Tectonic compaction shortening in toe region of isolated listric normal fault, North Taranaki Basin, New Zealand

Abstract

Industry 2D and 3D seismic data across the North Taranaki Basin displays two listric normal faults that formed during Pliocene shelf edge clinoform progradation. The faults die out in the downtransport direction with no evidence for contractional structures, except for two small thrust faults in one narrow zone. When active, the detachments lay at depths of about 1000 m below the seafloor. The overlying section had high initial porosities (30-60%). It is estimated that loss of about 17-20% pore volume by lateral compaction, and fluid expulsion over a distance of about 4-6 km in the transport direction occurred in place of folding and thrusting. Seismic and well evidence for abnormally highly compacted shales suggests there is about 6% less porosity than expected for in the prekinematic section, which possibly represents a residual of the porosity anomaly caused by lateral compaction. The observations indicate significant shortening (~20%) by lateral compaction and probably some layer parallel thickening are important deformation mechanisms in near-surface deepwater sediments that needs to be incorporated into shortening estimates and 'balanced' crosssections. A key factor in listric fault initiation near the base of slope is inferred to be transient, increased pore fluid pressure due to lateral expulsion of fluids from beneath the prograding Giant Foresets Formation.

Link between growth faulting and initiation of a mass transport deposit in the northern Taranaki Basin, New Zealand

“…Preliminary observations of the Karewa Fault MTD and its coincidence with the Karewa Fault syn‐kinematic (growth) section led to speculation as to whether the relationship can be explained in two basic scenarios (Morley & Naghadeh, ). In Scenario 1 the MTD was derived from upslope and filled the accommodation space created by faulting.…”

“…). These growth faults, named the Karewa and Mangaa faults, were initiated as a result of lateral compaction and fluid migration due to loading of overlying progradational sequences (Morley & Naghadeh, ). This resulted in loss of shear strength at the base of the progradation front followed by initiation of the growth fault.…”

“…Doust & Omatsola, ; Morley & Guerin, ; Rouby & Cobbold, ; Ajakaiye & Bally, ; Hooper et al ., ; Morley et al ., ; Pochat et al ., ; Back et al ., , , ; Fazli Khani & Back, ). However, the Karewa Fault within the study area shows no evidence of any mobile shale zone and there is no obvious loading trigger for the faulting (Morley & Naghadeh, ). These authors suggested that oceanwards‐driven overpressures were responsible for triggering fault activity.…”

“…Seismic section exhibiting well‐defined progradational sequences of the Giant Foresets Formation ( GFF ) and two main growth faults, the Karewa and Mangaa faults, named by Morley & Naghadeh (). See Fig.…”

“…The growth fault section of the Karewa Fault is occupied by a large‐scale discontinuous unit (MTD). The apparent link between the Karewa growth faulting and a large MTD was first described in Morley & Naghadeh (), they did not, however, investigate the geometry of the MTD in detail as they were focused on the effect of growth fault displacement being transferred into compaction in the hangingwall section.…”