THAILAND BANGKOK A. Kornsawan and C. K. Morley The Origin and Evolution of Complex Transfer Zones (Graben Shifts) in Conjugate Fault Systems Around the Funan Field, Pattani Basin, Gulf of Thailand By

Outlines:  Introduction  Interpretation and results  Cross sections  Structural and Isochron maps  Conjugate fault geometries  Discussion and conclusions

Funan BANGKOK Thailand Malaysia Myanmar Cambodia Location Map

TECTONIC FRAMEWORK OF ‘PATTANI BASIN’

PATTANI BASIN STRATIGRAPHIC SUMMARY PATTANI BASIN STRATIGRAPHIC SUMMARY

Possible Origins of “Graben Shift”  Random features confined to the post-rift section  Related (in some way) to active strike-slip faulting  Related to some kind of passive pre-existing basement fabrics

Pre-Tertiary Seq.1 Seq.2 Seq.3-4 Seq.5 Graben centre West East Graben centre West East Graben centre West East Graben centre East West N

Sequence 1 Isochron Map Time Structural Map

Sequence 2 Isochron Map Time Structural Map

Sequence 3 Time Structural Map Isochron Map

Fault Plane Maps SouthNorth

Fault Displacement Contours

Graph of Fault Dimensions (maximum dip length against strike length)

Evidences 1. Coincidence of Features in Sequence 1  Boundary fault low displacement (linkage) zone  Synthetic transfer zone  Secondary faults stop  Curved fault tips  Graben shift faults appear to be influenced by pattern of Seq. 1  Restricted nature of graben shift faults  Absence of Seq. 1 features 2. Sequence 2 3. Sequence 3 and Younger

Origins of “Graben Shift”  Random features confined to the post-rift section  Related to active strike-slip faulting

Origins of “Graben Shift” Related to some kind of passive pre-existing basement fabrics

What ‘basement features’ might cause this graben shift? Passive strike-slip fault in basement

What ‘basement features’ might cause this graben shift? Basement weakness zone Strong discrete basement fabric

Conclusions 1. Graben shifts trend NE-SW and NW-SE at a high angle to the N-S striking normal faults. 2. Fault displacement diagrams show vertical linkage of two initially separate faults as suggested by two displacement maxima. 3. Graben shift boundaries coincided with fault segment linkage geometries. The minor fault tips tend to curve into boundary line. 4. “Laterally restricted” geometries. 5. No indication of active strike-slip faulting affecting the graben shift geometry. 6. The presence of normal faults deeper in the section exerted an influence on the development of later faults, higher in the section.