PALEOMAGNETISM AND MAGNETOSTRATIGRAPHY OF TRIASSIC STRATA IN THE SANGRE DE CRISTO MOUNTAINS AND TUCUMCARI BASIN, NEW-MEXICO, USA

We report palaeomagnetic data and a composite magnetic polarity sequen ce for Middle and Upper Triassic rocks assigned to the Anton Chico Mem ber of the Moenkopi Formation and Chinle Group, respectively, exposed along the eastern flank of the Sangre de Cristo Mountains and in the T ucumcari Basin of eastern and northeastern New Mexico. Thermal demagne tization isolates a well-defined, dual polarity, characteristic magnet ization, carried in most cases by haematite and interpreted as an earl y acquired chemical remanent magnetization (CRM). Characteristic magne tizations from 74 palaeomagnetic sites (one site = one bed) are used t o define a magnetic polarity sequence, which we correlate with previou sly published Triassic data obtained from both marine and non-marine r ocks. Preliminary correlation suggests that the resolution of magnetos tratigraphic data derived from continental strata is not necessarily o f lesser quality than that from marine rocks. On the basis of the magn etostratigraphic data, a profound unconformity is believed to separate lower-middle Norian and upper Norian-Rhaetian strata of the Chinle Gr oup. Palaeomagnetic poles derived from selected sites in steeply dippi ng (> 85 degrees) strata for the Middle Triassic (Anisian, similar to 240 Ma: 50 degrees N 121 degrees E; N = 8), late Carnian-early Norian (similar to 225 Ma: 53 degrees N 104 degrees E; N = 16), and late Nori an-Rhaetian (similar to 208 Ma: 59 degrees N 77 degrees E; N = 8) are in relatively good agreement with previously published data for the Mo enkopi Formation and Chinle Group and related strata in southwest Nort h America. None the less, comparison with palaeomagnetic poles obtaine d from gently dipping or flat-lying Triassic strata from this study (A nisian, 46 degrees N 112 degrees E; N = 13; late Carnian, 54 degrees N 87 degrees E; N = 12) and previously published Triassic poles in sout hwest North America suggest that a modest 'apparent rotation' not grea ter than about 5 degrees affects declinations from steeply dipping roc ks. The distribution of palaeomagnetic poles indicates similar to 25 d egrees (angular distance) of apparent polar wander between about 240 a nd 208 Ma.