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Abstract

Carbonate buildups developed in deep, quiet water settings during the evolution of the Abenaki Jurassic-Cretaceous carbonate platform, offshore Nova Scotia. Two types of deep water buildups are recognized from the subsurface: thrombolite-stromatolite buildups and sponge bioherms.

The thrombolite-stromatolite buildups form mud rich mounds, constructed by a framework of micropeloidal waekestone-mudstone and micrite crusts. The principal biotic constituents are siliceous sponges and Tubiphytes. Micrite encasement of the framework and void-lining marine cements produce fabrics resembling “stromatactis.” Early lithification of the thrombolite-stromatolite mud mounds is evident by extensive brecciation of the framework. Associated mud mound lithologies include interbeds of skeletal debris reworked from shallow water platform settings and local accumulations of mud mound debris.

The sponge bioherm is formed of hydrozoans, calcareous and siliceous sponges, Tubiphytes, and benthic foraminifera in a micritic matrix. The calcareous sponges form a self-supporting framework from broken stick-shaped forms, though in situ plate-shaped and cup-shaped forms occur.

Thrombolite-stromatolite buildups are a common deep water facies association on ramps and steepened platform margins. Both types of profiles developed during the evolution of the Jurassic-Cretaceous carbonate platform. The sponge bioherm developed after widespread drowning of the carbonate platform.

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