GEOMORPHIC CONSTRAINS ON THE EVOLUTION OF THE AGGITIS RIVER BASIN NORTHERN GREECE (A PRELIMINARY REPORT)

Στην παρούσα εργασία αναλύουμε την γεωμορφολογική εξέλιξη της κοιλάδας του Αγγίτη ποταμού και παρουσιάζουμε τον συσχετισμό των μορφολογικών χαρακτηριστικών από το σπήλαιο του Μααρά (Σπήλαιο πηγών Αγγίτη) με τις διάφορες γεωμορφές στην κοιλάδα του ποταμού. Παράλληλα, επιχειρούμε να θέσουμε ένα γενικό χρονολογικό πλαίσιο για την εξέλιξη της κοιλάδας. Για τον σκοπό αυτό μελετήσαμε το σπήλαιο και τις γεωμορφές στο εσωτερικό του ενώ παράλληλα μελετήθηκε και η επιφανειακή μορφολογία. Η τρισδιάστατη χαρτογράφηση του σπηλαίου έδειξε ότι η οροφή του σπηλαίου έχει κυματοειδές σχήμα ενώ το δάπεδό του παρουσιάζει μικρή κλίση και είναι καλυμμένο με κλαστικές αποθέσεις μεγάλου πάχους. Η γεωμορφολογική χαρτογράφηση έδειξε πως στο νότιο τμήμα της κοιλάδας υπάρχουν δύο windgaps. Αξιολογώντας τα αποτελέσματα καταλήγουμε στο συμπέρασμα ότι τέσσερα εξελεκτικά στάδια διαμόρφωσαν την κοιλάδα του Αγγίτη ποταμού κατά την περίοδο από το Νεογενές ως το Τεταρτογενές.In this paper we discuss the landscape evolution of the Aggitis River basin by correlating the morphological characteristics of the Maaras Cave (Aggitis River spring) with the main geomorphological features of the Aggitis fluvial valley. We combine the various morphological features that are hidden inside the Maaras Cave with the surface geomorphology of the river valley in order to trace the imprint of the different evolutionary stages on the landscape. Also, we provide a relative chronological framework for the evolution of the area. The 3D survey of the Maaras Cave shows that the roof of the cave is looping-like shaped in contrast to the floor of the cave that shows low slopes and holds thick clastic sediment deposits. Furthermore, the geomorphological mapping of the Aggitis River valley shows two prominent windgaps at the southern part of the basin that formed as the result of river capture. Our results suggest that the Aggitis River basin suffered four major evolutionary stages from the Neogene until the Quaternary

Log-linear modeling using conditional log-linear structures

Categorical data, Conditional log-linear model, Graphical model, Hierarchical model, Interaction factor, Log-linear model, Möbius inversion, Model combining,

Pleistocene environments and human presence in the middle Atbara valley (Khashm El Girba, Eastern Sudan)

A 50 mthick Pleistocene fluvial succession is extensively exposed in the karib (badlands) area along the Atbara river from Khashm El Girba to Halfa Al Jadida. Through a widespread major unconformity this succession has been subdivided into the Butana Bridge Synthem (BBS) and Khashm El Girba Synthem (KGS). In the latter minor unconformities mark the boundaries between KGS1, KGS2 and KGS3 subsynthems. The BBS is 10 m thick, starts with braided stream gravel and terminates with high-sinuosity river sand. An intermediate silty interval with a well-developed calcrete marks a period of reduced clastic input and morphological stability. The BBS yielded vertebrate remains and many Acheulean artefacts and was deposited from the late Early Pleistocene to the early Middle Pleistocene. After a gap of some hundred thousand years the sedimentary record continues with 40 m thick KGS fluvial deposits. They are quite diversified and include sands from meandering rivers (KGS1) abruptly interrupted by braided river deposits that evolve to sinuous river sands (KGS2), and, finally, from braided river pebbly sands to sheet flows (KGS3). The KGS yielded abundant vertebrate remains and late Acheulean to Middle Stone Age artefacts. Mollusc patch reefs with stromatolitic coatings at the base of the KGS2 and KGS3 gave U/Th ages of 126.1 kyr+/−1.0 kyr and 92.2 kyr+/−0.7 kyr, respectively. These datings, together with fossil assemblages, and artefacts indicate a late Middle Pleistocene to Late Pleistocene age for the KGS. The entire succession makes a northward (Goz Regeb area) transition into fluvio-lacustrine deposits related to the “Atbara palaeolake”. Through palaeohydrological analyses bankfull discharges have been estimated in some KGS1 and KGS2 fluvial channels. They resulted into one order of magnitude less than the present-day Atbara river. The variations in fluvial style and discharge were connected with climatic changes, river network modifications induced by tectonics, and palaeolake Atbara level variations. Due to defined time constrains, the climate changes recorded in the KGS are matched with the Pleistocene Marine Isotope Stages (MIS). The KGS1 meandering rivers can be referred to the MIS 7 wet period, and the episodes of increasing rainfall in KGS2 and KGS3 to the Eemian MIS 5.5 and MIS 5.3 followed by arid conditions (MIS 4?). Despite fossils and facies indicate environmental changes from arid savannah during the BBS to grassland with water pools during the KGS, the Atbara valley was always favourable to human settlement. Our study allowed to reconstruct, although discontinuously, the environments and the occurrence of human presence from the late Early Pleistocene to the Holocene. During this period hominins on their way from East Africa to Eurasia found abundant faunas and more or less perennial streams in the Atbara valley