MICROPAIJAEONTOLOGY OF A M O R O C C A N
ORDOVICIAN DEPOSIT YIELDING
SOFT-BODIED ORGANISMS SHOWING
EDIACARA-LIKE P R E S E R V A T I O N
JOAKIM S A M U E L S S O N ,
PETER V A N ROY, MARCO V E C O L I
Samuelsson, J., Van Roy, P., Vecoli, M., 2001. Micropalaeontology of a Moroccan Ordovician deposit yielding softbodied organisms showing Ediacara-like preservation [Micropal6ontologie d'un d6p6t ordovicien marocain produisant des organismes ~ corps mou pr6serv6 d'une fa~on comparable ~ la pr6servation 6diacarienne]. Geobios 34 (4),
365-373. Villeurbanne, le 30.09.2001
Manuscrit d6pos6 le 25.04.2000; accept6 d6finitivement le 22.12.2000.
ABSTRACT - A newly discovered locality of an hitherto unknown age, but now estimated to the Late Ordovician, in
south-eastern Morocco has yielded numerous specimens of problematic soft-bodied metazoans preserved in coarse
sandstones. The excellent preservation of the recovered specimens permits an improved understanding of both the
palaeobiology of these Ordovician metazoans and the taphonomic processes associated with them. This style of softtissue preservation is closely comparable to that of the late Neoproterozoic problematic Ediacaran organisms, and
is virtually absent in the Phanerozoic. Palynological analysis (chitinozoans and acritarchs) of shaly intercalations
in an ophiuroid-bearing sandstone slab facilitates accurate identification of the site as belonging to the Upper
Ktaoua Formation and thus a relative dating of the associated fossils. The chitinozoan assemblage is relatively well
preserved, moderately diverse and closely comparable to the previously described chitinozoan fauna from the Upper
Ktaoua Formation (Rawtheyan, late middle Ashgill age). Acritarchs are abundant but mostly ill-preserved; nonetheless they clearly indicate an undifferentiated Ashgill age, consistent with the chitinozoan chronostratigraphic
result. These datings prove that the newly discovered Moroccan metazoan assemblage contains one of the oldest
known paropsonemids, and possibly some of the youngest protolyelloids and aglaspidids. The new finds also show
that Ediacara-like coarse-clastic preservation did not completely vanish with the onset of the Phanerozoic. © t~ditions scientifiques et m6dicales Elsevier SAS
KEYWORDS: ACRITARCHS, ASHGILL, CHITINOZOANS, MOROCCO, ORDOVICIAN, SOFT-TISSUE PRESERVATION.
Rt~SUMt~ - Une localit6 d'un ~ge jusq'ici inconnu mais maintenant estim6 dans l'Ordovicien du sud-est au Maroc
r6cemment d6couverte a produit un grand nombre de sp6cimens de m6tazoaires probt6matiques ~ corps mou pr6serv6s dans un gr6s ~ gros grains. La pr6servation excellente des sp6cimens d6couverts permet de mieux comprendre aussi bien la pal6obiologie de ces m6tazoaires ordoviciens que le processus taphonomique qui a abouti ~ ce
mode de fossilisation. Le mode de pr6servation de tissus mous rapelle celui des organismes probl6matiques 6diacariens du N6oproterozoique sup6rieur et ne se produit presque jamais au Phan6rozoique. L'analyse palynologique
(chitinozoaires et acritarches) de lentilles schisteuses dans un bloc de gr6s contenant des ophiuroides facilite l'identification pr6cise du site comme appartenant ~ la formation sup6rieure du Ktaoua et fournit ainsi une datation relative de l'association des fossiles. Cet assemblage de chitinozoaires est relativement bien conserv6, assez diversifi6 et
comparable ~ la faune chitinozoaire ant6rieurement d6crite et appartenant ~ la Formation du Ktaoua sup6rieur
(d'~ge Rawtheyan, Ashgill moyen sup6rieur). Les acritarches sont abondants mais g6n6ralement mal pr6serv6s.
N6anmoins, ils sont incontestablement d'~ge Ashgill, ce qui est compatible avec l'information chronostratigraphique
des chitinozoaires. Ces datations prouvent que l'assemblage de m6tazoaires r6cemment d6couvert au Maroc contient
un des plus anciens paropsonemides connus, ~t probablement des sp6cimens de protolyelloides et des agalaspidides
les plus r6cents connus. Ces nouvelles d6couvertes prouvent aussi que la pr6servation de tissus mous dans des gr6s
n'avait pas compl6tement disparue au d6but du Phan6rozoique. © Editions scientifiques et m6dicales Elsevier SAS
MOTS-CLES: ACRITARCHES, ASHGILL, CHITINOZOAIRES, MAROC, ORDOVICIEN, PRESERVATION DE TISSUS MOUS
INTRODUCTION
Several i m p o r t a n t new localities p r e s e r v i n g labile
tissues a n d completely a r t i c u l a t e d a s t e r o z o a n s a n d
o t h e r e c h i n o d e r m s were r e c e n t l y discovered in
s o u t h - e a s t e r n Morocco. At one of t h e s e sites n e a r
Erfoud (Fig. 1), p r e s u m a b l y in the L a t e Ordovician
U p p e r K t a o u a F o r m a t i o n , a b u n d a n t a n d well preserved s p e c i m e n s of a new p a r o p s o n e m i d (problematica, u s u a l l y considered as either s t e m - g r o u p
echinoderms; F r i e n d 1995, u n p u b l i s h e d , or lopho-
phorates; Chen et al. 1995; Fig. 2.2) together w i t h
r a r e fossils of possible protolyelloids (largely E a r l y
C a m b r i a n problematica, s o m e t i m e s allied to cnidarians; Seilacher 1994; Seilacher & Goldring 1996;
b u t also considered to be of p r o t e a n or inorganic
origin; J e n s e n 1997) a n d a possible aglaspidid (arac h n o m o r p h arthropod, p r e d o m i n a n t l y a C a m b r i a n
group; Dunlop & Selden 1998) occur. The mode of
p r e s e r v a t i o n of the p r e s e n t p a r o p s o n e m i d s is comp a r a b l e t o the so-called ' E d i a c a r a - t y p e p r e s e r v a tion', as the fossils are p r e s e r v e d as moulds in coat-
366
Rabat
Casablan~¢2~
A palynological sample for age determination was
taken from a thin shaly intercalation within an
ophiuroid-bearing massive sandstone unit. The
sample yielded relatively well-preserved chitinozoans and abundant acritarchs.
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The recovered chitinozoan assemblage is closely
comparable to that previously described from the
Upper Ktaoua Formation, which was attributed to
the Rawtheyan Stage of the Ashgill (Destombes et
al. 1985). The acritarch assemblage corroborates
this age attribution. Unfortunately, several
attempts to date two other sections which also yielded new metazoan fossils, by using the same
method, were unsuccessful.
31o3ffN
ALGERIA
Upper Ktaoua Formation
j
Lower Ktaoua Formation
I
let gani Group
I
FIGURE i - Simplified geological map of the Erfoud area showing
the lateral distribution of the most important Ordovician units:
the First Ban] Group and the Lower and Upper Ktaoua
Formations. The locality investigated for its palynomorphs is
marked with a star (in the middle of the map). Inset: overview
map of Morocco showing the position of the investigated area
(hatched oval). Carte gdslogique simplifide de la rdgion d'Erfoud
montrant la distribution latdrale des plus importantes unitgs
ordoviciennes: le Groupe ler Bani et les Formations de Ktaoua
infdrieurs et supdrieurs. La localitg de laquelle provient l~chantillon contenant les palynomorphes etudids est marquge d'une
dtoile (au milieu de la carte). Insertion: carte offrant une vue gdndrale du Maroc. L'oval hachd indique la rdgion examinde.
se grained, sand-sized sediments, with large portions of their soft parts preserved. This type of softtissue preservation is considered typical for the late
Neoproterozoic ('Neoproterozoic IIr or 'Vendian');
however, the youngest Ediacaran organisms showing the typical preservation are reported from the
earliest Cambrian of Australia (Jensen et al. 1998).
Accordingly, this Moroccan site is of considerable
palaeobiological as well as taphonomic significance
and therefore requires accurate dating. In addition,
the site is denoted as Quaternary cover on the geological map (Fig. 1), which created the need for the
present palynological study. The soft-bodied fauna
is currently the subject of an extensive separate
study by P. Van Roy, and in this paper, we will
concentrate on the micropalaeontology of this
important site.
Palynological dating permits high chronostratigraphic resolution. In particular, chitinozoans, interpreted by some workers .as the egg-capsules of
extinct metazoans (e.g. Miller 1996; Paris & NSlvak
1999), have been proven to be among the most efficient biostratigraphic tools for the entire lower
Palaeozoic. The stratigraphic accuracy obtained
from carefully identified chitinozoan assemblages
is fully comparable to that provided by graptolites
(Paris 1996). Acritarchs, probably the resting cysts
of marine phytoplankton, also have great value in
biostratigraphic applications, especially in the
lower Palaeozoic (e.g. Strother 1996).
A number of papers dealing with the micropalaeontology of the Moroccan lower Palaeozoic deposits
have been published. Among these, a few treat chitinozoans. Rahmani (1983) presented chitinozoan
biostratigraphy of two outcrops in the area of Oued
Bou-Regreg, south of Rabat, where the Arenig and
lower Llandeilo was represented. Of particular
interest for the present investigation is ElaouadDebbaj (1984a), who investigated the chitinozoan
assemblages in the Upper Ktaoua and Lower
Deuxi~me Bani formations, both in the Zagora
area. That work was followed by a study of chitinozoans in the Lower Ktaoua Formation (ElaouadDebbaj 1986). Chitinozoans from 'Boutonniere des
Zekkara' in the Oudja region were investigated by
Elaouad-Debbaj et al. (1987). Soufiane & Achab
(1993) analysed core samples from the Ordovician
rocks of the Tadla Basin in the western M~s~ta
region and identified chitinozoan assemblages of
Arenig, Llandeilo, Caradoc and Ashgill ages, thus
re-evaluating palynologically the borehole successions first investigated by Cramer in the 1970's.
Moroccan lower Palaeozoic (especially Ordovician)
sedimentary successions have been extensively
investigated for acritarchs. Important works on
Ordovician acritarch biostratigraphy of Morocco
are those by Cramer et al. (1974a, b) and Cramer &
Diez (1976, 1977). These early investigations focused mainly on subsurface material from the Tadla
Basin. Less comprehensive accounts on Moroccan
Ordovician acritarchs are those of Deunff (1977),
Marhoumi et al. (1982), and Fournier-Vinas (1985).
Detailed studies of lower and upper Ordovician
acritarchs from the Anti-Atlas were published by
Elaouad-Debbaj (1984b, 1988a, b).
Our results show that the new locality belongs to
the Upper Ktaoua Formation, and is of a Rawtheyan (late middle Ashgill) age. This age-assignment is supported by comparison with other chitinozoan and acritarch assemblages from North
Gondwana (e.g. Libya and Saudi Arabia).
GEOLOGICAL SETTING
During the Ordovician, an epicontinental sea covered most part of Morocco, with coarse clastic sedimentation prevailing. In the study area, the effects
of the Variscan orogeny were negligible, causing
only the formation of large folds (Destombes et al.
367
1985) and, locally, small scale faulting. Our results
show that the site under discussion (Fig. 1) belongs
to the Upper Ktaoua Formation, where independent stratigraphic controls provided by trilobites
and brachiopods are indicative of the Rawtheyan
Stage (Elaouad-Debbaj 1984a; Destombes et al.
1985; Paris 1990). The Ktaoua Formation is a
transgressive unit that consists mostly of argillaceous deposits intercalated with sandstones. In
places, conglomerates are also present. For a more
complete treatment of the geology of this formation,
see Destombes et al. (1985).
THE INVESTIGATED LOCALITY
The site is situated to the east of Erfoud, and on the
geological map it falls in an area denoted as
Quaternary cover (Fig. 1), which necessitated the
present palynological study in order to unequivo-
cally establish the age and stratigraphic assignment of this important outcrop. The deposits dip to
the west at an inclination of approximately 20 °.
They mainly consist of coarse sandstones, exhibiting frequent ripple-marks, locally cross beds, and
desiccation cracks. Trace fossils, conulariids, brachiopods and trilobites co-occur with the possible
protolyelloids, paropsonemids and a possible aglaspidid. About 10 m lower, the sandstone is massive,
moderately coarse with small shaly lenses that are
discontinuously distributed and have a dark bluish-grey colour. Exceptionally large conulariids (Fig.
2.1), odontopleurid (Selenopeltis), trinucleid and
other asaphid trilobites, orthid brachiopods, rare
partially articulated crinoids and crinoid debris
and articulated ophiuroids (Fig. 2.1) occur here.
The sample yielding the palynomorphs was taken
from this level. No unconformities were observed
between this and the paropsonemid horizon.
Because of intense weathering, which heavily cove-
FIGURE 2 - The illustrated specimens are deposited at the Research Unit Palaeontology, Department of Geology and Pedology, Ghent
University, Belgium. 1. Large three-dimensionally preserved conulariid specimen (P4672) with an ophiuroid (upper left, arrowed) compacted onto it. This specimen was recovered from the same level as the investigated sample. Note the wrinkles caused by deformation
of the phosphatic conulariid test (not preserved in this specimen) and the apparent lack of corner grooves. The lack of corner grooves is
typical for the monospecific Ordovician genus Anaconularia, which hitherto has only been reported from the Czech Republic (x 0.54). 2.
Example ofa paropsonemid specimen (P4673), viewed from the convex side. These fossils are locally very abundant. The depression caused by the collapse of the internal coiled sac is clearly visible. Also note the typical radial ornamentation, and the faint traces left in
some places of the concentric ornamental ridges (× 0.78). Les exemplaire illustrds sont deposds & Research Unit Palaeontology,
Department of Geology and Pedology, Ghent University, Belgique. 1. Spdcimen d'un grand conulariide (P4672) prgservg ~t trois dimensions avec impression d'un ophiuro~de (en haut &gauche, fl~che). Ce specimen provient du m~me niveau que l~chantillon examing. Notez
les rides causeds par la ddformation du tdgument phosphatique du conulariide (qui n'est pas dtd prdserve dans ce spdcimen) et l'abscence
apparente de sillons angulaires. Le manque de ces sillons est typique pour le genre monospdcifique Anaconularia de l'Ordovicien et n'a
dtg signald que dans la Rdpublique Tch~que (x 0,54). B. Example d"un paropsongmide (P4673) vu du cord convexe. Ces fossiles sont localement tr~s abondants. La d~pression produite par l'gffondrement interne du "coiled sac'est manifeste. Notez aussi l'ornementation radiale typique et, par endroits, les faibles traces des cStes ornementales concentriques (x 0,78).
368
red the outcrop with scree, and the small-scale
n a t u r e of the fossil excavations, it has hitherto not
been possible to construct a lithological column.
p a l y n o m o r p h debris, was present in the 63 p m fraction. We have closely followed the recommendations in Paris et al. (1999) for the taxonomic treatm e n t to the genus level. For the complete list of chitinozoans recovered in the ophiuroid sample, see
Appendix.
MATERIAL AND METHODS
For the m e a s u r e m e n t s of the chitinozoans in the
following sections, the symbols are used as in Paris
(1981) where L = total length; L , = c h a m b e r length;
D_ = c h a m b e r diameter, D c = d i a m e t e r of oral tube.
T~e dimensions given below are with a n approxim a t e accuracy of _+ 2 pm. M e a s u r e m e n t s and statistical analyses were m a d e on the flattened specimens and no correction factors sensu Paris (1981)
were employed to obtain p r e s u m e d three-dimensional sizes.
The size of the ophiuroid-bearing slab from which
the shale sample was taken, is about 60 × 40 x 20
cm. The sampled shale lenses are usually less t h a n
1 cm thick, and t h e y r a r e l y occupy an area of more
t h a n a few square cm. F u r t h e r in the text, this
single palynomorph-yielding sample will be referred to as the 'ophiuroid sample'.
Approximately 30 g of fine grained sediment was
carefully scraped off from the above-mentioned slab
with the help of a small stainless steel spatula.
G r e a t care was t a k e n t h a t the scraped-off pieces
were as large as possible. Exactly 20 g of the finegrained material was t h e n subjected to s t a n d a r d
palynological t r e a t m e n t with HC1 and H F (Wood et
al. 1996). The r e m a i n i n g organic residue was filtered in 96 % ethanol at a mesh-size of 63 pm. The
larger fraction was used for the chitinozoan analysis, and the finer fraction for the acritarch studies.
For scanning electron microscopy (SEM) and optical microscope investigations of the chitinozoans, a
subsample of r a n d o m l y chosen chitinozoans was
obtained by picking all microfossils in 5 ml of the
alcohol/organic residue m i x t u r e after thorough stirring from the 63 p m fraction until the total n u m b e r
of chitinozoans was ca. 250. Eighty-five of the chitinozoans were t r a n s f e r r e d to SEM stubs for detailed
examination u n d e r the SEM. For the acritarch
investigation, strew slides were prepared.
Slides for optical microscopy were p r e p a r e d using
C a n a d a B a l s a m as m o u n t i n g m e d i u m for the chitinozoans, and Epoxy for the acritarchs. The SEM
micrographs were t a k e n on a J E O L Scanning
Microscope JSM-6400 at 10 kV of the D e p a r t m e n t
of Geology and Pedology, G h e n t University. All
illustrated specimens are housed in the collections
of the Research U n i t Palaeontology, D e p a r t m e n t of
Geology and Pedology, G h e n t University, Belgium.
MICROPALAEONTOLOGICAL RESULTS
CHITINOZOANS
The chitinozoans are m o d e r a t e l y well-preserved,
albeit flattened, but with fine details showing some
wear (Fig. 3). The fossils are very a b u n d a n t (no
exact q u a n t i t a t i v e e s t i m a t i o n was done), a n d
almost no kerogenous organic matter, except for
N O T E S ON T H E RECOVERED CHITINOZOANS
Here, only brief notes concerning the recovered
t a x a are provided. For a more complete taxonomic
t r e a t m e n t of the taxa u n d e r discussion, see e.g.
Elaouad-Debbaj (1984a). Paris (1988, 1990) discusses the stratigraphic implications of a similar
assemblage.
Some of the t a x a were r e p r e s e n t e d by a relatively
large n u m b e r of well-preserved specimens. Included among those are Desmochitina m i n o r subsp.
typica EISENACK.Armoricochitina nigerica (BouCHE)
is an easily recognisable species (average of the
p r e s e n t specimens: L = 144 ~m, N = 5; D~ = 84 pm,
N=5;D c=88~m,N=5;L~=120pm;N=2)
of
biostratigraphic significance (Paris 1990). The present specimens (Fig. 3.1) are closely comparable in
overall s h a p e to those p r e s e n t e d by E l a o u a d Debbaj (1984a) as Armoricochitina aff. armoricana
(e.g. her P1.2, Fig. 22), and to those figured by Paris
in Molyneux & Paris (1985) from wells in Libya.
However, our m e a s u r e d specimens are ca. 100 ~ m
smaller t h a n those of Elaouad-Debbaj (1984a), b u t
well within the interval given by Bouch~ (1965) in
his original description of the taxon. A single specim e n is referred to Armoricochitina sp. A h e r e i n
(Fig. 3.2), since it has a spongy surface, and is some
100 p m longer t h a n A. nigerica. It is m u c h s h o r t e r
and more compact t h a n T a n u c h i t i n a fistulosa
(TAuGOURDEAU& DE JEKHOWSKY,1960), and probably
r e p r e s e n t s a new species. The species Conochitina
brevis was poorly described by T a u g o u r d e a u & de
J e k h o w s k y (1960), but the present specimens (Fig.
3.4) are similar both in outline and size to t h e i r
holotype (average of the p r e s e n t specimens: L = 194
~m, N = 5; D~ = 92 pm, N = 5; D c = 66 ~m, N = 5;
L D = 137 ~m; N = 3). Another species, or r a t h e r
gr'oup of species, are the specimens referred to Belonechitina micracantha h e r e i n (Fig. 3.11). Although
G r a h n et al. (1994) dealt with u p p e r Ordovician
FIGURE3 - Chitinozoans recovered from the opiuroid sample (P4674). 1. Armoricochitina nigerica (BoucHI~,1965) (x 300). 2. Armoricochitina sp. A (x 210). 3. Ancyrochitina ? merga (JENKINS, 1970) (x 425). 4. Conochitina brevis TAUGOURDEAU• DEJEK~OWSKY,1960 (X
285). 5. Ancyrochitina ? merga (JENKINS, 1970) (x 415), same specimen as in Fig. 3.7. 6. Ancyrochitina sp. (x 485). 7. Detail of process of
Ancyrochitina ? merga, same specimen as in Fig. 3.5 showing the multipode arrangement of the appendage base (x 1260). 8. Base of the
specimen of Tanuchitina cylindrica (TAUGOURDEAU& DE JEKI~OWSKY,1960) portrayed in Fig. 3.12, showing the small carina (x 860). 9.
Ancyrochitina ? onniensis (JENKINS, 1967) (x 575). 10. ? Belonechitina sp. A (x 340). 11. Belonechitina micracantha (EISENACK,1931) (x
500). 12. Tanuchitina cylindrica (TAUGOURDEAU& DE JEKHOWSKY,1960), detail of carina is depicted in Fig. 3.8 (x 320).
369
FIGURE3 ( S U I T E ) - Chitinozoaires trouvds dans 'l~chantillon ophiuroide' (P4674). 1. Armoricochitina nigerica (SoucHfi,, 1965) (x 300). 2.
Armoricochitina sp. A (x 210). 3. Ancyrochitina ? merga (JENKINS, 1970) (x 425). 4. Conochitina brevis TAUGOURDEAU• DEJEKHOWSKY,1960
(x 285). 5. Ancyrochitina ? merga (JENKINS, 1970) (X 415), re#me spdcimen que dans la Fig. 3.7. 6. Ancyrochitina sp. (x 485). 7. Ddtail de
l'appendice d'Ancyrochitina ? merga, m~me spdcimen que clans la Fig. 3.5 montrant l'arrangement multipode de la base de l'appendice
(x 1260). 8. Base du spdcimen de Tanuchitina cylindrica (TAuGOURDEAU& DE JEKHOWSKY,,1960) repr#sent# dans la Fig. 3.12, montrant la
petite carina (x 860). 9. Ancyrochitina ? onniensis (JEgKINS, 1967) (x 575). 10. ? Belonechitina sp. A (x 340). 11. Belonechitina micracantha (EISENACK, 1931) (X 500). 12. Tanuchitina cylindrica (TAuGOURDEAU& DE JEKHOWSKY,1960), ddtail de la carina est montrde dans Fig.
3.8 (x 320).
370
deposits in Baltoscandia (the Oslo-Asker and
Ringerike districts, Norway), their comment under
Belonechitina micracantha, that the current species concept incorporates a number of species,
seems to hold true also for the present population,
as the specimens show a high degree of variability.
Lagenochitina prussica EISENACKis only represented by two specimens.
Those specimens where the taxonomic attribution
proved less clear can be divided in two categories:
those that were too poorly preserved to allow for a
sound taxonomic treatment, and those taxa that
were represented by too few specimens to allow for
a complete judgement of all the morphological characters.
In this first category several specimens apparently
belonging to Armoricochitina nigerica fall; they are
treated separately as A. ? nigerica. The specimens
attributed to Rhabdochitina spp. were most similar
to R. magna EISENACKand R. gracilis EISENACKin
outline, but because all specimens were incomplete,
specific attribution was impossible. All the Ancyrochitininae are also incomplete, the spines and processes are very worn, in some cases totally absent.
The specimens here attributed to Ancyrochitina ?
merga (JENKINS)have only retained the bases of the
processes (Figs 3.3, 5, 7). The other characteristics,
however, are typical for A. merga, such as shape of
vesicle (average of the present specimens: L = 138
~m, N = 4; D~ = 82 ~m, N = 4; D c = 41 pm, N = 3;
L, = 68 pm, 1~ = 4), a more wide than long chamber,
br'anching process bases (Fig. 3.7), flaring oral tube
(Fig. 3.3) and small spines covering the vesicle (Fig.
3.5). The shorter neck and the differently developed
processes in specimens kept under open nomenclature as Ancyrochitina ? onniensis (average measurements: L = 123 ~m, N = 4; D~ = 84 pm, N = 5; D c
= 42 ~m, N = 4; L~ = 72 ~m, N "-- 5) makes them different from A. ? r~erga.
Two taxa, Belonechitina aff. sp. A and ? Spinach#
tina cf. bulmani (JANsONIUS), are only represented
by poorly preserved, rare specimens; hence they fall
in both earlier mentioned categories of taxa treated
under open nomenclature herein. Chitinozoans
attributed to Belonechitina aff. sp. A are similar to
a specimen figured by Paris in Molyneux & Paris
(1985; their Ph 7: Fig. 8a, b). Both shape (Fig. 3.10)
and dimensions are comparable, but besides the
relatively poor preservation of the majority of the
present specimens (and the lack of a systematic
description of the Paris specimen), there are too few
specimens to allow for an accurate comparison.
Three specimens attributed to ? Spinachitina cf.
bulmani have the overall shape in common with S.
bulmani (JANsONIUS), but the most discriminate
character for the generic attribution, the crown of
processes, is absent among the recovered specimens.
Specimens attributed to Tanuchitina cylindrica
(TAuGOURDEAU• DE JEKHOWSKY)show a poorly developed carina (Figs 3.8, 12). Specimens showing the
Ancyrochitina:shape of their vesicles, but with neither spines nor processes preserved, were grouped
as Ancyrochitina spp. (e.g. the specimen illustrated
in Fig. 3.6).
ACRITARCHS
A low diversity, high abundance acritarch assemblage was recovered. The numerous specimens are
mostly ill-preserved, dark brown to black in colour,
and in the majority of cases do not allow for precise
species determination. At the generic level, the
assemblage is dominated by Multiplicisphaeridium
STAPLIN, 1961 emend. Turner 1984 and Veryhachium DEUNFF, 1954 emend. Sarjeant & Stancliffe
1994, and secondarily by Micrhystridium DEFLANDRE, 1937 emend. Sarjeant & Stancliffe 1994 and
Polygonium VAVRDOV_~,1966 emend. Sarjeant &
Stancliffe 1994. One single, incomplete specimen
attributable to Orthosphaeridium EISENACK, 1968
emend. KjellstrSm 1971 was also observed.
Species of Multiplicisphaeridium are characterised
by numerous, short multifurcate processes and can
tentatively be attributed to M. cf. M. microcladum
(DowNIE) Eisenack, 1969, while forms featuring
few, longer processes may be attributed to M. cf. M.
ramispinosum STAPLIN, 1961. Among the Veryhachium, both three- and four-processed species are
common. The former are here grouped under the
Veryhachium trispinosum group, while the latter
can be attributed to Veryhachium cf. V. lairdi (DEFLANDRE)Deunff, 1959 ex Downie 1959. No specific
discrimination is possible among the numerous
specimens generically attributable to Polygonium
and Michrystridium.
The only age-significant species occurring in the
present sample is Villosacapsula cf. V. setosapellicula (LOEBLICH)Loeblich & Tappan 1976, which is
preferably left here in open nomenclature because
of the frequent corrosion of the diagnostic sculptural elements in many specimens. V. setosapellicula,
originally described from the North American
Ashgill (Loeblich 1970), is frequently encountered
in upper Ordovician sediments of North Africa,
including Morocco (Deunff & Massa 1975; Jardin~
et al. 1974; Hill & Molyneux 1988; Elaouad-Debbaj
1988b; Vecoli 1999) and other parts of North
America (Indiana: Colbath 1979; Kansas: Wright &
Meyers 1981; Missouri: Wicander et ah 1999) and
Europe (Bohemia: Vavrdov~ 1988).
DISCUSSION AND CONCLUSIONS
AGE DETERMINATION AND
ENVIRONMENTAL CONTROL
The chitinozoan assemblage proved to be moderately diverse; as such, it yielded enough taxa to
allow for a detailed biostratigraphic evaluation. In
itself, the present assemblage is indicative of a
broad Ashgill age, as evidenced by the presence of
Armoricochitina nigerica, known from the Pusgillian to the Hirnantian (Paris 1990). Although not
conclusive, the Ashgill age can be narrowed down
by the presence of Ancyrochitina ? merga, as A.
merga is only known from the Rawtheyan (Paris
1990).
371
However, in this particular case, a biostratigraphic
evaluation is straightforward: several of the chitinozoan taxa reported by Elaouad-Debbaj (1984a)
from the Upper Ktaoua Formation were recovered
also from the ophiuroid sample, supporting a
Rawtheyan age assignment for the fossils, and
most importantly, the probable affinity of the
ophiuroid sample, and hence the outcrop, to the
Upper Ktaoua Formation. Elaouad-Debbaj (1984a)
reported Armoricochitina nigerica, Ancyrochitina
merga, ? Tanuchitina sp., Lagenochitina prussica
and Euconochitina lepta and the present assemblage yielded forms closely comparable to these. The
most striking difference between the assemblage
reported by Elaouad-Debbaj (1984a) and the present is the apparent lack of the biostratigraphically important Ancyrochitina longispina (ACHAB,
1978) and Plectochitina sylvanica (JENKINS)in the
ophiuroid sample. This is most likely a consequence of the poor preservation of delicate details such
as spines and processes, and bona fide specimens of
both A. longispina and P. sylvanica are probably
grouped among Ancyrochitina spp. herein.
The age assignment of the Upper Ktaoua Formation is discussed by Destombes et al. (1985) and a
Rawtheyan (late middle Ashgill) age, based on the
presence of stratigraphically significant trilobites
and brachiopods was put forward. The Upper
Ktaoua Formation has been correlated with other
North African Ordovican strata, including the well
J1-81A in north-east Libya (Molyneux & Paris
1985; Paris 1988). The Ashgill assemblages of this
well yielded chitinozoan species such as Armoricochitina nigerica, Plectochitina sylvanica and Ancy-
rochitina merga.
Lately, much emphasis has been put into elucidating the Lower Palaeozoic chitinozoan biostratigraphy of Saudi Arabia. A1-Hajri (1995) presented a
local chitinozoan biostratigraphic zonation for the
Ordovician of the Arabian Peninsula by focusing on
drillcores from the northern part of Saudi Arabia.
In the local Ancyrochitina merga Biozone (Middle
Ashgill), a characteristic chitinozoan assemblage
similar to the present yielded e.g. Armoricichitina
nigerica, Plectochitina sylvanica, Euconochitina
lepta, Tanuchitina elongata (BoUCHE, 1965) and
Belonechitina micracantha typica (EIsENACK, 1965).
Paris et al. (2000) investigated the Ordovician chitinozoans in a number of drillholes in central Saudi
Arabia. In the Late Ordovician of the well Berri - 84
(Quwara Member of the Qasim Formation), another assemblage directly comparable to the present
was recovered, yielding e.g. common A. nigerica,
Acanthochitina sp. nov. and rare Ancyrochitina longispina, possibly A. merga, and a few doubtful P.
sylvanica. It thus seems that a chitinozoan assemblage where A. nigerica and A. merga are important constituents is typical for Middle Ashgill strata in North Gondwana. In contrast, strata of a similar age deposited on the microcontinent Avalonia
yielded a different chitinozoan assemblage (e.g.
Samuelsson & Verniers 2000).
Chronostratigraphically, although rather poor, the
acritarch assemblage conforms with the Rawtheyan age and the attribution to the Upper Ktaoua
Formation as suggested by the chitinozoans; a comparison between the present assemblage and that
described by Elaouad-Debbaj (1988a) from the
Ashgill of the Anti-Atlas of Morocco is also possible.
It should be noted here that all Upper Ordovician
microphytoplankton assemblages described from
the North African region are characterised by unfavourable preservation and low diversity (e.g.,
Elaouad-Debbaj 1988a; Hill & Molyneux 1988;
Vecoli 1999). According to recently developed
models (e.g. Tongiorgi et al. 1998) low-diversity (oligotaxic) communities are expected to develop
during sea-level lowstands because of the establishment of eutrophic conditions in the platforms.
The organic matter preservation of the ophiuroid
sample, therefore, may also be linked to this particular environmental control on microphytoplankton production.
IMPLICATIONS FOR THE METAZOAN
FOSSILS
The Rawtheyan age of the soft-bodied metazoans
discovered in Morocco has several important
palaeobiological implications. In particular, the
new Moroccan paropsonemids can be said to be the
second oldest known, the oldest being Discophyllure peltatum HALL, 1847 from North America,
which has a probable Caradoc age (Friend 1995,
unpublished). In contrast, the Moroccan supposed
protolyelloids, would be the youngest fossils of this
type, unequivocal protolyelloids being Early Cambrian in age. It must however be noted that
Archaeonectris benderi HUCKRIEDE, 1967 from the
Late Ordovician of Pakistan possibly also falls in
the protolyelloids (Seilacher 1994; Seilacher &
Goldring 1996). If the arachnomorph is shown to be
a true aglaspidid, it would be one of the latest
known representatives of this group, aglaspidids
being largely restricted to the Late Cambrian
(Dunlop & Selden 1998). There are other undescribed aglaspidids from the Early Ordovician of North
America (Dunlop & Selden 1998) and from the
Silurian of China (Fortey & Theron 1994); the placement of the Devonian sinaglaspidids (Youchong
& Shaowu 1984) in this group is dubious (Dunlop &
Selden 1998). The Moroccan ophiuroids are fairly
early representatives of this group, which first
appears in the Early Ordovician; as such, they add
more data to the meagre early fossil record of these
echinoderms. The presence of Late Ordovician softbodied fossils in sandstones also indicates that
coarse clastic Ediacara-style preservation was not
completely abolished in the Phanerozoic.
Acknowledgements - Our colleaguesat Ghent University,Prof.
Jacques Verniers, Ms. Baharak Bashar, Dr. Dirk Van Damme,
Prof. Achilles Gautier, and Ms. Sabine Van Cauwenberghe all
helped in various ways in the preparation of this paper. Thanks
are also extendedto Prof. Helmut Heinish for accessto the stateof the-art palynological facilities of the Institute of Geological
Sciences, Halle University. We are obliged to Dr. Mohammed
Boutaleb (Minist~re de G~ologieet des Mines, Morocco)for his
willingness to collaborate. Mr. Paul Van Royprovidedthe French
translations. Mr. Michel Wagenaar is gratefully acknowledged
for macrofossil photography. Mr. Mohammed Segaoui and Mr.
M'barek Segaouiprovidedinvaluable help in the field. Christoph
372
Schneider, Till Lindemann, Richard Z. Kruspe, Paul Landers,
Christan Lorenz, and Oliver Riedle (Rammstein, Germany) are
acknowledged for inspirational support during our efforts. The
study was supported by a grant offered by the Flemish Institute
for support of Scientific and Technological research in the
Industry (IWT) to P.V.R, and by the European Union TMR
Network project PACE which provided financial support to J. S.
and M. V. The paper is a contribution to the IGCP project N° 410
'The Great Ordovician Biodiversification Event'. We thank Dr
Florentin Paris (Rennes) and an anonymous reviewer for their
helpful comments.
APPENDIX
The following chitinozoan taxa were recovered from the
ophiuroid sample. Numbers within parenthesis are the
relative frequency of the taxon expressed in percent.
Total n u m b e r of chitinozoans counted was 258. Forty-one
percent (41%) of the chitinozoans r e m a i n u n d e t e r m i n e d
because of poor p r e s e r v a t i o n a n d / o r f r a g m e n t a r y
vesicle.
Ancyrochitina ? merga (JENKINS,1970)
Ancyrochitina ? onniensis (JENKINS,1967)
Ancyrochitina spp.
Armoricochitina nigerica (BoucHE, 1965)
Armoricochitina ? nigerica
Armoricochitina sp. A
Belonechitina micracantha (EISENACK,1931)
Belonechitina aft. sp. A sensu PARRSin
Molyneux & Paris (1985)
Belonechitina spp.
Conochitina brevis (TAuGOURDEAU&
DEJEKHOWSKY,1960)
Conochitina spp.
Desmochitina minor subsp, cocca (EISENACK,1931)
Desmochitina minor subsp, typica (EISENACK,1958)
Desmochitina minor subsp, indet.
? Desmochitina sp.
Euconochitina cf. lepta (JENKINS,1970)
? Euconochitina sp.
Lagenochitina prussica (EtSENACK,1931)
Pistillachitina ? elegans (EISENACK,1931)
Rhabdochitina spp.
? Spinachitina cf. bulmani (JANSONtUS,1964)
Tanuchitina cylindrica (TAuGOURDEAU& DEJEKHOWSKY)
Tanuchitina spp.
(8 %)
(2 %)
(7 %)
(4 %)
(2 %)
(0.4 %)
(8 %)
(3 %)
(0.4 %)
(4 %)
(3 %)
(0.4 %)
(2 %)
(2 %)
(0.4 %)
(2 %)
(0.4 %)
(1%)
(0.4 %)
(8 %)
(2 %)
(0.4%)
(1%)
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J. S A M U E L S S O N * & P. VAN ROY
Research Unit Palaeontology
Department of Geology and Pedology, Ghent University
Krijgslaan 281/$8
B-9000 Ghent
e-mail: [email protected]
*Present address: Institute of Earth Sciences
Historical Geology and Palaeontology
Norbyv~gen 22
752 36 Uppsala, Suede
e-maih j [email protected]
M. VECOLI
Institut ftir Geologische Wissenschaften
Martin-Luther Universitat Halle/Wittenberg
Domstrasse 5
D-06108 Halle (Saale)
e-mail: [email protected]