Bioerosion in the Miocene Reefs of the northwest Red Sea,Egypt

Macroborings provide detailed information on the bioerosion, accretion and palaeoenvironment of both modern and fossil reefs. Dolomitized reefal carbonates in the Um Mahara Formation exhibit an outstanding example of spatially distributed, well‐preserved bioerosion structures in tropical to subtropical syn‐rift Miocene reefs. Ten ichnospecies belonging to five ichnogenera are identified; three belonging to the bivalve‐boring ichnogenus Gastrochaenolites, three attributed to the sponge‐boring ichnogenus Entobia, and four ichnospecies assigned to three worm‐boring ichnogenera Trypanites, Maeandropolydora and Caulostrepsis. The distribution of the reported borings is strongly linked to the palaeo‐reef zones. Two distinctive ichnological boring assemblages are recognized. The Gastrochaenolites‐dominated assemblage reflects shallower‐marine conditions, under water depths of a few metres, mostly in back‐reef to patch‐reef zones of a back‐reef lagoon. The Entobia‐dominated assemblage signifies relatively deeper marine conditions, mostly in reef core of the fringing Miocene reefs. These ichnological assemblages are attributed herein to the Entobia sub‐ichnofacies of the Trypanites ichnofacies. This ichnofacies indicates boring in hard carbonate substrates (such as corals, rhodoliths, carbonate cements and hardgrounds) during periods of non‐sedimentation or reduced sediment input.     

Bioerosional structures and pseudoborings from Late Jurassic and Late Cretaceous-Paleocene shallow-water carbonates (Northern Calcareous Alps, Austria and SE France) with special reference to cryptobiotic foraminifera

Examples of bioerosional processes (boring patterns) are described from shallow-water limestones of the Late Jurassic Plassen Carbonate Platform (PCP) and the Late Cretaceous to Paleocene Gosau Group of the Northern Calcareous Alps, Austria. Some micro-/macro-borings can be related to distinct ichnotaxa, others are classified in open nomenclature. In the Alpine Late Jurassic, bioerosional structures recorded from clasts in mass-flows allow palaeogeographical conclusions concerning the source areas. In particular, these are borings of the Trypanites-ichnofacies detected from clasts (Barmstein limestones) of the PCP or special type of bored ooids of unknown source areas or restricted autochthonous occurrences. In the Lower Gosau Subgroup, Gastrochaenolites macroborings occur in mobile carbonate clast substrates of shore zone deposits (“Untersberg Marmor”). Different types of borings are recorded from rudist shells and coral skeleton, some of which are referable to the ichnotaxon Entobia produced by endolithic sponges. In the present study, special attention is paid to the occurrences of the cryptobiotic foraminifera Troglotella incrustans Wernli and Fookes in the Late Jurassic and Tauchella endolithica Cherchi and Schroeder in the Late Cretaceous. The latter is so far only known to be from the Early Cenomanian of France and is reported here for the first time from the Late Turonian-Early Coniacian stratigraphic interval where it was found in turbulent carbonate deposits within borings penetrating bivalve shells or coralline algae. The records of cryptobiotic foraminifera from the Northern Calcareous Alps are supplemented by a single finding from the Middle Cenomanian of SE France. A palaeoenvironmental interpretation of the occurrences of the cryptobiotic foraminifera is provided.     

Late Cambrian hard substrate communities from Montana/Wyoming: the oldest known hardground encrusters

Hardground surfaces from the Late Cambrian Snowy Range Formation in Montana/Wyoming are the oldest known non-reefal hard substrates exhibiting encrusting fossils. These surfaces range in age from Early Franconian to early Trempealeauan. Hardgrounds were developed on slightly hummocky to planar, truncated surfaces of glauconite-rich, carbonate, flat pebble conglomerates, which were deposited during episodes of storm scouring in shallow subtidal environments of the Montana/Wyoming shelf. Snowy Range hardgrounds are encrusted by a low diversity assemblage of fossils dominated by simple discoidal holdfasts of pelmatozoans, probably crinoids, and including small conical spongiomorph algae? and probable stromatolites. Macroborings (e.g. Trypanites) are notably absent from all hardground surfaces, although sharp-walled, vertical, cylindrical holes (borings?) occur in micrite clasts imbedded in certain flat pebble conglomerates. No evidence of faunal succession or microecologic partitioning of irregular surfaces was observed on these Cambrian hardgrounds.     

Ichnofacies and microbial build-ups on Late Miocene rocky shores from Menorca (Balearic Islands), Spain

Angular unconformites between Jurassic and Miocene strata are exposed in the sea cliffs of Cala Cigonya on the northwest coast of Menorca in the Balearic Islands of Spain. The geological discontinuities represent rocky shores on opposite sides of a former headland with 15 m of topographic relief. On the east flank, Jurassic dolomite is overlain by Upper Miocene (Tortonian to Messinian) breccia and laminated limestone. Here, a partially exhumed dolomite surface records Miocene bivalve borings of the ichnospecies Gastrochaenolites torpedo and G. lapidicus that achieved a density of >1,000 borings/m². Other associated traces include sponge borings (Entobia isp.) and polychaete borings (Caulostrepsis isp.). A breccia deposit 0.8 m thick was derived from the underlying dolomite and angular clasts still retain evidence of bivalve borings. Above follows a succession of laminated limestone beds more than 5 m thick, including some levels with dome-shaped stromatolites and other horizons with reworked dolomite clasts. Thin-section analysis of the laminated limestone reveals dark and light couplets 0.2 mm thick consistent with microbial origins. In contrast, the west flank was buried by coarse sandstone and laminated sediments. Here, dwelling structures of regular echinoids (Circolites kotoncensis) are the dominant traces preserved on the dolomite surface, reaching a maximum density of 66 borings/m². Associated borings include Entobia geometrica as well as rare traces of Gastrochaenolites isp. and Trypanites isp. Notable for the absence of a basal Miocene breccia, the west flank is interpreted as a sheltered rocky shore coeval with an exposed rocky shore on the east flank. Today, heavy surf on the north coast of Menorca is related to the Tramontana winds that blow out of Spain during winter months. Similar atmospheric circulation patterns must have prevailed during the Late Miocene, but the replacement of ichnofacies by microbial build-ups resulted from increased salinity during the Messinian crisis.     

Palaeocology of Hard Substrate Faunas from the Cretaceous Qahlah Formation of the Oman Mountains

Skeletal encrusters and carbonate hardgrounds are rare in siliciclastic sands and gravels because of high levels of abrasion and sediment movement. An exception to this is the Maastrichtian Qahlah Formation of the Oman Mountains, a sequence of coarse siliciclastic sediments deposited on a shallow marine shelf above wavebase and at an equatorial palaeolatitude. This unit contains intercalated carbonate hardgrounds and other hard substrates which were encrusted and bored. The hard substrates, comprising carbonate and silicate clasts, calcareous bioclasts (mollusc shells and coral fragments) and wood, supported a diverse encrusting and boring fauna dominated in biomass by the oyster Acutostrea . There are twelve bryozoan species and at least two serpulid worm species, most living cryptically. Other encrusters on exposed surfaces include the agglutinated foraminiferan Placopsilina and several species of colonial corals. Borings in the carbonate clasts and shells are predominantly those of bivalves ( Gastrochaenolites ), with subsidiary clionid sponge ( Entobia ) and acrothoracican barnacle ( Rogerella ) borings. The woodgrounds are thoroughly bored by teredinid bivalves ( Teredolites ). Of the common substrate types, carbonate hardground clasts support the greatest number of taxa, followed by chert clasts, with limestone rockground pebbles being depauperate. Clast composition and relative stability probably explain these differences. Individual clasts probably had variable and typically long colonisation histories. Detailed palaeoecological interpretation is constrained by taphonomic loss, time-averaging and clast transportation and reorientation. Evidence from the Qahlah Formation shows that tropical rocky-shore biotas in the Cretaceous were not impoverished as previously believed.     

Recent borings in limestone cobbles from Marloes Bay, southwest Wales

Limestone clasts from the beach at Marloes Sands, southwest Wales, contain slender, straight to sinuous borings cross-cut by younger, clavate borings. The former were probably produced by sipunculids or polychaetes; the latter preserve shells of the boring bivalve Gastrochaena dubia (Pennant). Unusually, the calcareous linings of the clavate bivalve borings extend into many of the slender worm borings. Such linings are considered part of the hard parts of the producing bivalve, but the chance association of the two morphologies of borings has led to the lining becoming intimately associated with both of them. The modified linings of the bivalve borings have a similar morphology to the crypt of certain clavagellid bivalves, perhaps presenting an analogue for the morphology of a pre-clavagellid, boring ancestor.     

Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus.     

Microboring in a Freshwater Fluvial Unionid Bivalve Substrate

Samples of the unionid bivalve Elliptio complanata were collected from the channel of the freshwater Saint John River, from Fredericton, New Brunswick, Canada. Scanning electron microscopy imaging of prepared shell samples revealed an assemblage of microborings. No borings are noted on the periostracum or prismatic shell layers. Boring structures are instead confined to the underlying nacreous aragonitic shell material, together with its associated organic conchiolin layers. Three main styles of boring are encountered, encompassing both predominantly surficial structures and penetrative tubular borings. Surficial structures are represented by a polygonal network on an exposed conchiolin shell layer. The penetrative borings take two forms, one being simple unbranched tubes, steeply aligned (perpendicular to the shell surface) and traversing the full thickness of the nacreous shell layer. The other penetrative boring style, again occurring within the nacreous layer, comprises a complex irregular network of randomly oriented rarely branching tubular borings. Borings generally display diameters of micron scale. Biofilm and extracellular polymeric substances, with bacterial, diatomaceous and filamentous components are also observed, often displaying a close association with both the borings and the conchiolin layers within the shell. The formation of the borings may be attributed to cyanobacteria, cyanophyte or fungal progenitors.     

Occurrence of Giant Borings of Osprioneides kampto in the Lower Silurian (Sheinwoodian) Stromatoporoids of Saaremaa,Estonia

The distribution of Osprioneides is more environmentally limited than that of Trypanites in the Silurian of Baltica. Osprioneides probably occurred only in large hard substrates of relatively deepwater muddy bottom open shelf environments. Osprioneides were relatively rare, occurring in 4.7% of all stromatoporoid specimens in that environment, in contrast to small Trypanites-Palaeosabella borings, which occur in 88.4% of stromatoporoids and 88.9% of heliolitid corals. Osprioneides is reported only from the lower Sheinwoodian stromatoporoids of the exposed Silurian of Saaremaa (Wenlock to Pridoli). Osprioneides borings probably played a minor role in the general bioerosion in the Silurian of Baltica.     

A New Ichnospecies of Gastrochaenolites Leymerie from the Pleistocene Port Morant Formation of Southeast Jamaica and the Taphonomy of Calcareous Linings in Clavate Borings

The ichnospecies Gastrochaenolites pickerilli isp. nov. is based on ten borings found in a shell of the gastropod Strombus gigas Linné from the Pleistocene (Sangamonian) Port Morant Formation of southeast Jamaica. These borings bear morphological similarities to Gastrochaenolites torpedo Kelly and Bromley but differ from all other Gastrochaenolites ispp. in having prominent and numerous calcareous meniscate structures arrayed adjacent to one side of the boring. These menisci are concave towards the center of the boring and are the remnants of calcareous tubes that lined earlier boreholes, that the boring bivalve treated as part of the lithified substrate when relocating. They are thus evidence of the former positions of borings that, unusually, were breached as the bivalve migrated sideways. Although this was a common behavior for Gastrochaenolites-producing bivalves within this substrate, the reason for it occurring is uncertain.     

Taphonomy of Logs Bored with Teredolites longissimus Kelly and Bromley in the Danian (Lower Paleocene) of West Greenland

The boring Teredolites longissimus Kelly and Bromley is recorded infesting silicified logs in the Fossil Wood Member, Kangilia Formation (Lower Danian, Paleocene) of West Greenland. There are two morphologies of T. longissimus, probably representing two different episodes of invasion of the wood. The initial borings of Morphology 1 are large, deformed to an elliptical section, and confined to a direction of boring parallel to sub-parallel to the wood grain. Morphology 2 borings are less common, narrower and shorter, sinuous, markedly crosscut the grain of the wood and, where preserved intact, retain their circular cross-section. They were a later infestation than Morphology 1. Following the infestation by Morphology 1, the logs were deformed, probably by weight of overburden, and then reworked, when some of them were infested by Morphology 2 producers. Final burial was followed by brittle collapse of some Morphology 2 borings and lithification before further deformation could occur. The occurrence of T. longissimus in deeper water deposits close to a land mass with a steep slope indicates that transport in the marine realm was minimal before waterlogging.     

Rocky-shore unconformities marking the base of Badenian (Middle Miocene) transgressions on Mt. Medvednica basement (North Croatian Basin,Central Paratethys)

Badenian (Middle Miocene) transgressive deepening-upward successions located in the NE part of Mt. Medvednica (North Croatian Basin, Pannonian Basin System) unconformably overlie Mesozoic basement. Triassic and Upper Cretaceous limestone pebbles, cobbles, and boulders of the Badenian basal conglomerates display abundant in situ bivalve borings of Gastrochaenolites and sponge borings of Entobia. This Gastrochaenolites-Entobia ichnoassemblage is related to the Entobia subichnofacies of the Trypanites ichnofacies, characterizing littoral rocky-shore environments (wave-cut platforms and marine transgressive surfaces with a low or null rate of sedimentation). Gastrochaenolites torpedo, Gastrochaenolites lapidicus, and Entobia recorded in Badenian basal conglomerates (compared with modern Northern Adriatic rocky-shore environments), enabled more precise palaeoenvironmental interpretations. The occurrence of G. torpedo (produced by lithophaginid bivalves) on all sides of individual limestone lithoclasts in the Gornje Ore?je basal conglomerate, coupled with truncation of the formation (possibly indicating multiphase colonization), reflect gravel transport, roll-over, overturning and erosion by wave action in high-energy rocky-shore settings. Gornje Psarjevo-2 basal conglomerate boulders were probably not subjected to significant movement and abrasion, as suggested by good preservation of both G. lapidicus (potentially produced by gastrochaenid bivalves), associated G. torpedo, as well as abundant shallow Entobia borings. The Badenian Gastrochaenolites-Entobia ichnoassemblage also could be the result of a composite development. However, direct cross-cutting relationships between G. torpedo and G. lapidicus and/or Entobia were rarely observed. In addition, Badenian boring tracemakers might have coexisted at the same water depth. Northeast Mt. Medvednica Badenian successions probably formed during different Central Paratethys transgressive pulses (NN5 and NN6 Zones). However, exact timing of Badenian transgressions, stratigraphic correlations and tectono-eustatic implications are unresolved, due to sparsely integrated biostratigraphic and high-precision geochronological studies of Early–Middle Miocene North Croatian Basin deposits and due to the absence of a uniform biostratigraphic zonation and regional chronostratigraphic division of Central Paratethys.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

Holes in Bones: Ichnotaxonomy of Bone Borings

Bone is a substrate for bioerosion at equal rank with xylic and lithic substrates. Accordingly, borings in bone have to be identified in an analogous way to other ichnogenera coined for one type of substrate. In due course, the new ichnogenera Osteichnus n. igen. and Clavichnus n. igen. are established within the new ichnofamily Osteichnidae. Gastrochaenolites and Trypanites are here restricted to lithic substrates, and Asthenopodichnium only occurs in xylic substrates. Only with this approach, ichnotaxobases of trace fossils in bone are identical to those in other hard substrates. Cuniculichnus variabilis n. igen. n. isp. is introduced for variably shaped pits to tunnels bored into bone by beetle (arguably dermestid) larvae; its ethological character is close to a pupichnion.     

中国湘南早侏罗世双壳类壳体内的遗迹化石--兼论遗迹化石属Talpina Hagenow, 1840

论文描述的双壳类壳体内的钻孔遗迹组合发现于湖南省东南部宜章县下坪附近的心田门组上部(早侏罗世,早辛涅缪尔期)浅海沉积地层中。这个遗迹化石群中,帚虫类动物制造的钻孔Talpinahunanensisichnosp.nov.(新遗迹化石种)明显地占据了大部分,偶尔共生的其它钻孔包括:Rogerellaichnosp.(蔓足亚纲尖胸类的遗迹)、Calcideletrixichnosp.(可能是藻类的遗迹)、藻或菌造的遗迹(暂定为"Mycelites"ichnosp.)、以及一种可能被海绵动物制造的未定钻孔。生物侵蚀者侵害了海底上较大的双壳类壳体。钻孔保存为天然印模(石核),它们是文石质壳体溶解后留下的空间中的充填物。此外,文中还讨论了遗迹化石属TalpinaHagenow,1840,尤其讨论了有关遗迹种颇为复杂的鉴别问题,同时校正了该遗迹属的属征。     

Bioerosion of gastropod shells: with emphasis on effects of coralline algal cover and shell microstructure

Organisms boring into fifty nine species of gastropod shells on reefs around Guam were the bryozoan Penetrantia clionoides; the acrothoracian barnacles Cryptophialus coronorphorus, Cryptophialus zulloi and Lithoglyptis mitis; the foraminifer Cymbaloporella tabellaeformis, the polydorid Polydora sp. and seven species of clionid sponge. Evidence that crustose coralline algae interfere with settlement of larvae of acrothoracian barnacles, clionid sponges, and boring polychaetes came from two sources: (1) low intensity of boring in limpet shells, a potentially penetrable substrate that remains largely free of borings by virtue of becoming fully covered with coralline algae at a young age and (2) the extremely low levels of boring in the algal ridge, a massive area of carbonate almost entirely covered by a layer of living crustose corallines. There was a strong negative correlation between microstructural hardness and infestation by acrothoracian barnacles and no correlation in the case of the other borers. It is suggested that this points to a mechanical rather than a chemical method of boring by the barnacles. The periostracum, a layer of organic material reputedly a natural inhibitor of boring organisms, was bored by acrothoracican barnacles and by the bryozoan. The intensity of acrothoracican borings is shown to have no correlation with the length of the gastropod shell.     

Composite Trace Fossil Assemblage in a Distal Carbonate Setting from the Tethys (Middle Jurassic,Betic Cordillera,Southern Spain)

Ichnological analysis of a Middle Jurassic carbonate surface from the Betic Cordillera (southern Spain) reveals a complex trace fossil assemblage, including softground Ophiomorpha, firmground Arenicolites, Thalassinoides and Gastrochaenolites, and hardground Trypanites as well as possible Gastrochaenolites. The ecological replacement in the macrobenthic community is interpreted according to successive suites that are controlled mainly by substrate consistency. Variations in composition and abundance of trace fossils between suites can be ecologically and/or taphonomically determined.     

Determination of a Late Miocene rocky palaeoshore by bioerosion trace fossils from the Bozcaada Island, Çanakkale,Turkey

Bioerosion is a common process in hard substrates. This study introduces an example from the rocky palaeoshore cropping out at a sea cliff on the Bozcaada Island. It includes bioerosion trace fossils preserved in limestone boulders of the shallow marine and lacustrine Alcitepe Formation of Late Miocene age. The ichnotaxa include borings produced by duraphagous drillers (Oichnus isp.), phonorids (cf. Conchotrema isp.), clionid sponges (Entobia cf. goniodes, Entobia geometrica, Entobia laquea, Entobia ovula, E. cf. solaris, Entobia isp.), endolithic bivalves (Gastrochaenolites torpedo, Gastrochaenolites lapidicus, Gastrochaenolites isp., Phrixichnus isp.), polychaete annelids (Maeandropolydora isp., Maeandropolydora sulcans, Maeandropolydora decipiens, Caulostrepsis taeniola, Caulostrepsis isp.), echinoids (cf. Circolites isp.) and spinculid worms (cf. Trypanites isp.). Barnacles are also common as encrusters. The borings can be ascribed to the Gastrochaenolites-Entobia assemblage, which is typical of Neogene rocky-shores. They belong to the Entobia ichnofacies indicating various conditions of light, energy, and depth. Therefore they can reveal environmental changes and play an important role in forming palaeo-rocky shores and wave-cut platforms during marine trangressive events.     

Bioerosion in Late Permian Rugosa from reefal blocks (Hawasina Complex,Oman Mountains): implications for reef degradation

Summary Rugose corals are known from allochthonous Late Permian reefal blocks of the A1 Jil and Ba’id Formation (Hawasina Complex), Oman Mountains. In contrast to many Late Permian Rugosa found elsewhere in the Tethys, they occurred in sponge reefs and contributed to reef construction. The waagenophyllid warm water coral fauna is moderately diverse comprising cerioid, thamnasterioid, and fasciculate taxa. In contrast to sponges, chaetetids, and low-growing reefbuilders, the corals secreted diagenetically stable, most probably Mg-calcitic skeletons. Borings in coral skeletons are consequently well preserved providing important data for the interpretation of reef destructive processes. Thin-section analysis revealed three taxa of infaunal borers includingEntobia Bronn 1837, uncertain thallophyte borings, and borings of unknown bioeroders. Macroborers were more important than microborers, because of the dominance of clionid sponges. Good evidence exists also for the occurrence of two types of undetermined grazers which destroyed the coral surfaces. The amount and distribution of bioerosions is variable among different coral taxa. The fasciculate coralPraewentzelella regulare Flügel 1995 was the favorate substrate. Up to 33% of the calices were bored. Dendroid and compound corals were bored subordinately. Bioerosion of these colonies does not exceed 2%. There is good evidence for substrate preference amongst the borers. Major controlling factors affecting borer distribution are believed to be variations of skeletal density and gross morphology. The borer assemblage could not limit reef accretion significantly. Factors controlling boring activity might have been quality of substrate, sedimentation rate, rapid incrustation of substrates, and competition for food with reef constructors including sponges, chaetetids, and rugose corals.     

Bioerosion versus colonisation on Bivalvia: A case study from the Upper Miocene of Cacela (southeast Portugal)

A study of the bioerosion structures and the skeletobionts associated with the most common bivalves (infauna and epifauna) from the classic Upper Tortonian site of Cacela, Algarve region, SE Portugal, revealed 24 different ichnotaxa and five systematic groups of encrusters (Foraminifera, Annelida, Bryozoa, Balanomorpha and Bivalvia).Despite a relatively high ichnodiversity, the percentage of bioerosion in the specimens analysed is quite low (10-12%). This is explained by rapid sedimentation with only short periods of exposure on the sea-floor.The dominant bioerosion structures were linked to the boring activity of nonpredatory organisms. Algal microborings are the most common, followed by annelid borings (Caulostrepsis-Maeandropolydora), sponge borings (Entobia) and ctenostome bryozoans (Pinaceocladichnus).Spatial distribution of bioerosion structures and encrusters allow the reconstruction of three successive stages. The first was restricted to the biosubstrate lifetime, with structures showing a preferred orientation and situated exclusively on the outside of the shells. The second comprises the period immediately after death, with structures that extend outwards and start with the colonization of the interior of the valves, losing their initial orientation. The third stage relates to later postmortem colonisation, with structures on both sides of the valves and without a preferential orientation.