Local geological sections and regional stratigraphy based on physical geology and chemical stratigraphy of the Serra Geral Group from Araraquara to Avaré, SP

ABSTRACT: From Araraquara to Avaré, in the Serra Geral Group outcropping area, 22 detailed geological sections were elaborated. The stratigraphic relationships and the chemical analysis allowed the identification of seven [P2O5] basalt classes, all of them pertaining to the Pitanga type, showing a consistent stacking order across the studied region. Thus, each class is considered to correspond to a specific lava flow, allowing a general stratigraphic column to be proposed. Besides the stacking order, the validation of P2O5 as a tool for lava correlation at great distances was also based on the values obtained from samples collected at different positions in a single flow, and on the remarkable [P2O5] contrast between adjacent flows. Minimum lateral extensions range from 75 to 185 km, and thickness from 20 to 80 m. Vertical tectonic displacements, which took place in different periods, were inferred from the altitude of specific flows, and also from the Botucatu and Piramboia formations. They are noticeable in a region bounded by EW drainage lineaments, which contains a large area where Piramboia and Botucatu formations crop out, probably due to the tectonic activity causing this region to be a generalized structural high.

摘要：在Serra Geral群（Serra Geral Group）出露区域内，从阿拉拉夸拉（Araraquara）至阿瓦雷（Avaré）一带，共编制了22条详细地质剖面。通过地层接触关系与化学分析，共识别出7类以五氧化二磷（P₂O₅）为判别指标的玄武岩，全部隶属于皮唐加型（Pitanga type），且在研究区内呈现出统一的叠置序列。据此可认为每一类玄武岩对应一期特定的熔岩流，由此可构建研究区的综合地层柱。

除叠置序列外，五氧化二磷（P₂O₅）作为远距离熔岩流对比工具的有效性，还得到了两方面数据的验证：一是单期熔岩流内不同采样点位的五氧化二磷含量数据，二是相邻熔岩流间显著的五氧化二磷含量差异。单期熔岩流的最小横向延展规模为75至185千米，厚度介于20至80米之间。

研究人员通过特定熔岩流的海拔高度，以及博图卡图组（Botucatu Formation）与皮兰博亚组（Piramboia Formation）的产出特征，推断出研究区经历了多期垂直构造位移。该类构造位移在东西向水系线性构造所围限的区域内尤为显著，该区域内分布有大面积博图卡图组与皮兰博亚组的出露区，其成因大概率为构造活动使该区域整体抬升为构造高地。