Cementation of holocene beachrock in the Aqaba and the Arabian Gulfs: Comparative study

Abstract

Extensive precipitation of aragonite and high-Mg calcite (12-14% MgC0 3 ) cements in the intertidal sediments ofthe Gulf of Aqaba, Egypt and the Arabian Gulf, Qatar results in the formation of dominant beachrock exposures. The 20-60 ern thick beachrocks in both areas are parallel to the shoreline and slope gently seaward. The 14 C dating values show that the cement of the Gulf ofAqaba beachrock (2470±60y) are rather older than those ofthe Arabian Gulf (1360±45y). Framework grains in the Gulf of Aqaba beachrock are moderate to unsorted coarse terrigenous rock fragments, which differ than the unsorted carbonate particles ofthe Arabian Gulfbeachrock. Carbonate cements in both the Aqaba and the Arabian Gulfs display the same architecture, which comprises: 1) thin isopachous crust made up of high-Mg calcite mosaics and/or aragonite needles that surround grains and 2) intergranular cryptocrystalline high-Mg calcites, which fill the rest of the pores. Minor dolomite mosaics may associate with the intergranular cement. The co-existence of the aragonite needles, of the isopachous crust, with the micritized grains and micritic envelopes is evidence that marine phreatic processes are dominant in the intertidal zone and that lithification has started in this zone. The bi-mineralic composition of the isopachous crust in the Aqaba beachrock is attributed mairily to kinetic factors (i.e. the rate of supply of carbonate ions) and to the composition of the substrate and/or organic control in the beachrock of the Arabian Gulf. Some physico-chemical, kinetic, hydrologic and biologic factors are believed to be effective in controlling the precipitation rates ofthe isopachous cement. The oxygen and carbon isotopic composition of the intergranular high-Mg calcite cement of the Aqaba Gulf (+2.0 to -1.6 and +2.9 to +4.4 %0 PDB respectively) is in accord with their precipitation in equilibrium with marine water. However, the relatively depleted 0 180 (-0.5 to -3 %0 PDB) and 013C (+0.3 to +2.2 %0 PDB) values of the intergranular high-Mg calcite cement of the beachrock of the Arabian Gulf is attributed to extraneous source of bicarbonate ions. The minor dolomite rhombs are formed directly from seawater within microenvironments created in response to the release of Mg 2 + ions to the pore water following the partial dissolution of some high-Mg calcite carbonate particles.

An historical review of the Quaternary sedimentology of the Gulf (Arabian/Persian Gulf) and its geological impact

“…During the 1950s and 1960s there were numerous brief reports of modern contemporary cementation of carbonate sediments in a variety of environmental settings (see reviews in Bricker, 1971): Sugden (1963b) described aragonitic cements and the development of composite grains, "grapestones" of Illing (1954), and the penecontemporaeous cementation of intertidal flat sands; Taylor & Illing (1969, 1971a, Evamy (1973), Evans et al (1973), Shinn (1973), Kendall et al (1994), Holail et al (2004) and Whittle et al (1998), described modern cementation in the shallow-water intertidal and subtidal sediments of the UAE and Qatar.…”

Unraveling cementation environment and patterns of Holocene beachrocks in the Arabian Gulf and the Gulf of Aqaba: stable isotope approach

“…The high amounts of terrigenous frag ments, in clud ing plutonic, meta mor phic and vol ca nic rock frag ments, in the Gulf of Aqaba beachrocks most prob a bly were de rived from the adja cent Pre cam brian base ment which is nearby the study area and be came a pri mary source for the beachrock com po nents (Holail et al, 2004). Siliciclastic grain sup ply might also have re - Large gas tro pod and bi valve frag ments.…”

“…The micritic en ve lope pro vided a substrate for the growth of acicular ar agon ite ce ment and fa cil i tated nu cle ation of the ce ment mo sa ics on the grain sur face (Holail et al, 2004;Vieira and Ros, 2006). 212 Ardiansyah Koeshidayatullah and Khalid Al-Ramadan Cal i bra tion of sam ples based on cal i bra tion da ta base in for ma tion (MARINE09 from INTCAL09; Reimer et al, 2009;Erginal et al, 2013) Ta ble 2…”

Beachrock as a Paleoshoreline Indicator: Example from Wadi Al-Hamd, South Al-Wajh, Saudi Arabia

“…Figure 6. Bivariate plot between carbon and oxygen stable isotope composition of the Wadi Al-Hamd beachrocks and other beachrocks in the Arabian and Aqaba gulfs [32], Bahamian beachrocks [43], Red Sea and Mediterranean Sea [19], Mediterranean beachrocks of Israel [42].…”

“…They consist mainly of gravel-and sandsized siliciclastic grains and/or calcareous skeletal remains, cemented by aragonite and/or high Mg-calcite (HMC) and, rarely, low Mg-calcite [22,[26][27][28][29]. The beachrocks along the Saudi Red Sea and the Gulf of Aqaba coasts have received little attention compared to the Egyptian and Jordanian coasts ( [19,25,[30][31][32]]. An interesting, not previously documented beachrock crops out far inland, 1.1 km from the recent shoreline at the mouth of Wadi Al-Hamd, 50 km south of Al-Wajh City, at latitude N 25 • 57.737 and longitude E 36 • 42.721 (Figure 1).…”