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

• Published in: Journal of South American earth sciences Vol. 133; p. 104658
• Main Authors: Ferreira Chueng, Karina, Gomes Coe, Heloisa Helena, Vasconcelos, Alessandra Mendes Carvalho, Rodet, Joel, Battilani, Gislaine Amorés, Machado, David Oldack Barcelos Ferreira, Ricardo, Sarah Domingues Fricks
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2024
• Subjects: Brazil; Monte Cristo cave; Paleobiogeoclimatic reconstruction; Silica biomineralization; Brazil; Paleobiogeoclimatic reconstruction; Silica biomineralization; Monte Cristo cave
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2023.104658

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. •The phytoliths found inside the cave indicate that this material is of allochthonous origin.•The Monte Cristo cave can be understood as 2 different formation systems, one being formed before the other, which were later connected by lateral openings due to the capture of water through lowering of the base level. The phytoliths would therefore bring answers from the cave's own dynamics.•It was possible to observe evolution phases in the Monte Cristo cave and its surroundings between 4440 and 4230 years cal BP and 2740 to 2430 years cal BP (exterior profile samples) and between 1000–920 years cal BP and 660 to 550 years cal BP (samples from inside the Cave).•There was no major change in the vegetation during the studied period (from 4440–550 years cal BP), which has always been rupestrian fields. The indices show an increase in temperature in the last 2740 years cal BP and favorable conditions for the evolution of the cave.