Tasman Sea to the Alstonville Plateau
Following the
Cretaceous during the Paleogene and possibly as a result of the action of the
Tasman Sea formation, volcanic systems began to form throughout parts of
eastern Australia. In the New England, the Hunter and Sydney areas swiftly flowing lavas
erupted from long vents and covered large areas with basalt. The same
thing happened in our region and until now it is one of the relatively unknown
parts of our history. At around 43Ma during the Eocene
Epoch basalt lava flowed from vents somewhere in the area now known as the
Alstonville Plateau (The area between Lismore to Lennox Head). The lava flow
(called the Alstonville Basalt) tended to flow towards the North and West
because the hills of the Blackhall Range formed a barrier to the South. The old
Wilsons River seems to have been deflected from its southerly course and sent
inland to join the Richmond River as lava flows dammed off the rivers original
course. Small lakes were formed where the lava flows dammed streams and created
little areas of sedimentary rock known as diatomite and even poor quality opal.
It is interesting to note that during the 20th century diatomite was
even been mined for use as a filter medium from layers between basalt at
Tintenbar and Wyrallah.
Layers of diatomite
were subsequently covered by new layers of lava and during the time between
lava flows rich red soils developed and were subsequently covered by new lava. The
rate of soil formation was high during this time because the world climate was
the warmest (more than 10 degrees C hotter than the average today) it had been
for 400 million years and be when combined with atmospheric moisture this time
was known as the Mid-Eocene Climate Optimum. The lava covered soils (known as
paleosols) are important today because they are conduits for groundwater (aquifers)
which create long lasting springs resulting continually running streams and
ecosystems dependent upon them. The aquifers are also drilled into for
groundwater for some of the livestock, irrigation and town water supply on the
Alstonville Plateau today. Eventually, the eruptions stopped and lovely fertile
deep red soils developed and continue to develop today.
