A review of the origin and setting of tepees and their associated fabrics

Abstract

Carbonate hardgrounds often occur at the surface of shallow subtidal to supratidal, lacustrine, and subaerial carbonate shelf sediments. These are commonly disrupted and brecciated when the surface area of these crusts increases. In the subtidal environment, megapolygons form when cementation of the matrix causes the surface area of the hardgrounds to expand. Similar megapolygons form in the supratidal, lacustrine and subaerial settings when repeated incremental fracturing and fracture fill by sediment and/or cement also causes the area of the hardgrounds to expand. The arched up antiform margins of expansion megapolygons are known as tepees. The types of tepees found in the geological record include: (1) Submarine tepees which form in shallow carbonate‐saturated waters where fractured and bedded marine grainstones are bound by isopachous marine‐phreatic acicular and micritic cements. The surfaces of these brecciated crusts have undergone diagenesis and are bored. Unlike tepees listed below they contain no vadose pisolites or gravity cements; (2) Peritidal and lacustrine tepees are formed of crusts characterized by fenestral. pisolitic and laminar algal fabrics. This similarity in fabric makes these tepees of different origins difficult to separate. Peritidal tepees occur where the marine phreatic lens is close to the sediment surface and the climate is tropical. They are associated with fractured and bedded tidal flat carbonates. Their fracture fills contain geopetal asymmetric travertines of marine‐vadose origin and/or marine phreatic travertines and/or Terra rossa sediments. The senile form of these peritidal tepees are cut by labyrinthic dissolution cavities filled by the same material. Lacustrine tepees form in the margins of shallow salinas where periodic groundwater resurgence is common. They include groundwater tepees which form over evaporitic ‘boxwork’ carbonates, and extrusion tepees which also form where periodic groundwater resurgence occurs at the margins of shallow salinas, but the dominant sediment type is carbonate mud. These latter tepee crusts are coated and crosscut by laminated micrite; the laminae extend from the fractures downward into the underlying dolomitic micrite below the crust. Both peritidal and lacustrine tepees form where crusts experience alternating phreatic and vadose conditions, in time intervals of days to years. Cement morphologies reflect this and the crusts often contain gravitational, meniscus vadose cements as well as phreatic isopachous cement rinds. (3) Caliche tepees which are developed within soil profiles in a continental setting. They are formed by laminar crusts which contain pisolites, and fractures filled by micritic laminae, microspar, spar and Terra rossa. Most of the cements are gravitational and/or meniscoid. In ancient carbonates, when their cementation and diagenetic fabric can be interpreted, tepee structures can be used as environmental indicators. They can also be used to trace the evolution of the depositional and hydrological setting.

Facies, stratigraphy, and evolution of a middle Ediacaran carbonate ramp: Khufai Formation, Sultanate of Oman

“…Cementation is extensive and includes calcite rim cements and coatings on breccia clasts, calcite spar in vugs, and silica replacement. Vadose pendant cements and large pisoids commonly associated with tepee structures in other locations are not observed in the Khufai Formation (Assereto and Kendall, 1977;Kendall and Warren, 1987). Thin beds of red siltstone are locally preserved on the upper surface of tepee breccia deposits.…”

“…Tepees grade from mild upwarping ( Figure 11B) to extensive breccias ( Figure 10C) (Kendall and Warren, 1987) and form meter-scale polygonal fractures across exposed bedding planes.…”

Karst Surface Features of the Hard Laminated Crust (Caliche Hardpan) in the Mersin Area, Southern Turkey

“…It is typically composed of a cream coloured, evenly discontinuously laminated, indurated, wavy horizon of calcium carbonate with an average thickness of 1 to 1.5 m. The carbonate crust displays a sharp upper surface and a gradual lower surface, passing into nodular to tubular caliche horizons. The upper surface commonly shows dome-and ridge-like morphologies termed caliche tepees (Kendall & Warren 1987) or pseudo-anticlines (Price 1925;Jenning & Sweeting 1961;Aristarain 1970;Watts 1977) with wider troughs between them. These antiform structures are described in more detail in Eren (2007).…”

Estromatólitos e estruturas associadas na Capa Carbonática da Formação Mirassol D'Oeste, Grupo Araras, Faixa Paraguai (Neoproterozoico, MT)

“…Esta laminação apresenta curvatura de ângulo obtuso, formando cristas. Embora lembrem estruturas tepee, não apresentam as formas poligonais de tepees do Fanerozóico (Shinn 1983, Kendall & Warren 1987; ao contrário, possuem cristas alongadas que se estendem por mais de 3 m, com orientação NNW-SSE, e internamente exibem estruturas produzidas por onda como laminação truncada de baixo ângulo e com padrão em chevron e "pinch and swell". Estas estruturas foram interpretadas como megamarcas onduladas geradas por "hypercanes", muito mais fortes do que os furacões atuais, como discutido acima (Allen & Hoffman 2004).…”

“…Estas estruturas resultam da expansão volumétrica de crostas de sais debaixo de sedimentos superficiais incipientemente litificados em ambientes evaporíticos (Aitken, 1991;Porter et al, 2004;Kendall & Warren, 1987), em nada parecidos com os ambientes postulados para a Formação Mirassol D'Oeste.…”