A model for the palaeoenvironmental distribution of larger foraminifera based on late Middle Eocene deposits on the margin of the South Pyrenean basin (NE Spain)

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: Paleoecological Interpretationmentioning

confidence: 93%

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

Vaziri-Mogaddam

et al. 2017

BSGM

“…Foraminifera with porcelaneous test (miliolid) shows existence of light in the depositional zone of this facies (i.e. it is formed in photic zone) [31] [32] [33] and [34]. Detected cementation proposes the notable level of energy in the shoreline part of lagoon.…”

Section: Benthic Foraminifera Peloids Grainstone-packstone (Mf4)mentioning

confidence: 99%

Sedimentary Environment and Relative Sea Level Changes of the Asmari Formation Deposited in Lurestan Basin, Southwest of Zagros

Alizadeh¹,

Jahani²,

Kamali³

2017

OJG

Asmari Formation is deposited in the Zagros Foreland basin during OligoMiocene time. In the presented research, Sheykh Makan (north of Kabir-Kuh Anticline) section located at Lurestan Basin is studied to achieve an understanding of facies changes, paleoenvironment and also sequence stratigraphic framework (relative sea level changes) of the Asmari Formation. Results of this study revealed that 15 microfacies grouped to four facies belts named as tidal flat, lagoon, barrier and open marine are the main constituents. A homoclinal ramp is determined as the depositional setting of the Asmari Formation. In Sheykh Makan Section, studied interval contains three third-order sequences aging oligmiocene. It overlies gradually shaly Pabdeh Formation and is overlain by evaporitic Gachsaran Formatin.

“…Functional morphological studies of orthophragminids point to a general adaptation of these foraminifera to symbiosis with unicellular photosynthetic algae, as in nummulitid foraminifera (Ferràndez-Cañadell and Serra-Kiel, 1992;Ferràndez-Cañadell, 1998;Romero et al, 2002;. Most of the living symbiont-bearing larger foraminifera need mean annual water temperatures higher than 18°C to support reproduction (Murray, 1973;Adams et al, 1986;Wilson and Vecsei, 2005).…”

Section: Change In Carbonate Factorymentioning

confidence: 99%

“…3). Additionally, the disappearance of Discocyclina and Asterocyclina, which thrived in the lower part of the photic zone in outer platform settings (Romero et al, 2002;Beavington-Penney and Racey, 2004), within the bryozoan beds (Fig. 4) suggests a major environmental perturbation rather than a simple deepening of the depositional environment (see Cotton et al, 2014).…”

Section: Change In Carbonate Factorymentioning

confidence: 99%

Bryozoan beds in northern Italy as a shallow-water expression of environmental changes during the Oligocene isotope event 1

Jaramillo‐Vogel

Bover‐Arnal

Strasser

2016

Sedimentary Geology

Shifts in carbonate-producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm. The shallow-marine Calcare di Nago Formation exposed in the San Valentino section (northern Italy) covers the Late Eocene and Earliest Oligocene. The succession is characterized by the occurrence of light-dependent biota such as coralline algae and larger benthic foraminifera. In the uppermost part of the section, however,\ the fossil association is dominated by bryozoans, which are filter-feeder organisms. This ca. 12 m thick interval locally contains up to 86% bryozoans, while coralline algae as well as larger benthic foraminifera are absent. Coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds, whereas orthophragminids do not recover. The gradual disappearance of larger foraminifera and coralline algae within the bryozoan-dominated deposits is coeval with a pronounced positive shift in δ 13 C. Based on its biostratigraphic position, this positive shift is interpreted to be linked to the positive shift in δ 13 C recognized in deepsea records shortly above the Eocene-Oligocene boundary, which in turn is associated to the positive shift in δ 18 O leading to the Oi-1 (Oligocene isotope event 1) cooling phase. Total phosphorus content increases in the bryozoan beds, suggesting enhanced nutrient supply to the neritic ecosystem. This phosphorous peak is coeval with the globally recognized increment in ocean productivity around the Oi-1 and δ 13 C positive shift. Thus, disappearance of light-dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower seasurface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters, resulting from enhanced primary productivity. As bryozoan beds occur in several Italian localities around the Eocene-Oligocene boundary, they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice-house Earth.