POSSIBLE CORRELATION BETWEEN MIOCENE GLOBAL CLIMATIC CHANGES AND MAGNETIC PROXIES, USING NEURO FUZZY LOGIC ANALYSIS IN A STRATIGRAPHIC WELL AT THE LLANOS FORELAND BASIN, COLOMBIA

Abstract

In this work we have assessed the hybrid algorithm of NeuroFuzzy logic (NFL), to establish a correlation between global climatic changes (benthic foraminiferal δ18O data), experimental S-ratio (factor characterizing stability of remanent magnetization) and magnetic susceptibility (). Magnetic proxies have been measured in 44 samples of the Colombian stratigraphic well Saltarín 1A (distal Llanos foreland basin).  and S- ratios were linked to global δ18O data assuming a constant accumulation rate for a 305 meters thick stratigraphic interval flanked by the two palynological age constrains available. This interval encompasses, from top to base, the bottom of the Guayabo formation, the León, and the upper unit of the Carbonera formations (lower to middle Miocene). The best inference is accomplished applying a Takagi-Sugeno-Kan (TSK) fuzzy model with four fuzzy rules and the δ18O, S-ratios and  data used in a linear form to train the system. These results are interpreted as the outcome of a significant influence of global climatic changes upon magnetic proxies. Astronger correlation is perhaps prevented by the likely influence of local and regional tectonic events and climatic changes that could have affected the distal segment of the Colombian Llanos foreland basin during Miocene times. We argue that late diagenesis of primary magnetic minerals and the assumption of a constant accumulation rate might have a minor influence on these results