The Organic-Rich and Siliceous Bahloul Formation: Environmental Evolution Using Facies Analysis and Sr/Ca & Mn Chemostratigraphy, Bargou area, Tunisia

Mohamed Soua*, Hela Fakhfakh-Ben Jemia*, Dalila Zaghbib-Turki**,
Jalel Smaoui*, Mohsen Layeb***, Moncef Saidi* and Mohamed Moncef Turki**

 

*Entreprise tunisienne d’activités pétrolières, ETAP–CRDP, 4, La Charguia II, Tunisie
**Département des Sciences de la Terre, Faculté des Sciences de Tunis, Université Tunis El Manar,
***Institut supérieur arts et métiers, Siliana Tunisia

Soua etal 2011b.pdf

 

 

Geology / Book 2

ISBN 978-953-307-468-9

Edited by: Dr. Imran Ahmad Dar

 

 

Published by InTech

Janeza Trdine 9, 51000 Rijeka, Croatia

 

Geochemical Record of the Cenomanian–Turonian Anoxic Event in Tunisia: Is it Correlative and Isochronous to the Biotic Signal?

Mohamed Soua*, Dalila Zaghbib-Turki**, Hela Ben Jemia*, Jalel Smaoui* and Amel
Boukadi***

* Exploration & Studies Department, Entreprise Tunisienne d'Activités Pétrolières (ETAP), Charguia II, 2035 Tunisia
** Département of Geology, Faculty of sciences of Tunis, University of Tunis El Manar 1068 Tunisia
*** Petroleum Research & Development Center (CRDP-ETAP), Charguia II, 2035 Tunisia

Soua et al 2011a.pdf

Abstract: In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/ Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleoenvironmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.

Key words: Bahloul Formation, Foraminifera, chemostratigraphy, OAE-2

Productivity and bottom water redox conditions at the Cenomanian- Turonian Oceanic Anoxic Event in the southern Tethyan margin, Tunisia

Mohamed SOUA

Entreprise Tunisienne d'Activités Pétrolières, Charguia II, Tunisia. E-mail: [e-mail].

 

Soua (2010b)

 

Abstract

In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analysed for major and trace elements. These high-resolution chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight on the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relative short period (400 kyr), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probable fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favouring the preservation of organic matter at the sea floor. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian – earliest Turonian times. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulphate-reduction reactions.

Key words: Bahloul Formation, Major and trace elements, Chemostratigraphy, OAE-2.

Soua M. /Revue Méditerranéenne de l’Environnement 4 (2010) 653-664

Time series analysis (orbital cycles) of the uppermost Cenomanian-lower Turonian sequence on the southern Tethyan margin using foraminifera

 

Mohamed Soua

Entreprise tunisienne d’activités pétrolières, ETAP–CRDP, 4, rue des Entrepreneurs, La Charguia II 2035, Tunisia

[e-mail]

[e-mail]

soua 2010.pdf

 

Abstract

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was applied to two foraminiferal genera: the biserial Heterohelix, an oxygen-minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the oceanic anoxic event (OAE2) in each studied section were estimated. The fluctuations in abundance of these two opportunistic species can be related mainly to both precessional (ca. 20 kyr) and eccentricity (100 and 400 kyr) cyclicity suggesting that changes in surface water fertility were linked to climate changes in the Milankovitch frequency band.

Key words: Cenomanian-Turonian boundary, time series analysis, cyclostratigraphy, Milankovitch cyclicity, Heterohelix spp., Guembelitria spp.

 

Modèle de sédimentation au passage Cénomanien/Turonien pour la formation Bahloul en Tunisie

 Mohamed Soua a,*, Nicolas Tribovillard b

Soua & Tribovillard, 2007.pdf

 

a. Entreprise tunisienne d’activités pétrolières, ETAP–CRDP, 4, rue des Entrepreneurs, La Charguia II, 2035, Tunisie

b. UMR 8110 et FR1818, Sciences de la Terre, université Lille-1, bâtiment SN5, 59655 Villeneuve-d’Ascq cedex, France

  

Résumé

Plusieurs études multidisciplinaires ont été effectuées sur les couches riches en matière organique (MO) de la formation Bahloul. Nos études de terrain et les synthèses géologiques, géochimiques, isotopiques et minéralogiques disponibles ont permis d’apporter des précisions nouvelles d’ordre paléogéographique et paléocéanographique. Ces données ont contribué à l’élaboration d’un modèle de dépôt sous une zone à minimum d’oxygène (ZMO) dans des bassins marins profonds et subsidents de type bathyal, où se sont accumulées et préservées d’importantes quantités de MO (jusqu’à 18,7 % de COT). Le présent modèle a permis la corrélation de la formation Bahloul à d’autres coupes de référence à l’échelle globale, ce qui permet de mettre en évidence que le  d13 C mesuré sur MO serait un meilleur outil de corrélation que le  d13 C mesuré sur carbonates pour reconnaître la limite Cénomanien/Turonien.

Abstract

Several multidisciplinary studies were undertaken on the Cenomanian/Turonian organic-rich Bahloul Formation. These studies, as well as our new data, led to some new palaeogeographic and palaeoceanographic interpretations. Based on these data, a depositional model was elaborated, pointing out that at the C/T transition an oxygen minimum zone (OMZ) impinged onto the South Tethyan margin through the Tunisian intrashelf basins formed during Early Cretaceous. This model allows correlating the Bahloul Fm. to other OAE-2 formations throughout the world. It also indicates that the  d13Corganic carbon seems to be a better correlation tool than d13Ccarbonate

LES RÉPONSES BIOTIQUES DES RADIOLAIRES À L’ÉVÉNEMENT ANOXIQUE DU CÉNOMANIEN SUPÉRIEUR DANS LA MARGE SUD TÉTHYSIENNE (TUNISIE)

 

Mohamed Soua 1; Dalila Zaghbib-Turki 2; Luis O’Dogherty 3

Soua et al., 2006.pdf

1.Entreprise Tunisienne d'Activités Pétrolières, Tunisie

2. Faculté des Sciences de Tunis, Tunisie

3. Université de Cadiz, Espagne

 

 

RÉSUMÉ

Pour la première fois en Tunisie, la Formation Bahloul d’âge Cénomanien supérieur – Turonien inférieur est étudiée pour son contenu en radiolaires dans la région de Bargou. Cette Formation présente à la fois un faciès laminé riche en matière organique et en silice. La microfaune observée est d’une diversité faible, avec un maximum de dix huit espèces par échantillon. Vingt-cinq espèces ont été déterminées au total. Les assemblages sont représentés par des nassellaires à test sphérique cryptothoracique / cryptocéphalique et à test multisegmenté, durant tout le Cénomanien supérieur, notamment les représentants des genres Stichomitra, Pseudodictyomitra et Rhopalosyringium. Au Turonien inférieur, la dominance des spumellaires est observée. La préservation des radiolaires (ou indice de préservation PI) déterminée dans cette étude est relativement faible, ce qui suggère une influence d’altérations diagénétiques. En se basant sur la courbe de d 13Corg, cet intervalle correspondant à l’événement anoxique du Cénomanien-Turonien (EAO-2) a été identifié dans la série étudiée. Deux zones de radiolaires ont été reconnues pour cet intervalle. La rareté d’échantillons ayant livré des radiolaires au sein de l’EAO-2 indiquerait une productivité primaire élevée avec des répercussions de conditions chimiques défavorables pour la prolifération de ce groupe durant tout l’intervalle.

Mots clés : radiolaires ; Cénomanien-Turonien ; Foraminifères planctoniques ; Formation Bahloul ; EAO-2.

ABSTRACT

The late Cenomanian-early Turonian Bahloul Formation is investigated for the first time in Tunisia for its radiolarian content. It includes a characteristic interval of organic-rich black laminated and siliceous shales. These deposits yielded twenty five radiolarian species. These assemblages are composed of spherical cryptothoracic / cryptocephalic and multisegmented nassellarians during the whole late Cenomanian interval, represented mainly by Stichomitra and Pseudodictyomitra species. Preservation Index (PI) identified in this study is relatively moderate to poor reflecting some diagenetic alteration influence. Based on the d 13Corg curve, the OAE-2 was recognized inside the Bahloul Formation. Two radiolarian zones are identified in this paper. The scarcity of radiolarian samples along the OAE-2 may indicate a high primary productivity with unfavourable chemical conditions influx for the thriving of this group.

Keywords: radiolarians; Cenomanian-Turonian; planktonic foraminifera; Bahloul Formation; OAE-2