Facies and architectural variability of sub‐seismic slope‐channel fills in prograding clinoforms, Mid‐Jurassic Neuquén Basin, Argentina

Abstract

Most slope‐channel outcrop studies have been conducted at continental margin‐scale on seismic data. However, in foreland and back‐arc deepwater settings, sub‐seismic scale slope channels hold equally important information on deepwater sediment delivery, often in hydrocarbon‐bearing provinces. One such slope‐channel system is examined in Lower Jurassic prograding shelf‐margin clinoforms in Bey Malec Estancia, La Jardinera area, southern Neuquén Basin, Argentina. In a 4 km wide, 300 m tall, slightly oblique‐ to depositional‐dip section of Jurassic Los Molles Formation deepwater slope deposits, seven clinoform timelines were identified by isolated slope‐channel fills with thicknesses less than 50 m. Sedimentary logs, satellite images, a digital elevation model and drone photogrammetry were used to map variations in downslope channel geometry and infill facies. The slope channels are filled with sediment density flow deposits: poorly sorted conglomeratic debrites, structureless sandy high‐density turbidites and well‐sorted, fine‐grained, graded low‐density turbidites. The debrite portion decreases downslope, whereas high‐ and low‐density turbidites increase. A grain‐size analysis reveals a broad downslope fining trend of turbidite and debrite beds within slope channels with increasing water depth, and some notable bypass of conglomeratic facies to the lowermost slope channels and basin floor fans. The architecture of the slope channels changes from lateral to aggradational infill downstream. The Bey Malec clinoforms and its slope channels add new knowledge on downslope changes for sediment delivery in relatively shallow (<500 m water depth), prograding‐dominant deepwater basins. They also highlight one of very few outcropping examples of oblique‐type clinoforms.

River‐dominated and tide‐influenced shelf‐edge delta systems: Coarse‐grained deltas straddling the Early–Middle Jurassic shelf–slope break and transforming downslope, Lajas–Los Molles formations, Neuquén Basin, Argentina

“…The sharp bases of beds and bedsets associated with the characteristic aggradational stacking in this clinothem indicate repeated cutting and filling of channels. The turbidite deposits are interpreted as the infills of channels that are sited, according to the outcrop, on the uppermost parts of the deepwater slope (see also Gan et al ., ).…”

Clinoforms and clinothems: Fundamental elements of basin infill

“…Amorosi et al, 2019;Plink-Bjorklund, 2019) to shelf-edge scale (e.g. Bryn et al, 2019;Gamberi et al, 2019;Gan, Steel, Olariu, & Almeida Jr, 2019;Olariu et al, 2019;Patruno et al, 2019;Steel et al, 2019) and continental-margin scale (Chen, Steel, Wang, Zhao, & Olariu, 2019;Midtkandal et al, 2019). Continuous and repeated erosion is commonplace in the topset areas, F I G U R E 3 Conceptual section of nested clinoforms as the result of incremental margin growth: as in Matryoshka dolls, progressively smaller-scale clinoforms and clinothems 'appear' as we gradually zoom into a continental margin succession.…”

“…Mass-transport processes mainly affect the margin slope. Archive potential increases in modern mud belt of the proximal, outer shelf and deepest sectors the margin as highlighted by frequent downcutting of fluvial and delta-distributary channels (Gan et al, 2019) and by shelf-edge incisions . Thick successions showing vertically stacked progradation-transgression units or an overall tendency to stack units from a progradation to aggradation style (as judged from the shelf-break trajectory).…”

“…Bryn et al, 2019; Gamberi et al, 2019; Gan, Steel, Olariu, & Almeida Jr, 2019; Olariu et al, 2019; Patruno et al, 2019; Steel et al, 2019) and continental‐margin scale (Chen, Steel, Wang, Zhao, & Olariu, 2019; Midtkandal et al, 2019). Continuous and repeated erosion is commonplace in the topset areas, as highlighted by frequent downcutting of fluvial and delta‐distributary channels (Gan et al, 2019) and by shelf‐edge incisions (Olariu et al, 2019). Thick successions showing vertically stacked progradation–transgression units or an overall tendency to stack units from a progradation to aggradation style (as judged from the shelf‐break trajectory).…”

“…Gan et al, 2019 , present outcrop data on channels up to 50‐m‐thick situated on deep‐water clinothem slopes fronting an active back‐arc basin (the Jurassic Los Molles Formation, southern Neuquén Basin, Argentina). Most studies of slope channels have focused on seismically defined units on continental margins, whereas this study provides an assessment of such features at sub‐seismic scale and in a back‐arc tectonic setting.…”