Cambrian sponge spicules and Chancelloriid sclerites from the Argentine Precordillera: A Review

M.S. Beresi

Description

Abstract
Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the
La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which
were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordillera)
and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks, which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and sclerites of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexactines, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Sombreros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ? and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Anthaspidellid sponges had been reported from the La Laja Formation and now from the San Martín olistolith (Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian platform and slope facies of the Precordillera contribute additional data for a better understanding of the relationships between the eastern and the western facies assemblages, which developed in the Precordillera during the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the Cambrian depositional framework.

Sujets

• Sponge spicule
• Cambrian
• Precordillera
• San Juan
• Mendoza
• Argentina

Informations

• Publié par: erevistas
• Publié le: 01 janvier 2003
• Nombre de lectures: 46
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Geologica Acta, Vol.1, Nº1, 2003, 73-84
Available online at www.geologica-acta.com
Cambrian sponge spicules and Chancelloriid sclerites
from the Argentine Precordillera: A review
M.S. BERESI
IANIGLA, CRICYT
Avda. Ruíz Leal s/n, Parque Gral. San Martín (5500) Mendoza, Argentina.
E-mail: [e-mail]
ABSTRACT
Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the
La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which
were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordi-
llera) and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were
deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks,
which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope
environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid
assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable
us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle
Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and scleri-
tes of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and
hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexacti-
nes, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Som-
breros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ?
and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Ant-
haspidellid sponges had been reported from the La Laja Formation and now from the San Martín olistolith
(Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian
platform and slope facies of the Precordillera contribute additional data for a better understanding of the rela-
tionships between the eastern and the western facies assemblages, which developed in the Precordillera during
the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the
Cambrian depositional framework.
KEYWORDS Sponge spicules. Chancelloriids. Cambrian. Precordillera. San Juan. Mendoza. Argentina.
archaeocyatha and stromatoporids, were primary reefINTRODUCTION
builders even in the Early Cambrian (Wood, 1991).
Sponges are the most primitively organized among
The knowledge of the fossil record of siliceousmulticellular animals. In most sponges, specialized cells
sponges is based on complete, relatively rigid skeletons orsecrete a mineral skeleton, generally in the form of
on isolated spicules, which are studied in thin sections orspicules. Sponges have been a highly successful group
recovered as insoluble residues from sedimentary rocks.throughout the Phanerozoic, colonizing most marine and
However, most of the evidence of fossil sponges consistssome fresh water environments. Siliceous sponges,
© UB-IJA 73M.S. BERESI Cambrian Sponges and Chancelloriids from the Argentine Precordillera
FIGURE 1 Outcrop zones and fossil localities with Cambrian sponge spicules and chancelloriid sclerites in the Argentine Pre-
cordillera. a. Location of the provinces of San Juan and Mendoza within Argentina. b. Fossil sponge localities within the Pre-
cordillera region: Precordillera Occidental of San Juan: Outcrop zones 1 (Los Ratones Gulch) and 2 (Tres Saltos Gulch), both
in the Tontal Range. Precordillera Oriental of San Juan: Outcrop zone 3, Las Lajas Gulch in the Chica de Zonda. Precordille-
ra of Mendoza, outcrop zone 4 including Empozada Gulch, Agua de La Cruz Gulch and San Isidro Gulch, San Isidro region.
Geologica Acta, Vol.1, Nº1, 2003, 73-84 74M.S. BERESI Cambrian Sponges and Chancelloriids from the Argentine Precordillera
TABLE 1 Distribution of the sponge spicules and Chancelloria in the two fossil spicule assemblages of the Precordillera.
Spicule assemblages
Spicule assemblages in allochthonous units
in autochthonous sequences
San Juan Precordillera Mendoza Precordillera
La Laja Los Sombreros Empozada
Formation Formation Formation
Diagoniella ? La
LateKiwetinokia sp. hexactines Cruz
Cam-Olisto-Protospongia sp. stauractines
brianlithroot tuft
San
hexactines Martín
Stauractines of stauractines Olisto-
protospongiid-like structure Protospongia sp. prodiaenes lith hexactines pentactines Middle
diagoniellid-like structure stauractines Cam-
brianprodianes
San
Kiwetinokia sp. pentactines Kiwetinokia uthaensis ? Isidro
Chancelloria eros Chancelloria eros Olisto-
lith
Anthaspidellidae
hexactines
monactines ?
Earlyprodiaenes
Cam-pentactines
brian
of isolated spicules. Most Cambrian siliceous sponges have dealt with spicule assemblages collected from the
were composed of relatively simple spicules such as mon- Cambrian rocks of Argentina and in particular from Cam-
axons, stauractines, hexactines or pentactines. brian successions of the Precordillera.
The fossil record of Porifera in the Cambrian The presence of Protospongia was cited by Pernas (1964)
sequences of the Precordillera (western Argentina) con- and then by Devizia (1973), from the San Isidro area in the
sists mainly of disassociated spicules in carbonate rocks, Precordillera of Mendoza. Bordonaro and Martos (1985)
whereas complete skeletons are very scarce. The aim of described sclerites of Chancelloria WALCOTT, from
this paper is a taxonomic review of the sponge-spicule autochthonous succesions of the La Laja Formation, Pre-
assemblages and sclerites of chancelloriids from the Mid- cordillera of San Juan. Also, Heredia et al. (1987) described
dle and Upper Cambrian sequences in the Precordillera of hexactinellid spicules from the Upper Cambrian of the La
San Juan and Mendoza Provinces. These data should be Cruz olistolith (Empozada Formation) in the Precordillera of
useful for the palaeoenvironmental and palaeogeographic Mendoza. Farthermore, Beresi and Rigby (1994) described
interpretation of the Cambrian record in the study area. assemblages tentatively identified as Kiwetinokia utahensis
WALCOTT, 1920, from latest Early Cambrian, and also
spicules and chancelloriid sclerites from upper Lower and
PREVIOUS WORKS Middle Cambrian localities of the Precordillera of San Juan
and Mendoza. Beresi and Heredia (1995) also described stau-
Since the first report of Chancelloria and Protospon- ractines, hexactines and pentactines from the San Martín olis-
gia from a Middle Cambrian olistolith of the Empozada tolith (Empozada Formation) in the Precordillera of Men-
Formation by Rusconi (1955), only a few publications doza. Finally, Mehl and Lehnert (1997) described silicified
75Geologica Acta, Vol.1, Nº1, 2003, 73-84M.S. BERESI Cambrian Sponges and Chancelloriids from the Argentine Precordillera
sponge spicule assemblages, which were recognised in the stones and conglomerates (Banchig et al., 1990). These
residues resulting from the search for conodonts in the Cam- slope deposits crop out mainly in the Tontal Range (Fig. 1,
brian olistoliths of the Los Sombreros Formation. localities 1 and 2) in the Precordillera Occidental, to the
west of San Juan city. The siliciclastic and carbonate
sequence of the Los Sombreros Formation records several
GEOLOGICAL SETTING olistostromic events. The ancient Cambrian shelf margin
collapsed during the Ordovician and the resulting calcare-
The Cambrian rocks containing spicules are located in ous blocks were gravitationally emplaced in association
the Precordillera of San Juan and Mendoza provinces, with muddy gravity flows. As a consequence, this Ordovi-
western Argentina (Fig. 1 and Table 1). The depositional cian succession includes carbonate olistoliths derived
record of the Cambrian system in the eastern Precordillera from the Cambrian shallow, outer carbonate platforms and
consists of carbonate platform successions. These eastern talus-slope sequences. The trilobite faunas indicate a Mid-
successions graded laterally westward into facies assem- dle Cambrian (Bathyuriscus-Elrathina Zone) to Late
blages which record the development of a continental Cambrian age (Glyptagnostus reticulatus; Bordonaro and
slope (Bordonaro, 1985 and 1993, in this issue; Baldis and Banchig, 1996) for these olistoliths.
Bordonaro, 1982). Thus, major carbonate deposition on a
carbonate platform-slope system took place in the Pre- The carbonate olistoliths have yielded a variety of
cordillera, during the Cambrian. Thick siliciclastic-domi- Cambrian fossils, including sponge spicules. The spicules
nated sequences (Los Sombreros y Empozada Forma- described in this paper were collected from the limy mud-
tions), characterized the sedimentation in the slope stones of one of the Cambrian olistoliths included in Los
environments during the Ordovician. Cambrian carbonate Sombreros Formation (Los Ratones Gulch locality; Fig. 1,
olistoliths are widespread in these Ordovician slope locality l).
sequences (Figs. 1-3).
Sponge body fossils, with a preserved simple spicul