Lower Permian cyclic sediments and reef mounds

Comparative analysis of sedimentary cycles deposited during the same time interval but under, either, prevalent tectonic control or under glacio-eustatic forcing has the potential to better reveal controls on cycle archictecture than by study within a single area. In the late Carboniferous to early Permian icehouse world, glacio-eustatic sea- level changes induced by waxing and waning of the Gondwanian ice shield resulted in deposition of cyclothems of very large geographic extent. The objectives of the proposed project are the comparative study of architecture, composition and origin of (a) Lower Permian cyclothems and (b) reef mounds in the Southern Alps (Europe) and in southern New Mexico (USA). Comparison of cyclothems accumulated in different tectonic settings and in different areas should allow for better recognition of controls over cycle development. Such inquiry is useful for the understanding of cyclic deposition in general. In the Carnic Alps and the Karawanken mountains (Southern Alps, Austria), the Upper Carboniferous to Lower Permian succession throughout consists of stacked cyclothems. Conversely, for the overlying "middle" to upper Permian succession (Trogkofel Group), no cycles are documented as yet. Preliminary sections combined with biochronostratigraphy indicate that the Upper Carboniferous to Lower Permian succession consists of different types of cyclothems, and that cyclothem duration increased up-section. Because the Upper Palaeozoic of the Southern Alps accumulated between a phase of relative tectonic quiescence subsequent to the Varsican orogeny and the first indications of rifting related to the Alpine orogenic cycle, the change in cyclothem style may be related to changing impact of tectonism versus glacio-eustasy over time. In New Mexico, cyclothems of glacio- eustatic origin are known from the Pennsylvanian of the Pedregosa and Orogrande basins. In addition, cyclothems of Early Permian age also are present, but to date the architecture and controls over these latter cyclothems are little documented. We intend to study in detail (a) cycle architecture, (b) how cyclicity changed over time, and (c) if there is any cyclicity in some Upper Palaeozoic successions that to date are considered as "non-cyclic", such as the Trogkofel Group. Potential controls over cycle development shall be assessed by comparative analysis, that is, to check to which degree cyclothems of different areas may differ in architecture and duration. The other core topic of the project will be the study of reef mounds contained in many of the cyclothems. Late Palaeozoic reef mounds differ in several fundamental aspects from reefs of the present-day tropical to subtropical latitudes. Over their history, however, the late Palaeozoic mounds underwent distinct changes, and differ with respect to prevalent organisms and facies between the Southern Alps and New Mexico. In particular, in the Trogkofel Group, large mounds tens of meters thick are present, but as yet poorly documented. Our preliminary investigations indicate that the Trogkofel mounds are quite complex with respect to facies architecure, depositional geometry, biotic composition, and their relation to syndepositional tectonism. Better documentation of Trogkofel mounds and (continued) study of mounds in the older cyclothemic successions, integrated with consideration of tectonic setting and depositional style can improve our knowlegde on late Paleozoic reef mound development, and to better understand the differences with respect to modern reefs.

Comparative analysis of sedimentary cycles deposited during the same time interval but under, either, prevalent tectonic control or under glacio-eustatic forcing has the potential to better reveal controls on cycle archictecture than by study within a single area. In the late Carboniferous to early Permian icehouse world, glacio-eustatic sea- level changes induced by waxing and waning of the Gondwanian ice shield resulted in deposition of cyclothems of very large geographic extent. The objectives of the proposed project are the comparative study of architecture, composition and origin of (a) Lower Permian cyclothems and (b) reef mounds in the Southern Alps (Europe) and in southern New Mexico (USA). Comparison of cyclothems accumulated in different tectonic settings and in different areas should allow for better recognition of controls over cycle development. Such inquiry is useful for the understanding of cyclic deposition in general. In the Carnic Alps and the Karawanken mountains (Southern Alps, Austria), the Upper Carboniferous to Lower Permian succession throughout consists of stacked cyclothems. Conversely, for the overlying "middle" to upper Permian succession (Trogkofel Group), no cycles are documented as yet. Preliminary sections combined with biochronostratigraphy indicate that the Upper Carboniferous to Lower Permian succession consists of different types of cyclothems, and that cyclothem duration increased up-section. Because the Upper Palaeozoic of the Southern Alps accumulated between a phase of relative tectonic quiescence subsequent to the Varsican orogeny and the first indications of rifting related to the Alpine orogenic cycle, the change in cyclothem style may be related to changing impact of tectonism versus glacio-eustasy over time. In New Mexico, cyclothems of glacio- eustatic origin are known from the Pennsylvanian of the Pedregosa and Orogrande basins. In addition, cyclothems of Early Permian age also are present, but to date the architecture and controls over these latter cyclothems are little documented. We intend to study in detail (a) cycle architecture, (b) how cyclicity changed over time, and (c) if there is any cyclicity in some Upper Palaeozoic successions that to date are considered as "non-cyclic", such as the Trogkofel Group. Potential controls over cycle development shall be assessed by comparative analysis, that is, to check to which degree cyclothems of different areas may differ in architecture and duration. The other core topic of the project will be the study of reef mounds contained in many of the cyclothems. Late Palaeozoic reef mounds differ in several fundamental aspects from reefs of the present-day tropical to subtropical latitudes. Over their history, however, the late Palaeozoic mounds underwent distinct changes, and differ with respect to prevalent organisms and facies between the Southern Alps and New Mexico. In particular, in the Trogkofel Group, large mounds tens of meters thick are present, but as yet poorly documented. Our preliminary investigations indicate that the Trogkofel mounds are quite complex with respect to facies architecure, depositional geometry, biotic composition, and their relation to syndepositional tectonism. Better documentation of Trogkofel mounds and (continued) study of mounds in the older cyclothemic successions, integrated with consideration of tectonic setting and depositional style can improve our knowlegde on late Paleozoic reef mound development, and to better understand the differences with respect to modern reefs.