TY  - JOUR
A1  - Tomas, Sara
A1  - Homann, Martin
A1  - Mutti, Maria
A1  - Amour, Frederic
A1  - Christ, Nicolas
A1  - Immenhauser, Adrian
A1  - Agar, Susan M.
A1  - Kabiri, Lahcen
T1  - Alternation of microbial mounds and ooid shoals (Middle Jurasssic, Morocco) - response to paleoenvironmental changes
T2  - Sedimentary geology : international journal of applied and regional sedimentology
N2  - The occurrence of neritic microbial carbonates is often related to ecological refuges, where grazers and other competitors are reduced by environmental conditions, or to post-extinction events (e.g. in the Late Devonian, Early Triassic). Here, we present evidence for Middle Jurassic (Bajocian) microbial mounds formed in the normal marine, shallow neritic setting of an inner, ramp system from the High Atlas of Morocco. The microbial mounds are embedded in cross-bedded oolitic facies. Individual mounds show low relief domal geometries (up to 3 m high and 4.5 m across), but occasionally a second generation of mounds exhibits tabular geometries (<1 m high). The domes are circular in plan view and have intact tops, lacking evidence of current influence on mound preferred growth direction or distribution patterns, or truncation. The mound fades consists almost entirely of non-laminated, micritic thrombolites with branching morphologies and fine-grained, clotted and peloidal fabrics. Normal marine biota are present but infrequent. Several lines of evidence document that microbial mound growth alternates with time intervals of active ooid shoal deposition. This notion is of general significance when compared with modern Bahamian microbialites that co-exist with active sub-aquatic dunes. Furthermore, the lack of detailed studies of Middle Jurassic, normal marine shallow neritic microbial mounds adds a strong motivation for the present study. Specifically, Bajocian mounds formed on a firmground substratum during transgressive phases under condensed sedimentation. Furthermore, a transient increase in nutrient supply in the prevailing mesotrophic setting, as suggested by the heterotrophic-dominated biota, may have controlled microbial mound stages.
KW  - Microbial mounds
KW  - Thrombolites
KW  - Ooid shoals
KW  - Paleoenvironment
KW  - Jurassic
Y1  - 2013
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/34807
SN  - 0037-0738
VL  - 294
SP  - 68
EP  - 82
PB  - Elsevier
CY  - Amsterdam
ER  -