I. Steinhoff et C. Strohmenger, ZECHSTEIN-2 CARBONATE PLATFORM SUBFACIES AND GRAIN-TYPE DISTRIBUTION (UPPER PERMIAN, NORTHWEST GERMANY), Facies, 35, 1996, pp. 105-132
The Upper Permian Zechstein 2 Carbonate (Stassfurt Carbonate, or Ca2)
platform facies of Northwest Germany can be subdivided into twelve sub
facies types using slabbed cores from fifteen representative wells. Th
in section and scanning microscopic analysis further provide subfacies
-specific characteristics, based on distribution, size, shape, and spa
tial arrangement of the grains contained in the different subfacies ty
pes. Thirteen grain types can be distinguished within the different su
bfacies types on the Ca2-platform: 1) one type of oncoid, 2) one type
of grapestone, 3) three types of peloids, 4) four types of ooids and 5
) four types of aggregate grains. Both presence and composition of gra
ins are indicative of the different subfacies types. There is also a r
elation between grain composition and porosity of the Ca2-subfacies ty
pes. The size and quantity of ooids correlate positively with increasi
ng porosity, whereas an increasing amount of algal structures (algal-l
amination) correlates negatively with porosity. The Ca2-platform carbo
nates almost exclusively represent highstand systems tract and lowstan
d systems tract deposits. The presence or absence of type-3 aggregate
grains within the grainy shoal and algal-laminated shoal subfacies all
ows the assignment of these subfacies to highstand (grains absent) or
lowstand (grains present) systems tracts deposits. The Ca2-highstand d
eposits can be subdivided into four shallowing-upward parasequences (P
S3 to PS7) bounded by parasequence boundaries (PSB3 to PSB6) and Zechs
tein sequence boundary ZSB4. In contrast to macroscopic core studies,
microscopic studies to identify Ca2-subfacies types can utilize cuttin
g material. This allows reconstruction of the subfacies distribution o
n the Caa-platform, and delineation of potentially porous zones in unc
ored Ca2 intervals.