Field, B.D. 2015 Outcrop analogues for methane hydrate habitats, East Coast, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2015/37. 47 p. doi:10.21420/G2C93R.
Abstract: Modern methane hydrates occur in the offshore part of the Hikurangi margin, and this report outlines some potential outcrop analogues for them. Outcrop analogues are present for: methane conduits (as concretions); methane vents (as bioherms); sandstone reservoirs of various deepwater facies; and as fine-grained “reservoir” units. Analogues covering a wide range of ages are present, though this report focuses more on Neogene examples — the range in ages provides a range of burial depths and hence burial compaction and diagenesis to match the most likely offshore hydrate settings. Potential analogues are described for slope channel units, levee-overbank deposits, canyon and channel units, fan complexes and turbidite lobes, ponded turbidites, fine-grained units, tuffaceous units and fractured units. There are many more potential analogues that have not been described in this report; only some of the main, well-known analogues are mentioned. Many faults and some structural zones that are complexly deformed and fractured are also available for study, as potential analogues for hydrate habitats and fluid migration during hydrate dissociation. There is little rock property data available specifically for hydrate habitats in New Zealand, but the mercury capillary injection data available for some East Coast outcrops provides insights into pore diameters, ranging from 0.02 µm to about 1 µm; this range suggests sediments will likely offer a range of hydrate habitats in the offshore. Further work should include tabulation of parameters for the habitats of modern hydrates on the Hikurangi margin, and detailed studies of specific, high-priority analogues in outcrop. (auth)