Palaeomagnetic results from remagnetized mid-Cretaceous(Albian-Cenomanian)strata of northeastern Venezuela

We report palaeomagnetic and rock magnetic results of a sedimentary sequenc e (Pertigalete cement quarry) located in northeastern Venezuela. Sampling w as restricted to the vicinity of the contact between the upper Cretaceous C himana and Querecual formations. Biostratigraphic evidence reveals an upper Albian age for this formational transition. Profiles of site-averaged NRM intensity of the high-coercivity (over 30 mT) and high-temperature (over 40 0 degrees C) components appear to be related to the contact and distance fr om the contact. We interpret this profile as the probable outcome of overla pping thermochemical remagnetization events resulting from hydrothermal act ivity that was focused along the two formations. Direct spectral analyses p erformed on the site-averaged stable NRM intensity profile allow the separa tion of at least two of these remagnetization events. On the other hand, pa laeomagnetic results show a considerable streaking of site mean declination s, suggesting that tectonic or structural horizontal movements around a ver tical axis have occurred after NRM acquisitions. Horizontal rotation angles , plotted against stratigraphic levels for bedding-corrected data, show som e features that seem to coincide with the alteration peaks isolated in the profile of site-averaged stable NRM intensities. Thus, it appears that repe ated thermochemical remagnetizations with overlapping unblocking spectra, a nd horizontal movements around a vertical axis could have been responsible for much of the within-site dispersion. A simple three-stage reconstruction of the possible chain of thermochemical and tectonic occurrences that coul d lead to the present-day palaeomagnetic and rock magnetic evidence is prop osed. These events, including clockwise horizontal rotations around a verti cal axis, are tentatively placed in a geological time framework between mid dle Miocene and Pliocene times according to the main geological and geochem ical evidence available.