NICK.BROOK@cluthaleader.co.nz
A massive wash›up of submarine coal is due to natural erosion, a local expert says.
Clutha Leader was contacted last Thursday by two members of the Balclutha Walking Group who had come across slabs of fossil fuel — ‘‘some the size of tables’’ — during a long walk on the beach below Wangaloa domain three days earlier.
Coal fragments can often be picked up on Kaitangata beaches, but the recent lode is unusual.
‘‘I’ve never seen anything like it on these beaches in 70 years,’’ former top›dressing pilot David Renton said.
Retired farmer Neville King agreed and said the dark flotsam was scattered along the sand for several kilometres north and south.
Local mining engineer, geologist and general manager of Kaitangata’s Kai Point Coal Chris O’Leary said Frederick Tuckett ‘‘discovered the same thing in the same place in 1844’’.
‘‘We know a large outcropping of the seam extends out to sea like a reef and likely there’s been some natural erosion with strong easterly currents and a large piece has broken off and fragmented.’’
He explained the grams per cubic›centimetre (g/cc) scale for density, where water is the baseline at 1g/cc, and gold comes in at 19.3g/cc.
‘‘The density of quartz inthe sand and pebbles is about 2.65g/cc, but coal is only up to around 1.25g/cc, so it doesn’t float but the water can shift it around relatively easily, which is why it’s smooth and rounded.
‘‘Strong tides and waves will roll it right up on to the beaches in a similar way to driftwood logs,’’ MrO’Leary said.
A 2km thick mudstone shelf compressed the interlayered Kaitangata coal seams against a floor of quartz pebble conglomerate during the cretaceous and paleocene periods.
Among the evidence for this were round quartz stones encased in the coal from the gizzards of dinosaurs who lived at least 65 million years ago.
