autochthonous bindstones and bafflestones in many wells. Bindstones, dominated by microbial and calcareous algal (e.g., Verminporella, Hedstroemia) fabrics binding peloids, bioclasts and intraclasts, are more common. Stomatopora-algal frameworks occur sparsely in several drill cores. The reefal units are mostly several meters in thickness and low relief morphology. Calcimicrobial forms and calcareous algae are notable components in most reef-building units. Calcimicrobes and calcareous algal taxa are concentrated in the reefal units of the Lunnan Oil Field, indicating that the reefs formed a special ecosystem comparing with global equivalent analogues, which are mostly dominated by diverse metazoans.Type 2 comprises either peloidal or bioclastic grain to packstones, indicating a medium to high turbulent environment. Reworked bioclastic and peloidal grains are abundant, medium to well sorted, therefore, indicating some transportation. Type 3 consists of micritic limestones in several drill cores, indicating a relatively narrow, calm and deeper-water belt. Sparse and fine-sized bioclasts are less than 10% of the rock components. Correlations of the lithological units between well blocks allow reconstruction of temporal and spatial distribution patterns of the Lunnan carbonate platform. Depth changes with deepening towards the west (thus open sea) are considered to have had a key control in configuration of the ecological associations. A western-sloping ramp was thus optimized for reef occurrence. Intra-platform environments in the eastern wells are dominated by diverse intra-clastic banks.

国家自然科学基金(41702028)资助