939 resultados para Stratigraphic correlation.
Resumo:
The lacustrine deposits infilling the intramontane Guadix-Baza Basin, in the Betic Range of Southern Spain, have yielded abundant well-preserved lithic artifacts. In addition, the lake beds contain a wide range of micromammals including Mimomys savini and Allophaiomys burgondiae and large mammals such as Mammuthus and Hippopotamus together with the African saber-toothed felid Megantereon. The association of the lithic artifacts along with the fossil assemblages, themselves of prime significance in the Eurasian mammal biochronology, is providing new insight into the controversy of the human settlement in Southern Europe. Despite the importance of the artifacts and fossil assemblage, estimates of the geological age of the site are still in conflict. Some attempts at dating the sediments have included biochronology, uranium series, amino acid racemization, and stratigraphic correlation with other well-dated sections in the basin, but so far have failed to yield unambiguous ages. Here we present paleomagnetic age dating at the relevant localities and thus provide useful age constraints for this critical paleoanthropological and mammal site. Our data provide firm evidence for human occupation in Southern Europe in the Lower Pleistocene, around 1 mega-annum ago. The current view of when and how hominids first dispersed into Europe needs to be reevaluated.
Resumo:
The sedimentary record of the Tarcău and Vrancea Nappes, belonging to the flysch accretionary zone of the Eastern Carpathians (Eastern Carpathian Outer Flysch), registered Cretaceous-Miocene events during the evolution of the Moldavidian Basin. Our biostratigraphic data indicate that the deposits studied are younger than previously reported. The comparison of sedimentary record studied with the Late Cretaceous-Early Miocene global eustatic curve indicates that eustatic factor played a secondary role, after the tectonic one. Four main stages of different processes influenced by tectonics are recognized in the sedimentary record: (1) Campanian-Maastrichtian-earliest Paleocene; (2) latest Ypresian-Lutetian; (3) late Chattian-earliest Aquitanian, and (4) late Aquitanian-early Burdigalian. The late Chattian- earliest Aquitanian and late Aquitanian-early Burdigalian records indicate a high tectonic influence. The first event was related to the foredeep stage of the sedimentary domain studied, and the second one to the deformation stage of the same domain. The sedimentary records of tectonic influence recognized during these stages are useful tools for geodynamic reconstructions. The stratigraphic correlation of Tarcău and Vrancea sedimentary records are used
Resumo:
v.33:no.11(1975)
Resumo:
Morphological evolution in the late Neogene planktonic foraminifer Sphaeroidinella lineage involves a sudden increase of the percentage of specimens equipped with supplementary apertures (from <30% to >70%) in the mid-Pliocene (about 3.5 Ma). This evolutionary transition, marked by the first occurrence of specimens with large supplementary apertures in the lineage, is denoted the Sphaeroidinella event. Changes in the proportions of the supplementary apertures in the lineage were studied in 24 samples from ODP Hole 926A drilled in the equatorial Atlantic Ocean. In addition, detailed chronological models have been compiled for this section as well as for Pliocene sections from DSDP Holes 214, 502A, and 503B, where evolution in the lineage have been analyzed previously. Stratigraphic correlation of the studied sequences suggests that the Sphaeroidinella event took place at about 3.6 Ma in the eastern equatorial Pacific (Hole 503B) and at 3.5-3.6 Ma in the Caribbean (Hole 502A), while in the Atlantic Ocean (Hole 926A) and in the Indian Ocean (Hole 214) the event occurred after 3.5 Ma. The inferred diachrony of the mid-Pliocene Sphaeroidinella transition, which is considered to represent a prime example of punctuated anagenesis, suggests that this evolutionary modality may have an allopatric component. Its short duration (on average less than 50 kyr) and the detailed biochronology that could be established for this event qualifies it as a useful biostratigraphic tool in the low-latitude Pliocene oceans.