Climate, duration, and mineralogy controls on meteoric diagenesis, La Molata, southeast Spain

Abstract

We isolated the impact of climate, duration, and mineralogy on porosity enhancement and cementation associated with seven surfaces of subaerial exposure in Miocene carbonate strata of southeast Spain. We integrated new and published petrographic and geochemical studies on the same strata to quantify the approximate impact of each event of subaerial exposure. The results quantified that only minor dissolution and/or cementation occurred when subaerial exposure was short-lived (<533 thousand years) and in an arid climate, or when carbonate sediments were composed primarily of calcite. For such exposure surfaces, alteration was confined to the uppermost 0.5-2 m with 2%-5% porosity from dissolution and 3% cementation. After deposition of the last Miocene carbonate sequence, dolomitization and dissolution occurred during the initial stages of sea-level fall, associated with mixing during influx of meteoric water. This resulted in dissolution to create 10%-20% porosity over 83% of the platform system, and this indicated that even incipient subaerial exposure can lead to major porosity enhancement during times of high freshwater recharge and hydrogeology that promotes mixing. During a long-lived period of subaerial exposure (greater than 5.3 million years) associated with wet climate, major amounts of cementation reduced porosity in the phreatic zone and some porosity was enhanced in the vadose zone. This included 25% freshwater calcite cement affecting 53% of the platform. Dissolution during and after calcite cementation was approximately 8% throughout the platform. These observations predict that duration and climate combine to have the most significant impacts on porosity associated with subaerial exposure.

Seismic characterization of switching platform geometries and dominant carbonate producers (Miocene, Las Negras, Spain)

“…The carbonates that developed on the margins of the Cabo de Gata volcanic complex show an increased level of complexity due to sediment mixing with non‐carbonate material and dolomitization processes that originated from freshwater–mesohaline mixing in the subsurface (Li et al ., ). Throughout the carbonate platform, dissolution and subsequent recrystallization processes occur resulting in crystalline grains and cements (Li et al ., , ). The types of biota encountered in the Cerro de la Molata strata are dependent on the active carbonate factory (Fig.…”

“…The diagenetic modifications that have affected the sediments of the Cerro de la Molata have been studied extensively (Li et al ., , , ; Benson et al ., ). Dolomitization occurred as a result of freshwater–mesohaline mixing in the subsurface.…”

“…Diagenetic effects can also be related to structural events, where dolomite geobodies are formed as a result of fluid circulation through faults or fractures (Dewit et al ., ; Jacquemyn et al ., ). The sediments of the Cerro de la Molata Platform underwent multiple stages of diagenetic modifications that affected the petrophysical properties (Li et al ., , , ; Benson et al ., ). However, regardless of the diagenetic overprint, the individual facies remained a unique petrophysical signature and can therefore be distinguished from one another.…”

“…On top of the dolomitization, Li et al . () describe seven surfaces that are related to relative sea‐level fall and minor meteoric diagenesis. Three of the seven surfaces are coherent with the main sequence boundaries and the other four surfaces occur within the TCC.…”

“…The chemical and thermal interaction with the VB underlying the Miocene carbonate strata possibly triggered the dolomitization and dissolution processes (Li et al, 2013). On top of the dolomitization, Li et al (2014) describe seven surfaces that are related to relative sea-level fall and minor meteoric diagenesis. Three of the seven surfaces are coherent with the main sequence boundaries and the other four surfaces occur within the TCC.…”