Systematics and Paleoenvironment of Quaternary Corals and Ostracods In Dallol Carbonates, North Afar
No Thumbnail Available
Date
2017-11-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
There are reef structures developed in Dallol during the Quaternary Period as a result of flooding of the area by the Red Sea at least two times. Dallol area is situated in the northern most part of the Eastern African Rift system. The studied coral outcrops are aligned along the northwestern margin of the Afar rift. This research focused on the investigation of systematics of corals and associated fossils of mollusca, echinoidea, ostracoda and foraminifera together with the reconstruction of past environmental conditions. Different scientific methods were followed in order to achieve the objectives of the study. These are detailed insitu morphological descriptions; field observations and measurements; laboratory preparations and microscopic examinations; comparison of the described specimens with type specimens; and paleoecological calculations using PAST-3 software. Total of 164 fossil and 9 sediment samples are collected from the field and examined. The Dallol corals are classified into 12 Families, 29 Genera and 60 Species. The most common species include massive Porites, Porite lobata, Goniastrea pectinata, Goniastrea retiformis, Goniastrea stelligera, Echinopora hirsutissima, Echinopora gemmacea, Echinopora sp., Caulastrea furcata, Caulastrea tumida, Pavona venosa, Stylopora wellsi. Bivalvia classified into 9 Genera and 12 Species which are dominated by Tridacna maxima, Tridacna crocia, Arca boucardi and Crossastrea sp.; gastropoda classified into 6 Genera and 7 Species dominantly Cerithideopsilla cingulata, Canarium mutabile and Rhinoclavis sordidula; and echinoidea classified into 6 Genera and 8 Species dominantly Clypeaster humilis, Echinometra mathaei and Phyllacanthus imperialis. Ostracoda grouped into 15 Genera and 27 Species most of them are monospecific and dominantly Cyprideis torosa, Cyprideis longespina, Xestoleberis rotunda, Xestoleberis depressa, Leptocythere castanea, Loxoconcha carinata, Pontoparta salina, Keijia demissa and Cytherella sp. are recognized. Most of them are euhaline ostracoda species. Foramenifera grouped in to 9 Genera and 13 Species with dominant species Trocohamina sp., Quinqueloculina oblonga, Quinqueloculina lamarckiana, Quinqueloculina sagamensis, Elphideum crispum, Amphistegina lenssonii and Ammonia tepida. From paleoecological analysis of coral species 36% of total identified species are rare, 40% moderately abundant and 23% abundant. Shannon-Wiener index indicates that the older (MIS7) coral species are more diverse than the younger (MIS5) coral species. Paleoenvironmental interpretations are made from biofacies associations and paleoecological results. These are shallow open marine environments of two different phases with small sub – environments of shallow lagoon, brackish protected environment and lacustrine environment.
Description
Keywords
Dallol, Corals, Ostracoda, Mollusca, Systematics, Reef, Paleoecology, Paleoenvironment