Euendolithic cyanobacteria/cyanophyta
ENVIRONMENT: ECOLOGY AND GLOBAL CHANGE
INTRODUCTION
In marine environments, endolithic microorganisms are omnipresent in various calcareous substrates. The resulting borings are defined as micro-borings by tube diameters ranging in size from less than 1 Ilm to over 100Ilm.
They are frequently found in both, modem and ancient ecosystems. For an overview of relevant publications see Radtke et al. (1997).
Taxonomie and ecologic work on modem marine endoliths has greatly inftuenced geologicaVpaleontological research, and it provides data for modem-fossil comparisons. Among other results, cyanobacterialcyanophyta, chloro-phyta, rhodochloro-phyta, and fungi were identified to be the major producers of modem microborings.
Usually the extemal features of the euendolithic soft body are copied by the morphology of the boring system. A special artifical cast technique (Golubic et al., 1970), suitable for modem and fossil microborings, allows a three-dimensional view and permits morphologie comparisons. Modem-fossil comparisons often aid in matching the possible producer of a fossil micro-boring, and contribute to depth reconstructions in ancient environments.
Information about the paleo-depth of sedimentary basins assist in recon-structing regional geological history as well as in detecting minable deposits, since the development of sorne of them is linked to distinct water depths.
A research project, established in 1984 at the Frankfurt University, headed by K. Vogel, is addressing several questions, among others, frequency, variety, and paleoecoloy of fossil, marine microendolithic borings. Different periods of earth history are or have been under investigation.
This publication concentrates on four important trace fossils (ichnotaxa), similar to modem cyanobacterialcyanophyta. New data conceming their stratigraphie distribution are presented, and matches with modem boring sys-tems identified by recent research are reported. In addition, comments on the bathymetric range of the ichnotaxa relative to their modem counterparts are given.
MATERIAL AND METHODS
The present evaluation is based on samples from Paleozoic (230 Ma to 570 Ma ago), Mesozoic (65 Ma to 230 Ma ago), and Cenozoic (65 Ma to Recent) strata. The following periods are or have been under investigation:
Silurian (Bundschuh etai., 1989; Glaub& Bundschuh, 1997), Carboniferous (Vogel, 1991), Permian (e.g. Balog, 1996), Triassic (e.g. Schmidt, 1992;
Balog, 1996), Jurassic(e.g. Glaub, 1994), Cretaceous(e.g. Glaub, 1994; Hof-mann, 1996), Tertiary(e.g. Radtke 1991), and Quartemary (present)(e.g.Radtke, 1993, Vogel et al., 1996; Gektidis, 1997).
For each ancient period about 400 to 500 hard substrates (mainly brachio-podes, bivalves, corals, sponges, and belemnites) are examined, using the cast embedding technique (outlined in Golubic et al., 1970) and the SEM. The description and classification are based on morphologieal criteria. Taxa are treated as ichnotaxa. For further discussion of the terminology used refer to 136 Bulletin de l'Institut océanographique, Monaco, n° spécial 19 (1999)
EUENDOLITHIC CYANOBACTERIA AND THEIR TRACES IN EARTH HISTORY
e.g. Radtke (1991), Tavernieret al. (1992),Vogel et al. (1995). Classification resulted in 28 to 37 ichnotaxa for each period.
Morphological similarities of ichnotaxa to borings of modern endoliths allow the comparison of fossil microboring communities with modem endo-lithic assemblages. The resulting bathymetric classifications are verified by conventional paleo-depth reconstructions (Glaub, 1994; Vogel et al., 1995;
Glaub& Bundschuh, 1997; Glaub, in press).
A scheme of ichnocoenoses was developed, characterizing distinct index ichnocoenoses for the shallow euphotic zone II and III, the deep euphotic zone and the aphotic zone. They are named according to the two or three most important ichnotaxa, caIJed key ichnotaxa (Glaub, 1994; Vogelet al., 1995).
RESULTS
In the following sections short descriptions of the ichnotaxa are given, and their record in earth history is indicated (Fig. 1). Comparison to modem endo-liths is shown with respect to morphological similarities and ecological needs.
.0<::- '" Ichnotaxa
Eras ~0.~ ~ Periods
Fascicufus Fascicu/us Eurygonum Scofecia
,,~
0 acinosus dac/y/us nodosum fi/osa
ü Quaternary
0 2
N0 C
Q) Tertiary
u 65
ü Cretaceous
0 135
N 0(j)
Jurassic
Q) 190
~
230 Triassic
280 Permian
350 Carboniferous ? ?
'0ü
Devonian
N 405
0
Q)
<ii
[L Silurian
435
500 Ordovician 570 Cambrian Precambrian
Figure 1. Known stratigraphie record of four mieroendolithie iehnotaxa similar to modem eyanobaeteria/eyanophyta.
Bulletin de f'fns/i/ut océanographique, Monaco. nOspécial .19 (1999) 137
ENVIRONMENT: ECOLOGY AND GLOBAL CHANGE
Fasciculus acinosus GLAUB1994 - Fig. 2/1
DESCRIPTION. Based on studies of Jurassic/Lower Cretaceous samples (Glaub, 1994), Fasciculus acinosus is characterized by several cavities, arranged close to each other like a bunch of grapes. The distal swelling is large and elongated compared to the other swellings. Individual proximal swellings are 4 to 8 !lm in diameter, whereas the distal swelling measures 7 to
12 /lm in diameter and 7 to 14/lm in length.
RECORD IN EARTH HISTORY. Permian, Triassic, and Jurassic. In recent envi-ronments, Fasciculus acinosus borings are known from Hyella balani.
MODERN-FOSSIL COMPARISON.Fasciculus acinosus differs significantly from ail other borings by its densely packed boring system, that closely resembles Hyella balani (Pleurocapsales). There are some similarities with Hyella con-ferta, but it differs in measurements and morphology of the distal swelling.
(PALEO-)BATHYMETRY. Fasciculus acinosus is one of the key ichnotaxa of theFasciculus acinosus/Fasciculus dactylus- Ichnocoenosis (Glaub, 1994).This ichnocoenosis is typical for the shallow euphotic zone II which is equivalent to the intertidal zone.Fasciculus acinosus is restricted to this zone. Similar to Hyella balani it is mainly linked to tidal habitats.
Fasciculus dactylusRadtke 1991 - Fig. 2/2
DESCRIPTION. Fasciculus dactylus was named by Radtke (1991), based on studies of Tertiary molluscan shells. Fasciculus dactylus is characterized by cluster forming boring systems. From a central area of penetration several tunnels are radiating multidirectional, oriented mainly perpendicular to angu-lar, rarely parallel, to the substrate surface. Based on Radtke's original description the tubes are 4 to 9 !lm in diameter and are rarely ramified. In gen-eral, the tunnels do not vary significantly in diameter. Sometimes periodical tunnel constrictions are visible. In sorne cases the proximal end of the tubes is enlarged.
RECORD IN EARTH HISTORY. Permian, Triassic, Jurassic, and Tertiary. In recent environments,Fasciculus dactylus borings are produced by Hyella and Solentia species.
MODERN-FOSSIL COMPARISON. The boring pattern of Fasciculus dactylus closely resembles tunnels produced by Hyella caespitosa (Pleurocapsales).
Constrictions probably reflect cell morphology. According to recent investi-gations by Gektidis(1997),Fasciculus dactylus can also be similar to borings caused by otherHyella species or by sorne Solentia species. Fasciculus dac-tylus borings characterized by straight, elongated tunnels, are likely bored by Solentia species, whereas those with short tunnels may be produced by either.
(PALEO-)BATHYMETRY. Fasciculus dactylus is key ichnotaxon of two ichno-coenoses: (1)Fasciculus acinosus/Fasciculus dactylus- Ichnocoenosis, defined for the shallow euphotic zone II, and (2)Fasciculus dactylus/Paleoconchocelis starmachii-Ichnocoenosis, typical for the shallow euphotic zone III (Glaub,
138 Bulletin de l"!nstitut océanographique, Monaco, n° spécial 19 (1999)
EUENDOLITHIC CY ANOBACTERIA AND THEIR TRACES IN EARTH HISTORy
Figure 2. Artificial resin-casts of fossil microborings similar to modern cyanobacte-ria/cyanophyta. Seen From the inside of the substrate due to the cast embedding technique. 1. Fascicu/us acinosus Glaub 1994 in a Jurassic molluscan shell (Plero-perna sp.) From Consolaçao (Portugal) Arrow points to enJarged distal swelling.
2. Fascicu/us dacty/us Radtke 1992 in a Tertiary 11101luscan shell (Lucinidae) From Ferme de L'Orme (France). Arrow points to typical tunnel constriction. 3. Eury-gonum nodosumSchmidt 1992 in a Permian sponge From Djebel Tebaga (Tunisia).
Arrow points ta lateral globular swelling. 4. Scolecia fi/osa Radtke 1991 in a Silu-rian brachiopod shell From Herrvik (Gotland, Schweden). Arrow points to presumed X-ramification.
1994). As weil as its modern counterparts, Fasciculus dactylus is typical for the weil illuminated part of the euphotic zone.
Eurygonum nodosum Schmidt 1992 - Fig. 2/3
DESCRIPTION. Eurygonum nodosum is characterized by straight, elongated or gently curved tubes 9 bis Il flm in diameter (Schmidt, 1992). Ramification occurs with different angles.Eurygonum nodosum sometimes forms networks.
The main characteristic features of this ichnotaxon are globular swellings sit-uated laterally, which are connected to the main tunnel by a short lateral Bulletin de /"In.\lilul océanographique. Monaco. n° spécial 19 (1999) 139
ENVIRONMENT: ECOLOGY AND GLOBAL CHANGE
branch. Occasionally there is only a minor enlargement of the swellings visi-ble which makes this ichnotaxon hard to identify.
RECORD IN EARTH HISTORY. Carboniferous?,Permian, Triassic, and Jurassic.
In recent environments,Eurygonum nodosum borings are bored by Mastigo-coleus testarum.
MODERN-FOS SIL COMPARISON.Eurygonum nodosum fits very weil the boring system ofMastigocoleus testarum (Stigonematales). The globular swellings correspond to the cavities originated by heterocysts.
(PALEO-)BATHYMETRY.Eurygonum nodosum is not used as key ichnotaxon.
In the Jurassic period,itis restricted to thePaleoconchocelis starmachiilReti-culina elegans/RetistarmachiilReti-culina sp. l-Ichnocoenosis which characterizes the deeper euphotic zone. The investigations on Triassic samples, carried out by Schmidt (1992), indicate a similar bathymetric range. This contradicts the bathymetric range of its modern counterpart Mastigocoleus testarum which, in general, occurs in the shallow euphotic zone(e.g. Bahamas 0-30 m; Gektidis, 1997).
However, recent studies on the bathymetric distribution ofEurygonum nodo-sum in Permian and Triassic reef environments correspond to that (Balog&
Vogel, in prep.). Which factors are responsible for these different findings still need to be investigated.
Scolecia filosa Radtke 1991 - Fig. 2/4
DESCRIPTION. Scolecia filosa is described by long, slightly curved tunnels, sometimes forming loops (Radtke, 1991).Itmay form dense interwoven net-works. Usually, this ichnotaxon consists of tunnels 1-3 /lm in diameter.
Within one network the tunnel diameter does not vary significantly. Weil pre-served samples show characteristic X- or Y-ramifications.
RECORD IN EARTH HISTORY. Silurian, Carboniferous ?, Permian, Triassic, Jurassic, Cretaceous, and Tertiary. In recent environments, Scolecia filosa borings are known fromPlectonema species.
MODERN-FOSSIL COMPARISON. Boring systems similar toScolecia filosa are nowadays developed by Plectonema terebrans (Nostocales) as weil as by Plectonema endolithicum, often not differentiated from Plectonema tere-brans (Glaub, 1994; Gektidis, 1997). Their false branching modus seems to be reflected in the X- and Y-branching patterns ofScolecia filosa. In case of bad preservation, these tunnels, poor in features, may be misinterpreted as fungal borings. The latter can also develop loops, but show different branch-ing, and are usually characterized by distinctive sporangial swellings.
(PALEO-)BATHYMETRY.Scoleciafilosa is not used as key ichnotaxon. Its spa-tial distribution ranges from the shallow euphotic zone II to the dysphotic zone (Glaub& Bundschuh, 1997). The modern counterpartPlectonema tere-brans also shows a wide bathymetric distribution (Vogel et al., 1996). As eurybathic microboring,Scolecia filosa is of less importance for reconstructing paleo-depths than the ichnotaxa described above.
140 Bulletin de l'Institut océanographique, Monaco, n° spécial 19 (1999)
EUENDOLITHIC CYANOBACTERIA AND THEIR TRACES IN EARTH HISTORY
CONCLUSIONS
Ta conclude, even Paleozoic samples are significantly preserved to identify tiny details of the boring systems. The four ichnotaxa occur in Paleozoic, Mesozoic, and Cenozoic samples. They seem not to be influenced by the Per-mian!friassic boundary nor by the Cretaceousffertiary boundary.
However, none of the ichnotaxa is completely recorded from the Silurian to the present. Devonian samples have also been under investigation for microborings, but none of the ichnotaxa from this publication were observed in the samples studied (Vogel et al., 1987). Reasons for gaps in the historical record remain unclear.
Conceming the modem-fossil comparison, Fasciculus acinosus, Eury-gonum nodosum, and Scolecia fi/osa are weIl matching one specific modem endolith, whereas Fasciculus dactylus has several modem counterparts. Thus, the use of ichnotaxonomy is advantageous, because it allows updating of the modem-fossil comparison in case of new findings.
For bathymetric reconstructions Fasciculus acinosus and Fasciculus dac-tylus are extremly useful to identify subzones of the euphotic zone. Scolecia filosa was recorded from many periods, but as a eurybathic ichnotaxon its use for paleobathymetric classifications is limited. The bathymetric range of Eurygonum nodosum is, according to sorne investigations, contrary to that of its modem counterpart.
ACKNOWLEDGEMENTS
We would like to thankT. Le Campion-Alsumard (Marseille, France) and S. Golubic (Boston, USA) who supported the Frankfurt microboring research project in many respects. We are grateful toU.Quirant andW.Blackwell for correcting and improving the English manuscript.
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