Stratigraphy, sedimentology and diagenesis of the Lindsay Formation, Upper Ordovician, Ottawa Embayment, eastern Ontario

The Lindsay Formation (Upper Ordovician) of the Ottawa Embayment (eastern Ontario) represents the final stage of foreland carbonate platform development related to Taconic orogenesis along eastern Laurentia. The Lindsay Formation forms the upper unit of the regional Ottawa Group that underlies eastern Ontario. Available biostratigraphy (macrofauna, conodonts) indicates that the Lindsay is Edenian to Maysvillian in age, ∼453-452 Ma. The formation is divided into two members: the lower, newly defined, Nepean Point Member, and the upper Eastview Member, and conformably overlies the Verulam Formation. The Nepean Point Member is composed of highly bioturbated, nodular, fine to coarse grained, thin to thick, highly fossiliferous limestone beds with very thin discontinuous beds and laminae of calcareous shale. In contrast, the Eastview Member consists of sparsely fossiliferous lime mudstone and dark brown to black organic-rich calcareous to non-calcareous shale. Thin layers of densely compacted skeletal rudstones occur within the shale and cap some of the limestone beds. This unit underlies with apparent conformity deep-water shale of the Billings Formation.;Diagenetic alteration of the Lindsay Formation records marine through deep-burial realms. The marine phase includes bioturbation, micritized skeletal material, microbial encrustation, and fragmentation of skeletal material. Shallow-burial alteration includes non-ferroan calcite overgrowth cementation, which arrested mechanical compaction, then dissolution of aragonitic allochems. Fractures and ferroan void-fill calcite cement, then formation of horizontal (burial) stylolites complete deeper burial alteration. Carbon and oxygen isotopes of the cements support a shallow- to deep-burial transition. Sub-vertical stylolites record a following history of lateral compression, likely related to faults, but the specific timing remains unknown. Fe-poor zoned (CL) dolomite occurs scattered throughout the host limestone, and are overgrown by a relatively more abundant microzoned (ferroan, no CL) dolomite. Dolomite occurs in burrows, along stylolites and within secondary porosity paleocavities. The predominant dolomite is reflected isotopically to be of deep-burial origin. The early dolomite was not characterized isotopically, but its paragenesis suggests a complicated shallow-burial origin.;Eight lithofacies are defined for the Lindsay Formation: Five carbonate (C1-C5) lithofacies indicate deposition in a shallow (<50 m) ramp environment, and three siliciclastic (S1- S3) lithofacies represent deeper ramp deposition. Facies within the Lindsay Formation are characterized by a bryonoderm grain-type association that represents the predominance of brachiopods, crinoids, bryozoans, and mollusks, without grain types (ooids, micrite and aggregate grains) otherwise typical of warm-water conditions. This might indicate a cool-water environment, but there are fragments of the dasycladacean algae, Vermiporella sp., that require warm water conditions. The lack of other supporting evidence for temperate carbonate deposition suggests that other environmental factors such as salinity or local shoal development may have played an important role in the distribution of grain types and water temperature. The Eastview Member defines an environment in which there was alternating influx of shale, and episodic concentrations of skeletal material. The latter represents concentration lags related to low sedimentation rates. The shale-limestone stratigraphy of this unit likely reflects oceanographic controls superimposed on increased rates of platform subsidence.