Marin Ivanov

Paleoenvironment across the Cretaceous-Tertiary transition in eastern Bulgaria

The Cretaceous-Tertiary (K-T) transition in eastern Bulgaria (Bjala) was analyzed in terms of lithology, mineralogy, stable isotopes, trace elements, and planktic foraminifera. The sequence represents a boreal-Tethyan transitional setting, spans from the last 300 k.y. of the Maastrichtian (zone CF1) through the early Danian (zones P0-Plc), and contains several short hiatuses. It differs from low-latitude Tethyan sequences primarily by lower diversity assemblages, pre-K-T faunal changes, a reduced K-T dC shift, and the presence of two clay layers with platinum group element anomalies. The first clay layer marks the K-T boundary impact event, as indicated by an iridium anomaly (6.1 ppb), the mass extinction of tropical and subtropical planktic foraminifera, and cooling. The second clay layer is stratigraphically within the upper Parvularugoglobigerina eugubina (Pla) zone and contains a small Ir enrichment (0.22 ppb), a major Pd enrichment (1.34 ppb), and anomalies in Ru (0.30 ppb) and Rh (0.13 ppb) that suggest a volcanic source. Adatte, T., Keller, G., Burns, S., Stoykova, K.H., Ivanov, M.I., Vangelov, D., Kramar, U., and Stüben, D., 2002, Paleoenvironment across the Cretaceous-Tertiary transition in eastern Bulgaria, in Adatte, T., Koeberl, C., and MacLeod, K.G., eds., Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado, Geological Society of America Special Paper 356, p. 231–251. *E-mail: thierry.adatte@geo.unine *Present address: Department of Geosciences, 233 Morril Science Center, University of Massachusetts, Amherst, Ma 01003. INTRODUCTION Cretaceous-Tertiary (K-T) boundary studies have often concentrated on documenting the geochemical anomalies and the pattern of planktic foraminiferal species extinctions immediately below and above this boundary event in low latitudes (Fig. 1). Most of these studies reveal a major mass extinction of all tropical and subtropical species at or near the K-T boundary and iridium anomalies that have been variously attributed to the sole effects of an impact (e.g., Smit, 1990; D’Hondt et T. Adatte et al. 232 Figure 1. Paleolocations of Cretaceous-Tertiary (K-T) boundary sections that have good biostratigraphic control and relatively continuous sediment records. Note that current knowledge of K-T boundary event is primarily from sections in low-latitude northern Tethys, including Mexico, Spain, and Tunisia. Few K-T sections are currently known from middle and high latitudes. Bjala sections of Bulgaria provide critical information of this event in transitional environment between northern Tethys and boreal sea. Inset shows satellite photograph of Black Sea coast with Bjala locality, and simplified tectonic map of South Carpathian arc (modified from Preisinger et al., 1993a; Rögl et al., 1996). Ocean basins are white, continental platform is gray, continents are black (modified from MacLeod and Keller, 1991a). ODP is Ocean Drilling Program, DSDP is Deep Sea Drilling Project. al., 1996; Apellaniz et al., 1997; Olsson, 1997), or long-term environmental changes followed by an impact (e.g., Keller, 1988, 1996; Luciani, 1997; Abramovich et al., 1998). Few studies have attempted to evaluate some aspects of the K-T event on a regional or global scale, including studies of hiatus distributions (MacLeod and Keller, 1991a, 1991b), species survivorship, and records of pre-K-T extinctions (MacLeod and Keller, 1994; Abramovich et al., 1998; Pardo et al., 1999). The absence of more comprehensive integrated summary studies is largely because most K-T sections are separated by large distances (Fig. 1), and direct comparisons across latitudes are difficult due to little known regional effects, particularly in middle to high latitudes. The mass-extinction pattern of planktic foraminifera in high latitudes is quantitatively documented from a few localities in the southern ocean (e.g., Deep Sea Drilling Project [DSDP] Sites 690 and 738, Keller, 1993) and Northern Hemisphere (e.g., Denmark and Kazakhstan, Schmitz et al., 1992; Keller et al., 1993; Pardo et al., 1999; Fig. 1). These data suggest a diminished mass-extinction effect compared with low latitudes primarily because tropical and subtropical species are absent and assemblages are dominated by small species that tolerate environmental fluctuations, including Guembelitria cretacea, G. danica, G. trifolia, G. dammula, Heterohelix globulosa, H. navarroensis, H. planate, Hedbergella holmdelensis, H. monmouthensis, and Globigerinelloides aspera (MacLeod and Keller, 1994). Most of these species are also observed in Danian sediments of low latitudes, and between 4 and 12 species have been considered as survivors (e.g., Canudo, 1997; Keller, 1997; Masters, 1997; Olsson, 1997; Orue-etxebarria, 1997; Smit and Nederbragt, 1997; Luciani, 1997). Stable isotopes measured on some of these species in Danian sediments have been found to record Danian values, also suggesting that they are survivors (Barrera and Keller, 1994; Keller et al., 1993; MacLeod and Keller, 1994). Huber (1996) attributed the presence of these species in Danian sediments to reworking, citing relatively unPaleoenvironment across the Cretaceous-Tertiary transition in eastern Bulgaria 233 changed stable isotope values of Globigerinelloides multispinus across the K-T boundary at Site 738 as evidence (see also Huber et al., 1994; Keller and MacLeod, 1994). We do not argue that Danian sediments may contain reworked Maastrichtian species, as indeed any sedimentary interval may, but we disagree that the consistent presence of these small species in sections across latitudes can be attributed to reworking, and that the Danian isotopic signal of species can be explained as artifact of reworking. We suggest that these species are K-T survivors for two major reasons. (1) They are ecological generalists able to survive the K-T environmental changes, whereas the larger complex tropical and subtropical species are not. (2) Environmental effects of the K-T impact diminished into higher latitudes, as suggested by dC values that indicate a relatively minor decrease in primary productivity in high latitudes as compared with low latitudes (e.g., Keller and Lindinger, 1989; Zachos et al., 1989; Keller et al., 1993; Barrera and Keller, 1994). Environmental changes and the nature of the mass extinction between the extremes of the northern boreal sea (Denmark and Kazakhstan) and the low-latitude Tethys are still relatively unknown. This shortcoming is because K-T sequences with nearly continuous sedimentation and good microfossil preservation are very rare and currently only reported from Bjala in eastern Bulgaria (Preisinger et al., 1993a, 1993b; Rögl et al., 1996). We chose to study the Bjala sections in order to obtain a quantitative record that would allow evaluation of the mass extinction and environmental changes in this transitional environment and permit comparison with both lowand highlatitude records. To this end we analyzed the biostratigraphy, stable isotopes, bulk rock compositions, clay minerals, trace element abundances, and quantitative changes among planktic foraminiferal assemblages. PREVIOUS STUDIES IN BULGARIA The K-T boundary in eastern Bulgaria was first recognized on the basis of planktic foraminifera from boreholes (Juranov and Dzhuranov, 1983), and a subsequent search for outcrops in the vicinity of Bjala revealed a relatively complete K-T transition based on calcareous nannoplankton (Stoykova and Ivanov, 1992; Ivanov and Stoykova, 1994; Sinnyovsky and Stoykova, 1995). Geochemical and planktic foraminiferal data were given in Preisinger et al. (1993a, 1993b) and Rögl et al. (1996). In those publications the K-T biostratigraphy is based primarily on calcareous nannoplankton, the most complete sequences containing the Micula prinsii zone in the topmost 14– 17 m of the Maastrichtian, and zone NP1, spanning the basal 4 m of the Danian. The K-T boundary was recognized on the basis of a 2–3-cm-thick dark clay layer containing an Ir anomaly of 6.1 ppb (Preisinger et al., 1993a). A second, smaller Ir and Co enrichment was recognized 7–8 cm above this interval in a marly limestone layer, and was considered reworked. The first Danian nannofossil species Biantholithus sparsus and Cyclagellosphaera alta are reported from this marly limestone layer that also contains blooms of Thoracosphaera operculata and Braarudosphaera bigelowii (Preisinger et al., 1993a, 1993b; Ivanov and Stoykova, 1994). Rögl et al. (1996) reported the range of four Maastrichtian planktic foraminifer species (Hedbergella monmouthensis, Guembelitria cretacea, Racemiguembelina intermedia, Abathomphalus mayaroensis) and six undifferentiated genera in the 90 cm below the K-T boundary. They observed the first Danian species (Woodringina hornerstownensis, W. claytonensis, Globoconusa predaubjergensis) 2 cm above the base of the K-T clay layer. GEOLOGICAL SETTING AND LOCATION The studied outcrops are exposed along the Black Sea coast, close to the town of Bjala (Fig. 1). Tectonically, this area belongs to the Luda Kamchia unit of the Stara Planica zone, which is part of the High Balkan mountain range (Ivanov, 1983, 1988). The Bjala area was a well-differentiated basin characterized by rhythmic sedimentation of hemipelagic marls and marly limestones during the Late Cretaceous. Deposition of more detrital and turbiditic sediment began in the early Paleocene and appears to reflect the first pulse of alpine tectonic activity. Subsequent tectonic activity resulted in the numerous nappes, thrust folds, and faults that can now be observed in the area (Ivanov, 1988). Bjala-1 is located 800 m north of a trench leading down from the town of Bjala to the beach (Figs. 1 and 2). This section corresponds to the Bjala 2b section of Ivanov and Stoykova (1994) and Preisinger (1994), and can be observed laterally over 15–20 m. This locality represents the best exposure and structurally least disturbed outcrop of the K-T tr

Séquences de dépôt à l'articulation plate-forme urgonienne–bassin (intervalle Barrémien–Albien) dans le Prébalkan occidental (Bulgarie du Nord-Ouest)

Abstract In the western Fore-Balkan (northwest Bulgaria), the characterization of numerous depositional sequences within the Barremian–Albian interval allows us to reconstruct from southeast to northwest the successive palaeogeographies of this part of the north Tethyan margin: two carbonate (Urgonian) platforms flanking a central terrigenous basin during the Barremian; a single centrifugal terrigenous basin (Aptian) marked, along its axis, by an olistostrome and siliciclastic turbidites; a single Albian basin characterized by the stacking of glauconite-rich condensation sections and anoxic black marls.

The Sedimentary Sequences of Hurd Peninsula, Livingston Island, South Shetland Islands: Part of the Late Jurassic — Cretaceous Depositional History of the Antarctic Peninsula

The age of the sedimentary sequences of Hurd Peninsula (here referred to the Miers Bluff Formation (MBF), has been considered so far as Triassic, coeval of the Trinity Group. Recently, a Tithonian ammonite species was found in a non-in situ block, coming from the lowermost unexposed part of the Formation. Our micropal-eontological study reveals the occurrence of calcareous nannofossils in six sections. The recorded nannofossil association comprises the following species: Micula decussata, Calculites obscurus, Arkhangelskiella cymbiformis, Prediscosphaera cretacea, Lucianorhabdus cayeuxii, Cyclagelosphaera reinhardtii, Braarudosphaera bigelowii, Ceratolithoides aculeus, Broinsonia cf. parca, Thoracosphaera sp. indet., Nephrolithus sp. indet., Cretarhabdus sp. indet., Watznaueria sp. indet. It determines a Campanian-Maastrichtian age for the middle and upper part of MBF. Two calcareous nanofossil species, Prediscosphaera cretacea and ?Fasciculithus sp. indet., found in the Burdick Peak section suggest a Late Maastrichtian to (?) Paleocene age of the uppermost part of the MBF. The sediments of the MBF are possibly coeval of a part of Marambio Group (James Ross Island and Seymour Island) and Williams Point beds (Livingston Island).

Enregistrement sédimentaire de la tectonique extensive et de l'eustatisme dans le Jurassique terminal et le Crétacé basal du Prébalkan central et oriental (Bulgarie)

Abstract The thick (2 000 m) siliciclastic-dominated synrifi series, which fills up most of the internal troughs of the Central Fore Balkan from Uppermost Tithonian to Valanginian, is subdivided into ten tectono- eustatic depositional sequences. The sequences consist of a coarse and voluminous low stand wedge (block complex, canyon-cone conglomerates, megaslumps, calcareous breccias, etc.) induced by extensional tectonics; and above, a pelite-dominated high stand wedge, of eustatic origin, which contains most of the zonal and subzonal Ammonites allowing datations and correlations. To the NE, towards the Moesian Platform, only the high stand wedges (with or without the transgressive system tracts) of the successive sequences overflow the troughs and become richer in carbonates to the top of the parasequences.

Calcareous nannofossil and ammonite integrated biostratigraphy across the Jurassic – Cretaceous boundary strata of the Kopanitsa composite section (West Srednogorie Unit, southwest Bulgaria)

Abstract Calcareous nannofossil, calpionellid and ammonite occurrences have been directly constrained across the Jurassic–Cretaceous boundary interval in the section of Kopanitsa, SW Bulgaria. This section reveals a continuous and expanded sedimentary record through the Upper Tithonian and Lower Berriasian, besides an excellent calcareous nannofossil and ammonite record. The topmost part of the NJT 16b and the base of NJT 17a nannofossil Subzones correspond to the ammonite Microcanthum / Transitorius Subzone. The major part of the NJT 17a Subzone equates to the Durangites spp. ammonite Zone, whereas the NJT 17b Subzone correlates to the lower part of the B. jacobi ammonite Zone. The NKT nannofossil Zone approximately corresponds to the upper part of the B. jacobi Zone and the NK-1 nannofossil Zone correlates at least to the lowest part of the T. occitanica Zone. The FOs of Nannoconus globulus minor, N. wintereri, N. kamptneri minor, N. steinmannii minor, N. kamptneri kamptneri and N. steinmannii steinmannii are confirmed as reliable bio-horizons for correlations in the Mediterranean Tethys area. The first occurrence of Nannoconus wintereri is regarded as an almost concomitant event with the first occurrence of Berriasella jacobi. We suggest it could be the most useful nannofossil proxy for approximating the base of the B. jacobi Zone. Rare, but relatively well preserved calpionellids and calcareous dinoflagellates together with microfacies analysis were used additionally for stratigraphical and palaeoenvironmental interpretations. The investigated sediments are typical for the steep slope of a steepened ramp, with accumulation of hemipelagic and gravitational deposits.

New record of endolithic algae syn-vivo associated with an Early Cretaceous coral

Euendolithic microorganisms (boring endoliths) syn-vivo associated with modern corals are commonly reported, but their fossil record is extremely rare. This paper reports the new finding recognized in the colonial scleractinian coral Clausastrea saltensis from the Upper Barremian of Bulgaria. Large microborings (up to 50 µm, most ca. 15-25 µm in diameter) filled with calcite cement are distributed medially along coral septa of some corallites. Borings were produced by microeuendoliths growing from the skeleton interior outward during the life of the coral host. They are compared to traces produced by the recent oligophotic filamentous chlorophyte Ostreobium, which is known to be the most common skeleton-dwelling alga in modern living corals and regarded as neutral or beneficial to the coral. In terms of general morphology, diameter and distribution pattern, the borings are similar to those recently recognized in the Early Cretaceous microsolenid coral.