C. Strohmenger et C. Strauss, SEDIMENTOLOGY AND PALYNOFACIES OF THE ZECHSTEIN-2 CARBONATE (UPPER PERMIAN, NORTHWEST GERMANY) - IMPLICATIONS FOR SEQUENCE STRATIGRAPHIC SUBDIVISION, Sedimentary geology, 102(1-2), 1996, pp. 55-77
The Zechstein 2 Carbonate (Stassfurt Carbonate, or Ca2) of the second
Zechstein cycle has been subdivided into third-order and higher-order
sequences, using sedimentology and palynofacies analysis as complement
ary tools. This combination of tools provides a logical approach to th
e correlation of parasequences across different depositional settings
in a platform to basin transect. The Ca2 reservoir overlies the anhydr
ites of the first Zechstein cycle (Z1), the Werra Anhydrite (A1), and
is sealed by the anhydrites of the second Zechstein cycle (Z2), the Ba
sal Anhydrite (A2). The Ca2 can be subdivided into platform, upper slo
pe, middle slope, lower slope and basinal facies. These facies can be
further subdivided into a total of twenty-six subfacies types. The Ca2
comprises-a-nearly complete third-order sequence (ZS3) and part of th
e lowstand systems tract of the fourth Zechstein sequence (ZS4). It ca
n be further subdivided into seven parasequences identified by subfaci
es succession, gamma-ray-log response and palynofacies interpretation,
indicating higher-order intra-Ca2 relative sea-level fluctuations. Se
a-level fluctuations at third-order and higher-order scale are reflect
ed by cyclic changes in palynomaceral assemblages. Transgressive depos
its including the maximum flooding surface are characterized by a high
proportion of vitrinitic and inertinitic, frequently blade-shaped pal
ynomacerals, whereas various types of degraded palynomacerals occur mo
st frequently during lowstand and highstand progradation phases. Inter
tidal carbonates at the base of the Ca2 third-order lowstand wedge are
particularly distinct due to the abundance of palynomorphs resembling
colonial green algae (Plaesiodictyon spp.). The proposed chronostrati
graphic subdivision of the Ca2 into third- and higher-order sequences
improves the prediction of lateral and vertical reservoir facies distr
ibution.