Sukcesja zlepów ostrygowych na miękkim dnie

Jerzy Dzik



Particular stages in the succession of reef communities on the soft bottom are controlled by limiting factors ordered in time and having summarizing effect. There are: (a) rate of sedimentation, (b) water turbulency, (c) adaptation of reef organisms to colonization of bottom covered with sediment, (d) primary productivity, (e) influx of biogenes, and (f) insolation. Xenomorphism (21; Fig. 1, 2) of Late Jurassic oysters is used for study of the factor (c), i.e. mode of colonization of soft bottom by animals cementing themselves to hard substrate. It allows to reconstruct both distribution of substrate for settlement of larvae and distribution of productivity in fossil community independently of fossilization potential of particular species. Two fossil assemblages of Early Kimmeridgian oysters have been selected for study. Assemblage from Czarnogłowy, Pomerania, shows mode of colonization of oolite sands by oyster banks. Erect thalli of dasycladacean alga Goniolina geometrica were here primary substrate for small oysters and terebratulids (6; Fig. 3). Subsequently, their dead shells laying on sandy bottom allow settlement of larger oysters and anchoragement of other sessile animals. Assemblage from Strzałków boreholes, western margin of the Holy Cross Mts„ shows mode of colonization of clay bottom by oysters. Conchs of the herbivorous, possibly epiplanctonic gastropod Procerithium limaeforme were the most common substrate for settlement of small oysters. Lack of undoubtedly benthic organisms in the xenomorphic record and high juvenile mortalizy of oysters independently of substrate of attachment suggests that oysters were first benthic organisms in this environment.
Terminologie distinction between lumachelle originating by diagenetic cementation of loose shells (8) and rigid construction produced by biocemented shells of reef organisms (Polish name zlep) is proposed.

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