Foraminiferal studies have been used in palaeo-environmental reconstructions of the marine Cretaceous succession (upper Aptian to Maastrichtian) of the Sergipe Basin, in northeastern Brazil. The foraminiferal assemblages show broadly three types of response to changes in environment: (1) variations in morphotypes of the taxa present; (2) changes in specific and generic diversity; and (3) changes in relative abundance.Twelve palaeocommunities, characterised by the relative dominance of the major foraminiferal groups, can be recognised in the succession. Their palaeoenvironmental distribution is proposed as a model with reference to the Sergipe Cretaceous sequence.An intimate relationship is inferred among foraminiferal association distribution patterns, trophic structures (community feeding strategy, dwelling habits, substrate niche patterns) and water-mass conditions (depth-related in part). It is suggested that the distribution patterns may be a direct response of the functional adaptive morphology of the foraminiferal tests to individual characteristics of behavioural structure (preferential dwelling microhabitat and trophic strategy versus environment). The approach is a simple, yet very powerful tool, for the interpretation of foraminiferal palaeocommunities and palaeoceanographic research. It may also permit interpretation of palaeocommunity strategies in terms of adaptation rate and selection response (i.e. “r-selection” versus “k-selection”) to variable environmental conditions.

No abstract

No abstract

No abstract

A preliminary integrated study of a Cretaceous‐Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non‐graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea‐level lowstand, the former possibly generated by the K/T boundary Yucatán impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm‐thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock‐metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite‐like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact‐derived material has not been found in the uppermost Cretaceous beds.

No abstract

No abstract

A piston core drilled at a water depth of 2809 m off Rio de Janeiro, southeastern Brazil, recovered a 1.83-m thick section of unconsolidated muddy sediments, representing a complete stratigraphic succession across the Cretaceous-Paleogene (K/Pg) boundary. The sediments yielded abundant, strikingly pristine tests of planktic and benthic foraminifera, unaffected by diagenetic alteration or recrystallization.The sedimentary record ranges from the uppermost Maastrichtian (P. hantkeninoides Zone) to the lower Danian (zones P0-P1c), spanning a time interval of about 3-4 Myr through the K/Pg transition. A detailed taxonomic appraisal of the recovered planktic foraminiferal assemblages is presented, together with an evaluation of lineage relationships, phylogenetic trends, and the sequence of evolutionary events that took place among the Globigerinina at the beginning of the Cenozoic.The numerous recent taxonomic studies of Danian planktic foraminifera notwithstanding, the significance of phenotypic varieties has never been assessed in a paleoecological context. Whereas the cancellate-walled, low trochospiral, large-sized Praemurica (Truncorotaloididae) and Parasubbotina and Subbotina (Globigerinidae) lineages evidently underwent rapid speciation over a relatively narrow phenotypic range, the small-sized Praemurica, the distinctly elevated trochoid Eoglobigerina (Globigerinidae), the Parvulorugoglobigerina, and the coiled to elongate morphotypes of the Guembelitria and Woodringina (all members of the family Guembelitriidae) and Chiloguembelina (Chiloguembelinidae) lineages show phenotypic plasticity over a much broader range. This dichotomy correlates with inferred differences in life-history parameters among these planktic taxa, including pelagicdwelling preferences, related to reproductive and feeding strategies and to water-mass trophic levels.Two new early Danian planktic foraminiferal species are established herein: Praemurica nikolasi n. sp., the earliest recorded Truncorotaloididae and cancellate species, likely evolved directly from Hedbergella monmouthensis near the base of Zone P0 and probably giving rise to all subsequent cancellate lineages of the early Danian; and Globoconusa victori n. sp., evolved from Globoconusa daubjergensis within Zone P1c. A piston core drilled at a water depth of 2809 m in the Campos Basin, offshore of Rio de Janeiro, southeastern Brazil (Fig. 1), recovered a 1.83 m-thick interval of unconsolidated muddy sediments, representing a complete stratigraphic succession across the Cretaceous-Paleogene (K/Pg) boundary. The sediments yielded abundant, strikingly pristine tests of planktic and benthic foraminifera, unaffected by diagenetic alteration or recrystallization. The profuse and superbly preserved foraminiferal assemblages present a unique window to the past. They provide an outstanding basis for a detailed taxonomic appraisal, together with an evaluation of lineage relationships, phylogenetic trends, and the sequence of evolutionary events manifested among the Globigerinina at the be...