Brian R. Rosen

Tectonics from fossils? Analysis of reef-coral and sea-urchin distributions from late Cretaceous to Recent, using a new method

Abstract Biogeographical distribution is seen as a product of small- and large-scale factors, of which only the latter are important in palaeogeographical reconstruction. We review here previous methods for assessing the historical sequence of major events that have caused biogeographical distributions, and we argue that the most rigorous of these is cladistic biogeography. We also advocate our own new method, which uses parsimony analysis of taxa shared between sample localities. In not being dependent on prior phylogenetic analysis, this method is especially suitable for taxonomic groups which lack an adequate phylogeny. This new method takes contemporaneous distributional data from one or more narrow stratigraphic time planes (including the present), and generates a cladogram of sample localities for each of them. We interpret these cladograms as hypotheses of historical sequences of divergences between biotas, for which the sample localities provide geographical control. Congruence between cladograms from different organic groups and time planes provides an indication of those events which are most likely to have been the result of major (e.g. tectonic) historical factors. This method avoids prejudgement of areas of endemicity. We also argue that because younger major historical events can destroy the biogeographical patterns produced by older events, we can reach a more complete understanding of historical biogeography by using a combination of Recent and fossil data. The method however requires refinement and we summarize some of its present problems. We present area cladograms for Recent and Lower Miocene corals and echinoids, and for Eocene and late Cretaceous (Campanian-Maastrichtian) echinoids. Although these should be tested against area cladograms based on other taxa, we conclude, amongst our preliminary results, that: (1) the present Indo-Pacific fauna is a young biogeographical entity, not older than the Lower Miocene; (2) prior to this, Pacific faunas had been isolated since a time older than the Upper Eocene; and (3) the faunas of the Atlantic and western Tethys have been distinct from those of the Indian Ocean and eastern Tethys since a time long before the ‘terminal Tethyan event’ (Miocene), and since as far back, at least, as the late Mesozoic.

Quantitative approaches to palaeozonation and palaeobathymetry of corals and coralline algae in Cenozoic reefs

Abstract The value of quantitative surveys of ancient reef slopes for palaeobathymetric analysis is reviewed. Reefs are selected for palaeobathymetric analysis because they are characterized by in situ preservation of benthic communities which are often depth related. In addition, if the reef crest and slope are preserved then ancient water depths can be measured. The zonation of living reefs has been measured using semi-quantitative phytosociological methods as well as a range of plot and plotless techniques, but there is little agreement as to a single best method. For this study a modified line intercept transect method is selected as it may be used on both living reefs and on various types of outcrops of fossil reefs. This method minimizes problems arising from outcrop conditions, is faster than quadrat methods, can be used to assess different frame-building taxa, matrix, cement and porosity along ancient reef surfaces, and is also frequently used in studies of living reefs. The zonation of corals and coralline algae on living and fossil reefs can be characterized by three parameters: framework density, diversity and species abundance. The framework density of reef corals is normally greatest on external reef slopes between 1 and 30 m and decreases into shallow reef crest environments, and towards shorelines. Coralline algal frameworks are highest in reef crest environments and may also replace coral frameworks in deeper reef-slope environments. Variations in diversity are complex and relate to biogeographical constraints as well as local variations of physical factors and biological factors. The distribution of reef-building assemblages is often expressed as a zonation which may relate to depth but also to hydraulic energy. Examples of coral and coralline algal zonation are presented and discussed from Indo-Pacific and Caribbean reefs. Three case studies are presented based on the authors’ work on reef zonation. The Seychelles reefs (Indian Ocean) are used to illustrate depth and water energy related zonation of present-day living corals. Coralline algal zonation is illustrated from present-day St Croix reefs (Caribbean), together with preserved zones in sections through these reefs. Coral and coralline algal zonation on fossil reefs are characterized using our modified line intercept transect technique on exposures from late Miocene reefs of Mallorca (Spain). This review of reef zonation and introduction of a new technique for surveying ancient reef communities to establish depth related zones has important advantages over previous qualitative approaches. Direct measurements of palaeodepths in the field make subjective palaeobathymetric interpretations unnecessary and avoids the problems of assuming uniformitarianism. In situ organism assemblages are sampled which minimizes the effects of taphonomic changes on community composition. The technique allows the quantification of framework density, diversity, species abundance and zonation to be compared between different fossil reefs and between living and fossil reefs for the first time.

Carbonate deposition in accretionary prism settings: Early miocene coral limestones and corals of the Makran mountain range in Southern Iran

SummaryThe regional mapping of the Makran mountain range on behalf of the Geological Survey of Iran represents a unique coverage: the entire area of the mountain range was compiled in a unified programme. During this mapping, Miocene limestones containing rich coral and foraminiferal faunas were recorded over a strike length of several hundred kilometres, as minor developments within thick neritic clastic sequences which in turn overlie great thicknesses of Eocene-Miocene flysch. These limestones include rigid bioconstructional frame-works, loosely compacted coralline assemblages and foraminiferal calcarenites: they includein situ recfal deposits and material redeposited quite close to their original site of deposition. Most are Burdigalian, as shown by the benthonic foraminifera, but some are Aquitanian. The geotectonic setting was an accretionary prism in a zone of plate convergence. The limestones and enclosing clastic sediments comprise an intensely folded, reverse-faulted and locally dislocated sequence, the duplex structure being the result of a major Late Miocene-Pliocene episode of regional deformation. This concentration of the intense tectonic deformation in a late major episode requires a different model for this zone of plate convergence to the model widely applied to such zones. The possible controls on limestone deposition are discussed-tectonic uplift and shallowing of the sea, climatic warming and eustatic factors. Depositional features of reefal formations in the late Jurassic of the Caucasus, the Pliocene-Recent of Halmahera, and the early Miocene of SE France are discussed in comparison with the Makran model.The previously unknown corals from the limestones comprise more than 40 genera and 90 species and represent the largest recorded Miocene coral collection between the Mediterranean and Indonesia. A faunal list is provided and their significance is discussed, especially with respect to the apparent absence of higher energy assemblages. The respective influence of local ecological conditions, regional palaeogeographical setting, and late Cainozoic global change are assessed as causes of this pattern, and the latter favoured. The essential poritid-faviid character of most global coral communities remained relatively static for much of the Cainozoic notwithstanding background taxonomic turnover. Coral assemblages typical of higher energy, especially those dominated byAcropora, then appeared late in the Cainozoic alongside the older assemblages. However, a global increase in wave energy around this time is probably too naïve an explanation and causes arising from intensification of glacioeustasy should be considered instead.Associated algae, foraminifera and molluscs are briefly discussed. The Makran fossils have especial palaeobio-geographical and palaeogeographical interest as they come from localities close to the areas of Miocene uplift which finally severed the Middle Eastern seaways of Tethys. Together with several previously recorded faunas elsewhere in Iran, their original location lay within an arm of the Miocene Arabian Sea, named here ‘The Proto-Persian Gulf’, at a palaeolatitude of about 25°N. The corals and foraminifera show an almost entirely Indo-Pacific affinity which began to emerge even before the final Zagros closure, indicative of strong biogeographical discontinuity with the early Miocene Mediterranean region.

Late Cretaceous (Maastrichtian) echinoid-mollusc-coral assemblages and palaeoenvironments from a Tethyan carbonate platform succession, northern Oman mountains

Abstract Faunal associations observed in a Maastrichtian carbonate platform succession in the western borders of the North Oman mountains are established, based on field collections of more than 7000 macrofossils belonging to some 200 species. Lithofacies are also distinguished from petrographic analysis. The succession was deposited during a single sea-level cycle and the basal transgression preserves beach hardground faunas, with characteristic echinoid and coral taxa, and subtidal shore-face sands with an abundance of the cassiduloid echinoid Faujasia . Shallow-water offshore sediments deposited below active wave base make up the majority of the lower beds. This facies includes several distinct faunal associations, broadly divisible into those living in or on unconsolidated sands (with infaunal cassiduloids and bivalves), and those associated with stable, possibly algal-bound sedimentary bottoms (with pycnodont oysters, small solitary corals and the larger benthic foraminiferan Loftusia ). The semi-reclining rudist Dictyoptychus is most abundant in the transition facies between these two assemblages. The upper beds are composed of well-sorted calcarenites deposited within active wave base. These unconsolidated, but generally stable shoals had a fauna of large, infaunal, deposit-feeding holasteroid and cassiduloid echinoids with only occasional large algivorous gastropods ( Campanile, Pyrazus ) and large epifaunal regular echinoids ( Noetlingaster ).

Corals not serpulids: mineralized colonial fossils in the Lower Jurassic marginal facies of South Wales

Poorly preserved colonial corals occur near the base of the Lower Jurassic marginal facies at Southerndown, South Wales. Previously they have been interpreted as serpulid colonies, despite a dissimilarity to any serpulids known from elsewhere in the Lias or the few known extant colonial serpulids. However, local preservation of fine detail reveals evidence, in the form of corallites, septa and tabulae, that they are scleractinian corals of the Suborder Faviina, Family Stylophyllidae. These coral specimens occur in close association with barite-galena veins in the underlying Carboniferous Limestone and adjacent Lias marginal facies. Their widespread misindentification as ‘serpulid reefs’ is a consequence of coarse replacive mineralization by barite, which has largely obscured the diagnostic characters.

Recent coral facies of the Indian Ocean Coast of Somalia with an interim check list of corals

SummaryFrom a study of two areas, Jesira and the Bajuni Archipelago, about 400 km apart, a general pattern can be established for the Recent facies, together with the morphological and taxonomic features of the corals. Present day coral development is characterized by true fringing reefs in the Bajuni Archipelago and by scattered patches and knolls in the Jesira area. The coral fauna, consisting of 27 genera and 63 species so far (including all uncertainties, but not sight records), is rather poor, though coral communities are locally well developed. These figures probably reflect incomplete study and sampling. Although comparison with other areas may therefore be premature, a preliminary biogeographical analysis suggests that this fauna is more closely related to that of the Red Sea than to East Africa and the Seychelles. This differs from other published biogeographical work on Indian Ocean coral faunas, but further study of the corals in this and neighbouring areas of the Indian Ocean is needed in order to resolve this apparent anomaly.