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Origin of chert concretions inPaleozoic carbonates of NankinghillsHsia Pang-TungPublished online: 04 Sep 2009.

To cite this article: Hsia Pang-Tung (1969) Origin of chert concretions in Paleozoiccarbonates of Nanking hills, International Geology Review, 11:4, 406-415, DOI:10.1080/00206816909475069

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Origin of chert concretions in Paleozoic carbonates

of Nanking hills

Hsia Pang-Tung

Chert concretions are widely developed inthe Paleozoic carbonate strata of the Nanking hills(Ninchen -Shan) and their neighboring areas. Theyare principally composed of a mixture of quartzand chalcedony with a very small amount of opal,but may contain a certain quantity of carbonate.The crystallinity of the silica varies with the ageof the formations, ranging from cryptocrystallineto unequal granular textures. When found in dolo-mite, they are lighter in color, grayish white, red-dish brown, and grayish brown; they are darker -grayish black or black - when found in limestone.Those of j ade green, as recorded in the literature,were not found in the present areas. The red color,as was formerly pointed out by various authors,isdue to presence of oxidized iron; those assuming adark color or black are formed under reducing con -ditions, containing carbonaceous matter. Theirshape varies fromregular to irregular but has arange of sizes which can be classified into threegroups: greater than 50 cm, 50-10 cm, and lessthan 10 cm. The last two groups are more common.

Yeh Lien-tsuen studied the cherts collectedfrom the Carboniferous coal series of Ch aot'ung,.Yunnan and classified them as syngenetic and lit-toral(5). Siliceous concretions which occurredin the Sinian formation of Chinghsiang, Hupeh area,were thought by Jen To'-fu(3) to be mostly diagenic,with only a minor amount of syngenetic origin.

The origin of chert concretions, of interestsince the beginning of the last century, can be sum-marized into six schools of thought:

1. Syngenetic precipitation from inorganicsources. J. Prestwich proposed the hypothesis in1888 and was supported by W. A. Tarr and H. C.Sargent. Concretions on the sea floor were formedby precipitation of congealed colloidal silica dueto the reaction between a colloidal solution of sili-ca and the electrolites;. no biogenic process wasinvolved. (4) Those belonging to the same schoolare W. H. Twenhofel(13), R.. R. Shrock)1), W. C.Krumbein and L. L. Sloss(9), D. V. Nalivkin (19),N. B. Vassoyevich(13), and others.

2. Syngentic precipitation from organic sources. Coagulated silica concretions wereformed from dissolution of accumulated shells.G. J. Hinde, C. R. Van Hise, A. Geike, W. J.Solas and others held this view. ( 4 )

3. Derived from early stage lithification. This view is a present-day popular theory of Rus-sian authors: that chert concretions were formedwithin soft, loose sediments by accumulation in-to nodular concretions from the disseminatedsilicon dioxides of the sediments during lithifi-

cation processes. The outstanding member ofthis school is N. M. Strakhov(20); M.S. Shvet-zov(2), L.B. Lukhin(7), and others believe this isone of the principalways in which the concretionsoriginated. As to the origin of the disseminatedsilicon dioxide, opinions vary, with some con-sidering it organic and others, chemical.

4. Later stage lithification. This hypothe-sis places the origin- of chert concretions as the re-arrangement of matter not in the loose, softsediments but in an already consolidated rock.Authors like S. E. Bastin(8),and S. G. Vishnya-kov(18), hold this or similar views.

5. Displacement of percolated water hypothe-sis. Again, they originate after consolidation ofthe sediments during the uplifting; concretions areformed through the solution of silica (by dissemi-nated water in one part of the rock strata) whichthen migrated and was redeposited in pore spacesand fractures, or replaced part of another rockstrata Authors who advocated this hypothesis areR. Liesegang, G. A. J. Gole, W.A. Richardson( 11),and others.

6. Origin through weathering processes. Dissolved silica from rocks exposed to weatheringin the weathering zone replaced the country rockwith concretions. E.O. Ulrich, G.W. Robinson,and others suggested and attempted to prove thishypothesis(13).

. It should be noted that beyond the above pro-posed hypotheses there were also authors like M. S.Shvetzov, L.B. Lukhin, G.I. Teodorovich, W. H.Twenhofel, G.W. Tyrrell(4), and others who agreedthere could be more than one way in which siliceousconcretions originated. The present author holdsthis opinion.

I. RELATIONSHIPS BETWEEN CHERTCONCRETIONS AND INTERBED

BREAK SURFACES

The chert-bearing strata of the area com-monly carry surfaces of break between the beds,which can be traced for more than a meter long onthe quarry faces, underlain by thick-bedded dolo-mite and overlain by thin -bedded argillaceous dolo-mite. Convex upward bedding plains are seen tofollow an ancient erosional surface ;positive reliefas shown in Figure 1. The 20 mm long, 1-3 mmwide blabk chert concretion lies along the surfaceof break having the bottom surface of the concretion,undulatory with the break surface but with a topsurface rather simple and regular (fig. 1). On theleft side of the section (fig. 1), the interbed sur -face is lined with a red clayey thin layer.

The second example of the interbed surfacebreak which can be traced for several metersin distance is the dolomite of the bottom part ofCarboniferous located in a quarry of Kanchuan-Translated from Acta Geologica Sinica, 1965, v.45,

no.3, p.254 -264. shan, Chenchiang, a wavy surface with anInternat. Geology Rev. v. 11, no. 4

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FIGURE 3. Chart concretions deposited on breaksurface-stylolithic surfaces

(topmost undulated heavy black linerepre s ents chart)

HSIA PANG-TUNG

0 10.Cm

FIGURE I. Chert concretion deposited on top ofinterbed break surface (example 1)

- chert; dolomite; calcareous clay; - red clay

amplitude of more than 10 cm (fig. 2). Thereis a belt of bleached underlain dolomite assum-ing position parallel to the surface break. Thebleached dolomite belt (+20 cm wide) gradesdownward to the regular dolomite. On top of thebreak surface there are well rounded or partiallyrounded dolomite gravels derived from the un-derlain dolomite of this surface; these gravelsalso show an oxidized bleached crust. Immedi-ately on top of the surface break is the belt-likedeposit of light-colored chert, 1 - 2 cm in widthand in places clearly enclosing and cementingthe dolomite pebbles associated with sands andclayey matter. Parts of the chert are of con-centric texture. The principal composition ofthe chert is quartz-chalcedonite with crypto-crystalline and unequigranular texture.

22 cm

FIGURE 2. Chert concretions deposited on Inter-bed break surface (example 2)

A - dolomite;

B - cemented sand and gravel belt;

C - bleached dolomite belt;

D dolomite;

E - chert.

Figure 3 represents the extended portionof Figure 2; here the interbed break surfaceis gradually transformed into interbed stylolite

surface(6). 1 The lower amplitude wavy breaksurface-stylolite indicates a decrease in the de-gree of erosion intensity. The chert assumesa belt-like shape or the appearance of a chain ofconnected balls, on top of the stylolitic surface.

The above can be summarized as: 1) duringthe depositional history of the dolomite, it hadbeen eroded, as represented by interbed breaksurfaces; 2) the erosional interbed break sur -

face can be transformed into an interbed stylo-lite surface; and 3) chert concretions are col-loidal deposits formed during the depositionalbreak of the dolomite sedimentation process;thus their bottom surface coincides with thebreak surface and they cement the gravels.These chert concretions are therefore synge-netic in origin.

II. RELATIONSHIPS BETWEEN CHERTCONCRETIONS AND STYLOLITES

Many chert concretions associate withstylolites, two types of which can be regardedas genetically significant: 1) chert concretions

' Term proposed by the author, 1959, to represent thelarge -scaled, more persistent interbed stylolite surface (6).

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FIGURE 5. Chert concretions deposited on top ofsurface of stylolite (2)

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deposited on top of the interbed stylolite; and2) chert concretions cut by the stylolites.

1. The chert concretions found in thePermian Chihsia limestone near the vicinity ofChiinagong, Hsiashu -chen is angular in shape,3 cm wide in the middle part, extending 8 cmalong the stylolite and pinching out (fig. 4).

20 CITI

FIGURE 4. Chert concretions deposited on top ofsurface of stylolite (1)

When traced farther along the stylolite, twomore concretions appear in similar manner.These concretions exhibit similar styloliticsuture in their bottom surfaces but a ratherplane surface in their upper parts. An exampleof this stylolitic suture of the bottom surface ofa concretion is also shown in a more than 40 cmlong, 4-5 cm wide light-colored chert concretionfound in the dolomite of the Middle CambrianP'aot'aishan formation at Mufu-shan (fig. 5).

The stylolite contact of the bottom surface issharp, but the upper surface has an obscureand gradational contact with the dolomite. Thebedding and stylolite in this case are vertical.

2. The second type is exemplified by achart concretion found in the limestone of Chihsiaformation, Chinglung-shan, in the vicinity ofNanking (fig. 6). The chert is oblique with thebedding 12 cm x 5 - 7 cm in size, its top havingbeen cut across by a sty- lolite suture.

The two types of stylolite-chert concretionrelationships described above indicate that thisstylolite cannot possibly be formed by "pressure-solution theory". (6) First, the chert is extremelyhard to dissolve and one is unlikely to find thepresent uninterrupted sty lolithic suture cuttingacross the chert concretion so smoothly, withoutshowing reliefs as reflected by the differentialresistences to dissolution between the chert andits enclosing rock, the limestone; second, even

f2 Cm

FIGURE 6. Top surface of chart concretion cutacross by stylolite suture

granted the chert and limestone can be simul-taneously dissolved to form stylolite, why doesthe stylolite occur only either on the top or thebottom surface, but not on both top and bottomsurfaces of the chert concretion at the sametime? These are some of the difficulties theyexplained as being due to the secondary pressur-ized solution.

These stylolites were, therefore, formedbecause of short erosional breaks during depo-sition, as demonstrated by the transition froman interbed surface break into an interbed stylo-lite.

Hence, type 1 shows chert concretionswere deposited syngenetically on the erosional-stylolite surface with the carbonates; and type 2indicates that the chert concretions were syn-genetically deposited with their country rocks,and with their country rocks were cut by theerosional surface, not the interbed stylolite.

It should be noted that the syngenetic ex-planation can also be applied to the case de-scribed by S. E. Bastin(8), where both bottom andtop surfaces of the concretions were transectedby stylolite. Later, the chert concretion wasdeposited on top of the stylolite erosional sur-face, and its top was again eroded with its sur-rounding limestone by another erosional stylo-lite surface. It is not necessary (as explainedby S. E. Bastin) that the chert was of replacementorigin after the limestone with mineralized solu-tion was introduced from both the top and bottomstylolitic surfaces.

III. RELATIONSHIPS BETWEEN CONCRE-CRETIONS AND BEDDING PLANES

OF THEIR COUNTRY ROCKS

In the literature there are three types ofrelationships: 1) concretions cut across thebedding plane; 2) overlying beds wrapped aroundconcretions but underlain ones rather horizontaland straight; and 3) both overlying and under-lain beds wrapped around the concretion. Authorshave assigned those of type 1 to diagenic re-placement or secondary replacement origin; of

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type 2 , to syngenetic; and type 3 as principallydiagenetic but also possibly syngenetic in origin.

There are plenty of examples in the presentarea of overlying beds wrapped around the con-cretions. These are black chert concretions inthe limestone of Chihsia formation near Fent'o,T'angshuichen, along an asymmetrical lenticularbody in cross-section (fig. 7), 5 cm along thelong axis and 3 cm along the short axis, with asmooth outlined surface. The bedding planesend abruptly against the steep slope of the uppersurfaces of the concretion; where they areagainst the gentle slope of this surface the planesslant similarly, until the uppermost planes wraparound the top surface of the concretion. Thelower surface of the concretion is extremelyhorizontal and straight, indicating that the con-cretion is syngenetic and that its outline con-trols the overlying beds.

q]cm

FIGURE 7. Overlying beds of country rock are

wrapped around the concretion, butbottom beds are flat and straight

A case which had not been found recordedin the literature is the chert concretion in thelimestone of the Chihsia formation of the Ching-lungshan, a planoconvex body (fig. 8) lying alonga bedding plane surface for a distance of over70 cm; the downward convex portion is about9-10 cm wide, narrowing down on both flanksto 2-3 cm wide. As compared to the ratherflat, straight, overlying surface the bottomsurface undulates considerably. Where thedownward lens-shaped swelling of the concre-tion lies, the underlain beds of thin bedded lime-stone are also warped accordingly; however,overlying beds of thickly bedded limestone re-main unchanged. Thus it may be seen thatthere was local movement of silicious materialsafter they were deposited, and this local move -

ment caused the relatively soft underlain sedi-ments to warp downward. This movement,possibly preceding deposition of the overlyingsediments, had no apparent effect on the over-lying beds; therefore the concretion is syngenetic.

;CI Cm

FIGURE 8. Where the bottom outline of theconcretion is swollen, underlain

beddings are correspondingly pressed downward

Another chert concretion was found exposedon top of the limestone of Chihsia formation nearFent'o, Wukueishan, T'anghsiachen (fig. 9). Itis pillow-shaped, 60 x 30 cm, and externallywell rounded. The underlain limestone lamel-lae are wrapped around the lower surface ofthe concretion in the manner of an onion-skin(photo 1). These lamellae syrrounding the con-cretion contain rather large amounts of sandyand clayey matter, which denies the explanationthat the concretion was formed due to secretionfrom the silica disseminated within the sur-rounding rocks, or has a secondary enrichmentor replacement origin.

.Virig4e4gei

FIGURE 9. Chert nodule lying on top ofbedding plane and wrapped around bedding

PHOTO. I. Chert concretion wrapped by beddingson top of bedding plane of Lower Permian

Chihsia limestone(Wukueishan, Fent'ao, Tangshan)

The above examples demonstrate the syn-genetic origin of the chert concretions. However,there are also many examples, of both the over-lying and underlain beds of the "wrapped-around"chert concretions, which were possibly formedduring lithification and may be of diageneticorigin. But it should also be added that in theearly stage of the diagenesis the original con-cretion may have been reshaped and thus havebent both the overlying and underlain beds. Inthe present article the writer will not recountthis type of relationship in further detail.

IV. SHAPE OF CHERT CONCRETIONSAND THEIR ENCLOSED 'BEDS

W. H. Twenhofel stated "The large-scaledconcretions, if there were no replacement

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textures presented, and concretions occurringalong the bedding planes are syrigenetic. "(13)W. A. Richardson pointed out that the sphericalconcretions can readily be explained as synge-netic but the flat concretions are more likely tobe diagenic in origin. (10) Many authors em-phasized that when the concretions are irregularin shape they offer one of the proofs of replace-ment origin.

In the present district, the chert concre-tions can be classified into three types, accord-ing to their shapes and enclosed rocks:

1. First type: Interbedded, multiple-direction-extending chert concretions with thefollowing characteristics:

a) Ordinary deposit on bedding planesbut sometimes on the interbed break sur-faces or on interbed stylolites. Overlyingand underlain rocks may be different litho-logically.

b) Strictly extended along the beddingplanes, their lengths several to tens oftimes their thicknesses; may at timesgrade from chert nodules into chert bands.

c) Separated sharply from both theoverlying and underlain, especially theunderlain beds. There is no trace of re-placement texture present.

d) On the beddings, they are flat-lying,disc-shaped, irregular slab-shaped (fig. 5), -belt-shaped (figs. 2 and 3), or rectilinear-shaped. In sections, they are two-dimen-sionally extended: slabby, belt-shaped,lima bean-shaped (fig. 9), chain-beddedshaped (fig. 4), and others. Chert nodulesof this type are all syngenetic.

30 Cm

FIGURE 10. Flat-lying bean-shaped chertconcretion

There are still many related but not clearlydefined chert concretions that may be classifiedas type 1 , such as the flat bean-shaped one(fig. 10), seen in the limestone of Lunshanformation of Early Ordovician at T'angshan.Sixty cm long and only 4-5 cm thick, it coin-cides with the bedding plane and has slight un-dulatory curvatures; its upper and lower sur-faces and its outline are marked sharply against

its enclosed rock. Examples like this arenumerous, it should be emphasized, in the multi-ple expressions of the interbed break surfaces.Like the two cited above (break and stylolite)they may be clearly shown or less apparent;the same is true of the bedding planes. G. I.Teodorovich, D. V. Nalivkin, D. A. Azhgireyand the author (6,14,19) have discussed the factthat the interbed stylolite can be an expressionof the interbed break surface. Those concre -

tions along the bedding planes are geneticallydeposited and should be regarded in the sameway as those deposited on interbed breaks orstylolites.

It should be further observed that the authornot only emphasizes the importance of the inter-bed chert concretions being syngenetic but alsothe importance of postdepositional changes afterthe formation of chert on top of the underlain,before or after the deposition of the overlyingcarbonates at the time when the country rockwas not completely solidified. Factors such as(during the diagenesis) changes in the medium,its physical or chemical conditions, and changesin CO2 contents, pH values, Eh values, tempera-ture, pressure, etc. would alter the shape ofthe ellen concretion from relatively homogene-ous to heterogeneous, regular to irregular, orto slabby, lenticular, or chain-beaded shape,etc. The lima bean-like concretion of Figure 9,before the deposition of the overlying coveringrocks, was actually slab-shaped, the presentlima bean shape having resulted from later con-traction. In Figure 5 one end of the slab-shaped concretion shows a clear partial protru-sion, explainable as due to early stage lithifica-tion deformation. It would be hard to imaginethat during the prolonged lithification process(including deposition, early stage diagenesis,and later stage diagenesis) no change in shapehad taken place with the concretions.

2. Interbed rod-shaped chert concretions. There are characterized by -

a) deposition between beds, with sharpboundaries against the country rocks;

b) commonly oblong, oval-shaped; arerarely round-shaped, also some equidimen-sional irregular forms. They are distrib-uted on bedding planes in isolation but canbe transitional to type (a) or even transi-tional to chert bands.

c) There is no trace of replacementtextures.

d) In cross-section, the beddings wraparound this top surface but there are also caseswhere beddings of both the overlying and bottomsediments wrap around the concretions.

Figures 7 and 9 illustrate such concretions.They are syngenetic not only in their relation-ships with the sedimentary structures but alsowith their smooth, well-rounded shapes. In

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gel matter, before the deposition of the coveringsediments, the action of gravitational and cohe-sive forces would give these gel substances asmooth surface and regular, oval-sphericalshape. According to Richardson (10)the spher-oidal shape was formed without the influence ofoverlying sediments and was the result of growthin all directions; the flat-lying concretions wereformed under the loading pressure of coveredsediments and as a result assumed a lateralform. In fact, chert concretions rarely assumespherical shape. Richardson neglected thefinding that the concretions may later, duringdiagenesis, change their shape.

Other shapes, like the one found on top of abedding plane of the limestone of Chihsia forma-tion at Wukueishan, Fent'o, Tangshuichen islike a doughnut (photos1 - 3; fig. 11). The diam-eter of the large ring is about 25 cm, that of thesmall adjacent one is 20 cm. The width of thering is several centimeters. The country rocksboth outside and inside the ring are of the samelimestone. The croSs-section of the ring islenticular. The shape is difficult to explain asof secondary replacement origin; neither can itbe explained as of segregation origin from thedisseminated silica of the country rock. Itmight more reasonably be said that it was ofsyngenettc deposition, as both the overlyingand underlain beddings wrap around the concre-tion; possibly it is partly diagenetic in origin.

PHOTO 2. Doughnut-shaped chert concretion

on top of bedding plane of Chihsia limestone

(location same as photo 1)

PHOTO 3. Doughnut-shaped chert concretionon top of bedding plane of Chihsia limestone

(location same as photo 1)

25 Cm

FIGURE 11. Doughnut-shaped concretion rests

on bedding plane

3. Third type. Intrabed chert concretions.Concretions of this type are also abundant inoccurrence. Their relationship to the beddingplanes of the country rocks is not clear and theyare characterized by:

a) individual concretions ordinarilysmall and having irregular outlines;

b) concentrated distribution in a de-fined stratigraphic horizon and not occur-ring along secondary fractures;

c) clear concretion outlines againsttheir country rocks.

PHOTO 4. lnterbed chert concretion (onbedding plane) and intrabed chert

concretions (on cross-section)

(location same as photo 1)

Although not enough observations have yetbeen made on concretions of this type, they canagain be regarded as syngenetic in origin. InFigure 12 the veinlet-like limestone crossingthe thin end of a smokestack-like concretion isexactly the same as that of the country rock ofthe concretion; this vein let is therefore s ynge -netic, since the cracking has been caused bycontraction, during the rock formation, whenthe sediments were still soft and removable. Thus

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1 0, Cm

FIGURE 12. Cracks of a chert concretionfilled with "limestone veins"

this inttabedding, irregular though it is, is stillsyngenetic.

20.cm

FIGURE 14

According to shape, the concretions of thisWukueishan area (figs 13 and 14) can be classi-fied as:

A) regular-shaped, spherical, ellips-oid, flat-ellipsoid, with exterior surfacessmooth, regular, without any protuburantprojections;

B) subregularly-shaped, partial sur-face portions with protuburant projections;

C) subirregularly-shaped, with pro-nounced singular projections;

D) irregular-shaped, having numerousprojections; and

E) complex-shaped, not only irregularin exterior shape but with their projectionstwisted, even engulfing or enclosing thecountry rock as inclusions.

The shapes from A to E are progressivelymore complicated stepwise; shapes D and Eare regarded as originally of regular shape butdeformed through subsequent diagenesis. That

CID

B

cps

of Figure 12 is of the class C . It is not toreject the fact that there were no syngeneticirregular-shaped chert concretions; the studyof transformation of their shape during lithifica-tion would certainly reveal the genesis of thechert concretions, and the stages of lithificationof sediments.

Concretions of this type can also be of earlystage diagenetic origin. Since there is no evi-dence of secondary replacement texture structure,secondary replacement, groundwater replace -ment or formation due to weathering processesmust be ruled out.

V. DISTRIBUTION OF CHERT CONCRE-TIONS IN STRATIGRAPHIC COLUMN

Chert concretions developed in the followingcarbonate horizons:

Dolomite of Early Cambrian Mufushanformation - concretions small in size, mostlyof interbedded type, not abundant.

Dolomite of Middle Cambrian P'aot'aoshanformation - concretions medium and small, ofinterbedded type, not abundant.

Limestone and dolomite of Middle Ordo-vician Lunshan formation - concretions princi-pally small-sized, both interbedded and intra-bedded-type, occurrences moderate.

Basal dolomite of Middle CarboniferousHuanglung formation - they are interbedded,medium- and small-sized, abundant.

Limestone of Early Permian Chihsia forma-tion - concretions medium to small-sized, bothinterbedded and intrabedded types, extremelyabundant.

Limestone of Lower and Middle TriassicChinglung group - concretions dominantly small-sized, of both interbed and intrabed types, notabundant.

0

10 Cm It is worthwhile mentioning that in thefollowing carbonates almost no chert concretions

FIGURE 13 are found: Early Carboniferous Chingling stage,

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PHOTO 5. Chert concretions of Chihsia limestonedeveloped along stylolites , and parallel to

bedding planes

(Chimakang, south of Hsiashu)

PHOTO 6. Chert concretions of Carboniferous

dolomite of Laohutung stage developed'

along bedding planes

(Huanglungshan, Lungt'an)

Hocho stage, Middle Carboniferous Hunglung formation, Late Carboniferous Chuanshan formationand others.

In the limestone of the Chihsia formation of the area, chert concretions are concentrated inthree stratigraphic positions: the bottom part adjacent to the lower siliceous bed, the middle andupper parts adjacent to the tipper siliceous bed. Their occurrence in the upper part is the mostabundant. The Chinglungshan section of Chihsia formation may be described, from bottom to top,as follows:

Thickness(m)42. 2

5. 5

2.7

8.8

13.2

33. 0

23. 9

1. 13 i tu m inou s li me s tone: in the middle of which, a 1. 0 m bed of lime-stone contains isolated chert concretions

2. Lower siliceous bed : bedded siliceous rock and limestone, siliceousshale. Limestone beds contain chert concretions

3. Chihsia formation:

a) Dark colored bedded limestone, chert concretionsextremely rich

b) Dark colored bedded limestone, diert concretions rare

c) Dark colored bedded limestone, contains considerableamount of small chert concretions

d) Dark colored bedded limestone; does not contain chertconcretions

e) Dark colored bedded limestone; contains many chert concre-tions, a small fraction of which is very large in size ....

4. Upper s iii ceou s bed: bedded siliceous rock, argillaceous limestone,calcareous shale, and siliceous shale. Limestone beds containchert concretions.

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In a given area, chert concretions occur ina definite geologic time and stratigraphic horizon.This seems to indicate the supply and depositionof the siliceous materials tend to be periodical;whether the sources of the present studied areaare volcanic or terrigenic is still a question to beanswered. In all the concretions examined nosiliceous organic remains were ever found andthe author does not believe the concretions werederived through organic activities. Judgingfrom the facts that certain concretions yield theconcentric collodial structures, in addition totheir morphological outline, and that the majorityare of interbed type, the concretions are there-fore colloidal siliceous deposits. These col-lodial matters, when engulfed with organisms,were capable of preserving the delicate oxganicstructure better than the country rock, and hencein the chert concretions there have lately beenfound numerous determinable corals and brachio-pods never before found in their country rock,the basal dolomite of the Hung-lung formation.

VI. CONCLUSIONS

1. The chert concretions of the area canbe classified into three major types: interbedlong, multiple dimensional stretched type; in-terbed isometric type and intrabed type. Thefirst two can be the interbed type concretionswhich, judging from their shape, structuralrelationship to the beddings, stylolites, andaltitude of the enclosing beddings of the countryrocks, are syngenetic. Concretions belongingto the intrabed type can be partly syngenetic andpartly diagenic.

2. The syngenetic concretions were de-posited during brief intervals of depositionalbreaks. Their underlain surfaces are often theunconsolidated bedding planes, interbed stylo-lites, or interbed depositional breaks.

3. Deposition of the concretions is accom-plished in the colloidal silica gel state.

4. After their deposition, silica mattercan be continuously added and constituted in thegrowth of the concretions; in the meantime, dur-ing the long period under the diagenetic process,the shapes of concretions may become increas-ingly irregular, and alterations can sometimesbe very intense.

5. Chert concretions in the area occur ina definite geological period and stratigraphichorizon, indicating the chert concretion-formingsiliceous matter was supplied periodically, andthat it was closely connected with intense ero-sion of the landmass and with paleovolcanicactivities.

REFERENCES

1. Shrock, R. R. , 1948, SEQUENCE IN LAY-ERED ROCKS: p. 160-161, Geology Press.

2. Shvetsov, M. S., 1948, PETROLOGY OFSEDIMENTARY ROCKS: v. I, p. 250-254, Geology Press.

3. Hen Leifu, 1959, SILICEOUS CONCRE -

TIONS OF SINIAN STRATA IN VICINITYOF CHINGMEN -HSIANGYANG, HUPEH:Geological Sciences, no. 6.

4. Tyrrell, G. W., 1929, PRINCIPLES OFSEDIMENTARY PETROLOGY: p. 116-173, Geology Press.

5. Yeh Lien-Chuen, 1935, ORIGIN OF CHERTAND ITS DEPOSITIONAL ENVIRONMENT:Geol. Rev., v. 10, nos. 5-6.

6. Hsia Pang-tung, 1959, STYLOLITE SU-TURES IN CARBONATE FORMATIONSOF SOUTHEASTERN CHINA: ActaGeologica Sinica, v. 39, no. 2.

7. Lukhin, L. V., 1953, PRINCIPLES OFSEDIMENTARY PETROLOGY: v. I,p. 262-267, Geology Press.

8. Bastin, S. P., 1933, RELATION OFCHERTS TO STYLOLITES OF CAR-THAGE, MISSOURI: J. Geol. , v. 41,p. 371-381.

9. Krumbein, W. C. and L. L. Sloss, 1956,STRATIGRAPHY AND SEDIMENTATION(Russian translation): p. 48-49.

10. Richardson, W. A. , 1958, RELATIVE AGEOF CONCRETIONS: Geol. Mag. , p. 114-124.

11. , 1956, ORIGIN OF CRETA-CEOUS FLINT: Geol. Mag. , p. 533-547.

12. Tarr, W. A., 1935, CONCRETIONS INCHAMPLAIN FORMATION OF CON-NECTICUT VALLEY: Bull. Geol. Soc.Amer. v.46, p.1493-1534.

13. Twenhofel, Ii. H., 1953, PRINCIPLES OFSEDIMENTATION: p. 402-414, v. 594-603.

14. Azhgirey, D. A., 1956, STRUCTURALGEOLOGY: p. 105 and ff.

15. Bruyevich, S. V., 1953, GEOCHEMISTRYOF SILICA IN SEA: lzv. AN SSSR, ser.geol. , no. 4, p. 67-78.

16. Bushinskiy, G. N., 1958, SILICEOUSROCKS. IN REFERENCE HANDBOOKON SEDIMENTARY PETROGRAPHY,v.11: p. 261-226 [sic]. Gostoptkhizdat.

17. Vassoyevich, N. B., 1958, TEXTURES OFSEDIMENTARY ROCKS. IN REFERENCEHANDBOOK OF SEDIMENTARY PETROG-RAPHY, v. I; p. 116-118.

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18. Vishnyakov, S. G. , 1953, SILICEOUS FOR-MATIONS IN CARBONATES OF LOWERAND MIDDLE CARBONIFEROUS OFNORTHWESTERN LIMB OF SUB -MOSCOWBASIN: AN SSSR, ser. geol. , no. 4.

19. Nalivkin, D. V., 1956, STUDIES OF FA-CIES I: Izv. AN SSSR, ser. geol., no. 4,p.118-123.

20. Strakhov, N. M., 1962, FUNDAMENTALTHEORIES OF LITHOGENESIS II: Izv.AN SSSR, p. 538-542.

21. Teodorovich, G. I., 1962, STYLOLITICAND SUTURAL SURFACES AND MI-CROSTRUCTURES: Bull. MOIP (Mos-cow Soc. of Naturalists), no. 6.

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