Geochemical Characterisation and Correlation of Palaeogene Sequences and Volcanics, Encountered in Gjoa G-37 and Hekja O-71 from the Saglek Basin of the Davis Strait

Timothy Pearce

Roach, C. Riley, D. Norry, M.J. & Pearce, T.J. The Mesozoic/Tertiary sediments of the Saglek Basin, offshore Baffin Island, represent a frontier exploration target. Due to few well penetrations the stratigraphy is poorly understood. To address this, a pilot chemostratigraphic study was conducted on Upper Cretaceous-Miocene strata in two exploration wells - Hekja O-71 and Gjoa G-37. Both wells have thick intervals of Palaeogene basalts at their base, which interfinger with marine siltstones of Danian age (Markland Formation = chemostratigraphic packages P1 and P2) in Gjoa G-37. No Danian sediments are encountered with the volcanics in Hekja O-71. New geochemical and published isotopic data confirm that the basalts in the two wells are not correlative. In addition, these basalt sequences are depleted in Cr, Ni and MgO relative to the picritic basalts on Baffin Island, implying that they have gone through a greater degree of fractional crystallisation. Furthermore, the basaltic sequences have depleted LREE normalised patterns, rare in Cenozoic basalts. Log[La/Yb]-n versus Δ-La highlights differences between basalts in each well, produced by progressive re-melting of mantle material. They demonstrate fractional crystallization and continental crust contamination trends. The overlying siliciclastic sequences can be sub-divided into 7 chemostratigraphic packages based on variations in reworked volcanic and heavy minerals (Ti, Sc, Cr, Zr, Th, Nb & Ta). In addition, variations in U, S, P, Ca, K, Rb, Cs and Ga are linked to organics, phosphate and clay mineralogy, attributable to fluctuations in facies and palaeoclimate. Packages P3-P5 correspond to a composite sequence of progradational clastics (Cartwright Formation). Packages P3 and P5 are organic rich (high U and P content) silty claytsones and siltstones. Package P4 corresponds to calcareous sandstones (Gudrid Member) in Hekja O-71. Package P6 exhibits high Ti, Cr, Nb, Zr, Sc and Si and is associated with volcaniclastic sandstones in both wells. Volcanigenic material is especially abundant in Gjoa G-37. Packages P6-P8 correspond to marginal marine sequences of the Kenamu Formation (Package P6), the Leif Member (Package P7) and the Mokami Formation (Package P8). All formations are marked by significantly lower Ti/Nb, Sc/Ta ratios and higher Zr/Ti, Nb/Sc. La/Sc ratios denote reworking from a more fractionated volcanic source and an influx of acidic continental material from the Labrador-Baffin margin. Package P9 corresponds to sandstones (often carbonate cemented) of the Saglek Formation. Overall, Palaeogene sequences are thicker in Hekja O-71 and suggest progradation from the Labrador-Baffin margin, although the volcaniclastic sequences of Package P6 appear more proximal in Gjoa G-37 and may have a different western origin.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013