The North Atlantic climatic events recorded in Cretaceous Naskapi Member cores, Scotian Basin

Abstract

The Cretaceous was a time when global temperatures and rainfall patterns were controlled by plate tectonic changes and intense volcanic activity. High temperatures, high weathering rates and unusual ocean circulation characterized this time period, resulting in preservation of organic carbon in sediment and the formation of black shale sequences. The Mid Cretaceous Aptian had two major positive carbon isotope excursions followed by negative carbon excursions that were recorded in marine and terrestrial organic matter. The changes from arid to humid conditions have been recognised in the Tethyan stratigraphy and similar facies elsewhere, including the Scotian Basin. This study investigates the value added by portable X-Ray Fluorescence Spectroscopy (pXRF) and colour spectrophotometry analyses in interpreting paleoclimatic and pale oceanographic changes preserved in shales from the early Aptian Naskapi Member of the Scotian Basin.The relationship of element ratios K/Ti, Th/Ti, V/Ti, Mn/Ti, Zr/Ti, K/Th and total organic carbon (TOC) measured on both in-situ core and powdered samples from core, rubble and cuttings was plotted to indicate the input of weathered material, redox conditions, dilution of shale, aridity/humidity conditions and the amount of organic carbon preserved in the shales. Colour measurements were also plotted to determine variations controlling sedimentation and environmental change. The analytical approach used identified environmental changes in shales from the Scotian Basin that have also been identified in the Tethyan Basin. The distribution of ammonites after flooding events in the Naskapi Member places the Selli Event in the Early Aptian,TOC concentration peaks correlate to episodes of humid conditions, high sea level events (facies 3) and the occurrence of other oceanic anoxic events as in western Europe. The use of powdered sample for both the pXRF and colour spectrophotometry analyses seemed to be more reliable and show better representation of the environmental conditions compared to the in-situ core samples.