Η λεπτομερής ιζηματολογική - πετρογραφική μελέτη των αποθέσεων του φλύσχη στη Λήμνο σε σχέση με την παλαιογεωγραφική εξέλιξη του Βορείου Αιγαίου στην κατεύθυνση της πιθανής ύπαρξης πεδίων υδρογονανθράκων

Abstract

Outcrops of both deep-water and shelf sediments were selected for study on Lemnos Island. During this time interval (NP18-Np21b) the study area was characterized by the deposition of submarine fans that overly shelf deposits with this swallowing upward trend to be owed to tectonic activity. The turbidity system is structured by a “basin floor” fan that is presented overlying a “slope” fan and was constructed under the simultaneous interaction of both progradation and aggradation processes. Both “basin floor” and “slope” fans constitute the lower parts of the stratigraphic column in the study area and have been interpreted as parts of a sand-rich submarine fan on the base of slope to basin floor environment. In order to determine the grain-size statistic and hydraulic parameters thirty (30) thin sections were cut perpendicular to bedding and essentially randomly oriented relative to flow direction. Data obtained from this study suggest that samples are consisted of very-fine to medium grained sandstones, are characterized by poor to very good sorting with their greater part consisting of very good, good and fair sorting sandstones. Moreover, derived from both high and low-density turbidity currents. In order to estimate the flow direction, palaeocurrent data were collected from outcrops. The number of measurements from each outcrop ranges from 10 to 15 and there were plotted in rose diagrams showing that the main palaeocurrent direction has a NNE trend. Twenty samples (20) from the Late Eocene- Early Oligocene turbidite and shelf deposits were selected from the Lemnos Island in order to determine the quantity and quality of the organic matter in each one. The total organic carbon content was determined using a LECO C-230 carbon determinator while the quality of the organic matter was evaluated using a common programmed temperature pyrolysis method, called Rock-Eval 6 pyrolysis by BASELINE RESOLUTION INCORPORATION (BRILABS). The results obtained from the research suggest that studied samples have from poor to excellent source rock potential while the shales of the Lemnos sedimentary rocks can be classified principally as secondary source rocks with potentials to generate gas. In order to assess the tectonic setting of the Lemnos Island, NE Greece, major elements and 14 trace elements were determined using a Thermo Jarrell-Ash ENVIRO II ICP plasma mass spectrometer (ICP-OES) while rare earth elements and additional ultra-trace elements were determined using a Perkin Elmer SCIEX ELAN 6000 (ICP-MS). The study suggests an active margin environment. The positive anomaly of Zr that reflects a heavy mineral input and could be considered typical of passive margin environment is owed to reworking and sorting during sediment transfer. Moreover, a mafic/ultramafic source should be considered as the major component controlling both submarine fans and shelf deposition. The determination of porosity and permeability was based on the “mercury porosimetry technique” as has been described by Katz and Thompson (1986, 1987). Data obtained from this technique suggest that although the majority (13) of the sandstone samples is presented having from fair to very good porosity only some samples (8) have fair to very good permeability.