Geochemical signatures of pervasive meteoric diagenesis of Early Miocene syn-rift carbonate platform, Red Sea, NW Saudi Arabia

Abstract

Al-Ramadan, K., 2017. Geo chem i cal sig na tures of per va sive me te oric diagenesis of Early Mio cene syn-rift car bon ate platform, Red Sea, NW Saudi Ara bia. Geo log i cal Quar terly, 61 (1): 239-250, doi: 10.7306/gq.1334 Dif fer ent diagenetic en vi ron ments have been rec og nized in the Early Mio cene car bon ate plat form of Musayr For ma tion in the Red Sea rift area. Early ma rine diagenesis in cludes micritisation that oc curs as thin en ve lope around skel e tal and non-skel etal grains in low-en ergy mud dom i nated fa cies and isopachous fi brous cal cite in high-en ergy grain-dom i nated fa cies. Per vasive me te oric wa ter diagenesis re sulted in ce men ta tion of the car bon ates by coarse-crys tal line blocky-drusy cal cite and me nis cus ce ments. De ple tion of ox y gen (avg. -9.08‰), car bon (avg. -1.6‰) iso topes and trace el e ments con cen tra tions (avg. val ues of Fe: 1387 ppm; Mn: 1444 ppm; Sr: 419 ppm; Na: 1194 ppm) in con junc tion with neg a tive cor re la tion be tween Mn 2+ and ox y gen iso tope data sug gest vari able de grees of fluid-rock in ter ac tions and per va sive me te oric diagenesis. The for ma tion of me te oric diagenesis in the Musayr For ma tion can be ex plained by two sub se quent mech a nisms: (1) the presence of me te oric lenses dur ing the time of de po si tion might have been as so ci ated with ac tive fresh wa ter in put from the hinter land (NE) due to fall in the rel a tive sea level; (2) later up lift ep i sode dur ing Plio-Pleis to cene may have also con trib uted to the per va sive me te oric diagenetic al ter ations of the car bon ates of the Musayr For ma tion. The first mech a nism is sup ported by the ce ment stra tig ra phy where the blocky-drusy ce ments post date the me nis cus ce ment. The lat ter mech a nism seems to have more pro nounced ef fect on the al ter ation of Musayr car bon ate se quence by ob serv ing the occurence of late ce ments such as blocky cal cite in most of the sam ples. The im pact of me te oric diagenesis on the stud ied sam ples sug gest that dis solu tion is less se vere than ce men ta tion, hence the vis i ble po ros ity is very low. Un der stand ing the tim ing of me te oric diagenesis pro vides use ful in for ma tion about the res er voir qual ity dis tri bu tion in syn-rift car bon ate se quences.

Structural diagenesis and dolomitization of Cenozoic post-rift carbonates in the Red Sea rift basin: A multiproxy approach

“…In addition, the 54 carbon and oxygen isotopic data points from Miocene carbonate situated in the Midyan Peninsula at four different locations, Wadi Waqb, Ad-Dubaybah, Wadi Hamd, and Magna, were re-visited in this study (Al-Ramadan, 2017;Al-Ramadan et al, 2019).…”

“…The creation of micrite envelopes by microboring organisms surrounding skeletal and non-skeletal grains may provide a substrate for a developing marine cement (Al-Ramadan et al, 2019). The depositional environment of the carbonate host rock is suggested to have been deposited in the platform interior to platform margin carbonate facies, characterized by a highly heterogeneous vertical succession (Koeshidayatullah et al, 2016;Al-Ramadan, 2017;Al-Ramadan et al, 2019). The dolomitization process is interpreted to be near-surface, early formed dolomite, based on its fabric-preserving mimetic texture (e.g., Sibley and Gregg, 1987;Swart, 2015).…”

“…In Magna and Wadi Alhamd, meteoric diagenesis has been interpreted as a product of early diagenesis (eodiagenesis) associated with several episodes of relative sea-level low stands during deposition in the Early Miocene. Subsequently, the peripheral uplift and influx of meteoric water resulted in dolomitization of pre-existing Miocene carbonate (Al-Ramadan, 2017). The meteoric diagenesis in Magna and Wadi Alhamd is characterized by clear blocky and drusy mosaic cement, followed by selective dissolution through the fractures.…”

“…The Miocene carbonate in the Red Sea Basin is an ideal location for studying paleo-fluid circulation along fractures, due to of the exposed carbonate outcrop and the existence of a network of fractures filled with diagenetic calcite crystals (Al-Ramadan, 2017;Hollis et al, 2017;Al-Ramadan et al, 2019). Carbonate rocks are of particular interest, due to the wide variety of diagenetic modifications that can occur as a result of paleofluid circulation along fractures (Stacey et al, 2021a;Stacey et al, 2021b;Koeshidayatullah et al, 2022).…”