Science and Technology Production
Article
Authorship
Rustán, Juan Jose
;
Benedetto, Juan Luis
;
Randolfe, Enrique Alberto
;
LÓPEZ, FERNANDO ENRIQUE
;
Braeckman, Alejandro
;
Contreras, Víctor
Date
2025
Publishing House and Editing Place
PALEONTOLOGICAL SOC INC
Magazine
JOURNAL OF PALEONTOLOGY
(pp. 1-17)
PALEONTOLOGICAL SOC INC
Summary
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We report a new stratigraphic section in the Argentine Precordillera (Zanja Honda, west ofPachimoco, San Juan Province), recording the Silurian-Devonian transition. It corresponds toparticular siliciclastics of the uppermost 75 m of the Los Espejos Formation (LEF) exhibitingcoquines at the base, noduliferous dark siltstones above, then greenish-brown sandstones, andsubsequently, a reddish, massive, fine-grained sandstone interval. The overlying shaly lowerinterval of the Talacasto Formation rec...
We report a new stratigraphic section in the Argentine Precordillera (Zanja Honda, west ofPachimoco, San Juan Province), recording the Silurian-Devonian transition. It corresponds toparticular siliciclastics of the uppermost 75 m of the Los Espejos Formation (LEF) exhibitingcoquines at the base, noduliferous dark siltstones above, then greenish-brown sandstones, andsubsequently, a reddish, massive, fine-grained sandstone interval. The overlying shaly lowerinterval of the Talacasto Formation records the homalonotid trilobite Burmeisteria notica(Clarke, 1913a), indicating the Lochkovian-Pragian interval. Brachiopods and trilobites of thebasal coquinites are typical of the upper Silurian of the LEF elsewhere. However, SlovinograptusUrbanek, 1997, the youngest graptolite from southwestern Gondwana, indicates the Silurian-Devonian transition in the basal coquine. The dalmanitid Pachimocaspis pachimocensis newgenus new species comes from this and other undoubted Silurian underlying coquinites. Thebrachiopod and trilobite associations disappear in the overlying dark nodular siltstone interval,replaced by an earliest Lochkovian Orthostrophia meridionalis Benedetto in Benedetto et al.,1992 brachiopod association and a monospecific Pachimocaspis pachimocensis n. gen. n. sp.Thus, we recognize a neat faunal turnover around the Silurian-Devonian boundary as in othersouthern South American localities. We refer to Pachimocaspis pachimocensis n. gen. n. sp.pygidia from the Silurian-Devonian of Bolivia and the lowest Pragian of the Talacasto Formationfrom Las Aguaditas locality in the Precordillera Basin. Pachimocaspis pachimocensis n. gen. n. sp.lacks the typical pygidial dalmanitid morphology, exhibiting instead a subelliptical shape with nocaudal spine. Also, thoracic pleural tips are variably blunt along the thorax in contrast with theevenly spinose dalmanitid morphology. The morphology of this taxon challenges its systematicposition in regarding Silurian-Devonian subfamilies from high paleolatitudes, resemblinginstead extra-Gondwanic, early Silurian synphoriines.
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Key Words
DevonianPrecordilleraTrilobitesSilurian