Characterization of the Rapanui mass-transport deposit and the basal shear zone: Mount Messenger Formation,Taranaki Basin,New Zealand |
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| Authors: | Sebastian Cardona Lesli J Wood Brandon Dugan Zane Jobe Lorna J Strachan |
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| Institution: | 1. Geology and Geological Engineering Department, Colorado School of Mines, 1516 Illinois St., Golden, CO, 80401 USA;2. Geophysics Department, Colorado School of Mines, 1318 Maple St., Bldg. 6, Golden, CO, 80401 USA;3. Earth Science School of Environment, University of Auckland, Private Bag 92019, Auckland, 1142 New Zealand |
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| Abstract: | Submarine mass-transport deposits are important in many ancient and modern basins. Mass-transport deposits can play a significant role in exploration as reservoir, seal or source units. Although seismic data has advanced the knowledge about these deposits, more outcrop studies are needed to better understand gravity mass flows and predict the properties of their resultant deposits. It is proposed that sufficiently well-exposed outcrops of mass-transport deposits can be divided into three strain-dominant morphodomains: headwall, translational and toe. The outcrops of the Rapanui mass-transport deposit, part of the Lower Mount Messenger Formation in the Taranaki Basin, New Zealand, are exposed along a ca 4 km transect in coastal cliffs that enable the identification of the three morphodomains. The aim of this study is to characterize the stratigraphic and sedimentological nature of the Miocene-age Rapanui mass-transport deposit outcrops and the evolution of its basal shear zone. The basal shear zone of a mass-transport deposit is defined as the stratal zone formed in the interface between the overriding mass flow and the underlying in situ deposits or sea floor. Accordingly, the deformation structures in the Rapanui mass-transport deposit and the basal shear zone were documented in an established spatial framework. Traditional methodologies were used to characterize the sedimentology of the Rapanui mass-transport deposit. Data collected from intrafolial folds, rafted blocks and samples from the Rapanui mass-transport deposit were used to investigate strain and matrix texture evolution, estimate palaeoflow direction, and calculate yield strength and overpressure at time of deposition. Additionally, a one-dimensional numerical model was used to test sedimentation-driven overpressure as probable trigger. This work demonstrates that the basal shear zone, as well as the matrix texture of a mass-transport deposit, can vary spatially as sediments from underlying deposits are entrained during shear-derived mixing. This phenomenon can impact the seal potential of mass-transport deposits and their interaction with fluids in the subsurface. |
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| Keywords: | Basal shear zone debrites mass transport deposits overpressure slump Taranaki Basin |
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