The T0 coal seam in the Latrobe Valley: a revised age and implications to Traralgon Formation stratigraphy
When you are missing pieces from the jigsaw, the result may be attractive and even comprehensible, but it is incomplete. The conventional geological picture of the ‘Traralgon Formation’ in the Gippsland Basin includes a variety of ages, uses and concepts, and the formation’s type section at Loy Yang has never been dated by palynology. The inclusion of new palynological data from bores at Loy Yang and elsewhere in the onshore part of the Gippsland Basin presents a more complete picture that reinterprets the age and distribution of the coal seams. The new data indicate that the Traralgon Formation coal seams in the Loy Yang area of the Latrobe Valley and the Lake Wellington Depression mostly comprise the youngest T0 coal seams, with Upper Nothofagidites asperus Zone (early Oligocene) ages. The Traralgon Formation coals in the Gormandale Syncline and Seaspray Depression, however, are mainly T1 and T2 coal seams of Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages. The Rosedale Monocline, situated between the Latrobe Valley–Lake Wellington and Gormandale–Seaspray depressions, acted as a hinge that reversed movements at the Eocene–Oligocene boundary. Using quantitative palynology, the paleoclimates of the T0 seam are examined where it straddles the transition between the Eocene ‘greenhouse’ and the Oligocene ‘icehouse’. In the Seaspray and Lake Wellington depressions below the T0 coal is an up to 150 m-thick regressive barrier sand of the upper Eocene Dutson Sand Member. The regression indicates that the climate transition began before end-Eocene and continued into the lower T0 coal. Mean annual temperatures (MATs) fell sharply from 16–17 °C to 14–16 °C to be ≤14 °C in the latest Eocene–earliest Oligocene. The lower T0 coal seams comprise a semi-continuous terrestrial record through the earliest Oligocene (the Oil glaciation event), marking the first significant glaciations in Antarctica. The upper part of T0 seam indicates a warmer, mesothermal climate, and MATs generally within the range of 14–16 °C.KEY POINTS
New palynology indicates that in the Loy Yang, Latrobe Valley, and the Lake Wellington depressions, the thickest Traralgon Formation coal seams have an Upper Nothofagidites asperus Zone (early Oligocene) age.
In the Gormandale Syncline and Seaspray Depression the major coal seams are T1 and T2 with Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages.
Using quantitative palynology the transition between the Eocene ‘greenhouse’ and the Oligocene ‘icehouse’ began in the upper Eocene Dutson Sand Member and continued into the lower T0 coal.
The upper part of T0 seam indicates a warmer, mesothermal climate, and mean annual temperatures generally within the range of 14–16 °C.
New palynology indicates that in the Loy Yang, Latrobe Valley, and the Lake Wellington depressions, the thickest Traralgon Formation coal seams have an Upper Nothofagidites asperus Zone (early Oligocene) age.
In the Gormandale Syncline and Seaspray Depression the major coal seams are T1 and T2 with Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages.
Using quantitative palynology the transition between the Eocene ‘greenhouse’ and the Oligocene ‘icehouse’ began in the upper Eocene Dutson Sand Member and continued into the lower T0 coal.
The upper part of T0 seam indicates a warmer, mesothermal climate, and mean annual temperatures generally within the range of 14–16 °C.
