Stratigraphy, Architecture, and Kinematics of a Seismic-Scale Mass-Transport Deposit, North Taranaki Coast, New Zealand

Detailed outcrop study is used to characterize the stratigraphy, structure, and kinematics of a seismic-scale mass-transport deposit (MTD). The informally-named “North Awakino MTD” outcrops for approximately twelve kilometers along the northern Taranaki coast of New Zealand. The scale and quality of these exposures, in both cliffs up to eighty meters high and wave-cut platforms, offer a unique opportunity to study the internal structure, deformational character, and kinematics of a large MTD. In addition, this MTD or its stratigraphic equivalents are imaged in a grid of 2D seismic-reflection lines just kilometers offshore of the study area. This dataset allows integration of outcrop- and seismic-scales of observation and provides important constraint on the character of mass-wasting in the northeastern Taranaki basin.

Considerable lithologic and structural heterogeneity have been identified within the North Awakino MTD. The northern portion of the study area is dominated by thick- to medium-bedded volcaniclastic sandstone and mudstone, whereas the southern portion of the study area is characterized by thin-bedded volcaniclastic sandstone and mudstone. The North Awakino MTD preserves spectacular examples of folds with amplitudes that approach the scale of the outcrop (i.e., 10’s of meters). Pre-lithification faults (normal and reverse) are also commonly observed in the North Awakino MTD with typical displacements of centimeters to several meters. The northern three kilometers of the study area is characterized by a surprisingly coherent style of deformation with approximately 40 meters of stratigraphy repeatedly deformed in a series of recumbent, isoclinal folds often accompanied by detachment of their cores along thin, fine-grained intervals. Preliminary kinematic analysis suggests that the MTD transport direction is not consistent along the outcrop extent but locally varies by up to ninety degrees. Future work will focus on continued outcrop characterization, kinematic analysis, forward-seismic modeling, and integration of outcrop and seismic-reflection datasets.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California