Diagenetic rejuvenation of raised coral reefs and precision of dating. The contribution of the Red Sea reefs to the question of reliability of the Uranium-series datings of middle to late Pleistocene key reef-terraces of the world (original) (raw)
Related papers
Stratigraphy and evolution of emerged Pleistocene reefs at the Red Sea coast of Sudan
Journal of African Earth Sciences, 2016
Emerged Pleistocene coral reefs constitute a prominent landform along the Red Sea coast of Sudan. They are well exposed with a thickness of up to 12 m and extend over a width of about 3 km parallel to the coastline. Four major reef units that represent different reef zones are distinguished. Unit 1 is located directly at the coastline and is assigned to the rock-reef rim, while unit 2 represents the reef-front zone. Unit 3 is attributed to the reef-flat zone and unit 4 to the back-reef zone. The stratigraphic position and age of the four units respectively the facies zones are based on field relationships and d 18 O analysis. Results of d 18 O analysis of coral, gastropod and bivalve samples were correlated to previous age dating of correlative reefs in Sudan and other parts of the Red Sea region. Estimation of reef ages was mainly based on d 18 O values of the reef-front zone (unit 2) and the observed sedimentary succession of the reefs. d 18 O values of two Porites coral samples from the reef-front zone strongly suggest equivalent ages of 120 and 122 ka that correspond to marine isotope stage MIS 5.5. Based on d 18 O values and the field relationship to the reef-front zone, ages of reef-flat zone (unit 3) and back-reef zone (unit 4) could be assigned to MIS 9 and MIS 7 respectively. MIS 5.1 is suggested for the reef-rock rim (unit 1). The relationship of the reef zones to individual MIS might be explained by the predominance of a specific zone during a certain stage, while other facies were less well developed and/or later eroded by wave action. The reef unit most distal from the recent coastline formed during interglacial stage MIS 7, while former studies assign this unit to interglacial stage MIS 9. Unique flourishing, high diversity and excellent preservation of corals in the back-reef unit of MIS 7 reflect growth in troughs landward of the oldest reef-flat formed during previous interglacial stage MIS 9.
Pleistocene coral reefs along the Red Sea coast occur in three stratigraphically different units. Theyform terraces of different elevations above the present sea level and are characterized byfringing reef types, comparable to their recent counterparts. The three reef units show a progressive diagenetic sequence. The lower unit (youngest) is characterized by almost unaltered primary microstructure. Meteoric leaching in only documented is the form of open trabecular centers of coral skeletons. Marine micritic linings of aragonitic biota arefrequent features. marine cements of aragonite and high-magnesium calcite (HMC) are wellpreserved. The middle unit is characterized by an increased leaching of the trabecular centers. Low magnesium calcite (LMe) started to prcipitate, while aragonitic biota show an intense leaching. They are frequently recorded as molds with meteoric lining. The upper unit (oldest) is characterized by complete loss of any primary microstructure, a continuous reduction of biota from the fossil record, an increase in meteoric LMC cements and a decrease inporosity. A number of stable isotope datafrom selected coral species underline these changes.
Sequential evolution and diagenesis of Pleistocene coral reefs (South Sinai, Egypt)
Sedimentary Geology, 1992
Strasser, A., Strohmenger,,Ch., Davaud, E. and Bach, A., 1992. Sequential evolution and diagenesis of Pleistocene coral reefs (South Sinai, Egypt). Sediment. Geol., 78: 59-79.
Quaternary Science Reviews, 1997
Five Quaternary coral reef terraces have been recognized along Sharm E1Sheikh-Ras Mohammed coast, of which terraces 'V to II' form a well developed staircase at Um Seed, while recognized separately at Ras Mohammed. Terrace T was only observed as a reef patches at Sharm E1Sheikh-Ras Mohammed road. Terraces 'V to I' exist at elevations of-l(b.s.1.) to 0 m, 3-6 m, 10o12 m, 15-20 m and 25-35 m (a.s.1.), respectively. Uranium series dates of samples representing terraces 'V, IV, III, II and I' show ages grouped as ka, 118-125ka, 200ka, 280-300ka and older than 300ka, which are related to isotope stages 1, 5e, 7, 9 and 11, respectively. The variation of 8~80 for samples from these terraces show evidence of at least four major warm-wet climatic periods in relationship to high sea level and contemporaneous with the formation of the reef terraces. Faulting affects only the older terraces 'I and II', and along with the occurrence of terrace 'IV' of Last Interglacial age at elevation of 3-6 m suggest that the coastal area has not been subjected to major tectonic activities at least with the last 125 ka.
Late Pleistocene raised coral reefs in the eastern red sea – Rabigh, Saudi Arabia
2011
Professor Colin Woodroffe for his particular insights into the world of coral. Also, I would like to thank Professor Colin Murray-Wallace for his efforts in the area of quaternary dating methods. I would like to extend my thanks to Professor Amin Ghaith for his guidance and expertise in the field work. Many thanks to my colleague AbdulGhani who provided specific support and assistance at various steps of the research process. A final word of thanks goes to my family for their support and patience during this extended research period.
Late Pleistocene raised coral reefs along the Saudi Arabian Red Sea coast
2016
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Environmentally controlled succession in a late Pleistocene coral reef (Sinai, Egypt)
Coral Reefs, 2013
The concept of ecological succession has been frequently applied in the study of ancient reefs. Whereas Paleozoic and Mesozoic reefs are commonly thought to reveal an autogenic primary-climax zonation, patterns in Neogene and Quaternary reefs are much more diverse. Here, we describe a well-preserved late Pleistocene coral reef from Dahab on Sinai Peninsula (Egypt), which shows a distinct zonation that resembles an ecological succession. In contrast to classical examples of ecological successions, species composition, paleoenvironmental conditions, and coral biodiversity of the Dahab reef indicate an allogenic, sea-level controlled community change, from marginal marine to reef slope and back reef. A review of the literature confirms that autogenic, short-term successions are virtually absent in Quaternary reefs. We predict that long generation times of corals make it unlikely that classical autogenic successions develop in reefs at all, unless environmental conditions are unusually stable.
Sedimentary Geology, 2001
In the tectonically stable area of the Egyptian coast of the Red Sea, the uppermost marine deposits of the Last Interglacial (Eemian, 5e 5:5 Marine Isotopic Substage) consist of two contrasting sedimentary units: a subcontinuous fringing coral reef and, on its backward side, shelly and subaqueous gypsum deposited in erosive depressions elongated parallel to the shore. The entrenched geometry and the marine to brackish evolution of the pre-evaporite faunas indicate that during this very short period of time, a brief sea-level drop responsible for the limited erosion separated the succession of reef to marine gypsum and that the coastal area underwent several climatic variations. The marine ingression into drowned valleys (early MIS 5.51) developed khor environments (non-brackish lagoon on the Arabic arid shores) which were quickly replaced by highly restricted conditions leading to gypsum precipitation. Permanence of the salina waters and seasonal lamination interrupting crystal growth suggest an anchialine salina system (littoral haline lakes) fed by permanent seeping of seawater , balanced by re¯uxing dense brines. A semi-arid climate is assumed, with seasonal rains allowing limited continental sulphate contribution (from Miocene gypsum outcrops). Both climate and sea-level changes were responsible for the complex evolution of this area. Compiled data enable generalization concerning the climatic oscillations during the Last Interglacial sedimentation. A model derived from these Red Sea Quaternary deposits, as an analogue for the marginal Miocene evaporite deposits in the Mediterranean and Red Sea, is discussed.
Dating Quaternary raised coral terraces along the Saudi Arabian Red Sea coast
Marine Geology
Late Pleistocene raised coral reef terraces form extensive outcrops up to 5 km wide along the Saudi coast. Porites coral were dated using U/Th while clastic sediment from Jeddah was dated using thermoluminescence. The pooled mean age for the coral samples is 121.5±0.2 ka suggesting MIS 5e, even for the uplifted 16-20 m high terrace in the north at Haql. In Jeddah the MIS 5e back-reef succession is overlain by fluvial sediment that gave a TL age of 66±13 ka. The structure and faunal composition of the coral terraces suggests that they accumulated in broad shallow embayments following the last interglacial transgression. The consistent elevation of these terraces suggests that the central and southern Saudi coast has been tectonically stable for at least the past 125,000 years and the coral reef terraces (at 3.5-5.5 m elevation) are consistent with the MIS 5e sea level high-stand that peaked at 6-9 m above present sea level. The Saudi coastal coral terrace north of Duba shows progressive uplift to 16-20 m near Haql since 108-120 ka as a result of ongoing transform faulting in the Gulf of Aqaba.
Last interglacial sea levels and regional tectonics from fossil coral reefs at the Gulf of Aqaba
AGUFM, 2017
Elevated reef terraces in the northeast Gulf of Aqaba (GOA) constrain the history of tectonic uplift and local relative sea level changes during the last interglacial period. These relative sea level changes were inferred from measured elevations coupled with U-Th ages of aragonite precipitation and recrystallization to calcite. All studied reef terraces were formed, and the corals comprising them were recrystallized from aragonite to calcite, when sea-level was at or close to its stable MIS5e elevation a few meters above the modern GOA level. The terraces comprise fringing reefs, some with clear reef structure consisting of a reef flat and a shallow back lagoon accurately marking sea levels at low tide. Terrace R3 probably formed at the earlier stage of MIS5e at~130e132 ka and recrystallized to calcite at 124 ± 8 ka. Terrace R2, comprising a wide and developed reef flat, formed during the stable sea-level of peak MIS5e at~129e121 ka and was recrystallized to calcite at 104 ± 6 ka. Terrace R1 formed during a short stillstand at 117 ± 3 ka. The recrystallization age of Terrace R2 implies that at around 104 ± 6 ka (MIS5c) sea-level was close to its MIS5e elevation. The elevation and ages of the reef flats indicate a slow average uplift, 0.13 ± 0.05 m/kyr, similar to rates inferred for other last interglacial reef terraces along GOA and the Red Sea. This suggests an overall long-term slow uplift of the Arabian lithosphere at the flanks of the Dead Sea Transform during the late Quaternary.