Estudo De Ciclicidade Orbital Com Base Em Dados Sísmicos

Cyclostratigraphic analysis of a sonic well log and a seismic trace in a sedimentary succession of the Miocene in<br>Campos Basin allowed to evaluate the potential of applying cyclostratigraphy to high-resolution seismic data. The<br>method used to identify cycles in a sonic well log and put them in a hierarchical order, to establish their temporal<br>magnitude and the mean accumulation rate of sediments was a combination of visual and spectral analysis. The<br>correlation between the periodicities obtained from the spectral analysis with those of the Milankovitch band was then<br>evaluated using a comparison of the similarity of their ratios. Similar analysis was done to the converted-to-depth seismic<br>trace that coincides with the well projection on the seismic section. Different levels of success were obtained. They were<br>dependent on the thickness of the sedimentary cycles and the seismic resolution. Cycle thickness is a function of<br>accumulation rate; seismic resolution, considering the same acquisition parameters, varies conversely to the<br>investigation depth. The sonic well log analysis revealed cycles associated to eccentricity (100 ka), obliquity (41 ka) and<br>precession (23 and 19 ka). The rithmicity in the sedimentary succession seems to be mostly influenced by precession<br>cycles, excepts to the segment N-570c, where obliquity prevails. Accumulation rates range from 16.8 to 40cm/ka. The<br>seismic trace spectral analysis allowed the identification of cycles with periods around 100 ka (eccentricity). Since the<br>accumulation rates increase it is possible to relate cycles to obliquity (41 ka).<br>Potentially, seismic may be a useful tool in cyclostratigraphy. However, it´s necessary to maximize the temporal<br>resolution, especially in the environments with lower accumulation rates.