New characterization of the Early Triassic Sonoma Foreland basin (western USA) and its controlling factors using multi-scale integrated approaches
Résumé
In the aftermath of the end-Permian mass extinction (~252 Ma), the Early Triassic Sonoma Foreland Basin (SFB) provides excellent sedimentary and fossil records to describe and understand the Early Triassic biotic recovery. Nevertheless, despite its importance, this basin is still poorly constrained and its controlling factors rather unclear. A new multi-disciplinary and integrated study is proposed based on ~50 sections from the literature and field-based data. Sedimentary, geochemical, paleontological, geodynamical and structural analyses have been conducted at various scales, from the section to the entire basin. Based on a high-resolution biostratigraphic framework, SFB depositional settings and their paleogeographical distribution are reconstructed, as well as their spatio-temporal and geodynamical evolutions. The SFB sedimentary record allows to characterize several facies associations representing depositional settings laterally evolving from transitional continental to intertidal tidal flats and high energy shoal, and to open marine outer platform settings. Nevertheless, marked differences are documented between the northern and southern parts of the SFB. Indeed, the sedimentary record shows differences in lithology and in spatial distribution of the sedimentary thicknesses. These observations are also reflected in the paleontological record, displaying the presence or absence of several biotic assemblages such as microbial communities. Microbial limestones are mainly restricted to the southern SFB while siliciclastic microbially induced sedimentary structures are locally observed in the northern part. Moreover, geochemical analyses indicate a spatially-heterogeneous influence of secondary alteration over the carbon isotope signals. In the southern part of the SFB, this record is highly altered and does not reflect the primary sedimentary signal. Conversely, the northern part of the basin shows a “pristine” sedimentary signal, representative of the ocean-atmosphere system. These North/South differences can result from processes interacting at different scales. On the one hand, at the basin scale, we notably show that heritage of the ~2 Gyr-long tectono-sedimentary history of the SFB is reflected in marked regional differences in subsidence rates. On the other hand, controls such as the geochemistry of the water column or terrestrial influxes have influenced the local evolution of the depositional settings. To sum up, we highlight a complex interplay of local to basin-scale controlling factors over the spatial distribution and lateral migration of depositional settings observed in the SFB and demonstrate that two sub-basins should be considered within the Early Triassic Sonoma Foreland Basin.
Origine : Fichiers produits par l'(les) auteur(s)