Cerro de los Fragmentos (CF2): Maastrichtian, Argentina
collected by G. Casal 2015
List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
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Polypodiopsida
- Marsileaceae
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Crybelosporites sp. megaspore
Dettmann 1963
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3 specimens | |||||||||
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Marsileaceaephyllum sp. leaf
Nagalingum 2007
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2 specimens | |||||||||
| UNPSJB PB 198-199, leaves and leaflets | ||||||||||
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Polypodiopsida
- Salviniales
- Salviniaceae
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Azolla informal sp. 2 megaspore
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5 specimens | |||||||||
| see common names | ||||||||||
Geography
| Country: | Argentina | State/province: | Chubut |
| Coordinates: | 45.6° South, 68.5° West (view map) | ||
| Paleocoordinates: | 45.4° South, 57.2° West (Wright 2013) | ||
| Basis of coordinate: | stated in text | ||
| Geographic resolution: | outcrop |
Time
| Period: | Cretaceous | Epoch: | Late Cretaceous |
| Stage: | Maastrichtian | 10 m.y. bin: | Cretaceous 8 |
| Key time interval: | Maastrichtian | ||
| Age range of interval: | 72.2 - 66 m.y. ago |
Stratigraphy
| Geological group: | Chubut | Formation: | Lago Colhué Huapi | ||
| Local section: | Cerro de los Fragmentos | Local bed: | 7,5 m | ||
| Local order: | bottom to top | ||||
| Stratigraphy comments: The Lago Colhue Huapi Formation was defined by Casal et al. (2015) for the lithostratigraphic interval in the uppermost part of the Chubut Group (Lesta and Ferello, 1972), which represents the main sedimentary filling in the Golfo San Jorge Basin. This unit overlies the Bajo Barreal Formation and underlies the Laguna Palacios Formation or the Salamanca Formation, according to its geographic position in the basin. The Lago Colhue Huapi Formation shows gradational top and basal contacts and occasionally an erosion surface (local unconformity) separates this unit from the Salamanca Formation (Casal et al., 2015; Vallati et al., 2016). In addition, at the studied locality (Fig. 1C), a laterally discontinuous basalt flow with a radiometric age of 67.31 ± 0.55 Ma (La Angostura Basalt) lies on top of the Lago Colhue Huapi Formation (Clyde et al., 2014). | |||||
Lithology and environment
| Primary lithology: | medium,yellow sandstone |
| Secondary lithology: | lime mudstone |
| Includes fossils? | Y |
| Lithology description: The upper layer containing the megafossil remains here reported, with the leaves of Marsileaceaephyllum (CF2), is less than 10 cm thick, and overlies an erosion surface. The yellowish medium-grained sandstones, which are badly sorted, include plant remains with a disordered arrangement. This upper layer is a sheet-like deposit interpreted herein as the result of a high-density flow. | |
| Environment: | channel lag |
| Geology comments: This upper layer is a sheet-like deposit interpreted herein as the result of a high-density flow. | |
Taphonomy
| Modes of preservation: | soft parts |
| Degree of concentration: | dispersed |
| Size of fossils: | microfossils |
| Preservation of anatomical detail: | good |
| Abundance in sediment: | common |
| Articulated whole bodies: | none |
| Associated major elements: | none |
| Disassociated major elements: | some |
| Disassociated minor elements: | many |
| Fragmentation: | none |
| Bioerosion: | none |
| Encrustation: | none |
Collection methods and comments
| Collection methods: | core,mechanical,hydrochloric,hydroflouric,field collection | ||
| Reason for describing collection: | general faunal/floral analysis | ||
| Collectors: | G. Casal | Collection dates: | 2015 |
| Collection method comments: The samples were mechanically disaggregated and treated with HF (70%) and HCl (19%).
The non-oxidized residuewaswet sieved usingmesh sizes 1.2mm and 74 mm. Later, after being perfectly dried, it was sieved again and the megaspores were picked out under a stereo microscope (Motic SMZ-168) from fractions between 250 and 177 mm. Selected material was gold-coated (Quorum, Q150R ES) and photographed using a JEOL JSM-6510LV Scanning Electron Microscope at the Universidad Nacional de la Patagonia San Juan Bosco (UNPSJB). The mesofossils are housed in the micropalaeontological collection of the Scientific and Didactic Repository “Dr. Eduardo A. Musacchio” UNPSJB at Comodoro Rivadavia (catalogue numbers: UNPSJB-MFP 1-70). Part of the residue was oxidated briefly using HNO3 (1e2 min) for light microscope (LM) examination. The samples were studied under a Carl Zeiss KF 2 microscope and the micrographs were taken with a digital Nikon Coolpix P2 camera at the Biostratigraphic Laboratory of the UNPSJB. The palynological slides are housed in the micropalaeontological repository at the UNPSJB, under the initials UNPSJB-MFP-CV. The palynomorphs are cited according to the corresponding slide identification followed by the coordinates of the Vernier Scale in the Zeiss Microscope. The megafossils (compressions and impressions of leaves and leaflets) were collected by G. Casal in 2015 from the Cerro de los Fragmentos outcrop at the headwaters of the Río Chico. The examined material is housed at the repository of the UNPSJB under the catalogue number UNPSJB-PB 198-199. | |||
Metadata
| Also known as: | Headwaters of the Río Chico | ||
| Database number: | 233995 | ||
| Authorizer: | E. Vlachos | Enterer: | F. Aspromonte | Research group: | paleobotany |
| Created: | 2024-03-11 20:04:06 | Last modified: | 2025-02-22 15:12:02 |
| Access level: | the public | Released: | 2024-03-11 20:04:06 |
| Creative Commons license: | CC0 | ||
Reference information
Primary reference:
| 87801. | P. Vallati, A. De Sosa Tomas, G. Casal and M. Calo. 2017. Salviniales from the Late Cretaceous of the Golfo San Jorge Basin. Cretaceous Research 74:45-55 [E. Vlachos/F. Aspromonte] |