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A chelonian egg from the Vraconian of South East France, Paleogeographic implications
A CHELONIAN EGG FROM THE VRACONIAN OF SOUTH EAST FRANCE PALEOGEOGRAPHIC IMPLICATIONS
by PIERREJEAN-LOUISMASSE
ABSTRACT
P~SOMg
An egg has been discovered in the Vraconian of South-East France. Its morphology, size and ornamentation allow us to attribute it to a Chelonian. It is associated with a littoral fauna (essentially oysters). The egg is complete and well preserved, and as reptile laying sites are always subaerial, it has not undergone sizeable reworking from the laying site. An episode close to emersion is thus detected in a series which was believed to be marine.
Le Vraconien de Salazac (Gard, France) a livr~ un exemplaire entier d'ceuf de reptile. Sa morphologie, sa tailie et son ornementation nous permettent de l'attl"ibuer aux CMloniens. I1 provient d'un niveau de marnes glauconieuses sableuses appartenant A une formation d'~ge vraconien. Celle-ci est form& it sa base de mames glauconieuses sableuses ~. faunes marines vari&s, passant A des marnes plus pauvres en faunes (anndlides et juvdniles d'huitres), mais ayant fourni l'exemplaire dtudi~ et un fragment du m~me type. La conservation et la bonne preservation d'un oeuf entier, et tr~s fragile au ddpart, impliqnent une absence quasi-totale de remaniement. Les sites de ponte des reptiles marins &ant toujours au moins supratidaux, il existe donc un dpisode dmersif dans cette sdrie vraconienne, encadrd par deux pulsations marines.
KEY-WORDS: ALBIAN,PALEOECOLOGY,EGG,TURTLE,PALEONTOLOGY,F2IERSION. MOTS-CLt~S: ALBIEN,OEUF,TORTUE,PALt~Ot~COLOGIE,EMERSION,PALI~ONTOLOGIE.
1. INTRODUCTION The spheroidal egg-like specimen under discussion was found in the Upper Albian of South-East France (Gard). The remnants of a radiating needle-like structure on its outer surface suggest that it once was a chelonian egg (a fragment also found in the same levels is only an internal mold showing the same structure).
red their microstracture to that of geocbelone e[epbantopus. Hirsch 1983, Hirsch & Lopez-Jurado 1987, girsch & Bray 1988 also described Tertiary chelonian eggshell. Eggshell structure of several different modem species has been described in detail by Packard 1979, Packard & Packard 1979, Packard et alii 1982, 1984.
Older and also more recent studies of Mesozoic eggshell deal mostly with dinosaur eggs (Penner 1983). Some spherical dinosaur eggs have been described recently by Srivastava et aHi 1986, however, they are significantly bigger (160-200 mm) than the egg studied here. The only known Mesozoic chelonian eggs are from England and have been described by Van Straelen 1928 and, in more detail, by Hirsch 1983 who also compa-
The chelonian eggshell is the only that is composed of aragonite; in all other amniote eggshells the calcium carbonate is found in the form of calcite. The calcareous Iayer of turtle eggshell consists of spherolitic shell units which are more or less coalescent (Packard 1980, Packard et alii 1982, Vlirsch et alii 1987). Each unit is
* Centrede S6dimentologieet Pal6ontologie&U.RA.1208CNRS,Universit6d'Aix-IVlarseilleI, PlaceV.Hugo,13331Marseille,France. Geobios, n o 22, fasc. 4
p. 523-530, 5 fig., 1 pl.
Lyon, aofit 1989
- 524 -
composed of needle-like crystals diverging (radiating) from a nucleation point. The chance of fossilization is good for rigidshelled eggs found in some of the terrestrial species, however,
poor to non-existing for the soft-shelled marine turtles (Hirsch & Lopez-Jurado 1987).
II. LOCALITY AND STRATIGRAPHY
•
Valbonn~
Pont
j.,'~e ~
~i/'/~
Fig. 1- Map of location. Carte de loealisation.
The locality is in South-East France (Gard), between Valbonne and Pont-Saint-Esprit (fig. 1) at the place named La Tranchde. Two eggs have been discovered, one entire, the other incomplete° Vraconian ammonites (Breistroffer 1940) have been found at the discontinuity between albian glanconitic sandstones and the overlying formation in which the eggs were discovered. Also found, under the same discontinuity, was the "layer with big
Puzosia" of Breistroffer (fig. 2) The following formation (Formation of Salazac) reaches 40 meters and has yielded at its base Beudanticeras beudanti, Epiaster distincttts, both upper albian fossils, Hechti~there derooi, Costacythere aptensis (not younger than the Vraconian). It grades progressively into more and more sand-rich sediments, whose upper part is generally attributed to the Cenomanian (Orbitolina concava).
II1. BIO- AND LITHOFACIES Paleoecological and sedimentoiogical data show three faunistic associations in the formation of Salazac, linked with different substrates. Those are (fig. 2) :
Facies I, at the base. Sandy glauconitic marine mud, rich in benthos (irregular urchins, oysters and other pelecypods, annelids, ostracods) and necton (nautilids, ammonites).
abundant, and by hydrozoan (Parkeria, in lfCbert et Toucas 1875). The microfacies contains quartz, glauconite and bioclastes (peloids are dominant with scarce fragments of echinids, bryozoa and red algae).
-
- Facies II, at the top. Groups of calcareous gritty layers (local channels), with a variety of benthic fauna (pectinids, trigonia, rhynchonella, gastropods) and rich in horizontal and vertical trace fossils (Skolithos). Epipelagic fauna is represented by planktonic foraminifera (Heterohelicidae), sometimes
Facies III, in the middle. Fine sandy glauconitic mud, with nodules and nodular layers. The fauna are very scarce : some young oysters (Amphidonte obliquatum), bristles of echinids, and two eggs of turtles. -
The facies (I) is present at the base of the serie only. It is followed by the facies 011). Then, the facies (II) appears more and more frequently, up to the presence of coarser sandstones.
- 525 -
Fig. 2 - The formation of Salazac: from left to right : - Lithologic column : A, Coarse glauconitic sandstone with Pusozia. B, Fine sandy glauconitic blue marls with nodules. G, nodular layer of glauconitic and argillaceous limestones. D, calcareous and glauconitic sandstones. - Fauna : 1, echinids. 2, oysters. 3, annelids. 4, other pelecypods. 5, brachiopods. 6, cephalopods. - Interpretation of the evolution of the serie as an oscillation between 1 (subtidal fla0, Ill (shallow lagoon and/or tidal creek) and II (offshore shoal) Star : position of the eggs. La Formation de Salazac : - Lithologie : A, gr~s grossiers giauconieux ~ Pusozia. B, Mames bleues glauconieuses b. nodules calcaires. C, calcaires noduleux argileux et giauconieux. D, gr~s calcaires glauconieux. - Faune : 1, echinid6s. 2, hu~tres. 3, annelides. 4, autres p616cypodes. 5, brachiopodes. 6, c6phalopodes. - L'6volutiou de la s6rie est iuterpr6tde comme ]e r6sultat d'une oscillation entre pal6oenvironnelnent marin ouvert prot6g6 (I), [agon c6tier on bale parrots 6merg6 (III) et barre sableuse subtidale (ll). Etoile : position des oeufs.
A
B
G
n
Jim
IV. DESCRIPTION OF THE EGG The lightly crushed specimen is almost spherical (Plate I-l) with a diameter of 55 ram. The sedimentary filling is an argillaceous and glauconitic limestone, identical to the external sediment.
PI. i[,3 and 1,6 show that this network seems ~o support the crystallites. The fibrous network has a thickness of 50 to 60 microns (Pl. 1,7) and is directly superposed on the sedimentary filling.
The outer surface is in many places covered by a thin layer of an irregular, reticulate network, with many small circular depressions (Planche 1,2). Under the binocular microscope (fig. 3) it can be seen that this network is composed of radial needles. Fragments removed from the specimen for study under Scanning Electron Microscope (SEM) revealed the following (P1. I, 3 to 7) : 1. The reticulate network is composed of walls formed around the depressions by two rings (each 20 to 50 microns wide, P1. 1,3) of radiating crystallites (P1. 1,5) which coalesce at the edge of each unit (Pl. 1,4). 2. The numerous depressions have a diameter ranging from 170 to 450 microns (PI. 1,4). 3. in the center of the depressions, extending below the radiating crystals, a randomly fibrous network can be seen.
Fig. 3 - Top-view of the egg. x 1OO. Note reticulate pattern, anti spaces (areas with oblique lines) between wedges of radiating crystals. gue de la surface de l'oeuf. Des espaces libres (aires barr6es) existent en dehors de la trame r6ticul6e fibreuse.
PLATE I
Fig. I-1- View of the egg, x 0,61. Vue d'ensemble de l'oeuf.
Fig. I-2 - Note layer with reticulate pattern (arrow), x 3. Noter l'existence d'une couche ~. trame rdticul6e (fl~che).
Fig. I-3 - General aspect of the network of the eggshell units. Note needle-like crystals, x 178. Remarquer la prdsence de cristaux aciculaires.
Fig. I-4 - Detail view of the crystallites: between the units the "eroded" wedges of crystals do not always coalesce and leave some space (arrow), x 1 ] 60. Vue ddtaill6e des cristallites : entre chaque unit6, la ceinture "6rodde" de cristaux fibreux n'est pas toujours coalescente et lib~re de petits espaces (fli~che), x 1160.
Fig. I-5 - As I-4, x 2950, note needles are incomplete, and have angulose edges. Comme I-4, x 2950, remarquer que les cristaux sont incomplets et ont des bords anguleux.
Fig. I-6 - This fragment shows two layers : 1, radial custals , 2, randomly organised crystals (at left), x 530. Ce fragment montre deux couches : 1, "acristaux radiaires, 2, i~ cristaux A disposition d6sordonn6e (~. gauche).
Fig. 1-7 - Transversal view of the basal layer under needles, x 780. Vue transversale de la couche basale fibreuse, x 780.
3 to 7 : Viewed under scanning electron microscope. 3-7 : clichds pris au microscope dlectronique ~. balayage.
Pl. t PO.-L. Masse
Geobios n ° 22, fasc. 4
IB 3
5
4
6
7
- 528 -
V. DISCUSSION Size and shape of the specimen are similar to chelonian fossils described by Van Straelen 1928, Hirsch 1983, and Hirsch & Lopez-Jurmdo 1987 ; they also compare well to Geoahelone elephantopus eggs. X-Ray determinations have revealed the presence of phosphate and of a minor proportion of calcite (probably from the matrix). The phosphatic nature of the analyzed fragments could result from a transformation of the basal fibrous network. The radiating (aragonitic ?) crystallites could be replaced either by calcite or by phosphate (Lucas et alii 1976)
The randomly oriented fibrous network (PI. I,7) visible within the central cores and between those and the egg-filling could be equivalent to remnants of egg membrane, they have some similarity to those shown by Packard 1980, Packard et alii 1979, Pl. 3, fig. 3 ; 1984, fig. 6, C. The presence of large interstices (voids) between the remnant of the shell units suggests that this egg might have been of pliable nature as described by Hirsch 1983.
Hirsch 1983 has demonstrated that - even though the aragonite was absent - other criteria could be used to identified chelonian eggs. Photomicrographs of avian, dinosaurian and crocodiliun eggshells show only more or less tightly packed groups of massive crystals. Moreover, the inner surface of these eggshells lacks the radiating needle-like crystals whose remnants are seen here (Hirsch 1985, fig. 4, 1-4, Hirsch & Packard 1987, fig. 30-32, 50-56). The network with central cores and radiating needles on the outer surface of the Albian specimen is very similar to shell remnants found on the outer surface of the shell membrane of Chelydra serpentina (Packard 1980, fig.10-11) and is also seen on the inner surface of the calcareous layer from an egg of Sternotherus minor (Packard et aBi 1984, fig. 5,d). It suggests that on the Albian specimen the outer part of the shell layer dissolved, weathered or abraded leaving only the most inner part of the basal units, which is the layer with the central cores and radiating crystals, intact (fig. 4).
, , ,, h~, , ~ -c-17-7< I~"\k ~ l lltl l / ; l \ \~ III I i'~1 i
E.m.
h
iii
[
- -
T.
C.
Fig. 4 - Side view of chelonian spherolitic eggshell unit. Darklines show remnants preservedin fossilspecimen, stippledlines represent abradedor eroded part of shell units, T =tangential crystalsof most inner section of shell unit, Em =Egg membrane, e =central core (nucleationpoint). Vue lat6rale d'une unit(: sph6rolitique de la eoquille d'oeuf de torrue. Les traits appuy6sindiquent les parties conserv6essur I'exemplaire fossile, les traits interrompus les parties dissoutes ou 6rod6es de la coquille. T =erlstaux ~tdispositiontangentiellede la partie la plus interne de la coquille,Em =membrane de l'oeuf, C =noyau central (centre de nucl6ation).
VI. PALEOENVIRONMENTALAND PALEOGEOGRAPHICALCONSEQUENCES - The presence of an entire reptilian egg in an autochthonous setting is a good criterion of paleoenvironmental (paleobathymetric)interpretation. Laying sites of actual reptiles are always aerial (continental to supratidal). The probability of an important resedimentation of an already indurated mold is low since the superficial ornamentation is preserved and the nature of the filling is identical to the sediment. - Thus a new interpretation of the evolution of the Formation of Salazac can be proposed (fig. 2) : this succession could be interpreted as the succession - in an estuarine environment - of a marine episode of low hydrodynamism (facies I, subtidal flat) followed by the setting up of very coastal environments
(facies III, coastal lagoon and/or tidal creek), and finally the progressive return to marine influences (facies II, subtidal shoal). The paleoenvironment of the facies 11 would have inhibited the development of a various benthos. Local emersions would be favourable to the laying of eggs. An environment of coastal lagoon and/or tidal creek, episodically emerged, is possible, at least when the eggs are present. Then a gradual and periodic opening to marine influences (III) finds expression in a new diversification of the benthos and the appearance in a littoral environment of epicontinen-
- 529 -
tal planctonic foraminifera (facies 1I). Those (Heterohelicidae, Hedbergella), which occur alone, are not indicative of great depth, but are rather typical of open shallow marine environments (Leckie 1987). From the basal discontinuity recognized by Breistroffer 1940, the environment would be successively : subtidal --> intertidal to supratidal -> subtidal. This conclusion differs from those of Triat 1982 and Guendon et alii 1983 who have described the whole upper Albian as continuousIy marine, and identified the "vraconian transgression", highlighted by Masse & Philip 1976, with a relative deepening (Triat 1982). Rubino 1984, 1988 has put forward a new sedimentological interpretation of the aptian-albian vocontian basin. According to the interpretation proposed here, it seems that the "high sea level period" suggested for the upper Vraconian (Rubino 1988) is rapidly ended in an emersian. When compared with the nearest waconian platform deposits (i.e, the Vraconian of the mountain of Ventoux-Lure, cf Le Goc 1977, Fries 1987), Gard's deposits reveal common aspects. From bottom to top the former is marine, then shows at several times a regressive drift, up to intertidal paleoenvironments, during the upper Vraconian (Fries 1987).
20km
-
Thus we may underline an important paleogeographic consequence : during the Vraconian, coastal deposits would have separated two marine areas (fig. 5) : vocontian (Moullade 1966) and provencal (Tronchetti 1981, Machhour 1988, Masse P.J.L. 1988).
Hg.5 Simplified paleogeographic map at Yraconian in South East France. Relatively deep marine deposits are represented by close lines a¢ North (Vocontian Basin) and South (Touionnais Basin and Nerthe). The stars correspond to coastal waconian deposits and the dotted area to a probable coastal region (1, this paper, 2 and 3, in the Ventoux~Lure region). Av. Avignon,A. ALx, M. Marseille. Carte pal~og~ographtque simplifi~e d'une pattie du Sud-Est de la France au Vraeonlen. Les lignes horizontales indiquant des d6p6ts ranfins reiativement profonds au Nard (r6gion vocontienne) et au Sud (Bussin toulonnais et Nerthe). Les &oiles correspondent aux sites signal6s ici (1, Gard, Salazae, 2 et 3, r6gion de Ventoux-Lure) et l'aire marqude en pointil[6 ~.une r6gion cSti~re probable. Av.Avignon, L ALLM. Marseiile. -
VII. CONCLUSIONS Reptilian eggs are relatively rare during Middle Cretaceous. Turtle eggs from Salazac are the oldest known, with Van Straelen's. The use of turtle eggs as marker of shoreline has highlighted the paleoenvironmental evolution of the Vraconian of Salazac, revealing the existence of an episode of emersion previously ignored. Other data on the regional evolution of the Vraconian indicate a progressive shallowing.
Consequently, several problems may now be studied, especially the influences of this emersion, if more than local, on other vraconian deposit~ of South-East France and the evolution of those coastal paleoenvironments during the Lower Cenomanian.
Acknowledgments I would like to express my special thanks to K,F. Hirsch (University of Colorado, Boulder) for providing helpful comments on the text and recent reprints on turtle's eggs and to J. Philip (Aix-Marseille I University) for his critical reading of the manuscript and his participation in the field work. I thank F.
de Brain for her critical remarks, A. Dhondt, F..4medro, J.F. Babinot and B. Clavel for paleontologic determinations and C. Froget for X-Ray realization.
- 530
-
REFERENCES
BREISTROFFERM. (1940) - Rdvision des ammonites du Vraconien de Salazac (Gard) et considdrations g~n6rales surce sousdtage albien. Tray. Lab. Gdol. Fac. Sci. Grenoble, 22 : 71171. FRIES G. (1987) - Dynamlque s6dlmentaire du bassin subalpin it l'Apto-Cdnomanien. Th6se Doct. Sci. naturelles, Univ. P. et M. Curie, Paris (inddit, 1986) et Mdm. Sci. Term, 4, (1987), Ecole des Mines, Paris. GUENDORJ. L., PARRONC. & TRIATJ.M. (1983) - Incidences des alt6rations crdtac6es sur la notion de Sid6rolithique dans le Sud-Est de la France. BuIl. Soc. g6ol. France, (7), 25, 1 : 41-50. HEBERT E. & TOUCAS.4. (1875) - Description du bassin d' Uchaux. Ann. Sci. G6ol., Paris, 6 : 1-132. HIRSCH K.F. (1983) - Contemporary and fossil chelonian eggshells. Copeia, Washington, 2 : 382-397, HIRSCH K.F. & LOPEZ-JURADOL.F. (1987) - Pliocene chelonian fossil eggs from Gran Canaria, Canary lslands.J. Vertebrate Palaeontology, Norman (USA), 7, I : 96-99. HIRSCH K.F. & PACKARDN.J. (1987) - Review of fossil eggs and their shell structure. Scanning Microscopy, Chicago, 1, 1 : 383-400. HIRSCH K.F. & BRAYE.S. (1988) - Spheroidal eggs -avian and chelonian- from the Miocene and Oligocene of the western interior. Hunteria, Boulder, 1, 4:1-7. LECKIER.M. (1987) - Paleoecology of Mid-Cretaceous planktonic foraminifera : a comparison of open ocean and epicontinental sea assemblages. Micropaleontology, New York, 33, 2 : 164-176. LE Goc B. (1977) - Contribution it l'dtude gdologique, stratigraphique et paldog~ographique du Gargasien au Sdnonien de la rdgion Ventoux-Lure (Chaines subalpines mdridiohales), D.E.S. Univ. CI. Bernard, Lyon, 157 p. (in~dit). LocASG., CROSP. & LANOJ.(1976) - Les Roches sddimentaires, 2, Etude microscopiques des roches meubles et consolid6es, Doin Ed., Paris, 503 p. MACHHOIJRL. (1988) - Le bassin toulonnais au Crdtacd moyen (Aptien-C~nomanien). Doct. Univ. Aix-Marseille I, 592 p. (inddit). MASSEJ.P. & PHILIPJ. (1976) - Pal6ogdographie et tectonique du Crdtacd moyen en Provence. Rdvision du concept d'isthme durancien. Rev. G~ogr.phys. & GeoL dyn., Paris, ( 2 ) , 18, 1 : 49-66, MASSEP.J.L. (1988) - Evolution de la marge proven~ale ~t PAptien supdrieur et it l'Albien. Sddimentologie, Paldotectoni-
que, Pal~o#ographie. Boct. Univ. Aix Marseille I, 300 p, (inddit). MOULLADEM. (1966) - Etude stratigraphique et micropaldontologique du Cr&acd infdrieur de la fosse vocontienne. ThSse Etat, Lyon, 2 vol., 369 p. &Doc. Lab. G~ol. Fac. Sci. Lyon, 15, 369 p. PACKARDN.J. & PACKARDG.C. (1970) - Structure of the shell and tertiary membranes of eggs of softshell turtles (Tryonyx spinifents).J. Morphology, Philadelphie, 159: 131-144. PACKARDN.J. (1980) - Ultrastructural morphology of the shell and shell membrane of eggs of common snapping turtles (Chelydra serpentina). J. Morphology, Philadelphie, 165 : 87-2 04. PACKARDN.J., PACKARDG.C.& BOAROMANT.J. (1982) - Structure of eggshells and water relations of reptilians eggs. Herpatologica, Los Angeles, 38 : 136-155. PACKARDM.J., HIRSCHK.F. & IVERSONJ.B. (1984) - Structure of Shells from Eggs of Kinostemids Turtles. J. Morphology, Philadelphie, 181 : 9-20. PENNERM.M. (1983) - Contribution it l'&ude de la microstructure des coquilles d'oeuf de dinosaures du Crdtacd supdrieur clans le bassin d'Aix. Applications biostratigraphiques. Th~se Doct. Paris VI et Mdm. Sci. Terre, Paris, 83, (52), 234 p. RUBINOJ.-L. (1984) _ Sedimentology of upper aptian and albian turbidites and shelf sandstones in the vocontian basin (S.E. France). 5th Eur. reg. Meet. Sedimentology, Abstracts : 388-389. RtlBINOJ.-L. (1988) - Organisation des sdquences de ddpSts de la plateforme au bassin dans l'Aptien et l'Albien du bassin vocontien (S.E. de la France). In : FERRYS., RUBINOJ.-L. et alii, Eds : Eustatisme et Sdquences de ddpSt dans le Crdtacd du Sud-Est de la France. G6otrope, Lyon, 1 : 56-82. SRIVASTAVAS., MOHABEYD.M., ASHOKSAHN1& PONT S.C. (]986) Upper Cretaceous dinosaur egg. Clutches from Kheda District (Gujarat India). Their distribution, shell ultrastructure and paleoecology. Palaeontographica, Stuttgart, A, 193, 5-6 : 219-233. TRIATJ.M. (1982) - Pal~oalt6rations dans le Cr&ac6 sup6rieur de Provence rhodanienne. Sci. g6oL, Strasbourg, 68, 202 p. TRONCHE~TIG. (1981) - Les foraminif~res cr6tac4s de Provence (Aptien-Santonien). Thbse Doctorat d'Etat &Trav. Lab. Gdol. hist. &FaI6onL, Marseille, 12, 3 vol., 547. VAN STRAELENV. (1928) - Les oeufs de reptiles fossiles. Paleobiologica, Vienne, I : 297-312.
Manuscrit ddposd le 22.03.1989 Manuscrit ddfinitif r ~ u le 20.07.1989
by PIERREJEAN-LOUISMASSE
ABSTRACT
P~SOMg
An egg has been discovered in the Vraconian of South-East France. Its morphology, size and ornamentation allow us to attribute it to a Chelonian. It is associated with a littoral fauna (essentially oysters). The egg is complete and well preserved, and as reptile laying sites are always subaerial, it has not undergone sizeable reworking from the laying site. An episode close to emersion is thus detected in a series which was believed to be marine.
Le Vraconien de Salazac (Gard, France) a livr~ un exemplaire entier d'ceuf de reptile. Sa morphologie, sa tailie et son ornementation nous permettent de l'attl"ibuer aux CMloniens. I1 provient d'un niveau de marnes glauconieuses sableuses appartenant A une formation d'~ge vraconien. Celle-ci est form& it sa base de mames glauconieuses sableuses ~. faunes marines vari&s, passant A des marnes plus pauvres en faunes (anndlides et juvdniles d'huitres), mais ayant fourni l'exemplaire dtudi~ et un fragment du m~me type. La conservation et la bonne preservation d'un oeuf entier, et tr~s fragile au ddpart, impliqnent une absence quasi-totale de remaniement. Les sites de ponte des reptiles marins &ant toujours au moins supratidaux, il existe donc un dpisode dmersif dans cette sdrie vraconienne, encadrd par deux pulsations marines.
KEY-WORDS: ALBIAN,PALEOECOLOGY,EGG,TURTLE,PALEONTOLOGY,F2IERSION. MOTS-CLt~S: ALBIEN,OEUF,TORTUE,PALt~Ot~COLOGIE,EMERSION,PALI~ONTOLOGIE.
1. INTRODUCTION The spheroidal egg-like specimen under discussion was found in the Upper Albian of South-East France (Gard). The remnants of a radiating needle-like structure on its outer surface suggest that it once was a chelonian egg (a fragment also found in the same levels is only an internal mold showing the same structure).
red their microstracture to that of geocbelone e[epbantopus. Hirsch 1983, Hirsch & Lopez-Jurado 1987, girsch & Bray 1988 also described Tertiary chelonian eggshell. Eggshell structure of several different modem species has been described in detail by Packard 1979, Packard & Packard 1979, Packard et alii 1982, 1984.
Older and also more recent studies of Mesozoic eggshell deal mostly with dinosaur eggs (Penner 1983). Some spherical dinosaur eggs have been described recently by Srivastava et aHi 1986, however, they are significantly bigger (160-200 mm) than the egg studied here. The only known Mesozoic chelonian eggs are from England and have been described by Van Straelen 1928 and, in more detail, by Hirsch 1983 who also compa-
The chelonian eggshell is the only that is composed of aragonite; in all other amniote eggshells the calcium carbonate is found in the form of calcite. The calcareous Iayer of turtle eggshell consists of spherolitic shell units which are more or less coalescent (Packard 1980, Packard et alii 1982, Vlirsch et alii 1987). Each unit is
* Centrede S6dimentologieet Pal6ontologie&U.RA.1208CNRS,Universit6d'Aix-IVlarseilleI, PlaceV.Hugo,13331Marseille,France. Geobios, n o 22, fasc. 4
p. 523-530, 5 fig., 1 pl.
Lyon, aofit 1989
- 524 -
composed of needle-like crystals diverging (radiating) from a nucleation point. The chance of fossilization is good for rigidshelled eggs found in some of the terrestrial species, however,
poor to non-existing for the soft-shelled marine turtles (Hirsch & Lopez-Jurado 1987).
II. LOCALITY AND STRATIGRAPHY
•
Valbonn~
Pont
j.,'~e ~
~i/'/~
Fig. 1- Map of location. Carte de loealisation.
The locality is in South-East France (Gard), between Valbonne and Pont-Saint-Esprit (fig. 1) at the place named La Tranchde. Two eggs have been discovered, one entire, the other incomplete° Vraconian ammonites (Breistroffer 1940) have been found at the discontinuity between albian glanconitic sandstones and the overlying formation in which the eggs were discovered. Also found, under the same discontinuity, was the "layer with big
Puzosia" of Breistroffer (fig. 2) The following formation (Formation of Salazac) reaches 40 meters and has yielded at its base Beudanticeras beudanti, Epiaster distincttts, both upper albian fossils, Hechti~there derooi, Costacythere aptensis (not younger than the Vraconian). It grades progressively into more and more sand-rich sediments, whose upper part is generally attributed to the Cenomanian (Orbitolina concava).
II1. BIO- AND LITHOFACIES Paleoecological and sedimentoiogical data show three faunistic associations in the formation of Salazac, linked with different substrates. Those are (fig. 2) :
Facies I, at the base. Sandy glauconitic marine mud, rich in benthos (irregular urchins, oysters and other pelecypods, annelids, ostracods) and necton (nautilids, ammonites).
abundant, and by hydrozoan (Parkeria, in lfCbert et Toucas 1875). The microfacies contains quartz, glauconite and bioclastes (peloids are dominant with scarce fragments of echinids, bryozoa and red algae).
-
- Facies II, at the top. Groups of calcareous gritty layers (local channels), with a variety of benthic fauna (pectinids, trigonia, rhynchonella, gastropods) and rich in horizontal and vertical trace fossils (Skolithos). Epipelagic fauna is represented by planktonic foraminifera (Heterohelicidae), sometimes
Facies III, in the middle. Fine sandy glauconitic mud, with nodules and nodular layers. The fauna are very scarce : some young oysters (Amphidonte obliquatum), bristles of echinids, and two eggs of turtles. -
The facies (I) is present at the base of the serie only. It is followed by the facies 011). Then, the facies (II) appears more and more frequently, up to the presence of coarser sandstones.
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Fig. 2 - The formation of Salazac: from left to right : - Lithologic column : A, Coarse glauconitic sandstone with Pusozia. B, Fine sandy glauconitic blue marls with nodules. G, nodular layer of glauconitic and argillaceous limestones. D, calcareous and glauconitic sandstones. - Fauna : 1, echinids. 2, oysters. 3, annelids. 4, other pelecypods. 5, brachiopods. 6, cephalopods. - Interpretation of the evolution of the serie as an oscillation between 1 (subtidal fla0, Ill (shallow lagoon and/or tidal creek) and II (offshore shoal) Star : position of the eggs. La Formation de Salazac : - Lithologie : A, gr~s grossiers giauconieux ~ Pusozia. B, Mames bleues glauconieuses b. nodules calcaires. C, calcaires noduleux argileux et giauconieux. D, gr~s calcaires glauconieux. - Faune : 1, echinid6s. 2, hu~tres. 3, annelides. 4, autres p616cypodes. 5, brachiopodes. 6, c6phalopodes. - L'6volutiou de la s6rie est iuterpr6tde comme ]e r6sultat d'une oscillation entre pal6oenvironnelnent marin ouvert prot6g6 (I), [agon c6tier on bale parrots 6merg6 (III) et barre sableuse subtidale (ll). Etoile : position des oeufs.
A
B
G
n
Jim
IV. DESCRIPTION OF THE EGG The lightly crushed specimen is almost spherical (Plate I-l) with a diameter of 55 ram. The sedimentary filling is an argillaceous and glauconitic limestone, identical to the external sediment.
PI. i[,3 and 1,6 show that this network seems ~o support the crystallites. The fibrous network has a thickness of 50 to 60 microns (Pl. 1,7) and is directly superposed on the sedimentary filling.
The outer surface is in many places covered by a thin layer of an irregular, reticulate network, with many small circular depressions (Planche 1,2). Under the binocular microscope (fig. 3) it can be seen that this network is composed of radial needles. Fragments removed from the specimen for study under Scanning Electron Microscope (SEM) revealed the following (P1. I, 3 to 7) : 1. The reticulate network is composed of walls formed around the depressions by two rings (each 20 to 50 microns wide, P1. 1,3) of radiating crystallites (P1. 1,5) which coalesce at the edge of each unit (Pl. 1,4). 2. The numerous depressions have a diameter ranging from 170 to 450 microns (PI. 1,4). 3. in the center of the depressions, extending below the radiating crystals, a randomly fibrous network can be seen.
Fig. 3 - Top-view of the egg. x 1OO. Note reticulate pattern, anti spaces (areas with oblique lines) between wedges of radiating crystals. gue de la surface de l'oeuf. Des espaces libres (aires barr6es) existent en dehors de la trame r6ticul6e fibreuse.
PLATE I
Fig. I-1- View of the egg, x 0,61. Vue d'ensemble de l'oeuf.
Fig. I-2 - Note layer with reticulate pattern (arrow), x 3. Noter l'existence d'une couche ~. trame rdticul6e (fl~che).
Fig. I-3 - General aspect of the network of the eggshell units. Note needle-like crystals, x 178. Remarquer la prdsence de cristaux aciculaires.
Fig. I-4 - Detail view of the crystallites: between the units the "eroded" wedges of crystals do not always coalesce and leave some space (arrow), x 1 ] 60. Vue ddtaill6e des cristallites : entre chaque unit6, la ceinture "6rodde" de cristaux fibreux n'est pas toujours coalescente et lib~re de petits espaces (fli~che), x 1160.
Fig. I-5 - As I-4, x 2950, note needles are incomplete, and have angulose edges. Comme I-4, x 2950, remarquer que les cristaux sont incomplets et ont des bords anguleux.
Fig. I-6 - This fragment shows two layers : 1, radial custals , 2, randomly organised crystals (at left), x 530. Ce fragment montre deux couches : 1, "acristaux radiaires, 2, i~ cristaux A disposition d6sordonn6e (~. gauche).
Fig. 1-7 - Transversal view of the basal layer under needles, x 780. Vue transversale de la couche basale fibreuse, x 780.
3 to 7 : Viewed under scanning electron microscope. 3-7 : clichds pris au microscope dlectronique ~. balayage.
Pl. t PO.-L. Masse
Geobios n ° 22, fasc. 4
IB 3
5
4
6
7
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V. DISCUSSION Size and shape of the specimen are similar to chelonian fossils described by Van Straelen 1928, Hirsch 1983, and Hirsch & Lopez-Jurmdo 1987 ; they also compare well to Geoahelone elephantopus eggs. X-Ray determinations have revealed the presence of phosphate and of a minor proportion of calcite (probably from the matrix). The phosphatic nature of the analyzed fragments could result from a transformation of the basal fibrous network. The radiating (aragonitic ?) crystallites could be replaced either by calcite or by phosphate (Lucas et alii 1976)
The randomly oriented fibrous network (PI. I,7) visible within the central cores and between those and the egg-filling could be equivalent to remnants of egg membrane, they have some similarity to those shown by Packard 1980, Packard et alii 1979, Pl. 3, fig. 3 ; 1984, fig. 6, C. The presence of large interstices (voids) between the remnant of the shell units suggests that this egg might have been of pliable nature as described by Hirsch 1983.
Hirsch 1983 has demonstrated that - even though the aragonite was absent - other criteria could be used to identified chelonian eggs. Photomicrographs of avian, dinosaurian and crocodiliun eggshells show only more or less tightly packed groups of massive crystals. Moreover, the inner surface of these eggshells lacks the radiating needle-like crystals whose remnants are seen here (Hirsch 1985, fig. 4, 1-4, Hirsch & Packard 1987, fig. 30-32, 50-56). The network with central cores and radiating needles on the outer surface of the Albian specimen is very similar to shell remnants found on the outer surface of the shell membrane of Chelydra serpentina (Packard 1980, fig.10-11) and is also seen on the inner surface of the calcareous layer from an egg of Sternotherus minor (Packard et aBi 1984, fig. 5,d). It suggests that on the Albian specimen the outer part of the shell layer dissolved, weathered or abraded leaving only the most inner part of the basal units, which is the layer with the central cores and radiating crystals, intact (fig. 4).
, , ,, h~, , ~ -c-17-7< I~"\k ~ l lltl l / ; l \ \~ III I i'~1 i
E.m.
h
iii
[
- -
T.
C.
Fig. 4 - Side view of chelonian spherolitic eggshell unit. Darklines show remnants preservedin fossilspecimen, stippledlines represent abradedor eroded part of shell units, T =tangential crystalsof most inner section of shell unit, Em =Egg membrane, e =central core (nucleationpoint). Vue lat6rale d'une unit(: sph6rolitique de la eoquille d'oeuf de torrue. Les traits appuy6sindiquent les parties conserv6essur I'exemplaire fossile, les traits interrompus les parties dissoutes ou 6rod6es de la coquille. T =erlstaux ~tdispositiontangentiellede la partie la plus interne de la coquille,Em =membrane de l'oeuf, C =noyau central (centre de nucl6ation).
VI. PALEOENVIRONMENTALAND PALEOGEOGRAPHICALCONSEQUENCES - The presence of an entire reptilian egg in an autochthonous setting is a good criterion of paleoenvironmental (paleobathymetric)interpretation. Laying sites of actual reptiles are always aerial (continental to supratidal). The probability of an important resedimentation of an already indurated mold is low since the superficial ornamentation is preserved and the nature of the filling is identical to the sediment. - Thus a new interpretation of the evolution of the Formation of Salazac can be proposed (fig. 2) : this succession could be interpreted as the succession - in an estuarine environment - of a marine episode of low hydrodynamism (facies I, subtidal flat) followed by the setting up of very coastal environments
(facies III, coastal lagoon and/or tidal creek), and finally the progressive return to marine influences (facies II, subtidal shoal). The paleoenvironment of the facies 11 would have inhibited the development of a various benthos. Local emersions would be favourable to the laying of eggs. An environment of coastal lagoon and/or tidal creek, episodically emerged, is possible, at least when the eggs are present. Then a gradual and periodic opening to marine influences (III) finds expression in a new diversification of the benthos and the appearance in a littoral environment of epicontinen-
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tal planctonic foraminifera (facies 1I). Those (Heterohelicidae, Hedbergella), which occur alone, are not indicative of great depth, but are rather typical of open shallow marine environments (Leckie 1987). From the basal discontinuity recognized by Breistroffer 1940, the environment would be successively : subtidal --> intertidal to supratidal -> subtidal. This conclusion differs from those of Triat 1982 and Guendon et alii 1983 who have described the whole upper Albian as continuousIy marine, and identified the "vraconian transgression", highlighted by Masse & Philip 1976, with a relative deepening (Triat 1982). Rubino 1984, 1988 has put forward a new sedimentological interpretation of the aptian-albian vocontian basin. According to the interpretation proposed here, it seems that the "high sea level period" suggested for the upper Vraconian (Rubino 1988) is rapidly ended in an emersian. When compared with the nearest waconian platform deposits (i.e, the Vraconian of the mountain of Ventoux-Lure, cf Le Goc 1977, Fries 1987), Gard's deposits reveal common aspects. From bottom to top the former is marine, then shows at several times a regressive drift, up to intertidal paleoenvironments, during the upper Vraconian (Fries 1987).
20km
-
Thus we may underline an important paleogeographic consequence : during the Vraconian, coastal deposits would have separated two marine areas (fig. 5) : vocontian (Moullade 1966) and provencal (Tronchetti 1981, Machhour 1988, Masse P.J.L. 1988).
Hg.5 Simplified paleogeographic map at Yraconian in South East France. Relatively deep marine deposits are represented by close lines a¢ North (Vocontian Basin) and South (Touionnais Basin and Nerthe). The stars correspond to coastal waconian deposits and the dotted area to a probable coastal region (1, this paper, 2 and 3, in the Ventoux~Lure region). Av. Avignon,A. ALx, M. Marseille. Carte pal~og~ographtque simplifi~e d'une pattie du Sud-Est de la France au Vraeonlen. Les lignes horizontales indiquant des d6p6ts ranfins reiativement profonds au Nard (r6gion vocontienne) et au Sud (Bussin toulonnais et Nerthe). Les &oiles correspondent aux sites signal6s ici (1, Gard, Salazae, 2 et 3, r6gion de Ventoux-Lure) et l'aire marqude en pointil[6 ~.une r6gion cSti~re probable. Av.Avignon, L ALLM. Marseiile. -
VII. CONCLUSIONS Reptilian eggs are relatively rare during Middle Cretaceous. Turtle eggs from Salazac are the oldest known, with Van Straelen's. The use of turtle eggs as marker of shoreline has highlighted the paleoenvironmental evolution of the Vraconian of Salazac, revealing the existence of an episode of emersion previously ignored. Other data on the regional evolution of the Vraconian indicate a progressive shallowing.
Consequently, several problems may now be studied, especially the influences of this emersion, if more than local, on other vraconian deposit~ of South-East France and the evolution of those coastal paleoenvironments during the Lower Cenomanian.
Acknowledgments I would like to express my special thanks to K,F. Hirsch (University of Colorado, Boulder) for providing helpful comments on the text and recent reprints on turtle's eggs and to J. Philip (Aix-Marseille I University) for his critical reading of the manuscript and his participation in the field work. I thank F.
de Brain for her critical remarks, A. Dhondt, F..4medro, J.F. Babinot and B. Clavel for paleontologic determinations and C. Froget for X-Ray realization.
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REFERENCES
BREISTROFFERM. (1940) - Rdvision des ammonites du Vraconien de Salazac (Gard) et considdrations g~n6rales surce sousdtage albien. Tray. Lab. Gdol. Fac. Sci. Grenoble, 22 : 71171. FRIES G. (1987) - Dynamlque s6dlmentaire du bassin subalpin it l'Apto-Cdnomanien. Th6se Doct. Sci. naturelles, Univ. P. et M. Curie, Paris (inddit, 1986) et Mdm. Sci. Term, 4, (1987), Ecole des Mines, Paris. GUENDORJ. L., PARRONC. & TRIATJ.M. (1983) - Incidences des alt6rations crdtac6es sur la notion de Sid6rolithique dans le Sud-Est de la France. BuIl. Soc. g6ol. France, (7), 25, 1 : 41-50. HEBERT E. & TOUCAS.4. (1875) - Description du bassin d' Uchaux. Ann. Sci. G6ol., Paris, 6 : 1-132. HIRSCH K.F. (1983) - Contemporary and fossil chelonian eggshells. Copeia, Washington, 2 : 382-397, HIRSCH K.F. & LOPEZ-JURADOL.F. (1987) - Pliocene chelonian fossil eggs from Gran Canaria, Canary lslands.J. Vertebrate Palaeontology, Norman (USA), 7, I : 96-99. HIRSCH K.F. & PACKARDN.J. (1987) - Review of fossil eggs and their shell structure. Scanning Microscopy, Chicago, 1, 1 : 383-400. HIRSCH K.F. & BRAYE.S. (1988) - Spheroidal eggs -avian and chelonian- from the Miocene and Oligocene of the western interior. Hunteria, Boulder, 1, 4:1-7. LECKIER.M. (1987) - Paleoecology of Mid-Cretaceous planktonic foraminifera : a comparison of open ocean and epicontinental sea assemblages. Micropaleontology, New York, 33, 2 : 164-176. LE Goc B. (1977) - Contribution it l'dtude gdologique, stratigraphique et paldog~ographique du Gargasien au Sdnonien de la rdgion Ventoux-Lure (Chaines subalpines mdridiohales), D.E.S. Univ. CI. Bernard, Lyon, 157 p. (in~dit). LocASG., CROSP. & LANOJ.(1976) - Les Roches sddimentaires, 2, Etude microscopiques des roches meubles et consolid6es, Doin Ed., Paris, 503 p. MACHHOIJRL. (1988) - Le bassin toulonnais au Crdtacd moyen (Aptien-C~nomanien). Doct. Univ. Aix-Marseille I, 592 p. (inddit). MASSEJ.P. & PHILIPJ. (1976) - Pal6ogdographie et tectonique du Crdtacd moyen en Provence. Rdvision du concept d'isthme durancien. Rev. G~ogr.phys. & GeoL dyn., Paris, ( 2 ) , 18, 1 : 49-66, MASSEP.J.L. (1988) - Evolution de la marge proven~ale ~t PAptien supdrieur et it l'Albien. Sddimentologie, Paldotectoni-
que, Pal~o#ographie. Boct. Univ. Aix Marseille I, 300 p, (inddit). MOULLADEM. (1966) - Etude stratigraphique et micropaldontologique du Cr&acd infdrieur de la fosse vocontienne. ThSse Etat, Lyon, 2 vol., 369 p. &Doc. Lab. G~ol. Fac. Sci. Lyon, 15, 369 p. PACKARDN.J. & PACKARDG.C. (1970) - Structure of the shell and tertiary membranes of eggs of softshell turtles (Tryonyx spinifents).J. Morphology, Philadelphie, 159: 131-144. PACKARDN.J. (1980) - Ultrastructural morphology of the shell and shell membrane of eggs of common snapping turtles (Chelydra serpentina). J. Morphology, Philadelphie, 165 : 87-2 04. PACKARDN.J., PACKARDG.C.& BOAROMANT.J. (1982) - Structure of eggshells and water relations of reptilians eggs. Herpatologica, Los Angeles, 38 : 136-155. PACKARDM.J., HIRSCHK.F. & IVERSONJ.B. (1984) - Structure of Shells from Eggs of Kinostemids Turtles. J. Morphology, Philadelphie, 181 : 9-20. PENNERM.M. (1983) - Contribution it l'&ude de la microstructure des coquilles d'oeuf de dinosaures du Crdtacd supdrieur clans le bassin d'Aix. Applications biostratigraphiques. Th~se Doct. Paris VI et Mdm. Sci. Terre, Paris, 83, (52), 234 p. RUBINOJ.-L. (1984) _ Sedimentology of upper aptian and albian turbidites and shelf sandstones in the vocontian basin (S.E. France). 5th Eur. reg. Meet. Sedimentology, Abstracts : 388-389. RtlBINOJ.-L. (1988) - Organisation des sdquences de ddpSts de la plateforme au bassin dans l'Aptien et l'Albien du bassin vocontien (S.E. de la France). In : FERRYS., RUBINOJ.-L. et alii, Eds : Eustatisme et Sdquences de ddpSt dans le Crdtacd du Sud-Est de la France. G6otrope, Lyon, 1 : 56-82. SRIVASTAVAS., MOHABEYD.M., ASHOKSAHN1& PONT S.C. (]986) Upper Cretaceous dinosaur egg. Clutches from Kheda District (Gujarat India). Their distribution, shell ultrastructure and paleoecology. Palaeontographica, Stuttgart, A, 193, 5-6 : 219-233. TRIATJ.M. (1982) - Pal~oalt6rations dans le Cr&ac6 sup6rieur de Provence rhodanienne. Sci. g6oL, Strasbourg, 68, 202 p. TRONCHE~TIG. (1981) - Les foraminif~res cr6tac4s de Provence (Aptien-Santonien). Thbse Doctorat d'Etat &Trav. Lab. Gdol. hist. &FaI6onL, Marseille, 12, 3 vol., 547. VAN STRAELENV. (1928) - Les oeufs de reptiles fossiles. Paleobiologica, Vienne, I : 297-312.
Manuscrit ddposd le 22.03.1989 Manuscrit ddfinitif r ~ u le 20.07.1989