Upper Jurassic ammonites and bivalves from the Cucurpe Formation, Sonora (Mexico)
Four new molluscan assemblages from north-central Sonora indicate that the Cucurpe Formationranges in age from late Oxfordian to early Tithonian. These assemblages extend the known paleogeographicrange of Late Jurassic Tethyan fossil groups several hundred km to the northwest and improve correlation...
| Authors: | , , , |
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| Format: | article |
| Status: | Published version |
| Publication Date: | 2005 |
| Country: | México |
| Institution: | Universidad Nacional Autónoma de México |
| Repository: | Redalyc-UNAM |
| OAI Identifier: | oai:redalyc.org:57222107 |
| Online Access: | https://www.redalyc.org/articulo.oa?id=57222107 |
| Access Level: | Open access |
| Keyword: | Ciencias de la Tierra Sonora Mexico bivalves ammonites Upper Jurassic |
| Summary: | Four new molluscan assemblages from north-central Sonora indicate that the Cucurpe Formationranges in age from late Oxfordian to early Tithonian. These assemblages extend the known paleogeographicrange of Late Jurassic Tethyan fossil groups several hundred km to the northwest and improve correlationof Upper Jurassic strata in northern Mexico. At Rancho La Colgada, near the town of Tuape, the upperpart of the Cucurpe Formation consists of 515 m of shale, siltstone, basaltic flows and minor sandstone.The oldest fossil assemblage is assigned to the Bifurcatus Zone of the lower upper Oxfordian and containsthe ammonites Perisphinctes (Dichotomoceras?) sp., Sequeirosia? sp., and the bivalves Grammatodon(Grammatodon) hersilius (d´Orbigny), Parainoceramus sp., Lucina potosina Aguilera, Lucinasp., and Isocyprina? sp. The second assemblage is assigned to the lower Tithonian (lower part of theAlbertinum/Darwini Zone) and consists of the ammonites Mazapilites mexicanus (Aguilera), Schairerianeoburgensis (Oppel), Subplanitoides sp., and Glochiceras (Lingulaticeras?) sp. The third fossilassemblage from the uppermost part of the section includes the ammonites Sublithacoceras cf. sphinctum(Schneid), Sublithacoceras sp., and Pachysphinctes sp., and the bivalves Lucina potosina Aguileraand Integricardium (Integricardium) sp. This assemblage belongs to the Semiforme-Verruciferum Zoneto Richteri Zone of the middle lower Tithonian. A fourth assemblage is assigned to the lower Tithonian,representing the middle to upper part of the Albertinum-Darwini or the lowermost part of the Semiforme-Verruciferum Zone. This assemblage was collected from the upper part of the Cucurpe Formation ata nearby locality and contains the ammonites Torquatisphinctes subbleicheri (Burckhardt), T. cf. lauri(Aguilera) and Torquatisphinctes sp. cf. T. diversecostatus (Burckhardt). The absence of Kimmeridgianfossils in the measured section at Rancho La Colgada and a conglomerate between the Oxfordian andTithonian assemblages combine to indicate an unconformity in the Upper Jurassic interval that omitsthe Kimmeridgian. A single Kimmeridgian ammonite was recently collected in the Cucurpe Formationabout 40 km northwest of the study area.The reported molluscan fossils have close affinities with Tethyan faunas known from other parts ofMexico, Cuba and western Europe. These affinities indicate a possible connection of these regions withSonora through the young Central Atlantic Ocean and possible faunal dispersal from east to west; however,eastward dispersal across the paleo-Pacific realm is also a possibility. Some endemic species, such asMazapilites mexicanum and Lucina potosina in Sonora permit correlation with other areas of northcentralMexico and indicate a marine connection throughout the region during the Late Jurassic. |
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