Palaeogeographic significance of ordovician conodonts from the Lachlan fold belt, Southeastern Australia

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Abstract
Conodont faunas from eight new localities within Ordovician rocks of the Lachlan Fold Belt are identified and discussed. Ordovician rocks of the Lachlan Fold Belt have been assigned to two distinct lithological provinces: the Quartzose Sedimentary Province and the Molong Volcanic Province. Three of the eight new faunas are from the deep‐marine Numeralla Chert of the Quartzose Sedimentary Province and five are from chert members of the deep‐marine Triangle Formation of the Molong Volcanic Province. One of the Triangle Formation samples contains the Bendigonian, Bel‐2 (Early Ordovician) conodont Paracordylodus gracilis the oldest fossil identified from deep‐marine strata east of the Molong Volcanic Belt in the north‐eastern Lachlan Fold Belt. All other new conodont faunas indicate either Darriwilian‐Gisbornian (Middle‐Late Ordovician) or generalised Ordovician ages. Conodont faunas of both major Ordovician faunal realms (Warm Faunal Realm [WFR] and Cold Faunal Realm [CFR]) are found in the Lachlan Fold Belt. The distribution of these two faunal realms across the fold belt during the Early, Middle and Late Ordovician provides a framework for Ordovician palaeogeographic reconstructions of the Lachlan Fold Belt. Vol‐canism began in the Early Ordovician and continued episodically in at least three of the four volcanic belts in central‐western New South Wales throughout the Ordovician; however, the volcanic edifices did not become emergent until the Darriwilian (late Middle Ordovician). Throughout the Early Ordovician and continuing to Darriwilian time, conodont faunas from most of the Lachlan Fold Belt exhibited CFR affinities. However, by Gisbornian‐Eastonian time (middle Late Ordovician) many areas of the Molong Volcanic Province were emergent and partially surrounded by shallow marine limestone in which conodont faunas associated with the WFR became dominant. Offshore from the Volcanic Highs, volcaniclastic detritus formed widespread aprons which interfingered with siliceous black shale deposits in adjacent deep‐marine basins. Conodont faunas from these Late Ordovician siliceous rocks continued to reflect CFR affinities.