Biofacies, taphonomy and palaebiogeography of the Kamar-e-Mehdi Formation of east-central Iran, a Middle to Upper Jurassic shelf lagoon
Fürsich F, Pan YH, Wilmsen M, Majidifard MR (2016)
Publication Language: English
Publication Type: Journal article, Original article
Publication year: 2016
Journal
Book Volume: 62
Pages Range: 1-23
Journal Issue: 2
DOI: 10.1007/s10347-015-0452-6
Abstract
The Callovian–Lower Kimmeridgian Kamar-e-Mehdi Formation of the western Tabas Block, part of the Central-East Iranian Microcontinent, represents the fill of an extensive carbonate shelf lagoon situated between a barrier carbonate platform in the east and the uplifted Yazd Block in the west. In the course of its development, the shelf lagoon experienced increasing isolation which, together with a climatic change to more arid conditions, led to deposition of evaporites and severe restriction of the benthic fauna. Sedimentation in the predominantly low-energy lagoon was controlled by an influx of fine-grained carbonate from the neighboring platform, biogenic carbonate production within the lagoon and episodic influx of siliciclastic material by high-density currents from the uplifted western margin. Much of the succession is composed of meter-scale asymmetric cycles that record decreasing terrigenous input as well as increasing shelliness and substrate firmness due to a decreasing sedimentation rate. They are interpreted as small-scale climatic cycles recording changes in humidity. Larger-scale cycles, comprising 250–400 m in thickness, document changes in terrigenous influx and may also be climate-controlled, although a tectonic origin cannot be excluded. The shelf lagoon was populated by several level-bottom communities and small patch reefs. The latter are of low diversity, composed of calcareous sponges, corals, or oysters, and are usually associated with thick microbial crusts. The level-bottom assemblages are dominated by bivalves, and rarely also by gastropods or brachiopods. Fossils occur scattered or concentrated in pavements and beds. Shell concentrations are autochthonous to allochthonous, most commonly parautochthonous. Concentrating agents were storm-induced flows and low sedimentation rates, less commonly also storm-waves. Within the small-scale cycles, infaunal assemblages prevail but are replaced by epifaunal assemblages at their top. The latter are commonly dominated by the bivalves Pseudopecten tipperi and Camptonectes (Grandinectes) teres, the two most characteristic faunal elements of the shelf lagoon. Diversity values of the benthic fauna were low to moderate. Environmental stress was mainly produced by elevated salinity values, at times possibly intensified by lowered oxygen values and soft substrate conditions. Paleobiogeographically, the benthic macrofauna exhibits a close relationship to that of European shelf seas but contains some immigrants from the southern shores of the Tethys and the northwestern Pacific. The degree of endemism was low (two taxa).
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APA:
Fürsich, F., Pan, Y.-H., Wilmsen, M., & Majidifard, M.R. (2016). Biofacies, taphonomy and palaebiogeography of the Kamar-e-Mehdi Formation of east-central Iran, a Middle to Upper Jurassic shelf lagoon. Facies, 62(2), 1-23. https://dx.doi.org/10.1007/s10347-015-0452-6
MLA:
Fürsich, Franz, et al. "Biofacies, taphonomy and palaebiogeography of the Kamar-e-Mehdi Formation of east-central Iran, a Middle to Upper Jurassic shelf lagoon." Facies 62.2 (2016): 1-23.
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