Geoscience Reference
In-Depth Information
Provenance
DEPOSITIONAL MODEL AND
STRATIGRAPHIC FRAMEWORK
An integrated sediment provenance study using
provenance-sensitive heavy mineral ratios, min-
eral chemistry and U/Pb dating of detrital zircons
suggested that the main source area of the Åre
Formation shifted between the western basin mar-
gin (East Greenland source) towards the eastern
basin margin (Norwegian mainland source;
Morton
et al
., 2009). The lowermost, non-marine
part of the Åre Formation shows evidence of prov-
enance from the East Greenland margin (Fig. 2).
This provenance signal decreases upwards within
the Åre Formation and the uppermost part of the
Åre and the overlying Tilje Formation are inter-
preted to have a Norwegian margin source
(Martinius
et al
., 2001). This change in source
material is ascribed to restricted sediment supply
from East Greenland following gradual sea-
level rise. In-house provenance age data derived
from Sm/Nd isotope analysis confirm this trend.
Published studies from the time-equivalent
Statfjord Formation of the Tampen area in the
North Sea (~300 km south of Heidrun) by Mearns
et al
. (1989) and Brekke
et al
. (1999) imply a
structural high to the north or the west of the
basin (Fig. 2) that may have acted as a significant
source area for fluvial systems on the Norwegian
Shelf during Rhaetian to Sinemurian time (cf.
Ryseth, 2001).
A total of 49 lithofacies (Fig. 6B) and 18 facies
associations are recognised from core material
and interpreted to have formed in a range of
coastal plain to marine paralic environments
(Figs 4 and 7). The facies associations are grouped
into four main depositional settings: 1) fluvial/
alluvial coastal plain; 2) lower delta plain/
brackish-water interdistributary bay; 3) mixed
wave-influenced and tide-influenced estuary
and 4) transgressive shoreface (Fig. 4). Significant
shifts in depositional environments during dep-
osition of the Åre Formation are recorded in the
stratigraphy and define reservoir zone bounda-
ries (Fig. 4). A combination of facies stacking
patterns and correlation of key stratigraphic sur-
faces are used to interpret the sedimentological
history and establish a stratigraphic framework.
The previous reservoir zonation of the Åre
Formation on Heidrun utilised the Åre 1 and 2
subdivision proposed by Dalland
et al
. (1988).
Thirty two reservoir subzones were defined
mainly reflecting a separation of flow and
no-flow units (Fig. 4). The reservoir zonation
presented in this study divides the succession
into 7 reservoir zones (Åre 1 to Åre 7 and 17 sub-
zones; Fig. 4).
(A)
LEGEND FOR CORE DESCRIPTION
SEDIMENTARY STRUCTURE
TRACE FOSSILS
LITHOLOGY
Horizontal stratification
Arenicolites
Conglomerate
Arenicolites carbonarius
Low-angle cross-strat.
Sandstone
Asterosoma
Ta bular cross-strat.
Bivalve burrows
Diplocraterion parallelum
Silty sandstone
Tr ough cross-strat.
Sandy siltstone
Herring-bone cross-strat.
Escape (general)
Hummocky cross-strat.
Excavation trace
Siltstone
General burrow mottling
Pinstripe bedding
Palaeophycus
Claystone
Lenticular bedding
Phycosiphon
Wavy bedding
Flaser bedding
Planolites isp.
Coal
Planolites montanus
Psilonichnus
LITHOCLASTS
Current ripples
Pebbles
Resting/dwelling (general)
Wave ripples
Coarse sand/granules
Rhizocorallium irregulare
Synaeresis cracks
Roots
Sandstone
Mudstone
Coal fragments
Mud drapes
Skolithos
Taenidium
Fig. 6.
(A) Legend for the litho-
facies and facies association
schemes; also core descriptions.
Teichichnus
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