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Acorn barnacles are sessile crustaceans common in shallow-water settings, both in modern oceans and in the Miocene geological record. Barnacle-rich facies occur from polar to equatorial latitudes, generally associated with shallow-water, high-energy, hard substrates. The aim of this work is to investigate this type of facies by analysing, from the palaeontological, sedimentological and petrographical points of view, early Miocene examples from Northern Italy, Southern France and South-western Peru. Our results are then compared with the existing information on both modern and fossil barnacle-rich deposits. The studied facies can be divided into two groups. The first one consists of very shallow, nearshore assemblages where barnacles are associated with an abundant hard-substrate biota (e.g., barnamol). The second one includes a barnacle-coralline algae association, here named “barnalgal” (= barnacle / red algal dominated), related to a deeper setting. The same pattern occurs in the distribution of both fossil and recent barnacle facies. The majority of them are related to very shallow, high-energy, hard-substrate, a setting that represents the environmental optimum for the development of barnacle facies, but exceptions do occur. These atypical facies can be identified through a complete analysis of both the skeletal assemblage and the barnacle association, showing that barnacle palaeontology can be a powerful tool for palaeoenvironmental reconstruction.

The Bragantina Platform is an important sedimentary package that occurs in northwestern Brazil, typically around the equatorial western Atlantic coast. Most of the latest Neogene succession of this carbonate-siliciclastic platform consists of the Pirabas Formation of Miocene age (Burdigalian to Serravalian). High-energy coastal storms and hurricanes as a consequence of trade wind anomalies during the Neogene impacted the shallow-water inner marine heterozoan assemblage deposits of the Pirabas Formation. A chaotic overlap of benthic infauna and epifauna, and of demersal and pelagic species in the same section was analyzed using petrography, petrophysics, micro- and macropaleontology, taphonomy, and geochemistry in order to understand sedimentary and paleoenvironmental processes. The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. This high-energy wave environment caused severe damage to shallow-water heterozoan assemblages at the seafloor, resulting in chaotic faunal arrangements, and removing fine-grained particles thus improving the petrographic properties of the rock (porosity and permeability). • The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. • MicroCT, paleontology, petrography, porosity, and geochemistry analysis show high accuracy of storm interpretation. • The analysis shows a useful dataset of diagenesis and porosity for the carbonate reservoir model. • The Pirabas Formation carbonate-siliciclastic is an appropriate experimental reservoir model. [ABSTRACT FROM AUTHOR]

Seismic characterization of Eocene-Oligocene heterozoan carbonate strata from the Browse Basin, Northwest Shelf of Australia, defines marked progradation of nearly 10 km. Stratal terminations and stacking subdivide the succession into mappable seismic units. Stratal architecture and seismic geomorphology varies systematically through the succession. Individual surfaces, discerned by toplap, onlap, and truncation, outline sigmoidal to tangential oblique clinoforms with heights of ranging from 350 to 650 m and maximum gradients between 8 and 18°. Sigmoidal clinoforms can include aggradation in excess of ∼200 m, prograde more than 500 m, and have slopes characterized by inclined, wavy to discontinuous reflectors that represent ubiquitous gullies and channels. In contrast, the overlying tangential oblique clinoforms include downstepped shelf margins, limited on-shelf aggradation (<100 m) and toplap, subdued progradation (<500 m), and continuous parallel inclined reflectors on the slope. Wedges of basinally restricted reflectors at toe of slope onlap surfaces of pronounced erosional truncation or syndepositional structural modification. The succession includes repeated patterns of seismic units that onlap, aggrade, and prograde, interpreted to represent sequence sets and composite sequences. The associations of shelf aggradation, shelf-margin progradation, and slope channeling within sigmoidal seismic units and the less marked progradation and channeling within tangential oblique seismic units contrast with the classic sequence model in which sediment delivery to the slope and pronounced progradation is favored by limited shelf accommodation. This distinct divergence is interpreted to reflect the prolific heterozoan production across the shelf during periods of rising and high base level when the shelf is flooded, perhaps enhanced by downwelling. Comparison with purely photozoan systems reveals similarities and contrasts in seismic stratigraphic heterogeneity and architecture, interpreted to be driven by distinct characteristics of heterozoan sedimentary systems. [ABSTRACT FROM AUTHOR]

Locally exposed Middle to Upper Eocene conglomerates in the western part of the Cenozoic Thrace Basin are interpreted as products of continuous marine erosion of a rocky coast (consisting of Lower Cretaceous carbonates) and subsequent redeposition of the land-derived limestone material in a wave-dominated nearshore setting during a prolonged transgression. Contemporaneous biological activity in the warm-temperate marine environment contributed to the accumulation of mixed coarse-grained clastic-carbonate sediments on the upper shoreface. The formation of a relatively thick sedimentary succession was favoured by the interplay of several controlling factors as only shoreface deposits were preserved in the rock record. The results may help to elucidate the evolution of the hydrocarbon-bearing Thrace Basin and to assist with the regional correlation of its basal deposits. Copyright [ABSTRACT FROM AUTHOR]

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]

The Saumane-Venasque compound palaeovalley succession accumulated in a strongly tide-influenced embayment or estuary. Warm-temperate normal marine to brackish conditions led to deposition of extensive cross-bedded biofragmental calcarenites. Echinoids, bryozoans, coralline algae, barnacles and benthic foraminifera were produced in seagrass meadows, on rocky substrates colonized by macroalgae and within subaqueous dune fields. There are two sequences, S1 and S2, the first of which contains three high-frequency sequences (S1a, S1b and S1c). Sequence 1 is largely confined to the palaeovalley with its upper part covering interfluves. Each of these has a similar upward succession of deposits that includes: (i) a basal erosional surface that is bored and glauconitized; (ii) a discontinuous lagoonal lime mudstone or wackestone; (iii) a thin conglomerate generated by tidal ravinement; (iv) a transgressive systems tract series of cross-bedded calcarenites; (v) a maximum flooding interval of argillaceous, muddy quartzose, open-marine limestones; and (vi) a thin highstand systems tract of fine-grained calcarenite. Tidal currents during stages S1a, S1b and S1c were accentuated by the constricted valley topography, whereas basin-scale factors enhanced tidal currents during the deposition of S2. The upper part of the succession in all but S1c has been removed by later erosion. There is an overall upward temporal change with quartz, barnacles, encrusting corallines and epifaunal echinoids decreasing but bryozoans, articulated corallines and infaunal echinoids increasing. This trend is interpreted to be the result of changing oceanographic conditions as the valley was filled, bathymetric relief was reduced, rocky substrates were replaced as carbonate factories by seagrass meadows and subaqueous dunes, and the setting became progressively less confined and more open marine. These limestones are characteristic of a suite of similar cool-water calcareous sand bodies in environments with little siliciclastic or fresh water input during times of high-amplitude sea-level change wherein complex inboard antecedent topography was flooded by a rising ocean. [ABSTRACT FROM AUTHOR]

Abstract: The Miocene Sommières Basin in SE France is a semi-enclosed depression that was connected to the Mediterranean Sea by a flooded paleo-incised valley and then filled by a suite of sediments comprising carbonate grains coming from temperate factories that were largely deposited in tidal-dominated paleoenvironments. The strata are partitioned into two sequences that reflect repeated flooding of the incised valley system, one of several similar situations in this region of France. The carbonate grains are mostly bioclasts, namely from barnacles, bryozoans, coralline algae (encrusting, branching, and rhodoliths), echinoids, and benthic foraminifers (large and small) with ostracods, sponge spicules and planktic foraminifers prominent in muddy facies. Particles were produced by shallow water carbonate factories on hard substrates (valley walls in particular), associated with subaqueous dunes, and in deeper water basinal settings. Each depositional sequence is underlain by an eroded and bored hard surface that is progressively overlain by TST subaqueous tidal dunes or storm deposits that grade up, in one case, into HST marls (the HST of the upper sequence has been removed by erosion). The lower sequence is ebb tide dominated whereas the upper sequence is flood tide dominated. The succession is interpreted to represent a TST whose tidal currents were focused by the narrow valley and a HST that reflected flooding of the overbanks. This stratigraphic and depositional motif is comparable to that in other spatially separated Neogene paleovalleys that are filled with tide-dominated clastic carbonates in the region. Together with other recently documented similar systems, these limestones constitute an important new group of carbonate sand bodies in the carbonate depositional realm. [Copyright &y& Elsevier]

Abstract: The soft bottom of the Mediterranean continental shelf is characterized by a heterozoan skeletal assemblage (sensu [James, N.P., 1997. The cool-water carbonate depositional realm. In: James, N.P., Clarke, J. (Eds), Cool-water Carbonates. Spec. Publ. Soc. Sediment. Geol., vol. 56, pp.1–20.]). Although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established [Tortora, P., 1996. Depositional and erosional coastal processes during the last postglacial sea-level rise: an example from the Central Tyrrhenian continental shelf (Italy). J. Sed. Res. 66, 391–405.; Fornós, J.J., Ahr, W.M., 1997. Temperate carbonates on a modern, low-energy, isolated ramp: the Balearic Platform, Spain. Journal of Sedimentary Research, 67, 364–373.; Fornós, J.J., Ahr, W.M., 2006. Present-day temperate carbonate sedimentation on the Balearic Platform, western Mediterranean: compositional and textural variation along a low-energy isolated ramp. In: Pedley, H.M., Carannante, G. (Eds.) 2006, Cool-water Carbonates: Depositional Systems and Palaeoenvironmental Controls. Geological Society, London, Special Publications, 255, pp. 121–135], the interactions between carbonate and terrigenous–siliciclastic sedimentation has not been documented well enough. A total of 33 surface sediment samples from the Pontinian shelf (Tyrrhenian Sea, central Mediterranean) have been analysed. Sampling stations range from 15 to 250 mwd (meter water depth) and are located along five transects (PonzaW, PonzaNW, Ponza NE, Ponza E, Zannone), plus four samples collected around Palmarola Island. Sectors colonized by seagrass meadows have not been sampled. A total of 6 sedimentary facies (F) and 10 microfacies (mf) have been recognized by using component analyses, grain size percentage, sorting, carbonate content and authigenic mineralization rate. These facies and microfacies represent the Pontian Islands shelf sedimentation, in the interval between the upper infralittoral and the epibathyal zones that represent shelf-break and upper slope sedimentation. The Maerl facies (F4a,b; mf4a,b) and the skeletal sands (F2a,b; mf2a1, mf2a2, mf2b) fall within the circalittoral zone. The circalittoral zone in the water depth interval between 82 m and 112 m display relict facies (F6, mf6). Finally facies F5 (Siliciclastic sands) includes subfacies F5b (mf5b), located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of Ponza, and subfacies F5a in the upper infralittoral zone (15 mwd/25 mwd) where erosional processes prevail. Carbonate content analyses indicate that maximum carbonate production on the Pontinian shelf took place in the 60–80 mwd interval. Facies F4 (Maerl) represents the environment characterized by the highest carbonate production rates. In the Pontian area siliciclastic–carbonate mixing took place in the infralittoral zone and in the lower circalittoral zone. In the infralittoral zone erosional processes on the rocky shoreline produced lithoclasts and vulcanoclastic deposits that were reworked by wave-induced near-shore currents. In the lower circalittoral zone the prolific production by photic biota (red algae) ends, while skeletal remains of the aphotic environment mixes with planktonic sediments characterized by low carbonate values. Sand (63 μm–2 mm) is the dominant grain size class, however gravel-dominated facies (F4 Maerl) are present in water depths (50 to 112 mwd) which are significantly below the storm wave base. Glauconite mineralization appears on the Pontinian shelf from 50 mwd and increases in abundance along the deeper bathymetries. The compositional characteristics of relict facies F6 shows the concurrence of biota assemblages of the infralittoral and circalittoral zones, likely representing the record of the last Holocene transgressive event (18 ky) and expressed by the overlapping of components of different environments. [Copyright &y& Elsevier]

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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]

This study utilized three-dimensional exposures to evaluate how sea-level position and palaeotopography control the facies and geometries of heterozoan carbonates. Heterozoan carbonates were deposited on top of a Neogene volcanic substrate characterized by palaeotopographic highs, palaeovalleys, and straits that were formed by subaerial erosion, possibly original volcanic topography, and faults prior to carbonate deposition. The depositional sequence that is the focus of this study (DS1B) consists of 7–10 fining upward cycles that developed in response to relative sea-level fluctuations. A complete cycle has a basal erosion surface overlain by deposits of debrisflows and high-density turbidity currents, which formed during relative sea-level fall. Overlying tractive deposits most likely formed during the lowest relative position of sea level. Overlying these are debrites grading upward to high-density turbidites and low-density turbidites that formed during relative sea-level rise. The tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level. The cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow-water carbonate production and partial drowning of substrates. The cycles are dominated by two end-member types of facies associations and stratal geometries that formed in response to fluctuating sea-level position over variable substrate palaeotopography. One end-member is termed‘flank flow cycle’ because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys. Those cycles drape the substrate, have more debrites, high-density turbidites and erosion on palaeovalley flanks, and in general, the lithofacies fine down the palaeovalley flanks into the palaeovalley axes. The second end-member is termed‘axial flow cycle’ because it indicates a dominance of sediment transport down the axes of palaeovalleys. Those cycles are characterized by debrites and high-density turbidites in palaeovalley axes, and lap out of strata against the flanks of palaeovalleys. Where and when an axial flow cycle or flank flow cycle developed appears to be related to the intersection of sea level with areas of gentle or steep substrate slopes, during an overall relative rise in sea level. Results from this study provide a model for similar systems that must combine carbonate principles for sediment production, palaeotopographic controls, and physical principles of sediment remobilization into deep water. [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]

Based on their shell content, the coarse carbonate sands/gravels sampled from 13 to 39 m water depth from the Norwegian inner shelf are shown to belong to the heterozoan association of James. They are dominated mainly by molluscs, polychaetes, cirripeds and foraminifera. Some of the dead mollusc species found indicate an origin in shallow water rocky areas (Mytilus edulis) and algal and seagrass communities (Rissoa parva). On the other hand, other species are typical of an inner shelf (Modiolus modiolus). The presence of intertidal/shallow subtidal species on the inner shelf (down to 39 m depth) is interpreted as due to transport by currents or waves during storm events. Analyses of mollusc shell surfaces were also undertaken and show three types of texture: unaltered, corroded and polished. The latter two are an alteration of the ornament of the shells. The corroded texture is the dominant type on the mollusc shells. Another important feature of the mollusc shells is the high amount of microboring and in some cases also evidence of dissolution. These carbonate sediments are shown to have a complex origin, consisting of a mixture of bioclasts from different contemporary adjacent environments, and with destruction of bioclasts ranging from zero (unaltered texture) to severe (corroded due to microborings and dissolution), and with some reworking of older bioclasts into the surface sediment layer. [ABSTRACT FROM AUTHOR]

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]