This study explores the possibilities of using carbonate-aluminosilicate mergel raw materials typical of Karakalpakstan as an additional cementing material in low-carbon composite portland cement systems. The main goal of the study is to identify the physicochemical changes occurring during thermal activation of the marl and to evaluate its influence on hydration kinetics, microstructural development and mechanical properties of cement systems. Under control conditions, the pozzolanic activity of crude corl was enhanced by calcification and partial amorphization of aluminosilicate phases as well as structural changes. Phase structure, morphology and thermal characteristics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS) and differential thermal and thermogravimetric analysis (DTA/TGA). Mechanical properties were evaluated using compression strength tests at various hardening times, and hydraulic activity was determined using the Student t-test. The results show that natural mergel has low reactivity due to its crystalline structure, while thermally activated mergel has high activity, accelerating the formation of secondary hydration products and leading to the collapse of the cement matrix. Research results show that thermally activated mergel as an effective mineral additive reduces clinker consumption, increases resource efficiency, and reduces carbon emissions.