Ordovician rocks are prominent in Wales, where they were first studied by early British geologists. The Ordovician extended from 500 to 420 MYA. The Ordovician period is prominent for the widespread deposition of sediments and emplacement of granites in the Glenelg Basement Sequence. Ordovician marine sandstone and Ordovician marine siltstone are found near Ballarat. Shale, mudstone, and quartz-rich sandstones and turbidites are the common rock types. These sediments have generally been deposited in a deep marine environment and have subsequently been deformed and faulted. Older Ordovician rocks are typically covered by younger sedimentary rocks, granite intrusions and volcanic formations, and although they form a significant part of the local landscape they are not generally visible.
The railway cutting you are travelling through exposes a section of Ordovician sandstone. The weathered rock is pastel shades of tan, yellow and light grey. Part of the exposed section is covered with a dark brown surface patina. Closer inspection will reveal book leaf weathering of the interbedded sandstone. The book leaf weathering indicates the direction of folding of the original horizontal sediment.
You are welcome to log a "Found it" log when you message or email the answers for the following questions. any "Found it" logs without the answers being sent will be deleted.
Q1 What is the angle of the book leaf weathering? What does this angle indicate has happened to the rock?
Q2 What do you think has formed the dark surface patina? Do you think the patina is growing or shrinking?
Q3 Are you enjoying your walk/bike ride along the BSRT?