Late Cenozoic Evolution of the Greater Caucasus
First order structures and earthquake locations in the Greater Caucasus. Divisions show different tectonic zones based on structural geometries, location of active structures, and crustal architecture. Modified from Forte et al., 2014, Tectonics. Earthquake catalog from Mumladze et al., 2015, GeoResJ.
1) Active Deformation in the Southeastern Greater Caucasus Foreland
The Savalan Thrust exposed along the Goy River in the eastern Kura fold-thrust belt, Azerbaijan. Middle Apsheron sediments (Unit 1) thrust over upper Apsheron sediments (Unit 2) with preservation of a footwall syncline. Modified from Forte et al., 2013, Tectonics.
Most prior work within the Greater Caucasus assumed that the majority of active shortening was accommodated on a range-front thrust system along the southern margin of the range, often referred to as the Main Caucasus Thrust. Through a combination of remote and field mapping I have demonstrated that in the eastern Greater Caucasus, the surface trace of the Main Caucasus Thrust is largely inactive with deformation instead localized within the Kura fold-thrust belt, a series of shallow (< 5 km deep), south-vergent thrusts and folds that deform late Cenozoic sediments of the Kura Basin. My work indicates that this Kura fold-thrust belt progressively youngs from west to east, initiated at ~1.5 Ma at its eastern tip, and has accommodated upwards of 50% of total Arabia-Eurasia convergence since its initiation.
Relevant Publications:
Forte, A.M., Cowgill, E., Murtuzayev, I., Kangarli, T., and Stoica, M., 2013, Structural geometries and magnitude of shortening in the eastern Kura fold-thrust belt, Azerbaijan: Implications for the development of the Greater Caucasus Mountains: Tectonics, v. 32, doi: 10.1002/tect.20032 [Link to Journal Page]
Forte, A.M., Cowgill, E., Bernardin, T., Kreylos, O., Hamann, B., 2010, Late Cenozoic deformation of the Kura fold-thrust belt, southern Greater Caucasus: Geological Society of America Bulletin, v. 122, p. 465-486. [Link to Journal Page]
Forte, A.M., Cowgill, E., Bernardin, T., Kreylos, O., Hamann, B., 2010, Late Cenozoic deformation of the Kura fold-thrust belt, southern Greater Caucasus: Geological Society of America Bulletin, v. 122, p. 465-486. [Link to Journal Page]
2) Stratigraphy of the Northern Kura Basin
Backlimb of the Sarica fold exposing the contact between conglomerates of the Productive Series (Unit S1) and the overlying Akchagyl muds and sands (Unit S2). A population of ~2.5 Ma detrital zircons within the upper portions of the Productive Series indicates that the Akchagyl flooding event, which occurred at ~3.0 Ma near the Caspian Sea coast, took > 0.5 Ma to reach the interior of the northern Kura Basin. Modified from Forte et al., 2014, Basin Research.
The stratigraphic record of the interior Kura Basin, which is the main foreland basin of the southeastern Greater Caucasus, is largely undescribed in peer reviewed and readily accessible literature. Over the course of three field seasons, I measured five stratigraphic sections through Miocene-Pleistocene sediments exposed within the Kura fold-thrust belt. The stratigraphy of the northern Kura Basin records a dynamic interaction between tectonic and climatic forcing. Within these stratigraphic packages, the growth of the Greater Caucasus and later initiation of the Kura fold-thrust belt is represented by local variations in facies and stratal thicknesses, whereas on a more basin-wide scale, facies are dominantly controlled by the large base-level (>1000 meters) variations of the internally drained Caspian Sea. The results of this work generally suggest that extracting tectonic histories from foreland basins can be complicated by the large base-level variations that can occur in internally drained foreland basins.
Relevant Publications:
Forte, A.M., Sumner, D.Y., Cowgill, E., Stoica, M., van Baak, C.G.C., Vasiliev, I., Murtuzayev, I., Kangarli, T., In Prep, Stratigraphy and paleogeography of the southeastern Greater Caucasus foreland during the Late Miocene to Pleistocene
Forte, A.M., Sumner, D.Y., Cowgill, E., Stoica, M., I., Murtuzayev, I., Kangarli, T., Elashvili, M., Godoladze, T., and Javakishvili, Z., 2014, Late Miocene to Pliocene stratigraphy of the Kura Basin, a subbasin of the South Caspian Basin: Implications for the diachroneity of stage boundaries, Basin Research, doi: 10.1111/bre.12069 [Link to Journal Page]
Forte, A.M., Cowgill, E., 2013, Late Cenozoic base-level variations of the Caspian Sea: A new review of its history and proposed driving mechanisms: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 386, p. 392-407, doi: 10.1016/j.palaeo.2013.05.035 [Link to Journal Page]
Van Baak, C.G.C., Vasiliev, I., Stoica, M., Kuiper, K., Forte, A.M., Aliyeva, E., and Krijgsman, W., 2013, A magnetostratigraphic time frame for Plio-pleistocene transgression in the South Caspian Basin, Azerbaijan: Global and Planetary Change, v. 103, p. 119-134. [Link to Journal Page]
Forte, A.M., Sumner, D.Y., Cowgill, E., Stoica, M., I., Murtuzayev, I., Kangarli, T., Elashvili, M., Godoladze, T., and Javakishvili, Z., 2014, Late Miocene to Pliocene stratigraphy of the Kura Basin, a subbasin of the South Caspian Basin: Implications for the diachroneity of stage boundaries, Basin Research, doi: 10.1111/bre.12069 [Link to Journal Page]
Forte, A.M., Cowgill, E., 2013, Late Cenozoic base-level variations of the Caspian Sea: A new review of its history and proposed driving mechanisms: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 386, p. 392-407, doi: 10.1016/j.palaeo.2013.05.035 [Link to Journal Page]
Van Baak, C.G.C., Vasiliev, I., Stoica, M., Kuiper, K., Forte, A.M., Aliyeva, E., and Krijgsman, W., 2013, A magnetostratigraphic time frame for Plio-pleistocene transgression in the South Caspian Basin, Azerbaijan: Global and Planetary Change, v. 103, p. 119-134. [Link to Journal Page]
3) Tectonic Evolution of the Greater Caucasus
Normalized steepness indices for rivers from the Greater Caucasus. Zones of elevated steepness suggest regions of active uplift. Modified from Forte, 2014, Tectonics.
The first order crustal and structural architecture of the Greater Caucasus is unconstrained, being variably described as either a singly-vergent or a doubly-vergent orogen and a product of crustal thickening and detachment of a crustal root or active subduction by different authors. Based on new syntheses of bedrock geology, earthquake distributions, neotectonic mapping, stratigraphy, and tectonic geomorphology, my work suggests that in detail the Greater Caucasus appear to capture the transition from a singly- to doubly-vergent orogen along-strike and may be characterized by active subduction in the east and slab detachment in the west [Video of earthquake distributions beneath the Greater Caucasus from Mumladze et al., 2015]. These results also suggest that the structural evolution of the orogen is influenced by the incipient collision of the Greater and Lesser Caucasus.
Ongoing work is focused on understanding the role that climate may play in further shaping the structural and topographic evolution of the orogen. The Greater Caucasus are an interesting place to examine these interactions because they are characterized by large along-strike gradients in both precipitation and convergence velocity, which together should produce a west to east increase in orogen width and relief, and yet orogen width and relief is largely invariant along-strike. I am using various topographic, hydrologic and climatic metrics to assess the extent to which the topography is influenced by climate, tectonics, or some combination thereof.
Ongoing work is focused on understanding the role that climate may play in further shaping the structural and topographic evolution of the orogen. The Greater Caucasus are an interesting place to examine these interactions because they are characterized by large along-strike gradients in both precipitation and convergence velocity, which together should produce a west to east increase in orogen width and relief, and yet orogen width and relief is largely invariant along-strike. I am using various topographic, hydrologic and climatic metrics to assess the extent to which the topography is influenced by climate, tectonics, or some combination thereof.
Relevant Publications and Abstracts:
Forte, A.M., Whipple, K.X., Bookhagen, B., Rossi, M.W., Accepted, Decoupling of modern shortening rates, climate, and topography in the Caucasus: Submitted to Earth and Planetary Science Letters.
Forte, A.M., Whipple, K.X., Cowgill, E., 2015, Drainage network reveals patterns and history of active deformation in the Eastern Greater Caucasus: Geosphere, doi: 10.1130/GES01121.1 [Link to Journal Page]
Mumladze, T., Forte, A.M., Cowgill, E., Trexler, C.C., Niemi, N.A., Yikilmaz, M.B. and Kellogg, L.H., 2015, Subducted, detached, and torn slabs in the Greater Caucasus: Implications for seismic hazard: GeoResJ, v. 5, p. 36-46, doi: 10.1016/j.grj.2014.09.004 [Link to Journal Page]
Forte, A.M., Cowgill E., Whipple, K.X., 2014, Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus: Tectonics, v. 33, no. 11, p. 2077-2101, doi: 10.1002/2014TC003651 [Link to Journal Page]
Cowgill, E., Forte, A.M., Niemi, N.A., Avdeev, B., Javakhishvili, Z., Elashvili, M., In Prep, Relict basin closure accommodates continental convergence with minimal crustal shortening or deceleration of plate motion as inferred from detrital zircon provenance in the Caucasus
Forte, A.M., Whipple, K.X., Cowgill, E., 2015, Drainage network reveals patterns and history of active deformation in the Eastern Greater Caucasus: Geosphere, doi: 10.1130/GES01121.1 [Link to Journal Page]
Mumladze, T., Forte, A.M., Cowgill, E., Trexler, C.C., Niemi, N.A., Yikilmaz, M.B. and Kellogg, L.H., 2015, Subducted, detached, and torn slabs in the Greater Caucasus: Implications for seismic hazard: GeoResJ, v. 5, p. 36-46, doi: 10.1016/j.grj.2014.09.004 [Link to Journal Page]
Forte, A.M., Cowgill E., Whipple, K.X., 2014, Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus: Tectonics, v. 33, no. 11, p. 2077-2101, doi: 10.1002/2014TC003651 [Link to Journal Page]
Cowgill, E., Forte, A.M., Niemi, N.A., Avdeev, B., Javakhishvili, Z., Elashvili, M., In Prep, Relict basin closure accommodates continental convergence with minimal crustal shortening or deceleration of plate motion as inferred from detrital zircon provenance in the Caucasus
Where are These Mountains?
Geologically, the Greater Caucasus are in the central portion of the Alpine-Himalaya Belt, nestled between their better studied neighbors, the Alps to the west and the Himalaya to the east. Geographically, the range spans the borders of Georgia (country, not state), Azerbaijan and Russia. The Caucasus have long represented a crossroads, and even today, they are variably considered as a part of Europe, Asia or the Middle East depending on who you ask (this includes people living in the Caucasus, per the results of an informal survey conducted by me). I have worked in both Azerbaijan and Georgia, spending the most time in Azerbaijan. They are both lovely countries with friendly people, unbelievably gorgeous scenery and fascinating geology and I feel privileged to have had the chance to spend so much time traipsing about this sometimes forgotten corner of the world.
