Juan C. Braga

Hopping Hotspots: Global Shifts in Marine Biodiversity

Hotspots of high species diversity are a prominent feature of modern global biodiversity patterns. Fossil and molecular evidence is starting to reveal the history of these hotspots. There have been at least three marine biodiversity hotspots during the past 50 million years. They have moved across almost half the globe, with their timing and locations coinciding with major tectonic events. The birth and death of successive hotspots highlights the link between environmental change and biodiversity patterns. The antiquity of the taxa in the modern Indo-Australian Archipelago hotspot emphasizes the role of pre-Pleistocene events in shaping modern diversity patterns.

Patterns and average rates of late Neogene-Recent uplift of the Betic Cordillera, SE Spain

Abstract The facies distribution in the sedimentary units infilling a series of Neogene basins has been used to reconstruct the relief generation and uplift across the Internal Zone of the Betic Cordillera in southern Spain. Uplift amounts and average rates can be estimated using the current elevation of the outcrops of well-dated deposits indicative of ancient sea-level positions. Coral reefs and coastal conglomerates record the initial development of emergent Betic relief during the Langhian. Continental and marginal marine deposits indicate the existence of a large island centred on the present Sierra Nevada–Sierra de los Filabres chain by the end of the Middle Miocene. The precursor of the Sierra Nevada–Sierra de los Filabres chain, originally part of this large island, remained emerged whilst the surrounding areas were re-invaded by the sea during the early Tortonian. At the end of the Tortonian the inland basins (Granada and Guadix basins) became continental, while the Sierras de la Contraviesa, Sierra de Gador and Sierra Alhamilla emerged, separating the Alboran Basin from the Alpujarra, Tabernas and Sorbas basins, which became narrow passages of the Mediterranean Sea. In contrast, the Sierra Cabrera emerged during the late Messinian, suggesting a progressive uplift from west to east of the sierras south of the Sierra Nevada–Sierra de los Filabres chain. During the Pliocene, only the low areas closest to the present-day coast remained as marine basins and progressively emerged throughout this stage. The highest average uplift rate recorded is 280 m/Ma for the Sierra de Gador, although the average uplift rates of upper-Neogene coastal marine rocks since depositon have maximum values of approximately 200 m/Ma. Most of the uplift of the Betic mountains took place before the early Pliocene. The recorded uplift of Neogene rocks was highest at the margins of western Sierra Nevada, where peaks higher than 3000 m occur. The average rates of uplift were lower to the east of this major relief. The main sierras and depressions in the present-day landscape correspond respectively to the emergent land, in which uplift was concentrated, and to the marine basins that existed before the final emergence of the region. The altitude of the sierras reflects the time at which they became emergent, the highest mountains being the first to rise above sea level.

Messinian events in the Sorbas Basin in southeastern Spain and their implications in the recent history of the Mediterranean

Abstract The Messinian (Late Miocene) marine stratigraphic record of the Sorbas Basin (S.E. Spain) is well preserved and can be considered as being representative of the entire western Mediterranean. It exhibits a series of features relating to: (1) the composition, characteristics and evolution of coral reefs; (2) changes between temperate and subtropical climates; and (3) the extensive development of microbial carbonates (stromatolites and thrombolites) at the end of the Messinian. Each of these features has global significance. Porites , which is the major and almost only coral component in reefs, is heavily encrusted with stromatolites. These reefs grew at the edge of the subtropical belt and were totally eliminated at the end of the Messinian because of global cooling. Lowermost-Messinian carbonate sediments in the Sorbas Basin reflect a temperate climate, whereas those immediately above, which contain bioherms and coastal reefs, are subtropical. The shift from temperate to subtropical conditions during the early Messinian was accompanied by an important change in water circulation within the western Mediterranean. Temperate times were marked by cold surface Atlantic waters entering the Mediterranean, whereas subtropical times coincided with warm surface waters entering the western Mediterranean from the east. The subtropical waters were thermally stratified, which favoured the deposition of euxinic marls and diatomites at the centre of the basin. The upwelling of nutrient-rich water promoted stromatolite development within reefs and Halimeda growth on adjacent slopes. Lastly, microbial carbonates (stromatolites and thrombolites) attained giant dimensions during the late Messinian, which can be regarded as a measure of their success in occupying a variety of ecological niches. This abundance of available habitats is believed to have resulted from the Messinian “salinity crisis”, which was followed by a re-colonization of the western Mediterranean. In this context stromatolite proliferation was due to opportunism of microbial communities in colonizing the new environments, rather than to a complete absence of other competitive biota. We do not believe that hypersaline conditions were a causal factor in stromatolite development because of the normal-marine biota associated with them.

Diversity of coralline red algae: Origination and extinction patterns from the Early Cretaceous to the Pleistocene

Abstract Data from a comprehensive literature survey for the first time provide stage-level resolution of Early Cretaceous through Pleistocene species diversity for nongeniculate coralline algae. Distributions of a total of 655 species in 23 genera were compiled from 222 publications. These represent three family-subfamily groupings each with distinctive present-day distributions: (1) Sporolithaceae, low latitude, mainly deep water; (2) Melobesioid corallinaceans, high latitude, shallow water, to low latitude, deep water; (3) Lithophylloid/mastophoroid corallinaceans, mid- to low latitude, shallow water. Raw data show overall Early Cretaceous–early Miocene increase to 245 species in the Aquitanian, followed by collapse to only 43 species in the late Pliocene. Rarefaction analysis confirms the pattern of increase but suggests that scarcity of publications exaggerates Neogene decline, which was actually relatively slight. Throughout the history of coralline species, species richness broadly correlates with published global paleotemperatures based on benthic foraminifer δ18O values. The warm-water Sporolithaceae were most species-abundant during the Cretaceous, but they declined and were rapidly overtaken by the Corallinaceae as Cenozoic temperatures declined. Trends within the Corallinaceae during the Cenozoic appear to reflect environmental change and disturbance. Cool- and deep-water melobesioids rapidly expanded during the latest Cretaceous and Paleocene. Warmer-water lithophylloid/mastophoroid species increased slowly during the same period but more quickly in the early Oligocene, possibly reflecting habitat partitioning as climatic belts differentiated and scleractinian reef development expanded near the Eocene/Oligocene boundary. Melobesioids abruptly declined in the late Pliocene–Pleistocene, while lithophylloid/mastophoroids increased again. Possibly, onset of glaciation in the Northern Hemisphere (∼2.4 Ma) sustained or accentuated latitudinal differentiation and global climatic deterioration, disrupting high-latitude melobesioid habitats. Simultaneously, this could have caused moderate environmental disturbance in mid- to low-latitude ecosystems, promoting diversification of lithophylloids/mastophoroids through the “fission effect.” Extinction events that eliminated >20% of coralline species were most severe (58–67% of species) during the Late Cretaceous and late Miocene–Pliocene. Each extinction was followed by substantial episodes of origination, particularly in the Danian and Pleistocene.

Coralline algal assemblages in upper Neogene reef and temperate carbonates in Southern Spain

Reef and temperate carbonate units alternate in the upper Miocene^Pliocene stratigraphic record of Betic basins palaeogeographically connected to the Mediterranean. Shallow-water coralline algal assemblages in temperate units differ in taxonomic composition from those in reef carbonate units. The difference attains the subfamily level since the temperate lithofacies are characterised by assemblages dominated by lithophylloids (Lithophyllum), whereas mastophoroids (Spongites and Neogoniolithon) predominate in the reef units. The proportion of lithophylloids, however, can be high in samples from shallow-reef palaeoenvironments. The distinction is less marked in deeper platform deposits since melobesioids (Lithothamnion, Mesophyllum and Phymatolithon) are the major elements in the assemblages from both reef and temperate units. Sporolithon, the only representative of the family Sporolithaceae, is frequent in reef-slope deposits but very rare in temperate lithofacies. The change in coralline algal assemblages from temperate to subtropical/tropical units is probably the result of the palaeophytogeography of the coralline red algae during the Late Neogene along climatic belts. Shallow-water floras were dominated by lithophylloids in cooler periods, during which the western Mediterranean was within the temperate belt, as in the present-day situation. In warmer episodes, subtropical/tropical conditions enveloped the region and the tropical coralline floras, in which mastophoroids predominate, together with reef corals and green algae inhabited the Betic basins. Similar, less pronounced, phytogeographic patterns can be roughly recognised in modern oceans. Fossil coralline algal assemblages can, therefore help to identify the palaeoclimatic context of sedimentation of the rocks in which they are recorded. They constitute a palaeontological tool supplemental to lithofacies and other fossil indicators for characterising such contexts in Cenozoic platform deposits. fl 2001 Elsevier Science B.V. All rights reserved.

Coral reefs in coarse-terrigenous sedimentary environments (Upper Tortonian, Granada Basin, southern Spain)

Abstract During the Upper Tortonian coral reefs developed on fan deltas and braid deltas along the active eastern edge of the Granada Basin. The corals grew in environments characterized by deposition of coarse sands and conglomerates. Frequency of sedimentation together with sea level rises controlled reef development and determined the architecture and composition of the carbonate deposits. In direct contrast to these reefs, others flourished at the same time along stable coastal margins of the basin. Their structure was influenced mainly by periodic rises in sea level. The mapping of all these reefs serves as an accurate guide to the Upper Tortonian geography of the Granada Basin.

Geometries of reef advance in response to relative sea-level changes in a Messinian (uppermost Miocene) fringing reef (Cariatiz reef, Sorbas Basin, SE Spain)

Abstract The pre-evaporitic Messinian sequence in the Sorbas Basin includes two reef units. At the northern margin of the basin, near Cariatiz, the uppermost unit consists of a fringing reef advancing 1150 m towards the basin centre. Reef-facies distribution and geometries in three N-S sections parallel to reef progradation reveal cyclic relative sea-level changes during reef development. Two orders of cyclicity can be recognised. The lower order (C1 cyclicity) is represented by one cycle and by the beginning of another one that is interrupted in its ascending phase. This cyclicity is modified by higher-frequency cycles (C2 cyclicity), which developed between consecutive wedges of calcarenite beds that onlap an erosive surface on previous deposits and pinch out landwards (inverted wedges). The inverted wedges are thought to represent the lowstand deposits of C2 cycles and no coeval reef growth is recorded. Sea-level rise within C2 cycles results in reef aggradation and aggradation combined with progradation. Reef deposits prograded during the highest sea level, and offlapped during sea-level fall. Relative proportions of aggrading, prograding, and offlapping geometries inside C2 cycles depend on the interference of C1 and C2 cycles. The estimated relative sea-level change in the complete C1 cycle is about 100 m. Sea-level oscillations in C2 cycles have an amplitude of several tens of metres. Biostratigraphic and magnetostratigraphic data indicate that the Cariatiz reef developed in less than 0.36 Ma. If eustasy was the major factor controlling relative sea-level change, this temporal range, together with the observed amplitudes and relative frequencies, would suggest that C1 and C2 cycles may represent short eccentricity and precession cycles, respectively. However, the estimated sea-level changes are greater than the high-frequency eustatic oscillations reported from Upper Miocene deposits from other areas. Fan-delta siliciclastics locally interfered with reef growth. Main fan-delta activity took place during the high and descending sea-levels of the first C1 cycle but there was no significant clastic influx during the lowstand.

Drowning of the -150 m reef off Hawaii: A Casualty of global meltwater pulse 1A?

We present evidence that the drowning of the 2150 m coral reef around Hawaii was caused by rapid sea-level rise associated with meltwater pulse 1A (MWP-1A) during the last deglaciation. New U/Th and 14 C accelerator mass spectrometry dates, combined with reinterpretation of existing radiometric dates, constrain the age of the coral reef to 15.2-14.7 ka (U/Th age), indicating that reef growth persisted for 4.3 k.y. following the end of the Last Glacial Maximum at 19 ka. The drowning age of the reef is roughly synchronous with the onset of MWP-1A between 14.7 and 14.2 ka. Dates from coralline algal material range from 14 to 10 cal ka (calibrated radiocarbon age), 1-4 k.y. younger than the coral ages. A paleoenvironmental reconstruction incorporating all available radiometric dates, high-resolution bathymetry, dive observations, and coralgal paleobathymetry data indicates a dramatic rise in sea level around Hawaii ca. 14.7 ka. Paleowater depths over the reef crest increased rapidly above a critical depth (30-40 m), drowning the shallow reef-building Porites corals and causing a shift to deep- water coralline algal growth, preserved as a crust on the drowned reef crest.

Coralline algal nodules off Fraser Island, eastern Australia

SummaryCalcareous red algal nodules growing on mobile substrates have been sampled from 28 to 117m off Fraser Island in southern Queensland, eastern Australia. This is a subtropical, transitional area between the tropical Great Barrier Reef to the north and temperate, cooler waters to the south. Red algal nodules are the most common components in bioclastic gravels that extend from about 50 to 110 m and locally cover 40–50% of the seafloor. Variations in the overall character and floristic composition of the nodules with depth can be observed. Algal nodules comprise algal covered pebbles/cobbles and rhodoliths in depths shallower than 60 m whereas only rhodoliths occur in deeper settings. No changes in nodule shape occur but shallower algal nodules have larger mean size with higher standard deviation than the deeper ones (39.2 vs. 30.5 mm and 20.5 vs. 6.3 mm s.d.). Living and subrecent red algae in nodules shallower than 60 m are mainly Melobesioideae and peyssonneliaceans with minor Lithophylloideae and Mastophoroideae. Most plants belong to a few species of the generaPhymatolithon andLithothamnion. Below 68 m, rhodoliths are dominated by the family Sporolithaceae, melobesioids and peyssonneliaceans.Sporolithon is the main component below 80 m. Algal growth forms are mostly smooth encrusting to warty with no depth variation. Maximum plant thickness, however, decreases with increasing depth. Thallus thickness in the deeper water samples is more than three times smaller than in those from shallower waters. These data are important for understanding the paleoenvironmental context of deposition of the abundant coralline algal limestones with similar algal nodules found in the geological record.

Neogene coralline-algal growth-forms and their palaeoenvironments in the Almanzora river valley (Almeria, S.E. Spain)

Abstract The Almanzora river valley is an elongate E-W depression containing mainly Neogene sediments. During the Late Tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts: (a) on coastal platforms and talus slopes, (b) on fan deltas and (c) associated with corals in patch-reefs growing at the furthermost extremes of coastal fan deltas. In the former two cases the predominant growths are as rhodoliths associated with mobile substrates. In the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths. With depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself. The massive crusts and columns, which mark the limit of development of the shallow-water rhodoliths, in the deeper examples are covered by branching and thin, leafy (laminar) growths. In the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones. In the patch-reefs the specific composition of the algal associations changes somewhat and the growths, developed on a stable substrate under low-energy conditions, are mainly vertical branches arising from thin crusts.