Tafonomía, sedimentología, paleoambientes

Breve sintese e análise ao caminho cientifico da Zooarqueologia em território português, a afirmação da Zooarqueologia como subdisciplina no seio da Arqueologia, os seus objetivos, métodos, dificuldades e paradigmas do que é e deve ser hoje a Zooarqueologia.

El rol de la vizcacha (Lagostomus maximus) en los procesos de formación de los sitios arqueológicos de la llanura Interserrana argentina The role of the vizcacha (Lagostomus maximus) in the formation processes of archaeological sites from the Argentinian interhill plains Resumen El movimiento de sedimentos que generan los mamíferos cavadores constituye uno de los principales procesos de formación que sufren los sitios arqueológicos de la región pampeana. En este trabajo se presentan los resultados de un estudio actualista realizado sobre una colonia de vizcachas ubicada en la localidad arqueológica El Trebolar, provincia de Buenos Aires. El objetivo principal fue describir el impacto que estos roedores generan sobre el paisaje, con el fin de identificar su accionar en los sitios arqueológicos de la región. A partir del relevamiento de 21 vizcacheras se pudo establecer que las vizcachas afectan al registro arqueológico de diferentes maneras. Por un lado, su actividad cavadora altera las secuencias estratigráficas y genera asociaciones de materiales de distinta cronología. Por otra parte, las vizcacheras son ocupadas por otros animales, dando lugar a conjuntos faunísticos con alta riqueza taxonómica. Además, estos roedores acarrean a sus madrigueras objetos disponibles localmente. Por último, un alto porcentaje de especímenes óseos presentan surcos que generan las vizcachas para mantener funcionales sus incisivos. En conclusión, las distintas evidencias presentadas permitirían reconocer el accionar de este roedor en el registro fósil, diferenciándolo de otros animales fosoriales que habitan la región pampeana.
The movement of sediments generated by digging animals/burrowing mammals is one of the main formation processes affecting the archaeological sites in the Pampas region. In this article, we present/report the results of an actualistic study conducted on a vizcacha colony, in the archaeological locality El Trebolar, province of Buenos Aires. The main objective was to describe the impact that these rodents generate on the landscape in order to identify their action on the archaeological sites of the region. The analysis of 21 vizcacheras showed that the vizcachas affect the archaeological record in different ways. Firstly, their digging activity alters stratigraphic sequences and generates associations of material of different chronology. Secondly, the vizcacheras are occupied by other animals, producing/giving rise to taxonomically rich faunal assemblages. In addition, these rodents carry locally available objects to their burrows. Finally, a high percentage of bone specimens present/shows grooves generated by vizcachas to keep their incisors functional. In conclusion, evidence would allow recognizing the action of this rodent in the fossil record, distinguishing it from other fossorial animals that inhabit the Pampas region.

Los restos esqueléticos faunísticos y humanos ofrecen información acerca del tipo de vista de las poblaciones pasadas, que pueden representar evidencia directa para un grupo de estudio, que se convierte en una gran fuente de información para el arqueólogo (Brito,  1999:13).  Lamentablemente  los  restos  óseos  no  se mantienen intactos, debido a diferentes factores ambientales y climáticos.

El campo de tafonomía ayuda al estudio arqueológico, en el momento de analizar los diversos contextos ofreciendo una interpretación más cercana a la realidad, ya que por ejemplo en caso de los restos óseos animales podríamos encontrar un pequeño número de individuos y decir que hubo poca o nula población de ese taxón, pero con ayuda de la tafonomía podríamos decir que la ausencia de huesos es debido al proceso de trasporte, entre otros factores  trópicos y antrópicos.

El objetivo del presente ensayo es dar a conocer como los restos óseos se preservan y/o se destruyen desde al momento de su deposición hasta su hallazgo por un arqueólogo en este caso y los tratos que recibe en este momento y conocer cómo pueden terminar estos restos.

En este trabajo se realiza un análisis preliminar del registro arqueológico recuperado en el
sitio Médanos de Escobar. Se trata de un depósito situado en los Bajíos Ribereños meridionales
(humedal del río Paraná inferior). Se presenta la estratigrafía y la cronología del sitio, algunos
aspectos geomorfológicos del área y las principales características del registro arqueológico
recuperado. Finalmente se discute y compara la información generada con la obtenida en otros
sitios con el fin de establecer similitudes y diferencias que nos permitan avanzar en el conocimiento
de la variabilidad arqueológica generada por las poblaciones cazadoras-recolectoras
que habitaron el área de estudio en los últimos 2500 años 14C AP (Holoceno tardío).

Sediments deposited in the Etzatlán-Magdalena Basin were analyzed to reconstruct the paleohydrological variations and generate a new Holocene paleoclimate record for the less studied western part of central Mexico. Concentration of Ti, abundance of CaCO 3 , Zr/Ti ratio and TOC/Ti ratio were compared with their average values to infer variations in runoff, lake water salinity, transportation of clastic minerals by aeolian activity and total organic productivity. In general, conditions were wetter during ~9.6–5.7 ka (early-middle Holocene) and ~2.2–0.7 ka (late Holocene) compared to ~5.7–2.2 ka (middle-late Holocene). Transportation of above-average amounts of Zr-bearing clastic minerals from an arid watershed and deposition of the highest abundance of CaCO 3 at ~3.5–2.8 ka occurred within the drier interval of middle-late Holocene. Except for the interval of ~2.2–0.7 ka, the El Niño Southern Oscillation (ENSO) and Inter Tropical Convergence Zone (ITCZ) controlled summer precipitation forced the hydrological variations. The Etzatlán-Magdalena Basin remained wet and some sites in central Mexico were dry over a large part of ~2.2–0.7 ka. The activity of tropical cyclones and frontal systems may have increased in the northeastern Pacific during this interval of enhanced ENSO. Either of them, or the combination of both, possibly contributed more autumn and winter precipitation to western-central Mexico.

Lo studio archeozoologico e tafonomico del campione faunistico di Ferento è particolarmente interessante perché ci permette di investigare in senso diacronico, all'interno di uno stesso sito, le modalità di sfruttamento delle risorse animali e le attività produttive ad esse legate.

The knowledge of climatic and environmental changes at the onset of the Holocene and its impact on human populations and cultures is key for the understanding of their both past and future evolution. In this sense, the study through trenching and cores of the Holocene archaeosedimentary record in the surroundings of the Los Cascajos Neolith-ic archaeological site (Los Arcos, Navarra), provides valuable information not only for the establishment of the environmental evolution of this area, but also for the knowledge of the activities that the inhabitants of the settlement developed in the Odrón riverbanks. In this work the results of the stratigraphic, sed-imentological and geochemical study (XRF-CS) of the LAC1 core are presented. The obtained data denote a trend towards long-term aridification throughout the Holocene, recorded by an aggradation-incision cycle in the fluvial evolution of the Odrón River. In the fluvial sedimentary record, anthropic activity proxies coetaneous to Los Cascajos settlement are also detected during a relatively more humid period than nowadays, this fact evidences the subsequent aridification of this area of the Ebro valley along the late Holo-cene (Meghalayan). .

En este trabajo se presentan parte de los resultados obtenidos del análisis tafonómico sobre los entierros humanos del sitio arqueológico Arroyo Seco 2 (partido de Tres Arroyos, provincia de Buenos Aires). Se destaca la pérdida de unidades óseas en frecuencias elevadas, con una tendencia a la subrepresentación de huesos de pequeño tamaño. Dada la modalidad primaria de inhumación de la mayoría de los individuos, se descarta que la manipulación antrópica intencional haya ocasionado estos faltantes. A partir del bajo impacto de aquellos agentes tafonómicos con potencial para destruir y/o remover los huesos, se propone que la acción sucesiva y alternada de procesos postdepositacionales de bajo impacto (roedores, procesos diagenéticos y actividad humana prehistórica y actual) produjeron la exposición y destrucción ósea. En la última etapa de la historia tafonómica, ante la exposición y la acción antrópica actual, se profundizaron las alteraciones en la integridad ósea provocadas previamente por factores diagenéticos.

Foi analisada a presença de espículas de esponjas em sedimentos turfosos visando detalhar as mudanças paleoambientais na região do baixo curso do rio Ribeira de Iguape (Iguape/SP - 24º34’17”S/47º37’33”O), sudeste do Brasil. O testemunho de sondagem (520 cm de profundidade) foi datado por 14C, como segue: (i) 6.240±30 anos AP (430 cm); (ii) .500±25 anos AP (225 cm); (iii) 2.920±25 AP (145cm). Identificou-se gemoscleras de esponjas continentais da espécie Oncosclera navicella (Carter) e microscleras de Corvoheteromeyenia
sp. Também foram detectadas espículas de esponjas marinhas, no entanto, sem determinação específica. As variações entre o conteúdo de espículas de esponjas continentais e marinhas indicam: (i) fluxos de água doce com mar mais baixo que o atual, posterior há 6.240 anos AP; (ii) fase de transgressão marinha iniciada há pelo menos 6.240 anos AP; (iii) fase com grandes oscilações do nível do mar entre 6.240 e 4.500
anos AP; (iv) fase com predomínio de fluxos de água doce entre 4.500 e 2.920 anos AP. Os resultados também sugerem possível mudança do canal do rio Ribeira de Iguape, para oeste do local pesquisado, durante o Holoceno.

This study documents the occurrence of brachiopod shells (Bouchardia rosea) in wrack-lines from backshore deposits of a tropical beach (Itamambuca beach), in the northern coast (Ubatuba County) of the state of São Paulo, Brazil. The main goals are: (a) to analyze the provenance and sorting of the brachiopod shells; (b) to provide the taphonomic signatures of the shells, which may favor the recognizance, description and diagnoses of similar shell concentrations in ancient rocks, and (c) to discuss the taphonomic meaning of these detrital accumulations. Sampling transects were done at the reflective and dissipative sectors of the Itamambuca beach. For this project, two thousand brachiopod shells were collected and examined. In general, shells are minute, pale in color, and extremely rounded with reduced shell micro-relieves. Abrasion is the main taphonomic signature recorded. Abraded shells are characterized by V-shaped scars on the external surface, exposing the secondary fibrous layer of the shell microstructure. In some cases, holes produced by abrasion (facets) are recorded in the most convex portion of the shells. A pronounced bias in favor of ventral valve is also noted, and the size frequency distribution of shells is shaped by taphonomy. Finally, shells show intense taphonomic overprinting, but the taphonomic

Herein, it is presented the first detailed taphonomic study on bivalve mollusk shells preserved in the oolitic limestones of the Teresina Formation (probably Kungurian-Roadian, Lower-Middle Permian) in the eastern margin of the Paraná basin. The selected beds are located in two quarries (informally named PRU 1 and PRU 2) in Prudentópolis municipality (Center-South Paraná State), and positioned approximately in the middle of the formation and probably in the Pinzonella illusa Zone. The PRU 1 limestone (~30 cm thick), which is partially silicified and intercalated with predominantly pelitic rocks, is classified as a bivalve oolitic grainstone. The basal contact is erosive and the top shows symmetrical ripple marks, which are draped by shale with mud cracks. There are two fining-upwards successions characterized by dense to dispersed packing of the shells, which are usually disarticulated, randomly oriented (many nested/stacked) and mixed with some pelitic intraclasts. Microhummocky cross-stratification occurs a little below the top of the bed. The PRU2 bed is classified as ooid bivalve rudstone (~5 cm thick), where all shells are disarticulated and fragmented, showing dense packing. The bivalves probably inhabited a muddy substrate and were mixed (as parautochtonous and allochthonous bioclasts) with ooids during high-energy storm events, including posterior shell displacement as a result of bioturbation. Thus, the calcareous beds represent amalgamated proximal tempestites with a complex taphonomic history, strong temporal/spatial mixing of bioclasts and limited paleoecological resolution. They are a typical example of shell beds generated in a huge epeiric sea, which was not necessarily connected to the ocean and where very low depositional-slope gradient, very slow subsidence and minimum sediment accommodation space caused frequent sediment reworking by storm related processes.

To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of themarine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected fromsurface sediments atmultiple sites across a sediment-starved shelf in the shallowsub-tropical São
Paulo Bight (São Paulo State, Brazil). The resulting 14C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges frommodern to 10,307 cal yr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.

The occurrence of subfossil material in bottom sediments of Couve Island, Ubatuba region, Sao Paulo State, is confirmed. The analyzed material consists of a bivalve shell that was dated by the electron spin resonance technique. By the additive irradiation method an archaeological absorbed dose of ( 25+/-75) Gy was obtained and calibration with other dating works in the same area allows the inference of an age of  (25+/-75) 102 years years. The importance of this finding and its paleoecological implications could contribute to elucidating the nature of short-term environmental changes in the Brazilian coastline during the Holocene, as well as becoming an important tool to the understanding of the distribution and biological aspects of the bivalve fauna.

Las investigaciones arqueológicas y geoarqueológicas llevadas a cabo en la Localidad Paso Otero (Pdo. de Necochea, Pcia. de Buenos Aires) han producido información pertinente para analizar aspectos referidos a los procesos de formación naturales y culturales del registro arqueológico. Un rasgo común a todas las secuencias estratigráficas analizadas es la presencia de horizontes “A” de suelos enterrados interpretados como superficies de estabilización del paisaje que se registran entre ca. 3.000-10.400 años AP. Los objetivos de este trabajo son describir y comparar los perfiles de tres sitios arqueológicos de la localidad (Paso Otero 1, 3 y 5) y discutir la relevancia que las superfices de estabilización tienen para el análisis del registro arqueológico. Entre los resultados más importantes alcanzados se observa que a) los depósitos arqueológicos registrados se vinculan, sin excepción, a dichas superficies de estabilización; b) las mismas han sido indispensables para el establecimiento de secuencias radiocarbónicas a través del análisis de materia orgánica de suelos cuando otros materiales (e.g., huesos) no pudieron ser datados debido a problemas diagenéticos y c) se regista un patrón recurrente en la asignación funcional de los sitios (actividades específicas) localizados en estas antiguas planicies de inundación y suelos asociados en el paleoambiente del río Quequén Grande.

revistapesquisa.fapesp.br /2002/11/01/registros-vivos-do-tempo/ Cada vez que precisa coletar os pequenos animais marinhos invertebrados usados em sua pesquisa, o paleontólogo Marcello Guimarães Simões sof re com as viagens ao mar. Assim que o Progresso, um pesqueiro de camarões adaptado para pesquisas, zarpa do cais de Ubatuba, no litoral norte paulista, começam os enjôos, que só cessam na volta a terra f irme. Mas nem o mal-estar o f az desistir do seu objetivo: capturar pequenos invertebrados conhecidos como braquiópodes -semelhantes a moluscos encontrados nas praias, com os quais têm em comum apenas as conchas -que estão ajudando a compreender as alterações que o ambiente marinho sof reu nos últimos milhares de anos e, no f uturo, devem permitir propor f ormas de recuperação para essas áreas.

This study represents one of the first contributions to the knowledge on the quantitative fidelity of the recent freshwater molluscan assemblages in subtropical rivers. Thanatocoenoses and biocoenoses were studied in straight and meandering to braided sectors, in the middle course of the Touro Passo River, a fourth-order tributary of the Uruguay River, located in the westernmost part of the State of Rio Grande do Sul. Samplings were carried out through quadrats of 5 m2, five in each sector. A total area of 50 m2 was sampled. Samplings were also made in a lentic environment (abandoned meander), with intermittent communication with the Touro Passo River, aiming to record out-of-habitat shell transportation from the lentic communities to the main river channel. The results show that, despite the frequent oscillation of the water level, the biocoenosis of the Touro Passo River shows high ecological fidelity and undergoes little influence from the lentic vicinal environments. The taxonomic composition and some features of the structure of communities, especially the dominant species, also reflect some ecological differences between the two main sectors sampled, such as the complexity of habitats in the meandering-sector. Regarding the quantitative fidelity, 60% of the species found alive were also found dead and 47.3% of the species found dead were also found alive, at river-scale. However, 72% of the dead individuals belong to species also found alive. This value might be related with the good rank order correlation obtained for live/dead assemblages. Consequently, the dominant species of the thanatocoenoses could be used to infer the ecological attributes of the biocoenoses. The values of all the indexes analyzed were very variable in small-scale samplings (quadrat), but were more similar to others registered in previous studies, when they were analyzed in a station and river scale.

Nearby the city of Santa Cruz do Sul (central region of Rio Grande do Sul State in Brazil), an outcrop of the Triassic Santa Maria Formation contains a rather unusual fossil occurrence consisting of a concentration of disarticulated therapsid skeletons dominated by herbivorous and carnivorous cynodonts. Noncynodont remains are restricted to a single specimen of Rhadinosuchidae (Archosauriformes: Proterochampsia). The taphocoenosis is characterized by the chaotic accumulation of tens of isolated fossil bones within a block of mudrock 10 m wide and 20 m long, and approximately 5 m thick. The site lies within an approximately 30 m thick succession of red mudstone displaying horizons of rhizoliths and carbonate nodules which are interpreted as palaeopedogenic carbonate precipitation in alluvium on a semi arid floodplain. Preservation of the fossil bones at this site is unusually good. Microstructure of the bones shows external and internal precipitation of calcite and quartz in the vessel cavities and pores in the bone matrix indicating that they were initially filled by calcite, and than partially replaced by quartz. These features combined with the presence of calcareous rhizoliths and carbonate nodules, suggest that the bones were accumulated on a playa lake margin with the position of the shoreline being controlled by the groundwater table movements between dry and wet seasons. The taphocoenosis shows a predominance of disarticulated and disassociated skulls and mandibles. Commonly large and very small bones occur side-by-side with no preferred orientation. This taphonomic style suggests a biogenic agent of concentration of the bones by selective predation.