Base of the Kiaman: Its definition and global stratigraphic significance

Defining and dating the base of the Kiaman (the long period of reverse pola rity that spans the time from the Late Carboniferous to the middle Permian) have proven difficult. In an attempt to do this an integrated stratigraphi c, paleomagnetic, and geochronologic study was undertaken in Carboniferous rocks in the northern Tamworth Belt of the New England orogen, eastern Aust ralia. New paleomagnetic measurements at 145 horizons (sites) in the New England o rogen of eastern Australia provide an accurate record of the late Namurian to Westphalian geomagnetic field. They have high unblocking temperatures, s atisfy tilt, conglomerate, and slump tests, and show excellent agreement be tween a wide variety of igneous and sedimentary rock types, indicating that magnetism was acquired at, or soon after, deposition. Magnetite and, to a lesser degree, hematite are the carriers of magnetization. The record is co ntained in sequences of glaciogene sediments and are-derived volcano-sedime ntary units, folded into broad structures in the Late Permian to Triassic. New isotopic dates for the volcanic units indicate ages from 321 to 306 Ma (late Namurian to Westphalian). Magnetizations are steeply inclined downwar d (reversed polarity in the Southern Hemisphere) except within the Clifden Formation of the Rocky Creek syncline, where a change from normal to revers e polarity referred to as the Wanganui reversal records the onset of the Ki aman superchron. Integrating complex stratigraphic, isotopic, and paleomagnetic data, we cor relate the Wanganui reversal to the top of N6 in the Joggins section Nova S cotia, Canada, and estimate that its age is between 318 and 316 Ma. Further work may substantiate a younger normal zone in Australia that mould suppor t a slightly younger age, but within these limits. These considerations ind icate that the Wanganui reversal occurs in the late Namurian (Marsdenian) a nd after the time of the Mississippian-Pennsylvania boundary. The mean dire ction of magnetization of the Upper Carboniferous Australian sequences is d eclination (D) = 195.3 degrees, inclination (I) = 76.9 degrees, kappa = 25, alpha(95) = 3.1 degrees, with a paleopole at 51.9 degrees S, 141.2 degrees E, alpha(95) = 5.7 degrees, and a paleolatitude of 65.0 degrees +/- 5.6 de grees S (P = 0.05). This paleolatitude is consistent with the glacial origi n of some of the sedimentary units.