THIS note deals with the geochemical behavior of elements near the water/sediment interface of a fossil seafloor. The Nandan-Hechi basin, located in northwest Guangxi, Southern China, is selected for exemplified study. It is an elongated basin, and developed on a Caledonian basement. Its Devonian strata hosthydrtothermally sedimentary formations, and are typical of the intra-platformal basin facies sediments oversouthern China. A steady sedimentary sequence may be observed, commonly going from carboniferouspelite at bottom, upward through bedded chert, thickly banded argillaceous limestone, thinly bandedsiliceous limestone and small lensiod argillaceous limestone in the middle, to coarse lensoid siliceousand/or argillaceous limestone at the top. The chert and some argillaceous limestone are related to hydrothermally sedimentary origin. The present study focuses on the lensoid argillaceous limestone formation. This formation contains the following characteristic sedimentary structures: small lensoid structure,vermiform structure, wave-shaped banded structure, massive structure, white framboid structure, andcage netting structure. THIS note deals with the geochemical behavior of elements near the water / sediment interface of a fossil seafloor. The Nandan-Hechi basin, located in northwest Guangxi, Southern China, is selected for study. It is an elongated basin, and developed on a Its Devonian strata hosthydrtothermally sedimentary formations, and are typical of the intra-platformal basin facies sediments oversouthern China. A steady sedimentary sequence may be observed, commonly going from carboniferouspelite at bottom, upward through bedded chert, thickly banded argillaceous limestone, thinly bandedsiliceous limestone and small lensiod argillaceous limestone in the middle, to coarse lensoid siliceousand / or argillaceous limestone at the top. The chert and some argillaceous limestone are related to hydrothermally sedimentary origin. This formation contains the lensoid argillaceous limestone formation. This formation contains the following characteristic sedimentary structures: small lensoid structure, vermiform structure, wave-shaped banded structure, massive structure, white framboid structure, andcage netting structure.