Palynofacies Analogues and Applications to Hydrocarbon Exploration in New Zealand

Abstract

Visual kerogen and palynofacies analyses are useful tools for determining the origin, composition and petroleum generative potential of organic-rich sedimentary rocks and the depositional conditions for a wide range of sediments and sedimentary rocks. Firstly, we provide examples of analogues to test existing palynofacies models through comparing quantitative palynofacies and environmental data from sediments deposited over the last 1500 yr. Secondly, we use the palynofacies model to interpret the conditions of deposition for a potential Paleocene source rocks in New Zealand's sedimentary basins, the coeval Tartan and Waipawa Formations. Results from the analogue study show that the distribution of particulate organic matter in environments ranging from near-shore to deep-sea is controlled by the distance from the shore and water depth. Phytoclasts and amorphous matter represent the major components of the total assemblage in coastal and shelfal settings; phytoclasts are rare to absent in the distal, deep-water sediments. In deep-water, palynomorphs consist of a selection of organic material, which could result from transport, sorting or grading. In the Great South Basin, palynofacies analysis of the Tartan Formation (early Late Paleocene) (10% average TOC) indicates that it was deposited in a marginally marine environment with strong influx of terrestrial plants. Analysis of the underlying and overlying units indicates that they were deposited in more distal conditions. The changes observed are best explained by as base-level fall and short-lived regression, including deposition of the Tartan Formation, followed by latest Paleocene–Eocene transgression. To the north, analysis from the Tartan Formation in the Canterbury Basin and the Waipawa Formation in the East Coast Basin shows that they share palynofacies and geochemical characteristics, indicating that a base-level fall also controlled the deposition of the these units in northern basins, although it occurred over a wider range of depositional settings. The extent of the area affected by the base-level fall indicates that it was probably caused by eustasy. Associated studies also show that deposition was accompanied by short-lived but pronounced climatic cooling at ~59 Ma. Implications for hydrocarbon potential are that these units may have a larger and possibly more continuous offshore distribution than previously thought.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015