Excursion Guidebook - Geoloogia Instituut

10 th International Symposium on Fossil Cnidaria and Porifera. Excursion B2: Field Guidegrained dolomite of the upper part of a mud-mound.The upper surface of the mound has very intense pyriteimpregnation and may be erosional.(2) 0.2-0-7 m - grey dolomite with relict fine-grainedtexture (dolomitized packstone or grainstone) whichoccurs only on the sloping upper surface of themound.(3) 0.8 m - brownish-grey flaggy fine-crystallineslightly argillaceous dolomite (dolomitized wackestoneor packstone), which contains specific tubularstylolitic structures in the upper part.(4) 2.30 m - brownish-grey flaggy argillaceous dolomitewith partings of brown kerogenous argillaceousdolomite on the bedding planes.The fauna in the Koguva quarry is poor containingbrachiopods Leptostrophia filosa (Sowerby), Atrypareticularis (L.), Leptaena sp., chitinozoans Conochitinaclaviformis Eisenack, C. cf. mamilla Laufeld, C.cf. leptosoma Laufeld, Margachitina margaritana(Eis.), Ancyrochitina sp. and trilobites Encrinuruspunctatus (Wahlenberg), Calymene sp. indet.The replacement of dolomitic marlstones of thetransitional facies belt with the peculiar facies of mudmoundscan be examined in the regressive successionof the outcrop. And they are replaced with the kerogenousargillaceous dolomites of probably restrictedshelf genesis in the upper part of section. The depositsof the mud-mound facies, which resemble sedimentsof semi-isolated patch-reef environments are representedhere. No skeletal remains of frame-buildingorganisms have been found in the massive reef bodiesof the Kesselaid Member therefore the latters aretreated as mud-mounds of microbial origin, formed inrestricted shelf environment.42