Milburn is locally famous for its limeworks. Many thousands of tonnes of crushed limestone are trucked out of the hills separating the Tokomairiro Plain and Lake Waihola annually to be used in fertilizers.
A large whale fossil is on display at the lookout near GZ over looking the limeworks, Tokomairiro Plains and Lake Waihola.
Be careful when turning off SH1 on to the local roads to GZ as the Quarry trucks uses these roads with regular frequency.
Milburn was named after Morris Milburn, who came to New Zealand from Sunderland, North East of England in The United Kingdom in 1858. He arrived at Lyttleton harbour aboard The Zealandia. He journeyed overland to Dunedin doing the greater part of the trip by foot. In Otago he followed the goldfields with varying fortune incidental to a miners life. Working successfully at Gabriel's Gully at Molyneux and at Milburn, the last mentioned place being named after him.
Quarries give us a geological window into the past as they cut through the layers of material which also represent moments in time.
Rocks are grouped according to their mode of origin. The classical grouping of rocks is into three groups – Sedimentary, Metamorphic and Igneous. This Earth Cache deals with a type of Sedimentary Rock being Limestone. Much of Otago is covered in Schist which is a Metamorphic Rock while there are many good examples of Igneous Rocks around Dunedin. Both these rock types are already represented by other earth caches in the Otago. South-east Otago is low rolling country with elongated north-west – south east fold ridges of Upper Paleozoic and Mesozoic sedimentaries. Limestone is one of these sedimentaries which gives this spot its unique features.
The limestone in this area is relatively geologically young (refer the information board at GZ) while the oldest Limestones in the world are over 400 million years old. Limestone along with shale (another fine grain sedimentary rock), is one of the best preservers of fossils (Sandstone is not so good due to its coarser grains). Over time, sedimentary rock presses down around what were once living things to preserve the basic outline of their appearance and physical characteristics. Limestone is mostly formed from calcite. Calcite is a form of Calcium Carbonate, which has the chemical formula CaCO3. Calcium Carbonate is removed from seawater by the animals as they grow. When the animals die, their skeletons accumulate on the sea floor and are later turned to rock by a process known as lithification.
Lithification is the process that turns sediment into rock. The first stage of the process is compaction. Compaction occurs as the weight of the overlying material increases. Compaction forces the grains closer together, reducing pore space and eliminating some of the contained water. Some of this water may carry mineral components in solution, and these constituents may later precipitate as new minerals in the pore spaces. This causes cementation, which will then start to bind the individual particles together.. New Zealand was once largely under the oceans but as inland seas receded these limestone deposits, many containing shellfish, dolphins, and whales from the period, were left behind, as is the case at this site.
Fossilisation occurs in a number of different ways:
Unaltered Remains
– Soft parts - mummies, frozen in ice, buried in bogs,, preserved in amber
- Hard parts - original bones, teeth, shells
Altered Remains
– May happen to soft or hard parts
– Replacement - change from original chemical makeup to something different
– Recrystallization - transformation of original crystalline structure to a new form, preserving shape
– Compression - flattening of fossil due to weight of overlying sediments
- Carbonization - remains converted to a carbon film or residue by heat/pressure of burial
– Molds and Casts - impression in sediment of a body or skeleton. All of the original parts are dissolved away, leaving only the impression
(Molds - direct impression of an organism, appear as a mirror image in the rock surface)
(Casts - later fillings of molds with additional sediment, creates a duplicate of the original organism’s outward form)
Logging Requirements:
Email the answers to me (which can be obtained from the information at GZ).
1. During what period (name and age) did the limestone form?
2. What part is the largest part of the fossilised on display and how big is it?
3. Explain why this limestone is Important for Fossil records?
OPTIONAL: Take a picture of yourself or GPSr looking toward Lake Waihola