Evolution of a Late Pleistocene palaeolake in Dali Nor area of southeastern Inner Mongolia Plateau,China

Lithological,geochronological,granulometric,and scanning electron microscope(SEM)analyses of eight lacustrine outcrops indicate the existence of a large palaeolake in Dali Nor area during 149-24.6 ka(MIS5-3)and a small one in upstream of the Xilamulun River during 12.96-11.69 ka.The large palaeolake recorded its highest water level above 1300 m during the MIS3 and covered the whole Dali Nor basin and upstream of the Xilamulun River within an area of about 3000 km^2.However,the small palaeolake with a highest water level above 1200 m,covered an area of about 600 km^2.Besides the reconstruction of palaeolake areas,this study also looked into the evolutionary process of the palaeolake during the Late Pleistocene.Our data provide insights on the timing of appearance of the large palaeolakes and a better understanding of the mechanism responsible for variations in the environment conditions of dry lands in middle latitudes.

Geological Observations from a Palaeolake Basin, Lamayuru, Ladakh, Northwestern Himalaya

A well known Buddhist monastery of Lamayuru is located in a village about 128 Km West of Leh. It is situated on more than 100 m thick Late Quaternary palaeolake deposits which are surrounded by rocks of Lamayuru Formation. Geologically, the Lamayuru Formation includes the Lamayuru and Namikala flysch deposits of Triassic-Jurassic age. This Formation is composed of shales, schist and phyllites. This Lamayuru Formation forms the base and source of palaeolake deposits. In Late-Pleistocene (35 ka B.P.) the Lamayuru River was dammed due to tectonically triggered landslide and the Lamayuru palaeolake came into existence. The sedimentation in the palaeolake basin commenced at 35 ka B.P. and culminated at 1 ka B.P. The deposits of palaeolake consist of carbonaceous mud, sand, silty clay and matrix supported breccia. The palaeolake deposits are a product of complex interplay of lacustrine, fluvio-deltaic to colluvial processes. The research study shows the prevalence of glacio-lacustrine conditions during the major part of depositional history as evidenced by the dominance of varves in these deposits.

Palaeolake and palaeoenvironment between 42 and 18 kaBP in Tengger Desert,NW China

Comprehensive field investigations and laboratory analyses show that palaeolakes, including fresh-mesohaline water Megalake Tengger and other semi-connected, isolated water bodies, during late Pleistocene covered an area of more than 20000 km2, which is more than half of the Tengger Desert in NW China. Stratigraphic correlation and chronological evidence indicate that before ca. 42000 aBP the area was more arid. The palaeolakes started to develop around 40000 uncal. 14C aBP but until 37000 14C aBP their scope was limited. High water levels established from 35000 14C aBP lasted until 22000 14C aBP. Lake levels regressed between 22000 and 20000 14C aBP but transgressed from 20000 to 18600 14C aBP. Subsequently, water level declined further and the Megalake Tengger finally desiccated at around 18000 14C aBP. Megalake Tengger possessed a fresh-mesohaline water property, implying that the regional precipitation increased significantly. During the period of Megalake Tengger, the climate was warmer-humid

A combined tectono-climatic control on Holocene sedimentation in Ladakh Himalaya,India:Clues from Anisotropy of Magnetic Susceptibility(AMS)of lake sediments

Anisotropy of Magnetic Susceptibility(AMS)data from a~27.8 m thick soft sedimentary mud sequence(~10.5-3.25 k yrs)from the Spituk Palaeolake Sequence(SPSS)of Holocene age,located in the northern bank of the Indus River in the Leh-Ladakh Himalaya,show effects of tectonic versus climate dynamics responsible for the Himalayan sedimentation.The sedimentary sequence,consisting of alternating of aeolian sand and glacio-fluvial mud flow deposits,has been subdivided into an older Last Glacier Phase I(LGP 1)and a younger Last Glacier Phase II(LGP 2),where the termination of each phase is marked by the occurrence of gravel beds of thickness≤1 m,which were deposited due to glacial melting.The present AMS data along with previously published information on sedimentology confirm that the mudflow deposits of the LGP 1 and LGP 2phases were deposited in a lacustrine environment under glacio-fluvial conditions.However,a weak fluvial flow towards NW and NE could have existed for the LGP 1 and LGP 2,respectively.The glacial beds terminating LGP 1 and LGP 2 appear to have formed by climatic warming and tectonic activity,respectively.Hence,the Holocene Himalayan sedimentation was influenced by both climatic and tectonic activities.However,the thickness of the gravel bed(~0.8 m)terminating LGP 2 occupies only~2.8 vol%of the total studied thickness~28 m,of the SPSS in the present study,which indicated a lesser control of tectonism in the growth of the Himalaya in and around the study area.

Damming of River Indus during Late Quaternary in Ladakh Region of Trans-Himalaya, NW India: Implications to Lake formation-climate and tectonics

Indus river valley basin in Northwest Indian Himalaya is tectonically unstable, exhibiting a complex topography, landscape relief and varied Quaternary sedimentation. A 422 km transact along the Indus river valley from Nyoma to Batalik in Ladakh(Trans Himalayas) reveals the damming of the river four places and existence of four major palaeolakes in the Late Quaternary Period. The commencement and breeching of the palaeolake sequences and the seismites preserved therein mark of the tectonic pluses in the area but the contribution of climate cannot be ruled out. The major geomorphic landforms are alluvial fans, debris cones, unsorted pedestals, fluvio-lacustrine deposits, scree, talus cone etc. Ubiquitous mass movements and catastrophic land sliding, due to tectonic activity and abnormally high precipitation has transported the material from steep slopes to valley bottoms, was responsible of forming lakes(preserved as thick piles of fine sediment), while the outburst floods redistributed the sediment down valley. Chronologies of two lakes are available which reveal the presence of one during post LGM times around 17000 a BP which breached out prior to Older Dryas indicating of warmer and congenial rainfall and melt water supply between these two globally marked cold episode. Other lake was formed after the Younger Dryas and existed till ~1000 a BP indicative of the Holocene warming responsible for its sustenance.