Conceptual basin-filling models in continental succession based on the interaction of depositional and pedogenic processes: examples from Upper Cretaceous basins (Bauru and La Rioja basins) and its implications in vertebrate paleontology

GIORGIO BASILICI; LUCAS FIORELLI; PAOLO LORENZONI; ÁQUILA FERREIRA MESQUITA; MARTÍN HECHENLEITNER; THIAGO DA SILVA MARINHO; AGUSTÍN MARTINELLI

La Rioja

Jornada; 36º Jornadas Argentinas de Paleontología de Vertebrados; 2023

CRILAR - Ministerior de Turismo y Culturas

Sedimentological and stratigraphic studies of continental successions involving only deposits could turn out an erroneous study, because (i) continental sedimentary successions consist largely of palaeosol profiles and (ii) the palaeosols constitute a mighty source of s.l. palaeoenvironmental information. Simultaneous analyses of deposits and palaeosols in continental successions allow to discriminate differences in the spatial and temporal processes and sediment filling of basins that would not be detectable. We apply this kind of analysis and the significant outcomes in two large Upper Cretaceous intracratonic basins: the Bauru (SE Brazil) and La Rioja (NW Argentina) basins. The Bauru Basin has an extension of ~300,000 km2. We studied the upper succession (Marília and Serra da Galga formations) in three areas 350-420 km apart, identified as NW, NE and SE areas. In these areas, the succession is interpreted as distributive fluvial system, although with significant differences on the type and alternation of palaeosol/deposits sequences. The NW area has welldeveloped aridisols with time of development until 175 ky and mean annual precipitation (“map”) <500 mm/y. Most deposits formed in aeolian sand sheet and the cyclicity deposit/palaeosol seems to be controlled by climatic variations. The NE shows Entisols, Inceptisols, Vertisols with development order of 102-103 y, controlled by channel and flood plain sedimentation, with a “map” of ~900 mm/y. SE area palaeosol/deposit cycles are controlled by unconfined deposition in a distal distributive fluvial system; Inceptisol with development time between 8 and 60 ky, showing “map” between 750 and 1,000 mm/y. Geochemical and petrographic data show a mafic rock provenance of the deposits in the NE and NW areas and felsic provenance in SW area. In La Rioja Basin we analysed two isolated localities of Los Llanos Formation: Tama and Olta. The Tama succession is completely constituted of palaeosols: the lower portion displays Aridisols followed by cumulative Inceptisols. Microtextural data of sand grains indicate aeolian-dominated depositional processes with minor contribution of subaqueous transport in a sand sheet environment at the foot of coalescing alluvial fans. Olta displays a temporal transition by an erg to a fluvial system with palaeosols developed in humid conditions as evidenced by gleyed horizons. These studies inevitably interact with paleoecological, biostratigraphic, and taphonomic matter, and are key to understanding the preservation of vertebrate fossil remains. Some cases will be presented: borrowings from incipient palaeosols of Ponto Ponto 1 do Price (Baurú) and preservation of dinosaur egg-clutches and bones alterations in cumulative palaeosols of Los Llanos.