Fine-grained sedimentary rocks

a key rock type bearing shale oil and gas

are characterized by fine grain size

colour uniformity and strong heterogeneity.Traditional sedimentological study based on visual observation and optical images alone becomes inadequate to precisely characterize such fine-grained rocks.Therefore

a "chemo-sedimentary facies" model for analyzing fine core-scale samples is established based on the high-resolution(down to 30 μm measurement intervals) 2D inorganic geochemical element mapping of rock slabs obtained by in-situ XRF scanning and optical images.Through the model

it is possible to unambiguously recognize the rock compositions and sedimentary fabrics.And then certain environment-sensitive elemental parameters(ratios) can be calculated in situ from individual chemo-sedimentary facies at millimeter-centimeter scales for the effective interpretation of depositional environment and provenance of fine-grained sediments

as well as their origin.Meanwhile

the method also avoids information interference in the conventional bulk compositional analyses whereby homogenized sample powders are often used.In conclusion

the method can help to establish more fine-scale sedimentary facies models and to provide reliable data for the exploration and development of tight and shale oil & gas.