Paleoenvironmental implications of an extensive maceriate microbialite bed in the Furongian Chaomidian Formation, Shandong Province, China Jeong-Hyun Lee a , Jitao Chen a,b , S.K. Chough a, ⁎ a School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Republic of Korea b College of Geological Science and Engineering, Shandong University of Science and Technology, Qingdao 266510, China abstract article info Article history: Received 2 March 2010 Received in revised form 11 September 2010 Accepted 14 September 2010 Available online 18 September 2010 Keywords: Microbialite Maceria structure Paleoenvironment Furongian North China Platform This study focuses on the unique occurrence of an extensive microbialite bed (10–20 m thick) in the Chaomidian Formation (Furongian) in Shandong Province, China in order to understand its paleoenviron- mental implications. The microbialite bed can be traced for over 6000 km 2 in area. The microbialites are characterized by centimeter- to decimeter-scale branching maze-like constituents (maceriae) of microbial and muddy sediments with chaotic texture, including tabular maceriate microbialite (type 1), columnar maceriate microbialite (type 2), and columnar chaotic microbialite (type 3). Within the bed, each microbialite unit is generally well correlated for tens of kilometers. The entire bed is bounded by limestone–marlstone alternation at the base, and an erosional surface at the top that is subsequently overlain by a grainstone bed of various thicknesses. The microbialite bed formed when the seafloor reached suitable water depth for the microbial growth during sea-level rise accompanied with carbonate production. The maze-like maceria structures formed to acquire a larger surface area under a relatively large input of lime mud. The tabular maceriate microbialites initially formed in relatively deep-water environments and flourished on broad and flat seafloor, whereas the columnar microbialites (types 2 and 3) developed under the influence of strong waves and currents. The microbialite bed was eroded and terminated by frequent storm events and buried under the reworked grainstone. Further rise in sea level and increased metazoan activities afterwards limited the resurgence of microbes in the late Furongian. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Microbialites are organosedimentary deposits formed by benthic microbial communities which trap detrital sediments and/or induce mineral precipitation (Burne and Moore, 1987; Riding, 2000). Microbialites prevailed in the Middle Cambrian to Furongian after the extinction of archaeocyatha and dwindled in the Ordovician with the appearance of corals, sponges, and stromatoporoids (Riding and Liang, 2005; Riding, 2006). In the North China Platform, deposition of microbialites initiated in the middle Early Cambrian (Zhushadong and Mantou formations) and prevailed during the middle to late Middle Cambrian (Zhangxia Formation) (Chough et al., 2010). After the platform drowning in the late Middle Cambrian (Gushan Formation), microbialites significantly dwindled (Chough et al., 2010). The primary purpose of this study is to describe a thick biostromal microbialite bed (10–20 m thick) with branching maze-like struc- tures (maceriae) in the middle part of the Chaomidian Formation (Furongian), Shandong Province, China (Fig. 1). The bed can be traced over 100 km, about 6000 km 2 in area. This microbialite bed is unique, because it extensively occurs in the middle of the dwindling stage of microbial growth after the platform drowning. How did microbes thrive on the seafloor during continued rise in sea level? What caused the termination of the microbialite without significant resurgence? How did the maceria structures originate? In order to answer these questions, the present study focuses on the characteristics of the microbialite internal structures and the associated sedimentary facies in well-exposed outcrop sections in Shandong Province. 2. Geological setting The North China Platform formed on a stable craton, the Sino- Korean Block. It comprises an extensive area of ~1500 km east–west and ~ 1000 km north–south (Meyerhoff et al., 1991)(Fig. 1A). The western boundary of the platform is characterized by a thick sequence of platform-margin and deep-basinal sediments. The northern, southern, and eastern margins are bounded by major folds and suture zones (the Hinggan fold belt, the Dabieshan belt, and the Tanlu fault, respectively) (Fig. 1A). Sedimentation in the North China Platform initiated in the Early Cambrian and lasted until the Early Ordovician, when the entire platform was subaerially exposed (Meyerhoff et al., 1991; Meng et al., 1997). Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 621–632 ⁎ Corresponding author. E-mail address: sedlab@snu.ac.kr (S.K. Chough). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.09.012 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo