Comparative Assessment of Isobase and Polynomial Trend Surface Methods for Paleo-Shoreline Prediction in Lebanon.

The emergence of Lebanon during the Miocene reflects the combined effects of regional tectonic uplift and sea-level fluctuations along the Levant margin. This study applies geomorphometric methods to reconstruct paleotopography and predict paleoshoreline positions using SRTM30 PLUS Digital Elevation Model data. Two independent approaches were evaluated: isobase surface construction from Strahler-ordered valley networks and polynomial trend surface modeling based on regression analysis of elevation data. Four successive orders of isobase and trend surfaces were generated and compared.

Zero-elevation contours extracted from each surface were interpreted as paleoshorelines and analyzed using correlation statistics (R²), hypsometric classification, fractal dimension, and sinuosity indices. The modeled shorelines were validated against the spatial distribution of documented marine deposits and fossiliferous sites in Lebanon.

Results indicate that lower-order surfaces closely resemble present-day topography, whereas higher-order surfaces reflect progressive regional emergence. Although higher-order trend and isobase surfaces appear statistically similar due to terrain smoothing, shoreline geometry and spatial validation indicate that isobase-derived reconstructions better preserve morphostructural complexity and align more closely with marine depositional evidence. The study confirms that isobase geomorphometry provides a more reliable framework for paleoshoreline prediction in tectonically active continental margins.