巴西圣弗朗西斯科克拉通（S?o Francisco Craton）南部伊雷塞盆地（Irecê Basin）中，存在深成洞穴形成机制与浅层硫酸环境下的迷宫状洞穴形成过程

《Geomorphology》：Deep-seated cave inception and shallow sulfuric acid maze cave genesis in Southern Irecê Basin, S?o Francisco Craton (Brazil)

巴西伊雷塞盆地Ioi?迷宫洞穴形成于多阶段过程：早期深部热液流体导致鬼岩和石英 vein，晚期浅层硫酸酸化引发CO?气化，形成近地表碳酸盐岩层。研究揭示了深部构造（如卡斯特岩层、Brasiliano期构造活动）与表层水循环共同作用机制，为热带地区深层洞穴形成提供新证据。

　　
Ioi? Cave System: A Multiphase Speleogenetic Case Study in the Irecê Basin, Brazil

1. Study Overview
The Ioi? Cave System, located in the southern tip of the Irecê Basin (Bahía, Brazil), presents a unique combination of hypogene and epigenic speleogenesis processes. This 4.7-kilometer maze cave, still actively forming, preserves rare primary hypogene features largely unaffected by surface runoff processes that modify most caves in the region. The research team, including geologists and speleologists from University Cote d'Azur and Polytech'Lab, documents this cave's exceptional value for understanding multiphase karstification.

2. Geological Context
The study area belongs to the Neoproterozoic carbonates of the Salitre Formation, overlain by Mesoproterozoic clastics. Tectonic history is critical:
- Ediacaran period (670-600 Ma): Regional fracturing and deformation
- Brasiliano orogeny (Lower Cambrian): Major hydrothermal activity
- Plio-Quaternary exhumation: Current surface processes affecting caves

The Irecê Basin's structural complexity includes strike-slip faults, anticline hinges, and fracture corridors that control fluid pathways. These features, analyzed through field structural geology and petrography, reveal the subsurface conditions necessary for hypogene speleogenesis.

3. Speleogenetic Phases
3.1 Deep Hydrothermal Phase (Neoproterozoic-Cambrian)
- Sulfide-rich hydrothermal fluids ascend through fractured carbonates
- Creates ghost-rock (metasomatized carbonates) along faults and anticlines
- Silicification via quartz/dolomite veins suggests silica-rich fluids
- Possible CO? degassing from carbonate decarbonation

3.2 Shallow SAS Phase (Plio-Quaternary)
- Pyrite oxidation in shallow aquifers generates H?SO?
- CO? degassing creates carbonic dissolution
- Develops maze networks through horizontal fluid diffusion
- Supersaturation leads to calcite shelves with bubble trails

3.3 Epigenic Superimposition
- Surface runoff from quartzite hills since Plio-Quaternary
- Sulfuric acid speleogenesis affected by meteoric water
- Biogenic modifications (bat activity, evaporation) in recent phases

4. Structural Controls
4.1 Primary Fractures
- NNW-SSE and NW-SE sets form natural channels
- Strike-slip components facilitate fluid migration
- Oblique orientation relative to cave passages

4.2 Tectonic Evolution
- Ediacaran fracturing created initial permeability
- Brasiliano orogeny enhanced structural complexity
- Pangea breakup (Jurassic-Cretaceous) influenced fluid chemistry

5. Methodological Approach
5.1 Field Studies
- High-resolution structural mapping (Fig. 6)
- Petrography of speleothems and wall deposits
- Isotopic analysis (1?O, 13C) of carbonates

5.2 Laboratory Analysis
- Stable isotope measurements
- Evaporative calcite verification
- Electric conductivity monitoring in water bodies

5.3 Comparative Analysis
- Contrasts with Toca da Boa Vista (综合机制)
- Differs from Cristal Cave (纯上升流体)
- Similar to Calixto Cave (混合沉积岩系)

6. Key Findings
6.1 Multiphase Development
- Early hypogene phase (deep fluid alteration)
- Middle SAS phase (shallow sulfide oxidation)
- Late epigenic modification (surface runoff and biological activity)

6.2 chronological Markers
- Ghost-rock alteration dates to Brasiliano orogeny (~510 Ma)
- Carbonic speleothems show Plio-Quaternary activity
- Epigenic features postdate洞穴 formation

6.3 Fluid Pathways
- Upward migration along buried faults
- Fracture corridors facilitate gas transport
- Shallow aquifer interaction with CO? degassing

7. Scientific Implications
7.1 Tectonic-Hydrologic Linkages
- Provides timeline for regional tectono-thermal activity
- Clarifies fluid migration pathways in fractured systems

7.2 Karst Evolution
- Demonstrates transition from deep hypogene to shallow SAS
- Shows interaction between magmatic hydrology and biogenic processes

7.3 Carbonate Reservoir Management
- Case study for understanding fluid migration in karst reservoirs
- Potential analog for CO? degassing processes in other caves

8. Technological Applications
- Improved 3D mapping of karst systems
- New methodologies for structural analysis in speleology
- Insights for hydrocarbon exploration in fractured carbonates

9. Future Research Directions
- Radiometric dating of speleothems to establish precise timelines
- 3D fluid simulation models for karst systems
- Comparative studies with similar hypogene caves worldwide

This research significantly advances karstology by demonstrating:
1) Primary hypogene structures preserved under minimal epigenic influence
2) Sequential interaction between deep hydrothermal systems and shallow SAS processes
3) Importance of structural controls in cave formation timing and morphology

The findings challenge previous assumptions about hypogene cave preservation in tropical basins, providing a model for cave documentation in active tectonic regions. The integration of structural geology, petrography, and speleothem analysis offers a comprehensive framework for multiphase karst studies.