ABSTRACT The relationship between the Vizcaíno ’composite‘ Terrane and the ‘Antimonio Terrane’ du... more ABSTRACT The relationship between the Vizcaíno ’composite‘ Terrane and the ‘Antimonio Terrane’ during the Upper Triassic Eric Heerwagen* & Rossana Martini* * Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva (eric.heerwagen@unige.ch) The North American Cordillera, from Alaska in the north to Mexico in the south, consists of several terranes that have a doubtful paleogeography (e.g. Coney et al. 1980). The major reason for this circumstance is, that the outcrop-situation for the time interval of the Upper Triassic is difficult. On the base of todays reconstructions for paleogeography, and tectonic history of the Cordillera, two potential terranes with shallow-water carbonates of Norian age were selected. These terranes are the “Antimonio Terrane” (Sonora, Mexico), and the Vizcaíno ’composite‘ Terrane (Baja California Sur , Mexico) (fig. 1). During field trips in 2012, and 2014, samples for the comparison of litho-, and microfacies of the two localities were collected. With this study we try to prove a proximal relationship between the Antimonio, and Vizcaíno areas, allowing us to reconstruct these two potential terranes as a single “joint terrane” environment. Furthermore we want to compare these two localities with the previously-investigated Wallowa terrane in the Blue Mountain Province (Oregon, USA), also containing Upper Triassic shallow water carbonates. The Upper Triassic succession of the Antimonio Terrane consists of shallow-marine sediments (González-León, 1997), whereas the deposits of the Vizcaíno ’composite‘ Terrane near the village of San Hipólito represent slope to deeper marine environments (Orchard et al. 2007). In Sonora, we found limestones, calcareous siltstones, and fine grained sandstones. The first two lithologies contain shallow-water fossil assemblages that include chambered sponges, and scleractinain corals. Near San Hipólito deepwater limestone, chert, a limestone breccia, and sandstone crop out. The Norian-dated clasts of the breccia contain shallow-water fossils. In particular the sponges, and corals show strong affinities to the fossils observed in the Antimonio area. Acknowledgements: This project has been funded by the Swiss National Science Foundation No. RM 200020-13766. Figure 1. Map of Northwest Mexico with the terranes under investigation. REFERENCES Coney, P. J., Jones, D. L. & Monger, J. W. H. 1980: Cordilleran suspect terranes, Nature, 288, 329–333. González-León, C. M. 1997: Sequence stratigraphy and paleogeographic setting of the Antimonio Formation (Late Permian-Early Jurassic), Sonora, Mexico, In Stanley, J., George D. and Gonzalez-Leon, C. M. (Editors), Special issue dedicated to the International workshop on the geology of northwestern Sonora, volume 14 of Revista Mexicana de Ciencias Geologicas, 136–148. Orchard, M. J., Whalen, P. A., Carter, E. S. & Taylor, H. J. 2007: Latest Triassic conodonts and radiolarian-bearing successions in Baja California Sur, New Mexico Museum of Natural History and Science Bulletin, 41, 355–365.
ABSTRACT Like the margins of other continents around the Pacific Ocean, western North America con... more ABSTRACT Like the margins of other continents around the Pacific Ocean, western North America consists from Alaska to Mexico of terranes. Several decades of extensive research on Upper Triassic sediments, mainly focused on the Tethyan provinces in the Alps, have been conducted. For this reason the paleogeographic, as well as the paleoenvironmental reconstructions for the Panthalassa Ocean remain undetailed. For many of these terranes the origin and their paths through Panthalassa persist mysterious. The REEFCADE-project addresses these issues, by investigating individual terranes, reconstructing their respective geologic history in a multi-disciplinary approach, and in a final comparison to unravel the respective paleotectonic evolution. For this study two potential terranes in Mexico, with Upper Triassic carbonate occurrences have been chosen: the Antimonio Terrane (Sonora), and the Vizcaíno ‘composite’ Terrane (Baja California Sur). Due to the scarcity, and discontinuity of the outcrops, a simple paleoenvironmental reconstruction is impossible. The sedimentary successions of the investigated localities are of very different nature. On the one hand those found in Sonora show shallow marine deposits, comprising carbonates with variable amounts of siliciclastics, and calcareous-bound, commonly fossiliferous silt- to fine sandstones. On the other hand, the series found in Baja California Sur are interpreted as deeper marine, and slope derived. Inside the limestone clasts of the Breccia member of the San Hipólito Formation, shallow water faunal assemblages have been identified. Through comparison of the two areas, we want to proof/disproof a proximal relationship between the investigated terranes. During two field campaigns, samples for thin section preparation, palynological analysis, and zircon separation were taken. Due to the advanced recrystallization levels, fossil-derived information is limited. On the contrary, petrographic data can provide useful data supporting paleoenvironmental, as well as paleogeographic reconstructions. The siliciclastic components represent remains of an arkosic arenite. Potential protoliths are plutonic intrusions inside the North American craton. We separated, and dated zircons from Sonora by LA-ICP-MS. By comparison with known ages from intrusions, we expect to grab new insights into the paleolatitude, and ultimately also the sense of movement of the investigated terranes. Acknowledgements: This project has been funded by the Swiss National Science Foundation RM #200020-137661 and #200020-156422.
Tyrrhenian (Upper Pleistocene) coastal deposits in Sardinia have been studied since the last cent... more Tyrrhenian (Upper Pleistocene) coastal deposits in Sardinia have been studied since the last century, but have never been interpreted in terms of detailed sedimentology and sequential pattern. The present paper deals with an outcrop close to San Giovanni di Sinis on the western coast of Sardinia, where three depositional sequences can be identified. The lowermost sequence overlies an erosion surface which cuts into Messinian marls. A basal conglomerate including coralline algae, and sandstones displaying current ripples and beach lamination point to a coastal-marine depositional environment. The bulk of the sequence, however, is made up of eolian dunes with interstratified paleosols, and of colluvial deposits. An erosional surface terminates this sequence. The basal conglomerate of the second sequence contains pebbles with pedogenetic features, and is overlain by beach-laminated sands. Superimposed bioturbation and an important bed of in-situ Mytilus shells suggest that the coastal-marine environment passed into a lagoonal one. Ostracods, charophytes and pedogenesis indicate fresh-water influence and local emersion at the top of this sequence. Again, an erosional surface truncates the deposits. The third sequence starts with shoreface and foreshore deposits rich in coralline algae and ends with eolian facies. Locally, the eolian dunes prograde directly over shoreface and tidal-channel deposits. The major erosion surfaces probably formed during important drops of sea•level and correspond to sequence boundaries. The conglomerates are interpreted as transgressive deposits, whereas the shallowing-upward facies successions represent regressive highstand deposits. The three sequences of San Giovanni di Sinis may thus have formed during three successive sea-level fluctuations, which can tentatively be correlated with the three climatic cycles during the last interglacial, i.e. between 130,000 and 70,000 years B.P.
The western margin of the North American continent consists from Alaska towards Mexico of several... more The western margin of the North American continent consists from Alaska towards Mexico of several terranes. After some decades of extensive research on the Upper Triassic, conducted mainly on the Tethyan realm, the paleogeography and paleoenvironments of the Panthalassa Ocean remain widely unknown. Many of these terranes are still of unidentified origin and the paths they took persist mysterious. The REEFCADE-project addresses these issues, by investigating individual terranes, reconstructing their respective geologic history in a multi-disciplinary approach, and in a final comparison to unravel the respective paleotectonic evolution. For this part of the project two potential terranes in Mexico have been chosen: the Animonio Terrane (Sonora), and the Vizcaíno 'composite' Terrane (Baja California Sur). The outcrop situation for the time interval of Upper Triassic is difficult. Scarcity, and discontinuity of the outcrop localities, prevents a simple paleoenvironmental reconst...
The goal of the on-going research project “REEFCADE” of the group of Prof. Rossana Martini is the... more The goal of the on-going research project “REEFCADE” of the group of Prof. Rossana Martini is the establishment of a stratigraphic correlation between the different parts of the former Panthalassa realm. Therefore Upper Triassic limestones from various localities e.g. Japan, USA and Mexico have been sampled and analyzed. Through the determination and comparison of the composition and the paleoecology of the fossil assemblages we try to improve the tectonic and geodynamic models for the respective terranes. As a part of the North American Cordillera, Mexico consists of numerous potentially allochthonous terranes. But only the in northwest Sonora located Antimonio terrane contains Upper Triassic shallow water limestones. For the reconstruction of the depositional environment and the paleogeography of this particular terrane we investigated and sampled three outcrop localities. Along detailed lithological sections samples for thin section preparation have been taken. The thin sections ...
ABSTRACT The relationship between the Vizcaíno ’composite‘ Terrane and the ‘Antimonio Terrane’ du... more ABSTRACT The relationship between the Vizcaíno ’composite‘ Terrane and the ‘Antimonio Terrane’ during the Upper Triassic Eric Heerwagen* & Rossana Martini* * Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva (eric.heerwagen@unige.ch) The North American Cordillera, from Alaska in the north to Mexico in the south, consists of several terranes that have a doubtful paleogeography (e.g. Coney et al. 1980). The major reason for this circumstance is, that the outcrop-situation for the time interval of the Upper Triassic is difficult. On the base of todays reconstructions for paleogeography, and tectonic history of the Cordillera, two potential terranes with shallow-water carbonates of Norian age were selected. These terranes are the “Antimonio Terrane” (Sonora, Mexico), and the Vizcaíno ’composite‘ Terrane (Baja California Sur , Mexico) (fig. 1). During field trips in 2012, and 2014, samples for the comparison of litho-, and microfacies of the two localities were collected. With this study we try to prove a proximal relationship between the Antimonio, and Vizcaíno areas, allowing us to reconstruct these two potential terranes as a single “joint terrane” environment. Furthermore we want to compare these two localities with the previously-investigated Wallowa terrane in the Blue Mountain Province (Oregon, USA), also containing Upper Triassic shallow water carbonates. The Upper Triassic succession of the Antimonio Terrane consists of shallow-marine sediments (González-León, 1997), whereas the deposits of the Vizcaíno ’composite‘ Terrane near the village of San Hipólito represent slope to deeper marine environments (Orchard et al. 2007). In Sonora, we found limestones, calcareous siltstones, and fine grained sandstones. The first two lithologies contain shallow-water fossil assemblages that include chambered sponges, and scleractinain corals. Near San Hipólito deepwater limestone, chert, a limestone breccia, and sandstone crop out. The Norian-dated clasts of the breccia contain shallow-water fossils. In particular the sponges, and corals show strong affinities to the fossils observed in the Antimonio area. Acknowledgements: This project has been funded by the Swiss National Science Foundation No. RM 200020-13766. Figure 1. Map of Northwest Mexico with the terranes under investigation. REFERENCES Coney, P. J., Jones, D. L. & Monger, J. W. H. 1980: Cordilleran suspect terranes, Nature, 288, 329–333. González-León, C. M. 1997: Sequence stratigraphy and paleogeographic setting of the Antimonio Formation (Late Permian-Early Jurassic), Sonora, Mexico, In Stanley, J., George D. and Gonzalez-Leon, C. M. (Editors), Special issue dedicated to the International workshop on the geology of northwestern Sonora, volume 14 of Revista Mexicana de Ciencias Geologicas, 136–148. Orchard, M. J., Whalen, P. A., Carter, E. S. & Taylor, H. J. 2007: Latest Triassic conodonts and radiolarian-bearing successions in Baja California Sur, New Mexico Museum of Natural History and Science Bulletin, 41, 355–365.
ABSTRACT Like the margins of other continents around the Pacific Ocean, western North America con... more ABSTRACT Like the margins of other continents around the Pacific Ocean, western North America consists from Alaska to Mexico of terranes. Several decades of extensive research on Upper Triassic sediments, mainly focused on the Tethyan provinces in the Alps, have been conducted. For this reason the paleogeographic, as well as the paleoenvironmental reconstructions for the Panthalassa Ocean remain undetailed. For many of these terranes the origin and their paths through Panthalassa persist mysterious. The REEFCADE-project addresses these issues, by investigating individual terranes, reconstructing their respective geologic history in a multi-disciplinary approach, and in a final comparison to unravel the respective paleotectonic evolution. For this study two potential terranes in Mexico, with Upper Triassic carbonate occurrences have been chosen: the Antimonio Terrane (Sonora), and the Vizcaíno ‘composite’ Terrane (Baja California Sur). Due to the scarcity, and discontinuity of the outcrops, a simple paleoenvironmental reconstruction is impossible. The sedimentary successions of the investigated localities are of very different nature. On the one hand those found in Sonora show shallow marine deposits, comprising carbonates with variable amounts of siliciclastics, and calcareous-bound, commonly fossiliferous silt- to fine sandstones. On the other hand, the series found in Baja California Sur are interpreted as deeper marine, and slope derived. Inside the limestone clasts of the Breccia member of the San Hipólito Formation, shallow water faunal assemblages have been identified. Through comparison of the two areas, we want to proof/disproof a proximal relationship between the investigated terranes. During two field campaigns, samples for thin section preparation, palynological analysis, and zircon separation were taken. Due to the advanced recrystallization levels, fossil-derived information is limited. On the contrary, petrographic data can provide useful data supporting paleoenvironmental, as well as paleogeographic reconstructions. The siliciclastic components represent remains of an arkosic arenite. Potential protoliths are plutonic intrusions inside the North American craton. We separated, and dated zircons from Sonora by LA-ICP-MS. By comparison with known ages from intrusions, we expect to grab new insights into the paleolatitude, and ultimately also the sense of movement of the investigated terranes. Acknowledgements: This project has been funded by the Swiss National Science Foundation RM #200020-137661 and #200020-156422.
Tyrrhenian (Upper Pleistocene) coastal deposits in Sardinia have been studied since the last cent... more Tyrrhenian (Upper Pleistocene) coastal deposits in Sardinia have been studied since the last century, but have never been interpreted in terms of detailed sedimentology and sequential pattern. The present paper deals with an outcrop close to San Giovanni di Sinis on the western coast of Sardinia, where three depositional sequences can be identified. The lowermost sequence overlies an erosion surface which cuts into Messinian marls. A basal conglomerate including coralline algae, and sandstones displaying current ripples and beach lamination point to a coastal-marine depositional environment. The bulk of the sequence, however, is made up of eolian dunes with interstratified paleosols, and of colluvial deposits. An erosional surface terminates this sequence. The basal conglomerate of the second sequence contains pebbles with pedogenetic features, and is overlain by beach-laminated sands. Superimposed bioturbation and an important bed of in-situ Mytilus shells suggest that the coastal-marine environment passed into a lagoonal one. Ostracods, charophytes and pedogenesis indicate fresh-water influence and local emersion at the top of this sequence. Again, an erosional surface truncates the deposits. The third sequence starts with shoreface and foreshore deposits rich in coralline algae and ends with eolian facies. Locally, the eolian dunes prograde directly over shoreface and tidal-channel deposits. The major erosion surfaces probably formed during important drops of sea•level and correspond to sequence boundaries. The conglomerates are interpreted as transgressive deposits, whereas the shallowing-upward facies successions represent regressive highstand deposits. The three sequences of San Giovanni di Sinis may thus have formed during three successive sea-level fluctuations, which can tentatively be correlated with the three climatic cycles during the last interglacial, i.e. between 130,000 and 70,000 years B.P.
The western margin of the North American continent consists from Alaska towards Mexico of several... more The western margin of the North American continent consists from Alaska towards Mexico of several terranes. After some decades of extensive research on the Upper Triassic, conducted mainly on the Tethyan realm, the paleogeography and paleoenvironments of the Panthalassa Ocean remain widely unknown. Many of these terranes are still of unidentified origin and the paths they took persist mysterious. The REEFCADE-project addresses these issues, by investigating individual terranes, reconstructing their respective geologic history in a multi-disciplinary approach, and in a final comparison to unravel the respective paleotectonic evolution. For this part of the project two potential terranes in Mexico have been chosen: the Animonio Terrane (Sonora), and the Vizcaíno 'composite' Terrane (Baja California Sur). The outcrop situation for the time interval of Upper Triassic is difficult. Scarcity, and discontinuity of the outcrop localities, prevents a simple paleoenvironmental reconst...
The goal of the on-going research project “REEFCADE” of the group of Prof. Rossana Martini is the... more The goal of the on-going research project “REEFCADE” of the group of Prof. Rossana Martini is the establishment of a stratigraphic correlation between the different parts of the former Panthalassa realm. Therefore Upper Triassic limestones from various localities e.g. Japan, USA and Mexico have been sampled and analyzed. Through the determination and comparison of the composition and the paleoecology of the fossil assemblages we try to improve the tectonic and geodynamic models for the respective terranes. As a part of the North American Cordillera, Mexico consists of numerous potentially allochthonous terranes. But only the in northwest Sonora located Antimonio terrane contains Upper Triassic shallow water limestones. For the reconstruction of the depositional environment and the paleogeography of this particular terrane we investigated and sampled three outcrop localities. Along detailed lithological sections samples for thin section preparation have been taken. The thin sections ...
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