Refining stratigraphy and tectonic history using detrital zircon maximum depositional age: an example from the Cerro Fortaleza Formation, Austral Basin, southern Patagonia

Abstract

The north–south trending, Late Cretaceous to modern Magallanes–Austral foreland basin of southernmost Patagonia lacks a unified, radiometric, age‐controlled stratigraphic framework. By simplifying the sedimentary fill of the basin to deep‐marine, shallow‐marine and terrestrial deposits, and combining 13 new U‐Pb detrital zircon maximum depositional ages (DZ MDAs) with published DZ MDAs and U‐Pb ash ages, we provide the first attempt at a unified, longitudinal stratigraphic framework constrained by radiometric age controls. We divide the foreland basin history into two phases, including (1) an initial Late Cretaceous shoaling upward phase and (2) a Cenozoic phase that overlies a Palaeogene unconformity. New DZ samples from the shallow‐marine La Anita Formation, the terrestrial Cerro Fortaleza Formation and several previously unrecognized Cenozoic units provide necessary radiometric age controls for the end of the Late Cretaceous foreland phase and the magnitude of the Palaeogene unconformity in the Austral sector of the basin. These samples show that the La Anita and Cerro Fortaleza Formations have Campanian DZ MDAs, and that overlying Cenozoic strata have Eocene to Miocene DZ MDAs. By filling this data gap, we are able to provide a first attempt at constructing a basinwide, age‐controlled stratigraphic framework for the Magallanes–Austral foreland basin. Results show southward progradation of shallow marine and terrestrial environments from the Santonian through the Maastrichtian, as well as a northward increase in the magnitude of the Palaeogene unconformity. Furthermore, our new age data significantly impact the chronology of fossil flora and dinosaur faunas in Patagonia.

Interpreting large detrital geochronology data sets in retroarc foreland basins: An example from the Magallanes-Austral Basin, southernmost Patagonia

“…Based on outcrop, core, and seismic observations, clastic deposition appears to have been continuous during Cretaceous time, with no significant basinwide hiatus in deposition from the end of Jurassic extension through the transition to compression and Cretaceous flexural subsidence (Figs. 2B and 4;Wilson, 1991;Arbe, 2002;Sickmann et al, 2018). The only apparent basinwide unconformity occurs between Upper Cretaceous and Middle Eocene deposits (Fig.…”

“…Depositional systems associated with this transition indicate shallower water depths in the north compared to southern temporal equivalents due to a long-lived, southward-dipping depositional gradient in the basin (Figs. 2B and 4;Arbe, 2002;Sickmann et al, 2018). Due to lithospheric weaknesses that were inherited from the extensional phase of the basin, the Magallanes-Austral Basin foredeep appears to have been deeply subsided and "pinned" for an extended period of time with a subdued forebulge (Fosdick et al, 2014).…”

“…The three successions represent: (1) an underfilled period of deposition in environments similar to those that were present during foreland initiation (e.g., shallow-marine to deep-marine environments, depending on the location; Wilson, 1991;Fildani and Hessler, 2005;Malkowski et al, 2015a); (2) a period of rapid filling, during which the shelf-slope break prograded more than 100 km southward in 5-10 m.y. (e.g., Hubbard et al, 2010;Schwartz et al, 2016;Daniels et al, 2017;Sickmann et al, 2018); and 3…”

Sedimentary Evolution and Provenance of the late Permian‐middle Triassic Raggyorcaka Deposits in North Qiangtang (Tibet, Western China): Evidence for a Forearc Basin of the Longmu Co‐Shuanghu Tethys Ocean

“…Tectonics be the most robust method (Orme et al, 2015;Sickmann et al, 2018). We used this algorithm and found that it produced reasonable results for the Raggyorcaka samples (Figures 3, S2, and S3 and Table 2).…”

New theropod remains and implications for megaraptorid diversity in the Winton Formation (lower Upper Cretaceous), Queensland, Australia

“…The South American record is the most extensive, diverse and abundant, with six taxa named to date: Aoniraptor libertatem [37], Orkoraptor burkei [33], Megaraptor namunhuaiquii [32,38,39], Murusraptor barrosaensis [30,40,41], Aerosteon riocoloradensis [28], and Tratayenia rosalesi [42]. Numerous fragmentary specimens have also been reported from South America (see supplementary table 7 in [1]), which include the oldest (Albian [43]) and the youngest (Campanian [44]).…”