Carbonate factories: A conundrum in sedimentary geology

Vaziri-Mogaddam

et al. 2017

BSGM

RESUMEN ABSTRACTIn this study, biostratigraphy and paleoecology of the Asmari Formation have been investigated. The study area is located in the Izeh zone, Zagros Basin. Four outcrop sections (Halayjan, Kuh Shur, Kuh-e Bad and Gharibi Ha) have been sampled. Based on distribution of the larger benthic and planktonic foraminifera, five assemblage zones have been recognized. Assemblages 1 and 2 indicate Chattian; assemblage 3 is restricted to Aquitanian and assemblages 4 and 5 suggest Burdigalian. During the Chattian, the carbonate deposits of the Asmari Formation are mostly composed of coralline red algae and large and flat benthic foraminifera. The common components of the Aquitanian are abundant imperforate foraminifera and Favreina asmaricus. The Burdigalian is characterized by coral, coralline algae, and perforate and imperforate foraminifera. During the Burdigalian toward the SE of study area (Gharibi Ha section), the shallow water deposits are abruptly overlain by pelagic limestone. It is interpreted as the result of a regional tilting that started in the upper part of the Burdigalian. The biotic associations suggest that carbonate sedimentation occurred in tropical to subtropical waters under oligotrophic to mesotrophic conditions. The carbonate grain associations in the Asmari Formation suggest heterozoan association. According to paleoecological parameters (such as: nutrient, depth, light and salinity) in the study area, the Asmari Formation belongs to nannofor-foralgal to foramol association which were deposited in slightly hyper to normal saline environment. In the euphotic zone, abundant imperforate foraminifera are present. Basinward, lens shaped rotalids developed in mesophotic conditions, and large lepidocyclinid-nummulitids characterize the sediments of the deeper oligophotic zone.Keywords: Asmari Formation, Oligocene-Miocene, biostratigraphy, paleoecology, larger benthic foraminifera, Zagros Basin.

Section: Burdigaliansupporting

confidence: 65%

Biostratigraphy and paleoecology of the Oligo-Miocene Asmari Formation in the Izeh zone (Zagros Basin, SW Iran)

Vaziri-Mogaddam

et al. 2017

BSGM

“…Their mixotrophic diet gains an energy advantage of several orders of magnitude over purely autotrophic or heterotrophic diets in environments that are well-lit but have poorly dissolved nutrients (Pomar & Hallock, 2008). Algal symbiosis allows larger foraminifera to be mixotrophic (to feed as well as photosynthesize) and thus thrive in oligotrophic environment.…”

Section: Biofacies Cmentioning

confidence: 99%

Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India

2017

The shallow marine carbonates of Kutch temporally correspond to the globally recognised warming period called Middle Eocene Climatic Optimum (MECO) that extended from later part of planktic foraminiferal zone E11 to E12 and Shallow Benthic Zone (SBZ) 17. The present study aims to investigate how foraminifera responded ecologically to the warming event. It involves identification and distribution of foraminifera, and cluster and detrended correspondence analyses of the species distribution data. Selected samples across E11 and E12 were analysed for carbon isotopes. The major conclusions are: (i) bloom of Jenkinsina columbiana in zone E11, possibly marking the initiation of warming in a shallow, eutrophic sea, (ii) increased foraminiferal diversity, appearance of Orbulinoides beckmanni and Acarinina and a sharp rise in the sea level in the early part of E12 (iii) significant jump in diversity and abundance of larger benthic foraminifera in E12, signifying warm, clear-water oligotrophic seas, promoting the formation of platform carbonates, (iv) MECO does not seem to have adversely impacted the foraminifera in shallow seas, and larger benthic foraminifera were rather ultimately superior in their diversity, abundance, size and latitudinal distribution and (v) δ 13 C excursions up to 1.5 ‰ are noted in the upper parts of E11 and lower parts of E12.

“…The minerals in the microbial-mat communities represented by stromatolites in oligotrophic waters of the Bahamas precipitate by complex interactions involving many bacterial agents (Visscher et al 2000;Paerl et al 2001;Visscher and Stolz 2005). The microbial calcification that has characterized reef construction throughout the Phanerozoic (Webb 1996;Pomar and Hallock 2008) is due to many players (Visscher and Stolz 2005). All these cases of microbially induced calcification occur in sediments, on and in microbial mats, and in other situations that are not intimately associated with multicellular organisms.…”

Section: Valve Thicknessmentioning

confidence: 99%

The oyster enigma variations: a hypothesis of microbial calcification

Vermeij¹

2014

Paleobiology

Oysters, whose inner shell layer contains chambers, vesicles, and sometimes chalky deposits, often have extraordinarily thick shells of large size, prompting the idea that there is something unusual about the process of shell fPormation in these and similarly structured bivalves with the oyster syndrome. I propose the hypothesis that calcifying microbes, especially sulfate-reducing bacteria growing on organic substrates in fluid-filled shell-wall chambers, are responsible for shell calcification away from the shell-secreting mantle of the host bivalve. Other phenomena, including the formation of cameral deposits in fossil cephalopods, the cementation of molluscs and barnacles to hard substrata, the formation of a calcified intriticalx on the shell's exterior, and cementation of objects by gastropods on the shell for camouflage, may also involve calcifying bacteria. Several lines of inquiry are suggested to test these hypotheses.