Palynology, 2014 http://dx.doi.org/10.1080/01916122.2014.961664
The Middle Jurassic palynology of the Daohugou area, Inner Mongolia, China, and its implications for palaeobiology and palaeogeography Yuling Naa,b,c, Steven R. Manchesterc, Chunlin Suna,b* and Shuqin Zhanga,b a Key Laboratory for Evolution of Past Life and Environment in Northeast Asia, Ministry of Education, Changchun 130026, Jilin, China; bResearch Center of Palaeontology and Stratigraphy, Jilin University, Changchun 130026, Jilin, China; cFlorida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA
Although abundant palaeontological discoveries have been documented in the Daohugou area in Chifeng City, Inner Mongolia, China, no record of the palynoflora has been reported previously. We collected palynological samples from the same level as megafossil plants, and conducted a detailed taxonomic analysis of the pollen and spores in order to augment the megafossil record, to extend documentation of the Middle Jurassic palynoflora, and to examine implications for palaeogeography, palaeoecology and palaeoclimate in north China during the Jurassic. Forty-four genera and 87 species of palynomorphs were identified. Pollen of gymnosperms dominates numerically, followed by spores of pteridophytes. Most taxa, including bisaccate pollen of conifers, monosulcate pollen of Cycadales, Bennettitales or Ginkgoales, along with Cyathidites, Deltoidospora, Granulatisporites, Osmundacidites and Classopollis, are common elements known elsewhere during the Jurassic. Based on comparisons with similar palyno-assemblages in the Jurassic of China, the age of the Daohugou locality is interpreted to be late Middle Jurassic. According to the palaeobotanical and palaeopalynological information, the Daohugou flora is attributed to the warm-temperate to medium temperate zone with seasonal change. By studying the ecological and climatic preferences of the main plant groups, five types of palaeolandscape in the Jurassic of Daohugou are proposed: (1) mesic upland (Pinaceae, Podocarpaceae, Czekanowskiales and Bennettitales), (2) mesic lowland (Pinaceae, Podocarpaceae, Ginkgoales, Czekanowskiales and Cycadales, together with some hygrophilous bryophytes, lycophytes and ferns), (3) dry upland (Czekanowskiales), (4) dry lowland (Czekanowskiales and Cheirolepidiaceae) and (5) waterside (plants growing along streams or near lakes, including bryophytes, lycophytes, ferns and probably some pteridosperms). According to the plant assemblage, the Daohugou flora corresponds to that of the Middle Jurassic Northern Floristic Province of China, which experienced a transition from a humid, warm climate to a hotter climate with seasonal drought. Keywords: palynology; palaeobiology; palaeogeography; Middle Jurassic; Daohugou; Inner Mongolia; China
1. Introduction Daohugou village in Ningcheng County, Chifeng City, Inner Mongolia, China, is located adjacent to the borders of Liaoning Province, Hebei Province and the Inner Mongolia Autonomous Region (Figure 1). Since the discovery of the salamander Jeholotriton (Wang 2000), this area has drawn increasing attention from palaeontologists. The Daohugou area has become a world-renowned palaeontological area widely recognized for its amazing discoveries, including fossil tadpoles (Yuan et al. 2004), dinosaurs (Zhang et al. 2002), pterosaurs (Ji & Yuan 2002), salamanders (Gao & Shubin 2003; Wang 2000), mammals (Ji et al. 2006; Meng et al. 2006), bivalves (Jiang 2006), crustaceans (Shen et al. 2003), insects (Chang et al. 2009; Engel & Ren 2008; Hao & Ren 2009; Huang et al. 2008; Kirejtshuk et al. 2010; Li & Ren 2009; Liu et al. 2012; Liu et al. 2013a; Liu et al. 2013b; Liu &
*Correponding author. Email:
[email protected] Ó 2014 AASP The Palynological Society
Ren 2008; Ren 2002; Ren et al. 2002; Ren & Yin 2003; Shi et al. 2011; Sun et al. 2007; Wang et al. 2002; Wang & Ren 2009; Zhang et al. 2008; Zhang 2013), plants (Heinrichs et al. 2014; Li et al. 2004; Pott et al. 2012; Zhang et al. 2011; Zhang et al. 2012; Zheng et al. 2003) and insect oviposition on fossil leaves (Na et al. 2014). No record of palynoflora has been published from the Daohugou area previously. In this paper, a detailed taxonomic analysis of palynomorphs from the Daohugou flora is presented, aimed at documentation of the pollen and spore assemblage, and comparison to the composition of megafossils from the same strata. This work is of importance for extending our understanding of the Daohugou fossil-bearing strata, and for the interpretation of palaeobiological and palaeogeographical conditions in this part of northern China during the Jurassic.
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Figure 1. Map showing fossil locality in the Daohugou area, Inner Mongolia, China.
2. Geological setting The palynological samples were collected from the Middle Jurassic Jiulongshan Formation at Daohugou village, Ningcheng County, Inner Mongolia, China (N41 180 3400 , E119 130 1500 ) (Figure 2). All the specimens were collected from the same stratigraphic level (with a thickness of 30 cm) of a single outcrop the same site from which megafossil plants of bryophytes, lycophytes, horsetails, ferns, cycads, ginkgoaleans, czekanowskialeans and conifers were collected by Dr. Chunlin Sun and some colleagues at Jilin University.
According to field observations, the Jiulongshan Formation consists mainly of lacustrine deposits, mostly containing tuffaceous conglomerate, grand conglomerate, siltstone, shale and mudstone. It unconformably overlies the Archean gneiss regionally, and underlies the volcanic rocks of the Tiaojishan Formation (Liu & Jin 2002; Ren et al. 2002; Figure 3). Radiometric dating of volcanic materials from the Tiaojishan Formation has supported a Bathonian age (164165 Ma, Chen et al. 2004; Liu et al. 2004; 168-152 Ma, Liu et al. 2006a; 164158 Ma, Liu et al. 2006b). Therefore, the minimum age of the Jiulongshan Formation
Figure 2. Photographs of the outcrop in the Daohugou area. A. The arrow indicates the volcanic rocks from the Tiaojishan Formation, the oval outline shows the outcrop where all samples were collected; B, C. Enlargement of the outcrop.
Palynology
Figure 3. Lithological column of the Middle Jurassic Jiulongshan Formation from the Daohugou area. Arrow indicates the horizon where the samples were collected.
underlying the Tiaojishan Formation should be the Bathonian. 3. Methods Seven samples were collected from the tuffaceous siltstone in the lower part of the Jiulongshan Formation.
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Two of the collected samples were treated according to a modified pollen preparation protocol following Traverse (1988). Eleven slides (Na004-1Na0045 and Na0071Na007-6) were prepared, and then observed with a light microscope (Nikon Eclipse E600). Photographs were taken through the same microscope with a Canon EOS Rebel XSi. Position coordinates on the slides are listed in the plate captions. Sometimes, successive images of the same grain were composited with Helicon Focus software to reconstruct surface features in focus. All the preparations and observations were done in the palaeobotanical laboratory of the Florida Museum of Natural History, University of Florida, Gainesville, FL, USA. All specimens and slides are deposited in the Research Center of Palaeontology and Stratigraphy, Jilin University, Changchun, Jilin, China. Quantitative data (percentage composition) are computed from counts of all grains (2093 in total) on prepared slides. 4. Systematics Forty-four genera and 87 species of palynomorphs are identified in the Daohugou palynoflora (Plates 16). Most of them have been attributed to species already known from other sources cited in Table 1 and 2. Here, we only describe the taxa with tentative taxonomic assignments, including indeterminate species and
Table 1. Botanical affinities and percentage composition of pollen taxa from the Daohugou flora Pollen taxon
Botanical affinity
Abietineaepollenites Alisporites Callialasporites Cedripites Chasmatosporites Classopollis Cycadopites Erlianpollis Hunanpollenites Monosulcites Parvisaccites Piceaepollenites Piceites Pinuspollenites Platysaccus Podocarpidites Protopinus Pseudopicea Pseudopinus Pseudowalchia Psophosphaera
Pinaceae (3, 10) Conifers/Pteridospermae (3, 5, 12, 13) Araucariaceae/Podocarpaceae (1, 2, 4) Pinaceae (3, 10) Cycadales? (11) Cheirolepidiaceae (3, 6, 12, 14) Cycadales/Bennettitales/Ginkgoales (1) unknown unknown Cycadales/Bennettitales/Ginkgoales (1, 5, 7, 13) Podocarpaceae (9) Pinaceae (3, 10) unknown Pinaceae (3, 10) Podocarpaceae (3, 10) Podocarpaceae (8) unknown unknown unknown unknown unknown
Quantity
Percentage (%)
27 279 1 60 15 211 144 10 23 191 2 11 166 129 16 342 31 72 53 13 148
1.3 13.3
