Gino Cantalamessa

Distribution of fossil marine vertebrates in Cerro Colorado, the type locality of the giant raptorial sperm whale Livyatan melvillei (Miocene, Pisco Formation, Peru)

Hundreds of fossil marine vertebrates cropping out at Cerro Colorado (Pisco Basin, Peru) are identified and reported on a 1:6500 scale geological map and in a joined stratigraphic section. All the fossils are from the lower strata of the Pisco Formation, dated in this area to the late middle or early late Miocene. They are particularly concentrated (88%) in the stratigraphic interval from 40 to 75 m above the unconformity with the underlying Chilcatay Formation. The impressive fossil assemblage includes more than 300 specimens preserved as bone elements belonging mostly to cetaceans (81%), represented by mysticetes (cetotheriids and balaenopteroids) and odontocetes (kentriodontid-like delphinidans, pontoporiids, ziphiids, and physeteroids, including the giant raptorial sperm whale Livyatan melvillei). Seals, crocodiles, sea turtles, seabirds, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common throughout the investigated stratigraphical interval, whereas other shark teeth, mostly of carcharinids, are concentrated in one sandy interval. This work represents a first detailed census of the extraordinary paleontological heritage of the Pisco Basin and the basis for future taphonomic, paleoecological, and systematic studies, as well as a much needed conservation effort for this extremely rich paleontological site.

Basin physiography and tectonic influence on sequence architecture and stacking pattern: Pleistocene succession of the Canoa Basin (central Ecuador)

Facies, shell bed features, and sequence stratigraphic framework for the shallow-marine Pleistocene upper Canoa and Tablazo Formations are presented, based on outcrop data from the southern coast of Cabo San Lorenzo, Ecuador. Sediments of this succession exhibit a distinct cyclic pattern, consisting of a stack of eight depositional sequences (cyclothems) likely developed under the main control of orbitally induced sea-level changes. As a rule, within the studied interval an idealized cyclothem is composed of a transgressive systems tract (TST) and a highstand systems tract (HST), whereas deposits attributable to the lowstand and falling-stage systems tracts are not present. Transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface (back-barrier wedge) and by upward fining shoreface to inner-shelf facies successions above the ravinement (backstepping shelf wedge). Separated by an expanded siliciclastic core, hiatal shell concentrations occur at the base (onlap shell beds) and the top (backlap shell beds) of the transgressive shelf wedges, and some occur at the base of highstand systems tracts (downlap shell beds). On the basis of sedimentary facies, geometry, taphonomy, and paleoecology of shell beds, and the nature of the transition between siliciclastic and mollusk-bearing sediments, cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration: sheltered (in the upper Canoa Formation) and exposed (in the Tablazo Formation). Notwithstanding the different synsedimentary tectonic and climatic regimes, the Ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world. This suggests that (1) hiatal shell bed development is not just a temperate-latitude phenomenon; (2) a global process, such as glacio-eustatic sea-level change, is the primary mechanism of control for the general architecture of sequences; and (3) specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds, the nature of their contacts with the encasing sediments, and the type of the component set of facies. At a multicycle time scale, tectonics influenced the long-term trend of the relative sea-level changes and consequently the large-scale stratigraphic organization. Owing to the continued tectonic uplift of the area, successive high-frequency depositional sequences are nested to form a longer-order falling-stage sequence set.

Shell concentrations as tools in characterizing sedimentary dynamics at sequence-bounding unconformities: examples from the lower unit of the Canoa Formation (Late Pliocene, Ecuador)

Abstract The Canoa Basin in Manabi, Ecuador, contains a mainly marine, clastic sedimentary succession of Late Pliocene and Pleistocene Age (Canoa Formation and Tablazo Formation). A stratigraphic and sedimentologic study of the entire sedimentary succession indicated that sedimentary facies recur in consistent deepening–shallowing transgressive–regressive patterns and that on this basis it can be divided into three different informal units (Clow, Cupp, Tb). The lowest of these units (Clow) is composed of at least four depositional sequences, each bounded by a ravinement surface and containing a basal environmentally time-averaged shell bed accumulated during rapid sea-level rise under conditions of reduced terrigenous sediment supply (transgressive systems tract). Owing to intense heavy bioturbation, the internal architecture of these shell beds is not recognizable. Each of these shell beds is mantled by poorly fossiliferous sandy and silty shales accumulated during subsequent progradation (highstand and regressive systems tract). Fossil assemblages, accounting for inner/middle shelf settings, are dominated by infaunal suspension-feeding bivalves (Linga cancellaris, Chione mariae, etc.), most of which require sandy substrate or are ubiquitous. In terms of trophic/life-habit groups, the total succession shows an increase of infaunal suspension-feeder species’ richness from the lowest (C1) to the upper (C4) shell bed, whereas epifaunal taxa decrease in richness. Shell packing density also decreases from C1 to C4. The reconstruction of the short-term sedimentary dynamics based on taphonomic and paleoecologic observations indicates a slightly progradational staking pattern of depositional sequences, representing high-frequency sixth-order eustatic sea-level fluctuations within a third-order tectonically induced cycle.

Fossil marine vertebrates of Cerro Los Quesos: Distribution of cetaceans, seals, crocodiles, seabirds, sharks, and bony fish in a late Miocene locality of the Pisco Basin, Peru

ABSTRACT One-hundred and ninety-two fossil marine vertebrate specimens, preserved as bone elements cropping out at Cerro Los Quesos (Pisco Basin, Peru), are identified and reported on a 1:4,000 scale geological map and in the corresponding stratigraphic section. All the fossils originate from the Pisco Formation, which is dated in this area to the late Miocene (from 7.55 Ma to ≥6.71 Ma, based on 40Ar/39Ar analyses of three volcanic ash layers along the section). Specimens are particularly concentrated near the top of the two main hills, where the geologically youngest portion of the examined section crops out. The impressive fossil assemblage includes cetaceans (91.6%), represented by mysticetes (balaenopteroids and cetotheriids) and odontocetes (phocoenids, physeteroids, and ziphiids, including the holotype of Nazcacetus urbinai). Seals, a crocodile, a seabird, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common and, in several instances, associated to mysticete skeletons. Together with a similar work recently published for the other late Miocene locality of Cerro Colorado, this work represents a case study for the detailed inventory of the extraordinary paleontological heritage of the Pisco Basin. As such, it constitutes the basis for future taphonomic, paleoecological, and systematic studies, as well as for a much-needed conservation effort.

Stratigraphic framework of the late Miocene Pisco Formation at Cerro Los Quesos (Ica Desert, Peru)

The enormous concentration of marine vertebrates documented within the Pisco Formation is unique for Peru and South America and places this unit among the prime fossil Lagerstätten for Miocene to Pliocene marine mammals worldwide. In order to provide a robust stratigraphic framework for the fossil-bearing locality of Cerro Los Quesos, this study presents a 1:10,000 scale geological map covering an area of about 21 km2, a detailed measured section spanning 290 m of strata, and a refined chronostratigraphy for the studied succession well constrained by diatom biostratigraphy and high-resolution 40Ar/39Ar isotopic dating of three interbedded ash layers. Within the apparently monotonous, diatomite-dominated sedimentary section, the Pisco Formation has been subdivided into six local members, with stratigraphic control over the different outcrops facilitated by the establishment of a detailed marker bed stratigraphy based on 15 readily distinguishable sediment layers of different nature.

Sedimentology and high-resolution sequence stratigraphy of the late middle to late Miocene Angostura Formation (western Borbón Basin, northwestern Ecuador)

An integrated analysis of facies and palaeontological content of the middle to late Miocene (c. 12.4–9.1 Ma) Angostura Formation led to the identification of facies associations indicative of shoreface and inner-shelf settings. The Angostura Formation comprises eight high-frequency sequences that are stacked to form a tectonically driven lowstand sequence set. The most complete examples of sequences are bounded by transgressively modified unconformities and exhibit a threefold subdivision: (1) a basal suite of deepening-upward shoreface sediments (transgressive systems tract), including a base-of-cycle shell concentration; (2) a mid-cycle shell bed, consisting of molluscan shells dispersed in a matrix of inner-shelf muddy fine-grained sandstones; (3) a shallowing-upward unit of inner-shelf to lower shoreface sediments almost barren of mollusc fossils (highstand systems tract). Biostratigraphic constraints allowed a reasonable correlation between sequence bounding unconformities and the late middle to late Miocene high-frequency glacio-eustatic changes derived from recent δ18O studies. This correlation has far-reaching implications and leads to the following conclusions: (1) glacio-eustasy in tune with oxygen isotope changes at fourth-order frequency (200 ka–1 Ma duration) may have been the principal factor regulating stratigraphic packaging in the Angostura Formation; (2) these sequences provide an excellent shallow-marine outcrop record of late middle to late Miocene Antarctic glaciations.

TAPHONOMIC AND PALEOECOLOGICAL ANALYSES (MOLLUSKS AND FISHES) OF THE SÚA MEMBER CONDENSED SHELLBED, UPPER ONZOLE FORMATION (EARLY PLIOCENE, ECUADOR)

Abstract The early Pliocene sediments of the Súa Member (Onzole Formation) are spectacularly exposed along coastal cliffs in the surroundings of Súa (northwestern Ecuador). The shellbed at the base of these strata contains rich mollusk and fish assemblages and provides a rare opportunity to document the virtually unknown Pliocene shallow-water faunas of Ecuador. Stratigraphic context, faunal composition (both mollusks and fishes), biofabric trend, ichnological signatures, and taphonomic features presented here, all indicate that the shellbed is a stratigraphically condensed (hiatal) skeletal concentration generated primarily by low rates of net background sedimentation. Shellbeds of this type, immediately overlying a Glossifungites-demarcated ravinement surface, are regarded as onlap shellbeds and record landward stratal convergence and attenuation during the earliest phases of marine transgression. Although composed of largely autochthonous-parautochthonous specimens, the fossil assemblage contains mollusk species from a range of water depths and both soft- and hard-bottom habitats, implying in situ time averaging and admixture of different assemblages as transgression proceeded on a sediment-starved shoreline. The mollusk assemblage is composed of 54 taxa (26 bivalves, 26 gastropods, 2 scaphopods), and the fish assemblage of 31 taxa belonging to 16 families. Both are indicative of a well-oxygenated marine biotope swept by currents and waves, and devoid of a benthic macrophyte cover. With the exception of a few fish species and a single gastropod, the largest number of the mollusk and fish taxa are presently distributed throughout the Tropical Eastern Pacific Biogeographic Region.

SEQUENCE STRATIGRAPHY AND PALEONTOLOGY OF THE UPPER MIOCENE PISCO FORMATION ALONG THE WESTERN SIDE OF THE LOWER ICA VALLEY (ICA DESERT, PERU)

The sequence stratigraphic framework and a summary of the fossil fauna of the upper Miocene portion of the Pisco Formation exposed along the western side of the Ica River (southern Peru) is presented through a new geological map encompassing an area of about 200 km 2 and detailed chronostratigraphic analyses. Extensive field mapping and sedimentological study of outcrop sections have shown that the Pisco Formation is a cyclical sediment unit composed of at least three fining-upward, unconformity-bounded depositional sequences, designated P0, P1, and P2 from oldest to youngest. In the study area, these sequences progressively onlap a composite basal unconformity from southwest to northeast. Integration of biostratigraphic and tephrochronologic age determinations constrains the ages of the three Pisco sequences within the study area. Based on the age of surrounding sediments, a conservative estimate of the age of P0 suggests deposition of these strata between 17.99 ± 0.10 Ma and 9.00 ± 0.02 Ma, whereas diatom biostratigraphy and calculated 40 Ar/ 39 Ar ages converge to indicate that strata of the P1 sequence were deposited sometime between 9.5 Ma and 8.9 Ma and that those of the P2 sequence are younger than 8.5 Ma and older than 6.71 ± 0.02 Ma. Our survey for both vertebrate and macro-invertebrate remains in the three sequences confirms the outstanding paleontological value of the Pisco Formation and contributes to depict regional faunal shifts in the fossil assemblage.

Warm-water mollusc assemblages from northern Chile (Mejillones Peninsula): new evidence for permanent El Niño-like conditions during Pliocene warmth?

Although results have been controversial, understanding the tropical Pacific climatic state during the Pliocene warm interval (c. 4.5–3.0 Ma) is crucial if insight is to be gained into the dynamic processes of present and future global warming. In the multi-proxy effort to reconstruct ancient climates, a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature-sensitive marine molluscs. Shallow-water strata of the Mejillones Peninsula, northern Chile (23°S), contain dense faunal assemblages in which molluscs exclusive to, or characteristic of, Pliocene deposits (Chlamys simpsoni, Chlamys vidali, Chorus blainvillei, Concholepas nodosa, Fusinus remondi, Herminespina mirabilis) coexist with surprisingly abundant and varied populations of extant warm-water species (Bulla punctulata, Cerithium stercusmuscarum, Olivella sp., Turbo cf. fluctuosus, Anomia peruviana, Argopecten ventricosus, Donax peruvianus, Dosinia ponderosa, Mexicardia procera, Undulostrea megodon), most of which have their current southern zoogeographical limit at 6°S. These tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures (SST) along the northern Chile coast were at least 2 °C warmer in the mid-Pliocene than at present, and that these very different conditions lasted long enough to allow stable colonization of the area. Such a significantly warmer SST pattern strongly resembles general climatic conditions accompanying modern El Niño events, when warm tropical waters propagate southward along the western margin of South America; this supports the existence in this area of persistently El Niño-like conditions during the mid-Pliocene.

A new vertebrate fossiliferous site from the Late Quaternary at San José on the north coast of Ecuador: preliminary note

A new fossiliferous site is described south of Manta on the north coast of Ecuador. Estuarine sediments overlying Quaternary terraced deposits contain abundant vertebrate remains belonging to the following taxa: Eremotherium cf. laurillardi or E. rusconii, Haplomastodon chimborazi, and Geochelone s.l. On the basis of geological context and the fossil assemblage, a probable Early Holocene age is suggested, although a latest Pleistocene age cannot be ruled out. This discovery will provide crucial new information to enhance knowledge of the geologic and faunistic evolution of the area.