TY  - JOUR
A1  - Sponholz, Barbara
A1  - Baumhauer, Roland
A1  - Felix-Hennignsen, P.
T1  - Fulgurites in the southern central Sahara, Republic of Niger and their palaeoenvironmental significance
N2  - The mineralogical and chemical characteristics of fulgurites ( = natural glasses forrned by lightning strikes to the ground) from the southern Centrat Sahara (Niger) are presented. The fulgurites are indicators of thunderstorms. The northernmost important fulgurite formation in the study area reached up to about l8°N, with decreasing fulgurite concentration from south to north. Their distribution pattern and the relative dating of their formation in relation to Iandscape history from the Late Pleistocene onwards (e.g., palaeolakes, palaeosols), and to Neolithic settlement reveals their value as palaeoenvironmental indicators. They indicate: (1) local palaeoenvironmental conditions depending on the topographical situation in a complex dune relief; (2) climatic change during the mid-Holocene from northerly rains to southerly rains; and (3) the northernmost Iimit of important thunderstorrns and rainfall activity since this time in the southern Centrat Sahara.
KW  - Sahara
KW  - Niger
KW  - Fulgurite
KW  - fulgurites
KW  - lightning
KW  - thunderstorms
KW  - Sahara
KW  - Holocene
KW  - climatic change
KW  - palaeosols
KW  - Neolithic
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-63337
ER  - 
TY  - JOUR
A1  - Sponholz, Barbara
T1  - Phénoménes karstiques dans les roches siliceuses au Niger oriental
N2  - Dans le Niger oriental, des phénomenes karstiques sont fréquents dans les roches siliceuses: gres, silcretes, croûtes ferrugineuses, roches cristallines. A partir des études géomorphologiques et micromorphologiques, on peut conclure a une kartsification, au sense de production de formes par dissolution. Les résultats permettent de dater du Tertiaire inférieur la principale période de karstification. La répartition régionale des formes induites par cette karstification indique une dépendance probable des conditions paléoclimatiques. Actuellement le karst influe encore sur le développement des autres formes de relief.
N2  - In North-Eastern Niger karstic features occur commonly in siliceous rocks (sandstones, silcretes, ironcrusts, crystalline). On the base of geomorphological field studies and micromorphological analyses karst forming caused by rock solution is verified. The results render possible the datation of the main karstification period in Early Tertiary. The widespread distribution of similar results indicates the dependance of karstification on palaeoclimatic conditions; actually the karstic systems influence significantly the development of othe landforms.
KW  - silicate karst
KW  - geomorphology
KW  - palaeoclimatology
KW  - Sahara
KW  - Sahel
KW  - Niger
KW  - karst siliceux
KW  - geomorphologie
KW  - paléoclimat
KW  - Sahara
KW  - Sahel
KW  - Niger
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86833
ER  -