DEVONIAN-CARBONIFEROUS STRATIGRAPHY OF THE SOUTHERN HASTINGS BLOCK, NEW-ENGLAND OROGEN, EASTERN AUSTRALIA

Devonian and Carboniferous rocks within the Hastings Block represent a n are-related basin fill located, out of place, on the outboard margin of the subduction complex and juxtaposed along strike from the fore-a re basin of the southern New England Orogen. The stratigraphic sequenc e, structural style and history of rocks in the southern part of the H astings Block differs from that in the northern part of the block. The stratigraphy of the southern part of the Hastings Block consists of a succession of nine formations (eight new) ranging in age from Late De vonian (Frasnian) to Late Carboniferous (Namurian). A further five for mations (three new) ranging in age from Siluro-Devonian to Late Devoni an (Famennian) are confined to fault-bounded blocks. Three of the latt er are probably correlative with parts of the continuous Frasnian-Namu rian succession. The Port Macquarie Block is considered part of the so uthern Hastings Block because it contains two closely comparable forma tions. Late Devonian formations include the sequential Bitter Ground V olcanics, Birdwood Formation (both Frasnian in age) and the interdigit ating Rollans Road/Cowangara Formations (Famennian-earliest Tournaisia n), together with the fault-bounded Ellenborough Volcanics, a probable equivalent to the Birdwood Formation, and the Famennian Wallibree For mation and the undated and possibly equivalent Touchwood Formation. Th ese are characterized by the association of basaltic to andesitic volc anics with deep-water turbidites and radiolarian-bearing sedimentary r ocks. Whilst there is an overall similarity with coeval units within t he Tamworth Belt of the southern New England Orogen, no detailed litho logical correlations are possible between correlative formations in th e two areas. The Early Carboniferous Kindee Conglomerate, Nevann Silts tone, Pappinbarra Formation and Hyndmans Creek Formation, alternating proximal to distal deep-water turbidites with minor ash-fall tuffs, ha ve an andesitic provenance similar to that of the northern part of the Hastings Block but different from equivalent parts of the Tamworth Be lt, which changed from andesitic to dominantly dacitic provenance at t he Devonian-Carboniferous boundary. Following a possible hiatus, and a change to a dacitic provenance, the Mingaletta Formation (Namurian) w as deposited in shallow marine to continental environments; it is clos ely comparable lithologically and faunally to equivalent units in the northern Hastings Block and Myall Block of the Tamworth Belt. Differen ces between the northern and southern parts of the Hastings Block are explained by variations in location within the same sedimentary basin. Comparison with the Tamworth Belt suggests that whilst sequences in t he two areas were deposited in are-related settings, conditions of dep osition and the nature and timing of geological processes, particularl y the composition of volcanics and processes of shallowing upwards, va ried between the two regions until the Namurian. This suggests possibl e separation of the two regions prior to the Namurian.