Geology topics

Brian W. Romans

Publications and source records attributed to Brian W. Romans.

3 recordsLinked to original sources

USGS2022

Tectonic subsidence modeling of diachronous transition from backarc to retroarc basin development and uplift during Cordilleran orogenesis, Patagonian-Fuegian Andes

Backstripped tectonic basin subsidence histories are critical for interpreting phases of lithospheric deformation and paleoenvironmental change from the stratigraphic record. This study presents new subsidence modeling of the Rocas Verdes Backarc Basin (RVB) and Magallanes-Austral retroarc foreland basin (MAB) of southernmost South America to evaluate along-strike changes in tectonic subsidence related to the Late Jurassic through Miocene history of the Southern Andes. We compiled composite stratigraphic sections for seven basin localities that span 47°–54°S from published sedimentological records of paleoenvironment, paleobathymetry, and geochronology. Modeling results resolve regional trends in basin tectonic subsidence, uplift, and sedimentation rate that influenced the depositional environment during five broad phases of RVB-MAB development: (a) Late Jurassic tectonic subsidence and basin deepening associated with rift-related backarc extension that postdated regional diachronous rift-related magmatism. (b) Southward younging of Early to Late Cretaceous pronounced acceleration in tectonic subsidence interpreted as the initiation of flexural loading and development of the MAB foreland basin system. (c) Late Cretaceous (ca. 85–70 Ma) tectonic uplift within the central foredeep ∼49° to 52°S, coeval with a shift from slope to shelf deposition at these latitudes. (d) A protracted period of low-magnitude basin uplift and relative tectonic quiescence during the Paleogene, with the exception of southernmost localities; and (e) Synchronous latest Oligocene-early Miocene tectonic subsidence linked to basin deepening and transgression across the northern and central basin sectors. Backstripped tectonic subsidence analysis corroborates existing interpretations for orogenic development in the RVB-MAB and sheds new light on complex polyphase basin histories where extension precedes convergence.

Andes Mountains, Magallanes-Austral retroarc forel↗

USGS2013

Spatial and temporal variations in landscape evolution: historic and longer-term sediment flux through global catchments

Sediment generation and transport through terrestrial catchments influence soil distribution, geochemical cycling of particulate and dissolved loads, and the character of the stratigraphic record of Earth history. To assess the spatiotemporal variation in landscape evolution, we compare global compilations of stream gauge–derived () and cosmogenic radionuclide (CRN)–derived (predominantly 10 Be; ) denudation of catchments (mm/yr) and sediment load of rivers (Mt/yr). Stream gauges measure suspended sediment loads of rivers during several to tens of years, whereas CRNs provide catchment-integrated denudation rates at 10 2 –10 5 -yr time scales. Stream gauge–derived and CRN-derived sediment loads in close proximity to one another (<500 km) exhibit broad similarity ( stream gauge samples; CRN samples). Nearly two-thirds of CRN-derived sediment loads exceed historic loads measured at the same locations (). Excessive longer-term sediment loads likely are a result of longer-term recurrence of large-magnitude sediment-transport events. Nearly 80% of sediment loads measured at approximately the same locations exhibit stream gauge loads that are within an order of magnitude of CRN loads, likely as a result of the buffering capacity of large flood plains. Catchments in which space for deposition exceeds sediment supply have greater buffering capacity. Superior locations in which to evaluate anthropogenic influences on landscape evolution might be buffered catchments, in which temporary storage of sediment in flood plains can provide stream gauge–based sediment loads and denudation rates that are applicable over longer periods than the durations of gauge measurements. The buffering capacity of catchments also has implications for interpreting the stratigraphic record; delayed sediment transfer might complicate the stratigraphic record of external forcings and catchment modification.

The Journal of Geology↗

USGS2008

Stratigraphic models for deep-water sedimentary systems

Stratigraphic models predict sedimentary architecture. Prediction requires understanding systems across a sufficient range of scales. To be predictive a model must address the interaction of multiple process-response relationships. For deep-water systems these processes include (1) subaqueous flow initiation and transformation, (2) linkages between channel, levee and lobe processes, and (3) shelf-to-basin profile evolution. Thickness, lithology and the geomorphic hierarchy of sedimentary bodies are responses that can be used to define phases in deep-water episodes recording both external (allogenic) and internal (autogenic) controls. Shelf-to-basin studies of the Middle Permian Brushy Canyon Formation demonstrate that the more complete basinal record correlates to an incomplete shelf record; this incongruity impacts recognition of allogenic forcing. Preserving the signature of external controls, internal changes in local gradient and topography also impact the deep-water record requiring complete basin analysis. Independent but nested autogenic and allogenic stratigraphic models address these challenges and predict patterns of deep-water sedimentation. Tectonics and climate modulate sediment supply and sea level, which are considered the principal allogenic controls on deep-water sedimentation as described by the phases of the AIGR ( Adjustment-Initiation-Growth-Retreat ) model. The complete AIGR cycle commences with the Adjustment (A) phase, which defines the initial profile gradient and topography. The Initiation (I), Growth (G), and Retreat (R) phases describe variations in sedimentary response. Autogenic controls on deep-water sedimentation include (1) lateral offset and compensational stacking of lobes, (2) channel migration, switching and avulsion, and (3) longitudinal translation of the channel-lobe transition zone. The BCFS ( Build-Cut-Fill-Spill ) model describes autogenic controls on local gradient and confinement based on a hierarchy of channel-fill, channel-flank, and lobe sedimentary bodies, which vary in proportion and arrangement in each phase. The sedimentation phases of the AIGR and BCFS models describe the systematic increase and decrease in sedimentation energy recorded in hierarchical stratigraphy. When linked to gradient, the models form the axes of a sedimentary system energy matrix (SSEM) for sedimentary architecture. The BCFS model for submarine channels is embedded within the AIGR basin model and, together they facilitate the correlation of a hierarchy of internally and externally generated stratigraphic cycles.

Book chapter↗