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Calcified Rivulariaceans from the Ordovician of the Tarim Basin

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Calcified Rivulariaceans from the Ordovician of the Tarim Basin Palaeogeography, Palaeoclimatology, Palaeoecology 448 (2016) 371–381 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Calcified rivulariaceans from the Ordovician of the Tarim Basin, Northwest China, Phanerozoic lagoonal examples, and possible controlling factors Lijing Liu a, Yasheng Wu a,⁎, Jiang Hongxia a,RobertRidingb a Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China b Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA article info abstract Article history: A distinctive association of rivulariacean-like calcified microfossils is recognized in back-reef lagoon facies on the Received 21 June 2015 Bachu-Tazhong Platform in the Lianglitag Formation (Katian Stage, Upper Ordovician) of the Tarim Basin, based Received in revised form 19 August 2015 on investigation of 4500 thin sections from 35 well drill cores. The genera include Hedstroemia, Ortonella, Accepted 25 August 2015 Zonotrichites, Cayeuxia, and Garwoodia, most of which have features comparable with present-day calcified Available online 16 September 2015 cyanobacteria such as Rivularia, Calothrix and Dichothrix (Rivulariaceae, Nostocales). A similar association is pres- Keywords: ent in lagoonal and other restricted nearshore shallow-marine carbonate environments during much of the Pa- Calcified cyanobacteria leozoic and Mesozoic. This suggests the sustained presence of a rivulariacean-dominated cyanobacterial Lagoon association characteristic of back-reef/lagoonal environments. At the present-day, uncalcified Rivularia, Calothrix N2-fixation and Dichothrix remain common in back-reef, lagoon, mangrove-swamp, rocky shore, salt-marsh, and saline lake Phanerozoic environments. The ability of these cyanobacteria to grow in environments low in inorganic nitrate and phosphate Phosphate could help to explain this distribution. Cenozoic decline in marine calcified rivulariaceans is attributed to global Rivulariaceae reduction of seawater carbonate saturation state. The Phanerozoic record of calcified rivulariacean cyanobacteria appears to sensitively reflect long-term variations in the carbonate and nutrient chemistry of marine environments. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Examination of well-preserved ~450 Ma calcified cyanobacteria from the Katian (Late Ordovician) of the Tarim Basin revealed an associ- Cyanobacteria have a soft body-fossil record of at least ~1900 Ma ation of the genera Hedstroemia, Ortonella, Cayeuxia, Zonotrichites and (Hofmann, 1976) and possibly much earlier (Schopf, 2006), and are Garwoodia in back-reef lagoon facies of the Bachu-Tazhong Platform. widely assumed to have been extant when signs of oxygenation ap- Cayeuxia and Zonotrichites are common in similar environments in the peared ~3000 Ma ago (Buick, 2008). Some cyanobacteria can stimulate Jurassic and Cretaceous (Riding, 1991a). Similarly, Hedstroemia, CaCO3 precipitation within or upon their sheath by photosynthetic up- Ortonella and Garwoodia occur in restricted and semi-restricted envi- take of inorganic carbon (Pentecost and Riding, 1986; Merz, 1992), ronments in the Paleozoic (Mamet, 1991). These genera, particularly and this calcification can produce filamentous microfossils (Riding, Hedstroemia, Cayeuxia, Ortonella and Zonotrichites, resemble extant 2012) that date back at least ~1200 Ma (Kah and Riding, 2007)and cyanobacteria such as the rivulariaceans Rivularia, Calothrix and probably ~2500 Ma (Klein et al., 1987). Marine calcified cyanobacteria Dichothrix. Here we suggest that this persistent association of genera are locally common during the Paleozoic and Mesozoic (Konhauser in Paleozoic-Mesozoic marine carbonate back-reef/lagoonal environ- and Riding, 2012) and played important sedimentological roles in build- ments in part reflects the ability of rivulariaceans to cope with nitrogen ing reefs, stromatolite and thrombolites, as well as in producing finer- and phosphate limitation. The decline in calcification of these organisms grained and fragmentary material (Riding, 1991a; Flügel, 2004). in marine environments during the Cenozoic could reflect progressive long-term reduction in seawater carbonate saturation state. We support our data from Ordovician Rivularia-like calcified fossils in China with a global review of their occurrence during the remainder of the Phanero- ⁎ Corresponding author at: No.19, Beitucheng Western Road, Chaoyang District, fi 100029, Beijng, P.R. China. Tel.:+1 8613241929326. zoic. This suggests that calci ed rivulariaceans and accompanying taxa E-mail address: [email protected] (Y. Wu). constitute a long-lived Phanerozoic association typical of protected http://dx.doi.org/10.1016/j.palaeo.2015.08.034 0031-0182/© 2015 Elsevier B.V. All rights reserved. 372 L. Liu et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 448 (2016) 371–381 shallow-marine environments that can be linked to seawater, including with argillaceous limestone (Feng et al., 2007; Zhang et al., 2007; Cai nutrient, composition. This new insight into the paleoecology of these and Li, 2008; Yang et al., 2011). organisms could assist the environmental interpretation of ancient plat- The Lianglitag Formation contains the conodonts Yaoxianognathus form interiors. yaoxianensis, Belodina confluens,andBaltoniodus alobatus, and is attrib- uted to the Katian Stage (Li et al., 2009). Based on lithological and paleo- 2. Geological setting biological data, the Lianglitag Formation can be divided into three members from bottom to top: (1) argillaceous limestone (50-550 m), The Tarim Basin in Xinjiang Province is bordered by the Kunlun, consisting of dark micrite and grainstone, interbedded with irregular si- Altun, Tianshan and Kuluketake mountains (Fig. 1). Precambrian, Paleo- liceous mudstone; (2) grainstone (50-150 m), dominated by grainstone zoic and Mesozoic rocks occur around the margins of this extensive de- and reef limestone; and (3) argillaceous-striped limestone (20-100 m), sert basin, which is up to 500 km wide and over 1000 km in length. The composed of micrite interbedded with striped mudstone, and some underlying Tarim Block consists of pre-Neoproterozoic basement, a late grainstone and reef limestone (Yang et al., 2000; Yang et al., 2010). Neoproterozoic to Early Permian marine succession, and Late Permian- This succession has been divided into three depositional sequences Quaternary continental facies (Jia, 1997). It experienced several stages (Gao et al., 2014). During the SQ1 and SQ2 stages (Early to Middle of tectonic development that show both similarities and differences Katian), the Bachu-Tazhong platform was a rimmed carbonate platform. from those of North and South China (Zhang et al., 2012), and can be di- Reef limestones, built by corals, stromatoporoids, and calcareous algae, vided into a number of subunits (Fig. 1; Jia et al., 1995). characterized the southern and northern margins of the Bachu- Current reconstructions locate the Tarim Block at low latitudes Tazhong Platform (Gu et al., 2005; Cai et al., 2008; Li et al., 2009; throughout the Ordovician (Cocks and Torsvik, 2002; Webby, 2002) Wang et al., 2009; Yang et al., 2010; Wang et al., 2013; Gao et al., when extensive carbonate platforms developed on the Tazhong and 2014; Zhang et al., 2014, 2015). Mainly wackestone and lime mudstone Bachu uplifts, as revealed by outcrop, well and seismic data (Fig. 1C, occur in the interior, indicating a restricted platform, including tidal flat Feng et al., 2007; Zhao et al., 2009). These 2 to 6 km thick carbonate plat- and lagoon facies (Fig. 2A, B; Yang et al., 2010; Gao et al., 2014). During forms been penetrated by 35 drilling wells that provide the samples for the SQ3 Stage (Late Katian), the Bachu-Tazhong Platform became more our research (Fig. 1). They include the lower part of the Lower Ordovi- open and appeared to have lost its reef-margins (Fig. 2C; Gao et al., cian, and middle and upper parts of the Upper Ordovician. Most of the 2014). Middle Ordovician and the lower Upper Ordovician have been removed Previous research revealed numerous calcimicrobes preserved in the by erosion. The Upper Ordovician in the Bachu-Tazhong Platform is Lianglitag Formation. Of these, Girvanella, Subtifloria, Razumovskia, largely represented by two formations: the Lianglitag and Sangtamu. Acuasiphonoria, Hedstroemia, Cayeuxia, Bija, Apophoretella, Ortonella, The Sangtamu Formation is mainly a mixed terrigenous clastic and car- Zonotrichites and Bevocastria are regarded as cyanobacteria, Proaulopora, bonate deposit of greenish sandy argillaceous mudstone interbedded Phacelophyton and Gomphosiphon as probable cyanobacteria, and Renalcis, Fig. 1. A. Location of the Tarim Basin. B. Tectonic/depositional divisions. C. Locations of wells in this study. L. Liu et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 448 (2016) 371–381 373 Fig. 2. Lithofacies paleogeography of the Bachu-Tazhong platform during Katian Stage (Late Ordovician) Lianglitag Formation deposition (modified from Zhang et al., 2007; Feng et al., 2007; He et al., 2007; Zhao et al., 2009; Lin et al., 2011; Gao et al., 2014). Izhella, Wetheredella, Rothpletzella and Garwoodia are classed as Formation in these areas. The thin sections were investigated using Microproblematica (Riding and Fan, 2001; Liu et al., 2011, 2015). Paleo- transmitted light microscopy and microphotography (see Liu et al., ecological distributions of these calcimicrobes
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