Lower palaeozoic history of the Southwestern broken river province, North Queensland

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Abstract
The southwestern segment of the Broken River Province, here termed the Graveyard Creek Sub‐province, possesses a distinctive history of sedimentation, igneous activity, and structural development. Its lower Palaeozoic stratigraphy provides insight into the early tectonic setting of a part of the northern Tasman Orogenic Zone. Within the sub‐province an angular unconformity separates an undated older sequence, the Judea Beds, from a Middle Silurian to Lower Carboniferous succession more than 10 km thick. The Judea Beds comprise unfossiliferous quartz‐rich flysch and spilite which were intruded by trondhjemite plutons before the mid‐Silurian. The compositional maturity of this eugeosynclinal facies was inherited from an adjacent quiescent cratonic source. The Middle and Upper Silurian Graveyard Creek Formation overlies the unconformity. It is heterogeneous, and includes immature turbidites, shale, redeposited conglomerate, acid volcaniclastics, and coralline limestone. The Lower and Middle Devonian Broken River Formation, comprising coralline limestone and interbedded immature clastics, overlies the Graveyard Creek Formation. These formations resulted from a Siluro‐Devonian tectonic regime characterized by acid igneous activity and unroofing of crystalline basement in adjacent cratonic areas, and rapid deposition of synorogenic marine sediments in the Broken River Province. Relict sequences in the Blue Rock Creek and Mount Brown areas indicate that this Siluro‐Devonian sedimentation lapped on to the crystalline rocks of adjacent cratonic areas.

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