Spatial variations in distributive fluvial system architecture of the Upper Cretaceous Marília Formation, SE Brazil

Abstract

Conceptual models developed from modern distributive fluvial systems (DFSs) show a predictable spatial variation of facies progression from the margin to the interior of continental sedimentary basins. The Upper Cretaceous Serra da Galga Member of the Marília Formation has recently been interpreted to be a result of DFS deposition in the intracratonic Bauru Basin. This paper describes the spatial variations in stratigraphic architecture from the proximal to medial regions of the studied DFS and presents the implications of the recorded changes for fluvial reservoir characterization. The proximal areas are dominated by amalgamated channel-fill deposits and weakly developed, well-drained palaeosol profiles with only sparse floodplain deposits. The medial areas display a reduction in channel-fill deposits, an increase in the preserved thickness of floodplain deposits and the occurrence of sheetflood deposits and well-developed, poorly drained palaeosols. This spatial trend is accompanied by changes in the net : gross ratios of the geological bodies, forming possible high net : gross reservoirs in the proximal areas and reservoirs with very variable net : gross ratios in the medial areas. This down-system change in preserved stratigraphic architecture is evidenced for the first time in the studied sedimentary succession and follows the same pattern of facies progression described from modern examples of DFSs.

Quantifying Downstream, Vertical and Lateral Variation in Fluvial Deposits: Implications From the Huesca Distributive Fluvial System

“…Currently, outcrop analogues are used to aid subsurface exploration to better understand the distribution and connectivity of reservoir bodies, as well as aid paleogeographic reconstructions. Although qualitative descriptions are present for DFS (e.g., Nichols, 1987;Kelly and Olsen, 1993;Willis, 1993a;Willis, 1993b;Nichols and Fisher, 2007;Gulliford et al, 2014;Klausen et al, 2014;Ielpi and Ghinassi, 2016) at present, very few ancient DFS have been quantitatively examined across the whole system in the geologic record, largely due to limitations in exposures (e.g., Allen, 1983;Hirst and Nichols, 1986;Hirst, 1991;Cain and Mountney, 2009;Pranter, 2014;Rittersbacher et al, 2014;Owen et al, 2015a, Owen et al, 2017aFühr Dal' Bó et al, 2018;Wang and Plink-Björklund, 2019). However, it is clear from studies of DFS deposits that downstream trends are present.…”

Sedimentology of a distributive fluvial system: The Serra da Galga Formation, a new lithostratigraphic unit (Upper Cretaceous, Bauru Basin, Brazil)

“…The Serra da Galga Formation demonstrates a channel‐to‐interchannel thickness ratio that varies approximately from 7, at the Price 1 type‐section, to 2 at the BR050 type‐section. This downflow increase in interchannel deposits relates to the fact that cannibalization of overbank deposits by avulsing channels tends to be greater towards fan apices along a distributive fluvial network, according to which channel bodies bifurcate outwards from the proximal zone (Price 1 type‐section) to the medial zone (BR050 type‐section) in a NNW direction (Dal'Bó, Soares, Basilici, Rodrigues, & Menezes, 2019; Soares et al, 2018; cf. Cain & Mountney, 2009; Hartley, Weissmann, Nichols, & Warwick, 2010; Weissmann et al, 2010).…”

The geoengineering approach to the study of rivers and reservoirs

“…In this section a number of studies on modern systems (Blum 2019;Sinclair et al 2016;Nicholson et al 2019) are compared with ancient counterparts, from the Cenozoic (Stow et al 2016) and Mesozoic (Dal' Bó et al 2018;Yeste et al 2018;Fambrini et al 2019) through to the Paleozoic (Reesink 2016;Ellen et al 2018). In reconciling these two timescales, it is necessary to find common ground between studies which focus on the plan-view (topdown) evolution of fluvial systems (often the focus of modern studies) and the cross-sectional view often employed by studies of ancient relict landforms in the geological record.…”