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This study was supported through funds from ESF/CHECKREEF project (EI272/22-1 to AE; DU129/141-1 to W-CD; 20MA21-115944 and 200020-140618 to ES), by the collaborative research initiative CHARON (DFG Forschergruppe 1644 – Phase II) funded by the German Research Foundation, and by the GEOMAR Helmholtz Centre for Ocean Research Kiel. The Ph.D. program of RR was financially supported by the Tanzania Ministry of Education and Vocational Training (MoEVT) in collaboration with DAAD (Deutscher Akademischer Austauschdienst) fellowship. AR acknowledges support from Swiss National Science Foundation Project Number SNF 200021_149247. Coral-based reconstructions of sea surface temperatures (SSTs) using Sr/Ca, U/Ca and δ18O are important tools for quantitative analysis of past climate variabilities. However, post-depositional alteration of coral aragonite, particularly early diagenesis, restrict the accuracy of calibrated proxies even on young corals. Considering the diagenetic effects, we present new Mid to Late Holocene SST reconstructions on well-dated (U/Th: ∼70 yr to 5.4 ka) fossil Porites sp. collected from the Society Islands, French Polynesia. For few corals, quality pre-screening routines revealed the presence of secondary aragonite needles inside primary pore space, resulting in a mean increase in Sr/Ca ratios between 5-30%, in contrast to the massive skeletal parts. Characterized by a Sr/Ca above 10 mmol/mol, we interpret this value as the threshold between diagenetically altered and unaltered coral material. At a high-resolution, observed intra-skeletal variability of 5.4 to 9.9 mmol/mol probably reflects the physiological control of corals over their trace metal uptake, and individual variations controlled by CaCO3– precipitation rates. Overall, the Sr/Ca, U/Ca and δ18O trends are well correlated, but we observed a significant offset up to ± 7°C among the proxies on derived palaeo-SST estimates. It appears that the related alteration process tends to amplify temperature extremes, resulting in increased SST-U/Ca and SST-Sr/Ca gradients, and consequently their apparent temperature sensitivities. A relative SST reconstruction is still feasible by normalizing our records to their individual mean value defined as ΔSST. This approach shows that ΔSST records derived from different proxies agree with an amplitudinal variability of up to ± 2°C with respect to their Holocene mean value. Higher ΔSST values than the mean SSTs (Holocene warm periods) were recorded from ∼1.8 to ∼2.8 ka (Interval I), ∼3.7 to 4.0 ka (Interval III) and before ∼5 ka, while lower ΔSST values (Holocene cold periods, Interval II and IV) were recorded in between. The ensuing SST periodicity of ∼1.5 ka in the Society Islands record is in line with the solar activity reconstructed from 10Be and 14C production (Vonmoos et al., 2006), emphasizing the role of solar activity on climate variability during the Late Holocene. Publisher PDF

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Cool-water carbonate sedimentation has dominated Mediterranean shelves since the Early Pliocene. Skeletal sand and gravel herein consist of remains of heterozoan organisms, which are susceptible to reworking due to weak early cementation in non-tropical waters. This study documents the Lower Pleistocene carbonate wedge of Favignana Island (Italy), which prograded from a 5 km wide passage between two palaeo-islands into a perpendicular, 10 to 15 km wide strait between the palaeo-islands at one side and Sicily at the other during the Emilian highstand (1·6 Ma to 1·1 Ma). The clinoformed carbonate wedge, which is 50 m thick and 6 km long, formed by east/south-east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo-islands. Platform-slope clinoforms evolved from initial aggradation (thin and low-angle) into a progradation phase (thick and high-angle). Both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by: (i) subaqueous dunes associated with dilute subcritical currents; and (ii) upper-flow-regime bedforms associated with sediment-laden supercritical turbidity currents. Focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body, here named carbonate delta. The carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait. This study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway-related carbonate accumulation.

Carbonate mounds are important and ubiquitous components of the sedimentary rock record throughout the Phanerozoic. Nevertheless factors controlling their occurrence and growth remain enigmatic in particular because the depositional depths of such mounds are poorly constrained and it is assumed that fossil examples lack modern analogues. Factors currently used to constrain the water depth that ancient mounds grew in include water energy occurrence of specific organisms that perform photosynthesis (particularly calcareous algae) and distinct non biogenic components. In reviewing the main criteria used to delineate water depth of formation of fossil carbonate mounds most (if not all) criteria traditionally used to assume shallow water settings appear to be no longer substantiated in the light of current knowledge gained from modern carbonate mounds. High energy assumed to indicate shallow water conditions is ongoing in water as deep as > 1000 m. The occurrence of peloids and processes such as micritization is not diagnostic of water depth. Furthermore virtually none of the calcareous algae assumed to indicate the photic zone have a taxonomically granted affiliation. Over the last years research in the deep ocean in particular thanks to the deployment of new devices and techniques provided a good database revealing a wide distribution of modern carbonate mounds. Reviewing the characteristics of ancient carbonate mounds with emphasis on depositional settings and confronting the criteria used with current knowledge from sub recent and modern carbonate mounds we conclude that for many ancient mounds a bathyal origin is (at least) as likely as a shallow water origin. This conclusion is well supported by the sedimentary records left by these modern mounds that are astonishingly similar to those seen in Palaeozoic and Mesozoic carbonate mounds.

In this study, we present the first experimental results for stable barium (Ba) isotope (¹³⁷Ba/¹³⁴Ba) fractionation during low-temperature formation of the anhydrous double carbonate BaMn[CO₃]₂. This investigation is part of an ongoing work on Ba fractionation in the natural barium cycle. Precipitation at a temperature of 21±1°C leads to an enrichment of the lighter Ba isotope described by an enrichment factor of−0.11±0.06‰ in the double carbonate than in an aqueous barium-manganese(II) chloride/sodium bicarbonate solution, which is within the range of previous reports for synthetic pure BaCO ₃ (witherite) formation.

Preliminary geological investigations on Providenciales (Caicos) and Mayaguana (Bahamas) show disparities between the two islands, possibly related to differences in the area of emerged land on platform tops.The Mayaguana and Caicos platforms are located in the SE Bahamas. Caicos is a large (100x70 km) edifice supporting small islands along its northern margin. Mayaguana is smaller (55x15 km) and comprises one island covering most of the platform surface. Providenciales and Mayaguana islands predominantly consist, in different proportion, of reefal framestones and oolitic grainstones dating from the last interglacial period. Oolitic ridges are widely exposed on Providenciales where reefal deposits are confined to the west coast. In Mayaguana, oolitic ridges are subordinate to the reefs that occur along most of the island shorelines. In Providenciales, the older substrate consists of oolitic and bioclastic eolianites of middle Pleistocene age. In Mayaguana, oldest rock units include fine-grained dolostone and bioturbated marine facies, exposed at about +8 m, containing fragments of benthic foraminifers that became extinct in the Pliocene.This difference in the distribution of Pleistocene facies could be related to the extent of emerged land on platform tops. The Caicos physiography was favourable to water circulation and thus to ooid production on the platform. By contrast, the setting in Mayaguana was more conducive to reef growth. The oolitic and bioclastic substrates exposed on Providenciales are similar to those observed in the northern Bahamas. If confirmed, the pre-Quaternary age of the dolomitic and elevated marine units on Mayaguana would question some fundamentals of Bahamian geology.

Algal buildups from five stratigraphic intervals in the Pennsylvanian of eastern Kansas, Midcontinent, U.S.A., display three basic fabrics based on their: a) dimension, b) morphology, c) fossil content, d) algal growth forms, and e) nature of framework cavities. Type 1. Constructional mounds composed of cup-shaped in situ algal growth forms are typically small bioherms, either isolated (e.g., Frisbie Limestone Member) or thickened intervals within carbonate banks (e.g., Sniabar Limestone Member), and are basically formed by phylloid green algae. Fossil diversity is very low. Mud and cement fill the abundant small intercup voids within individual mounds. Calcareous sponges, crinoids, and bryozoans, probably cavity dwellers, fill the larger intermound cavities between the smaller mounds. Type 2. Constructional mounds of algae with undulatory growth forms are basically red algae with recognizable thalli characteristics of Archaeolithophyllum, and, only rarely, of phylloid green algae. Buildups of this kind are laterally persistent. Thickening of the banks is generally recognizable at a large scale (ten of meters to kilometers). Smaller, meter-scale bioherms constructed of algae with undulatory growth forms do not occur in the sites studied. Fossil diversity is higher than in type (1) mounds, with calcareous sponges, brachiopods, and bryozoans common throughout the mound, rather than exclusively in cavities between small mounds of the type 1 cup-shaped algae. When built by green algae (e.g., parts of the Captain Creek Limestone Member), mounds have a lower diversity than those constructed by red algae (e.g., Spring Hill Limestone Member). Solitary corals, calcareous sponges, and bryozoans occur attached to the walls of the cavities. The abundance of open pores is striking. Type 3. Mounds of accumulated algae with undulatory growth forms are formed by the red algae Archaeolithophyllum missouriense, Archaeolithophyllum lamellosum, and the green alga Eugonophyllum. Depositional relief is not visible on the outcrop, but large-scale variations in bank thickness are notable (e.g., lower part of the Captain Creek Limestone Member). Bryozoans and Thartharella (a probable worm tube) are common. Multiple types of cavities occur, and most are cement-filled. Although the mound types differ in their form, fossil content, and type and distribution of voids, they share an overall common peloidal clotted matrix that accumulated in specific areas, along with an abundance of gravity-defying peloidal micritic structures in the matrix, and of thin crusts within marine cement that may be related to microbial activity. Microbes probably played a crucial role in carbonate precipitation and in lithification of algal-dominated buildups.