Within its deepest part in the Nakdong Trough, the Gyeongsang Basin sequence attains a maximum thickness of about 9000m. In general, the sequence mainly strikes north-northeast to north-south, dipping gently-moderately to the southeast. It is an extensional basin characterized by an interconnected set of listric extensional faults and associated transfer faults. These faults extend into the basement and are in part formed by the reactivation of basement structures, which were the locus of magmatic activity both in the basin and the basement to the west. The Gyeongsang Basin can be subdivided into 3 distinct tectono-sedimentary cycles/episodes of tectonism, sedimentation and associated igneous volcanism and intrusive activity, including:

Cycle 1

During Cycle 1, the Gyeongsang Basin developed initially as an intra-arc basin with deposition of a non-marine sequence comprising the basal Early Cretaceous continental “red bed” Sindong Group into the Nakdong Trough. The sedimentary environments evolved from alluvial fan through floodplain to lacustrine and were deposited under arid climatic conditions.

Cycle 2

During Cycle 2 in the Middle Cretaceous, scattered andesitic and basaltic-andesitic volcanic centres formed, resulting in deposition of the volcano-sedimentary Hayang Group under prevailing semi-arid climatic conditions.

Cycle 3

The basin then evolved rapidly during Cycle 3 into a mature volcanic arc during the Late Cretaceous, with extrusion of alternating lava flows and pyroclastics of the volcanic-dominated Yuchon Group. The composition of the volcanic rocks changed from intermediate to late acid volcanism.

Emplacement of stocks and batholiths of the Bulgugsa Series was essentially co-magmatic with Cycle 3. The composition of the volcanic and igneous rocks changed from initial intermediate to late-stage acid intrusions. The wide variety of igneous rocks indicates a multi-phase, highly fractionated and evolved intrusive magma underlies the basin.