Abstract. This study presents a detailed palynofacies analysis integrated with lacustrine sequence stratigraphy to evaluate the role of climate-driven hydrological balance on basin infill and its impact on the organic matter accumulation in the Jurassic Cañadón Asfalto Formation, Cerro Cóndor depocentre, Extra-Andean Patagonia, Argentina. It provides valuable insights into the changes in the nature and taphonomic history of the organic matter throughout the different stages of a lacustrine system's evolution based on the analysis of 51 outcrop samples from the Cañadón Lahuincó “A” section. Two depositional sequences are recognised. Sequence I documents the evolution from underfilled to balanced-fill/overfilled lake stages. Underfilled conditions are characterised by extreme lake-level variability, while the transition to balanced-fill/overfilled conditions is marked by stacked coarsening-upward successions. Sequence II is bounded by an abrupt accommodation increase and initially records renewed underfilled conditions, followed by the establishment of a fully overfilled lake stage characterised by persistent progradational stacking patterns. The most conspicuous feature of the Cañadón Asfalto Formation's organic matter is the overall dominance of land-derived fraction. The variations between the allochthonous and autochthonous (algae and algal-derived amorphous organic matter) material suggests variable climatic conditions, with the alternation of wetter and drier periods at least during the Sequence I and part of the Sequence II. Four palynofacies types (PT-A to PT-D) were defined recording variations in depositional energy, redox conditions, and sediment–water balance. PT-A and PT-D indicate wetter periods, while PT-B indicates relatively drier intervals. PT-C shows the changes between these two opposite situations. The underfilled stage is characterised by the dominance of reworked terrestrial phytoclasts (indicating high-energy inflow events) and poor sporomorph preservation. Conversely, the balanced-fill stage shows sporomorph-rich palynofacies. In both lake stages, blooms of well-preserved strong fluorescence Botryococcus colonies (chlorophytic algae) are registered during drier periods. The overfilled conditions are characterised by the lack of palynomorphs. Kerogen varies from Type III (PT-A) to mixed Type I/III in algae-rich intervals (PT-B, PTC), confirming hydrological balance as the control on organic matter preservation.
Olivera et al. (Wed,) studied this question.