778
Journal of Paleontology 89(5):768–790
allochthonous debris layers (such as the sampling horizons of W-6-1 and HT-3-1) are interbedded within the autochthonous rocks at the Wuhai sections, and this indicates that fossils in the allochthonous beds have been transported. Judging from the excellent preservation and the imperceptible diachroneity of the conodonts obtained from the allochthonous debris layers, the redeposition might occur instantly, and the fossils were probably deposited not too far from their living sites. As noted above, the conodonts from the two investigated
Figure 5. Middle Darriwilian to earliest Sandbian conodont biofacies in North China and its relation to paleo-tectonic regimes. Basic map of paleo-tectonic regimes is modified from Feng et al. (1998). (A) Rhipidognathus—Plectodina biofacies, (B) Periodon biofacies, (C) Protopanderodus biofacies, (D) Costiconus biofacies, (E) Spinodus biofacies. The black spot denotes the depth zone of the study area.
He suggested that either model cannot single-handedly answer the distributional dilemmas of conodonts, and a far better approach in the solution of each biofacies problem is a flexible use of the two models based on the distributional data. Zhen and Percival (2003) proposed an ecological model that combined attributes of the vertical and lateral stratification models. This model suggested that the shelf carbonate facies are presumably dominated by shallow-water benthic (or nektobenthic) and that epipelagic forms, deeper water benthic or nektobenthic forms and mesopelagic forms occasionally found in distal platform sediments were mainly introduced by upwelling currents, and faunas of slope facies are dominated by cosmopolitan and widespread species. Zhen and Percival’s model better explains the distributional patterns of pelagic and benthic or nektobenthic Ordovician conodont forms. As the foregoing brief review shows, North China was
within the tropical zones throughout the Ordovician, and can be subdivided into a broad shelf settings and the westernmost slope settings. According to An et al. (1983), Pei and Cai (1987), An and Zheng (1990), and Wang et al. (2014), the middle Darri- wilian and earliest Sandbian conodont faunas of the shelf are characterized by abundant endemic species of the genera Rhipidognathus, Plectodina, Tangshanodus, Aurilobodus, Tasmanognathus, etc. Therefore, a shallow and warm water Rhipidognathus–Plectodina biofacies (Sweet, 1988) principally composed of benthic or nektobenthic conodonts can be dis- cerned in the shelf region. However, depositional regimes of the slope are much more complex. It is observable that several
sections are very similar to those from the Guniutan and Miaopo formations of south-central China. Most species in common between them have been found in the Cold and Temperate Domains or deep marginal areas of the Tropical Domains (Zhen and Percival, 2003), and are broadly accepted to be pelagic and living in cold water. Based on a detailed survey of the relationship between conodont contents and palaeogeo- graphic setting of the Yangtze platform, Zhang (1998a) dis- tinguished four kinds of depth-dependent biofacies in the Middle Ordovician as follows, from shallow water to deep water: the Periodon, Protopanderodus, “Walliserodus” (=Costiconus of this paper), and Spinodus biofacies. The stu- died sections are abundant in these facies indices, and this suggests that the Wuhai area shared a similar biological- sedimentary pattern as south-central China during the investi- gated time interval. Thus, the Middle Ordovician conodont biofacies of south-central China also may be recognized in the westernmost slope facies of North China. The most remarkable difference between these is perhaps that the depth of each biofacies of the later was greater than that of the former, because to achieve the same water temperature as in the high latitudes requires a greater depth in the tropics. The taxa from the two investigated sections are dominated
by the genus Periodon (represents 40.3% of all collected specimens), followed by Pygodus (20.8%), Costiconus (7.1%), Protopanderodus (5.6%), Oslodus (4.5%), Coelocerodontus (3.6%), Phragmodus (2.3%), Venoistodus (2.3%), Dzikodus (1.8%), and Spinodus (1.7%), whereas remaining genera account for 10%. There are clear variations in the taxonomic diversity and relative frequency of genera in the conodont fauna through the stratigraphic successions. Although species of the genera Periodon, Protopanderodus, and Costiconus comprise high proportions separately in the biota, it is worth noting that the abundance of each genus shows a irregular stratigraphic distribution, and the numbers of elements belonging to these
Figure 6. (1–4) Ansella crassa Bauer, 1994; (1) Pa, outer lateral view, from W-4-3, CUGB-jxch650; (2) Sa, lateral view, from W-9-3, CUGB-jxch765; (3) Sb, lateral view, from W-7-1, CUGB-jxch739; (4) Sc, lateral view, from W-7-1, CUGB-jxch740. (5) Ansella jemtlandica (Löfgren, 1978); Sa, lateral view, from HT-6-2, CUGB-jxch855. (6) Ansella nevadaensis (Ethington and Schumacher, 1969); Pa, inner lateral view, from W-8-1, CUGB-jxch750. (7, 8) Cornuodus longibasis (Lindström, 1955); Sa, lateral view, from W-9-2, CUGB-jxch758, CUGB-jxch759. (9–18) Costiconus ethingtoni (Fåhræus, 1966); (9, 10) Pb, inner lateral view, from W-6-1, CUGB-jxch698, CUGB-jxch700; (11, 12) M, inner lateral view, from W-6-1, CUGB-jxch724, CUGB-jxch726; (13, 14) Sa, lateral view, (13) from W-8-1, CUGB-jxch749, (14) from W-6-1, CUGB-jxch706; (15) Sb, lateral view, from W-6-1, CUGB-jxch 730; (16, 17) Sc, lateral view, from W-6-1, CUGB-jxch704, CUGB-jxch701; (18) Sd, lateral view, from W-6-1, CUGB-jxch707. (19, 20) Besselodus semisymmetricus (Hamar, 1966); (19) distacodiform, lateral view, from HT-5-2, CUGB-jxch788; (20) drepanodontiform?, lateral view, (20) from HT-5-2, CUGB-jxch808; (21) Besselodus variabilis (Webers, 1966); drepanodontiform?, from W-7-1, CUGB-jxch735. (22–24) Dapsilodus viruensis (Fåhræus, 1966); Sc, lateral view, (22) from W-2-2, CUGB-jxch627, (23) from W-10-3, CUGB-jxch781, (24) from W-9-2, CUGB-jxch755. (25) Drepanodus arcuatus Pander, 1856; Pb, lateral view, from W-9-2, CUGB-jxch756. (26, 27) Drepanodus reclinatus (Lindström, 1955); (26) Sa, lateral view, from W-9-3, CUGB-jxch766; (27) Sb, lateral view, from HT-6-1, CUGB-jxch839. (28–36) Dzikodus tablepointensis (Stouge, 1984); (28) sinistral Pb, from W-4-1, CUGB-jxch636; (29, 30) Pa, upper view, from W-6-1, CUGB-jxch709, CUGB-jxch664; (31, 32) dextral Pb, upper view, from W-6-1, CUGB-jxch710, CUGB-jxch713; (33, 34) Sa, (33) posterior view, from W-2-2, CUGB-jxch631, (34) lateral posterior view, from W-4-1, CUGB-jxch644; (35, 36) Sb, outer lateral view, (35) from W-3-1, CUGB-jxch634, (36) from W-9-3, CUGB-jxch764. (37) Onyxodus acuoliratus Watson, 1988; Sb, lateral view, from W-6-1, CUGB-jxch731. (38, 39) Polonodus sp. ; (38) Pa, upper view, from W-4-1, CUGB-jxch637; (39) Sa, posterior view, from W-6-1, CUGB-jxch716. (40) Gen. et sp. indet.; Sa, posterior view, from W-6-1, CUGB-jxch717. Scale bars represent 50 μm.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212
