Provenance changes and glauconite formation in the Broken River to Iron Creek/Waipara Greensand Formations marks the late Cretaceous-Eocene transgression. (2005)
AuthorsKapoutsos, Davidshow all
Detailed provenance analysis and glauconite morphology of the Broken River and Iron CreeklWaipara Formations and other correlatives were conducted at 6 localities: the MandamusDove River area, Waipara River, Avoca-Iron Creek, Castle Hill Basin, Malvern and Mt Somers. The basal Broken River Formation is a fluvial boulder conglomerate interbedded with sandstones, mudstones and coal dated as Haumurian (Late Cretaceous) by pollen. The transgression is marked by a gradual drowning of the fluvial conglomerates with minor glauconite appearing in the beds immediately overlying the conglomerates in alllocali ties. The estuarine-marginal marine I lower shoreface succession of the Broken River Formation contains minor nascent micaceous glauconite. This increases in the overlying Iron Creek I Waipara Formations to 30-60% glauconite composed of nascent-micaceous to evolved/mature glauconity types characteristic oflower shoreface I foreshore to shallow shelf depositional setting. Up section, evolved mature glaucony dominates, in some beds formed in situ (autochthonous) and in other beds transported from nearby (parautochthonous) to line foresets. An extremely low sedimentation rate is necessary to form the evolved I mature type of glauconite. The age of the greensands is Teurian to Whaingaroan (Late Paleocene-Late Eocene). Overall the glauconite analysis indicates extremely low sedimentation rates with autochthonous I parautochthonous glaucony formation in nearshore marine settings, possibly even estuary environments. Clast counts from the basal conglomerates indicate derivation from local sources such as the underlying Torlesse greywackes (Pahau and Rakaia Terranes) and/or the Mandamus Igneous Complex. Sandstone composition indicates the addition of more distal sources. Quartzose sandstones plot in the interior craton province in QFL plots for both Broken River and Iron Creek/Waipara Greensand Formations. Sandstone lithics are probably derived from the underlying Torlesse greywacke. Alkali feldspar dominates over plagioclase indicating a probable plutonic felsic source. SEM-cathodoluminescence on quartz grains indicates a bimodal metamorphic to plutonic quartz grains with minor volcanic input. Plutonic grains are identified by healed microcracks, and are possibly derived from Western Province plutonic suites such as the Karamea and Separation Point Batholiths. Polycrystalline/dark CL quartz grains indicate a relatively high grade metamorphic source such as the OtagolHaast Schist while dark CL monocrystalline quartz grains indicate a low to medium metamorphic grade source such as the Alpine Schist. Volcanic quartz is zoned with straight extinction and was most likely derived from the Cretaceous Mount Somers Volcanics Group. Overall the provenance suggests local derivation of sediments when coarse fluvial deposition occurred followed by more distal derivation once transported in the nearshore marine setting.