This paper discusses the preservation of elemental and isotopic source identification of sedimentary organic matter. It highlights that while only a small fraction of the initial aquatic organic matter survives sinking and sedimentation, the remaining organic matter retains information about its source and paleoenvironment. The C/N ratio and δ¹³C values of total organic matter are particularly useful for identifying the source of organic matter over long time periods. These parameters are relatively stable despite early diagenetic modifications, making them valuable for paleoenvironmental studies. The paper reviews examples of lacustrine and marine C/N and δ¹³C sedimentary records and considers their paleoenvironmental significance. It discusses how the C/N ratio and δ¹³C values can distinguish between algal and land-plant origins of sedimentary organic matter. Algae typically have lower C/N ratios compared to vascular plants, and δ¹³C values can differentiate between marine and continental plant sources. The paper also examines how organic matter alterations continue to sub-bottom depths, but source and paleoenvironmental information remains preserved in the molecular, elemental, and isotopic compositions of organic matter. The paper presents case studies from various lakes and marine sediments, including Mangrove Lake, Lake Baikal, Lake Bosumtwi, and Lake Biwa, showing how C/N and δ¹³C values can be used to identify organic matter sources and track changes in paleoenvironmental conditions over time. It also discusses marine sediments, such as those from DSDP Site 619 and ODP Site 689, highlighting the importance of C/N and δ¹³C values in identifying organic matter sources and understanding long-term paleoceanographic changes. The paper concludes that while diagenetic processes can alter the composition of organic matter, the C/N and δ¹³C values of total organic matter retain source information for millions of years. These parameters are essential for understanding the paleoenvironmental and paleoclimatological records of sedimentary organic matter. The study emphasizes the importance of considering diagenetic effects when interpreting organic matter source estimates and highlights the value of sedimentary matrices in providing information about the reasonableness of source estimates based on organic constituents.This paper discusses the preservation of elemental and isotopic source identification of sedimentary organic matter. It highlights that while only a small fraction of the initial aquatic organic matter survives sinking and sedimentation, the remaining organic matter retains information about its source and paleoenvironment. The C/N ratio and δ¹³C values of total organic matter are particularly useful for identifying the source of organic matter over long time periods. These parameters are relatively stable despite early diagenetic modifications, making them valuable for paleoenvironmental studies. The paper reviews examples of lacustrine and marine C/N and δ¹³C sedimentary records and considers their paleoenvironmental significance. It discusses how the C/N ratio and δ¹³C values can distinguish between algal and land-plant origins of sedimentary organic matter. Algae typically have lower C/N ratios compared to vascular plants, and δ¹³C values can differentiate between marine and continental plant sources. The paper also examines how organic matter alterations continue to sub-bottom depths, but source and paleoenvironmental information remains preserved in the molecular, elemental, and isotopic compositions of organic matter. The paper presents case studies from various lakes and marine sediments, including Mangrove Lake, Lake Baikal, Lake Bosumtwi, and Lake Biwa, showing how C/N and δ¹³C values can be used to identify organic matter sources and track changes in paleoenvironmental conditions over time. It also discusses marine sediments, such as those from DSDP Site 619 and ODP Site 689, highlighting the importance of C/N and δ¹³C values in identifying organic matter sources and understanding long-term paleoceanographic changes. The paper concludes that while diagenetic processes can alter the composition of organic matter, the C/N and δ¹³C values of total organic matter retain source information for millions of years. These parameters are essential for understanding the paleoenvironmental and paleoclimatological records of sedimentary organic matter. The study emphasizes the importance of considering diagenetic effects when interpreting organic matter source estimates and highlights the value of sedimentary matrices in providing information about the reasonableness of source estimates based on organic constituents.