The Capo di Fiume site is located at the north-eastern margin of the Monte Porrara. The fossiliferous section outcrops with a reduced lateral extension along the state road n° 84 “Frentana” a few kilometers south of the town of Palena, in the Chieti province, Abruzzo, Italy. This site is part of the Porrara tectonic unit (Patacca et al. 1992), which consists of a thick lithostratigraphic succession of Jurassic-Cretaceous shelf carbonates overlain by upper Cretaceous to Eocene distal ramp deposits. The Cretaceous-Paleogene distal ramp deposits are usually unconformably overlained by Miocene (Langhian – Tortonian) heterozoan limestone (Bryozoan – Lithothamnium Limestone), comparable to that of the Bolognano Formation (see Di Napoli Alliata, 1964; Crescenti et al., 1969). In the north-eastern margin of the Monte Porrara, however, the Cretaceous distal ramp carbonates (Saccharoidal Limestone) are overlained by terra rossa soils, covered by marls and clayey marls, followed by a rhythmic succession of diatomitic marls and calcareous marls and, successively, by hemipelagic argillites and turbidites. The succession outcropping at Capo di Fiume has been discussed by many authors (e.g., Bellatalla et al., 1992; Carboni et al., 1992; Patacca et al., 1992; Mazza et al., 1995; Miccadei & Parotto, 1998; Carnevale, 2003), who described its lithological and paleontological features with different degrees of detail. Carboni et al. (1992) presented a description of the lower part of the succession, evidencing the progressive transition from continental to fully marine facies. As reported above, the succession overlies on Upper Cretaceous carbonates, represented therein by light-brown calcilutites. The base of the succession consists of terra rossa soils with interspersed nodular calcarrous and ferrouginous pisolitic concretions. Fissile marls and laminated argillites (Lithothamnium Limestone equivalent) lie upon the terra rossa soils. These deposits contain abundant mollusk remains and record the passage from palustrine to brackish (freshwater marshes, tidal creeks, swamp, estuarine bay) paleobiotopes. Marine deposits (Tripoli Formation equivalent) lie upon the freshwater to brackish marls; these deposits consist of not less than six cycles of alternated dark grey calcareous marls and finely laminated ichthyolitiferous diatomitic marls. The first marine cycle exhibits a relatively complex architecture, whereas the succeeding cycles primarily consists of a sharp alternation of calcareous marls and diatomitic marls. In general, the sequence is characterized by a progressive decrease of the thickness of the diatomitic marl intervals, which ranges from about 180 cm in the first cycle to 50 cm in the sixth one. The age of the continental to paralic portion of the succession is unclear. According to Mazza & Rustioni (1996), the terra rossa soils may be correlated to the vertebrate-bearing deposits of Scontrone, which date back to the Tortonian, approximately 10 Ma (see Patacca et al., 2008a). More generally, the bauxites may be correlated to the Oligo-Miocene terra rossa soils that are widespread in the central Adriatic area (Patacca et al., 2008b). On the other hand, the marine portion of the succession is well constrained from a biostratigraphic point of view. The presence of the benthic foraminiferan Bulimina echinata in the dark grey marls underlying the first diatomitic marl interval is clearly indicative of a Messinian age (see Colalongo et al., 1979); the appearance of Bulimina echinata in the Mediterranean is estimated to have occurred at about 6.8 Ma. Moreover, a Messinian age of the upper portion of the succession is also supported by the occurrence of Turborotalita multiloba in the calcareous dark grey marls of the sixth cycle; the first common occurrence of this planktonic foraminiferan dates back to 6.4 Ma (Sprovieri et al., 1996; Krijgsman et al., 1999). Therefore, the marine sediments of the Capo di Fiume section were deposited mainly in the lower portion of the Messinian stage between about 6.8 and 6.4 million years ago. Overall, the diatomitic marls outcropping at Capo di Fiume consist of a dense series of clastic-biogenic (diatomitic) couplets. Several types of laminae have been identified based on chromatic characters, thickness, lateral extension and other morphological features. These were analyzed at the nannoscale in order to define their paleoenvironmental significance. Based on a slightly modified version of the classification proposed by Chang et al. (1998), at least four types of laminae have been recognized, including: detrital (clastic) laminae; thin biosiliceous laminae; thick and continuous diatomaceous laminae containing monospecific or oligospecific assemblages of Coscinodiscus spp. and/or Thalassionema nitzschioides; and thick and discontinuous diatomaceous laminae, which consists of compact and strongly amalgamated diatom flocs containing oligospecific assemblages of Thalassionema nitzschioides and/or Coscinodiscus sp. and representing the sedimentary product of aggregated diatom mats characterized by densely interlocked frustules. The macrofossil content of the diatomitic marls is relatively rich and includes well-preserved articulated skeletal remains of teleost fishes primarily represented by the clupeid Spratelloides gracilis, a single nearly complete articulated skeleton assigned to the ochotonid species Prolagus cf. apricenicus (see Mazza et al., 1995), bird feathers, rare decapods crustaceans, insects, and bivalves apparently in life position and plant remains (leaves, seeds, pine cones, fruits). Foraminiferans are rather scarce in the laminated diatomitic marls exclusively represented by ammoniids, bolivinids and rare dwarfed globigerinids (Carboni et al., 1992; Patacca et al., 1992). Articulated skeletal remains of teleost fishes are relatively abundant in the diatomitic marls of the first two cycles, which also include very rare mass mortality layers. Fish remains are less common in diatomitic marls of the upper four cycles. Fish skeletons are mainly associated with thick continuous laminae of Thalassionema nitzschioides and/or Coscinodiscus sp. The origin of the thick continuous laminae of Coscinodiscus spp. appears to be related to the so-called “Fall dump”, a massive sedimentation of diatoms that have grown episodically in the Deep Chlorophyll Maximum during periods of water stratification (Kemp et al., 2000); the origin of thick continuous laminae of Thalassionema nitzschioides are associated to high productivity and nutrient abundance (Schuette and Schrader, 1981; Sancetta, 1982; Abrantes, 1988) and possibly represent the sedimentary evidence of bloom events. The preservation of fish skeletal remains is primarily due to the action of the bacterial and fungal film that proliferated on the mucilage of the diatom flocs, promoting the rapid mineralization of the bones; the sedimentary action of microbial/fungal film appears to be manifold since it protected the sediment from erosion sustaining the formation of laminated deposits, inhibited the decomposition of carcasses, scavenging and endofaunal settling and, promoted the rapid phosphatization of the bones and the mineralization of organic components. The large part of the fossil fishes are very well preserved and nearly complete. Some specimens are incomplete, showing evidence of scavenging activity and/or weak hydrodynamic transport. The single largely incomplete specimen of the Nile perch, Lates cf. niloticus, exhibits the anatomical and biostratinomical characters of a prolonged post-mortem floating. Evidence of predatory activity and biological packaging primarily involving the planktivore round herring Spratelloides gracilis are relatively common. Several hundreds of specimens have been analyzed, among which not less than 22 taxa belonging to 14 families have been identified (see e.g., Carnevale & Landini, 2000; 2001; Carnevale, 2002; 2003). The dussumierine clupeid Spratelloides gracilis sharply dominates the assemblage, represented by more than 75% of the recognized specimens. This planktivore species is represented by both adult and juvenile individuals and certainly constituted the trophic nucleus of the fish assemblages. The comparative analysis of the ecological categories indicates that the assemblage primarily consists of demersal neritic (Boops roulei, Callionymus sp., Capros sp., Diplodus cf. oranensis, Diplodus sp., Epinephelus sp., Halobatrachus cf. didactylus, Pagrus sp., Pomacentridae indet., Syngnathus sp.) and coastal epipelagic taxa (Alosa elongata, Etrumeus teres, Sardina pilchardus, Spratelloides gracilis, Trachurus sp.), with a diverse contingent of migratory pelagic and oceanic species (Diaphus edwardsi, Lestidiops sphekodes, Maurolicus cf. muelleri, Merluccius sp., Myctophum columnae, Paralepis albyi). The Nile perch is the only freshwater/marginally paralic taxon recognized in the assemblage. The comprehensive paleoecological analysis of the fish assemblage suggests that the deposition of the diatomitic marls occurred not far from the coastline in a moderately shallow basin surrounded by rocky or coral reefs and seagrass beds and influenced by the open sea. The presence of the Nile perch unequivocally indicates that a river system also contributed to the physiography of the basin. The heterogeneous composition of the assemblage, which is characterized by the co-occurrence of coastal and opportunistic pelagic taxa, is consistent with the unstable eutrophic conditions indicated by the monospecific or oligospecific accumulations of Coscinodiscus spp. and/or Thalassionema nitzschioides that formed the biogenic substrate of the fish bearing diatomitic laminae.
The Messinian fish fauna of Capo di Fiume, Abruzzo, Central Italy: Taphonomy and paleoecology
CARNEVALE, Giorgio
2011-01-01
Abstract
The Capo di Fiume site is located at the north-eastern margin of the Monte Porrara. The fossiliferous section outcrops with a reduced lateral extension along the state road n° 84 “Frentana” a few kilometers south of the town of Palena, in the Chieti province, Abruzzo, Italy. This site is part of the Porrara tectonic unit (Patacca et al. 1992), which consists of a thick lithostratigraphic succession of Jurassic-Cretaceous shelf carbonates overlain by upper Cretaceous to Eocene distal ramp deposits. The Cretaceous-Paleogene distal ramp deposits are usually unconformably overlained by Miocene (Langhian – Tortonian) heterozoan limestone (Bryozoan – Lithothamnium Limestone), comparable to that of the Bolognano Formation (see Di Napoli Alliata, 1964; Crescenti et al., 1969). In the north-eastern margin of the Monte Porrara, however, the Cretaceous distal ramp carbonates (Saccharoidal Limestone) are overlained by terra rossa soils, covered by marls and clayey marls, followed by a rhythmic succession of diatomitic marls and calcareous marls and, successively, by hemipelagic argillites and turbidites. The succession outcropping at Capo di Fiume has been discussed by many authors (e.g., Bellatalla et al., 1992; Carboni et al., 1992; Patacca et al., 1992; Mazza et al., 1995; Miccadei & Parotto, 1998; Carnevale, 2003), who described its lithological and paleontological features with different degrees of detail. Carboni et al. (1992) presented a description of the lower part of the succession, evidencing the progressive transition from continental to fully marine facies. As reported above, the succession overlies on Upper Cretaceous carbonates, represented therein by light-brown calcilutites. The base of the succession consists of terra rossa soils with interspersed nodular calcarrous and ferrouginous pisolitic concretions. Fissile marls and laminated argillites (Lithothamnium Limestone equivalent) lie upon the terra rossa soils. These deposits contain abundant mollusk remains and record the passage from palustrine to brackish (freshwater marshes, tidal creeks, swamp, estuarine bay) paleobiotopes. Marine deposits (Tripoli Formation equivalent) lie upon the freshwater to brackish marls; these deposits consist of not less than six cycles of alternated dark grey calcareous marls and finely laminated ichthyolitiferous diatomitic marls. The first marine cycle exhibits a relatively complex architecture, whereas the succeeding cycles primarily consists of a sharp alternation of calcareous marls and diatomitic marls. In general, the sequence is characterized by a progressive decrease of the thickness of the diatomitic marl intervals, which ranges from about 180 cm in the first cycle to 50 cm in the sixth one. The age of the continental to paralic portion of the succession is unclear. According to Mazza & Rustioni (1996), the terra rossa soils may be correlated to the vertebrate-bearing deposits of Scontrone, which date back to the Tortonian, approximately 10 Ma (see Patacca et al., 2008a). More generally, the bauxites may be correlated to the Oligo-Miocene terra rossa soils that are widespread in the central Adriatic area (Patacca et al., 2008b). On the other hand, the marine portion of the succession is well constrained from a biostratigraphic point of view. The presence of the benthic foraminiferan Bulimina echinata in the dark grey marls underlying the first diatomitic marl interval is clearly indicative of a Messinian age (see Colalongo et al., 1979); the appearance of Bulimina echinata in the Mediterranean is estimated to have occurred at about 6.8 Ma. Moreover, a Messinian age of the upper portion of the succession is also supported by the occurrence of Turborotalita multiloba in the calcareous dark grey marls of the sixth cycle; the first common occurrence of this planktonic foraminiferan dates back to 6.4 Ma (Sprovieri et al., 1996; Krijgsman et al., 1999). Therefore, the marine sediments of the Capo di Fiume section were deposited mainly in the lower portion of the Messinian stage between about 6.8 and 6.4 million years ago. Overall, the diatomitic marls outcropping at Capo di Fiume consist of a dense series of clastic-biogenic (diatomitic) couplets. Several types of laminae have been identified based on chromatic characters, thickness, lateral extension and other morphological features. These were analyzed at the nannoscale in order to define their paleoenvironmental significance. Based on a slightly modified version of the classification proposed by Chang et al. (1998), at least four types of laminae have been recognized, including: detrital (clastic) laminae; thin biosiliceous laminae; thick and continuous diatomaceous laminae containing monospecific or oligospecific assemblages of Coscinodiscus spp. and/or Thalassionema nitzschioides; and thick and discontinuous diatomaceous laminae, which consists of compact and strongly amalgamated diatom flocs containing oligospecific assemblages of Thalassionema nitzschioides and/or Coscinodiscus sp. and representing the sedimentary product of aggregated diatom mats characterized by densely interlocked frustules. The macrofossil content of the diatomitic marls is relatively rich and includes well-preserved articulated skeletal remains of teleost fishes primarily represented by the clupeid Spratelloides gracilis, a single nearly complete articulated skeleton assigned to the ochotonid species Prolagus cf. apricenicus (see Mazza et al., 1995), bird feathers, rare decapods crustaceans, insects, and bivalves apparently in life position and plant remains (leaves, seeds, pine cones, fruits). Foraminiferans are rather scarce in the laminated diatomitic marls exclusively represented by ammoniids, bolivinids and rare dwarfed globigerinids (Carboni et al., 1992; Patacca et al., 1992). Articulated skeletal remains of teleost fishes are relatively abundant in the diatomitic marls of the first two cycles, which also include very rare mass mortality layers. Fish remains are less common in diatomitic marls of the upper four cycles. Fish skeletons are mainly associated with thick continuous laminae of Thalassionema nitzschioides and/or Coscinodiscus sp. The origin of the thick continuous laminae of Coscinodiscus spp. appears to be related to the so-called “Fall dump”, a massive sedimentation of diatoms that have grown episodically in the Deep Chlorophyll Maximum during periods of water stratification (Kemp et al., 2000); the origin of thick continuous laminae of Thalassionema nitzschioides are associated to high productivity and nutrient abundance (Schuette and Schrader, 1981; Sancetta, 1982; Abrantes, 1988) and possibly represent the sedimentary evidence of bloom events. The preservation of fish skeletal remains is primarily due to the action of the bacterial and fungal film that proliferated on the mucilage of the diatom flocs, promoting the rapid mineralization of the bones; the sedimentary action of microbial/fungal film appears to be manifold since it protected the sediment from erosion sustaining the formation of laminated deposits, inhibited the decomposition of carcasses, scavenging and endofaunal settling and, promoted the rapid phosphatization of the bones and the mineralization of organic components. The large part of the fossil fishes are very well preserved and nearly complete. Some specimens are incomplete, showing evidence of scavenging activity and/or weak hydrodynamic transport. The single largely incomplete specimen of the Nile perch, Lates cf. niloticus, exhibits the anatomical and biostratinomical characters of a prolonged post-mortem floating. Evidence of predatory activity and biological packaging primarily involving the planktivore round herring Spratelloides gracilis are relatively common. Several hundreds of specimens have been analyzed, among which not less than 22 taxa belonging to 14 families have been identified (see e.g., Carnevale & Landini, 2000; 2001; Carnevale, 2002; 2003). The dussumierine clupeid Spratelloides gracilis sharply dominates the assemblage, represented by more than 75% of the recognized specimens. This planktivore species is represented by both adult and juvenile individuals and certainly constituted the trophic nucleus of the fish assemblages. The comparative analysis of the ecological categories indicates that the assemblage primarily consists of demersal neritic (Boops roulei, Callionymus sp., Capros sp., Diplodus cf. oranensis, Diplodus sp., Epinephelus sp., Halobatrachus cf. didactylus, Pagrus sp., Pomacentridae indet., Syngnathus sp.) and coastal epipelagic taxa (Alosa elongata, Etrumeus teres, Sardina pilchardus, Spratelloides gracilis, Trachurus sp.), with a diverse contingent of migratory pelagic and oceanic species (Diaphus edwardsi, Lestidiops sphekodes, Maurolicus cf. muelleri, Merluccius sp., Myctophum columnae, Paralepis albyi). The Nile perch is the only freshwater/marginally paralic taxon recognized in the assemblage. The comprehensive paleoecological analysis of the fish assemblage suggests that the deposition of the diatomitic marls occurred not far from the coastline in a moderately shallow basin surrounded by rocky or coral reefs and seagrass beds and influenced by the open sea. The presence of the Nile perch unequivocally indicates that a river system also contributed to the physiography of the basin. The heterogeneous composition of the assemblage, which is characterized by the co-occurrence of coastal and opportunistic pelagic taxa, is consistent with the unstable eutrophic conditions indicated by the monospecific or oligospecific accumulations of Coscinodiscus spp. and/or Thalassionema nitzschioides that formed the biogenic substrate of the fish bearing diatomitic laminae.
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