Carbonate Buildups in the Pernambuco Basin, NE Brazil

ABSTRACT The Pernambuco Basin represents one of the most prominent regions for deep water oil and gas exploration off the Brazilian coast. This study aims to identify and describe the occurrence of carbonate buildups in the offshore regions of the basin. The study was based on an analysis of a set of 143 2D time-migrated seismic sections that cover the offshore region of the Pernambuco Basin. An interpretation of the seismic dataset was used to define the main seismic sequences related to the main regional pulses of deposition and to identify three main groups of carbonate buildups: 1) shelf margin reefs, 2) patch reefs, and 3) isolated carbonate buildups. The carbonate buildups formed in two main intervals during post-rift sequences of the Santonian-Maastrichtian and Paleocene-Middle Miocene, which extend the known periods of carbonate deposit formation in the basin. The formation of carbonate buildups was controlled by the tectonic evolution of the Pernambuco Plateau, which created a series of paleotopographic highs that enabled the establishment of oceanographically and climatically favorable conditions for carbonate formation and deposition. These findings are important for understanding the evolution of the basin and for future evaluations of its petroleum potential.

Characteristics, distribution and diagenetic stages of chert in the La Silla Formation (Lower Ordovician), Argentine Precordillera

The late Cambrian - late Tremadocian La Silla Formation is a carbonate unit of the eastern Precordillera in Argentina whose facies indicate a shallow platform environment. Until this moment, there were no studies that referred to the diagenetic evolution of these rocks. The present study involves the characteristics and distribution of the silicification that affects this unit and determines its different diagenetic stages through petrographic (with cathodoluminescence support) and stratigraphic analyses. An early diagenetic chert, in a stage previous to the compactation, was observed. This chert is related to silica-rich seawater in contact with permeable and porous sediments. A later pulse of chert, associated with fracturing, also occurs. The knowledge provided by the characteristics and distribution of chert in these carbonates is significant, especially when considering that the La Silla Formation in San Juan province is the most quarried unit for the elaboration of lime.

A Formação La Silla (Neo Cambriano-Neo Tremadociano) é formada por depósitos carbonáticos da região da Pré-Cordilheira leste, Argentina. As faciologias encontradas em tais depósitos indicam um ambiente de deposição caracterizado por uma plataforma rasa. Até o momento, nenhum estudo tratou especificamente da evolução diagenética dessas rochas. O presente estudo envolve as características e distribuição da silicificação que afeta esta formação e apresenta os diferentes estágios diagenéticos ocorridos, através de análises petrográficas (auxiliadas por catodoluminescência) e estratigráficas. Foi identificado um pulso precoce de silicificação, anterior ao processo de compactação das rochas afetadas. Esta silicificação foi favorecida pela presença de água do mar rica em sílica em contato com sedimentos porosos e permeáveis. Também foi identificado um pulso de silicificação tardia, associado a eventos de fraturamento das rochas. O conhecimento adquirido sobre as características e a distribuição da silicificação nestes depósitos carbonáticos é importante, especialmente quando se considera que a Formação La Silla, na Província de San Juan, é a formação mais minerada para a produção de calcário.

C-reactive protein-guided approach may shorten length of antimicrobial treatment of culture-proven late-onset sepsis: an intervention study

Late-onset sepsis (LOS) (i.e., sepsis in a neonate after 72 hours of life) is associated with high mortality and significantly prolonged antibiotic exposure and hospital stay in neonates admitted to intensive care units (ICU). In this study, we assessed the reliability of serum C-reactive protein (CRP) as a determinant of antimicrobial treatment duration of LOS. From January 1996 to December 2002, all consecutive infants aged <28 days admitted to a single medical-surgical ICU and diagnosed with primary LOS were enrolled in a prospective, intervention trial with historical controls. Only blood culture-positive LOSs were included. Exclusion criteria were: age >28 days at diagnosis of LOS, development of site-specific infection, and central venous catheter-related LOS. From January 1996 to July 1998 (historical control group), antimicrobial treatment of LOS was offered for at least 14 days. From August 1998 to December 2002 (intervention group), neonates underwent serial semiquantitative measurements of serum CRP, and antimicrobial treatment was discontinued when CRP was <12 mg/L. Primary efficacy endpoint was the duration of antimicrobial therapy. Secondary efficacy endpoints were the proportion of relapsing sepsis within 72 hours of antibiotic withdrawal and the overall mortality rate. The historical control group comprised 76 neonates developing 85 episodes of LOS; 138 LOS occurring in 120 patients comprised the intervention group. Length of antimicrobial treatment of LOS was significantly shorter during the second study period (16 days vs. 9 days, p<0.001). Secondary efficacy endpoints showed similar rates of relapsing sepsis and overall mortality in both time periods.