105 research outputs found
Early Mesozoic Paleotectonic-Paleogeographic Reconstruction of Southern Sierra Nevada Region
A paleotectonic-paleogeographic reconstruction was
based on structural, petrologic, and geochronologic
studies of pre-Sierra Nevada batholith framework rocks
exposed between the San Joaquin River and the Garlock
fault. Most available fossil data from roof pendants
of this region indicate Late Triassic to Early Jurassic
ages. An additional fossil locality from the
western wall rocks yields a Late Permian Tethyan fauna.
This is a maximum age for the enclosing rocks, for
the fossils are in a limestone olistolith. As yet there is no
sign of Paleozoic strata in the region except perhaps
along the eastern Sierran crest in small metamorphic
septa, and in the western foothills where ophiolitic rocks
are present
First record of Rhabdoceras suessi (Ammonoidea, Late Triassic) from the Transylvanian Triassic Series of the Eastern Carpathians (Romania) and a review of its biochronology, paleobiogeography and paleoecology
Abstract
The occurrence of the heteromorphic ammonoid Rhabdoceras suessi Hauer, 1860, is recorded for the first time in the Upper Triassic limestone of the Timon-Ciungi olistolith in the Rarău Syncline, Eastern Carpathians. A single specimen of Rhabdoceras suessi co-occurs with Monotis (Monotis) salinaria that constrains its occurrence here to the Upper Norian (Sevatian 1). It is the only known heteromorphic ammonoid in the Upper Triassic of the Romanian Carpathians. Rhabdoceras suessi is a cosmopolitan species widely recorded in low and mid-paleolatitude faunas. It ranges from the Late Norian to the Rhaetian and is suitable for high-resolution worldwide correlations only when it co-occurs with shorter-ranging choristoceratids, monotid bivalves, or the hydrozoan Heterastridium. Formerly considered as the index fossil for the Upper Norian (Sevatian) Suessi Zone, by the latest 1970s this species lost its key biochronologic status among Late Triassic ammonoids, and it generated a controversy in the 1980s concerning the status of the Rhaetian stage. New stratigraphic data from North America and Europe in the subsequent decades resulted in a revised ammonoid biostratigraphy for the uppermost Triassic, the Rhaetian being reinstalled as the topmost stage in the current standard timescale of the Triassic. The geographic distribution of Rhabdoceras is compiled from published worldwide records, and its paleobiogeography and paleoecology are discussed
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