![]() ![]() Instead of developing deltas, as happens under present conditions, the sediment was transported down the relatively steep slope with some coming to rest on this surface and most making its way to the sediment fans and the deep abyssal environment. The mouths of these rivers were at, or near, the slope-shelf break where sediment was discharged. During these conditions, large streams that carried sediment extended across what is now the continental shelf, but was then the coastal plain. Much of this occurred during low sea-level stages during the Quaternary. The sediment on the continental slope typically is delivered in pulses or events by sediment gravity phenomena. A small portion of the terrigenous sediment and all of the biogenic sediment settle through the water column. Much of the terrigenous sediment comes to the abyssal plain via sediment gravity processes-especially turbidity currents. The sediments are delivered to their sites of accumulation differently. The biogenic sediments are mostly foraminifera with some diatoms. The terrigenous sediments are nearly all clay minerals that have come from the northern provinces of the Gulf States. The sediments are a combination of fine terrigenous sediments and biogenic sediments contributed by various planktonic organisms. The surface is rather flat with local relief of only a few meters. The deep Gulf environments are fairly similar to those of the world’s oceans. There is a veneer of terrigenous sediment on the Florida mainland, but the lack of well-developed drainage keeps it from being transported to the coast. There is virtually no sediment currently being delivered, nor has there been in the past, from the Florida Peninsula and the Yucatán Peninsula both have been carbonate platforms throughout their existence. Similar sediment delivery along the coast of Mexico has occurred in the area south of Laguna Madre and north of Campeche Bay, but the sediment is different because of the extensive volcanic source rocks. The northeast Gulf has also experienced a significant amount of terrigenous sediment influx. The greatest terrigenous sediment supply is at the Mississippi Delta next in volume is the Texas coast where numerous rivers cross the coastal plain regardless of the position of the shoreline. This has also had an influence on the sediments in the deep Gulf, from the continental slope to the abyssal plain. During that time, the shoreline migrated across virtually the entire continental margin, as we know it today. The nature and distribution of sediments in the shallow Gulf margin have been controlled largely by the rise and fall of sea level during the waxing and waning of Quaternary glaciers. It includes regions where huge volumes of terrigenous sediments are delivered and others where terrigenous sediments are generally absent. It is located in the low, mid-latitudes and extends over multiple climatic zones. The Gulf of Mexico is a unique basin on the globe. Sediment delivery is dominated by fluvial discharge, so climate and seasons are important factors. The estuaries tend to be shallow: thus, waves can be important in modifying sediment distribution. Tidal range on the Gulf is low, meaning that tidal currents are minimal except in the inlets. The Mississippi Delta is the extreme of this generality in that it covers almost the entire shelf. Generally, areas bounded by rivers receive the greatest volume of sediment at the highest rates of delivery. The rate of accumulation and the volume of modern sediment on the shelf range widely. The deep environments tend to be dominated by mud in a combination of terrigenous and biogenic sediments. Direct precipitation of calcium carbonate and evaporate minerals takes place primarily on the Florida and Yucatán platforms and some coastal lagoons. Most sediment originates from the adjacent land, primarily via fluvial transport. Waves, tides, currents, and gravity are the primary mechanisms that move sediment. The Gulf of Mexico includes a broad spectrum of depositional environments from the coast to deep water. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |