The charophytes (or stoneworts), a kind of'algae, grow in fresh or brackish waters including streams, ponds, lakes, lagoons, fjords and have a wide geographical distribution on all continents except Antarctica. Most of them live in the waters that are clear, transparent and rich in calcium, mostly with pH ranging from 7.0 to 8.0, e.g., alkaline, high-calcium lakes. Charophytes are present in running water only where movement is slight. They grow submerged in the water from shorewards to a depth u
¡209 Sketch map showing a living charophyte plant (Left, x 1; I, rhizoid; 2, axis; 3. branch) and its reproductive organs (Right, * 40; 4, antheridium; 5, oogonium; 6, coronular cells). (After Nordstedt, 18'J 1; redrawn by Yu-gao Ren/ NIGP)
of 18 m, compact or bushy. The structure of charophytes is relatively simple in vegetative organs, with no vascular bundles. However, their reproductive organs are rather complex. People usually place them in a separate division of the plant kingdom, the Charophyta.
The charophyte thallus is green, ranging from 0.5 to 200 cm in height (15 — 25 cm in average), and usually has an erect, central axis or stalk, regularly whorled branches arising from the very short nodal cells and rhizoids at the base to attach to the muddy or sandy substrate (Fig. 209). The plant cells contain small and elliptic chloroplasrs char carry our photosynthesis and convert inorganic compounds to organic nutrients. The plants commonly are monoecoius, i.e., a single plant producing both types of gametes. Both male-gametes (antheridia) and female gametes (oogonia) occur on the branches. Oogonia in living charophytes are elliptic to spherical, covered with five sinistral enveloping cells, whereas antheridia are spherical, protected with four to eight shield cells. Charophytes reproduce both vegetatively and sexually. Vegetative reproduction may occur by means of bulbils or fragments from mature plant. Greater or lesser degree of calcification rakes places in the plant during the growth of charophytes, especially within the enveloping cells of oogonia, which enables the good preservation of the lime shells. The term gyrogonite is commonly used to designate the fossilized oogonium.
Most charophyte fossils are remains of gvrogonites as shown in the figures (Figs. 210—223). The geological occurrence of fossil charophytes may trace back to the Late Silurian, nearly 400 million years ago. Quite a few species have wide geographic bur limited geologic range, which allow their use as stratigraphic indices for freshwater and brackish sediments as well as tools in environment reconstruction. The diagnoses in fossil charophytes classification and identification include the size and shape of gyrogonites, characters of calcification am! utricle, apical structures and depressions, rosettes and coronular cells, etc.
The Jurassic charophytes are absent in Northeast China. No charophytes have been reported from the upper part of the Yixian Formation and the lower part of the Jiufotang Formation at present. The fossil charophytes obtained from the lower pare of the Yixian Formation of northern Hebei and western Liaoning are predominant with Mesochara, Peckisphaera and Minhechara.
The upper part of the Jiufotang Formation to the Fuxin Formation yiel Js rich charophytes, including mainly Flabellochara bebeiensis, F. barrisi, Atopocbara irivohis triquetra, Aclistochara mundula, A. huihuibamnsis, Mesochara stipitata, /VI. valuta, Peckisphaera verticillata. These species are common in the middle part of the Lower Cretaceous deposits in northern China. Among them, Flabellochara bebeiensis and Atopocbara t rival vis triquetra have special stratigraphic significance, i.e., both are typical to the Barremian in the world. Charophytes from the Jiufotang, Shaliai and Fuxin Formations can be included in the third Clavatoraceae Biozone of China, namely the late Barremian Atopocbara trivolvis triquetra-Flabellocbara bebeiensis Biozone.
According to the charophyte distribution, the geological age of the lower part of the Yixian Formation can be attributed to the early Early Cretaceous; the upper part of the Jiufotang Formation as well as the Shaliai and Fuxin Formations are regarded as the late Barremian.
The figures show some fossil charophytes from Inner Mongolia, Hebei and Liaoning provinces. Their diagnoses are briefly stared as follows.
Aclistochara huihuibaaemis (Fig. 2 10); gyrogonites oval to prolate, 400—550 |im long, 350—500 pm wide, 8—9 convolutions visible in lateral view, spiral cells concave, intercellular ridges narrow and sharp; found from the Lower Cretaceous of China.
Aclistochara mundula (Fig. 211): gyrogonites urn-shaped, 370—600 J.im long, 250—400 pm wide, 10— 12 convolutions visible in lateral view; found from the Lower Cretaceous over the world.
Peckisphaera verticillata (Figs. 212, 213): gyrogonites spheroidal, apex broadly round and base narrowly round, 450—750 pm long, 400—600 pm wide, 10—12 convolutions visible in lateral view : found in the Lower Cretaceous over the world.
Mesochara xuanziensis (Fig. 214): gyrogonites very small, ovoid a I to subovoidal, 230 — 350 |im long, 200—250 Jim wide, 6—8 convolutions visible in lateral view; found in the Lower Cretaceous of Hebei, Shaanxi, Anhui, Henan, Gansu and Xinjiang, China; northern Spain and northwestern Germany in Europe.
Mesochara valuta (Fig. 215): gyrogonites small, conically ovoidal. 300—400 pm long, 210—330 pm wide, 8—9 convolutions visible in lateral view; having a worldwide distribution during the Late Jurassic and Early
Mesochamproducía (Fig. 216): gyrogonites ovoidal, apex broadly round, base contracted and forming a stalklike projection, 250—380 pm long, 200—250 pin wide, 8—9 convolutions visible in lateral view; found in the Lower Cretaceous of northern China.
Peckisphaera muitispira (Fig. 217): gyrogonites broadly ovoidal, apex round, base narrowly round or contracted to a stalk. 300—400 pm long, 200—300 |im wide, 10— I I convolutions visible in lateral view; found in the Lower Cretaceous of Inner Mongolia and Hebei.
Peckiiphaera paragrarinlifera (Fig. 218): gyrogonites ovoidal or subspheroidal, apex round, base round and protruding, basal end flat, 450—600 Jim long, 350—465 pm wide, 11 — 12 convolutions visible in lateral view: found in the Lower Cretaceous of China.
Atopochara trivolvis triquetra (Figs. 219~221): utricles 820—1080 pm long, 750—1000 pm wide, formed with 36 units, which are divided into three groups, basal view triangular; distributed in che Barremian over the world.
Flabellocbara Ixbeiensis (Fig. 222): utricles ovoidal, 620—800 pm long, 520—700 pm wide, lateral units consist of 5 or 6 cells; found in the Barremian over the world.
AMnhechara sp. (Fig. 223): gyrogonites subspheroidal, apex and base round, apical center projected, forming a columella, 750— 1050 pm long, 450—610 pm wide, 10—I 1 convolutions visible in lateral view; found in the Lower Cretaceous of Liaoning and Qinghai provinces.
(All fossils shown in this chapter are the fossilized oogonia. i.e. gyrogonites, of the plants. Photos were taken by Yong-qiang Mao and Zhou-qing Chen of the NIGP)
w 210 Aclistochara Imihuibaoensis. lateral view |550 |im long, am 211 Aclistochara mundula, lateral view (550 pm 440 jim wide), from Halawusu drilling sample (Shahat long, 250 (im wide), from Pijiagou locality formation) in Horqin Zuoyi Houqi, Inner Mongolia. (Jiufotang Formation) in Yixian, Liaoning.
212 Peckisphaera verticillata. apical view (550 nm wide), from Dongliang drilling sample (Fuxin Formation) in Fuxin, Liaoning.
216 Mesochara praducta. lateral view (360 urn long, 200 um wide), from Dadianzi locality (lower part ofYixian Formationl in Luanping. Hebei.
217 Peckisphaera multispira, lateral view (370 pm long, 300 ¿im wide). from Dadianzi locality (lower part ofYixian Formation) in Luanping. Hebei.
218 Peckisphaera paragranulifera. lateral view (450 (im long. 350 )im wide), from Pijiagou locality (Jiufotang Formation) in Yixian, Liaoning.
219 Atopochara trivolvis triquetra, apical view (860 )tm wide), from Halawusu drilling sample (Shahai Formationl in Horqin Zuoyi Houqi, Inner Mongolia.
1213 Peckisphaero verticillata, lateral view (575 pin long. 525 fim wide), from Dongliang drilling sample (Fuxin Formation) in Fuxtn, Liaoning.
1214 Mesochara xuanziensis, lateral view (290 pm long, 230 ^m wide), from Dadianzi locality (lower part of Yixian Formation) in Luanping. Hebei.
215 Mesochara valuta, lateral view (390 (im long, 300 pm wide), from Sanguanmiao locality (lower part of Yixian Formation) in Kazuo, Liaoning.
MP 220 Atopochara trivolvis triquetra. lateral view of the same fossil in Fig. 219 (900 |im long, 860 pm wide), from Halawusu drilling sample (Shahai Formation) in Horqin Zuoyi Houqi, Inner Mongolia.
■ 221 Atopochara trivolvis triquetra. basal view of the same fossil in Fig. 219 (860 pin wide), from Halawusu drilling sample (Shahai Formation) in Horqin Zuoyi Houqi. Inner Mongolia.
ttp 222 Flabellochara hebeiensis, lateral view (750 pin long, 660 pm wide|, from Qijiawopeng drilling sample (Shahai Formation) in Kangping, Liaoning.
■•223 Minhechara sp., lateral view (1030 pm long, 610 pm wide), from Sanguanmiao locality (lower part of Yixian Formation) in Kazuo. Liaoning.
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