Andrew Morton1, Claire Hallsworth1, Dave
Mundy2, and Gail Bingham3
1 HM Research Associates, Loughborough, United Kingdom
2 Talisman Energy Inc, Calgary
3 Talisman Energy (UK) Ltd, Aberdeen, United Kingdom
Upper Jurassic sandstones deposited in a shallow marine shoreface setting in the Piper Field of the UK Moray Firth area show high-frequency fluctuations in ATi (apatite:tourmaline ratio) that appear to be related to sea-level change. Since apatite and tourmaline are both stable during burial diagenesis and have similar hydraulic behaviour, variations in ATi either indicate differences in sediment provenance or in the extent of floodplain weathering, apatite being unstable during weathering. Other provenance-sensitive heavy mineral ratios (rutile:zircon, monazite:zircon, chrome spinel:zircon) and mineral-chemical data on detrital garnet assemblages show that both high-ATi and low-ATi sandstones have common provenance, indicating that the fluctuations in ATi are related to the extent of weathering during floodplain residence prior to the sediment entering the marine system. Sedimentological data indicate that the high-ATi sandstones were deposited during sea-level highstands, whereas the low-ATi sandstones were deposited during lowstands. The implication of this observation is that during sea level lowstands, sediment undergoes more prolonged floodplain residence than during highstands, apparently the direct result of the increased length of the fluvial system. The fluctuations in ATi offer an opportunity for high-resolution correlation in the Piper Field.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005