Description: Early‐diagenetic cementation of tropical carbonates results from the combination of numerous physico‐chemical and biological processes. In the marine phreatic environment it represents an essential mechanism for the development and stabilization of carbonate platforms. However, diagenetic cements that developed early in the marine phreatic environment are likely to become obliterated during later stages of meteoric or burial diagenesis. When lithified sediment samples are studied, this complicates the recognition of processes involved in early cementation, and their geological implications. In this contribution, a petrographic microfacies analysis of Holocene Halimeda segments collected on a coral island in the Spermonde Archipelago, Indonesia, is presented. Through electron microscopical analyses of polished samples, this study shows that segments are characterized by intragranular cementation of fibrous aragonite, equant High‐Mg calcite (3.9 to 7.2 Mol% Mg), bladed Low‐Mg calcite (0.4 to 1.0 Mol% Mg) and mini‐micritic Low‐Mg calcite (3.2 to 3.3 Mol% Mg). The co‐existence and consecutive development of fibrous aragonite and equant High‐Mg calcite results initially from the flow of oversaturated seawater along the aragonite template of the Halimeda skeleton, followed by an adjustment of cement mineralogy towards High‐Mg calcite as a result of reduced permeability and fluid flow rates in the pores. Growth of bladed Low‐Mg calcite cements on top of etched substrates of equant High‐Mg calcite is explained by shifts in pore water pH and alkalinity through microbial sulphate reduction. Microbial activity appears to be the main trigger for the precipitation of mini‐micritic Low‐Mg calcite as well, based on the presumable detection of an extracellular polymeric matrix during an early stage of mini‐micrite Low‐Mg calcite cement precipitation. Radiocarbon analyses of five Halimeda segments furthermore indicate that virtually complete intragranular cementation in the marine phreatic environment with thermodynamically/kinetically controlled aragonite and High‐Mg calcite takes place in about 100 years. Collectively, this study shows that early‐diagenetic cements are highly diverse and provides new quantitative constraints on the rate of diagenetic cementation in tropical carbonate factories.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: https://doi.pangaea.de/10.1594/PANGAEA.923980

Description: Decreases in seawater pH and carbonate saturation state (Omega) following the continuous increase in atmospheric CO2 represent a process termed ocean acidification, which is predicted to become a main threat to marine calcifiers in the near future. Segmented, tropical, marine green macro-algae of the genus Halimeda form a calcareous skeleton that involves biotically initiated and induced calcification processes influenced by cell physiology. As Halimeda is an important habitat provider and major carbonate sediment producer in tropical shallow areas, alterations of these processes due to ocean acidification may cause changes in the skeletal microstructure that have major consequences for the alga and its environment, but related knowledge is scarce. This study used scanning electron microscopy to examine changes of the CaCO3 segment microstructure of Halimedaopuntia specimens that had been exposed to artificially elevated seawater pCO2 of 650 µatm for 45 d. In spite of elevated seawater pCO2, the calcification of needles, located at the former utricle walls, was not reduced as frequent initiation of new needle-shaped crystals was observed. Abundance of the needles was 22 %/µm**2 higher and needle crystal dimensions 14 % longer. However, those needles were 42 % thinner compared with the control treatment. Moreover, lifetime cementation of the segments decreased under elevated seawater pCO2 due to a loss in micro-anhedral carbonate as indicated by significantly thinner calcified rims of central utricles (35-173 % compared with the control treatment). Decreased micro-anhedral carbonate suggests that seawater within the inter-utricular space becomes CaCO3 undersaturated (Omega 〈 1) during nighttime under conditions of elevated seawater pCO2, thereby favoring CaCO3 dissolution over micro-anhedral carbonate accretion. Less-cemented segments of H. opuntia may impair the environmental success of the alga, its carbonate sediment contribution, and the temporal storage of atmospheric CO2 within Halimeda-derived sediments.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1 m, 2 m, ..., 10 m) using percussion drilling (jackhammer: WACKER BH 23, Wacker Neuson SE, probe: direct push corer with internal liner (1m length & 46 mm diameter)). Samples were taken from lowest 10 cm of probe. Examples: BL1-1 is sample from location BL1 in depth interval 90-100 cm. BL4-7 is sample from location BL4 in depth interval 690-700 cm. Laboratory data was collected between 2019 and 2021. The provided dataset contains grain size (raw and processed data; using GRADISTAT by Blott & Pye, 2001), skeletal component analysis (counting of fragments, 500 per sample; raw data) and facies determination (based on grain size and skeletal composition) of each sample. Additionally, the dataset provides raw and calibrated radiocarbon ages from 20 selected samples (calibration curve by Heaton et al. 2020; marine reservoir correction by Southon et al. 2002; calibration tool OxCal v4.4 by Bronk Ramsey, 2009). For the radiocarbon analyses, picked and pooled foraminifera of the genus Calcarina were chosen. These 20 samples were furthermore classified in terms of abrasion (1=very good preserved,... 4=very poorly preserved), following suggestions by Fellowes et al. 2017. The calibrated ages cover the earlier to late Holocene (~7,000 to 2,000 years BP). The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago. It provides insight into the ecological background and the origin of the skeletal sediments.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1 m, 2 m, ..., 10 m). Laboratory data was collected between 2019 and 2021. The provided dataset contains skeletal component analysis (counting of fragments, 500 per sample; raw data). Microscope analysis of 200 components from fractions 〉2 mm and 2-1 mm and 100 components from fraction 1-0.5 mm. 12 different calcifying organisms were distinguished, of which 10 were identified in the present dataset. Non-identifiable grains were counted as bioclasts and not added to the sum of 200 and 100, respectively.The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago. It provides insight into the ecological background and the origin of the skeletal sediments.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1 m, 2 m, ..., 10 m). Laboratory data was collected between 2019 and 2021. The provided dataset contains raw grain sizes determined after dry sieving. Samples were weighed before sieving (initial mass). After sieving, fractions (diameters from 32 mm to 0.0063 mm) from each sieve were weighed to analyze grain size distribution. The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1 m, 2 m, ..., 10 m). Laboratory data was collected between 2019 and 2021. The provided dataset contains raw and calibrated radiocarbon ages from 20 selected samples (Marine20 calibration curve by Heaton et al. 2020; marine reservoir correction by Southon et al. 2002; calibration tool OxCal v4.4 by Bronk Ramsey, 2009; delta R = 0). For the radiocarbon analyses, picked and pooled Foraminifera of the genus Calcarina were dated in Poznan Radiocarbon Laboratory. The calibrated ages cover the earlier to late Holocene (~7,000 to 2,000 years BP). The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago. It provides insight into the ecological background and the origin of the skeletal sediments.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1 m, 2 m, ..., 10 m). Laboratory data was collected between 2019 and 2021. The provided dataset contains the classification of facies. Percentages of compositions in samples were calculated by adding up relative counts of skeletal components for each samples (i.e. 200 components from fraction 〉2 mm plus 200 from fraction 2-1 mm plus 100 from fraction 1-0.5 mm). The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago. It provides insight into the ecological background and the origin of the skeletal sediments.

Description: The dataset is based on 50 soft carbonate sediment samples from the reef island Barrang Lompo in the Spermonde Archipelago, Sulawesi, SE Asia. The subsurface samples were obtained by percussion drilling at 5 coring locations on the island. From each coring location, 10 samples were retrieved in 1 m intervals, thus providing samples from a maximum depth of 10 m below surface at each site (1m, 2m, ..., 10m). Laboratory data was collected between 2019 and 2021. The provided dataset contains grain size (raw and processed data; using GRADISTAT by Blott & Pye, 2001), skeletal component analysis (counting of fragments, 500 per sample; raw data) and facies determination (based on grain size and skeletal composition) of each sample. Additionally, the dataset provides raw and calibrated radiocarbon ages from 20 selected samples (calibration curve by Heaton et al. 2020; marine reservoir correction by Southon et al. 2002; calibration tool OxCal v4.4 by Bronk Ramsey, 2009). For the radiocarbon analyses, picked and pooled foraminifera of the genus Calcarina were chosen. These 20 samples were furthermore classified in terms of abrasion (1=very good preserved,... 4=very poorly preserved), following suggestions by Fellowes et al. 2017. The calibrated ages cover the earlier to late Holocene (~7,000 to 2,000 years BP). The collected data provides information of reef-derived sedimentation in the Holocene in the Spermonde Archipelago. It provides insight into the ecological background and the origin of the skeletal sediments.

Description: Early-diagenetic cementation of tropical carbonates results from the combination of numerous physico-chemical and biological processes. In the marine phreatic environment it represents an essential mechanism for the development and stabilization of carbonate platforms. However, diagenetic cements that developed early in the marine phreatic environment are likely to become obliterated during later stages of meteoric or burial diagenesis. When rock samples are studied, this complicates the recognition of processes involved in cementation, and their geological implications. In this contribution, a petrographic microfacies analysis of Holocene Halimeda segments collected on a coral island in the Spermonde Archipelago, Indonesia, is presented. Through electron microscopical analyses of polished sections, this study shows that segments are characterized by intragranular cementation of fibrous aragonite, equant Mg calcite (3.9 – 7.2 Mol% Mg), bladed low Mg calcite (0.4 – 1.0 Mol%) and mini-micritic Mg calcite (3.2 – 3.3 Mol% Mg). The co-existence and consecutive development of fibrous aragonite and equant Mg calcite results initially from the flow of oversaturated seawater above the aragonite template, followed by an adjustment of cement mineralogy towards Mg calcite due to reduced permeability and fluid flow rates in the pores. Growth of bladed low Mg calcite cements on top of etched substrates of equant Mg calcite is explained by shifts in pore water pH and alkalinity through microbial sulfate reduction. Microbial activity appears to be the main trigger for the precipitation of mini-micritic Mg calcite as well, based on the presumable detection of an extracellular polymeric matrix during an early stage of mini-micrite cement precipitation.