Paleobiogeoclimatic reconstruction of the Monte Cristo cave, Minas Gerais, Brazil, through phytolith analysis

Abstract

This study aims to contribute to the understanding of possible paleoclimatic variations during the Quaternary in the Serra do Espinhaço Mountain Range, Minas Gerais, Brazil, based on phytolith analysis. Two soil profiles were collected from the Monte Cristo cave, which is formed in quartzite, the first being an Organosol outside the cave and the second consisting of mostly sandy material from inside the cave, in layers varying between light and dark tones. The results showed that both profiles present a high stock of phytoliths. The phytoliths are well preserved, with a predominance of Spheroid echinate and Spheroid ornate morphotypes, in addition to the presence of Bulliform flabellate, Cross, Bilobate, Rondel, and Trapezoid. The tree density index (D/P) is between 0.19 and 0.36, indicating open vegetation. The values of the Bi% index (32.8–53%) indicate moderate water stress, which is similar to previous studies in nearby regions. The Ic (climatic) index showed variations in plant adaptation at lower temperatures, with a predominance of C3 grasses, while the Pa/P index (palm tree density) indicated the presence of palm trees along both profiles. The ages obtained using 14C-AMS in the Organosol were from 4440/4230 to 2740/2430 years cal BP, and the ages of the sandy material inside the cave were from 1000/920 to 660/550 years cal BP. The phytoliths found inside the cave may be an indication that this material has an allochthonous origin, probably transported by flooding in periods under different hydrogeomorphological conditions, which is one of the hypotheses that will continue to be investigated. The vegetation type remained stable during the analyzed period, being characteristic of rupestrian fields with the presence of trees in more humid environments.