Timing of deep-water slope evolution constrained by large-n detrital and volcanic ash zircon geochronology, Cretaceous Magallanes Basin, Chile

Abstract

Deciphering depositional age from deposits that accumulate in deep-water slope settings can enhance understanding of shelf-margin evolutionary timing, as well as controlling mechanisms in ancient systems worldwide. Basin analysis has long employed biostratigraphy and/or tephrochronology to temporally constrain ancient environments. However, due to poor preservation of index fossils and volcanic ash beds in many deepwater systems, deducing the timing of slope evolution has proven challenging. Here, we present >6600 new U-Pb zircon ages with stratigraphic information from an ~100-kmlong by ~2.5-km-thick outcrop belt to elucidate evolutionary timing for a Campanian-Maastrichtian slope succession in the Magallanes Basin, Chile. Results show that the succession consists of four stratigraphic intervals, which characterize four evolutionary phases of the slope system. Overall, the succession records 9.9 ± 1.4 m.y. (80.5 ± 0.3 Ma to 70.6 ± 1.5 Ma) of graded clinoform development punctuated by out-of-grade periods distinguished by enhanced coarse-grained sediment bypass downslope. Synthesis of our results with geochronologic, structural, and stratigraphic data from the basin suggests that slope evolution was largely controlled by an overall decline in basin subsidence from 82 to 74 Ma. In addition to providing insight into slope evolution, our results show that the reliability of zircon-derived depositional duration estimates for ancient sedimentary systems is controlled by: (1) the proportion of syndepositionally formed zircon in a strati

Clinoform architecture and along‐strike facies variability through an exhumed erosional to accretionary basin margin transition

“…The shelf-edge rollover trajectory and clinoform architecture of the Laingsburg basin margin (Figures 10 and 12a) shows a progressive upward decrease in clinoform slope and length, and an associated change from strongly progradational to aggradational style. This pattern has been also described in other examples, such as other examples, such as the Porcupine Basin, offshore Ireland (Ryan et al, 2009), the mid-Norwegian continental shelf (Bullimore, Henriksen, Liestøl, & Helland-Hansen, 2005), and the Magallanes Basin margin, Chile (Daniels et al, 2017;Hubbard et al, 2010). The Miocene clinothems of the New Jersey margin (Miller et al, 2013;Mountain, Proust, McInroy, & Cotterill, 2010;Proust et al, 2018) also display similar trajectory and gradient evolution, including flat progradational (like Unit G to WfC2), rising aggradational (like WfC 3-5), and flat-to-falling progradational trajectory (like WfC 6-8) (Figure 12a).…”

Tectonically controlled initiation of contemporaneous deep‐water channel systems along a Late Cretaceous continental margin, western British Columbia, Canada

“…Daniels et al . () established the utility of large‐n detrital zircon analyses for derivation of reliable maximum depositional ages (MDAs) in basins adjacent to an active arc. Rates of shelf margin progradation and aggradation were determined over a 10 Ma period during the Late Cretaceous in the Magallanes retroarc foreland basin.…”

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

“…S1 and Appendix S1 for a more detailed explanation of nomenclature. Magallanes stratigraphy is compiled from Bernhardt et al (2011) and Daniels et al (2017). (b) Area mapped by each study.…”

“…Fig. 2a; Bernhardt et al, 2011;Daniels et al, 2017). The Austral sector of the basin, however, lacks extensive age control ( Fig.…”