Flank Margin Cave Development in Telogenetic
Limestones of New Zealand
John E. Mylroie, Joan R. Mylroie, Campbell S. Nelson - (37/1,2008)
Coastal limestone outcrops, typically with advanced levels of
diagenetic maturity (i.e., are telogenetic carbonates), were examined
on North Island (Raglan Harbour, Kawhia Harbour,
Napier, and Waipu Cove) and South Island (Pohara, Paturau
River, Punakaiki, Kakanui, and Kaikoura), New Zealand, to determine
if flank margin caves, produced by mixing dissolution,
were present. In coastal settings, caves in carbonate rock can be
the outcome of pseudokarst process, primarily wave erosion, as
well as karst processes not associated with fresh and sea-water
mixing such as epikarst features and conduit-flow stream caves.
Flank margin caves were successfully differentiated from other
cave types by the following criteria: phreatic dissolutional morphologies
at the wall rock and chamber scales; absence of high-
velocity, turbulent-flow wall sculpture and sediment deposits;
and lack of integration of adjacent caves into a continuous flow
path. The active tectonics of New Zealand creates a variable sea-
level situation. The relatively short time of sea-level stability limits
the size of the New Zealand flank margin caves compared to
tectonically-stable environments, such as the Bahamas, where
glacioeustasy alone controls sea-level stability. Uplift events can
be identified as slow and steady when the flank margin caves
are uniformly elongated in the vertical direction, and episodic
when the flank margin caves show widening and tube development
at discrete horizons that cut across rock structure. New
Zealand flank margin caves contain information on uplift duration
and rates independent of other commonly used measures,
and therefore can provide a calibration to other methods.
Download pdf