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The architecture of lacustrine systems is the result of the complex interaction between tectonics, climate and environmental parameters, and constitute the main forcing parameters on the lake dynamics. Field analogue studies have been performed to better assess such interactions, and their impact on the facies distribution and the stratigraphic architecture of lacustrine systems. The Yacoraite Formation (Late Cretaceous/Early Palaeocene), deposited during the sag phase of the Salta rift basin in Argentina, is exposed in world‐class outcrops that allowed the dynamics of this lacustrine system to be studied through facies analysis and stratigraphic evolution. On the scale of the Alemania‐Metán‐El Rey Basin, the Yacoraite Formation is organized with a siliciclastic‐dominated margin to the west, and a carbonate‐dominated margin to the east. The Yacoraite can be subdivided into four main ‘mid‐term’ sequences and further subdivided into ‘short‐term’ sequences recording high frequency climate fluctuations. Furthermore, the depositional profiles and identified system tracts have been grouped into two end‐members at basin scale: (a) a balanced ‘perennial’ depositional system for the lower part of the Yacoraite Formation and (b) a highly alternating ‘ephemeral’ depositional system for the upper part of the Yacoraite Formation. The transition from a perennial system to an ephemeral system indicates a change in the sedimentary dynamics of the basin, which was probably linked with the Cretaceous/Tertiary boundary that induced a temporary shutdown of carbonate production and an increase in siliciclastic supply.

In this study, an integrated approach was applied using available sedimentary, geochronology, geochemical and isotopic datasets to better understand the complex interactions between production, destruction, and dilution processes that characterize the organic-rich sediments dynamic across the K-T boundary in a lacustrine system. This approach was tested here on the Late Cretaceous to Early Cenozoic Yacoraite Formation, a typical lacustrine source rock from the Salta rift Basin (NW Argentina). The Yacoraite Formation corresponds to a mixed carbonate-siliciclastic lacustrine sedimentary system, deposited during the sag phase (post-rift). We demonstrated here that new ashes U-Pb dating tie the K-T boundary during the deposition of the Yacoraite Formation.The Yacoraite Formation recorded major climate changes that can be documented in terms of catchment dynamic, erosion processes, carbonate accumulation trends, lacustrine dynamic and source rock quality. The pattern of organic carbon enrichment in the Yacoraite Formation illustrates how a biological pump came across a major climatic change. The background organic matter correspond to Type I dominated by algal growth (mean HI 600-800 mgHC/gTOC, TOC 0 1-2 wt.%). The K-T boundary was the climax of a climate change initiated ca. 0.3 Myr before and induced a major change in the catchment weathering processes, which temporally corresponds to the accumulation of poor quality source rock intervals (TOC 0 ≤ 0.2 wt.% and HI < 50 mgHC/gTOC) in these series. The K-T boundary is highlighted by the main negative anomaly in δ 13 C of the carbonate deposits of the Yacoraite Formation. It was followed by a major pulse in paleoproductivity, itself followed by a major pulse in TOC 0 (10-15 wt.%) under anoxia conditions. In ca. 0.2 Myr the lacustrine dynamic and its related organic-carbon enrichment resumed to their initial setting, just prior to the preluding K-T boundary climate change. Results suggest that the Yacoraite Formation can be considered as a world-class example to illustrate how the K-T boundary is recorded in lacustrine sediments.

A late diagenetic dolomitization pervasively affected Carboniferous carbonates of the Variscan Cantabrian Zone (NW Spain). The process generated replacive and void-filling dolomite phases, spatially related with various calcite cements. The nature of the diagenetic fluids has been investigated by cryo-Raman spectroscopy, i.e., a combination of Raman spectroscopy and low-temperature microthermometry, which reveals in great accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions. Fluid properties obtained only from microthermometry are distinctively different. The study demonstrates that this improved analytical method of fluid inclusions is a valuable contribution for the interpretation of fluids in dolomite research. In primary fluid inclusions of the Cantabrian dolomites, hydrohalite and two unknown salt hydrates, one of which resembles MgCl 2 ?12H 2 O, were detected by cryo-Raman spectroscopy, whereas only hydrohalite appeared in the calcite primary inclusions. The presence of CaCl 2 hydrates is suspected only from low eutectic temperatures. Dolomite formed from an evolving fluid, as reflected by the highly variable equivalent Na/Ca ratios calculated, at high and nearly constant total salinities. The approximately constant Na/Ca ratio in the first calcite cement reflects a homogeneous source for the salts. Cryo-Raman spectroscopy reveals that different cooling procedures may induce the formation of different phase assemblages within the same fluid inclusion in both dolomite and calcite. Consequently, fluid inclusions display different melting behaviors, corresponding to different values of calculated salinities. Salinity calculation only from microthermometry may lead to an underestimation of true salinities. According to an assumed hydrostatic geothermal gradient, maximum formation conditions for the dolomites are 150 6 30uC and 40 6 10 MPa, corresponding to a depth of 3.9 6 1.0 km. The first calcite formed at 130 6 20uC and 35 6 5 MPa, corresponding to a depth of 3.4 6 0.6 km. The minimum T-P of formation is defined by the homogenization conditions. CHARACTERIZATION OF DOLOMITIZING FLUIDS 1307 J S R