Inherited Depositional Topography Control on Shelf-Margin Oversteepening, Readjustment, and Coarse-Grained Sediment Delivery to Deep Water, Magallanes Basin, Chile

Abstract

A shelf-margin depositional system is the stratigraphic product of terrigenous sediment delivery to the ocean, comprising a flat to low-gradient shelf, or topset, which transitions to a steeper deep-water slope, and, ultimately, a relatively flat basin floor, or bottomset. Erosional and depositional processes across these physiographic domains approximate a clinoform in the stratigraphic record. The shelf margin is a critical environment for terrigenous sediment dispersal because it is a process-regime boundary that links the shelf to deep water and is a marker of basin evolution through time. Additionally, the coarse-grained deposits of strata associated with the shelf-margin zone are important subsurface reservoirs or aquifers. Here, we characterize the shelf-margin and upper slope stratigraphy of the outcropping Upper Cretaceous Tres Pasos and Dorotea formations, Magallanes Basin, southern Chile. The Late Cretaceous Magallanes retroarc foreland basin was an elongate trough oriented parallel to the southern Andean arc and fold-and-thrust belt. The Tres Pasos and Dorotea formations record southward (basin axial) progradation of a high-relief shelf and slope system (>1000 m paleo-water depth) represented by a stratigraphic succession up to 3 km thick that is exposed for tens of kilometers along depositional dip. The character and distribution of deposits that define shelf margins contain evidence for a variety of processes related to deposition, erosion, sediment bypass, and mass wasting. The overall architecture of the Magallanes Basin strata is indicative of a graded shelf-margin system interrupted by periods of slope oversteepening and development of out-of-grade conditions. These punctuated periods are recognized by sedimentological evidence for enhanced bypass of coarsegrained sediment across the upper slope, and thick submarine fan successions in more distal segments. Development of oversteepened depositional topography is particularly significant as it instigated the only two major periods of coarse-grained sediment delivery to deep water over ∼8 Myr during the Campanian. The controls on sediment dispersal beyond the shelf margin are commonly discussed in terms of allogenic forcings, such as tectonics, climate, eustasy, and receiving-basin geometry, as well as autogenic behavior,

Digital re‐evaluation of down‐dip channel‐fill architecture in deep‐water slope deposits: Multi‐scale perspectives from UAV‐SfM

“…Between 50 and 52°S (i.e., the Última Esperanza sector of the basin), the deep‐water depositional history of the basin is characterised by three discrete phases of infilling, including deposits of the Punta Barrosa, Cerro Toro and Tres Pasos formations (Figure 2A; Daniels et al, 2019; Katz, 1963; Romans et al, 2011). Together with the shallow‐marine Dorotea Formation, the Tres Pasos Formation records the terminal phase of marine sedimentation in this part of the basin (Bauer et al, 2020; Daniels et al, 2018; Hubbard et al, 2010).…”

“…(A) Summary of Late Cretaceous formations associated with the Magallanes‐Austral Basin. (B) Regional dip‐oriented stratigraphic cross‐section of the Tres Pasos and Dorotea formations showing large‐scale clinoform and clinothem for the studied strata (modified from Bauer et al, 2020). (C) Field location and oblique perspective satellite image of outcrop transect from Google Earth.…”

“…The Tres Pasos Formation largely records deposition along submarine slopes that were >40 km long and characterised by >1 km of relief (Figure 2B; Bauer et al, 2020). Although the Tres Pasos Formation consists predominantly of siltstone deposits, packages of sandstone up to 300 m thick crop out along the studied transect and are interpreted to represent the products of channelisation along the basin‐margin slope (Hubbard et al, 2010, 2014; Macauley & Hubbard, 2013).…”

Sedimentología de la Formación La Anita, Cretácico Superior de la Cuenca Austral, provincia de Santa Cruz, Argentina

“…Este sistema de talud se encuentra genéticamente relacionado con los depósitos de plataforma, marinos marginales y deltaicos del Campaniano y Maastrichtiano, conocidos como Formación Dorotea en Chile (Fig. 2.2; Schwartz y Graham, 2015; Gutiérrez et al, 2017;Bauer et al, 2020), así también como con los depósitos deltaicos de la sección inferior de la Formación La Anita en Argentina (Fig. 2.2; Manassero, 1988;Macellari et al, 1989;Moyano Paz et al, 2018 Tettamanti et al, 2018).…”

“…Vista (Malkowski et al, 2017;Daniels et al, 2017;Bauer et al, 2020 Catuneanu, 2006;Catuneanu et al, 2009;Moyano Paz et al, 2018. La SMI también se presenta separando a los depósitos del valle inciso de los depósitos finos de la planicie deltaica representando el desconfinamiento del relleno fluvial del valle inciso (Fig.…”