Abstract

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.

1. KEY POINTS

2. 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.

3. 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.

4. 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.

5. The upper part of T0 seam indicates a warmer, mesothermal climate, and mean annual temperatures generally within the range of 14–16 °C.

摘要

当您从拼图中遗漏了一些碎片时，结果可能很有吸引力，甚至可以理解，但它是不完整的。Gippsland 盆地“Traralgon 地层”的常规地质图包括各种时代、用途和概念，而 Loy Yang 地层的类型剖面从未通过孢粉学确定年代。包含来自 Loy Yang 和 Gippsland 盆地陆上部分其他地方的钻孔的新孢粉学数据提供了更完整的图片，重新解释了煤层的年龄和分布。新数据表明，Latrobe Valley Loy Yang 地区和惠灵顿湖坳陷的 Traralgon 组煤层主要包括最年轻的 T0 煤层，上Nothofagidites asperus带（渐新世早期）年龄。而 Gormandale 向斜和 Seaspray 凹陷的 Traralgon 组煤主要是中下Nothofagidites asperus 的T1 和 T2 煤层区（始新世晚期和中期）年龄。Rosedale Monocline 位于 Latrobe Valley-Lake Wellington 和 Gormandale-Seaspray 洼地之间，充当了扭转始新世-渐新世边界运动的铰链。使用定量孢粉学，检查 T0 煤层的古气候，它跨越始新世“温室”和渐新世“冰屋”之间的过渡。在 T0 煤层下方的 Seaspray 和惠灵顿湖洼地中，是上始新世 Dutson 砂岩段的高达 150 m 厚的回归屏障砂层。回归表明气候转变开始于始新世末期，并持续到较低的 T0 煤层。在最新的始新世 - 最早的渐新世，年平均气温 (MAT) 从 16-17°C 急剧下降到 14-16°C，≤14°C。较低的 T0 煤层包括最早的渐新世（石油冰川事件）的半连续陆地记录，标志着南极洲的第一个重要冰川。T0 煤层的上部表示较温暖的中温气候，MATs 通常在 14-16 °C 的范围内。

1. 关键点

2. 新孢粉学表明，在 Loy Yang、Latrobe Valley 和 Lake Wellington 洼地，最厚的 Traralgon 组煤层具有上Nothofagidites asperus Zone（渐新世早期）时代。

3. 在 Gormandale 向斜和 Seaspray 凹陷，主要煤层为 T1 和 T2，具有中、下Nothofagidites asperus带（晚始新世和中始新世）年龄。

4. 使用定量孢粉学，始新世“温室”和渐新世“冰库”之间的过渡始于始新世 Dutson 砂岩段上部，并继续进入 T0 煤层下部。

5. T0 煤层的上部表示较温暖的中温气候，年平均气温一般在 14-16 °C 范围内。