Paper No. 8
Presentation Time: 10:00 AM


LONGORIA, Jose F., 20111 SW 79 Av, Miami, FL 33189, CAMACHO-ORTEGON, Luis F., Escuela Superior de Ingenieria, Universiad Autonoma de Coahuila, Adolfo Lopez Mateos s/n, Nueva Rosita, 26800, Mexico and MONREAL, Rogelio, Departamento de Geologia, Hermosillo, 83170, Mexico,

Sierra El Muerto is a typical mega-structure of the Nuevoleonese Cordillera extending from the El Tejocote pass to the S-SE to the town of El Hondable. 25 km long and 5 km wide. The highest point known as Longoria Peak with a maximum elevation of 2400 m. The bulk of the range is made of Cretaceous marine sedimentary rocks, Jurassic marine rocks crop out around the northwestern rim of the sierra. The range is a large doubly plunging anticlinal box-fold with torsion along its axial, with an overturned stratigraphic succession as expected in this kind of mega structures as a result of tectonic transpression.

Seven lithic units were recognized on the northwest flank, from top to bottom:

Unit 7: 28 m thick- to massive-bedded calcareous sandstone barren of fossils. Shallow basin.

Unit 6: 125 m irregular alternation of thin-bedded limestone, and medium-bedded shale, fine calcareous sandstone, limestone nodules, abundant ammonites Micracanthoceras sp., Spiticeras (Kilianiceras) sp., Proniceras spp., Paradontoceras sp., Hildoglochiceras sp., Simoceras sp., Durangites sp., Berriasella sp., Lamellaptychus, Idoceras sp., Haploceras cf. H. costatum (Burchhardt). Upper part with Calpionella alplina and C. elliptica. Kimmeridigian –Tithonian. Shallow basin.

Unit 5b: 185 m medium- to thick-bedded sandy mudstone and calcareous shale. abundant ammonites Leopoldina, Olcostephanus and Neocomites. Hauterivian-Barremian. Shallow basin.

Unit 5a: 560 m heterogeneous package of fine to medium sandstone and coarse conglomerate. Fluvio-deltaic sequence. Valanginain-Berriasian.

Unit 4: 405 m homogenous package of medium- to thick-bedded limestone. Abundant shallow water fauna, corals, sponges, and microfossils, benthics. Barremian-Lower Aptian. Carbonate platform

Unit 3: 23 m rhythmic alternation of thin-bedded, medium-bedded limestone and thin-bedded shale. Abundant planktics Globigerinelloides ferreolensis and Globigerinelloides algerianus. Upper Aptian. Pelagic.

Unit 2: 25 meters of massive-bedded limestone abundant planktic. Cenomanian-Albian. pelagic

Unit 1: 395 m alternation of thin- to medium-bedded, clayey limestone and thin-bedded shale. Planktics including Globotruncana and Dicarinella. Santonian. Pelitic flysch