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The Middle to Late Miocene mixed carbonate-siliciclastic coastal wedge of the Pietra di Finale, unconformably overlying the Ligurian Alps succession, displays a carbonate portion dominated by Halimeda and Porites fragments that fall in the photozoan assemblages. Photozoan assemblages typically develop under tropical and oligotrophic conditions, while hetorozoan assemblages tend to thrive in high-nutrient settings. The Pietra di Finale Formation shows, however, that high weathering and an increase of nutrient inputs related to Alpine uplift and humid climatic conditions promoted Halimeda over the seagrass carbonate factory in the photic zone. The successful Halimeda proliferation was due to its efficient competition for nutrients, especially nitrogen. Thus, the Pietra di Finale Formation represents an interesting, counter-intuitive example in which increased nutrient concentrations promoted, instead of inhibited, a photozoan over a seagrass-related heterozoan carbonate production. [ABSTRACT FROM AUTHOR]

Trophic resources are an important control governing carbonate production. Though this importance has long been recognized, no calibration exists to quantitatively compare biogenic assemblages within trophic resource fields. This study presents a field calibration of carbonate producers in a range of settings against high-resolution in situ measurements of nutrients, temperature and salinity. With its latitudinal extent from 30° to 23° N, the Gulf of California, Mexico, spans the warm-temperate realm and encompasses nutrient regimes from oligo-mesotrophic in the south to eutrophic in the north. Accordingly, from south to north carbonates are characterized by: (i) coral-dominated shallow carbonate factories (5–20 m water depth) with average sea-surface temperatures of 25 °C (min. 18 °C, max. 31 °C), average salinities of 35·06‰ and average chlorophyll a levels, which are a proxy for nutrients, of 0·25 mg Chl a m−3 (max. 0·48, min. 0·1). (ii) Red algal-dominated subtidal to inner-shelf carbonate formation (10–25 m) in the central Gulf of California exhibiting average temperatures of 23 °C (min. 18 °C, max. 30 °C), average salinities of 35·25‰, and average Chl a levels of 0·71 Chl a m−3 (max. 5·62, min. 0). (iii) Molluskan bryozoan-rich inner to outer shelf factories in the northern Gulf of California (20–50 m) with average sea surface temperatures of only 20 °C (min. 13 °C, max 29 °C), average salinities of 35·01‰, and average contents of 2·2 mg Chl a m−3 (max. 8·38, min. 0). By calibrating sedimentological data with in situ measured oceanographic information in different environments, the response of carbonate producers to environmental parameters was established and extrapolated to carbonates on a global scale. The results demonstrate the importance of recognizing and quantifying trophic resources as a dominant control determining the biogenic composition and facies character of both modern and fossil carbonates. [ABSTRACT FROM AUTHOR]

The North West Shelf is an ocean-facing carbonate ramp that lies in a warm-water setting adjacent to an arid hinterland of moderate to low relief. The sea floor is strongly affected by cyclonic storms, long-period swells and large internal tides, resulting in preferentially accumulating coarse-grained sediments. Circulation is dominated by the south-flowing, low-salinity Leeuwin Current, upwelling associated with the Indian Ocean Gyre, seaward-flowing saline bottom waters generated by seasonal evaporation, and flashy fluvial discharge. Sediments are palimpsest, a variable mixture of relict, stranded and Holocene grains. Relict intraclasts, both skeletal and lithic, interpreted as having formed during sea-level highstands of Marine Isotope Stages (MIS) 3 and 4, are now localized to the mid-ramp. The most conspicuous stranded particles are ooids and peloids, which 14C dating shows formed at 15.4-12.7 Ka, in somewhat saline waters dining initial stages of post-Last Glacial Maximum (LGM) sea-level rise. It appears that initiation of Leeuwin Current flow with its relatively less saline, but oceanic waters arrested ooid formation such that subsequent benthic Holocene sediment is principally biofragmental, with sedimentation localized to the inner ramp and a ridge of planktic foraminifera offshore. Inner-ramp deposits are a mixture of heterozoan and photozoan elements. Depositional facies reflect episodic environmental perturbation by riverine-derived sediments and nutrients, resulting in a mixed habitat of oligotrophic (coral reefs and large benthic foraminifera) and mesotrophic (macroalgae and bryozoans) indicators. Holocene mid-ramp sediment is heterozoan in character, bill sparse, most probably because of the periodic seaward flow of saline bottom waters generated by coastal evaporation. Holocene miter-ramp sediment is mainly pelagic, veneering shallow-water sediments of Marine Isotope Stage 2, including LGM deposits. Phosphate accumulations at 200 m water depth suggest periodic upwelling or Fe-redox pumping, whereas enhanced near-surface productivity, probably associated with the interaction between the Leeuwin Current and Indian Ocean surface water, results in a linear ridge of pelagic sediment at 140 m water depth. This ramp depositional system in an arid climate has important applications for the geological record: inner-ramp sediments can contain important heterozoan elements, mid-ramp sediments with bedforms created by internal tides can form in water depths exceeding 50 m, saline outflow can arrest or dramatically slow mid-ramp sedimentation mimicking maximum flooding intervals, and outer-ramp planktic productivity can generate locally important fine-grained carbonate sediment bodies. [ABSTRACT FROM AUTHOR]

In addition to salinity and temperature, nutrient concentrations in surface waters are known to have a significant impact on distribution of carbonate-producing biota, but have never been quantitatively evaluated against different temperatures along a latitudinal transect. The western coast of the Gulf of California, Mexico, presents a natural laboratory for investigating the influence of oceanographic parameters such as salinity, temperature, and chlorophyll a, a proxy for nutrients, on the composition of a range of modern heterozoan and photozoan carbonate environments along a north-south latitudinal gradient spanning the entire warm-temperate realm (29°N-23°N). Chlorophyll a, measured in situ at halfhour resolution, is highly variable throughout the year due to short-term upwelling, and increases significantly from the southern to northern Gulf of California. Salinity, in contrast, fluctuates little and remains at an average of 35‰. From south to north, carbonate production ranges from oligotrophic-mesotrophic, coral reefdominated shallow-water areas (minimum temperature 18.6 °C) through mesotrophic-eutrophic, red algal-dominated, inner-shelf carbonate production in the central gulf (minimum temperature 16 °C), and to molluscan-bryozoan, eutrophic inner- to outer-shelf environments (minimum temperature 13.7 °C). The Gulf of California data, supplemented with oceanographic and compositional information from a database compiled from a spectrum of modern carbonate systems worldwide, demonstrates the significance of nutrient control in the formation of heterozoan, photozoan, and transitional heterozoan-photozoan carbonate systems and serves as a basis for more accurately interpreting fossil carbonates. [ABSTRACT FROM AUTHOR]

Modern mixed carbonate-siliciclastic warm-temperate environments were studied in the southern Gulf of California (GOC), Mexico. The combined heterozoan and photozoan character is defined by the absence of true coral reef structures, calcareous green algae and non-skeletal grains, and the dominance of rhodoliths (unattached coralline red algae), mollusks and small coral patch reefs. The major carbonate producing environments are pocket bays, a shallow carbonate bioherm, high-energy rocky and sandy shorelines and mid-shelf settings. Sediments characterizing the pocket bays display heavily bioturbated bioclastic wackestone and grainstone textures. The rhodolith dominated bioherm is composed of coarse sediments exhibiting grainstone and rudstone textures with fine material being winnowed away by tidal currents. Rocky and sandy shorelines are characterized by erosion and mixing of up to boulder size granitic and volcaniclastic material with coralline red algal and molluskan carbonates. The mid-shelf settings are defined by a silt and fine sand sized non-carbonate matrix mixed with abundant molluskan fragments and foraminifera. Peak carbonate production takes place between 10 and 15 m water depth; below 40 m production significantly decreases, combined with a steep increase in the amount of siliciclastics. This is in contrast to many temperate and cool-water mixed-carbonate siliciclastic systems, where most carbonate production occurs in mid- to outer shelf settings. A full spectrum of sediments from pure carbonates (90–100% carbonate), allochem carbonates (50–90% carbonate) and allochemic mud or sand (<50% carbonate) was encountered in the study area. The absence of early diagenetic binding and cementation of the non-tropical carbonates facilitates mixing of carbonates and siliciclastics. The latter are mainly derived from adjacent Tertiary volcaniclastics and Mesozoic granites. Mixing takes place (1) as punctuated mixing during periodic short-term storm or hurricane events, when coarse granitic and volcaniclastic derived material eroded from rocky shorelines is transported into the shallow carbonate factories, and (2) as facies mixing on the outer carbonate shelf below 40 m water depth where carbonates interfinger with olive-gray sandy and silty siliciclastics. [Copyright &y& Elsevier]

The Murray Supergroup records temperate-water carbonate deposition within a shallow, mesotrophic, Oligo-Miocene inland sea protected from high-energy waves and swells of the open ocean by a granitic archipelago at its southern margin. Rocks are very well preserved and exposed in nearly continuous outcrop along the River Murray in South Australia. Most facies are rich in carbonate silt, contain a background assemblage of gastropods (especially turritellids) and infaunal bivalves, and are packaged on a decimetre-scale defined by firmground and hardground omission surfaces. Bioturbation is pervasive and overprinted, resulting in rare preservation of physical sedimentary structures. Facies are grouped into four associations (large foraminiferan–bryozoan, echinoid–bryozoan, mollusc and clay facies) interpreted to represent shallow-water (<50 m) deposition under progressively higher trophic resource levels (from low mesotrophy to eutrophy), and restricted marine conditions from relatively offshore to nearshore regions. A large-scale shift from high- to low-mesotrophic conditions within lower Miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow, land-locked sea. Overall, low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone, a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity. Inshore, heterozoan facies became progressively muddier and restricted towards the shoreline. In contrast, periods of wet climate led to rising trophic resource levels, resulting in a shallowing of the euphotic zone, a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids. Rates of carbonate production and accumulation were relatively low. The Murray Basin is best described as an epeiric ramp. Wide facies belts developed in a shallow sea on a low-angled slope reaching many hundreds of kilometres in length. Grainy shoal and back-barrier facies were absent. Internally generated waves impinged the sea floor in offshore regions and, because of friction along a wide and shallow sea floor, created a low-energy expanse of waters across the proximal ramp. Storms were the dominating depositional process capable of disrupting the entire sea floor. [ABSTRACT FROM AUTHOR]

The acoustic properties of heterozoan and photozoan carbonates are compared and interpreted in the light of their distinct patterns of diagenetic evolution. The combined role of depositional and diagenetic processes on the petroacoustic signatures of both heterozoan and photozoan carbonates has been assessed on the basis of a multi-disciplinary and multi-scale study of Oligo-Miocene limestone outcrops from the Cape Range peninsula (NW Australia). This study integrates a detailed diagenetic analysis (using sedimentology, petrography and stable isotopes geochemistry), as well as physical properties characterization (through acoustic velocity laboratory and porosity measurements, petroacoustic modelling and 3D CT-scan imaging). The three formations studied are characterized by distinct patterns of diagenetic and petroacoustic evolution: heterozoan, non-tropical carbonates from the Mandu and Tulki formations are characterized by significant development of microporosity and pressure-solution compaction features which led to decreasing the pore network stiffness. Photozoan, sub-tropical to tropical carbonates from the Trealla formation are dominated by moldic, vuggy and partially cemented intergranular pores which tends to increase the pore network stiffness. The distinct petroacoustic signatures of heterozoan and photozoan limestones have been shown to be mainly related to (1) differences in compaction during burial resulting from an emersion phase and (2) differences in the mineralogy of dominant carbonate producers. Temperate High-Mg calcite dominated carbonate typically poorly cemented allowed for greater compaction degree, reducing the ratio of intergranular macropore. Furthermore, these dominant calcite producers (large benthic foraminifers, red algae ...) from the heterozoan Mandu and Tulki formations favoured the development of intragranular microporosity whereas less-stable aragonite dominated biota from the photozoan Trealla Limestone favoured the development of molds and vugs, during early meteoric diagenesis. Finally, petroacoustic modelling approaches such as α K inversion have proved to be efficient for quantifying the impact of diagenetic processes and associated pore types on acoustic properties. These results, emphasizing the strong variability in depositional and diagenetic features for distinct carbonate fabrics could have interesting implications in terms of reservoir properties 3D modelling and upscaling approaches. • We studied the petroacoustic signature of Oligo-Miocene limestones from NW Australia. • Heterozoan & photozoan carbonates are characterized by distinct diagenetic processes. • Distinct diagenetic paths led to different dominant pore types and acoustic signatures. • 2 main causes explain it: drastic change in carbonate factory type and emersion phase. • Pore types were successfully retrieved by equivalent pore aspect ratio modelling. [ABSTRACT FROM AUTHOR]