TY - JOUR
T1 - Trace fossils on a Late Ordovician glacially striated pavement in Algeria
AU - Le Heron, Daniel Paul
PY - 2010/11
Y1 - 2010/11
N2 - An exceptional exposure of Late Ordovician glaciogenic sediments crops out in Dider, SE Algeria, within the Tassili N'Ajjer region. The sediments consist of sandstones and diamictites sandwiched between a Mid Ordovician fluvial and tidal sandstone (In Tahouite Formation) below and Early Silurian shale (Oued Imirhou Formation) above. Stratigraphic discontinuities within the Late Ordovician glaciogene succession include palaeovalley incisions and glacially striated pavements. Striation and fluting of a soft-bedded sediment beneath an ancient ice sheet is supported by abundant dewatering structures and soft-sediment gouges interpreted to have been produced by the action of stone ploughing. In Dider, two types of previously undescribed circular structures sit in negative relief on this glacial pavement, namely 1) paired thumb-shaped impressions 2. cm in diameter and 3. mm in depth, and 2) a 5. cm wide impression with 3 segmented nested cycles. A framboid or aggregate origin may be appropriate for the smaller of the features but the larger impression is interpreted as biogenic: internal complexity is characteristic, discounting concretion moulds and water escape structures. A biogenic origin as a coelenterate resting trace is proposed with speculation on conditions of exceptional preservation in an ancient periglacial environment.
AB - An exceptional exposure of Late Ordovician glaciogenic sediments crops out in Dider, SE Algeria, within the Tassili N'Ajjer region. The sediments consist of sandstones and diamictites sandwiched between a Mid Ordovician fluvial and tidal sandstone (In Tahouite Formation) below and Early Silurian shale (Oued Imirhou Formation) above. Stratigraphic discontinuities within the Late Ordovician glaciogene succession include palaeovalley incisions and glacially striated pavements. Striation and fluting of a soft-bedded sediment beneath an ancient ice sheet is supported by abundant dewatering structures and soft-sediment gouges interpreted to have been produced by the action of stone ploughing. In Dider, two types of previously undescribed circular structures sit in negative relief on this glacial pavement, namely 1) paired thumb-shaped impressions 2. cm in diameter and 3. mm in depth, and 2) a 5. cm wide impression with 3 segmented nested cycles. A framboid or aggregate origin may be appropriate for the smaller of the features but the larger impression is interpreted as biogenic: internal complexity is characteristic, discounting concretion moulds and water escape structures. A biogenic origin as a coelenterate resting trace is proposed with speculation on conditions of exceptional preservation in an ancient periglacial environment.
KW - Glaciation
KW - North Africa
KW - Ordovician
KW - Striated pavements
KW - Trace fossils
UR - http://www.scopus.com/inward/record.url?scp=77956878229&partnerID=8YFLogxK
U2 - 10.1016/j.palaeo.2010.07.023
DO - 10.1016/j.palaeo.2010.07.023
M3 - Article
AN - SCOPUS:77956878229
SN - 0031-0182
VL - 297
SP - 138
EP - 143
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
IS - 1
ER -