Complex alluvial architecture, paleohydraulics and controls of a multichannel fluvial system: Bajo Barreal Formation (Upper Cretaceous) in the Cerro Ballena anticline, Golfo San Jorge Basin, Patagonia

Climatic control on stacking and connectivity of fluvial successions: Upper Cretaceous Bajo Barreal Formation of the Golfo San Jorge basin, Patagonia

“…Data using empirical equations derived from modern rivers (Leclair and Bridge, 2001;Leclair, 2002;Bridge and Tye, 2000;Bridge and Mackey, 1993) also allowed identify an increase in both average flow depth (dm), mean bankfull channel depth (db), and mean bankfull channel width of single channels (Wc) from Section A to Section B (Fig. 5B), with values of Wc very close to those obtained using GPS measurements of width of single channels (Paredes et al, 2018a: their Table II).…”

“…They also provided an Ar/Ar age of 91 +/-0.49 Ma from a distinctive level that separates Sections A and B, interpreted as an ignimbrite . In a recent re-evaluation of the Cerro Ballena exposures, Paredes et al (2018a) interpreted an anabranching fluvial system with seven distinctive fluvial styles, considerable spatio-temporal variation in channel geometries and dominance of avulsion deposits (Fig. 5).…”

“…5). Paredes et al (2018a: their Fig. 14) identified a systematic vertical (temporal) increase in single-channel dimensions of the formative rivers through Section A and B using GPS measurements on extremes of the channels (see Fig.…”

“…Converging results of both measurements of single-channel dimensions and use of empirical relations derived from set thickness of cross-beds within channel fills were considered as supporting evidence of discharge increase towards Section B, a trend that was associated with a climatic shift toward more humid climatic conditions (Paredes et al, 2018a). Based on current understanding, the present research aims to complement the previous results using several techniques (i.e., spectral gamma-ray logs, x-ray diffraction analysis, sandstone petrography), to find further evidence of climatic change in the analyzed fluvial succession, or alternatively to test other forcing factors that could be relevant to understand the alluvial organization of the fluvial succession.…”

“…In this research, we provide results of detailed outcrop SGR logging of the Cerro Ballena exposures, complemented with x-ray diffraction analysis and sandstone petrography within channel fills. These data, integrated with paleo-hydraulical estimations derived from measurements of cross-bed set thickness in channel fill and measurements of channel sizes (Paredes et al, 2018a), aimed at tracing climatically controlled variations in the overall stacking of the fluvial succession. The main purpose of this paper is to understand the stratigraphic organization of the fluvial succession and to discuss the main controls on the stacking pattern.…”