TY - JOUR
T1 - Alunite alteration of tuffaceous layers and zircon dating, Upper Permian Kennedy Group, Carnarvon Basin, Western Australia
AU - Lever, H.
AU - Fanning, C. M.
PY - 2004/4
Y1 - 2004/4
N2 - Alunite layers were found in two locations in the Binthalya Formation, Upper Kennedy Group, of Late Permian age, in the Merlinleigh Sub-basin, onshore Cornarvon Basin. Alunite has not previously been reported from the Kennedy Group, or from a similar setting in Western Australia. The alunite occurs in discrete layers that have different chemical signatures to surrounding, unaltered sedimentary rocks. The lack of alteration in surrounding sedimentary rocks suggests that alteration was localised by initial differences in lithology, rather than by fortuitous localisation of alteration in a single layer. Alunite is thought to be the product of alteration of K-feldspars, clay minerals and pyrite under acidic, specifically sulfuric, conditions. It is found in hydrothermal systems and weathering profiles. Because the precursor minerals of alunite are believed to be feldspars, clays and sulfur-rich minerals, tuffaceous layers are the probable precursors of the alunite layers. Sulfur for the reaction was derived from within the tuffaceous deposits or from the oxidation of pyrite, which was probably present as cementation of trace fossils in other beds. The alteration is thought to have occurred during extensive oxidation, weathering and laterite formation during the Cenozoic, because the low density and powdery nature of the alunite indicates that it developed at a shallow depth. U-Pb dates obtained from zircons extracted from the alunite layers returned ages ranging from ca 2690 Mo to ca 270 Ma. The majority of zircons are inherited from the some source as the Kennedy Group sediments, indicating mixing of the initial tuffaceous layers with background sedimentation, either during the sedimentation process or afterwards by reworking or biological disturbance.
AB - Alunite layers were found in two locations in the Binthalya Formation, Upper Kennedy Group, of Late Permian age, in the Merlinleigh Sub-basin, onshore Cornarvon Basin. Alunite has not previously been reported from the Kennedy Group, or from a similar setting in Western Australia. The alunite occurs in discrete layers that have different chemical signatures to surrounding, unaltered sedimentary rocks. The lack of alteration in surrounding sedimentary rocks suggests that alteration was localised by initial differences in lithology, rather than by fortuitous localisation of alteration in a single layer. Alunite is thought to be the product of alteration of K-feldspars, clay minerals and pyrite under acidic, specifically sulfuric, conditions. It is found in hydrothermal systems and weathering profiles. Because the precursor minerals of alunite are believed to be feldspars, clays and sulfur-rich minerals, tuffaceous layers are the probable precursors of the alunite layers. Sulfur for the reaction was derived from within the tuffaceous deposits or from the oxidation of pyrite, which was probably present as cementation of trace fossils in other beds. The alteration is thought to have occurred during extensive oxidation, weathering and laterite formation during the Cenozoic, because the low density and powdery nature of the alunite indicates that it developed at a shallow depth. U-Pb dates obtained from zircons extracted from the alunite layers returned ages ranging from ca 2690 Mo to ca 270 Ma. The majority of zircons are inherited from the some source as the Kennedy Group sediments, indicating mixing of the initial tuffaceous layers with background sedimentation, either during the sedimentation process or afterwards by reworking or biological disturbance.
KW - Alunite
KW - Carnarvon Basin
KW - Kennedy Group
KW - Permian
KW - Western Australia
KW - Zircon dating
UR - http://www.scopus.com/inward/record.url?scp=3042815552&partnerID=8YFLogxK
U2 - 10.1111/j.1440-0952.2004.01050.x
DO - 10.1111/j.1440-0952.2004.01050.x
M3 - Article
SN - 0812-0099
VL - 51
SP - 189
EP - 203
JO - Australian Journal of Earth Sciences
JF - Australian Journal of Earth Sciences
IS - 2
ER -