TY  - JOUR
A1  - Sebag, David
A1  - Garcin, Yannick
A1  - Adatte, Thierry
A1  - Deschamps, Pierre
A1  - Menot, Guillemette
A1  - Verrecchia, Eric P.
T1  - Correction for the siderite effect on Rock-Eval parameters
BT  - Application to the sediments of Lake Barombi (southwest Cameroon)
JF  - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry
N2  - Originally developed for use in the petroleum industry, Rock-Eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions. The standard Rock-Eval parameters provide information on the amount of total organic and inorganic carbon (TOC and MinC, respectively), and are usually interpreted as proxies for the source (aquatic or terrestrial) of the primary production of organic matter (Hydrogen Index vs Oxygen Index). Although this method usually provides valuable evidence, the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter (SOM). Indeed, the CO2 and CO released by the pyrolysis of siderite are integral to the calculation of the SOM-related standard Rock-Eval parameters. In this study, we analyze sediments from a core collected in the Lake Barombi (southwest Cameroon) and describe the impact of siderite on standard Rock-Eval parameters. We propose a workflow that allows standard Rock-Eval parameters to be corrected, based on the analysis of thermograms. The proposed corrections provide siderite-effect-free parameters, accurately reflecting the changes in sedimentary organic matter composition. (C) 2018 Elsevier Ltd. All rights reserved.
KW  - Organic geochemistry
KW  - Rock-Eval pyrolysis
KW  - Van Krevelen diagram
KW  - Siderite
KW  - Tropical lake
KW  - Western Central Africa
Y1  - 2018
U6  - https://doi.org/10.1016/j.orggeochem.2018.05.010
SN  - 0146-6380
VL  - 123
SP  - 126
EP  - 135
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Garcin, Yannick
A1  - Deschamps, Pierre
A1  - Menot, Guillemette
A1  - de Saulieu, Geoffroy
A1  - Schefuss, Enno
A1  - Sebag, David
A1  - Dupont, Lydie M.
A1  - Oslisly, Richard
A1  - Brademann, Brian
A1  - Mbusnum, Kevin G.
A1  - Onana, Jean-Michel
A1  - Ako, Andrew A.
A1  - Epp, Laura Saskia
A1  - Tjallingii, Rik
A1  - Strecker, Manfred
A1  - Brauer, Achim
A1  - Sachse, Dirk
T1  - Early anthropogenic impact on Western Central African rainforests 2,600 y ago
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the "rainforest crisis" to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. delta C-13-inferred vegetation changes confirm a prominent and abrupt appearance of C-4 plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. delta D values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era.
KW  - Western Central Africa
KW  - late Holocene
KW  - rainforest crisis
KW  - paleohydrology
KW  - human activity
Y1  - 2018
U6  - https://doi.org/10.1073/pnas.1715336115
SN  - 0027-8424
VL  - 115
IS  - 13
SP  - 3261
EP  - 3266
PB  - National Acad. of Sciences
CY  - Washington
ER  -