◄ Carnets Geol. 24 (3) ►
Outline:
[1. Introduction]
[2. Material and general setting]
[3. Descriptions of samples ...]
[4. Descriptions of some ooids and bothryoids from thin sections
...]
[5. Discussion]
[6. Conclusion]
and ... [Bibliographic references]
2 impasse Charles Martel, 29217 Plougonvelin (France)
Dépt. STU, Fac. Sci. Tech., UBO, 6 avenue Le Gorgeu, CS 93837, F-29238 Brest (France)
93 avenue des acacias, 91800 Brunoy (France)
Published online in final form (pdf) on January 20, 2024
DOI: 10.2110/carnets.2024.2403
[Editor: Michel Moullade; language editor: Phil Salvador; technical editor: Bruno R.C. Granier]
Asymmetric ooids are documented in a brackish Maastrichtian to Danian paleolake in NW Argentina. Their distinctive asymmetric growth pattern is likely related to an uneven distribution of the Extracellular Polymeric Substances (EPS) around the coated allochem, within which calcite fibers (i.e., the 'fibrite') have grown. This pattern is unlikely to be mistaken for that of other 'eccentric' ooids, such as wobbly ooids, spiny ooids, hiatus ooids, half-moon ooids, 'broken' ooids sensu lato, or collapsed oomolds (referred to as 'distorted' ooids).
• ooid;
• microbial carbonates;
• Salta;
• Argentina;
• Maastrichtian-Danian
Granier B.R.C. & Lapointe Ph. (2024).- The Kalkowsky Project - Chapter V. Asymmetric ooids from the Yacoraite Formation (Argentina).- Carnets Geol., Madrid, vol. 24, no. 3, p. 75-82. DOI: 10.2110/carnets.2024.2403
Le Projet Kalkowsky - Chapitre V. Ooïdes asymétriques de la Formation Yacoraïte (Argentine).- Nous décrivons des ooïdes asymétriques provenant d'un paléolac saumâtre d'âge Maastrichtien à Danien du nord-ouest de l'Argentine. Leur mode de croissance particulier, i.e., asymétrique, est probablement lié à une répartition inégale des substances polymériques extracellulaires (SPE) autour du grain cortiqué, au sein desquelles les fibres de calcite (i.e., la "fibrite") se sont développées. Il est peu probable que ce mode de croissance puisse être confondu avec celui d'autres ooïdes "excentriques", tels que les ooïdes bancals, les ooïdes épineux, les ooïdes hiataux, les ooïdes en demi-lune, les ooïdes "cassés" sensu lato ou les moules effondrés d'ooïdes (parfois appelés ooïdes "déformés").
• ooïdes ;
• carbonates microbiens ;
• Salta ;
• Argentine ;
• Maastrichtien-Danien
The petrographic analysis of thin sections reveals that there is still much to be gleaned from microbial carbonates (Granier & Lapointe, 2021, 2022a, 2022b); this is the core idea behind the Kalkowsky Project. The material presented here documents a new occurrence of 'eccentric' ooids from the lacustrine (Maastrichtian to Danian) Yacoraite Formation (e.g., Cónsole Gonella et al., 2012; Freire, 2012) in NW Argentina.
The material under study was
collected by one of us (P.L.) with the assistance of three IFP colleagues
(Bernard Colletta, Jean Letouzey, and Roland Vialy) from
two distinct localities in the provinces of Salta and Jujuy in NW Argentina (Fig. 1 
):
1) on October 6, 1988: The first
section (Fig. 2 ), already documented in Granier
and Lapointe (2022b, Figs. 3.D, 4-5), was
found approximately 60 km south of Salta. It is situated on a bend of Road 47
from Coronel Moldes to Puente Dique Cabra Corral (Fig. 1.D ), precisely at
25°17'04.4"S
65°24'56.1"W (Province of Salta,
Argentina). This outcrop, located in the Metán subbasin of the Salta Basin, is
referred to as "Afloramento Viñuales" of the "Sequência
Balbuena IV" of the Yacoraite Formation (Freire, 2012, Figs. 5.1, 5.10, 8.7) and is assigned a Danian age. Four petrographic thin
sections were prepared from two rock pieces labelled ARA 268 and ARA 269,
collected near the top of the logged section. Although the first two thin
sections (ARA 268 and ARA 269) are likely lost, two new thin sections (AG 268
and AG 269, registered as MHNG-GEPI-2024-10268 and 10269 in the collections of
the Musée d'Histoire Naturelle de Genève, Switzerland) were prepared from
offcuts of the initial two;
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Figure 1: A) Location map
of the provinces of Jujuy (red) and Salta (blue) in Argentina; B) location map
of the sampling localities 268-269 in the Province of Salta and 351 in the
Province of Jujuy; C) location of the sampling locality 351 in a canyon section
6.5 km south of Palma Sola, Province of Jujuy; D) location of the sampling
localities 268-269 on a bend of Road 47 from Coronel Moldes to Puente Dique
Cabra Corral, Province of Salta. |
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Figure 2: Shematic drawing
of the Salta section (Cabra Corral) with location of samples 269 and 270 in bold
red (excerpt from Granier & Lapointe,
2022b). |
2) on October 15, 1988: The second section, measured by the same
group of field geologists (Fig. 3.B ),
is exposed in a canyon located 6.5 km south of Palma Sola, west of the truck
road connecting this locality to El Sauzal, approximately 100 km east of San
Salvador de Jujuy (Fig. 1.C ),
at around
24°05'24.0"S 64°17'46.4"W
(Province of Jujuy, Argentina). This second Yacoraite section is situated in
the Lomas de Olmedo subbasin of the Salta Basin and is presumed to be of
Maastrichtian age. Two petrographic thin sections were prepared from one rock
piece labelled ARA 351, collected near the bottom of the exposed section (Fig.
3.B-C ).
While the first thin section (ARA 351) is likely lost, a second thin section (AG
351, registered as MHNG-GEPI-2024-10351 in the collections of the Musée
d'Histoire Naturelle de Genève, Switzerland) was prepared from an offcut of the
original.
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Figure 3: The Jujuy
section, a canyon section near Palma Sola: A) View of the canyon section;
B) schematic drawing of the canyon section with location of sample 351 in
red; C) lowermost oolites and stromatolites. |
Thin section ARA 268 (Fig. 4.A )
reveals three stromatolitic microcolumns, each approximately 1 cm wide,
containing silt and coated grains in the stromatolitic inner vugs and in the
intercolumnar space. In contrast, the microfacies of thin sections AG 268, AG
269, and ARA 269 (Fig. 4.B ) consist of 1) a floatstone of ooids and bothryoids
(also
spelled 'botryoids') with a silty matrix and 2) fibrous sparitic crusts growing on some
bothryoids. The matrix also
contains silt-sized quartz and some fish teeth.
The microfacies of both thin
sections ARA 351 (Fig. 4.C ) and AG 351 corresponds to a floatstone of bothryoids
and oolitic lithoclasts with an oolitic grainstone matrix. Some lithoclasts
exhibit a superficial oolitic coating. Ostracod shells are commonly observed as
nuclei of ooids.
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Figure 4: High resolution
scans of the thin sections: A) three stromatolitic microcolumns, each
approximately 1 cm wide, containing silt and coated grains in the stromatolitic
inner vugs and in the intercolumnar space, ARA 268, B) floatstone of bothryoids
and ooids with a silty matrix, ARA 269, C) floatstone of lumps and bothryoids
with an oolitic grainstone matrix, ARA 351 (all likely lost). Scale bar for all
scans = 5 mm. |
The nucleus of one specimen from
AG 268 (Figs. 5.B ,
6.A ) is a hemiooid sensu Kalkowsky's
(1908) classification. Similarly to most 'broken' ooids sensu
stricto, the break lines align with the calcite fibers of the cortical
layers. In this case, a half-piece of the ooid has undergone partial
regeneration, a phenomenon also observed in the second half (Fig.
5.C ), which
was found approximately 5 mm away in the same thin section (Fig.
5.A ).
However,
both pieces distinctly differ from typical 'broken and regenerated' ooids, i.e.,
'broken' ooids sensu lato, due to the non-continuous nature of their
'regenerated' cortices.
The siliciclastic nucleus of
another asymmetric ooid from AG 268 (Figs. 5.E ,
6.B ) is
protruding. Yellowish 'fibrite' (a neologism for 'fibrous calcite' as coined by Granier
and Lapointe, 2022a, i.e., "material with one large and two
small dimensions" following Folk, 1974) cortical layers are thicker
right above the nucleus, and thin laterally and downward. It appears that the
center of mass of the ooid did not change with the addition of a new fibrite
layer. The amber-yellow tint of the fibrite crystals is unquestionably related
to organic content (Granier, 2020), with
calcite fibers incorporating a diffuse organic network, possibly the remnants of
Extracellular Polymeric Substances (EPS).
A bothryoid from AG 269 (Fig.
5.D )
is composed of a cluster of ooids, including one asymmetric ooid with an
off-center siliciclastic nucleus, showing similarities with the previous
example. Initially, the latter likely formed a first aggregate with another ooid,
subsequently forming a biooid (cf. Granier & Lapointe,
2022b). New ooids joined to form a larger aggregate, then a bothryoid.
Ooids and bothyroids with
anisopachous fibrite cortical layers are common among the coated grains of AG
351 (Fig. 5.F ). The cortex of another asymmetric ooid from ARA 351
(Figs. 5.G ,
6.C ) exhibits significant variation in the thickness of its outermost
layers.
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Figure 5:
A-C, E)
thin section AG 268: A) microfacies (the two half ooids are arrowed); B-C;
broken and asymmetrically regenerated ooids; E) asymmetric ooid with a
protruding siliciclastic nucleus (arrowed); D) thin section AG 269:
bothryoid composed of a cluster of ooids, including one asymmetric ooid with its
off-center siliciclastic nucleus (arrowed); F) thin section AG 351: ooid
with an asymmetric cortex at the center of the photomicrograph; G) thin
section ARA 351: ooid with an asymmetric, non-continuous cortex. A-E: Road 47
from Coronel Moldes to Puente Dique Cabra Corral, Province of Salta; F-G: south
of Palma Sola, Province of Jujuy. A) scale bar = 1 mm; B-F) scale bar = 250 µm;
G) scale bar = 100 µm. |
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Figure 6:
A-B) thin
section AG 268, Road 47 from Coronel Moldes to Puente Dique Cabra Corral,
Province of Salta: A) following the ooid breakage, growth of the regenerated
cortex is restricted to a part of the fracture plane, one edge and the convex
part, see Fig. 5.B; B) the center of mass of the ooid is likely the protruding
siliciclastic nucleus controling the upward growth of the cortex, see Fig. 5.E; C)
cauliflower-like developments on the outermost cortical layers, thin section
ARA 351, south of Palma Sola, Province of Jujuy, see Fig. 5.G. Scale bar for all
photomicrographs = 500 µm. |
In this chapter, Argentinian (Jujuy and Salta) asymmetric ooids are discussed in terms of differences and similarities with some other specific ooid types: 'broken' ooids sensu lato, 'distorted' ooids, half-moon ooids, hiatus ooids, and wobbly ooids.
Differences:
1)
'Broken and regenerated' ooids
(Carozzi, 1961): As stated previously, the nuclei of two specimens from
AG 268 (Fig. 5.B-C ), which are found approximately 5 mm away in the same thin
section (Fig. 5.A ), represent the two halves of the same original
ooid. Both
pieces have undergone partial regeneration. However, whereas the first layer of
the 'regenerated' cortex is continuous in typical 'broken and regenerated' ooids,
the Salta specimens (Fig. 5.B-C ) are characterized by the non-continuous nature
of their outer cortical layers. The latter commonly abut against the inner
layers and include noticeable gaps.
2) 'Distorted' ooids (Cayeux, 1935) and 3) half-moon ooids (Wherry, 1915): Recently, Granier and coauthors (Granier et al., 2022; Granier & Kendall, 2022) demonstrated that some 'distorted ooids' are, in fact, collapsed oomolds, i.e., a result of diagenetic processes involving leaching of the ooids followed by mechanical compaction. Similarly, half-moon ooids are formed through the leaching of oolitic cortices, causing the nuclei and some impurities to settle at the bottom of oomoldic cavities. Both types are associated to diagenetic processes. In contrast, the features observed in our Argentinian oolites are 'genetic', i.e., indicating a relationship with synsedimentary growth processes.
4) Hiatus ooids: as defined by Berg
(1944), such ooids exhibit some obliquely truncated cortical layers, suggesting
that their asymmetry likely results from mechanical abrasion, indicative of
erosional processes. Partly abraded layers of the inner cortex terminate beneath
the boundary with the outer cortex. In contrast, in two ooids from AG 268 (Figs.
5.B-C ,
6.A ) some layers of the outer cortex terminate above the boundary with
the inner cortex. More generally, the asymmetry observed in the Argentinian
material is primarily associated with growth processes rather than abrasion.
5) Spiny ooids: According to Davaud and Strasser (1990), "the external cortices are deformed and detached from the underlying cortices near the points of contacts between the grains", which "strongly suggest a postdepositional origin for the spines". This type of ooid is associated with early diagenetic processes.
6) Wobbly ooids: In the case of
the Jujuy wobbly ooids (Granier & Lapointe,
2022a), the asymmetry is associated with the growth of micritic bumps, likely of
microbial origin, and successive shifts of the center of gravity. In the
material presented here, there are no micritic bumps; instead, incomplete
yellowish 'fibrite' coatings are present. These coatings either
thicken or thin and commonly abut against older layers. If these fibrite crusts
were made of micrite, the Argentinian aymmetric ooids would unequivocally be classified as
oncoids. In contrast to the previously described wobbly
ooids (Granier & Lapointe,
2022a),
the centers of mass in our Salta specimens of Figure 6.A-B, .D
(samples AG 268
and AG 269) did not significantly move during the latest growth stages.
Similarities:
Salta asymmetric ooids
(samples AG
268 and AG 269) exhibit some similarities with the modern "quiet water oölites
from laguna Madre, Texas", as described by Freeman
(1962). According to the latter, these asymmetric features
"seem not to be the result of etching or abrasion but rather they appear to
be primary features of these oölites" (op. cit., p. 478). The
specimen in figures 5.E
and 6.B
with its outlying siliciclastic nucleus (sample
AG 268) shows even more striking similarities with certain ooids documented by Freeman
(1962, Fig. 6, photomicrographs A and B). However, in contrast to Freeman's
ooids, the cortices of which are composed of aragonite, the Argentinian coated
grains were likely made of high-Mg calcite (Granier
& Lapointe, 2022b).
It is worth mentioning that,
whereas the nuclei of the ooids illustrated in figures 5.D-E
and 6.B
(samples AG
268 and AG 269) consist of siliciclastic grains, the ooid cortices never
incorporated any silt-sized quartz grains, even when present in the matrix. This
demonstrates that, unlike some stromatolites, ooids lack the capacity to
agglutinate or bind such exogenous grains.
The distinctive ooids from the Maastrichtian-Danian Yacoraite Formation in NW Argentina, as described here, belong to a unique class of 'eccentric' ooids. Unlike the wobbly ooids, the examples studied here do not exhibit any micritic bumps, and their fibrite cortical layers are not isopachous. Instead, a discontinuous, anisopachous fibrite coating and, eventually, an eccentric position for their center of gravity are determining factors to explain their cortical asymmetry. Because they should not be confused with 'broken' ooids sensu stricto, 'broken and regenerated' ooids (Carozzi, 1961), i.e., 'broken' ooids sensu lato, 'distorted' ooids (Cayeux, 1935), half-moon ooids (Wherry, 1915), hiatus ooids (Berg, 1944), spiny ooids (Davaud & Strasser, 1990), or wobbly ooids (Granier & Lapointe, 2022a), it is recommended to simply categorize them as asymmetric ooids.
The rock samples studied here were collected by the second author (P.L.) on the occasion of a joint mission of Total - Compagnie Française des Pétroles, and IFP - Institut Français du Pétrole from October 5 to November 3, 1988. He acknowledges the support of his IFP colleagues, Bernard Colletta, Jean Letouzey, and Roland Vialy, for fieldwork. The authors acknowledge the detailed reviews provided by Christopher G.St.C. Kendall (University of South Carolina) and André Strasser (Université de Fribourg/Univesität Freiburg) and their help in improving this short paper. The first author (B.G.) would like to thank Phil Salvador for his appreciated help with the final (English) text.
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