Search

The Cretaceous lacustrine carbonates of the offshore Brazilian and West African presalt basins represent some of the most extensive non-marine carbonates discovered in the geologic record. Despite being intensively studied over the past decade, the age of these carbonates and the overlying regional salt sequences is highly controversial. Similarly, the conditions under which these carbonates were deposited remains poorly understood. Here, we provide the first integrated geochronology-thermometry study of these carbonates to develop an improved understanding of when and under what conditions they formed. We utilize carbonate clumped isotope and 87Sr/86Sr geochemistry alongside traditional petrographic techniques to identify samples minimally altered from burial diagenesis that may yield reliable age and lake chemistry constraints. Carbonate clumped isotope apparent temperatures for the studied carbonates range from 36 °C to 91 °C, which we infer to represent a range in sample preservation from minimally altered depositional temperatures through to those that have been overprinted by burial diagenesis. 87Sr/86Sr values of our samples are consistent with those of previous studies for Cretaceous pre-salt carbonates that have not experienced significant alteration from hydrothermal fluids. Through this approach, we measured the first high resolution isotope dilution U-Pb age constraint of 115.83 ± 1.56 Ma (2σ) on a well preserved carbonate. Combined with overlapping lower resolution laser ablation U-Pb ages for time-equivalent stratigraphy on two separate carbonate platforms of 114.46 ± 4.72 Ma and 109.73 ± 9.26 Ma, these ages provide the first robust direct age calibration for pre-salt carbonates deposited on either side of the South Atlantic during the final stages of the break-up of Gondwana in the Early Cretaceous. These ages also provide the first calibration for a combined 87Sr/86Sr-facieslog based relative age framework within the Santos Basin, offshore Brazil. We further utilize δ18O constraints on samples that yield depositional clumped isotope apparent temperatures to constrain the δ18O of the water in these ancient lakes to between 1.9 and 4.9‰Vienna standard mean ocean water. Such heavy values reveal a picture of a hot and arid environment. This is consistent with prior biostratigraphic studies of the carbonates that show a decrease in faunal diversity in these lakes prior to marine ingress and the development of open marine conditions in the South Atlantic Ocean.

Objective: Falls are common among adults with leg amputations and associated with balance confidence. But subjective confidence is not equivalent with physical ability. This multivariate analyses of community-dwelling adults with leg amputations examined relationships among individual characteristics, falls, balance ability and balance confidence. Design: Cross-sectional study. Subjects/Patients: Community-dwelling adults with leg amputations recruited from a support group and prosthetic clinic. Methods: Subjects provided self-reported medical/fall history, prosthetic functional use, and Activities-specific Balance Confidence (ABC) questionnaire data. Balance ability was assessed with the Berg Balance Scale (BBS). Fall incidence was categorized as any fall (one or more) and recurrent falls (more than one). Multivariate logistic regression analyzed relationships within the two fall categories. Cross tabulations and ANOVA analyzed differences among subcategories. Results: Fifty-four subjects (mean age 56.8) with various etiologies, amputation levels, and balance abilities participated. 53.7% had any fall; 25.9% had recurrent falls. Models for both fall categories correctly classified fall history in > 70% of subjects with combinations of the variables ABC, BBS, body-mass-index, and amputation level. Conclusion: Falls occurred regardless of clinical characteristics. Total BBS and select item scores were independent determinants of fall history. Unlike other balance-impaired populations, adults with leg amputation and better balance ability had greater odds of falling.

For people with lower-limb loss, impaired balance is common and limits prosthetic function within the community. This cross-sectional study (1) analyzed relationships among prosthetic use for mobility, balance ability and confidence, and amputation-related variables and (2) determined multivariate models to identify level of prosthetic use. Subjects included 46 community-dwelling adults (mean age 56.2 yr) with limb loss (91.3% unilateral) of varied levels (52.2% transtibial) and etiologies (69.6% vascular). A three-variable linear regression model including balance ability, balance confidence, and years since amputation explained 63.7% of variance in the Houghton scale of prosthetic use score. A logistic regression model including the 14-task Berg Balance Scale, balance confidence, years since amputation, age, and number of comorbidities correctly differentiated between people who had reached a satisfactory level of prosthetic use or not 89.1% of the time. The first three variables demonstrated moderate accuracy with positive likelihood ratios from 2.34 to 4.35. The regression model was further reduced to correctly classify 87.0% of cases with three balance ability tasks (retrieving objects from floor, turning to look behind, and placing alternate foot on stool), balance confidence, and numbers of comorbidities. Logistic models that include balance ability, balance confidence, and numbers of comorbidities can identify level of prosthetic use in people with lower-limb loss. Increased balance confidence and ability when retrieving objects from floor, turning to look behind, and placing alternate foot on stool were most indicative of successful prosthetic use for mobility.