Investigations of the Lower Ordavieian of the Siljan District, Sweden

II.

Lower Ordavieian penetrative and enveloping algae fron1 the Siljan District

By

I var H essland

r. lntro duction . . . . . . . . . . . . . . .

2. On recent penetrative a lgae 3· The biocoenoti c importan c e of penetrative algae 4· O n previous observations o f fossi l penetrative algae .

S· The present algae-bearing deposits . . . . . . . .

6 . Description of the present pen etrative and envelopin g algae 7. Penetrative and enveloping algae as indicators of ch anges o f leve l in

the stratal sequence investigated 8. The importance of penetrative and enveloping algae for the precipita-

!'ag e

4°9 410 4 1 2 414 4 1 5 416

4 2 0

tion o f hydrous iron oxide and for the formation o f l imonitic ooids . 4 2 r

9· On the formation o f Jimonitic a n d hematit ic oolite according to some other authors Bibli ography

1. Introduction.

4 2 2 4 2 4

Certa in microscopic algae and possibly also fungi have the ab i l ity of bor ing i n calcareous rocks and i n hard organ ic tissues, such as carapaces and sheils of invertebrates, and in bone substances and scales of vertebrates. A few of them are supra-aquatic, but the majority are aquatic . Some occur in freshwater and others in the sea .

27-48705 Bull. of Geol. Vol. XXXIII

410 IVAR HESSLAND

In our day, aquatic boring or perforative algae (also called endol ithic a lgae) constitute a !arge group of species belonging to Cyanophyceae, Chloro­phyceae, and Rhodophyceae. They occur in practically a l l el irnatic regions, but their frequency is highest i n fai r ly stagnant and shallow bays of the warm seas .

Structures created by bor ing algae have been recognized in several fossi l iferous deposits of various ages . The oldest known are Ordovician . However, they cannot be said to be well-known by geolog ists . In Swedish and Estonian deposits, for i nstance, they do not seem to have been re­cognized at al l, i n spite of the fact that they are very numerous i n cer­tain strata .

The destructive activity of penetrative algae has been noticed by many investigators (destruction of sheils and bones, cora l and algal reefs; forma­t ion of furrows and p i ts in calcareous rocks; coastal erosion) . Their posit ive act iv ity, on the other hand, has not been sufficiently considered, v iz . their act1v1ty as a phytal partner of an imal societ ies, i . e . as a producer of oxygen and an absorber of the excretion products of the animals . In fact, the activ ity of boring algae i n combinat ion with that of other groups of algae is certain ly one important reason for the luxuriance of certain biotopes, and the reason for the fact that r ich faunae can l ive i n such surmundings where they otherwise would have succumbed on account of oxygen deficiency.

Furthermore, they are im portant as ind icators of c hanges of leve! : their presence indicates a fa irly shallow water du r ing the deposition of the algae­bearing stratum.

F inal ly, they are certain ly of great importance for the precipitation of hydrous iron oxide and for the formation of l imunit ic ooids .

These questions wi l l be disenssed in the present paper i n Connect ion with the description of the penetrative and enveloping algae in a part of the Lower Ordavie ian of the S i ljan Distr ict .

2. On recent penetrative algae.

Certain tubular structures i n shei ls were observed as early as the fifth clecade of the 19th century (cf. CARPENTER 1845, p . 13), but the nature of these structures was not recognized unt i l l ater.

CARPENTER was first of the opin ion that the structures were normal for the sheils and of taxonornie importance . QUEKETT (1854) considered at !east some of the tubul i of simi lar appearance in Madreporaria as products of "Confervae, Spongida, or of minute boring animals" . RosE ( r 8 55) referred s u ch structur es in fish-scales to "infusoria l parasites" .

WEDL (1859) exposed sheils to the action of d ilute hydrochloric acid and stated that the boring organisms were plants ; be thought they were polycel lu lar filamentons algae . KöLLIK ER ( r 86o) who investigated tubular structures of the present k ind i n several mar ine and l imnie animals con-

1.0\VER ORllOVICIAN PF.NETRATIVF. AND ENVELOl'ING ALGAF: 4 T l

s idered them to be bored by monocel lular plants, whether by fungi or algae was, according to him, d ifficult to decide.

CARPENTER later withdrew his former explanation of th e structure and referred them to parasit ic action of a fungus {cf. STJRRUJ' I 872).

LAGERHErM {I 886) was the first botanist who investigated these per­forating vegetable organ isms. He identified t\vo algal species which later appeared to have a very wide d istribution, v iz. the wel l-known Mastigocoleus testarum LAGERHEIM {Cyanophyceae) and Gomontia polyrltz"-':a {LAGERIIEIM ) HORNET and FLAIIAULT {Chlorophyceae).

These finds on the Swedish west coast gave rise to the undertaking of s imilar investigations by F ren ch botanists on their coast. In I 889 a paper appeared on this subj ect, v iz . the fundamental and often quoted investigation by BORNET and FLAHAULT. These authors recognized severa l penetrative species which are referable to th e bluegreen and green a lgal groups {8 genera), but also 2 genera which are colourless and referred to the algal f ungi {Phycomycetes) . In I 892 BATTERS reported a fin d of a perforating red alga from the British Isles .

Later, more and more perforat ive algae have become known. PIA { 1937)

made a survey of the boring Thallophytes, which were known at that t ime. This survey may be fa i rly complete, but the bor ing abi l ity does not seem to be completely proved in some cases . To give an idea of the abundance of boring Thallophytes I made a tabular survey of these organ isms on the bas is of PIA's work :

··- ··-

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,\.ote. Three Cyanophyceae and two Chlorophyceae genera occur both 111 the sea

and in lakes.

During later t imes, bor ing algae have been investigated with new and carefu l methods. KYI.IN (1935) studied their ontogenesis by means of labora· tory cultivations, which have also yielded important morphologic and taxo· nornie results.

412 IVAR HESSLAND

LAGERHEI:vr had already noted that t here are generally more than one species boring in the same she! l . The sociology of boring algae was studied by BORNET and FLAI-IAULT, and has been continued by later i nvestigators , for i nstance ERCEGOVIC ( 1934), who discerned severa l associat ions of d if­ferent rank.

Closely associated with this question is that on the vertica l distribut ion of aquatic perforative algae. Since algae are dependent on the insola tion, they l ive i n fair! y shallow w ater; very often the depth is ins ign ificant (man y species l ive in the ti da! zone). They are reported as abundant to about 20m or somewhat deeper. The lower l imi t is, of course, due to the trans­parency of the water. BERNER (1931) and ERCEGOVIC (1934) have examined the vertical zonation of endo- and epi l i th i c algae in th e Mediterrancan (French and Dalmatian coasts resp. ).

Much weight has been attached to the role which is played by penetrat ive algae as d is integrators of shel l substances , cora l and algal reefs , and ca l­careous rocks. Some authors have also pa id attention to the fact that the calc ium earbona t e d issolved by the action of th e algae may be re-precip itated as a calcareous mud (vVETZEL 1938).

The chemistry of the penetrative process is but poorly i nvestigated. Most I ikely the d issolution is eaused by an acid. Carbonic acid has been considered, but more probably i t is some organic acid. Jt is not known , to what extent and in which way the d issolved products leave the organism.

Jt has also been suggested that the penetrat ion is performed to a cer­ta in extent i n a mechanica l way, but this has been considered to play only a subordinate role.

3· The biocoenotic importance of penetrative algae.

vVhen penetrative algae were first described , they were denominated as parasi tes. Their destruct ive activ i ty on the sheils was easily seen , but only during recent years has one begun to understand that they are a lso useful to the an imal in the bard tissues of which they l ive. PARKE and MOORE

(1935) who i nvestigated the algal infection of the sheils of living Balanus ba!anoides pointed to the fact that the algae , in the daytime, contribute oxygen to the an imal; the algae , in return , benefit from the excretory products of the barnacle , and thus keep th e water around the anima l clean. However, the ful l s ignificance of the symbiosis between animals and penetrat ive algae does not seem to have been recogn ized.

A symbios is between an an imal and a plant is a perfeet arrangemcnt : the plant produces oxygen , necessary for the animal , and uses , i n return, the waste products of the an imal. co2 is consumed for synthes is of carbo­hydrates; other excretion products , especially potash salts , sulphur com­pounds , and compounds of phosphorus and nitrogen are made use of as

LOWER ORDOVICIAN PENETRA'l'IVE AND ENV ELOPING ALGAE

nutntwus substances ; phosphorus, n itrogen and sulphur are used for the further transformation of the carbohydrates into prote in, which is stored by those lower aquatic plants considered here .

The best resu lt of such a syrobios is i s reached when the p lant i s in­corporated i n the soft tissues of the animal . Th is is the case of the so­called zooxanthellae, small yel lowish-brown un icellular algae, wh ich occur i n many animal groups bu t which are especial ly numerous i n the reef-bui lding corals .

They may be a most essential reason for the luxur iance of the coral reefs, and they are certainly the factor which determines the position of the lower l imi t of the reefs (cf. HESSLAND 1946). When the algae, as i n th is case, are intra-cellular i n the soft t issues of the an imal, the ex­change of gases (02 and C02) takes place by d irect diffusion through the tissues , so that there will be no loss of gas . Furthermore, the v ital functions of the an imal wi l l be faci l itated by the fact that the zooxanthellae serve as excretion organs of the animals .

The effect of the symbios is is less i n those cases where the algae l ive i n the externa! bard tissues of the animals . The exchange of gases and the transference of animal waste products must take place via the water, and th is must mean a certa in i nefficiency . But in th is case also the symbiosis is valuable as stated above as regards Balanus balanoides. In the same respects, penetrative algae may be of great importance for such luxurious b iocoenoses as reefs . In the coenenchym of reef earals they are very abundant, and there is reason to bel ieve that the results of the vital activity of these algae are added to those of the zooxanthellae .

Penetrative algae must be considered to h ave a very great importance for animal communit ies l iv ing in shallow stagnant waters . However, recent surmundings of this type do not seem to have been investigated . They may not occur in temperate regions, where, among other things, seasonal convection currents prevent the formati on of such waters . In warm regions, on the other hand, they may be easi ly formed. Seasonal convection currents are not developed there . Furthermore, the fact may be noted that the specific gravity of the water varies by a larger amount for a temperature d ifference of I o at a h igher temperature than at a lower . Especial ly i n salt waters of warm regions a stratification may be easi ly developed but d ifficult to interrupt . Conditions as now described ma y be f o und i n coastal basins of lower l atitudes.

It is ev ident that a deficiency of oxygen wi l l appear i n stagnant waters, supposing that they do not include a producer of oxygen . Plants provided with chlorophyll have this abil ity. S ince such aquatic plants occur only in the upper layers, stagnant waters contain ing oxygen are shal low. In marine surroundings, algae are the majority of these plants, and among them pene­trative species may be of importance in such areas where penetrable sub­stances are present .

4T�4 _________________________ I_V_A_R _H_F_: S_S_L _A _N _D ________________ __

The fossi l occurrence of penetrative algae described in the present paper I s included i n a st ratum which was formed when the water , on the whole , was fairly stagnant , temporarily very stagnant. At the same time , i t was r ich in oxygen. These condit ions may be necessary for the formation of the l imonit ic ooids wh ich are abundant in th is stratum (cf. p. 421 and part IV of th is series of papers). The oxygen , to a great extent , must have been produced by the very m1merous penetrative and the partly abundant enve­loping algae. Certainly owing to th is productian of oxygen , a numerous fauna could l ive in the Siljan D istr ict during th is period. The flora , in return , profited by the excret ion products of the animals. Thus , i n th is closed water there existed a k ind of biocoenosis between the an imals and the plants , though the form of the biocoenosis was not the common one , s ince the plants , as a rule , d o not seem to have occurrecl i n the sheils o f l iving animals, but l ived i n dead shells.

4· On previous observations of fossil penetrative algae.

Structures in bard t issues of fossils eaused by penetrative algae have been known pract ically as Iong as corresponding structures in recent material.

RosE (1855) reportecl such structures from fossi l fish-scales. WEDL (1S59)

found them in fossi l gastropods , bi valves and brachiopods. KöLI.ICKER ( I 86o) examined other groups as weil, and DUNCAN (1876) made a special inves­tigat ion of penetrat ive algae i n foss il corals.

PlA, i n h is survey of penetrative organ isms , 1937, also gave a l ist of fossi l penetrative algae. He points out that fossi l boring Thallophytes were earl ier usually considered to be fungi , but that they in fact for the greater part were algae belonging to a few recent genera , or to genera closely relatecl to them.

PIA says , in th is connection (1937, p. 341), that canals of similar appear­ance can be bored by d ifferent species. Furthermore , he points out that the same alga can make canals of el issimilar appearance in different parts of a she!!. Nowadays , there are a Iot of penetrat ive algae , and during the past geological periods there certainly existecl a great many genera which are now ext inct. For this reason I agree with PIA that fossi l algal structures shoulcl not be confined to recent genera. I also agree with h im when he sa y s t hat i t is not possi b le to establ ish certain species with in the genera. PlA proposed the algal structures to be classified from other points of view , v iz. accorcling to the age of the formation and to the substance which is penetrated.

WETZEL (1938), referring to the papers of PIA (1937) and KHIK (1935),

rightly rejected such generic names of fossi l penetrat ive algae as C!taetophoritcs PRATJE and Gomontia BaRNET and FLAliAULT. lnstead, he proposed a morph­ological grouping of the canals bored by microscopical plants. He grouped

T.OWER ORDOVICIAN PENETR ATIVE AND ENVELOPING ALG AE 4 J 5 ----- ·-----�--···--

the canals of a few such recent organisms mainly according to their d ia­meter and intended to class fossi l canals i n th is system. Other d ist inctive features were the course of the canals , the ir ramification , and the appea­rance of certa in bladders. He d iscerned 6 groups d iv is ible into 2 divisions , v iz. one with proport ionally wide canals and another with narrow. The former should consist of green algae , the latter of phycomycetes or blue­green algae. However, h is system is seriously im paired by the fact that he d id not know the recent organisms which bad created the canals wh ich he proposed as standard types of the system.

Rather many structures bored by penetrative algae are known from the Pal;eozoicum. A few of them are referable to the Ordovician. ST0RMER ( 1931) described such structures in tri lobite carapaces (Middle and Upper Ordavieian ofNorway). H0EG , i n reporting Girvanellaprob!ematica NICTTOLSON

and ETI-IERIDGE from the Lower and Middle Ordavieian of the Trondheim Area in Norway, pointed to the fact that f. !umbrica!is of th is species "is not unl ike a perforat ing specimen. It should be compared with Pa!aeaclz!;,a perforans DUNCAN" (1932, p. 65). ROIJON and ZITTEL ( 1887) described canals bored by algae in Ordovician conodonts.

So-called Girvaue!!ae cred ited with the ab i l i ty of boring i n iron com­pounds are reported by CAYEUX (1909) and HAYEs ( 19 15). According to CA YEUX they occur abundantly in ooids of hematite , less abundantly in ooids of siderite , and occasionally in chamosite ; they were also observed i n opal. According to HAYES, they are best developed in spherules of hematite and chamosite but they also occur i n s ider ite. Like PIA ( 1937, p. 362), I am i ncl ined to consicler these structures as non-organic.

5· The present algae-bearing deposits.

The present deposits including perforat ive and enveloping algae belong to the Ordavieian section of the Si ljan District in the province of Dalarn a, Sweden.

Rock samples includ ing penetrative and enveloping algae from other parts of the Pal;eozo ic Scandoestonian Region have also been examined , viz. from the Island of Öland (stratum corresponding about to the stratum G of Dalarna investigated here) , the province of Uppland (drift boulders from the Sclzroeteri Limestone of the submarine region of the Bothnian Gulf, Lower Ordovician ) , and from Estonia (Obere Linsenschicht , Aseri stage , Lower Ordovician ).

In the paper of 0RVIKU ( 1940) on the i ron ool ite of the Aseri stage , canals bored by penetrative algae have been reproduced (PI. XXII , Fig. 6); they were i nterpreted by ORVIKU as inorganic structures.

Only a short seetian of the Lower Ordavieian of Dalarn a was examined , viz. the layer which in earlier l iterature was called the Lower Grey Ort/w-

fVAR HESSLAND

ceras Limestone (for instance TöRNQUIST r883), plus the uppermost part of the subjacent stratum (the Lower Red Ort/wceras Limestone), and the lowermost part of the superjacent one (the Upper Red Ort/wceras Limestone). Later, these s trata have been given other names, but they are partly un­suitable and are therefore not used in this paper. It is also scarcely possible to make com plete earrelations to the better investigated Estonian Region. Certain strata seem to be correlatable, however, such as the Lim bala Lime­stone (th e Lower Red) =Bli rx. Furthermore, the Ingermanland Asap/tus expaJtstts Zone (B III a) is represented in the middle part and somewhat below the midheight of the Lower Grey: fauna with AsapJtzts expansus (L) WAI!LENBERG, Illamus centrotus DALMAN, Ptychopyge anguslifrons (D ALMAN), Ampyx nasulus DALMAN, and Ortltis callactis DAUvlAN. In the upper part of the Lower Grey, the Estonian Asapla-ts raniceps Zone (B III {3) seems to be represented: fauna with Megalaspis heros (DALMAN), Megalaspis rudis ANGELIN, and Clitam bonites (i') zonala (DALMAN).

W hether the Estonian zones B II {3, B II y, and B III y are representecl in the Si ljan District is not ascertained. What the Upper Red corresponds to is no t known: i ts lower part may not be called Gigas Limeston e as is now done, since this fossi l appears first about 5 m above the lower limit of the Upper Red.

In order not to confine the results obtained to the prevailing but, m

several respects, inappropriate or erroneous stratigraphic names, provisional denaminations for the strata investigated have been used. I n the solution of these stratigraphic problems the whole necrocoenoses (not !east the semimicro- and microorganisms, especially the ostracods) and the inorganic sedimentary phase must be examined, but such in vestigatians have only begun.

In this paper, the main ly grey stratum (the Lower Grey), including the l!,xpansus and Raniceps Zones, is given as stratum G. The former zone is abundantly ooli tic (limonitic ooids), the latter is samewhat oolitic (parts of the ooids chamositic) . The subjacent reddish maroon stratum is called R J

and the maroon superjacent is narned R II. The bounclaries R l/G and G/R II may be mainly synchronous in the whole Si ljan District (cf. parts l and IV of the present series). Moreover , the Siljan District was in close connection with the ocean during the R J and R II stages, but the commu­nication was restricted during the G stage.

The positions of the loca lities investigated appear from the map, p. r 14,

111 part I o f th e present series.

6. Description of the present penetrative and enveloping algae.

Penetrative and enveloping algae are abundant i n stratum G, especially just bel o w the midheight of the stratum. They occur occasionall y in the uppermost part of stratum R J and the lowermost part of stratum R II (Fig. r ) .

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I t appears from Fig. 2 that the majority of the canals have a d iameter of I-Sfl-,

most of t hem I-3 fl (3 I 7 measurements i n 35 penetrated shel l fragments). Rather many have a somewhat larger d iameter ( 5-20 fl); a few isolated higher values were noted. Thinner canals branch off successively from the th ick canals : the finest ramifications are those which cons­titute the majority of the canals , i. e. those which have a d iameter of I-3 fl· In P I . VI, Fig. 3 a fragment is shown in which such a d imin ish ing of the d iameter can be followed from about IOO fl to about I fl· However , whether t h e th ickest canals contained more than one algal th read cannot be defin itely stated , but th is appears to have been the case.

The thickest branches are most often gently tortuous. Branches of median th ick­ness are not seldom rather straigh t. The most m inute canals are fairly straight or gently curved; the ir course is extremely minutely and somewhat i rregularly z igzag.

The fine canals are abundantly ramose with acute or right angles. At the points of ramification they sometimes form a triangular or rounded swelling. The ends of the algal threads are sometimes swoll en. There are also larger irregular swel l ings.

The algologist, Prof . H. SKUJA, had the courtesy to examine some preparations wh ich I had made by dissolv ing the cal­careous carbonate substance around the algae in acetic acid so that the algal threads were set free.' H e stated, mainly on account of the type of ramification and the thickness of the threads , that there are two or possibly th ree types of algae present :

' l wish to express my gratitude to Prof.

SKUJ A for his kind n ess to perform this examina·

tion and for valuable discussions on algae of the

present type.

D

'-0

LOWER ORUO VICIAN PENETRATIVE AND ENVELOPING AI.GAE

I. Bluegreen algae of Plectouema type , remin iscent of P. terebrans BaRNET and FLAHAUL T (th in threads with a false , acute ram ification).

II. Possibly green algae (th icker threads with a real , r ight ramification ) . III. Possible fungal hyfes (thin threads with a real , right ramification ) .

The present material helps to find the way i n which shel l fragments are infected by algae and thus d is integrated.

First may be ment ioned that especially sheils of tri lobites and orthoiels are i n fected. Shel ls of these groups are very numerous. Also a few fragments of strophomenoids and inarticulate brach iopods occur, and they were observed to be bored to some extent. Algal threads are often found i n the cavit ies of crinoids , but the crinoid skeleton was not observed to be bored. Shells of cephalopods, conulariae, and gastropods , as weil as the skeletons of bryozoans and calcareous algae, were not seen to be i n fected; ostra­cods may occasionally be sl ightly i n fected, but , as a rule , they are not bored.

Sometimes , the algal canals follow the structu res of the shel l , such as the laminae of orth ids , bu t th is seems on ly to be occasion al; i n most cases , the canals run quite i rregularly. The algae attacked the sheils from any part. In some cases one may observe, however , that the infection took place most easi ly from broken ends of lameliar sheils and that the algae fol lowed already exist ing pores and canals.

In newly i n fected sheils the canals are most abundant just below the surface, and only isolated canals traverse the inner parts of th e she!!. As the infection proceeded, the sheils became more and more filled with canals. Thick stems were developed , and these could traverse the whole sh e!!. In th is way , the shel l became parted. In fact , th is was in the present case an important phase i n the process of d isintegration of shells.

During the course of infiltration , angular parts of the sheils bad been more or less completely consumed, so that the fragments bad grown more and more rounded.

By the partition and consumption of shel l substance by the algae the shel l fragments had el iminished i n size. \Vhen th is process had proceecled so far that only a small part of the shel l was l eft , i t happened very often that the fragment was covered with layers of envelop ing algae. If these algae became filled with hydrous i ron oxide a l imonit ic ooid wi th concentric structures was formed. On the other hand , i f a fragment bad become en­crusted with l imonite at an earl ier stage , v iz. when a shel l fragment bad been parted i n to a suitable s ize , and the angles had become rounded so that an ovoid form had been created , a so-called false ( i. e. a non-stratified) ooid would have appeared. As a matter of fact, i n the present material one finels all stages of th is process : non- infected shel ls; slightly i n fected , angular fragments; rounded fragments i n different stages of parti tion; fai rly

420 IVAR HESSI.AND

small fragments , abundan tly bored , and covered with a th in layer of enve­loping algae; and finally very small and abundantly bored fragments sur­rouneled by a thick layer of regularly stratified enveloping algae.

Considering enveloping algae , such occur also around non-bored frag­ments . Sometimes cr ino ids are enveloped by a fai rly th in layer of algae .

Whether the enveloping algae are specifically different from the pene­trative is not known. Juclging from the th ickness of the threads , they possibly belong to the above-mentioned group Il (green algae) .

7· Penetrative and enveloping algae as indicators of changes

of level in the strata! sequence investigated.

As mentioned (p. 416), pt>netrat ive algae are most abu ndant m the middle part and somewhat below the midheight of stratum G. Enveloping algae are restricted to th is horizon . Penetrative algae also occur i n other parts of stratum G. Furthermore , they generally occur just below R l/G and just above &/R il. They were not observed i n samewhat deeper parts of stratum R l, and they generally soon disappear samewhat above G/R Il.

Consideri ng the fact that shell fragments occur abundantly i n those parts of R l and R II where penetrative algae are absent , one may conclude that the water was too deep for these organ isms dur ing those times .

On the other hand , the water must have been more shallow cluring the G stage , judging by the fact that penetrative algae were abundant dur ing th is stage and that the enveloping are confined to th is stratum . S ince the algal frequency culminates i n the micldle part an d just below the midheight , the depth of water may have been !east just during the sedimentation of this horizon . This is emphasized by the fact that the trans­parency of the water contemporari ly seems to have been decreased owing to the circumstance that !arge quantit ies of minerogene fine-particles were settled i n many cases . The sedimentation of m inerogene fine-particles was less comprehensive dur ing the next proceeding and following periods (cf. part IV of th is series of papers) .

From the appearance of the algae , the conclusion may be drawn that, in the Si ljan District , a regression took place dur ing the last part of the R I stage and the first part of the G stage , and that a transgression fol lowed dur ing the later part of the G stage and cont inued during the Rlf stage .

The fact that the S i ljan District dur ing the R l and R Il stages was i n closer commu nication with the ocean than during the G stage may not have i nfluenced the frequency of penetrative algae; such organisms are common both i n the open sea and in more or less closed ocean ic areas.

LOWF.R ORDOV!C!AN PENETRAT!VE AND ENVE!.OP!NC: AI.r.AE 421

8. The importance of penetrative and enveloping algae for the

precipitation of hydrous iron oxide and for the

formation of lirnonide ooids.

The precipitation of the hydrous iron oxide which fills up penetrative algal canals and enveloping algae is here considered to h ave been eaused by the activity of the algae themselves.

In discussing this question , one has first to consicler the fol lowing suppositions as regards the hydrology in the Si ljan District during the C stage , i. e. when algae of the present types constituted a quantitatively important part of the organisms in this district (the suppositions are ac­counted for and discussed in parts I and IV of the present series).

The communication with th e ocean was restricted , judging by the elevel­apment of th e ostracodal fauna and the appearance of the sediment. From the composition and structures of t he sediment i t appears , furthermore, that the water was stagnant to a rather high degree. The water's content o strong electrolytes was fairly low; but its C02-pressure may have been high , as is the case in corresponding recent surroundings. The pH may have been high (presumably around 8), at !east in the bottom layer of the water, where a buffer solution was probably formed of calcium carbonate (shells and other calcareous substances) and of carbonic acid , mainly formed at the decomposition. Finally, the water's content of 02 may have been rather considerable ; the oxygen was produced by algae.

Dissociable Fe-salts of volcanic and terrigenous origin , as wei l as those released from decaying organisms were, i n this water with high C02-pressure , and i n presence of oxygen , transformed into i ron bicarbonate:

I Fe .

. + 2C02 + H20 +- O. -+ Fe(HC03)2

2 -

Tron bicarbonate was probably also supplied by streams. The content of iron bicarbonate in the water could be high as Iong

as the C02-pressure was high. But , if th e C02-pressure was lowered (by the earbon dioxide assimilation of the algae) the instable iron bicarbonate was transformed in to ferrous oxid e :

Fe (HC03)2 ->- FeO + H20 + 2C02 The ferrous oxide, in turn , was oxidized into ferric oxide (oxygen

produced during the earbon dioxide assimilation of th e algae) : I

2FeO + - 02 -+ Fe203• 2

The iron oxicle was hydrolysed in to a hydrous iron oxide: Fe203 + nH20 -+ Fe203 - nH20 Under these conditions with a high pH, the hydrous iron oxide was

precipi tated , since its salubi lity product at such a pH is extremely low. As the content of strong electrolytes was fairly low, the hydrous oxide can be expected to have been precipitated i n a weak concentration.

422 IVAR HESSLAND -----··

The circumstance that this colloidal substance was precipitated i n such a h igh degree as was the case just around shel l fragments bored or sur­rouneled by algae is explained by the fact that, in the stagnant water, spheres around these fragments were formed where the deciding conditions in the process related above could appear, i. e. the C02-pressure was lowered and the 02-pressure was high. Whether the weakly concentrated colloid was incorporated intramembranously during the life-time of the algae or post­mortally is difficult to decide. I th ink that it took place during the life­time. SJÖSTEDT (1921), and NAUMANN and SJÖSTEOT (1923) found that an intramembranously enrichment of iron is common in algae, especially in Cyanophyceae.

The limoni tic ooids with a concentric structure were thus created by the fact that enveloping algal th reads were fixed by hydrous iron oxide. If, on the other hand , the surface of a shel l fragment, rounded and pene­trated by algae, was encrusted before having been enveloped, a false ooicl without concentric structures was formed.

9· On the formation of limonitic and hematitic oolite according

to some other authors.

Oolitic iron ores of great economic importan ce occur in several coun­tries. The genesis of i ron ooids has been discussed mainly in connection with mining investigations. Among the more prominent investigators on this subject are CA YEUX and HAYES.

The descr iptions of French ool itic iron ores by CA YEl;x , and h is re­productions of microscopic sections of thin slides are wel l-known (1909 and 1922). He bad stuelied several ty pes of iron ool ite (siderite, cha mosite, magnetite, pyrite, hematitc , and l imonite. )

In the earlier paper , CA YEUX considered limonite to be final product in a sequence of changes. The original substance in the ooids was thought to be calcium carbonate which vi a siderite , chamosite, and hematite h acl been transformed into limonite. Girvanella was considered to have taken a great part in the formation of the calcareous ooicls, but such algae were not thought of as precipitators of iron substances. (CA YECX in terpretecl some structures in iron ooicls as bored by algae - thus the borings should have been made in iron compounds - but, as pointed out by PJA 1937, p. 361, this interpretation is certain ly not tena ble. )

The opinion of CAYEUX on the replacement of calcareous ooids by iron ooicls is not chemi cally establishecl, and there 1s reason not to attach too great importance to these ideas.

In his later work, CAVEUX holels th at hematite (which according to F ren ch usage of this term also includes limonite -lzematite brune) is aclcli tion ally

l.OWER ORDOVICIAN PENETRATIVE AND ENVELOPING ALG A E

prccipitated directly. Bacterial activity is considered as most importan t for this type of i ron ooid formation.

False ooids should , according to CAYEUX , be formed by wave action. As a matter of fact , false ooids consisting of shel l fragments can be formed in this way, as is seen on certain beaches of lower parallels (PI. X, Fig. z) , but these ooids are not encrusted with limonite. For the precipitation of limonite in the form of false ooids the water must be assumed to be stagnant , as shown in the previous chapter. The false limonit ic ooids in CA YEUX's material are of the same type as the present ones and have certainly been formed in the same way.

The monograph by HAYES (1915) on the Lower Ordavieian oolitic vVabana ores in Newfoundland contains much of interest. In this investiga-tion , HA YES has noticecl the production of oxygen by algae. How ev er , he does not attach the same importance to this productian as is made in the present paper. Like other authors (for instance HARDER 1919) which have also recognizecl oxygen as the most important waste product of plants , HA YEs has not obsen·ed the important r61e of the algal-produced oxygen for the very precipi tation of hyclrous iron oxide as discussed in this paper. This process must be considered much more essential for the genesis of iron oolite than the oxidation of for instance chamosite in to hematite which these investigators consicler as the essential role of the algae in this case.

Furthermore, as a matter of fact, i t is very doubtful whether some struc­tures , as in terpreted by CAYEUX and HAYES , are bored by algae (cf. p. 415).

On the other hand, the canals in sheils of inarticulate brachiopods in ferrugineous sandstones (as i l lustrated by HAYEs) and in false ooids of different types (as il lustrated by CAVEUX) are certainly of algal origin.

An addition al interpretation of general interest in HA YEs' paper wi l l be shortly considered, viz. that the elimate should have been temperate during the deposition of the Wabana formation (Arenig and Llandeil ian). HA VES based this assumption on the f act that the content of calcium carbonate i n the strata! sequence is low and that there are traces of algae (as mentioned above, definite traces have not been founcl in the iron oolite but in interealating ferrugineous sandstones). He suggested, in warm seas, calcium carbonate is precipitated by denitrifying bacteria (DREW's important discovery of Pseudomonas calcis had recently become known ) , and for this reason the water in wann seas is considered poor in nitrogen substances , so that the algal vegatation is very scanty (Drmw's explanation ). On the contrary, in a temperate cl imate, the algal vegatation is r ich , but cal cium carbonate precipitation induced by bacteria is of no importance. Also if HA VES' idea shoulcl be correct that bacteria are the on ly or the most im por­tant inducers of calcium carbonate precipitation in warm seas , his argument is not tenable. It is true that non-calcareous algae are scarce in warm

IVA R HESSLAND

seas, but ealcareous algae generally form a greater part of the eoral reefs than the earals do themselves ; moreover, i n ealcareous skeJetans of different organisms, boring algae are very numerous, not !east in the reef-forming earals and ealcareous algae. Thus , HA YES' idea that the el imate during the Lower Ordavieian should have been temperate has to be rejeeted . On the eontrary, exaetly the iron pree ip i tation by means of penetrative and enveloping algae ind icates t h at the el imate was w arm : the required stagnation i n a

shal low water can seareely have been fonned elsewere than in a warm el imate, as ind icated above (p . 42 3 ) .

Bibliography.

R-I-TTERs, A . L. J 8 9 2 . On Conchocel is , a new genus o f perforati n g alga e . Phy­cological Memoirs . l . London .

BERN E R , L. 1 9 3 1 . Contributian a l ' etude sociologique des algues m arines dans l e golfe d e Marsei l l e . Ann. Mus . Hist . Natur. Marsei l l e . 2 4 . Mem . 1 . Marseil l e .

BONAR , L . 1 9 3 6 . A n unusual Ascomycete i n t h e sheils o f mari ne ani m a l s . Univ. Cali fornia Pub l . Botan y . Vol . I 9 . N o . S · B e r k eley, Cali fornia.

B O R N ET, Ed. and FLAHAULT, C h . I 8 8 9 . Sur quelques pl antes vi vant dans l e test calcaire des mollusques . Bull . Soc. Bot. Fran c e . XXXVI . Pari s .

C A RPENT E R , W . 1 8 4 5 . O n the microscopic structure o f shel l s . Rep . British A s s . Advan cement Sci . 1 8 4 4 . London .

CAYEUX, L. I 9 0 9 . Les minerais de f er o o lithique de Fran ce . F ase . I . Minerais d e fe r prim aires . Etudes Gltes Min . Fran c e . Paris . I 9 I o . Les algues calcaires du groupe des Girvanel la et l a form ation des oolith e s . C . R. Sci . I ' Acad . Paris . 1 9 I 4 . Existence de n o m breuses traces d ' algues perforantes dans les mi n e · r a i s de fer ool ithique de Fran c e . C . R. Sci . l ' Acad . T o rn e I s S . Pari s . 1 9 I 6 . lntroduct ion a l ' etude petrograph ique d e s roches sedim entaire s . Pari s _ 1 9 2 2 . L e s m i n erais de fer oolithique de France. F a s c . I l . M i nerais d e fer secondaires . Etudes Gltes Min . France. Pari s .

D A N G E A RD, L. J 9 3 S · L e s Piselithes a Girvanelies dans l e Jurassique de Nor­m andie . Bu l l . S o c . G e o l . Fran c e . Ser . S· Torne S· Paris .

DuN CAN, M. 1 8 7 6 . On som e Thal lophytes parasitic with in recent Madreporari a . Pro c . R o y . S o c . London . V o l . X X V . Londo n . I 8 7 6 . O n som e unicellular algae parasi t i c within Silurian a n d Tertiary Corals, with a n otice o f their presen ce i n Calceola sandalina and other fossi l s . Quart. Journ . G e o l . Soc. London . Vol. 3 2 . London .

ERCEGOVtc, A . I 9 3 4 · Wellengang und Lithophyten zone an der ostadriat ischen Ki.iste . Acta A driatica . I n s t . B i o l . -Ocean . Spl i t . N o . 3 · Split .

ETHERIDG E , R. I 8 9 o . On t h e o c curre n c e of microscopi c fun gi , al l i ed to t h e g e n u s Palaeachlya D uNCAN, i n th e Permo- Carbon i ferous rock s o f N . S . Wales and Queens l an d . Rec . G eol . Survey N e w South Wal e s . Vol . I . S i d n e y . 1 8 9 9 . O n t w o a d d i t i o n a l perforati n g bodi es, believed to b e T h a llophytic cryptogams, from the Lower Paleozoic rocks of N . S . Wale s . Rec . Austr . Mus . V o l . III . Sidney.

FEARNSmEs, W . G . I 9 J o. T h e Tremadoc siates a n d associated rock s of South East Carn arvon s h i r e . Qu art . J ourn . G e o l . S o c . Lon don . Vol . 6 6 . London .

LOWER ORD O V ICIAN PENETR ATI V E A N J > F.NVELOPING A L G A E . . p s

H A RDER, E. C. I 9 I 9 · Iron depositi n g h acteri a a n d their geologi c rel ati o n s . U . S . Geo l . Survey. Prof. P a per 1 I 3 . Washingto n .

H AYEs, A . O . I 9 I S . Wabana iron ore of Newfoundland . Canada D epartment o f Mines . Geo l . Survey Canada . Mem . 7 8 . N o . 6 6 . O ttawa .

H r.NSMAN, R . I 8 9 S · Some eauses o f the disintegration o f shell s . Irish Natura list . Vol . I V . N o . 6 . D ub l i n .

H ESSLAND, I . 1 9 4 6 . O m uppk o m sten av korallre v . Naturen . N o . 6 . 1 9 4 6 . Bergen . HuEG, O . A . I 9 3 2 . Ordavieian algae fro m the Tron d h e i m area . Skr. Norsk e

Vid . Akad. I . Mat . -Nat . K l . N o . 4 · Oslo . KvuN, H . I 9 3 5 · Uber einige kalkbohrende Ch lorophy ceen . Fysiogr . Sällsk .

Lun d . Förh . B d . S · N o . I 9 . Lun d . KöLLIKER, A . r 8 6 o . Ueber das ausgebreitete Vorkommen von p flan zl ichen Pa­

rasiten i n den Hartgebitden n i ederer Thiere . Zeits c h r . \Viss . Zoologie. Bd . r o . Leipzi g .

LAGERHEIM, G . I 8 8 6 . Cod iolum polyrhizum n . s p . E t t b i d ra g t i l l kännedomen o m s l ägtet Codi o lum A. B r . Ö fvers . K . Vet . A k a d . Förh . No. 8 . Stockhol m .

L\PPARENT, J . d e . I 9 2 3 . Le<;;o n s d e petrographi e . Pari s . L I N DGREN, W. 1 9 3 3 . Min era l deposits . New York . N A n soN, G. I 9 0 r . Die perforierenden (kalkbohrenden ) Algen und i h re Beden­

tung in der Natur . Scriptae B o t . U n i v . l m p . Petropol i t a n a e . Fasc. XV I I . St . Petersburg. I 92 7 . Les algues perforantes, leur d i stribut ion et le ur ro le dan s l a natu r e . C . R . Sci . l ' A cad . Pari s . Tome r 8 4 . Pari s . I 9 3 2 . Contributian il l ' etude des algues perforante s . B u l l. l ' A c a d . S c i . U . R . S . S . N o . 6 . Leningra d .

N AUMANN, E . and S;ösTEDT, G . I 9 2 3 . U b e r e i n e Lagynion-Siderocapsaartige Struk­tur in m arinem Au fwuch s vom Öresun d . U n dersökn i n g a r över Öresund X . Lunds Univ . Årsskr . N . F . A v d . 2 . B d . I 9 . N o . S · Lun d .

0 R V I K U , K . r 9 4 0 . Lith ologie der Tall i n n a-Seri e (Ordovizi u m , Est l a n d ) l . l 'ubl . Geol . lnst . Univ . Tartu . N o . s s . Tart u .

PARKE, M . W . a n d MooRE, H . B . I 9 3 S · T h e biology o f B a l anus b a l a n o i d e s . I l . A l gal i n fection o f the s h el l . Jotun . Mari n e Bio! . A ss . Vol . X X ( N . S . ) . N o . r . Plymouth .

P I A , J . v o n . 1 9 3 7 . Die kalklösenden Thallophyte n . Arch i v H y d robi ol . B d . X X X I . Stuttgart . ( Comprehmsive bibliography on boring organisms . )

PR A'l:JE, O . 1 9 2 2 . Fossile k a l k bohrende Algen ( Chaetophorites gomontoi des) 11 1 Liaskalk e n . Centralblatt M i n . etc . J a h r g . 1 9 2 2 . N o . r o . Stuttgart .

QuEKETT, J. 1 8 S 4 · Leetures on h i stology. London . RoHON, W . a n d ZrrTEL , K . v . 1 8 8 7 . Uber Conodonten . S . B . Bayr. Akad . \V i s s .

Math . -Phys . Kl . r 6 . Mi.inch e n . RosE, C . B . 1 8 s s . O n the d iscovery o f p arasiti c b o r ings i n fo ssi l fish-scales .

Transact. Microscop . S o c . London . N . S . 3 · S . 7 · Lon d o n . S;ösTEDT , G. I 9 2 1 . O m j ärnutfä l l n i n g hos h avsal ger v i d Sveriges kuster. B o t a ­

n i sk a Notiser . Lun d . SP itiNG, W . I 8 9 9 . U e b e r d i e eisen h a l tigen Farbstoffe sedi ment ärer Erdböden und

iiber den wahrscheinlichen Ursprung der roth en Fel sen . N . J ahrb . Min . , Geol . und Pa läont . Jahrg. 1 8 9 9 · B d . 1 . Stuttgart .

STENS!ö, E. 1 9 3 6 . On the placodermi o f t h e Upper D evon i a n of East Green­l a n d . Med d. Grönl an d . Bd. 9 7 . No. 2 . Kobenh avn . (Excel l e n t figures o f b o r i n g Thall ophytes i n d ermal bones of fi s h e s . )

STIRRUP, M . I 8 7 2 . O n sheils o f mol insea showing s o - c a l l e d fun g o i d growth s . Proc . Li t . Phi l . Soc . Manchester . Vol . X I . ses, ion 1 8 7 I - I 8 7 2 . M a n chester .

4 2 6 I V A R H ESSLAr\ IJ ·--------

S T 0 R M E R , L. I 9 3 I . Boring o rga n i s m s i n tr i lobite she I l s . Norsk G eol . Ti d sk r. B d . r z . O s l o .

Tö RNQUIST, s . L. J 8 8 3 . Ö fversigt ö fver be rgbyggnaden inom silj a n s o m rådet i Dalarn e . S v . Geol . U n ders . Ser . C . N o . 5 7 . Sto c k h ol m .

WEnL, C . I 8 5 9 · U b e r d i e Bedeutung d e r i n d e n Sch alen v o n manchen A ce p h a l e n und Gastropo den vorkom menden Canäl e . S . B . A k . \Vi s s . Wien . Math .-Nat . Kl . 3 3 · Wien .

W E T H E R E D , E. B . 1 8 9 5 · T h e fonnation of o o l i t e . Quart . J ourn . Geol . Soc . London . Vol . 5 I . London .

\V ETZEL, W . 1 9 3 8 . D i e Schal enzerstörung du re h Mi croorgan ismen . Erschei ­nungsform , Verbreitung u n d geol ogisch e Bedeutung i n G egenwart und V er· gangen h ei t . K i e l e r Meeresforsch . Bd. 1 1 . H . 2 . Kiel .

Explanation of plates.

Photographs taken by the author, no rctouch.

PAN PHOT photographic equipment, fi lter light green (y) , C EVAKRT H.epl ica ortho­

ch romatic plates .

Plate I. 265 x

Shel l fragments of orthoidean brachiopods penetrated and enveloped by algae.

The enveloping algae form a thick felt- like structure which appears black in the

photograph. The canals of the penetrative algae should be distinguished from the laminated

st ruetures of the s hel l ( Leskusänget I 5) .

Plate Il. 265 x

Shel l fragments of orthoidean brachiopods penetrated by algae.

Fig. I shows a thick stem branching off fine threads.

Fig. 2 shows, inter alia, a rounded excavation in the shel l , certainly formed by algae :

cx tremely fine canals radiating from the excavation.

( Fig. 1 : Leskusiinget 1 3 ; Fig. 2: Leskusänget 10.)

Slightly infected shell fragments.

Plate III. ! JO X

Fig. 1 : Trilobile fragment with perforating pores (the shel l "s own structure) and a

few canals bored by al gae (Bom-D ådran 4).

Fig. z: Another trilobite shell fragment with pares (broad perpendicular and straight

canals) and algal canals which have partly attacked the shell from the pares (Gul ler­

i'l sen 9).

Fig. 3: Trilobite shel l fragmen t s in the process of rounding by algal activity (Cul ler-

h sen r o\ Plate IV.

! JO X Orthoidean she l l fragments , partly fi l led with l imonite in fissures along the shel l ' s

o w n structures and partly penetrated by algae w hich. t o some extent, have attacl-:ed

from these fissures.

( Fig. 1 : Stenberg 4 ; Fig. 2 : Leskusänget 1 3 ; Fig. 3 : Leskusänget I 4.)

L O \V E R O R U O V ! C I A N l'ENET R A T I V E A N D E N V E L O P I N (; A L G A E

Plate V. J 30 x

Fig. I : Tri lobite shell fragment pierced by fair! y th ick algal thread s without rami­

fications (Röjeråsvägen 4).

Fig . 2 : Orthoidean s hel l fragments ; the !arge r penetrated by a thick al gal s te m

branching off t hin threads, and excavated by algae ; t h e smaller not penetrated bu t filled

with limonite along structural fissures (Röjeråsvägen 4).

Fig. 3 : Orthoidean s h el l fragment, pierced by broad, irregularly swollen al gal threads

(most I i kely green algae) and thin threads (most I ikely bluegreen algae) (Granmor 7 ) .

Plate VI. Figs. J , 2, and 4 : I 30 X ; Fig. J : I 9 X

Figs . I -3 (tri lobite shells) i l lustrate d ifferent stages of partition of shel ls by means

of algae.

Fig. I : Beginning wedge-like attacks from the upper side (Bom-Dåd ran 2).

Fig . 2 : Shell fragment almost completely partit ioned in two separate fragments

(Rävanä s 6). Fig. 3 : Shell fragment practical! y completely divided in to two parts (attack from the

upper part of the shel l ) ; a seeond spl i tting attack also took place from the under side

but had not extended so far (Gulleråsen g).

Fig. 4 : Orthoidean shell fragment excavated and penetrated by algae, and also part! y

fi l led with limoni te along structural fissures of the shell (Leskusänget I ?) .

Plate VII. J 30 x

Fig. 1 : Tri lobite shel l rich in algal canals and cavities , and fairly well rounded , but

not enveloped by algae (Gulleråsen 1 3).

Fig. 2 : W el! rounded Orthoidean she l ! , penetrated and samewhat enve lopecl by algae

(Röjeråsvägen around samble 4, sample taken by Prof. G. S.ii.VE·SÖDERBERGH). Fig. 3 : Limonitic ooid , consisting of a s hel l fragment , penetrated and enveloped by

a lgac (Stenberg 1 J ).

Plate VIII. Fig. I : 40 X ; Fig. 2: 265 x

Fig. I : Limonitic ooidic shell fragments and limoni tic ooids wi th a concentric struc­

ture for med because enveloping algae have been fi lled with hydrous i ron oxide

( Leskusänget I 2).

Fig. 2 : Detai l of the concentric structure showing separate algal thread s (Stenberg 6).

Plate IX. Fig. I : 40 X ; Fig. 2: 40 X ; Fig. 3 : I JO X

Fig. J : The specimen in centrum is a crinoid enveloped by algal threads , the el l ipsoidic

specimens are ooids with a concentric structure formed by enveloping algae (Röjeråsvägen

around sample 4, sample taken by Prof. G. SÄVE-SÖDERBERGH). Fig. 2 : Ooids with concentric algal structures (Röjeråsvägen 4).

F ig. J: Crinoid fragment with algal threads in the skeleton interspaces, and covered

wi th a chamosit ic l ayer (Stenberg I I ) .

I VA R HESSLA N D

Plate X . Fig . I : I JO X ; Fig. 2 : 30 X ; Fig. J : 27 '/z X

Fig. I : Fragment of a strophomenoidean s hell fragment (Piectambonitidae) showing

pseudo-punctae and Iaminatian which should not be taken for algal canals (a few traversing

algal canals discernible) (Leskusänget 1 4).

F ig. 2 : Recent false ooids consisting of fragments of L i thothamniace<e, and rounded

by wave action. Tropical beach sand.

Fig. J: Recent molluscan shell fragment crowded with canals bored by algae. Canals

fi lled with methylene blue. Tropical coral sand.

Bul l . G eo l . Inst . , Upsala. Vol . XXXI I I : 4 PI . l

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