High-frequency paleobathymetry oscillations in the Campos Basin driven by orbital cycles
Abstract
An integrated palaeoecological, biostratigraphic and cyclostratigraphic study was carried out on sedi-mentary rhythm sequences in the Oligocene-Miocene of the Campos Basin, Brazil. The biostratigraphic data combined with the spectral analysis performed on numerical data based on carbonate content variations of cores from well A, Campos Basin, reveal a periodicity related to the Milankovitch cycles. Ben-thic foraminiferal biofacies oscillations recognized in these cores have the same frequency and phase of long eccentricity cycles (400 Ka). Paleoceanographic changes (such as changes in ocean currents, water temperature and food supply) can modify the distri-bution and frequency patterns of foraminifera assemblages. However, the method used to interpretate the biofacies, the geological context of the studied area and the proposed genetic model to explain the origin of these rhythmically patterned rocks, suggest that changes in foraminiferal biofacies are directly related to the paleobathymetric variations induced by glacio-eustatic oscillations of relative sea level . According to the proposed model, productivity-di-lution cycles were instrumental in the origin of these marl-limestone couplets. During regressive phases, conditions were established to increase continental runoff to a bathyal setting. The increase of continental runoff with decrease of contribution of the main carbonate components led to the deposition of marlstone. During the transgressive phase, the relative reduction in clay input from continental sediments, favored a productivity growth of pelagic carbonate (calcareous nannofossil and planktonic foraminifera), which created conditions facilitating the deposition of limestone layers. The paleobathymetry oscillations, interpreted from the benthic foraminifera assemblage, and the formation of couplets, seems to be in phase with the transgressive-regressive cycles indicating a common cause to both processes.
