Higgs KE, Clowes CD, Strogen DP, Raine JI. 2022. Rift-related sedimentation patterns and sandstone provenance in the Aotea Basin. Part 1: stratigraphic framework. Lower Hutt (NZ): GNS Science. 55 p. (GNS Science report; 2022/44). doi:10.21420/GTBP-RB45.
Abstract
The main aim of this study is to investigate how the composition and provenance of early basin fill in Aotea Basin changes with respect to Cretaceous rifting. To date, only three wells have been drilled in Aotea Basin, all of which are included in the study (Romney-1, Hoki-1, Tane-1). Two Taranaki Basin wells are also included for comparison with Aotea Basin (Matuku-1, Maui 4). This first report (part 1) addresses Cretaceous stratigraphy and aims to build a stratigraphic framework; the second report (part 2) documents the chemical and mineralogical features with a discussion on source-to-sink composition (Higgs et al., forthcoming 2022). In this study, we have reviewed available biostratigraphy data through the Cretaceous section at the five study wells. Paleoenvironmental interpretations from biostratigraphic analyses are based largely on the abundance of dinoflagellate cysts, which are rare or absent in coastal plain environments, and rare in backshore environments, but abundant in shallow marine environments. These data have been used with conventional wireline log data to provide a broad facies interpretation; only two very short, cored intervals from Tane-1 are available for facies validation. Five main proximal to distal facies associations are defined: coastal plain, marginal marine, upper shoreface, lower shoreface to offshore transition zone, and offshore marine. Diagnostic criteria used in the interpretations include: (1) wireline log motif of stacked facies, (2) relative abundance of coals and (3) relative abundance of marine flora. Where possible, biostratigraphic dating has been assessed using both dinoflagellate and miospore zones. Dinoflagellates have only proven useful in the fully marine strata and are therefore restricted to the latest Cretaceous interval and sporadically through the older Cretaceous section at Romney-1 (the most distal study well). Because of the predominance of marginal marine environments, chronostratigraphic control is therefore mostly based on miospore zonal boundaries. However, given that the miospore zonal boundaries are based solely on the lowest occurrence of a single species, there are significant uncertainties. Boundaries may occur deeper than recorded, particularly where there is low palynomorph recovery and/or poor preservation; additionally, where caving is a problem, boundaries may actually be higher than recorded. (The authors)
