Facies (2005) 51: 233–241DOI 10.1007/s10347-005-0023-3

ORIGINAL PAPER

Wolfgang Kiessling · Eugenio Aragon ·Roberto Scasso · Martin Aberhan · Jurgen Kriwet ·Francisco Medina · Diego Fracchia

Massive corals in Paleocene siliciclastic sediments of Chubut(Argentina)

Received: 23 December 2004 / Accepted: 17 February 2005 / Published online: 19 October 2005C© Springer-Verlag 2005

Abstract A horizon with large, massive corals in growthposition was discovered in the Paleocene, probably upperDanian, part of the Maastrichtian–Paleocene Lefipan For-mation of Chubut (Patagonia, Argentina). All corals belongto one species, the cosmopolitan Haimesiastraea confertaVaughan, which survived the end-Cretaceous massextinction. The occurrence of massive corals at this siteis exceptional both because of the siliciclastic depositionalregime and because of the high palaeolatitude setting.An unusual autecology of this coral and strongly reducedsedimentation rates, were probably the prerequisites forcoral growth, but a link to palaeoclimate is less likely.

Keywords Bioerosion . Corals . Ecology . Massextinction . Paleocene . Siliciclastics

W. Kiessling (�) · M. AberhanInstitut fur Palaontologie, Museum fur Naturkunde,Humboldt-Universitat Berlin,Invalidenstr. 43,D-10115 Berlin, Germanye-mail: wolfgang.kiessling@museum.hu-berlin.deTel.: +49-30-2093-8576Fax: +49-30-2093-8868

E. AragonCentro de Investigaciones Geologicas, Universidad Nacional deLa Plata 1 No 644,1900 La Plata, Argentina

R. Scasso · F. MedinaDepartamento de Ciencias Geologicas, FCEN, Universidad deBuenos Aires, Ciudad Universitaria,Pab. 2, 1◦ Piso,1428 Buenos Aires, Argentina

J. KriwetDepartment fur Geo- und Umweltwissenschaften,Ludwig-Maximilians-Universitat Munchen,Richard-Wagner-Str. 10,D-80333 Munchen, Germany

D. FracchiaInstituto de Geologıa y Mineria, Universidad Nacional de Jujuy,C. Correo 258,4600 S.S. de Jujuy, Argentina

Introduction

The mass extinction at the end of the Cretaceous hasaffected most groups of marine animals. However,significant variation exists between the extinction ratesof different taxonomic groups. Scleractinian corals weresurprisingly little affected by the mass extinction andeven many corals inferred to have hosted zooxanthellae(photosymbiotic algae) in their tissues survived thisevent Kiessling and Baron-Szabo (2004). Here we reportan unexpected occurrence of large and massive corals,identified as Haimesiastraea conferta Vaughan, (1900)in coarse siliciclastic sediments of Paleocene age. Thisdiscovery sheds light on the autecology of an importantsurvivor of the end-Cretaceous mass extinction.

Geological setting and stratigraphy

The corals occur in the uppermost part of the LefipanFormation, the upper unit of a thick, siliciclastic sequencecomposed of the Paso del Sapo and Lefipan Formations,exposed along the Middle Chubut River Valley near thetown of Paso del Sapo (Fig. 1). The Lefipan Formationis capped by continental beds and rests conformably ona thick sequence of cross-bedded sandstones with somecoal beds and mudstones (Paso del Sapo Formation)of Campanian–Maastrichtian age (Fig. 2). The wholesequence is unconformably overlain by a volcanic–pyroclastic complex, the Ignimbrita Barda Colorada(IBC) of the Middle Chubut River volcanic–pyroclasticcomplex (Aragon and Mazzoni 1997). K/Ar analyses oftuffs from the IBC have indicated a Late Paleocene age(Archangelsky 1974). More recent K/Ar and 40Ar/39Aranalyses of associated tuffs and volcanic rocks haveindicated a Late Paleocene to Middle Eocene age for thecomplex (Mazzoni et al. 1991; Wilf et al. 2003).

The Lefipan Formation is composed of marine, fossil-iferous sandstones and mudstones with some intercalatedcoquinas and conglomerates, and ranges from theMaastrichtian to the Paleocene. The biostratigraphic

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Fig. 1 Geographic andgeological setting of the LefipanFormation and location ofcoral-bearing outcrops

Fig. 2 Schematic geological column of exposed rocks near Pasodel Sapo. Stratigraphic position of the coral locality at EstanciaDon Manuel is indicated. Not to scale. Camp - Campanian; Maa -Maastrichtian; Pal - Paleocene; Eoc - Eocene

resolution is currently exclusively based on assemblages ofbivalves and gastropods and is therefore quite coarse. Threemacrofossil assemblages have been separated in previouspapers, one in the Maastrichtian and two in the Paleocene(Medina et al. 1990; Medina and Olivero 1994). The depo-sitional environment in the latest Cretaceous changes froma fluvial to tidally influenced estuarine environment (Pasodel Sapo Formation) to an open marine environment in theLower Lefipan Formation (Spalletti 1996). Macrofossilsand sedimentary features indicate a shallow marine orestuarine environment for the lower part of the Lefipan

Formation, evolving to deltaic systems in the middle andupper part of the unit (Olivero and Medina 1994).

Field studies of our working group on a reference sec-tion (San Ramon) and several partial sections in the areasuggest that the lower part of the Lefipan Formation(Maastrichtian) was mainly deposited in a shallow marine,shoreface environment with strong tidal influence and aconspicuous association of trace fossils (Poire and Spalletti1998) and beds rich in phosphatic concretions (Pereira andScasso 2002). The palaeoenvironment evolved to a tide-to wave-dominated deltaic system in the middle part ofthe sequence, which comprises the Cretaceous–Paleogeneboundary (Ruiz and Scasso 2004). In the Paleocene, the en-vironment was deepening, developing into a fully marinesystem influenced by wave and storm activity.

Coral localities

We have measured and studied several sections in theLefipan Formation in the area, but corals have been foundat only two localities. Previous workers, with the exceptionof one (Camacho 1967), have not reported on the presenceof corals in the area. At both our localities (Estancia DonManuel in the Barda Colorado region and an unnamed lo-cality in the upper part of the San Ramon section), coralsoccur in a single horizon belonging to the Paleocene partof the Lefipan Formation.

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Estancia Don Manuel (Barda Colorado)

Abundant corals were discovered in the Barda Coloradoarea at a locality called Estancia Don Manuel (DM;42◦43′50′′S, 69◦58′38′′W). The Lefipan Formation in theBarda Colorado area is strongly folded and thrusted. Onlyparts of the unit are exposed, often in blocks separated bythrust planes. As a consequence, the stratigraphic relation-ships between the coral locality and the rest of the LefipanFormation and to the overlying pyroclastics belonging tothe IBC complex are not completely clear. The DM localityis apparently situated near the top of the Lefipan Formation.From base to top, the sedimentary sequence at this localityis (Fig. 3):

1. Brown, friable, mottled (intensely bioturbated) finesandstone typical of Lefipan Formation.

2. Conglomerates with interbedded sandstones. Conglom-erate with 50% of clasts made of well-rounded gravelup to 1 cm in diameter, fragmented bioclasts (bivalvesand gastropods). The sandstone matrix has carbonate ce-ment. Intercalated are two sandstone layers the lower ofwhich shows hummocky cross-bedding. This group ofbeds is capped by a hardground marked by reddish mud-stones infilling borings and encrustations of serpulidsand oysters. Gastropods (Turritella malaspina), bivalves(Venericardia feruglioi, Pseudolimea sp. and Pycn-odonte miradonensis), crustacean remains and sharkteeth have been identified in the conglomerates immedi-ately below the hardground, suggestive of a Paleocene,perhaps Danian age. The hardground is developed on anerosive surface.

3. Fossiliferous reddish conglomerate with large coralcolonies in growth position. Impregnated sandstone peb-bles up to 4 cm in maximum diameter occur in the bed.

4. Greenish sandstone, locally well-cemented.5. Red mudstone.6. Unwelded tuff.

The coarse-grained beds of unit 2 can be interpreted asshoreface deposits, marking a transgressive sand (Trans-

Fig. 3 Detailed local section of the outcrop at Estancia Don Manuel(weathering profile). Numbers correspond to the description in text

gressive Systems Tract) capped by the hardground repre-senting the maximum flooding surface. Horizons 4 and 5are preliminarily interpreted as early highstand deposits.

A total of 52 mature coral colonies were found at thislocality in our 2004 expedition, with up to 60 cm maxi-mum diameter. The majority of corals were found in scree.However, several massive corals occur in outcrop as well,where they are all in growth position forming a biostromallayer. This layer is up to 50 cm thick and can be laterallytraced for 20 m (Fig. 4A and B). Corals found in outcrop(horizon 3) are irregular massive or hemispherical and areup to 50 cm in diameter and up to 30 cm high (Fig. 4B).One of the authors (EA) has found a dome-shaped coral-lum of 80 cm height in a previous visit to the outcrop. Allcorals are identified as H. conferta Vaughan (Fig. 5A–H),a species ranging from the Maastrichtian to the MiddleEocene. The corals are exclusively massive exhibiting do-mal, hemispherical or irregular growth forms (Table 1). Thesmallest, complete adult corallum is hemispherical with adiameter of 7 cm.

The corals are moderately well preserved. Most of thecorals are superficially little affected by bioerosion andencrustation. Encrusting bivalves are small (Fig. 4G) andcover less than 5% of the coral surfaces. Serpulids were alsofound as encrusters, but there are no traces of encrustingalgae. We have identified the bioerosion ichnogenera Gas-trochaenolites, Trypanites and Entobia in the corals. The in-tensity of bioerosion is apparently stronger than visible ex-ternally because most of the cavities are internal (Fig. 4F).Internal cavities tend to be aligned with coral growth struc-tures and are thus interpreted as passive “borings”, formedby the attachment of organisms to the live coral surfaceleading to local growth inhibition of the coral skeleton(Scoffin and Bradshaw 2000). Less than 10% of the coralvolume has apparently been excavated by active bioerosion,which is surprisingly little considering the high nutrient lev-els Zubia and Peyrot-Clausade (2001) that can be inferredfor this inshore siliciclastic environment. Rapid burial ofthe corals by siliciclastic shedding was probably responsi-ble for the scarcity of post-mortem active bioerosion.

The in situ preservation of corals is remarkable given thehigh energy environment. Sandstone pebbles up to 2 cmin diameter are attached to the flanks of domal colonies(Fig. 4E). The pebbles are impregnated by iron-oxides.They are preferentially attached to depressions formed bybioerosion but also accumulated in pits formed by physicalerosion.

The corals grew on a hardground (Fig. 4C), marked inplaces by reddish carbonate mudstones infilling large bore-holes. The borings mostly stem from bivalves, but otherorganisms such as worms and sponges were also involved.The hardground is locally encrusted by oysters and ser-pulids, and corals grew directly on this hardground. At oneplace juvenile corals have been found on the hardground(Fig. 6). Although not all distinctive characters are devel-oped, these corals are also assignable to H. conferta. Wehave analyzed an area of 250 cm2 in detail to understand themode of larval settlement and development. Most of thesejuvenile corals are solitary. Out of 58 juvenile corallites,

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Fig. 4 Macroscopic features of the coral locality at Estancia DonManuel and its corals (A–C, E–G), and coral in the San Ramon section(D). A Overview of the outcrop Don Manuel. Geologists are at levelof the coral bed. Layered mountain in the background is ignimbriteof the IBC complex. B One of the largest Haimesiastraea foundin growth position. Massive irregular growth form (outlined). Noteinternal bioerosion (white arrows) and encrusting bivalves (black ar-rows). Camera cap for scale (4 cm). C Cross-section of hardgroundas found in the field. The sandstone is heavily bored by bivalvesand worms (?). Borings (outlined with white line) are filled with redcalcareous mudstone and mudstone is encrusted by oysters (arrow).

Camera cap for scale (4 cm). D Small coral fragment in the coralbed of the San Ramon section, probably a Cladocora sp. Width ofpicture is 1.5 cm. E One of the largest dome-shaped H. confertafound in our 2004 expedition. Length of ruler is at 30 cm. Note largegravel attached to the flank of the corallum. F Polished slab of adome-shaped corallum. Note external and intense internal bioero-sion (outlined) filled with coarse sandstone and gravel (stippled) andexternal mechanical erosion (outlined in white); centimetre scale. GUpper surface of corallum with encrusting juvenile oyster (arrow);centimetre scale

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Fig. 5 Details of H. conferta Vaughan from the outcrop at Es-tancia Don Manuel. A Tip of dome-shaped corallum; centimetrescale. B Close-up of unprepared coral surface; centimetre scale. CCross-section with internal bioerosion (note geopetal fabric). Unusu-ally large corallite on upper right. D Tangential section near base of

corallum. E Cross-section showing details of costate coenosteum anddissepiments in calice. F Detail of a corallite showing 12 septa of thefirst two cycles uniting in centre. G Detail of septothecate wall andthe third septal cycle. H Detail of a septum exhibiting rudimentarylateral projections

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Table 1 Growth forms of H.conferta at Estancia DonManuel

Domal Hemispherical Irregular massiveSmall (7–10 cm) Large (11–30 cm)

N 6 5 4 20Percentage 17 14 11 57Based on 35 nearly complete

corals

Fig. 6 Incipient colonization of hardground by corals (cf. H. con-ferta) at Estancia Don Manual. Note patchiness of distribution ofcoral recruits and predominance of solitary forms. Size of surface ca.20 cm × 14 cm. Inset shows details of juvenile corallites (millimetrescale in lower right)

only 21 (36%) were found in series showing evidence ofearly clonal growth. The majority of corallites shows fullydeveloped septal cycles just as the mature corallites in themassive colonies. The immaturity of the corals suggests thatthey were killed off soon after larval settlement. Althoughwe cannot detail the time involved in the ontogenesis of thisextinct species, neontological studies suggest that colonialcorals start budding a few days to several months after lar-val settlement (Babcock et al. 2003; Neves and da Silveira2003). The mass mortality of coral recruits, perhaps withinthe first year after larval settling, supports the view thatsuccessful recruitment may be limited by sediment loads(Te 1992) and indicates harsh environmental conditionsduring coral growth. It was only the second (at least) gen-eration of recruits which successfully developed into largecolonies.

San Ramon section

In the San Ramon section only three coral fragments werefound in a bed at 42◦41′11′′S, 69◦50′17′′W, close to thetop of our measured section. The bed is composed of aglauconitic sandstone with abundant carbonate nodules andshell hash. Similar to Estancia Don Manuel, the bed is un-derlain by hummocky cross-bedded sandstones and over-lain by sandy mudstones. Gastropods (Pseudamaura dubia,Struthioptera sp.) and bivalves (Venericardia sp., Meretrixchalcedonica) are common in the bed and serpulids, crabremains, shark teeth and corals are rare. Two of the coral

fragments are identified as H. conferta and one is a dendroidform, possibly a Cladocora (Fig. 4D).

Stratigraphic correlation

Based on several observations, we correlate the coral out-crop at DM with the upper part of our reference sectionat San Ramon. First, based on mollusc assemblages bothoccurrences belong to faunal “Asociacion III” of Medinaet al. (1990) indicative of the second faunal associationwithin the Paleocene of the region. Second, we have foundonly one level with corals in both sections although wehave studied the San Ramon section in detail over a thick-ness of 300 m. Third, the sequence stratigraphic position isidentical in both occurrences. The carbonate nodules andintense fragmentation of shells point to reduced sedimen-tation rates at San Ramon as does the hardground at DM.Fourth, both occurrences are associated with hummockycross-stratification and lack the heterolithic bedding, whichis very common in the rest of the section.

The precise stratigraphic assignment of our coral locali-ties has to remain open at this point, because palynologicalstudies have not provided unequivocal results so far(V. Barreda, personal communication, 2003) and othermicrofossils are virtually absent. Based on macrofossils(gastropods and bivalves), the age is certainly Paleoceneand probably Late Danian. Haimesiastraea itself is oflimited stratigraphic value. The oldest records of thegenus are from the Middle Cretaceous (Squires 1958),the youngest known record is from the Middle Eoceneof Mexico (Frost and Langenheim 1974). H. conferta hasa more limited range from the Campanian–Maastrichtian(Peru: Wells 1941; Argentina: Baron-Szabo in press) to theMiddle Eocene (Mexico). The acme in terms of the numberof occurrences and geographic distribution was in the Pa-leocene when H. conferta reached from central Patagonia(this study) to North America and Europe (Drobne et al.1988). Most well-dated occurrences of H. conferta in themore recent literature are from the Danian (Toulmin 1977;Turnsek and Drobne 1998; Baron-Szabo et al. 2003) andseveral of the occurrences formerly assigned to the Middleand Late Eocene have been reassigned to the Paleocene–Early Eocene (Floris 1972). This contrasts the opinionof Budd (2000) who sees Haimesiastraea essentiallyconfined to the Middle Eocene of the Caribbean.

Discussion

The occurrence of corals is not unusual in the Paleocene ofArgentina. Corals were recorded from Puelen, La Pampa

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(Baron-Szabo et al. 2003), Huantraico and Bajada delJaguel (own unpublished data), Neuquen and Tierra delFuego (Furque and Camacho 1949). These findings includemassive corals in Puelen and Huantraico but none of themassive corals are so closely associated with coarse sili-ciclastic sediments. Moreover, in none of these localitieshave such large colonies been found and the other placesare quite distant from our locality.

The discovery of such large and massive coral coloniesin a purely siliciclastic shelf setting was completely unex-pected and we know of no similar occurrence in the fossilrecord.

It was apparently the transient sediment starvation asso-ciated with a flooding surface that allowed for the growthof corals. There must have been little or no sedimenta-tion over a prolonged interval of time to first stabilize thesubstrate and then permit the corals to reach these large di-mensions. Our observations point to at least two successivecolonization episodes, the first unsuccessful and the secondsuccessful. Constraints on the duration of coral growth aredifficult to reconstruct without further data on their ecol-ogy. Specifically, we need to know if H. conferta was azooxanthellate or azooxanthellate coral.

Although not included in the list of Paleocene z-like(zooxanthellate-like, meaning likely to have hosted zoox-anthellae in their tissue) of Rosen (2000), many morpho-logical characters of Haimesiastraea point to a z-like status,applying the criteria of Coates and Jackson (1987): largesize of corallum, small size of corallites, multiserial ar-rangement of corallites and moderately high integration ofcorallites.

The geographic and environmental distribution ofHaimesiastraea suggests that the genus was cosmopolitan,opportunistic and able to thrive in siliciclastic settings.Haimesiastraea is known from palaeotropical regions(Peru) to very high palaeolatitudes (Greenland, palaeolat-itude 62◦N, Floris 1972; this study, palaeolatitude 45◦S)and occurs in carbonate platforms and reefs (Drobne et al.1988; Tragelehn 1996), coarse siliciclastics (Floris 1972;this study) and even claystones (Wasem and Wilbert 1943).These traits are untypical for z-like taxa and this was thereason why Kiessling and Baron-Szabo (2004) qualifiedHaimesiastraea as az-like (azooxanthellate-like, meaningunlikely to have hosted zooxanthellae in their tissue).

However, no modern az-coral is even distantly similarin size and morphology to Haimesiastraea. Moreover, inspite of its great environmental tolerance, Haimesiastraeahas exclusively been recorded in shallow water settings sug-gesting light as a prerequisite for coral growth. We there-fore argue that H. conferta hosted zooxanthellae in its tissueand had calcification rates comparable to modern massivecorals. The stress imposed by sedimentation may have re-duced skeletal growth rates (Hudson et al. 1994; Miller andCruise 1995) but not necessarily so (Edinger et al. 2000).That there was stress by contemporaneous sedimentationcan be inferred from the scarcity of active bioerosion, whichis typical for environments with high siliciclastic shedding(Sanders and Baron-Szabo 2005). With a reasonable es-timate of vertical accretion rates (5 mm year−1, e.g., the

minimum rates observed for modern healthy Montastreaannularis; see Dullo 2005), we achieve a live span of thelargest colony in our material of 160 years. The death ofthe successful coral recruits was apparently caused by re-newed rapid sedimentation. Rapid burial is inferred fromthe scarcity of encrustation and the in situ preservation ofcorals.

An open question remains the exclusively massive growthof our corals, although H. conferta has the plasticity for andcommonly exhibits ramose growth (Vaughan 1900; Wells1941; Frost and Langenheim 1974). Since vertical accre-tion rates of corals with ramose growth are usually greaterthan in massive corals (compare growth rates of modernAcropora and Montastrea; Dullo 2005), one would expectramose growth as an escape strategy from sedimentationstress in this siliciclastic setting. Indeed observations inmodern and Jurassic corals suggest that massive coloniesoften achieve a branching growth form where siliciclas-tic sedimentation is enhanced (Nose and Leinfelder 1997;Sanders and Baron-Szabo 2005).

Palaeoclimate does not seem to be a major trigger of coraldevelopment. The best palaeoclimatic data for the area arefrom Early Eocene plant associations in the Tufolitas La-guna del Hunco, which indicate a mean annual temperatureof 15.6 ± 2◦C and an overall warming trend of 6◦C (∼12to 18◦C) within the Ypresian based on leaf-margin anal-ysis (Wilf et al. 2003). There is little information on theearlier climatic history of the study area. However, globaldata suggest a continuous warming trend from the MiddlePaleocene to the Late Ypresian (Zachos et al. 2001). Ac-cording to our preliminary stratigraphic assignments, thecorals occur before the onset of this warming trend andthus temperature, at least as inferred from global data, areprobably not directly related to their occurrence.

Conclusion

Abundant massive colonies of H. conferta occurring in thePaleocene of the Lefipan Formation permit insights intothe autecology of an important Paleocene coral species.H. conferta had a peculiar autecology allowing it to thrivein a variety of habitats and a wide geographic range.Morphological characters and estimated growth ratesidentify H. conferta as a zooxanthellate-like coral, but itapparently had substantially broader physiological nicheboundaries than most modern zooxanthellate corals. Thiswas perhaps the reason why this species could survive theend-Cretaceous mass extinction.

Systematic palaeontology

The coral material is deposited in the Museum of La Plata(Argentina) under the inventory number MLP 31305.

Order: Scleractinia (Bourne, 1900)Suborder: Faviina (Vaughan and Wells 1943)Family: Columastreidae (?) (Alloiteau 1952)

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Genus: Haimesiastraea Vaughan (1900)Type species (by original designation): Haimesiastraea

conferta Vaughan (1900)Haimesiastraea conferta Vaughan (1900)Figs. 4B, E–G, 5, 6∗1900 Haimesiastraea conferta, sp. nov. - Vaughan, pp

145–146, pl. 15, Figs. 6–9, pl. 16, Figs. 1–7; [LatePaleocene–Early Eocene, Alabama]

1922 Peruviastrea peruviana, Vaughan, sp. n. - Vaughanin Bosworth, p 129, pl. 21, Figs. 6, 6a, 7, 7a;[Paleocene–Early Eocene, Peru]

1922 Haimesiastraea peruviana, Vaughan, sp. n. -Vaughan in Bosworth, p 130, pl. 22, Figs. 2–2b;[Paleocene–Early Eocene, Peru]

1922 Haimesiastraea humilis, Vaughan, sp. n. - Vaughanin Bosworth, p 131, pl. 22, Figs. 3, 3a, 4, 4a;[Paleocene–Early Eocene, Peru]

1922 Haimesiastraea distans, Vaughan, sp. n. - Vaughanin Bosworth, p 132, pl. 22, Figs. 5, 5a; [Paleocene–Early Eocene, Peru]

1922 Haimesiastraea conferta, Vaughan, - Vaughan inBosworth, pp 125, 131, pl. 22, Figs. 1, 1a

1933 Haimesiastraea conferta, Vaughan - Vaughan andPopenoe, pp 338–339, pl. 4, Figs. 1–2; [Paleocene,Texas]

1941 Montastrea parinasensis, n. sp. - Wells, p 7 (307),pl. 1, Fig. 2; [Maastrichtian, Peru]

1941 Haimesiastraea distans, Vaughan - Wells, p 15(315), pl. 2, Fig. 4; [Paleocene–Early Eocene, Peru]

1941 Peruviastrea peruviana, Vaughan - Wells, p 16(316), pl. 2, Fig. 5; [Paleocene–Early Eocene, Peru]

1943 Haimesiastraea conferta, Vaughan - Wasem andWilbert, pl. 31, Fig. 3; [Late Paleocene, Louisiana]

1974 Haimesastraea (Haimesastraea) peruviana,Vaughan - Frost and Langenheim, pp 193–194, pl. 59,Figs. 1–5; [Middle Eocene, Mexico]

1977 Haimesastraea conferta, Vaughan - Toulmin, pp145, 182, pl. 1, Fig. 7, pl. 10, Figs. 9–10; [Danian,Alabama]

1988 Haimesastraea peruviana, Vaughan - Drobne,Ogorelec, Plenicar, Zucchi-Stolfa and Turnsek, p 186,pl. 30, Fig. 3; [Danian, Slovenia]

1996 Hexakoralle, Morphotyp 18. - Tragelehn, p 198, pl.62, Figs. 8–9; [Paleocene, Austria]

1998 Haimesastraea peruviana, Vaughan, 1922 -Turnsek and Drobne, pp 134–135, pl. 3, Fig. 1; [Danian,Slovenia]

General remarks

Vaughan described the coral as Haimesiastraea, and it wasknown under this name until it was misspelled as Haime-sastraea in the Treatise (Wells 1956). Since then, the cor-rect genus name has only been used by Floris (1972). Werecommend using the original name of Vaughan (1900).A complete synonymy list including all citations in theliterature is provided by Baron-Szabo (in press).

The suprageneric classification of Haimesiastraea is con-troversial. No family assignment was provided by Vaughan(1900); Felix (1925) has assigned the genus to the Astro-coeniidae, Wells (1941) to the Haimesiastraeidae, Wells(1956) and Budd et al. (1992) to the Stylinidae and Frostand Langenheim (1974) to the Acroporidae. The most re-cent classification scheme grouped Haimesiastraea withthe Columastreidae (Baron-Szabo in press) based on thepresence of pali and columella.

Description (based on 11 thin sections from three corals)

One corallum domal, 30 cm in vertical and up to 25 cm inhorizontal dimension; the others irregular massive. Coral-lites plocoid to almost cerioid with subcircular calices, 1.3–3.1 mm in maximum diameter (mean = 1.86 mm, median= 1.8 mm, based on 42 measurements). Budding extraten-tacular. Corallites united by an open meshwork of costae,corresponding to all cycles of the septa, and linked by tab-ular exothecal dissepiments forming the coenosteum. Dis-tance between corallites (smallest distance between coral-lite walls) 0.45–0.7 mm.

Septa in three cycles, thin, thickening towards the wall.First two cycles of septa reaching into the centre of calices.Internal margins of these 12 septa fusing, to form a tra-becular to substyliform columella. Septal margins entire,sometimes with rudimentary lateral projections (Fig. 5H),inner ends somewhat thickened and bent (Fig. 5E). Paliformlobes present, indistinct. Third cycle of septa incompletein small corallites but complete in larger ones (>1.8 mmdiameter of calice). Microstructure not well preserved. Me-dian lines in septa distinct in cross-section (Fig. 5F), nocalcification centres visible. Endothecal dissepiments rare,tabular.

Comparison

The DM corals agree in nearly all details with the originaldescription of H. conferta of Vaughan (1900). The onlynotable difference is that endothecal dissepiments areusually rare in our material but were indicated as veryabundant by Vaughan (1900). In this respect and in thesubstyliform columella, our corals agree with the diagnosisof Peruviastrea Vaughan. However, because there areboth trabecular and substyliform types of columella inthe same colonies, we agree with Wells (1941) that thestyliform type is probably the result of diagenetic changes.Following the detailed discussion of Frost and Langenheim(1974) and the observations of Baron-Szabo (in press),we have consequently synonymized several species ofHaimesiastraea and Peruviastrea.

Acknowledgments Research on the KT boundary in Patagonia issupported by the Deutsche Forschungsgemeinschaft (DFG, Ki 806-1), the Antorchas Foundation (Republica Argentina) and the Euro-pean Community program “Improving Human Research Potentialand the Socio-Economic Knowledge Base”. We thank RosemarieBaron-Szabo for advice regarding the taxonomic status of H. con-ferta, and Lucas Ruiz and Sven Weidemeyer for assistance in the field.

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