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Pleistocene sediments at Novigrad Sea - evidence of glaciation of coastal Adriatic (northern Dalmatia, Croatia)

The representative exposure of Pleistocene sediments is the northeastward facing coast of the Novigrad-sea. The base rock are thick bedded Cretaceous limestones. The Pleistocene sediments form a rather narrow terrace stretching for almost 3 km along the coast. Exposure is very good due to the cliff-type coast, about 10 m high at most. However, total thickness of the Pleistocene sediments is unknown, because there are no drilling data. Along this section significant facies changes occur, and the following were differentiated: diamictons, conglomerates, calcarenites, fine-grained sediments s.str., and paleosols. Diamictons are genetically interpreted as basal moraines, Older moraine and Younger moraine. The Older moraine is 5 m thick at most Their base is below the sea level, so their thickness can be greater. It is exposed in length of about 1, 5 km, but with interruptions. Their surface relief is hummocky. This moraine is dominantly grain supported conglomerate, very poorly sorted and extremely large span of clast size, from gravel to boulders over 10 m in diametre. Boulders are rounded and more or less sphaerical, some fasseted and some elongated or platy. Glacial striae or grooves were found on some boulders, and some have pitted surface. Interspaces are filled with gravel which appears like matrix to large boulders and can be well cemented. Moraine seems to have been locally washed out and secondary sorting appears, commonly inverse so the largest boulders are well sorted on top of sorted interval, even imbricated. Sorting and imbrication parallel to the base rock slope could have been caused by glacial readvance. The Younger morane is thinner and massive matrix supported conglomerate. Unsorted debris from gravel to boulder size is floating in the finegrained matrix. Debris is medium to well rounded, commonly sphaerical. Younger moraine is overlying the Older moraine or the glacial lake sediments, which indicates on glacial readvance and significant erosion. Younger moraine lays in one place over lake sediments which indicates an older lake-phase, but can not be well documented yet. Debris in both moraines is of similar lithologies, various limestone types (predominantly Cretacous). Rudist-rich limestone blocks and finer debris of Paleogene foraminiferal limestone are found onlly in Older moraine. Flat-pebble conglomerates occur on top of glacial lake sediments or a paleosol. They are stratified in layers 10-50cm thick. It is grain-supported conglomerate predominantly. Sandy or clayey matrix occurs in few layers. Size of pebbles varies from 1 to 10 cm. Special characteristic of these conglomerates are zones of vertically oriented flatt pebbles or high angle imbrication in verious directions. Souch random and vertical orientation of flat pebbles is the effect of freezing of intersticial water, characteristic for periglacial areas. On the other hand zones of clear low angle imbrication indicates accumulation and reworking of pebbles in a beach zone around the lake. Glacial lake sediments form the coastal clifs about 1 km long. Visible thicness is locally ca 10 m. There are two intervals recognized: lower warved-like calcisiltites with drop stones, and upper wave-ripple dominated calcarenites. These sediments overlap the Younger moraine and fill depresions between moraine hummocks. Lake sediments are localy in contact with Older moraine which is due to erosion in a phase of glacial readvance. Lower warved-like sediment is a very finegrained homogenous sediment. Warved-like bedding is indistinct. Two level with dropstones have been recognized. Dropstones are 2-15 cm in diametre, rounded and sphaerical or facetted. Upper rippled sediments are alternating calcarenites and calcisiltites with dominating wave ripples indicating shallow water environments. Current ripples, starved ripples, parallel lamination and convolution also occur. Significant characteristic of this interval are linguoid structures formed by high-density sediment flows, occuring radially around kettle-like forms. Kettle forms occur in rippled calcarenites and are boal-shaped features 2-3 m in dimetre and 30 cm to 1 m deep, with flat or concave bottom. Sediment wedges occur in the upper zone of lade sediments and in moraine zone, probably Younger moraine. Wedges that occur in lake sediments are filled with either finegrained sediment, even layerd, or with fine gravel. They can be about 2 m wide and 3-4 m deep, or up to 0.5 m wide and less than 1 m deep. Wedges that occur in the moraine zone are either 1-2.5 m wide and 2-3 m deep, filled with coarse gravel around 10-20 cm in diametre, or filled with finegrained sediment which appears like frozen high-density sediment flow between blocks and boulders. Glaciofluvial/fluvial sediments are conglomerates and calcarenites partly well cemented. After retreat of glaciers and filling in the lake basin, fluvial erosion took place, and erosional remnants of fluvial channels (channel cross sections) are well visible along the Novigrad section at three locations. Conglomerates, representing channel lag deposit visible in one section, and calcarenites filled in the channels (up to 3 m thick). Channel width of 22m was measured at one place. One cross section whows well developed point bar built of planar cross bedded calcarenites. Analyses of channel cross sections showed a meandering character of at least two metres deep river with low sinuosity running in NW-SW or opposite direction.

glaciation; Dinarides; Dalmatia

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