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Champion; geological and structural setting

The Champion structure is a large anticline in Late Miocene to Early Pliocene sediments. The early structural development appears to be dominated by a rollover anticline, downthrown from a regional, down-to-basin (i.e. northwest hading) growth fault system, with a series of syn-depositional collapse grabens developed over its crestal area. The crestal collapse faults cut progressively younger stratigraphic levels in an easterly direction, related to the crest of the rollover anticline shifting towards the footwall of the controlling growth fault system (Figures 5.52 and 3.7).

In vertical section the central part of the growth fault system shows a flexure, with relatively steep upper and lower ramps connected by long, low-angle to nearly horizontal flats. These are the Champion top- and base Sliver faults, enclosing the Sliver block, with an easterly dipping stratigraphic succession (Figure 5.52). This flexure in the growth fault system is difficult to understand, but could relate to a very rapid fall of the highly mobile Setap clay mass in its footwall, resulting in very rapid backstepping of the growth fault activity eastward. The fall of the underlying clay diapir could relate to a deficit in mobile clay, or out-of-plane, lateral squeeze of the clay, due to wrench movements in the underlying, relative basement.

Later growth of the Champion anticline was partly controlled by transpressional deformation, possibly modified by further movements in the underlying clay mass. Major unconformities occurring at relatively shallow levels (the K- and L-unconformities), probably mark two main pulses in this additional transpressional uplift. Major shifts in regional dips are recognised across these main unconformities, and across several less well developed erosional surfaces and hiati in the crestal collapse area. These observations may indicate the recurrent, pulsing nature of deep-seated deformation, superimposed on the more continuous deformation driven by depositional loading. Considerable thickening of the stratigraphic succession in southeasterly direction accompanied the accumulation of throw on the controlling growth fault system and the related differential subsidence in the crestal collapse area.

The crestal collapse, over the early rollover, as well as over the superimposed transpressional anticline, has created complex antithetic / synthetic fault patterns. The interfering fault trends have resulted in numerous elongate fault blocks. A rather diffuse array of northerly trending faults and disturbances, which cut the collapse fault pattern at an acute angle, may relate to the influence of a small wrench component, transmitted to the levels of the shallow crestal collapse. In downward direction, the crestal collapse faults cancel each other and below 2,700 metres subsea, only a small, relatively unfaulted anticline remains defining the Peragam structure (see Figure 5.52).

To the northwest of the main anticline, the deeper, early crestal collapse graben defines the Champion West structure. The plane of symmetry between the synthetic and antithetic faults is dipping to the southeast, which points to post-depositional reclining of this early structure in the flank of the later Champion anticline.

The stacked accumulations in the Champion Southeast area, to the southeast of the Champion Main field, are largely controlled by numerous southeasterly dipping faults, belonging to the latest generation of crestal collapse. Most of the faults are antithetic into the main down-to-basin growth fault system (Figure 5.52).

The Peragam structure is a relatively unfaulted, periclinal structure directly below the Champion main and Champion West fields. Its eastern boundary is formed by the downdip part of the Sliver fault zone (Figure 5.51, 5.52, Figure 5.54)

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