Low Temperature Illitization through Illite-Dioctahedral Vermiculite Mixed Layers in a Tropical Saline Lake Rich in Hydrothermal Fluids (Sochagota Lake, Colombia)

Abstract

In this investigation, we showed that high salinity promoted by hydrothermal inputs, reducing conditions of sediments with high content in organic matter, and the occurrence of an appropriate clay mineral precursor provide a suitable framework for low-temperature illitization processes. We studied the sedimentary illitization process that occurs in carbonaceous sediments from a lake with saline waters (Sochagota Lake, Colombia) located at a tropical latitude. Water isotopic composition suggests that high salinity was produced by hydrothermal contribution. Materials accumulated in the Sochagota Lake’s southern entrance are organic matter-poor sediments that contain detrital kaolinite and quartz. On the other hand, materials formed at the central segment and near the lake exit (north portion) are enriched in organic matter and characterized by the crystallization of Fe-sulfides. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray spectrometry (EDX) data allowed for the identification of illite and illite-dioctahedral vermiculite mixed layers (I-DV), which are absent in the southern sediments. High humidity and temperate climate caused the formation of small-sized metastable intermediates of I-DV particles by the weathering of the source rocks in the Sochagota Lake Basin. These particles were deposited in the low-energy lake environments (middle and north part). The interaction of these sediments enriched in organic matter with the saline waters of the lake enriched in hydrothermal K caused a reducing environment that favored Fe mobilization processes and its incorporation to I-DV mixed layers that acted as mineral precursor for fast low temperature illitization, revealing that in geothermal areas clays in lakes favor a hydrothermal K uptake.

Transformation of S-Bearing Minerals in Organic Matter-Rich Sediments from a Saline Lake with Hydrothermal Inputs

“…Similar illitization processes in other saline and organic matter-rich environments, such as those occurring in mangroves, have been described [7]. On the other hand, the higher hydrodynamic conditions of the lake entrance and the low organic matter content of these materials avoided the formation and accumulation of the fine clay mineral particles in the southern area of the Sochagota Lake [32].…”

“…From the entrance to the inner portion and the northern border of the lake, the amount of fine particles of clay minerals (illite and mixed-layer clay mineral) increases. The formation of illite and I-DV was occurred during the strong interaction of the sediments with the saline water-pore under the reduced conditions provided by the high content in organic matter [32]. Similar illitization processes in other saline and organic matter-rich environments, such as those occurring in mangroves, have been described [7].…”