Depositional facies and platform architecture of microbialite-dominated carbonate reservoirs, Ediacaran–Cambrian Ara Group, Sultante of Om

Abstract

A B S T R A C TIntrasalt carbonates of the Ediacaran-Cambrian Ara Group constitute a significant reservoir element of the intrasalt "stringer" play in Oman, in which dolomitic carbonates are encased in salt at depths of 3 to 7 km (1.9 to 4.3 mi). These reservoir carbonates have significant microbial influences. Although Ara Group reservoirs are mostly latest Precambrian, the models developed here may be applicable to younger microbially dominated carbonate reservoirs in basins of higher salinity when higher organisms are excluded, in lacustrine settings where calcified invertebrates are not a significant source of carbonate, or after periods of mass extinction before faunal recovery. A broad range of carbonate facies provides the context in which to understand the origin of the microbialite-dominated reservoirs developed across both ramp and rimmed shelf profiles. Major facies associations include carbonate-evaporite transition zone, deep ramp and slope, subtidal microbialites, clastic-textured carbonates, and restricted peritidal carbonates. Microbialites are subdivisible into a number of facies that all have significance in terms of understanding environmental history as well as reservoir properties, and that help in predicting the location of reservoir fairways. Microbially influenced facies include shallow subtidal thrombolites with massive clotted textures and very high initial porosities (>50 ), shallow subtidal pustular laminites with cm-scale variability of lamina morphology, deeper subtidal crinkly laminites that show mm-scale variability of lamina morphology, and intertidal tufted laminates that

Facies analysis, sequence stratigraphy and chemostratigraphy of the Sete Lagoas Formation (Bambui Group), northern Minas Gerais State, Brazil: evidence of a cap carbonate deposited on the Januária basement high

“…The absence of domal and columnar morphologies is a recurrent feature in deep water microbialites (Playford et al 1976;Grotzinger and Al-Rawahi 2014), where low sedimentation rates and water energy favor planar, laterally extensive facies formation and preservation (Dromart 1992). The presence of pelitic intercalations and the lack of dessecative features, or intercalated higher energy facies as grainstones and rudstones, corroborate one calm, deep water environment for this facies, probably deposited below the storm wave base level.…”

Cavity‐filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: Responses to high‐frequency sea‐level fluctuations in an ‘aragonite–dolomite sea’

“…For the planar dololaminite, the horizontal laminae with variable microbial elements (branched, curved filaments/clots and micropeloids; Fig. G; Riding, ; Flügel, ; Harwood & Sumner, ; Grotzinger & Al‐Rawahi, ) and the coexistence of exposure‐formed indicators (Fig. A and B) suggest that it was deposited on the low‐energy intertidal to supratidal flat colonized by microbial mats.…”

“…Thrombolite is generally considered as deposition in the subtidal and even deeper environment (Flügel, ; Harwood & Sumner, ; Grotzinger & Al‐Rawahi, ; Zhang et al ., ). The stratal occurrence under the dolostromatolite as described above further confirms deposition in a shallow subtidal environment linked to the tidal flat landward.…”

Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran–Cambrian boundary, Sultanate of Oman

“…Allen (), Bowring et al. (), and Grotzinger and Rawahi () provide detailed geological reviews of the basin. We focused on the Ara Group deposited during late Ediacaran to earliest Cambrian time (Figure ).…”