Paleoenvironmental and stratigraphic significance of palynomorphs from Upper Eocene (Kaiatan) Beaumont Coal Measures and Orauea Mudstone, Waiau Basin, western Southland, New Zealand

Abstract

Studies of palynomorphs from three surface sections through the Upper Eocene Beaumont Coal Measures and Orauea Mudstone in the Waiau Basin, western Southland, together with sedimentological investigations, allow determination of the distribution of plant communities in relation to sedimentary environment Palynofloras from both formations are dominated by the southern beech, Nothofagus, particularly species representing the brassii group (Nothofagidites matauraensis). Fusca group (Nothofagidites flemingii) is also common, as are Casuarina, Myrtaceae, gymnosperms, and pteridophytes. Within the Beaumont Coal Measures and Orauea Mudstone three fades associations are recognised. The Beaumont Coal Measures and Orauea Mudstone were deposited in fluvio-deltaic and lacustrine environments, respectively. Deposition of the Orauea Mudstone in a lacustrine setting is confirmed by the presence of freshwater algae. Palynofloras from a fluvial channel-floodplain facies within the Beaumont Coal Measures have a high percentage of herbaceous angiosperms and pteridophytes, indicative of a low-statured swamp plant community. Levees during this phase of deposition supporteda shrub flora comprising members of the Myrtaceae, Proteaceae, Loranthaceae, and Casuarinaceae. A deltaic-lacustrine facies association within the Beaumont Coal Measures and lacustrine-delta front facies within the Beaumont Coal Measures and Orauea Mudstone are characterised by low percentages of local herbaceous taxa and correspondingly high percentages of palynomorphs derived from the regional rainforest community (e.g., Nothofagus). Locally, Cyatheaceae colonised emergent areas in the deltaic environment.

The Beaumont Coal Measures and Orauea Mudstone in the Waiau Basin are of Kaiatan (Late Eocene) age, based on comparison of these palynofloras with well-documented palynofloras from other regions of South Island, New Zealand.

Keywords:

• Beaumont Coal Measures
• Orauea Mudstone
• Kaiatan
• Late Eocene
• Waiau Basin
• Southland
• palynofloras
• fluvio-deltaic
• lacustrine
• plant communities
• Nothofagus